It is increasingly recognised, in public discussion and political discourse, that many of the practices and lifestyles of modern society – particularly but not exclusively industrialised society – simply cannot be sustained indefinitely. We are exceeding the capacity of the planet to provide many of the resources we use and to accommodate our emissions, while many of the planet’s inhabitants cannot meet even their most basic needs.

                         

          Sustainable development is the process of moving human activities to a pattern that can be sustained in perpetuity. It is an approach to environmental and a development issue that seeks to reconcile human needs with the capacity of the planet to cope with the consequences of human activities.

                      

          

 

          Figure introduced the idea that sustainability has three pillars – environmental, social and techno-economic – and that, in addition to the constraints implied, building on these pillars provides major opportunities for engineers and engineering.

                   

PRINCIPLES OF SUSTAINABLE DESIGN:    

 

            While the practical application varies among disciplines, some common principles are as follows:

·        Low-impact materials: choose non-toxic, sustainably-produced or recycled materials which require little energy to process.

·        Energy efficiency: use manufacturing processes and produce products which require less energy.

·        Quality and durability: longer-lasting and better-functioning products will have to be replaced less frequently, reducing the impacts of producing  replacements  

·        Design for reuse and recycling: "Products, processes, and systems should be designed for performance in a commercial 'afterlife'

·        Design Impact Measures for total carbon footprint and life-cycle assessment for any resource use are increasingly required and available. Many are complex, but some give a quick and accurate whole earth estimate of impacts. One is estimating any spending as consuming an average economic share of global energy use as 8000btu/$ and CO₂ production of 0.57kgCO₂/$ (1995$) from DOE figures.

·        Renewability: materials should come from nearby (local or bioregional), sustainably-managed renewable sources that can be composted when their usefulness has been exhausted.

·        Healthy Buildings: sustainable building design aims to create buildings that are not harmful to their occupants nor to the larger environment. An important emphasis is on indoor environmental quality, especially indoor air quality.

 

            There are a number of barriers to sustainable design. They include:

1.   Incomplete integration

a.    Each project phase is typically isolated.

b.    Feedback and reporting mechanisms are lacking.

Recommendation: Encourage communication throughout the design regarding process and solutions. Share lessons learned.

2.   Focus on first costs

Recommendation: Identify as early as possible those solutions that may have a positive impact on long-term cost. Provide information to Finance regarding these solutions and specific calculations showing estimates of long-term economic benefits.

3.   Lack of incentives

         a.              Builders and designers do not profit directly from a building’s operational cost savings, environmental performance or worker productivity.

Recommendation: State may develop incentives that not only promote sustainable building but also reward its application.

4.   Concerns about specific technologies

a.    Unfamiliarity with products, technologies, and systems.

Recommendation: Do not try to implement a huge quantity of sustainable solutions initially. Instead, select a smaller number of new technologies or products most likely to have the biggest long term impact for evaluation. Then be sure to record any research or conclusions drawn for use on future projects.

 

        Structural engineering “best practices” incorporates strategies that embrace the tenets of sustainable design. Sustainable design is not a novelty; it is a mainstream approach that reflects good design

             Human activity continues to impact the earth’s atmosphere in ways that are expected to modify the climate [IPCC]. The main greenhouse gases are carbon dioxide (CO₂), methane (CH₄), nitrous oxide (N₂O), and specialist chemicals (halogenated compounds). Of these gases, the greatest contributor to climate change is CO₂ [IEA]. Of CO₂ emissions, 30% to 50% is produced by the construction and operation of buildings. Cement production, for example, produced about 8% of the total CO₂ emissions in 2000.

         During the design phase of a project, the structural engineer can affect the sustainability of a project through

1) The choice of locally available resources,

2) The recyclability and reusability of materials and systems,

3) The efficiency of structural systems, and

4) Informed choices about demolition and preservation.

          

          The structural engineer should be aware of locally available materials, and make efforts to design using these materials. These materials would ideally be both harvested and manufactured in the local area. The designers set a goal to procure materials from manufacturers within a 500-mile radius of the site. The end result was that 31% of the building materials were obtained within this radius, and of these materials, 75% was harvested locally. All these decisions about local materials and labor must be balanced with decisions of availability, cost, scheduling and appropriateness for the project as a whole.

         

          The choice of the structural system during the design phase is another factor that affects the sustainability of a project. For both the gravity and lateral force resisting systems, the engineer has a choice of materials, which include wood, concrete, and steel. For example, steel cables can be extremely efficient tension members of a wood truss. Wood truss members can be supported by concrete walls and open web steel joists can be supported by wood shear walls. Taking advantage of the inherent properties of the material can result in a reduction of the amount of material.

           

          Detailing can be done on a similar level, as there are many types prefabricated steel connectors for wood members available. Lateral force-resisting systems have similar concerns. Various systems are appropriate for different scales, loads, functions, architectural requirements, and seismic performance levels. The efficiency and sustainability of the material chosen for the system, the various types of systems available for a given material, and the desired performance level must be determined.

          

          Some factors that affect material choice include weight per square foot, reusability, recyclability, deconstruction, and CO₂ emissions associated with the production and installation of the material, as well as all the traditional factors such as cost and performance. for example, steel moment frames could easily weigh twice as much as steel braced frames on a weight per square foot basis. However, during a seismic event, the structure will likely perform better and could save materials and labor by minimizing repairs, or in the worse case, avoiding demolition. In addition, time and cost savings can also be achieved since the building will be less disrupted for repair or rebuilding after an earthquake.

          

          In order to fully consider sustainability in the building design process, options other than demolition at the end of a building’s useful life should be considered in design. Adapting a building for other uses will conserve resources associated with demolition and reconstruction and also eliminate construction waste. To ensure that a structure can last into future building uses, it must to be designed for durability in a seismic environment or any other natural hazards to which it may be subjected. The structural engineer’s choice of structural systems during the design phase also affects how a building can be adapted for a future use. For example, designing a building with exterior perimeter structure, such as a perimeter moment frame, and interior partitions allows the building to easily change configuration. Deliberate placement of structure can integrate with the mechanical systems, openings for light and natural ventilation, all which allow for an energy efficient building even with changes of occupants and uses over time.

         

          However, the benefits of adaptability are the same as those associated with seismic rehabilitation of a structure. Generally, the principles are similar to those for constructability of a structure. Design practices that lend themselves to disassembly include the use of bolted connections in steel structures, pre-cast members in concrete construction, and prefabricated shear walls and metal fasteners in wood construction. Some of these principles may not be appropriate in high seismic areas, but may be appropriate to implement in low to moderate seismic environments. Modifying and reusing members consumes less energy than recycling. Lastly, recycling is still an option if the building or member cannot be reused. Recycled steel only consumes one quarter the energy it takes to produce virgin steel.  

Structural engineering is an integral part of sustainable design on a number of fronts: judicious and selective use of materials, resourceful use and application of structural systems, and provisions for future adaptability of the buildings that are designed today. Material selection can be optimized and recycled and reclaimed or salvaged materials can be used. The performance, reliability, and reparability of structural elements in the seismic force resisting system contribute to sustainable design.

          

As structural engineers, we have the opportunity to become an instrument of change in the industry. By encouraging the responsible use of our natural resources, and considering total building performance over its life cycle, we can proactively collaborate and participate in the “best practices” of structural engineering and sustainable design.