Gilles Pison

Catalina Torres

Christiaan Monden

Jeroen Smits

Peaks in twin births? An international comparison of trends in twinning rates in 30 developed countries (24-10-2021)

The twinning rate has increased dramatically over the last four decades in developed countries because of two main factors: (a) delayed childbearing, as older women tend to have twins more frequently than younger women, and (b) the expansion of medically assisted reproduction (MAR), which carries an increased risk of multiple births. In some developed countries, however, the twinning rate reached a peak in the early 2000s and has since decreased. This reversal has been observed in more and more developed countries since. It is linked to changes in MAR policies and practices following concerns raised by the increase of the frequency of twin deliveries, twin babies being more fragile than singletons. Using the Human Multiple Births Database (HMBD) and databases on MAR policies and practices, this paper describes twinning-rate trends in 30 developed countries. It examines several questions for particular peaks: at which level did the twinning rate peak in each country? When did it peak? Which factors might explain the recent drop and the lower level attained? For countries that have not yet peaked, when might this occur and at what level?

Extended abstract 1. Introduction

The twinning rate has increased dramatically over the last four decades in nearly all countries for which vital statistics are available [START_REF] Monden | Twin Peaks: more twinning in humans than ever before[END_REF][START_REF] Pison | Twinning Rates in Developed Countries: Trends and Explanations[END_REF][START_REF] Hoekstra | Dizygotic twinning[END_REF][START_REF] Pison | Frequency of twin births in developed countries[END_REF]. For example, it has increased in the United States from 9.5 twin deliveries per 1,000 deliveries in 1975 to 16.7 in 2015 [START_REF] Martin | Is Twin Childbearing on the Decline? Twin Births in the United States, 2014-2018[END_REF]. Over the same period, it has practically doubled in many developed countries, e.g. from 9.9 to 16.1 in England and Wales, from 9.2 to 18.4 in Germany, from 9.3 to 17.5 in France, from 9.6 to 16.7 in Denmark, and from 5.9 to 9.9 in Japan (Human Multiple Births Database [START_REF] Torres | Human Multiple Births Database (HMBD)[END_REF]).

Two main factors have driven this increase: delayed childbearing, as older women tend to have twins more frequently than younger ones, and the expansion of medically assisted reproduction (MAR), which carries an increased risk of multiple births [START_REF] Pison | Twinning Rates in Developed Countries: Trends and Explanations[END_REF].

MAR refers to a broader set of treatments than the often-used term Assisted Reproductive Technology (ART), which consists of treatments in which both sperm and oocytes are handled outside (i.e., in vitro) of the woman's body and embryos are transferred to establish a pregnancy. ART includes, but is not limited to, in vitro fertilization (IVF) and its variant, intracytoplasmic sperm injection (ICSI). MAR, however, also includes simpler techniques, like ovarian stimulation alone and artificial insemination. Techniques like ovarian stimulation and in vitro fertilization are associated with increased numbers of multiple births [START_REF] Hoekstra | Dizygotic twinning[END_REF][START_REF] Nyboer Andersen | Results generated from European registers by ESHRE[END_REF]. This significant rise constitutes an important public health challenge because multiple babies are more fragile than singleton ones. Compared to singletons, they tend to have lower birth weight, more complications at birth, and are more often born premature, which are all associated with many long-term health implications [START_REF] Johnson | Early-life origins of adult disease: national longitudinal population-based study of the United States[END_REF][START_REF] Delobel-Ayoub | Behavioral problems and cognitive performance at 5 years of age after very preterm birth: the EPIPAGE Study[END_REF][START_REF] Larroque | Survival of very preterm infants: Epipage, a population based cohort study[END_REF]. Stillbirth and infant mortality rates are also much higher among twins and other multiple children [START_REF] Pison | Twins in Sub-Saharan Africa: Frequency, Social Status and Mortality, in Mortality and society in Sub-Saharan Africa[END_REF][START_REF] Guo | Child mortality among twins in less developed countries[END_REF][START_REF] Monden | Mortality among twins and singletons in sub-Saharan Africa between 1995 and 2014: a pooled analysis of data from 90 Demographic and Health Surveys in 30 countries[END_REF][START_REF] Fresson | Analyse de la mortinatalité par le Programme de médicalisation du système d'information (PMSI): premiers résultats nationaux[END_REF]. Multiple-child pregnancies can have negative impacts on the parents as well. For instance, these pregnancies are associated with higher risk of gestational diabetes, pre-eclampsia, post-partum depression, and divorce [START_REF] Jena | Association between the birth of twins and parental divorce[END_REF][START_REF] Choi | Multiple births are a risk factor for postpartum maternal depressive symptoms[END_REF][START_REF] Rauh-Hain | Risk for developing gestational diabetes in women with twin pregnancies[END_REF][START_REF] Bdolah | Twin pregnancy and the risk of preeclampsia: bigger placenta or relative ischemia?[END_REF].

These health and wellbeing concerns led to changes in MAR policies and practices from the turn of the century onward, in particular reduction of the number of embryos transferred to the uterus [START_REF] Hazekamp | Avoiding multiple pregnancies in ART Consideration of new strategies[END_REF]. Consequently, twinning rates reached a peak in the early 2000s in several developed countries and have since decreased further. This reversal has been observed in more and more developed countries, but not in all of them. New MAR practices have not been implemented equally everywhere, and the number of treatments has continued to increase. This paper describes the trends of the twinning rate in developed countries and examines several questions about peaks: at which level did the twinning rate peak in each country? When did it peak? How much has it dropped since? How quickly? Did the twinning rate fall to the 'natural' rate (the rate expected if only the distribution of maternal age at birth had an influence)? More generally, which factors might explain the peak, the drop, and the lower level attained recently? For countries that have not yet peaked, when might it occur, and at what level?

In the next section, we describe the data sources and methods used. In section 3, we describe how twinning rates have changed in developed countries over recent decades, with a special focus on peaks and changes occurring afterwards. In section 4, we examine whether the trends and reversals can be explained by changes in age at childbearing and the spread of infertility treatments. We estimate each factor's contribution to the increase up to the peak, and their influence on the level attained in the last year for which statistics are available (often 2019). We also examine the relationships between trends, reversals, and changes in MAR policies and practices. The last section focuses on countries that have yet to witness a peak, examining when it might occur and at what level.

Data and methods

The Human Multiple Births Database (HMBD)

Our main source of information is the Human Multiple Births Database (HMBD) [START_REF] Torres | Human Multiple Births Database (HMBD)[END_REF], which provides national, annual time series of the number of deliveries by multiplicity (singletons, twins, triplets, quadruplets, and more) and the twinning and multiple rates. Twins are by far the most frequent among multiple deliveries; deliveries of triplets or more represent only a small fraction. For example, in France in 2010-2015, 97.9% of all multiple deliveries were those involving twins; the proportion of multiple deliveries of triplets and quadruplets and more was respectively 2.0% and 0.1% [START_REF] Torres | Human Multiple Births Database (HMBD)[END_REF]. In the United States over the same period, the corresponding proportions were 96.5%, 3.3%, and 0.2%. Consequently, the HMBD focuses on twin deliveries, although it does provide information on other multiple deliveries.

Only countries with available complete or nearly complete birth registration and data documentation are included in the HMBD. As of October 2021, the online database comprises 20 countries across Europe, North America, Oceania, and Asia. The annual series start as early as the mid-or late-19th century for some countries, and in the early-or mid-20th century for most of the others. The database is recent, and new countries are added regularly. It is expected that about 10 more countries will be included by mid-2021, at which time the HMDB will cover approximately 30 countries.

The method for separating the influences of the two main factors of the twinning rate

Two main factors are responsible for the increase in twinning rates since the 1970s: the increase in maternal age at childbearing and the development of MAR [START_REF] Pison | Twinning Rates in Developed Countries: Trends and Explanations[END_REF]. To assess how much of twinning-rate increase can be attributed to each of these factors, we use a simulation method [START_REF] Pison | Twinning Rates in Developed Countries: Trends and Explanations[END_REF].

In short, we first make the (broadly accepted) assumption that the monozygotic (MZ) twinning rate (the rate of identical twins) is constant and equals 4 per 1,000. Second, we suppose that the dizygotic (DZ) twinning rate (the rate of fraternal twins), in the absence of MAR, increases monotonously from 0 at age 15 to a maximum at age 37 and then decreases monotonously to 0 at age 50 [START_REF] Pison | Twinning Rates in Developed Countries: Trends and Explanations[END_REF][START_REF] Bulmer | The biology of twinning in man. The biology of twinning in man[END_REF]. The only factor that thereby differs among the countries is the maximum at age 37. Third, this maximum is estimated for each country as the best fit: when we derive the age-specific twinning rate function from this level and apply it to the observed age distribution of deliveries in 1970, our estimated twinning rate equals the observed rate for 1970. Fourth, we apply the estimated age-specific twinning rate function to the observed distribution of birth by mother's age for each year in each country, to obtain predicted overall twinning rates. Data on births by maternal age come from national statistics, the Human Fertility Database (HFD) [START_REF] Jasilioniene | Methods Protocol for the Human Fertility Database[END_REF], and the United Nations World Population Prospects [START_REF]World Population Prospects: The 2019[END_REF]. More details on the method are provided in [START_REF] Pison | Twinning Rates in Developed Countries: Trends and Explanations[END_REF].

In our previous study, we applied this method to 32 countries for which we had estimates of the twinning rate since 1970 and until 2005. We found that if age at childbearing had not changed and only MAR had been in action, the twinning rate would have increased only by 40% to 50% on average from 1970 to 2005 in the countries considered [START_REF] Pison | Twinning Rates in Developed Countries: Trends and Explanations[END_REF]. If, however, only age at childbearing had changed and MAR had not developed, the increase of the twinning rate would have been only 15% on average. On average, we found that over the period 1970-2005, the effect of MAR was thus about three times greater as the effect of delayed childbearing. However, we found large differences between countries: in Japan, the effect of MAR was more than ten times that of delayed childbearing; in Poland, it was much smaller, at one third of the effect of delayed childbearing; in Hungary and in New Zealand, both effects were similar. Note: The twinning rate is much lower in Japan than in the other countries. The frequency of dizygotic (DZ) twin births (fraternal twins) is highly variable according to the region or country. It has always been low in East Asia (about 2-4 per 1,000 total deliveries before the development of MAR), high in sub-Saharan Africa (about 15 per 1,000), and at an intermediate level in Europe and the United States (about 7 per 1,000). The development of MAR has mostly influenced the DZ twinning rate, without much changing the monozygotic (MZ) twinning rate (the rate of identical twins), which has remained at around 4 per 1,000 total deliveries everywhere. Nearly all the changes in the twinning rate are therefore due to the changes in the DZ twinning rate.

Trends and reversals of the twinning rate in developed countries

Figure 1 shows that, as mentioned above, the twinning rate has increased dramatically since the 1970s in the seven countries selected. It also shows that the twinning rate has reached a peak or a plateau and has subsequently decreased. However, there are important differences between the countries regarding the timing and the level of the peak. This is also shown in Table 1, where all the countries included in the HMBD as of October 2021 are included. It shows the year and the level when the twinning rate peaked in each country. The peak is observed first in Finland ( 1998 The twinning rate is in general much lower in Japan than in other countries, a feature of East-Asia compared to Europe and North America [START_REF] Bulmer | The biology of twinning in man. The biology of twinning in man[END_REF](see also note of Figure 1). If the year of the peak, or the period of the plateau, varies from one country to the other, so does the level attained by the twinning rate at the peak, the speed at which it occurs, and the speed and scale of the subsequent drop. For example, a clear reversal point can be identified in some countries with a fast decrease afterwards, whereas in other countries the decrease after the peak has been more gradual. Japan is the only country where the twinning rate has increased again following a decline after 2005 to a low level in 2011.

Reasons for a trend reversal

Pregnancies obtained through MAR result much more frequently in multiple births compared to pregnancies obtained naturally. One reason is that in the first decades of ART, medical doctors often transferred several embryos. In 2000, over two-thirds of women in the United States undergoing ART had three or more embryos transferred into their uterus. Around 35% of these pregnancies resulted in multiple delivery, and 53% of all ART infants were born as twins or triplets [START_REF] Mills | State-of-the-art report on the changing role of children: assisted reproduction, late fertility and childlessness, in Report to the European Union of the Collaborative project "Families And Societies. Changing families and sustainable societies: Policy contexts and diversity over the life course and across generations[END_REF].

As mentioned, the high rates of multiple deliveries after ART were considered problematic because of negative health outcomes infants and mothers [START_REF] Pinborg | IVF/ICSI twin pregnancies: risks and prevention[END_REF][START_REF] Hansen | Twins born following assisted reproductive technology: perinatal outcome and admission to hospital[END_REF]. Consequently, medical professionals proposed new criteria for evaluating the success of ART, centered on successful singleton live birth delivery. They suggested BESST (Birth Emphasizing a Successful Singleton at Term) as an indicator [START_REF] Min | What is the most relevant standard of success in assisted reproduction? The singleton, term gestation, live birth rate per cycle initiated: the BESST endpoint for assisted reproduction[END_REF]. Single embryo transfers became favored by health authorities and legislation because studies indicated that the chances of birth after elective single embryo transfer (eSTET)1 are identical to the chances of success after the transfer of two fresh embryos [START_REF] Min | What is the most relevant standard of success in assisted reproduction? The singleton, term gestation, live birth rate per cycle initiated: the BESST endpoint for assisted reproduction[END_REF]. ART multiple delivery rates then started to decline gradually in most of the developed countries during the 2000s, falling to 30% in the USA in 2009 and 20% in Europe in 2010 [START_REF] Mills | State-of-the-art report on the changing role of children: assisted reproduction, late fertility and childlessness, in Report to the European Union of the Collaborative project "Families And Societies. Changing families and sustainable societies: Policy contexts and diversity over the life course and across generations[END_REF][START_REF] Kupka | Assisted reproductive technology in Europe, 2010: results generated from European registers by ESHRE[END_REF].

However, this decline did not result in a reversal of the twinning-rate trend among the total population of all these countries because of the continuous increase in the use of ART and non-ART ovarian stimulation [START_REF] Kupka | Assisted reproductive technology in Europe, 2010: results generated from European registers by ESHRE[END_REF] and the ongoing shift towards childbearing at later ages.

The role of changes in age at childbearing and in infertility treatments

The full paper describes the trends of the twinning rate in all the developed countries for which statistics are available. It examines whether the trends and reversals can be explained by changes in age at childbearing and the spread of infertility treatments. Using the method presented above, we estimate each factor's contribution to the increase up to the peak and their influence on the level attained in the last year for which statistics are available (often 2019). We also examine the relationships between trends, reversals, and changes in MAR policies and practices as described by the literature.

Through a systematic examination of peaks, we try to bring answers to the following questions: for a particular country, why did the twinning rate peaked a particular year? Why at this level? How much has it dropped since? How quickly? Did the twinning rate fall to the 'natural' rate (the rate expected if only the distribution of maternal age at birth had an influence)? More generally, which factors might explain the peak, the drop, and the lower level attained recently. For countries that have not yet witnessed a peak, when might it occur, and at what level? And for those that experienced a peak and a subsequent drop, will the rate increase again after attaining a low level, as observed in Japan?

Figure 1

 1 Figure1shows the trends of the twinning rate since 1970 in a selection of developed countries based on the data from the HMBD[START_REF] Torres | Human Multiple Births Database (HMBD)[END_REF].

Figure 1 .

 1 Figure 1. Evolution of the twinning rate in selected developed countries, 1970 to 2019

  Figure1shows that, as mentioned above, the twinning rate has increased dramatically since the 1970s in the seven countries selected. It also shows that the twinning rate has reached a peak or a plateau and has subsequently decreased. However, there are important differences between the countries regarding the timing and the level of the peak. This is also shown in Table1, where all the countries included in the HMBD as of October 2021 are included. It shows the year and the level when the twinning rate peaked in each country. The peak is observed first in Finland (1998), then in Sweden (1998, Australia, New Zealand and Norway (2002), Japan and the Netherlands (2005), Iceland (2006), Denmark and Scotland (2008), Canada and England and Wales (2009), Czech Republic (2010), Austria (2011), Spain and the United States (2014), France (2015) and Germany and Italy (2017). In Greece, twinning rate has not yet peaked and it is still increasing in 2019.

Table 1 .

 1 Year and level when the maximum twinning rate was observed, by country

	Year	Rate*

One fresh embryo is transferred, and a second one is frozen for a second single embryo transfer if necessary.


André Orcesi

Alan O'connor

Emilio Bastidas-Arteaga

Mark G Stewart

Katerina Kreislova

Franck Schoefs

Olga Markogiannaki

Teng Wu

Yue Li

Abdullahi M Salman

Lara Hawchar

Paraic C Ryan

Investigating the effects of climate change on material properties and structural performance

Keywords: Climate change, impacts, vulnerability, durability, structural resistance

One major issue when considering the effects of climate change is to understand, qualify and quantify how the changing climate will likely impact infrastructure assets and services as it strongly depends on current and future climate variability, location, asset design life, function and condition. Expected changes to local climatic conditions may potentially lead to changes in the degradation processes of building materials, affecting the durability and service life of structures. A key question is how climate change may produce changes of vulnerability owing to physical and chemical actions affecting structural durability or changes of exposure in terms of the intensity/frequency of extreme weather events. In this context, this article focuses on the impact on structural resistance and associated challenges, considering some recent activities of members of the IABSE TG6.1. Several case studies of infrastructure assets worldwide are presented and discussed in this article.

Introduction

The ageing and deterioration of civil engineering structures is likely to be exacerbated in the coming decades by the adverse effects of climate change (IPCC 2014). On the resistance side, one may observe a change in kinematics of the materials degradation mechanisms being influenced by the surrounding environmental conditions (Nasr et al. 2020). As climate change may accelerate or decelerate processes depending on specific exposure and environmental conditions, there is a need to advance the understanding of how climate change may impact structural resistance and thereby structural reliability, and to gain better insights into the vulnerability to both slow and rapid phenomena [START_REF] Bastidas-Arteaga | Climate Adaptation Engineering: Risks and Economics for Infrastructure Decision-Making[END_REF]. At the European level, some work on standards integrating climate change formally started with the set-up of the Adaptation to Climate Change Coordination Group (ACC-CG) in early 2015 which focuses on buildings, infrastructures in the energy sector and infrastructures in the transport sector. The main expected contributions of this Group include revision or development of standards for infrastructures in the above sectors, linking infrastructure standards to future climatic conditions and scaling adaptation measures to the European level. Additionally, a new American 1. Chloride ingress, carbonation and corrosion propagation in reinforced concrete structures 1.1. Effects on deterioration processes Chloride ingress and carbonation are two main deterioration processes that affect the durability of RC structures by inducing corrosion initiation. The kinematics of both mechanisms could depend on surrounding conditions such as the atmospheric CO2 concentration, temperature, and humidity [START_REF] Nguyen | An Efficient Chloride Ingress Model for Long-Term Lifetime Assessment of Reinforced Concrete Structures Under Realistic Climate and Exposure Conditions[END_REF][START_REF] Bastidas-Arteaga | Reliability of Reinforced Concrete Structures Subjected to Corrosion-Fatigue and Climate Change[END_REF]. These environmental conditions could be affected by climate change. For example, some climate change scenarios suggest that the environmental CO2 concentration could increase from 379 ppm in 2005 to about 1000 ppm by the year 2100 (IPCC 2007(IPCC , 2013)). On the other hand, new temperature and humidity variations expected for certain climate change scenarios could also impact the rates of chloride and CO2 diffusion as well as corrosion initiation that could lead to greater corrosion damage. For the above-mentioned reasons, the effects of climate change should be considered for assessing the resistance of RC structures under new climate change conditions.

Assessing the effects of climate change on the kinematics of these deterioration processes requires using models able to account for environmental variations. For chloride ingress and carbonation, such models usually consider factors that increase or decrease the diffusion coefficients (chlorides, CO2, and moisture) when environmental variations in temperature and relative humidity are expected. For example, the effect of a time-variant temperature (𝑇(𝑡) in kelvins) on diffusion could be modeled based on the Arrhenius law for a reference temperature 𝑇 𝑟𝑒𝑓 =20°C:

𝑓 𝑇 (𝑡) = 𝑒𝑥𝑝 (𝐸/𝑅[1/𝑇 𝑟𝑒𝑓 -1/(𝑇(𝑡))])

(1

)
where 𝐸 is the activation energy of the diffusion process and 𝑅 is the gas constant (8.314x10 -3 kJ/mol.K). The effects of temperature variations on 𝑓 𝑇 are illustrated in Figure 1. It is noted that for several values of 𝐸 the CO2 diffusivity will increase for higher temperatures because 𝑓 𝑇 multiplies the CO2 diffusion coefficient in the chloride ingress and carbonation models. Therefore, chloride ingress and carbonation rates will increase for higher temperatures. Specific expressions can be found in the literature for considering relative humidity (Bastidas-Arteaga, 2018; [START_REF] Larrard | Effects of Climate Variations and Global Warming on the Durability of RC Structures Subjected to Carbonation[END_REF].

Assessing the effects of climate change on the corrosion rate of steel bars is not an easy task because of the complexity of the corrosion process itself. After corrosion initiation, the corrosion rate will depend on steel and concrete properties as well as surrounding environmental conditions (temperature and the availability of water and oxygen), which could in turn be affected by the presence of cracks. Therefore, there is no consensus about the best model that could be used for lifetime assessment purposes. Among the available models, the one proposed in the framework of the Duracrete project ( 2000) suggested a bilinear formulation to account for the effects of temperature on the corrosion rate in microamperes per square centimetre:

𝑖 𝑐𝑜𝑟𝑟 (𝑡) = 𝑖 𝑐𝑜𝑟𝑟,20 (1 + 𝐾 𝑐 [𝑇(𝑡) -20]) (2)
where 𝑖 𝑐𝑜𝑟𝑟,20 is the corrosion rate at 20 °C, which depends on the exposure conditions, 𝑇(𝑡) is the temperature at time 𝑡 (in degrees Celsius) and 𝐾 𝑐 is a factor that depends on the value of 𝑇(𝑡). For instance, 𝐾 𝑐 = 0.025 if T(t) < 20°C or 𝐾 𝑐 =0.073 if 𝑇(𝑡) > 20°C.

The effects of temperature variations on the corrosion rate estimated by using Equation 2 are illustrated in Figure 2. It is observed that larger corrosion rates can be expected when temperature increases. Therefore, a greater reduction in the structural resistance could be expected where temperature increases as a result of climate change. Further research is still required to assess better the evolution of the corrosion rate when RC structures are subjected to realistic exposure conditions including the effects of climate change.

Concrete carbonation

Several studies have estimated the increase of the carbonation depth due to climate change in a number of countries. [START_REF] Talukdar | Carbonation in concrete infrastructure in the context of global climate change: Part 2 -Canadian urban simulations[END_REF] found, for a pessimistic climate change scenario, potential increases in carbonation depth over 100 years of 45% in Toronto and Vancouver in Canada. Maximum increases ranging between 40% and 45% were also reported by [START_REF] Saha | Urban scale mapping of concrete degradation from projected climate change[END_REF][START_REF] Peng | Spatial time-dependent reliability analysis of corrosion damage to RC structures with climate change[END_REF][START_REF] Mizzi | Effects of climate change on structures; analysis of carbonation-induced corrosion in Reinforced Concrete Structures in Malta[END_REF] for other locations in the USA, China/Australia and Malta, respectively. Climate variables and their effect on concrete deterioration is region specific -there is a need to consider corrosion damage impact in time and space. For example, [START_REF] Stewart | Climate Change Adaptation for Corrosion Control of Concrete Infrastructure[END_REF] used advanced simulation procedures to predict increases in carbonation-induced corrosion damage risks under a changing climate in Australia in terms of changes in the probability of reinforcement corrosion initiation and corrosion induced damage. The detailed spatial and time-dependent probabilistic analysis included the random variability of cover, concrete strength, water-cement ratio, diffusion coefficient, corrosion rate, model uncertainty, time-dependent concentration of CO2, yearly mean temperature and relative humidity. In Figure 3, the variability of CO2 projection modelling errors is represented by a COV of 0.05. The uncertainty of climate projections for temperature and relative humidity was based on nine General Circulation Models (GCMs). For Sydney, this represents a variability in temperature of ±1.5°C and in relative humidity of ±4% by 2100 for the A1FI emission scenario. In the arid zone in central Australia, carbonation does not occur due to a lack of moisture. The area is extended when the future climate becomes drier around central Australia with a projected reduction of relative humidity of up to 15%. Hence, when compared to the 2000 baseline (no climate change) scenario, carbonation depths will be lower than otherwise would be the case. On the other hand, the damage probability is higher around the boundary between the arid climatic zone in central Australia and the temperate climatic zone in the west, south as well as the east of Australia. This is mostly caused by a lower cover requirement for concrete structures in arid and temperate climatic zones, which are also away from coasts. If damage is defined as corrosion-induced cracking greater than 1 mm, then carbonation-induced damage risks could increase by up to 16% by 2100. This suggests that up to one in six structures will experience additional and costly corrosion damage by 2100. It is important to recognize that CO2 levels in urban, suburban and rural locations are usually higher than the global mean value because of anthropogenic and natural sources. [START_REF] Peng | Climate Change and Corrosion Damage Risks for Reinforced Concrete Infrastructure in China[END_REF] estimate that the CO2 levels in urban centres are about 14% higher than the global mean value often reported by the IPCC. While many studies report only on the worst case (and least likely) unmitigated emission scenario (A1F1, RCP8.5), the corrosion impact of less severe CO2 projections is also considerable. For example, [START_REF] Peng | Climate Change and Corrosion Damage Risks for Reinforced Concrete Infrastructure in China[END_REF] show that under the medium RCP 4.5 emission scenario mean carbonation depths can increase by 18% from 19 mm in 2000 to 22.5 mm by 2100 for some cities in China (see Figure 4). Carbonation depth will increase to 28 mm for the RCP8.5 scenario. Sensitivity analyses show that concrete cover has the largest effect on damage risks, followed by relative humidity, and concrete strength has a negligible effect on damage risks.

Chloride ingress

RC structures also suffer from deterioration issues related to the coastal environment. Reductions in the cross sectional area of steel reinforcement bars, reductions in loading resistance, and concrete cover cracking are examples of the negative effects of the presence of high chloride concentrations in coastal areas. A characteristic example of a deteriorated RC structure is given in Figure 5. In this figure, the deterioration of a coastal RC power station on a Mediterranean island is shown. As sea level rise is a potential effect of climate change, coastal structures may become closer to the sea, which means that they will be more exposed to decay and corrosion actors [START_REF] Gao | Impacts of Global Warming and Sea Level Rise on Service Life of Chloride-Exposed Concrete Structures[END_REF]. Therefore, the marine environment effect is expected to be intensified on structures and to reduce their service life.

Concerning chloride ingress, (Bastidas-Arteaga 2010) found that climate change could produce lifetime reductions varying from 2% to 18% depending on the exposure conditions and climate change scenarios. Larger chloride concentrations in the vicinity of rebars (increments of 37%) have been reported by [START_REF] Khatami | Climate change impact on management of deteriorating bridges: A case study of US Midwest Region[END_REF] for structures located in the US Midwest region. Previous studies indicate that increases in carbonation depth, chloride concentration at the rebar level and corrosion rate produced by climate change, would result in premature corrosion initiation or time to failure. Therefore, it is paramount to account for these effects for designing and maintaining more climate resilient RC infrastructure. Additionally, it should be noted that in some regions, a decrease on cold spells during winter may have a beneficial effect in terms of less need to use de-icing salts on bridge decks (Railway Safety and Standards Board, 2011), making projections region specific.

A recent case-study based investigation by the IABSE working group in this area includes the study of Ferrycarrig Bridge, an Irish bridge in a chloride rich environment (Figure 6). This bridge was repaired in 2007 using five different concrete repair types on the bridge's seven crosshead beams (Ryan andO'Connor, 2013, 2014). The recent research has explored the possible effects of climate change on two of the concrete types used on the bridge, namely the Ordinary Portland Cement (OPC) repair and the 40% OPC + 60% Ground Granulated Blast Furnace Slag (GGBS) repair. The work considered the RCP4.5 and RCP8.5 scenarios, and modelled the chloride initiation phase based on the work of Bastidas-Arteaga et al. ( 2011), who developed a combined finite element and finite difference modelling approach. The crack initiation phase in the study was modelled using the work of El Maaddawy and Soudki (2007), while the work of [START_REF] Mullard | Corrosion-Induced Cover Cracking: New Test Data and Predictive Models[END_REF] was utilized to represent the crack propagation phase for the bridge. The study examined how each concrete was affected by predicted climate change, and how the performance of the OPC + GGBS relative to the OPC changed under various climate scenarios. This relative merit metric was obtained by dividing the time to severe cracking for OPC + GGBS by the time to severe cracking for OPC. As expected the OPC + GGBS repair outperformed the OPC repair in the model, with a relative merit of 4.75 for the no climate change scenario i.e. the predicted time to severe cracking was 4.75 times longer for the OPC + GGBS than for the OPC concrete under the no climate change scenario. This relative merit was however found to reduce owing to climate change, dropping to 4.11 under the RCP8.5climate change scenario. This was primarily due to the fact that climate change affects OPC + GGBS concrete to a greater extent as this concrete will last longer into the future climate owing to its increased durability in aggressive marine environments. Further details of the findings of this study can be found in [START_REF] Wallace | Modelling the impact of climate change on a novel Irish Concrete Bridge[END_REF]. Stochastic processes were used to model temperature and relative humidity variations by considering two climate change scenarios. For instance, the pessimistic scenario considers that there is a large use of fossil sources of energy, appreciable growth of population, with no policies to develop and extend the use of clean technologies (equivalent to scenarios RCP6-RCP8.5, depending on the location). Average increases of 6.5°C and 0.1 were considered for the temperature and relative humidity, respectively. Seven random variables were considered to account for the uncertainty related to chloride ingress, moisture and heat transfer. Two additional random variables were included to consider the uncertainty linked to concrete and steel resistance. The details of these stochastic processes and random parameters are to be found in [START_REF] Bastidas-Arteaga | Reliability of Reinforced Concrete Structures Subjected to Corrosion-Fatigue and Climate Change[END_REF]. In Table 1 are presented the mean and the coefficients of variation of the times to failure for various traffic frequencies, exposure conditions, and climate change scenarios. Two levels of aggressiveness are included in the analysis where each level is characterized by an environmental (surface) chloride concentration (𝐶 𝑒𝑛𝑣 ) and a corrosion rate (𝑖 𝑐𝑜𝑟𝑟,20 ): high (𝐶 𝑒𝑛𝑣 = 2.95 kg/m 3 and 𝑖 𝑐𝑜𝑟𝑟,20 = 5.0 μA/cm 2 ) and low (𝐶 𝑒𝑛𝑣 = 0.35 kg/m 3 , 𝑖 𝑐𝑜𝑟𝑟,20 = 0.5 μA/cm 2 ). The results in Table 1 show that the mean time to failure decreases for more aggressive environments and larger traffic frequencies. This trend is expected because larger environmental chloride concentration, corrosion rates and traffic frequencies would lead to shorter times to failure.

The environmental exposure includes two weather conditions (without climate change and a pessimistic scenario) for an oceanic environment placed in a middle latitude where the average temperature is 15°C and the average relative humidity is 0.7. The pessimistic climate change scenario is equivalent to an RCP8.5 scenario where it is expected that the temperature increases by 6.5°C and the relative humidity by 0.1. The results show that climate change could induce a reduction of a maximum 7% of the total lifetime for the worst case.

Nevertheless, these findings are conservative because they neglect the effect of climate change on the corrosion rate that was illustrated in Figure 2 for the Duracrete model. In addition, further research is required to establish an accurate model of corrosion rate accounting for relative humidity variations, which will improve the assessment of climate change consequences after corrosion initiation.

Corrosion of steel structures

There have been a number of reviews and discussions on possible impacts that climate change may have on corrosion of metals [START_REF] Cole | Possible effects of climate change on atmospheric corrosion in Australia[END_REF][START_REF] Roberge | Impact of climate change on corrosion risks[END_REF][START_REF] Kumar | Footprints of air pollution and changing environment on the sustainability of built infrastructure[END_REF]. The loss of material due to corrosion is the most significant effect on structural steel members because of the reduction in cross section thicknesses leading to loss of structural resistance and stiffness. The rate of corrosion penetration, which is the amount of thickness that is lost due to uniform corrosion, is influenced by several factors, such as the steel composition, the steel surface homogeneity, the Time Of Wetness (TOW) of the steel surface to be corroded, the water's chemical characteristics (temperature 𝑇, 𝑝𝐻, dissolved oxygen 𝑂 2 , salinity 𝑆), nutrients (bio-corrosion) and the microclimate conditions. In the tide and immersed areas, the effect of these parameters on the corrosion rate has been quantified from an experimental study [START_REF] Liu | Correlation between seawater environmental factors and marine corrosion rate using artificial neural network analysis[END_REF]. A response surface of the corrosion 𝐶(𝑡) calibrated from this database is proposed as 𝐶(𝑡) = (0.1576 + 0.0033𝑇 -0.0108𝑝𝐻 -0.0030𝑆 + 0.0133𝑂 2 )𝑡 (3) This model can be used for updating the probabilistic long term corrosion model without climate change effect [START_REF] Schoefs | Long-term stochastic modeling of sheet-pile corrosion in coastal environment from on site-measurements[END_REF] where the corrosion rate is computed from the corrosion at 𝑡 = 30 years divided by 30 years.

The content of pollutants (sulphur dioxide and chlorides) in the atmosphere surrounding the steel member also has a significant influence on the level of corrosion. Potential changes in temperature would affect the rate of electrochemical reaction of the corrosion process. Changes in relative humidity affect the TOW of the metal surface, which is the basic condition for the corrosion process to take place.

The prediction model for atmospheric corrosion of low-alloyed steels is based on the Dose-Response Function (DRF) according to ISO 9223 [START_REF] Mikhailov | The Classification System of ISO 9223 Standard and the Dose-Response Functions Assessing the Corrosivity of Outdoor Atmospheres[END_REF][START_REF] Knotkova | Corrosivity of atmospheres-derivation and use of information[END_REF], which defines the one-year corrosion rate as follows: 𝐴 = 1.77𝑆𝑂 0.52 𝑒 (0.02𝑅𝐻+𝑓 𝑆𝑡 ) + 0.102𝐶𝑙 0.62 𝑒 (0.033𝑅𝐻+0.04𝑇) (4)

where 𝑆𝑂 is the average annual deposition of 𝑆𝑂 2 (mg/(m 2 .d)), 𝑅𝐻 is the average annual relative humidity (%), 𝐶𝑙 is the average annual deposition of 𝐶𝑙 -(mg/(m 2 .d)) and 𝑇 is the annual (average) temperature (℃). 𝑓 𝑆𝑡 is a temperature factor where 𝑓 𝑆𝑡 = 0.15(𝑇 -10) if 𝑇 ≤ 10℃ and 𝑓 𝑆𝑡 = -0.054(𝑇 -10) otherwise. The average amount of corrosion (thickness loss) over time 𝐶(𝑡), at any time 𝑡, can then be estimated using the classical exponential corrosion model:

𝐶(𝑡) = A𝑡 𝐵 ( 5
)
where 𝐵 is an experimentally determined coefficient obtained through regression analysis on test results in different environmental exposure conditions. Equation ( 5) is useful in estimating the first year corrosion based on the actual exposure conditions (𝑆𝑂 2 , 𝑇, etc). However, the influence of long-term changes of exposure conditions (due to climate change and/or increase/decrease of the concentration of atmospheric pollutants) on the rate of corrosion over time cannot be considered using this model. To overcome this, the model of [START_REF] Klinesmith | Effect of environmental conditions on corrosion rates[END_REF], given by Equation ( 6) below, allows the calculation of thickness loss due to corrosion considering the evolution of the different climatic and atmospheric variables:

𝐶(𝑡) = 𝐴𝑡 𝐵 ( 𝑇𝑂𝑊 𝐶 1 ) 𝐷 (1 + 𝑆𝑂 2 𝐸 1 ) 𝐹 (1 + 𝐶𝑙 𝐺 ) 𝐻 𝑒 𝐽(𝑇+𝑇 0 ) ( 6
)
where 𝑇𝑂𝑊 is the time of wetness (h/year), 𝑆𝑂 2 is the sulphur dioxide concentration (μg/m 3 ), 𝐶𝑙 is the chloride deposition rate (mg/(m 2 .d)), 𝐶 1 = 3800 h/year (mean value), 𝐸 1 = mean of measured values of 𝑆𝑂 2 (μg/m 3 ), 𝑇 is the air temperature ( o C), and 𝑇 0 = 20 o C. For flat carbon steel specimens: 𝐴 = 13.4, 𝐵 = 0.98, 𝐷 = 0.46, 𝐹 = 0.62, 𝐻 = 0.34 and 𝐽 = 0.016.

A very significant parameter for corrosion of steel is chloride deposition. The model of atmospheric corrosion includes salinity parameters -the deposition rate of airborne salt spray for natural sources (e.g. sea salts) or deicing salt for winter maintenance of roads. The deposition rate of both these salinities is affected by climate change. Increase in seawater temperature results in increase in the amount of chloride concentration in water; storms and strong waves may also increase the effect of chloride deposition on the surfaces of steel structures. Climate change projections provide estimates of likely changes in mean wind speed (IPCC 2013) and by using the DRF these changes can be used to estimate changes of airborne salinity. Accordingly, the corrosion rate of carbon steel may decrease or increase depending on local climate changes.

The corrosion of steel structures begins after degradation of corrosion protection coatings that have been applied on them. Low alloyed steel structures are protected against corrosion by various types of protective coatings -metallic, organic or duplex. The most frequently applied metallic coatings are various types of zinc or zinc-alloyed coating. The zinc coatings are more sensitive to the effect of high humidity than steel. Unfortunately, there is no model for service life prediction of paint systems. A DRF for coatings has been suggested in the past [START_REF] Tidblad | UN ECE ICP Materials: Dose-Response Functions on Dry and Wet Acid Deposition Effects After 8 Years of Exposure[END_REF]) but the effect of climate change on the deterioration of coatings has not been investigated [START_REF] Sousa | Expected implications of climate change on the corrosion of structures, EUR 30303 EN[END_REF]. Research efforts for developing deterioration models for assessing the effectiveness of coatings on structural resistance can be found in [START_REF] Kallias | Performance profiles of metallic bridges subject to coating degradation and atmospheric corrosion[END_REF]. Practical experience shows that the maximum service life of paint systems is 25 years in contemporary conditions. In addition to the climate and pollution parameters, the service life of paint coatings is significantly affected by UV radiation. Thirty years of satellite data show that the amount of ultraviolet (UV) radiation reaching the Earth's surface has markedly increased over the last three decades [START_REF] Herman | Global increase in UV irradiance during the past 30 years (1979-2008) estimated from satellite data[END_REF]. Most of the increase has occurred in the mid-and-high latitudes, e.g., at latitude 32° the UV radiation has increased by 6% on average since 1980. These changes decrease the service life of paint coatings, but the amount of the degradation increase is based on laboratory data only [START_REF] Artemova | Influence of the UV Radiation on the Corrosion Resistance of the Carbon-Based Coatings for the Marine Industry[END_REF]).

Steel structures in atmospheric environment

Since 1986, one-year exposures of carbon steel panels have been performed every three years on the network of European atmospheric test sites within the framework of the United Nations Economic Commission for Europe (UNECE) International Cooperative Programme (ICP) Materials. Comparisons carried out on corrosion loss between exposures in the years 2012 and 2015, have shown some interesting results: (i) the increase of yearly corrosion loss of carbon steel was 50% on test sites where the yearly average temperature increased by 2°C; (ii) the amount of precipitation had a more significant effect although this parameter is not included into the doseresponse function -in the period 2014-15 the yearly amount of precipitation was higher by 60% on some test sites and yearly corrosion rate on the same test sites increased by 70%. It should also be noted that the winter season of 2014-15 was warmer and more humid than usual in Europe.

Nguyen et al. ( 2013) have conducted a study of climate change effects on atmospheric corrosion rate of steel and zinc structures. They found that corrosion rates vary quite markedly between different regions in Australia due to changes in temperature, relative humidity and airborne salinity. Table 2 shows that the corrosion rate is predicted to decrease by up to 11% for steel and zinc structures in Melbourne to 2100, most likely as a result of a 3% lowering of relative humidity. On the other hand, corrosion rates are predicted to increase by up to 36% in Brisbane, a city 2000 km to the north of Melbourne. A sensitivity analysis on the effect of different climatic and atmospheric variables on the long-term predictions of corrosion thickness losses is shown in Figure 7. The parameters investigated were TOW, temperature, chloride and sulphur dioxide concentrations. The results show that the latter two concentrations have the greatest impact on the long-term rate of corrosion with TOW having a smaller impact. Similar trends have also been reported by [START_REF] Chico | Annual Atmospheric Corrosion of Carbon Steel Worldwide. An Integration of ISOCORRAG, ICP/UNECE and MICAT Databases[END_REF]. A similar analysis carried out by [START_REF] Tidblad | Atmospheric corrosion of metals in 2010-2039 and 2070-2099[END_REF] showed that future atmospheric corrosion of metals in Europe will be dominated by the effects of chloride deposition in coastal and near-coastal areas. This effect will be higher in the future than it is today since a fixed chloride deposition will have a higher impact when the temperature increases. In another study, Imam (2019) estimated the time-dependent reliability of a typical plate girder railway bridge under different climate change and atmospheric pollution scenarios. It was found that the overall direct effect of increasing solely average annual temperature on bridge reliability is relatively small. On the other hand, the effect of 𝑇𝑂𝑊 on bridge reliability was found to be more influential, resulting in an order of magnitude increase in the probability of failure in the 2100s, for this specific case study, when 𝑇𝑂𝑊 increased from a range of 250-2500 hours/year to 2500-5500 hours/year, according to the ISO 9223 𝑇𝑂𝑊 categories. A risk-based assessment carried out in the same study also showed that mitigation of the atmospheric pollution (i.e. the reduction of 𝑆𝑂 2 over time) can have a positive influence but only after a period of several decades has evolved. Hence, any mitigation actions on improving air quality in urban areas may only be beneficial in the long-term. However, although the long-term reduction of 𝑆𝑂 2 concentration in an area can enhance the reliability and hence reduce the risk of the exposed structure, it was shown that the probability of failure over time and associated risk remain higher compared to a bridge exposed to a less polluted environment throughout its service life.

Steel structures in marine environment

In marine environments, climate change affects the long-term structural reliability of coastal infrastructures through three mechanisms: corrosion rate due to the decrease of sea water pH, structural stability and the corrosion location, both due to the rise in sea water levels. This section investigates the potential impacts of climate change on steel walls in harbor areas. Harbors play a major socio-economic role all over the world for trade exchange and defense and efficient management of steel structures, particularly steel walls, is crucial.

Concerning sea water pH, IPCC reports that pH could fall from 8.1 (in the 1980s) to 7.7 in 2100 according to the RCP8.5 projection [START_REF] Abram | Framing and Context of the Report[END_REF]. This can result in small changes in the corrosion rate [START_REF] Liu | Correlation between seawater environmental factors and marine corrosion rate using artificial neural network analysis[END_REF]. Sea water level rise could be in the range 0.7-1.1 meters in 2100 in comparison with the 1980's with a large scatter around the world. This can drastically affect the reliability of sheet piles by moving the location of extreme corrosion (area of low tidal sea level) [START_REF] Schoefs | Long-term stochastic modeling of sheet-pile corrosion in coastal environment from on site-measurements[END_REF]) and the pressure of water level in the embankment [START_REF] Boéro | Time-function reliability of harbour infrastructures from stochastic modelling of corrosion[END_REF]. Note that the mean elevation of sea level in 2100 is planned to reach 0.55m for scenario RCP 2.6 and 0.82m for scenario RCP8.5. Figure 8 gives the translation of mean corrosion profile of a sheet pile designed in [START_REF] Boéro | Time-function reliability of harbour infrastructures from stochastic modelling of corrosion[END_REF]) for a sheet pile in a tidal environment for scenario RCP 2.6. It is observed that the maximum corrosion (area 3, low tide) will move upwards causing more corrosion in the zone [-4m; -3m] where the tie-rod (see Figure 8 left) can be placed. The immersion area moves upwards also and the area (4) will be less corroded than predicted: which is usually the location of high stresses. This example illustrates the complexity of the effects that can decrease or increase the resistance of a structure.

Fig. 8. Left: evolution of a typical corrosion profile for a sheet pile in a tidal area due to sea water level: without climate change (dashed blue) and with climate change (dashed red). Right: typical sheet pile

Pitting corrosion is a serious concern for steel structures, and particularly so for those in marine conditions such as pipelines where perforation of steel can lead to leakage of pollutants. Many environmental factors are known to influence corrosion in sea water including bacteria, biofouling, nutrients, temperature, oxygen concentration, pH of the environment, carbon dioxide concentration, salinity, carbonate concentration, pollutants, pressure, stress, fatigue loading and stress, suspended solids, wave action and water velocity [START_REF] Melchers | Using models to interpret data for monitoring and life prediction of deteriorating infrastructure systems[END_REF]. Climate change may affect many of these variables, especially nutrient levels in sea water. A complete model was recently developed to account for more effects such as biocorrosion: an increase of up to 10% in the probability of failure of a sheet pile was computed [START_REF] Chaves | Probabilistic remaining life estimation for deteriorating steel marine infrastructure under global warming and nutrient pollution[END_REF]. [START_REF] Peng | Corrosion and Capacity Prediction of Marine Steel Infrastructure Under a Changing Environment[END_REF] found that sea temperature rise in itself will increase the mean of pitting corrosion depths by up to 10% for steel sheet piling. However, this effect is largely offset by sea level rise caused by climate change as it will shift the corrosion zone upwards and so expand the corrosion area resulting in shallower corrosion depths. Hence, sea water temperature increase and sea level rise can delay pit perforation by at most two years compared to the reference year 2015 scenario [START_REF] Peng | Corrosion and Capacity Prediction of Marine Steel Infrastructure Under a Changing Environment[END_REF]. This highlights the important need to model carefully the interdependencies associated with climate change.

Timber decay

The decay rate of timber is site-and material-specific and depends on exposure conditions (in-ground versus above ground), climatic conditions (temperature, rainfall, humidity), wood species, initial preservative treatment, and nature of fungal attack, among other factors. The main climate parameters that affect timber decay are humidity and temperature [START_REF] Teodorescu | Influence of the Climatic Changes on Wood Structures Behaviour[END_REF]. The exposure of timber to a humid environment increases its moisture content. An increase in the moisture content above the fibre saturation point will provide a viable environment for the establishment of a fungal mycelial mat and further fungal growth [START_REF] Viitanen | Brown rot decay in wooden constructions[END_REF]. Moisture content above the fibre saturation point results in the availability of free water in the timber, which is easily accessible to the fungi and leads to rapid decay (Wang & Wang 2012). The growth of decay (1)

(3) (4)

-12.5 m -0.5 m q fungi is also significantly affected by air and timber temperature [START_REF] Brischke | Influence of wood moisture content and wood temperature on fungal decay in the field: observations in different micro-climates[END_REF]. It is, therefore, clear that the long-term structural resistance of timber will be affected by any potential future climate variations.

Deterioration over time for timber structures has been incorporated into previous studies. Decay models are based on in-field or in-lab measures and report results for specific wood species and climatic conditions [START_REF] Brischke | Influence of wood moisture content and wood temperature on fungal decay in the field: observations in different micro-climates[END_REF]. Decay models developed for above-ground conditions include [START_REF] Leicester | Design of exposed timber structures[END_REF], [START_REF] Isaksson | Development of decay performance models for outdoor timber structures[END_REF][START_REF] Viitanen | Towards modelling of decay risk of wooden materials[END_REF]. Decay models for timber in ground contact are relatively rare. [START_REF] Li | Degradation-path model for wood pole asset management[END_REF]) developed a decay model based on field data from 13,940 poles ranging from age 1 to 79 years. About 8% of the poles showed various degrees of decay. Wang et al. (2008b) developed a decay model for wood in ground contact using in-field data from 77 commonly used commercial timber species buried at five test sites in eastern and southern Australia over a 35-year period. The developed model is a function of the type of timber, mean annual rainfall (including the number of dry months in a year), and the mean annual temperature. (Ryan et al. 2014) used this model to assess the effects of decay on the structural capacity of both treated and untreated timber power poles, with the effects of deterioration and network maintenance incorporated in the analysis. Salman et al. (2020) also used this model to study the impact of climate change on the decay rate of timber utility poles. Timber has been the material of choice for supporting power distribution lines around the world. For example, there are between 160 million and 180 million timber poles in the USA worth billions of dollars [START_REF] Mankowski | Wood pole purchasing, inspection, and maintenance: A survey of utility practices[END_REF]. Timber poles are preferred over other materials because they are relatively cheap to purchase, lighter and easier to transport, easy to climb and non-conductive, making them safer for utility workers [START_REF] Mankowski | Wood pole purchasing, inspection, and maintenance: A survey of utility practices[END_REF]. However, timber poles are susceptible to decay, which usually occurs at or just below the ground level.

The decay rate of timber poles is expected to be affected by climate change, which can increase the decay rate. Such an increase will require utility companies to invest more in periodic inspection and replacement of poles.

A study by [START_REF] Salman | Optimization of Condition-Based Maintenance of Wood Utility Pole Network Subjected to Hurricane Hazard and Climate Change[END_REF] investigated the impact of climate change on timber poles in two locations in the USA: Miami and New York City. These cities correspond to different types of climate. Miami is in the southeastern part of the USA and has a tropical monsoon climate with hot and humid summers and short and warm winters. New York City (NYC) is in the north-eastern part of the USA and has a humid subtropical climate, with cold winters and hot, moist summers. Projected precipitation and temperature data were obtained from the Coupled Model Intercomparison Project phase 5 (CMIP5) multi-model ensemble [START_REF] Maurer | Fine-resolution climate projections enhance regional climate change impact studies[END_REF]. Figure 9 shows the effect of climate change on the decay rates for the RCP4.5 and 8.5 scenarios. Under the RCP8.5 scenario, the decay rates are expected to increase by about 9% and 17% compared to the 2005 rate in Miami and NYC, respectively, by the end of the 21 st century. The higher increase in the decay rate in NYC can be attributed to a projected higher increase in precipitation. Figure 9 also shows how increased timber pole decay due to climate change will increase the number of poles that will fail due to extreme wind in the two locations at the end of the 21 st century. NYC Miami

The regional variation of the impact climate change on timber decay and resulting structural resistance has also been illustrated by [START_REF] Ryan | Probabilistic Analysis of Climate Change Impacts on Timber Power Pole Networks[END_REF], who examined the climate change impacts on timber power pole performance in five different regions of Australia. This analysis indicated that climate change impacts on power pole networks are likely to be substantial for some locations in Australia, with Brisbane experiencing a projected 12% increase in pole condemning rates, and a 59% increase in wind failure rates of deteriorated poles over the period 2015 to 2070. However, results were highly-regionally variable, with Melbourne experiencing negligible or even slightly positive climate change impacts (3% reduction in pole failures rates under medium climate scenario). Indeed the nature of the impacts across the five regions were not intuitive, depending on opposing interactions of temperature, rainfall and wind, the baseline climactic conditions in a region, and the nature of the uncertainty associated with future climatic predictions. Other work by these authors examined the probabilistic cost benefit analysis of climate adaptation options for power pole networks in Brisbane [START_REF] Ryan | Cost-benefit analysis of climate change impacts for power pole networks[END_REF], and the regional variability of climate change adaptation feasibility for such networks across Australia (Ryan and Stewart, 2021). The latter study showed that the cost-benefit performance of adaptation strategies are also highly regionally variable. This emphasized the need for detailed and regionally specific modelling of climate change adaptation feasibility to inform national and international policies, and increase the resilience of timber critical infrastructure to climate change in a cost effective manner.

More recent work by IABSE TG6.1 members has examined the impacts of climate change on timber power pole networks in Europe (Ryan et al. 2021). This analysis, which also utilized the probabilistic decay model developed by Wang et al. (2008a,b), explored climate change impacts on power pole networks in two Irish cities, namely Cork and Dublin. The study incorporated network maintenance, inspection error and structural reliability modelling. To incorporate the uncertainty associated with climate change projections in this study the changes in temperature, wind speed and rainfall were modelled probabilistically using distributions developed from the full ensemble of downscaled climate projection simulations available for Ireland. Further details are provided in Ryan et al. (2021). Figure 10 shows the cumulative wind failures of deteriorating poles under a number of climate change scenarios for the two cities. It is noted that wind failure in this study was defined as the bending failure of a deteriorated timber power pole under wind loading. This limit state was selected based on the most common failure model of timber power poles [START_REF] Winkler | Performance assessment of topologically diverse power systems subjected to hurricane events[END_REF]. Climate change impacts on both cities were similar, with approximately 16% more wind failures of deteriorated poles under the RCP4.5 scenario and 25% more for the RCP8.5 scenario. Figure 10 also illustrates the role that timber deterioration plays in power pole wind failures for any climate scenario. At the start of the modelling period (the year 2000), when the network of one million power poles were in an undeteriorated state, the power pole failure rate was very low (the slope of the line in the plot); however as the poles deteriorated prior to the first inspection after 20 years, deterioration led to a steady increase in power pole failure rates. Figure 10 thus illustrates the impact of timber decay on infrastructure, and the impacts of climate change on the performance of timber power pole networks in Europe.

Deteriorated structural resistance under intensified actions

The effects of climate change on long-term structural reliability result not only from the modification of structural resistance, but also from the influence on structural actions. Hence, it is important to consider both aspects (capacity and demand) under a changing climate. While more and more attention has been placed on the timedependent reliability analysis considering climate change impacts either on intensity and frequency of natural hazards (e.g. hurricanes) or on structural deterioration (e.g., corrosion of RC beams), an holistic analysis framework is lacking that simultaneously considers climate change impacts on deteriorating infrastructure resistance and intensifying hazard. [START_REF] Merschman | Assessment of the effectiveness of wood pole repair using FRP considering the impact of climate change on decay and hurricane risk[END_REF] considered the potential impact of climate change on both pole decay rate and hurricane hazard risk in their study investigating the effectiveness of Fiber-Reinforced Polymer (FRP) sleeving reinforcement of timber poles. It was found that, if climate change is only assumed to affect the decay of the pole, the probability of failure of the timber pole at the end of the 21st century under the RCP8.5 emission scenarios in Miami, Charleston and New York City increase by about 5%, 22%, and 20%, respectively. On the other hand, if both the decay of timber poles and the increase in hurricane risk (determined by hurricane intensity and frequency changes) under changing climate are considered, the corresponding increases in failure probability are 30%, 70%, and 73%, respectively. [START_REF] Salman | Age-Dependent Fragility and Life-Cycle Cost Analysis of Timber and Steel Power Distribution Poles Subjected to Hurricanes[END_REF] conducted a life-cycle cost analysis of timber poles that incorporated strength deterioration models in the fragility analysis. These studies have highlighted the susceptibility of the timber components of the critical infrastructure networks to deterioration, the influence of climatic parameters, and the resulting importance of considering potential changes in future climate when assessing timber infrastructure assets.

Masonry material decay and soiling is affected by freeze-thaw cycles, the time of wetness associated with projected warmer and wetter winters and exposure to chlorides [START_REF] Sesana | Climate change impacts on cultural heritage: A literature review[END_REF]. Different parts of Europe are likely to experience different changes in the climate parameters that affect brick and stone masonry structures but, in general, it has been suggested that freeze-thaw cycles, common now for mild climate e.g. in Central Europe, may newly endanger structures in regions with colder climates [START_REF] Lacasse | Durability and Climate Change-Implications for Service Life Prediction and the Maintainability of Buildings[END_REF]). On the other hand, any projected decrease in summer rainfall is likely to increase the soiling potential of masonry material.

In terms of prestressed-concrete, projected decreases in relative humidity along with higher expected temperatures may result in a higher creep rate for concrete leading to higher long-term deformations which can result in loss of pre-stressing forces [START_REF] Nasr | Bridges in a changing climate: a study of the potential impacts of climate change on bridges and their possible adaptations[END_REF]. Furthermore, higher solar radiation in some places may increase the temperature gradient between the top and bottom of bridge decks and result in stress increases.

Finally, it is noted that current studies of deteriorating structure failures subjected to intensified hazards under a changing climate are essentially based on static analyses, while the dynamic behaviour of structures may significantly complicate the analysis and corresponding results. One representative example is the effects of climate change on dynamic instability (i.e. the flutter phenomenon) of long-span bridges under strong winds. According to [START_REF] Selberg | Aerodynamic effects on suspension bridges[END_REF], the change of bridge critical flutter wind speed depends on the relative deterioration degree of the first-order vertical and torsional modal frequencies. With the example of long-span suspension bridges with steel twin-box girders, some long-term field monitoring data suggest that the decease of the firstorder vertical modal frequency due to structural deterioration is more obvious compared to that of the firstorder torsional modal frequency [START_REF] Chu | Life-cycle assessment for flutter probability of a long-span suspension bridge based on field monitoring data[END_REF]. Accordingly, the intensified deterioration due to climate change may potentially enhance the flutter performance of long-span bridges.

Conclusions

In this study, some potential climate-change impacts on structural resistance have been proposed through a review of recent research work on several construction materials, also including recent research outcomes of an international expert panel on the effects of climate change gathered by IABSE TG6.1. By considering specific examples where climate change may produce changes of vulnerability, this article provides projections of additional degradation under different scenarios of climate change (RCPs), on structural resistance. Concerning corroding RC structures (initiation and propagation phases), different environmental conditions are introduced considering climate change effects. The projected higher temperatures, increased precipitation and relative humidity in some areas, and higher carbon dioxide concentrations in the atmosphere may all contribute to an increased risk of structural deterioration. For the particular case of chloride ingress, as sea level rise is a potential effect of climate change, coastal structures may become closer to the sea, which means that they will be more exposed to decay and corrosion factors. However, it is highlighted that climate variables and their effect on concrete deterioration is regionally specific, and that there is a need to consider corrosion damage impact in time and space.

Concerning the corrosion of steel structures, the goal is to investigate the potential change in structural performance, in terms of strength and stiffness, capturing climate change effects on the long-term corrosion of steel elements, both in atmospheric conditions and also in a marine environment. It is shown how the rate of corrosion penetration is influenced by several factors, such as the steel composition, the steel surface homogeneity, the Time Of Wetness (TOW) of the steel surface being corroded, the water's chemical characteristics (temperature, pH, dissolved oxygen, salinity), nutrients (bio-corrosion), the microclimate conditions, the content of pollutants (sulphur dioxide) in the atmosphere and chloride deposition. A particular type of critical steel structure in harbour areas is considered namely steel sheet piles, where resistance might depend on sea water acidity (corrosion kinetics), change of mean level of tide (stability) and rise in sea water level (corrosion location). Also, the effects of deterioration on the structural resistance of timber, a natural material susceptible to decay, are considered, to see how deterioration may be affected by climate change in the future. Site-and materialspecific models from the literature are used to quantify the decay rate of timber under several exposure conditions (in-ground versus above ground), climatic conditions (temperature, rainfall, humidity), wood species, initial preservative treatment, and the nature of fungal attack, among other factors. This additional degradation can then be integrated in a structural reliability analysis to characterize how different scenarios of climate change may affect the residual capacity of timber structures. Finally, it was discussed how the modification of structural resistance can depend on the influence of structural actions, under intensified hazards. While this article focuses on the structural resistance side, the main challenges for designing and maintaining climate-resilient infrastructures are (i) to consider both resistance and load processes in the context of risk-based approaches, all the more so when intensified actions change the resistance of structures, and (ii) to include cost-benefit optimization under uncertainty of solutions to enhance the resilience of infrastructures to extreme weather events in the short, medium and long term.

Future work in the area should focus on investigating and comparing different climate change adaptation strategies based on their effectiveness in reducing risk, improving system resilience, reducing repair and replacement costs, their potential to reduce indirect losses to stakeholders and developing a system-level risk management framework to facilitate more targeted climate change adaptation that focuses on critical components that have a greater impact on system performance. Considering the large uncertainties associated with projections, it should be analysed how structural health monitoring techniques can play a key role in decision making for existing structures and in the design optimization of new structures.

Fig. 1 .

 1 Fig. 1. Effect of temperature variations on the temperature factor.

Fig. 2 .

 2 Fig. 2. Effect of temperature variations on the corrosion rate.

Fig. 3 .

 3 Fig. 3. Carbonation-induced corrosion of concrete structures by 2100: (a) mean carbonation depth without consideration of climate change, (b) change in carbonation depth for A1F1 emission scenario, (c) probability of corrosion damage without consideration of climate change, (d) probability of corrosion damage for A1F1 emission scenario[START_REF] Stewart | Climate Change Adaptation for Corrosion Control of Concrete Infrastructure[END_REF]. Note that in (d) a negative value indicates a reduction in damage probability).

Fig. 4 .

 4 Fig. 4. Mean carbonation depths for Xiamen in China[START_REF] Peng | Climate Change and Corrosion Damage Risks for Reinforced Concrete Infrastructure in China[END_REF].

Fig. 5 .

 5 Fig. 5. Concrete cover spalling, steel rebar corrosion and loss of concrete cross-section.

Fig. 6 .

 6 Fig. 6. Ferrycarrig Bridge showing the seven repaired crosshead beams.

Fig. 7 .

 7 Fig. 7. Effect of varying climatic and atmospheric pollutant parameters on the corrosion losses with time estimated through Equation (5): (a) Time-Of-Wetness (TOW), (b) Cl deposition rate, (c) SO2 concentration and (d) temperature.

Fig. 9 .

 9 Fig. 9. Left: impact of climate change on timber decay rate. Right: impact of climate change on number of failed poles.

Fig. 10 .

 10 Fig. 10. Impacts of climate change on the cumulative number of wind failures of decaying poles in Ireland (Ryan et al. 2021).

Table 1 .

 1 Mean

	Traffic frequency	High aggressiveness	Low aggressiveness
	(cycles/day)	Without	Pessimistic (RCP 8.5) Without	Pessimistic (RCP 8.5)
	50	54.1 (16%)	52.7 (15%)	159.3 (35%)	153.1 (36%)
	500	36.4 (22%)	35.1 (22%)	105.8 (41%)	99.4 (42%)
	1000	33.8 (23%)	32.6 (22%)	99.3 (41%)	92.5 (42%)
	2000	32.3 (24%)	30.8 (23%)	93.2 (40%)	86.7 (40%)

(in years)

and coefficient of variation (between brackets) of the time to failure for a RC beam placed in a oceanic environment and subjected to two climate change scenarios

[START_REF] Bastidas-Arteaga | Reliability of Reinforced Concrete Structures Subjected to Corrosion-Fatigue and Climate Change[END_REF]

.

Table 2 .

 2 Average

	City	Relative	Year 2030	Year 2050	Year 2070	Year 2100
		corrosion rates
	Melbourne	Zinc Steel	0.973 0.963	0.949 0.929	0.926 0.893	0.907 0.858
	Brisbane	Zinc Steel	1.020 1.019	1.045 1.045	1.083 1.082	1.139 1.138

effects of climate change on relative corrosion rates at certain years for Melbourne and Brisbane under A1FI scenario (adapted from

[START_REF] Nguyen | An assessment of climate change effects on atmospheric corrosion rates of steel structures[END_REF]

.

Acknowledgements

This study is an outcome of IABSE TG6.1.


Alexis Descatha

Yves Roquelaure

Jean-François Chastang

Bradley Evanoff

Diane Cyr

Annette Leclerc

Jean-Fran Ois Chastang

Description of outcomes of upper-extremity musculoskeletal disorders in workers highly exposed

Keywords: Adolescent, Adult, Arm Injuries, diagnosis, epidemiology, rehabilitation, Carpal Tunnel Syndrome, diagnosis, epidemiology, rehabilitation, Cross-Sectional Studies, Cumulative Trauma Disorders, diagnosis, epidemiology, rehabilitation, Disability Evaluation, Female, Follow-Up Studies, France, Health Surveys, Humans, Job Satisfaction, Male, Middle Aged, Occupational Diseases, diagnosis, epidemiology, rehabilitation, Pain Measurement, Prognosis, Rehabilitation, Vocational, statistics & numerical data, Rotator Cuff, injuries, Tennis Elbow, diagnosis, epidemiology, rehabilitation, Young Adult

INTRODUCTION

Even though upper extremity musculoskeletal (UEMS) disorders are an important problem in many countries, ( ) little is known 1 about its natural history in workers exposed to repetitive tasks. Cole and Hudak in 1996 reviewed the prognosis of non specific work-related UEMS disorders. Among the 13 relevant studies, none of them had sufficient validity to provide more than weak evidence on clinical course or prognosis of these disorders. ( ) The authors recommended that closer attention be made to the following criteria: clear 2 operational definition of cases; documentation of prognostic factors, including duration of symptoms and severity at baseline; incorporation of multiple follow-up assessments; inclusion of a range of outcomes; and analysis using stratified or multivariate methods.

Hagberg, in 2005, reviewed the clinical assessment, prognosis and return to work of UEMS disorders, and concluded that, despite the large number of patients with UEMS disorders, the scientific evidence for clinical criteria to determine prognosis was low. ( ) Kuijper et al with caution because of the small number of studies on which these conclusions were based, and the large heterogeneity among studies regarding follow-up, outcome measures, and analysis methods. We previously found that work with force was associated with a poorer prognosis, as were age and pain intensity at baseline.( ) 5

We aimed to describe the three-year outcome for workers suffering from UEMS symptoms or disorders in a population highly exposed to repetitive work.

MATERIALS AND METHODS

Subjects

This study used data from the repetitive task survey conducted in 1993 1994 with a follow-up in 1996 1997.

Diagnosis

In 1993 1994, subjects filled out a Nordic-style questionnaire about UEMS symptoms during the previous six months. The questionnaire included three pages for each anatomical region (shoulder, arm, elbow, forearm, wrist and hand) regarding pain, discomfort, ache with an anatomical diagram. The questionnaire was considered positive if the worker reported at least one symptom in the upper extremities for the recall period. Each worker was examined by one of 18 occupational physicians at baseline and again in 1996 1997.

-Examinations followed a standardised protocol and used a list of criteria for the diagnoses of UEMS disorders. These guidelines required the combination of symptoms and physical findings to meet criteria for UEMS disorders, and covered 33 diagnoses in 1993 1994 and 35 in 1996 1997. The only change between the two lists was limited to shoulder tendinitis, with more precision in the second questionnaire about the tendon involved). The questionnaires included rotator cuff syndrome, lateral epicondylitis and carpal tunnel syndrome but also thoracic outlet, medial epicondylitis, ulnar nerve entrapment at elbow, radial nerve entrapment at elbow, tendonitis of the forearm pain intensity in 1993 1994 (no strong pain versus strong and unbearable pain), and also satisfaction at work (yes or no).

-Workers were also asked in 1996 1997 about changes in work tasks in the three-year follow-up period and whether they had upper extremity surgery. Other treatments (physiotherapy and infiltration) in the last six month were also recorded.

Statistical analyses

Only workers with symptoms or UEMS disorders in 1993 1994 were included in the present study ( ). The outcome in 1996

RESULTS

health care in the French health care system, whatever the compensation status. The analyses considered only the presence or absence of UEMS symptoms or disorders, without distinguishing the sites or laterality involved. However, these limitations should not affect the results, since the objective was to observe the outcome for the worker.

The definition of UEMS disorders used in the study, as determined by the clinical examination, included proved , suspected and prior

" "
diagnoses. Three levels of diagnosis were initially distinguished to explore different aspects of clinical examination (table II), with the hypothesis of different prognosis in the three subgroups. However, prior diagnosis was mainly related to medical practices of the company:

for instance, occupational physicians of large companies followed workers more closely than occupational physicians of small ones, and tended to mention prior diagnosis instead of proved or suspected diagnosis. Suspected diagnosis could correspond to incomplete criteria " " " "

fulfilled or evocating symptoms (without objective physical signs); the difference with proved diagnosis was weak in many cases. We " "

thus combined the three levels of diagnosis.

Several authors have discussed the transient nature of symptoms in the early stages of musculoskeletal disorders. ( ) We had 12 -14 previously found from the same survey data that the risk of developing UEMS disorders was significantly increased to workers with UEMS symptom compared with those without symptom. ( ) We decided to include a range of outcomes to study the difference in 7

prognosis between subjects with UEMS symptoms and subjects without symptom. The present results indicated that workers with symptoms who did not meet criteria for a UEMS disorder had a better prognosis than those with a disorder at baseline. It is also interesting to note that there is some difference between UEMS outcomes in 1996 97 according to gender and age. ( ) However, further studies are -5 needed to appreciate the difference between outcome for workers with symptoms only and those with UEMS disorders.

We found that a large proportion of workers had persistent UEMS symptoms or disorders in this population exposed to highly repetitive tasks, depending on the site involved. Workers with multiple UEMS disorders had a high proportion of persistent or recurrent disorders. Hand surgeons could thus give this information about the outcome to their patients, especially those highly exposed to biomechanical constraints, and those injured from multiple sites. Those with symptoms and no UEMS disorder had a better prognosis than the workers with a UEMS disorder at baseline.

Figure 2

Three-year evolution of UEMS symptoms and disorders.

7 A

 7 (extensor, flexor), De Quervain s disease, trigger finger, other tendonitis or nerve entrapment of upper limb, and other musculoskeletal ' painful problems. Participating occupational physicians attended one or two regional meetings before the baseline survey, where the guidelines were presented and training took place for the standardised physical examination. The guidelines were again presented at regional meetings organised before the second survey. Clinical examination classified UEMS disorders into one of three categories: (i) diagnosis from clinical examination, (ii) diagnosis based on previous clinical examination (for example, previous diagnosis by a specialist for a problem present in the last six month), and (iii) suspected diagnosis (clinical examination did not identify all diagnostic criteria, or the diagnosis was based on the description of symptoms during the last six months but not present at the time of examination). Our definition of UEMS disorders determined by the clinical examination included proved , suspected and prior diagnoses, as in previous " " self-administered questionnaire was also filled out in 1993 1994. The list of questions was based on the results from other studies on risk or prognosis factors in work-related upper-limb disorders. For this study, considering previous results about prognosis factors,( ) 5 we took into account gender, age (in three categories: 16 30, 30 45, 45 60 years), work with force (any action performed with force),

  Further studies with repeated clinical measures of UEMS disorders, work, and disability factors are needed to clarify the role of personal and work-related factors in determining the prognosis of UEMS disorders in working populations. Details about treatments should also be obtained to clarify the strategy in specific populations.

Figure 1

 1 Figure 1 Flow diagram of the actual study (based on the Repetitive task survey).

reviewed prognostic factors of shoulder disorders in cohort studies. ( ) The authors emphasized that the results needed to be interpreted

Among the 549 workers included, 464 had been followed during the three-year period (84.5 ).. The mean age was 38.5 years 20 59 , % [ -] with 33.8 of smokers (n 156) and 9.8 of ex-smokers (n 45). The distribution for gender, pain intensity, and work with force are

presented in the table I. Most of the subjects suffered from a UEMS disorder (n 421, prevalence 70.4 ). Only 43 had self-reported = % symptoms without UEMS disorder.

There was a significant but very slight difference for age between the workers follow-up and those lost of follow-up (38yrs vs 36 yrs, P<0.05). There was also a difference for the work with force variable: 49.4 of the lost of follow-up subjects (n 42) worked with force

and 61.9 of the follow-up subjects did (n 287, P<0.05). No difference was observed considering symptoms or disorder: 14.0 of the

subjects with symptoms only (7/50) were lost for follow-up, whereas 15.6 (78/499) of subjects with disorders were followed (P>0.05).

%

The three major disorders diagnosed in 1993 94 were rotator cuff syndrome (n 169, prevalence 28.3 ), carpal tunnel syndrome (n

130, prevalence 21.7 ) and lateral epicondylitis (n 73, prevalence 12.2 ), with a high proportion of associated disorders: in the 421

workers with at least one UEMS disorder at baseline, 207 had multiple UEMS disorders (prevalence 34.6 ). The sites of the disorders = % differed according to age and pain intensity at baseline (Table I).

The three-year natural history was significantly different for workers with UEMS symptoms in 1993 1994 than for those who met observed between workers who declared their job changed in the last three years (n 114) and those who declared that it did not (n 350):

12 subjects (10.5 ) who declared their job changed had no symptom or disorder in 1996 1997 versus 49 (14.0 ) who declared that it did % -% not. Similarly, the outcome was not associated with satisfaction at work. Twenty-three workers had upper extremity surgery during the three years, and all of them had disorder in 1993 1994. Among them, 15 (62.5 ) suffered from association of UEMS disorders. In 1996

1997, only three of them (13.0 ) had no symptoms and no disorders. We have very little information about other treatments: in the 1996 % -1997 questionnaire, 64 workers (14.4 ) mentioned they received physiotherapy in the last six months and 32 (6.9 ) received infiltration % % in upper extremity, which is highly associated with pain intensity at baseline ( <0.05). P

The outcome differed according to the site of the disorders: the three-year recovery rate was high for elbow disorders only (10/21, 47.6

), moderate for neck/shoulder or hand/wrist disorders (respectively 17/74, 25.7 and 22/119, 18.5 ) and low for multiple sites of UEMS Some limitations could be discussed however, including the date of the survey, the number of examinations and the UEMS disorder definition. This initial survey was designed to analyse the impact of high biomechanical exposure and repetitiveness on some UEMS disorders, explaining the delay of publication of studies not initially planned. ( ) However, the quality of the dataset allowed publishing 6 results even fifteen years after the beginning of the study. ( ) Furthermore, the definition used for these disorders based on symptoms and 5 physical examination did not change in the last twenty years.

In this study there was one follow-up assessment three years later. The design of this study provided no information on events during the three years between examinations. That may be a limitation, given the rapid and cyclic evolution of these disorders. Cole and Hudak, in a review about prognosis of non specific UEMS disorders, recommended incorporation of multiple follow-up assessments.( )