10th International Conference on Short and Medium Span Bridges Quebec City, Quebec, Canada, July 31 – August 3, 2018 CURRENT CANADIAN BEST PRACTICES AND CHALLENGES TOWARDS SUSTAINABLE BRIDGES Jiang, Jianping1,4, and Kroman, Jadwiga2 WSP, Canada City of Calgary, Canada Jianping.Jiang@wsp.com Abstract: In 2015 Transportation Association of Canada published a new national guide on Sustainability Considerations for Bridges It provides some general and broad directions on sustainability considerations specific to bridge planning, design, construction and in-service management by developing 12 sustainability objectives and 22 sustainability practices The Guide is a good starting point to promote the importance of sustainable practices and to set the priority for sustainable bridges However, there are significant challenges for bridge engineers and owners to be able to clearly define what aspects and goals of sustainability should be targeted, and how they could be achieved by following a well-planned, systematic and consistent design and construction methodology This paper will start by providing a review of various definitions of sustainable bridges and the current Canadian approach to bridge sustainability It will follow up with a focus on next steps for sustainable bridges, including (a) introduction of design for service life; (b) challenges and benefits of adopting a probabilistic-based methodology for bridge service life design; (c) the need of building a sufficient database of deterioration models for Canadian bridges; and (d) considerations of impacts of climate change on durability of bridges INTRODUCTION In recent years there has been more focus on sustainability of transportation infrastructure including bridges, as the realization of its impacts on the environment, and the social and economic wellbeing of local communities and society at large have become widely recognized Given the growing awareness of sustainability, most transportation agencies across Canada start to recognize that sustainability should become an important consideration when making decisions, setting policies, and meeting performance measures sought by stakeholders As a result, Transportation Association of Canada (TAC) in 2013 retained WSP (formerly MMM Group) to develop a national guide that provides the framework and practices to improve the sustainability benefits (i.e social, economic and environmental) of bridges The guide document, entitled Sustainability Consideration for Bridges Guide (SCBG) (TAC, 2015), was published by TAC in 2015 The SCBG provides broad directions on sustainability considerations specific to bridge planning, design, construction and in-service management by developing 12 sustainability objectives and 22 sustainability practices, and furthermore it provides general guidance to bridge engineers and transportation agencies as to how they can improve the sustainable benefits of their projects and communicate these improvements to their stakeholders in a consistent, objective and credible way Since publication of the SCBG, there is a growing interest among bridge engineers and transportation agencies across Canada to see that sustainability be formally addressed in the Canadian Highway Bridge Design Code (CHBDC) From the standpoint of bridge designers, sustainability of a 137-1 bridge structure can be defined as its ability to fulfill its intended function and achieve a context-specific balance between the environmental protection, social responsibility and cost-effectiveness criteria over the service life of the structure In other words, the concept of bridge service life design is directly related to sustainability To achieve this goal, significant efforts are needed including (a) development of a probabilistic-based methodology for bridge service life design; (b) establishment of a sufficient data base of deterioration models for Canadian bridges; and (c) considerations of impacts of climate change on durability of bridges DEFINITION OF SUSTAINABLE BRIDGES Sustainability of a bridge project may be viewed by some engineers/scientists as involving the use of innovative materials, whereas designers may see it from an innovative design perspective Others may focus on the use of innovative techniques in construction, while some others may think of it from the least life-cycle cost perspective In fact, sustainability should include all these viewpoints and it is not limited to anyone of these objectives alone It has a much wider meaning and encompasses many interconnected dimensions As stated by the United Nation’s World Commission on Environment and Development, “Sustainable development is development that meets the needs of the present without compromising the ability of future generations to meet their own needs” (Brundtland Report, 1987) From this definition of sustainable development, three pillars affecting sustainability of transportation infrastructure such as highways and bridges can be identified: environmental, social and economic, which are often referred to as the “triple bottom line” This triple bottom line of sustainability is recognized as an interconnected process requiring balanced decision making among environmental, social and economic considerations Although at this time there is no universally accepted definition of a “sustainable bridge”, there are a number of variations using this triple bottom line concept to define “sustainability” or “sustainable transportation” For example, the American Society of Civil Engineer has the following definition of sustainability (ASCE, 2016): “ as a set of economic, environmental and social conditions in which all of society has the capacity and opportunity to maintain and improve its quality of life indefinitely without degrading the quantity, quality or the availability of economic, environmental and social resources Sustainable development is the application of these resources to enhance the safety, welfare, and quality of life for all of society.” Transportation Association of Canada has developed the following statement of sustainable transportation (TAC News, 2013): “Sustainable transportation is the result of a continuous decision-making process that seeks to achieve a context-specific balance between environmental integrity, social equity, and economic opportunity both within and among transportation systems, now and in the future.” Essentially, the goals of achieving sustainability in the context of bridge design and construction (IOWA DOT, 2018) are to • • • • • • • Minimize impacts to environmental resources Minimize consumption of material resources Minimize energy consumption Preserve or enhance the historic, scenic and aesthetic context of a bridge project Integrate bridge projects into the community in a way that helps to preserve and enhance community life Encourage community involvement in the transportation planning process Encourage integration of non-motorized means of transportation into a bridge/highway project 137-2 At a high level, sustainable bridges involve identifying and taking advantage of multiple, mutually reinforcing benefits while avoiding all potentially significant adverse effects CURRENT CANADIAN APPROACH TO BRIDGE SUSTAINABILITY Building upon the triple bottom line of sustainability, the SCBC uses the following three dimensions of sustainability: • • • Economic Development – maximizing economic efficiency and affordability and promoting regional/local economic development Environmental Integrity – natural resource preservation, pollution prevention and other factors influencing environmental integrity for current and future generations Social Quality of Life – social equity, human health, safety and security, accessibility to basic services, and overall quality of life In the process of developing the SCBC, the TAC membership (e.g most Canadian transportation agencies) and broader Canadian bridge community (e.g Canadian practising bridge engineers and experts) were surveyed to • • • Understand how most transportation agencies across Canada consider sustainability as it relates to their bridge projects Determine what most transportation agencies across Canada want to see in the SCBG Prioritize a list of sustainability objectives and practices for the SCBG Of the 425 survey recipients, a total of 78 responded with a response rate of 18.4% In summary the key findings from the 2013 survey include: • • • • There are considerable variations in what is meant by sustainability Current focus should be on small and medium span bridges The No perceived barrier to sustainability is cost, followed by lack of direction/policy The bridge community is looking for sustainability guidance on communicating practices, expanding current sustainability practices and increasing awareness of issues and considerations Based on the survey results and to meet the current needs of most transportation agencies across Canada, a total of twelve sustainability objectives were adopted for the SCBG as follows: - Reduce virgin material use Reduce energy use Maintain or improve hydrologic regime characteristics Engage community values and sense of place Improve access and mobility Increase lifecycle Efficiency - Optimize waste stream - Reduce emission to air - Maintain biodiversity - Improve safety - Improve local economy - Promote innovation In order to support implementing the SCBG sustainability objectives by the users, a total of twenty-two SCBG sustainability practices were developed Each SCBG practice comes with a standard format to provide consistency, readability and functionality across the entire set of practices in the SCBG For each SCBG sustainability objective, the users need to consider and apply a number of applicable SCBG sustainability practices The significance of each objective will vary from project to project, and from jurisdiction to jurisdiction It’s up to the users to decide which sustainability objectives be considered important for their bridge projects Furthermore, the current Canadian approach to bridge sustainability encourages considering sustainability in the whole and each stage of a bridge’s life so that one can avoid or mitigate significant adverse effects in each individual lifecycle stage, and can also contribute to the whole in achieving multiple, reinforcing and durable gains Details of this holistic approach are 137-3 documented in the SCBG DESIGN FOR SERVICE LIFE Sustainable management of bridge infrastructure requires strategic decisions and execution processes that focus on the entire life cycle while balancing social, economic and environmental aspects These aspects include adequate functional performance (adaptability), longer than standard service life for critical and complex bridges, structure resiliency throughout the life cycle and a level of investment that optimises the “return” in all aspects of sustainability Currently, Canadian bridge design has focused on strength and serviceability requirements in accordance with the Canadian Highway Bridge Design Code (CHBDC) Accordingly, an assumption has been made that a bridge structure will remain in use for a duration of the design life, for example 75 years used in CHBDC However, most commonly structures reach the end of their useful life not due to exceedance of a limit state, but rather due to the loss of capacity of structural elements and systems, as a result of material or element deterioration The current design Code does not make specific allowance for the effects of deterioration of structural components, nor is there much guidance for verification of the assumptions made during the initial design Quality of the construction as well as quality of maintenance throughout the structure life cycle may also compromise the original design assumptions Specifications for choice of construction materials and products are often based on the initial capital cost, perceived or claimed successful performance and in some cases on long-established standards Evidently, a more integrated and proactive approach to the design, construction and maintenance of bridge structures is needed as an effective measure of improving bridge infrastructure sustainability Adequate and consistent design for service life is one of the most important elements in increasing sustainability of bridges Service life is commonly defined as the specific period of time for which a bridge structure or its components are to be used for the intended purpose with anticipated maintenance but without unplanned major repairs or rehabilitation Accordingly, bridge structures and their components should be designed for durability, such that they maintain their performance throughout their service life, with adequate maintenance and under the intended use and exposure conditions Currently there is a limited expertise in the bridge design industry and no comprehensive guidelines have been offered by Canadian transportation agencies, for practical design for durability and prediction of service life Most bridge infrastructure owners and engineers rely on past experiences and perceived successful practices in making design decisions and specifying construction products To begin with, better guidance is needed with respect to the definitions and relevance of the terms “Design Life” and “Service Life” referenced in many bridge codes and guidelines “Design Life” is primarily used in derivation of reliability targets in limit states design for strength and serviceability AASHTO (LRFD) Specification for Bridges defines Design Life as: “Period of time based on which a derivation of transient loads and load factors is based” The Canadian Highway Bridge Design Code defines Design Life as “A period of time for which the structure is to remain in service” Service Life of a structure should be assumed and designed such that it meets or exceeds the duration of the Design Life A few large-scale signature bridges, such as Confederation Bridge have been designed for a specific service life considerably longer than a “standard” 75 years The design criteria reflected site-specific exposure conditions and local deterioration mechanisms, local experiences, best construction practices, as well as opportunities to use test models and developing material technologies Criteria used for establishing the duration of the service life of a structure may focus on anticipated functionality, technical conditions or economic justification for replacement, but usually are associated with durability of structure components or systems The service life design should achieve the following requirement: [1] Ts ≥ Td 137-4 where: Ts = service life, and Td = design life The design for durability and service life may take the format of limit states design This method relies on understanding of environmental conditions of the area in which the structure is located, the deterioration (transfer) mechanism, the protection mechanism, environmental actions (loads) and action effects The action effects should not exceed the resistance capacity at given time, t that is equal or less than the service life Ts The following represents steps in addressing durability during the structure’s service life Ts: [2] Action Effects (AE) ≤ Resistance Capacity (RC) Structure environment ►Transfer mechanism ►Environmental action ►Action effects (AE) Structure environment may include rain, snow, ice, road or natural salt spray, wind, humidity, sun, soil contaminants, air pollution, etc Transfer mechanism may include direct exposure, gravity, capillary migration, condensation, diffusion, ponding, etc Environmental Actions may include corrosion, carbonation, cracking, spalling of concrete, biological decay of timber structures, corrosion stress cracking of steel elements, loss of material strength due to UV exposure, etc Action effects may include loss of load bearing capacity, reduced resistance, loss of material, change in appearance, etc Resistance Capacity throughout the duration of service life is a function of several factors, such as: - Sustainable planning, including target service life, functionality and anticipated environmental exposure; - Proficient design, choice of materials, detailing of structure components and their connections and provision of maintenance access; - Quality of manufacture and construction; - Planned and regular maintenance and provision of minor repairs; - On-going assessment of the remaining service life or reliability of the structural components and systems Service life may be predicted based on evaluating the time at which the limit state of a performance (i.e level of deterioration) of a structural component subject to given action effects will be reached Service life design may take the following approaches: • Avoidance-of-deterioration method; • Conceptual modelling method; • Deemed-to-satisfy method; • Full probabilistic (reliability-based) method; 137-5 • Partial factor method Avoidance-of-deterioration (design-out) method aims to eliminate the deterioration process by: - Eliminating environmental actions, e.g use of membranes, coating or cladding; - Using non-reacting materials, e.g use of stainless steel reinforcing or alkali non-reactive aggregates; - Separation of “reactants”, e.g keeping the structure component below critical moisture level; - Inhibiting the deterioration mechanism, e.g use of cathodic corrosion protection The design-out method may prove to be very expensive, yet not 100% reliable, thus not sustainable Conceptual modelling method involves implementation of barriers that slow down the deterioration process throughout the service life of a structure This may be done using the deterministic approach based on local experience, best practices or a combination of experimental modeling with the deterministic approach This strategy includes a consideration for sustainable life cycle planning, design decisions, construction quality and maintenance The selected combination of dimensional measures (e.g concrete cover), materials (e.g highperformance concrete) and protection systems (e.g galvanized reinforcing and bridge deck membrane) may effectively be similar to the design-out option and likewise, it often falls short of sustainable value benefit as an over-designed or under protected system Ideally, the validity of the conceptual model should be verified through one of the probabilistic methods or through systematic surveying and tracking the performance of the selected models Deemed-to-satisfy method consists of a set of often complex provisions that are to ensure that under specific exposure conditions, the target reliability for not passing the relevant limit state during the service life is not exceeded The interlinked procedures used in deemed-to-satisfy include the following: - Material and product or system choice, e.g concrete composition; - Dimensioning, i.e concrete cover; - Execution specification and procedures, e.g curing regime The requirements for design, material selection and execution procedures may be obtained based on statistical evaluation of experimental data, field observations and on correlation of durability performance tests and models with actual performance in structures and in the specific environmental conditions The example of this method would be the use of a combination of concrete composition, e.g ratio of concrete binders and cover to reinforcing as a function of the exposure conditions, e.g chloride, carbonation or frost and the predicted service life The limitations of this approach include: - Variability of material properties, admixtures and test methods; - Variability in local exposure conditions; - Calibration of long term exposure with that assumed in the models; - Lack of correlation between durability performance of laboratory samples and the actual shape of the structural component and its restraint conditions 137-6 PROBABILISTIC-BASED METHODOLOGY FOR BRIDGE SEVICE LIFE DESIGN Full probabilistic method uses mathematical models that represent deterioration mechanisms in realistic environmental conditions Material and product parameters used in deterioration models should be verified by tests conducted in the specified environmental conditions The values and parameters used in these models should be validated by a sufficient database Test methods should be available to verify variables and parameters of material and product properties used in the probabilistic models Full probabilistic method verifies the limit state for durability at a target service life by satisfying the following limit state function: [3] Pf(t) < Pt where: Pf(t) is probability of reaching a limit of deterioration at time t and Pt is a target failure probability Typically, the target probability of failure for the durability of a structural component is based on the design life of the entire structure, the difficulty and cost of replacement and the consequence of the failure It includes mean values, uncertainties and distribution of loads and resistance Target reliability should be derived from a sufficiently large database The limitations of this approach include: - Complexity of analytical calculations; - Insufficient data used as input parameters, representing statistical variability of exposure conditions, materials, geometric characteristics and the effects of the deterioration Partial factor method uses model equations for environmental actions and resistance capacities and can be expressed by the following general equation: [4] αEA = βRC where: α = partial safety factor on environmental actions, and β = partial safety factor on resistance capacity Factors α and β reflect variabilities of parameters derived by statistical methods accounting for influences of geometric and material properties, use of protection systems, quality of construction, specific environmental conditions, etc The limitations of this approach include: - Need of a database for derivation of partial safety factors; - Complexity of mathematical models for derivation of the relevant factors; - Verification of reliability target for each limit state assumed in the design; - Need for standard QA/QC of execution to validate assumptions NEED OF DATABASE OF DETERIORATION MODELS FOR CANADIAN BRIDGES Service life design should be viewed and treated as an integral step in a process of designing sustainable bridge structures The effectiveness of the service life design is impacted by several factors, of which 137-7 availability of reliable data appears to be the most critical There is a need for quantification of exposure conditions, specific to geographic regions, including local impacts of natural and man-made hazards A database of the exposure conditions, deterioration mechanisms and action effects for typical bridge components and systems, use of various materials, details and protection systems would significantly help progress the development of deterioration models, statistically derived factors and design parameters The open source information bank would provide research opportunities and development of material performance tests, effectiveness of protection systems under various conditions, durability of the systems, development of performance specifications and service life prediction tools There is evidence of the correlation of quality control and quality assurance during the manufacture and construction, with the durability of bridges Detailed data would support the development of uniform construction standards, thus further improving sustainability of Canadian bridges IMPACTS OF CLIMATE CHANGE ON DURABILITY OF BRIDGES Changes in climatic characteristics have been noted throughout all regions of Canada Local governments and organizations have embarked on programs and initiatives to monitor, classify and quantify climate changes, and to develop strategies for adaptation to these changes Management of bridge infrastructure and adequate adaptation strategies are most effective when addressing impacts of local environmental characteristics and changes Monitoring and building a database of the environmental load characteristics (e.g freeze-thaw cycles, flash floods, icing, winds and extreme heat or cold waves) is required now, in order to be able to plan, design and build sustainable bridges in the future Adaptation of design decisions should be considered in evaluating the remaining service life and upgrading the existing infrastructure SUMMARY The sustainable planning, design, construction and through-life maintenance of bridges needs to consider a variety of economic, functional, environmental and societal aspects in an integrated and balanced way, in aiming to achieve the best value in desirable outcomes Current practices of designing bridges for the ultimate limit state and serviceability limit state not address the condition of structural components that might be compromised by quality of design and detailing, quality of construction or by time-related deterioration due to environmental or man-made hazards On the other hand, over-designed and overprotected structural components and systems, with multiple defence barriers against deterioration also fail sustainability targets of balanced best value Service life design is a key component of sustainable bridge delivery The most important step in service life design is recognition of a deterioration model(s) appropriate for local and specific hazards, and other circumstances It is recognized that the current models and methodologies for service life design need to be further developed, refined and verified Therefore, the design strategies may employ a combination of the conceptual and performance-based modeling methods It is extremely important that service life continues evolving as an integral part of delivery of new bridges, and evaluating existing bridges The development and progress of service life methodologies relies on the ability to verify and improve the performance-based prediction models and other design tools Therefore, observations, record-keeping and building a database of this information is of great importance A nation-wide open source database would be of great advantage Service life design is closely associated with quality of design, manufacture and construction There is a need for a uniform standard for quality assurance and quality control for construction of bridge structures Research and pilot projects aiming to advance methods of service life design should be encouraged and supported by bridge owners and other infrastructure funding organizations The development of a practical guide to service life design, associated with the Canadian Highway Bridge Design Code, would be of great benefit to the bridge engineering community Such a guide should be created as soon as the concept of service life is adopted by the Code 137-8 Support for innovation by bridge owners, transportation authorities and design engineers has a key role in progressing towards sustainable bridge infrastructure References American Society of Civil Engineers 2016 Policy Statement 418 – The Role of the Civil Engineer in Sustainable Development, American Society of Civil Engineers AASHTO 2017 AASHTO-LRFD Bridge Design Specifications American Association of State Highway Officials Associations, AASHTO, Washington, D.C CSA 2014 Canadian Highway Bridge Design Code, CSA-S6-14 Canadian Standard Association, Toronto, Canada IOWA DOT 2018 Sustainable Bridge Design, LRFD Bridge Design Manual, Office of Bridges and Structures, Iowa Department of Transportation Transportation Association of Canada 2015 The Sustainability Considerations for Bridges Guide PTMSCBG-E, Transportation Association of Canada Transportation Association of Canada 2013 Sustainable Transportation Guiding Statement Adopted by Transportation Association of Canada, TAC News, Volume 39 World Commission on Environment and Development 1987 Our Common Future, Brundtland Report, Oxford University Press, Oxford, UK 137-9 ... guidance on communicating practices, expanding current sustainability practices and increasing awareness of issues and considerations Based on the survey results and to meet the current needs of most... environmental and societal aspects in an integrated and balanced way, in aiming to achieve the best value in desirable outcomes Current practices of designing bridges for the ultimate limit state and serviceability... data base of deterioration models for Canadian bridges; and (c) considerations of impacts of climate change on durability of bridges DEFINITION OF SUSTAINABLE BRIDGES Sustainability of a bridge