International and Domestic Standards More than twenty countries have rating systems that recognize sustainable and environmentally friendly design. Several follow USGBC ideologies and methods, but all reflect local conditions and priorities. Weidlinger’s knowledge of international standards derives from and serves the firm’s international engineering practice, but the firm’s engineers are also undertaking broader and more detailed comparison studies to identify sustainable practices implemented abroad that could be adopted domestically.
Regional Factors In 2009, LEED incorporated regional factors for the first time. This is preferable to a “one size fits all” approach, as the local availability and cost of re-used wood, steel elements, and recycled aggregate for concrete vary significantly. Also, some heavy materials require less energy expenditure for transportation in a port city such as New York. Weidlinger is conducting research on the availability and cost of green structural materials and on the transport of common structural materials in the cities where the firm practices, to help us judge the importance of these local differences.
Sea-Level Rise and Global Warming The United Nations recently predicted a 1-foot to 3-foot rise in sea level in the United States by 2100. Coastal zones will be affected dramatically by land loss and damage to buildings and infrastructure, especially if, as projected for New York, there are simultaneous population increases. Weidlinger civil engineers are working to understand the sewer infrastructure modifications that may be required, including the redesign of pumping stations and sewer outfalls to minimize tidal surcharge effects. Weidlinger structural engineers are working to identify protective and remedial design measures for buildings and bridges. Armed with this information, they will be better able to advise owners about the impact sea-level rise may have on their new and existing properties.
Green and Blue Roofs Green and blue roofs that temporarily retain stormwater can reduce combined sewer overflows, particularly in older urban areas where storm and sanitary pipes are not separate. Green roofs increase natural habitat and reduce CO2, improve a building’s energy efficiency and acoustic properties, and reduce heat island effects in urban settings. But the additional weight of these roof systems and the water they retain creates complicated load patterns that can affect seismic behavior and produce localized ponding that is not accounted for by uniform design loads.
Wind Turbines Wind turbines, which have been in use for centuries, convert the kinetic energy from wind to mechanical energy and then electricity. Traditional horizontally oriented turbines support the main rotor shaft and electrical generator at the top of a tower and must be pointed into the wind. Versions that align vertically do not need to be pointed in a specific direction, allowing for the generator and gearbox to be positioned at the tower base for easier access. As current building codes do not explicitly address the use of wind turbines mounted onto structures, Weidlinger is identifying the structural requirements for mounting wind turbines onto buildings and bridges and determining how best to address the additional loads that the turbine equipment imposes on structures. Weidlinger is also assessing the utility of, and quantifiable parameters required for, a risk analysis of wind turbine failure in an urban environment.
Concrete Cement production emits one ton of CO2 for every ton of cement produced. Cement, however, can be replaced in part with industrial byproducts such as fly ash or slag cement, and member sizes can be reduced, using ultra-high-performance concrete. In New York, the building code is being rewritten to set maximum levels of Portland cement and minimum levels of recycled concrete aggregate in concrete mixes. LEED awards points to projects that recycle concrete construction waste to produce concrete aggregates, reduce stormwater runoff with porous concrete, and conserve energy by exploiting concrete’s thermal mass properties. Weidlinger is keeping current with these sustainable applications, but is also assessing harder-to-quantify characteristics of concrete, such as durability, which is not yet recognized as a sustainable design strategy by LEED. The firm is also looking at new concrete technologies that may one day sequester CO2 from gas-fired power plant exhaust and produce cement mixes that can oxidize air pollutants into less harmful compounds.
Steel and Welding Although steel is the world’s most recycled material, production processes differ in the amount of recycled content and the methods used to dissipate excess heat and minimize harmful chemical emissions. Weidlinger’s engineers are aware that higher-strength steels can enable longer beam spans, lower erection costs, and increase usable space, offsetting higher material costs. But there are potential drawbacks to higher-strength steels in terms of welded connections and structural serviceability, especially in seismic zones where connection ductility is critical. Weidlinger is educating sustainable design teams about these subtle aspects of steel specification.
Recycled and Reused Materials Weidlinger is conducting research on the recycling process, reuse potential, and environmental impact of various structural building materials. In some cases, such as glass, the use of recycled feedstock has only marginal benefits; in other cases, such as aluminum, such feedstock is critical to the economies of production. The performance of each material when recycled or reused is being compared with its performance as virgin or newly processed material, as the quality of the recycled materials may affect performance significantly. Weidlinger is also researching the availability of various recycled and reused materials in the cities where the firm practices.
Advances in Materials Science Weidlinger is following the development of new sustainable materials that are potentially applicable to buildings and infrastructure. Materials are traditionally judged in terms of their cost, constructability, and durability, but with recent emphasis on sustainability, they are being also being judged by their recycled content, reduced toxicity, environmentally friendly feedstock sources, and recyclability. Weidlinger examines new materials as well as modified versions of traditional products in this light.
Municipal Infrastructure National high-performance guidelines are not as well established for infrastructure as they are for buildings; the technical issues for municipal infrastructure, in particular, are broad and multidisciplinary. Recent New York City guidelines were written to achieve results in the areas of urban ecology; public health, safety, and quality of life; and optimum life cycle and performance; as well as mitigation of the effects of sea-level rise. Weidlinger is analyzing such strategies as porous pavements, pavements that lessen urban heat island effects, redesign of drainage facilities to limit flooding, innovative bridge construction, and bicycle-lane geometries.
Site and Stormwater Providing stormwater quantity and quality controls is a challenge for civil engineers in urban environments. Recent thinking points to a combination of solutions. Such a combination would include storage and reuse of stormwater for non-potable purposes, as well as the use of green and blue roofs. As part of Mayor Bloomberg’s Task Force on Sustainability, Weidlinger is participating in a multi-agency evaluation to promote the acceptance of stormwater reuse for both existing and proposed buildings in New York City.
Life Cycle for Environmental Impact Current green building standards such as LEED NC focus on the energy used to operate buildings. They do not explicitly address embodied energy—the energy used to extract raw materials and to manufacture and transport building components, which at present accounts for up to 62% of the energy used over a building’s lifetime, depending on its construction and usage. Weidlinger is examining the potential of life-cycle analysis to improve sustainable design practices and provide a framework for evaluating and quantifying the embodied energy and environmental impact of various materials and construction practices. As improvements to a building's operational energy efficiency are required to meet ever-stiffening standards, embodied energy will become more significant and constitute a larger portion of a building’s lifetime carbon footprint.
Durability Durable structures last longer and need to be repaired and replaced less frequently, reducing their environmental impact. Whereas owners have traditionally asked Weidlinger to assess durability in terms of first cost and life-cycle costs, to truly embrace sustainability the design team must look at durability as it relates to life-cycle environmental impact. Weidlinger’s research includes the review of existing studies relating durability to life-cycle costs, which should provide significant insight into the more complex link to life-cycle environmental impact. The firm is developing methods for quantitative analysis, with the goal of promoting a more holistic and precise assessment of the benefits of durable structures.
Construction Economics Although some green technologies are simply cheaper, most require a slightly larger up-front investment. This expenditure, however, can often be shown by a life-cycle cost analysis to be financially advantageous. Weidlinger is exploring various cost analysis methods, focusing on cases in which they give different life-cycle cost results, and critiquing the assumptions on which they are based. Pay-back period analyses often include an inappropriately high assumption of risk, which can steer decision makers away from viable sustainable strategies. Because most sustainable technologies actually carry low risks, more sophisticated analytical methods may open the door to greater funding for sustainable projects and elements.
Multihazard Integration Weidlinger is pursuing and promoting the concept of explicit multihazard design, a more sophisticated approach to the optimization of a structure. This also requires the structural designer to respect, at each step, the multidisciplinary factors that influence engineering decisions, such as the aesthetics desired by the architect and the spatial requirements of the HVAC system. As our profession progresses toward a greener future, sustainability must take its place among these multidisciplinary factors. Weidlinger is exploring the interface between sustainable design and multihazard structural engineering. Subjects addressed include the effect of a green roof’s higher dead load on a structure’s wind resistance, the effect of a green roof’s greater mass on a structure’s seismic resistance, and the effect of the multiple layers of material on a structure’s blast response.