Large parts of our nation’s transportation network are in need of repair, rehabilitation, restoration, or replacement, demanding massive amounts of resources. In the transportation design arena, structural engineers have a dominant voice in the selection of the form, type, and location of various elements of the infrastructure network, and thus, can exert greater influence in improving the sustainability aspects of these elements. Several aspects of design are discussed below.
Context-sensitive solutions—Structural engineers are encouraged to participate actively in context-sensitive design efforts and develop application of criteria and standards so that roads and bridges can better fit in their context. Context-sensitive solutions (CSS) is a collaborative, interdisciplinary approach that involves key stakeholders to develop a transportation facility that considers the total context within which a project will exist. Some of the areas for structural engineers to utilize the CSS methodology may include the following:
- specify use of locally available materials;
- consider during design phase the function of streets and roads relative to their context in terms of access, speed, and mobility for all users;
- improve the compatibility of roads and bridges with the environment by using vegetation, finishes, and other features that accentuate and improve esthetic appeal for users both on and off the roadway, while providing environmentally friendly surroundings; and
- select alignments, bridge skews, and pier locations to minimize footprint and environmental disturbance.
Life-cycle cost analysis—The importance of a proper life-cycle cost analysis (LCCA) cannot be over-emphasized. LCCA is an engineering economic analysis tool that allows transportation officials to quantify the differential costs of alternative investment options for a given project. During the initial type, size, and location selection phase of the project, various span arrangements, girder types, material types, and spacing should be studied along with cost estimates for various alternates to find the optimum solution, usually with the lowest life-cycle cost.
Complementary cementitious materials—When dealing with concrete members, structural engineers need to select the proper mix design carefully to include complementary cementitious materials (CCMs) such as fly ash, slags, silica fumes, or ultrafines. The use of fly ash, a by-product of the coal industry, has been proven for use in concrete with the benefits of greater workability, decreased permeability, and greater impedance to chloride intrusion. In road construction, the many benefits of incorporating fly ash include its use in creating flowable fills and structural fills (in lieu of conventional backfill materials), and as a mineral filler in hot-mix asphalt paving applications.
High-strength materials — Long-term benefits can be achieved in highway structures when high-strength materials, primarily steel or concrete, are properly used in the superstructure support system. The main benefits for utilizing high-strength materials in bridge elements are to extend span lengths of bridges with commonly fabricated girder types, reduce/eliminate intermediate piers, reduce the depth of superstructures, and eliminate girder lines to offer cost efficiency.
Prefabricated components—The benefits of using prefabricated components in accelerating bridge construction are well known. Besides minimizing traffic disruptions and congestion, prefabrication improves constructability and work zone safety, minimizes environmental impact, and aids in future bridge widening. Durability and quality also are improved as the production occurs in a controlled environment, which translates to longer life and lower life-cycle costs.
Other solutions—Adaptability and possible future widening/de-construction should be considered during design of new facilities, not only by using prefabricated panels, but also by considering phased construction techniques to minimize traffic impact, using semi-integral abutments that allow jacking-up of the superstructure when future widening is anticipated, using standard details with clear load paths, and using mechanical fasteners in lieu of adhesives and welding. Salvage of structure components to be demolished should be undertaken to reduce the amount of materials that are placed in landfills. When structural engineers are also responsible for roadway design, another aspect to consider is stormwater treatment along the edges of roadways.
The transportation infrastructure network plays an important role in the economic growth of our nation, and structural engineers should consider all available resources and design tools available in helping make it more sustainable.
Sandeep Mathur, P.E., SECB, M.ASCE, is a central region engineering manager for Gerdau AmeriSteel and a member of the ASCE-SEI Sustainability Committee. Mathur can be reached at firstname.lastname@example.org. The SEI Sustainability Committee website is www.seinstitute.org/committees/sustainable.cfm.