Wednesday, August 12, 2015

Hold Your Buildings to Higher Standards... of Resilient Design

Building codes are modeled to safeguard public health and safety, not necessarily to limit damage or maintain a building’s function after a natural or man-made disaster. As a result, performance based design guidelines have been developed allowing structural engineers to design structures to a certain structural performance objective. This can include reductions in damage, repair costs and/or recovery time. Structures designed to perform to higher than code standards will typically require more materials and incur greater costs associated with design and construction resources (i.e. design time, construction time, and cost associated with both). These structures, however, have the potential to be more resilient during a disaster. The upfront costs associated with these structures can result in large monetary savings in the future. The project team should consider all of the benefits associated with a more resilient structure and decide if those benefits outweigh the upfront costs.

Monetary damages from natural disasters have seen significant increases over the last 5 years (Source: SEI Committee Report). Structural engineers should consider this when making the choice to design to higher standards. There is a vital need for resilient design with more people migrating to the coasts (where natural disaster hazards are greatest), and the economic value of possessions increasing substantially (Source: SEI Committee Report). Spending time and money up front to reduce the likelihood of loss during a natural or man-made disaster can bring significant benefits to owners and communities. These benefits include lowering insurance costs, raising property values, providing security to residents, maintaining a consistent tax base, and minimizing the cost of disaster response and recovery. 

Structural engineers must also take holistic design approaches because the interaction between structural and non-structural systems varies greatly. A system may require larger initial investments in materials and resources, but could have significant savings due to reduced damage of non-structural building components during a natural or man-made disaster, implying lower expected lifetime costs of the building.  

Designing structures for higher standards will typically result in additional upfront costs: both monetary and environmental. These costs should be considered throughout the life cycle of a building, especially for those structures at risk of natural and man-made disasters.  Hazard mitigation techniques typically come with significant benefits, and. implementing resiliency strategies will allow for better protection before and better recovery after an event.    
Monday, June 22, 2015

What Do Structural Engineers Have to Do with Disaster Resilience and Climate Change Adaptation?

Structural Engineers have the most direct impact on the disaster resilience of new and existing buildings and their ability to adapt with ever-changing climate. Although we typically cannot impact the location of a new structure, we can often impact its orientation, shape and exposure to various risks. The orientation and shape of the structure and the location of movement joints may significantly impact how much force is transferred to the building cladding, framing and lateral system during a severe wind event, earthquake, extreme temperature event, tidal event or terrorist attack. The first step in the process is to identify which risk factors pose a significant risk to the structure.

Structural Engineers must determine the potential risks for a given location over the service life of the structure even if this risk is not addressed by the governing code. For instance, current FEMA flood elevations do not directly factor in the impacts of future sea-level rise; depending on the service life of the structure, this may have a significant impact on the building’s exposure risk. We must first determine what code-prescribed requirements apply for addressing these various disaster risks, based on the occupancy type and importance of the structure. Some questions that need to be addressed are as follows:
  • What design codes are currently available for addressing that specific risk?
  • Do these codes specify loading and serviceability requirements?
  • Where codes or design aides are not yet available, what design practices can be implemented to help address this risk?
  • Building codes represent minimum/baseline requirements. Are these sufficient for the structure given its location?

After the various risk factors have been identified and the magnitudes of forces to be applied to the structure are understood, the Structural Engineer must then select the proper structural system and determine how the exterior cladding is anchored and transfers forces back to the structure. Below are some items to consider in this exercise:
  • Building Material Type: Structural steel, reinforced concrete, wood, masonry, light gage, etc.
  • Lateral System Type: Load-bearing or non-load bearing shear walls, moment frames, braced frames, dual systems, etc.
  • Level of Ductility: Response Modification Coefficient (R-value) of lateral system, provision of alternative load paths (to address progressive collapse), decoupling of lateral system from gravity system, system redundancies (e.g. use of full depth shear connections that can transmit diaphragm shear in addition to vertical shear), etc.
  • Structural Movement Joints: Are structural movement joints required? Where and how often are structural movement joints to be placed? Where are the lateral system frames located relative to these joints? For instance, locating lateral frames further away from the center of the diaphragm will increase member forces during an extreme temperature event.
  • Cladding Anchorage: How and where is the cladding anchored to structure? It’s generally best to apply any lateral forces directly to floor diaphragms. Does the superstructure support the weight of the cladding? How can cladding spans be configured to absorb the most energy and to minimize the forces transferred to the building frame during a disaster?

Once the risks have been determined and the building frame system has been chosen, the Structural Engineer must determine the required level of performance during a design event based on the client’s objectives, the acceptable amount of damage after one of these events, and the client’s budget. For example, ASCE 41 categorizes the performance of a structure during a seismic event in three levels: Immediate Occupancy, Life Safety and Collapse Prevention. Similar performance levels can be established and specifically tailored for different types of disasters. The goal is to determine how quickly after an event the building must be operational. In addition, the Structural Engineer must determine how, where and what level of ductility and redundancy must be provided to avoid a disproportionate level of damage or progressive collapse of the structure.

There are many ways Structural Engineers can be proactive about disaster preparedness, providing the best possible service to their client, serving their local community as well the overall engineering community. A Structural Engineer must effectively communicate with the design team and owner on what potential disasters must be considered, identifying what the code requirements are, and what the most efficient tools and methods for addressing those risks are. Structural Engineers can serve on code committees to advance current literature on addressing the risks posed by various disasters. It’s also important to be prepared for disasters by undergoing training on performing structural assessments of existing buildings post-disaster (e.g. ATC-20-1: Postearthquake Safety Evaluation of Buildings, ATC-45: Safety Evaluation of Buildings After Wind-Storms and Floods). Our ability to quickly assess the condition and level of damage of a structure after such an event is critical to the local government’s ability to assess the overall impact to a geographic area and the resources that will be required to reconstruct or remediate the area, as appropriate.

Structural Engineers play a critical role in impacting the disaster resilience of new and existing buildings and it is incumbent on all of us to be mindful of these risk factors in our day to day work. As climate change, sea level rise, and the frequency of extreme weather events continues to escalate, our ability to address these risks on a variety of fronts will be critical to the long term sustainability of our communities.
Saturday, April 25, 2015

Disaster Resilience and Sustainability White Paper

Structural engineers can make a significant contribution to the sustainability of the built environment by considering disaster resilience in their designs. Download the SEI Sustainability Committee Disaster Resilience Working Group's definitive guide and learn how to design more resilient structures. Click here and look for the link to download at the bottom of the page.

Executive Summary

The importance of sustainability within structural engineering has become more widely accepted in recent decades. When structural engineers think of sustainability, they often limit their scope to material selection and recycling. Few structural engineers recognize the relationship between sustainability and disaster resilience, an area in which they can make significant contributions. Consequently, the aims of this report are to

  1. Raise awareness of the relationship between disaster resilience and sustainability by discussing how a holistic view of sustainability must recognize the need for disaster resilience, and to
  2. Provide a critical review of resilience-related efforts and resources available to practicing structural engineers and related professionals.

Sustainability encompasses three spheres: economic, environmental, and social. Within each of these spheres, sustainability requires providing for the needs of the present while allowing future generations to meet their own needs. Disaster resilience pertains to the ability to suffer less damage and recover more quickly from adverse events such as hurricanes and earthquakes. A resilient structure provides socially valuable services such as shelter and safety, even in the face of disaster, and it should do so while minimizing economic and environmental costs. Ignoring resilience during design can lead to structures that may seem green but that cannot reliably provide the services that we expect from them. Sustainability and disaster resilience are related in complex ways. Often times striving for one will help achieve the other as when a more robust structure reduces the environmental and economic cost of repairing extensive damage. Sometimes the two are at cross-purposes. For example, striving for material efficiency may render a structure less redundant, and hence less safe in a disaster.

The main section of this report discusses a variety of efforts to promote resilience and resources for resilient design. Some of these are prescriptive, offering a set of design rules more stringent than existing building codes. Others are performance-based, offering performance criteria and methods for predicting the performance. Prescriptive criteria are simpler, but do not explicitly assure better performance. Performance-based approaches allow the designer to provide specified improvements in performance, but this requires much more effort to achieve. Some of the efforts are voluntary and others are intended to become model codes. Voluntary efforts depend on the desire of the owner or developer to enforce the guidelines. Model codes aim to become law that all designers and builders must follow. Voluntary initiatives may become accepted more quickly and be more adaptable to changing times, but efforts to change model codes have the potential to effect change more broadly.

The report also discusses current efforts to quantify the connection between disaster resilience and sustainability through life cycle methods. There is no current agreement as to the best way of achieving this, nor are there standard tools for the structural engineer to use in everyday practice. However, it is important to remain aware of developments in this area, as it will likely become a common consideration in structural design. The structural engineer who stays abreast of developments, and even better, who contributes to them ñ will be at an advantage when these methods mature.

In the interest of encouraging positive and meaningful action, the report provides the following suggestions for structural engineers who are interested in supporting disaster resilience and sustainability:

  1. Becoming better informed by using the references and links in this document.
  2. Participating in the code adoption process to encourage resilient design standards.
  3. Supporting legislation that requires or provides incentives for resilient construction.
  4. Educating owners regarding the importance and value of resilient construction.
  5. advocating with insurance companies and portfolio managers to offer decreased costs for better performing facilities.
  6. Advocate with ASCE, SEI and other professional organizations to raise the profile of structural engineers.

Concluding the report is a thoughtful afterword on resilience and sustainability in developing countries. The afterword suggests considerations for those interested in projects in these countries and provides potential solutions to common challenges, some of which can inform design practices in developed countries such as the United States.

Monday, March 30, 2015

How are disaster resilience, climate change, and sustainability related?

Sustainability has many definitions and applications. A long view of the future is one important aspect of sustainability. The Brundtland definition of sustainable development supports this by stating, “sustainable development is development that meets the needs of the present without compromising the ability of future generations to meet their own needs.” The application of sustainable development pertains to three different spheres of life: economic, environmental, and social. These are sometimes called the three pillars of sustainability. To be sustainable, a project must respect the three pillars over a long time span.

Disaster resilience refers to the ability to suffer less damage and recover quickly from adverse events. Both man-made and natural disasters occur quickly and can have significant consequences on portions of the built environment. There are many definitions of resilience, but most of them identify two key aspects: robustness and rapidity. Robustness is the ability to limit damage. Ductility, redundancy and integrity are important characteristics that help limit damage in structures. Rapidity is the ability to restore service to pre-disaster conditions quickly after the disaster. Disaster resilience is necessary for sustainability. A facility with many features that would otherwise render it sustainable will be of no use if it is heavily damaged in a disaster. Reconstruction would incur significant financial, social, and environmental impacts. These impacts must be considered in sustainability assessments. A resilient design ensures the usefulness and longevity of other sustainability features.

Climate change refers to any significant difference in the measures of climate that lasts for a significant period of time. These changes include those related to an increase in greenhouse gasses in the atmosphere, which contribute to global warming. The scientific community is in near unanimous agreement that global warming is anthropogenic, i.e., caused by humans. Some segments of the population dispute the cause, but few dispute that climate change is occurring. Whatever the cause, weather-related disasters are expected to increase in severity and magnitude in many parts of the world. Weather events of increased severity underscore the need for a resilient built environment. In more hostile climates, resilience must be a more important component of sustainability. Moreover, construction and maintenance activities generate greenhouse gasses that can accelerate climate change. Meaningful reductions of such impacts can have positive effects in mitigating the severity of climate change.
Wednesday, February 4, 2015

Sustainably Designing for Acts of God

Yup, they thought about that too... Resources are available to aid the Structural Engineer in improving disaster resilience for building structures in flood plains, coastal regions, hurricanes, tornadoes, hail, and wildfires.

Flood plains

For flood damage resistance, structural components should comply with ASCE/SEI 24 as well as state building codes.

Coastal regions

Foundations located in FEMA Coastal Zone A should be designed to the same criteria as those located in FEMA Coastal Zone V. Levees and flood walls should not be considered flood protection when renovating or designing new buildings for resistance to flood damage. Additional recommendations include compliance with Appendix G of the International Building Code – Flood Resistant Construction.

Hurricane, tornado, and other high wind regions

For wind-damage resistance in general, buildings should be designed for an increase in basic design wind speed by 20 mph. Roof coverings, their attachments, and gutter attachments should comply with UL and FM standards.

In addition, if located in hurricane- or tornado-prone areas, use of exterior cladding that is susceptible to wind damage should be limited. Storm shelters should be provided for all building occupants when design wind speed is 160 mph or greater (in hurricane- and tornado-prone areas). Storm shelters should be designed according to ICC 500 – Standard for the Design and Construction of Storm Shelters.

If located in hurricane-prone areas, also use the above recommendations for buildings in flood plains and coastal regions.

Regions susceptible to hail

For hail damage resistance, if located in moderate-to-severe hail exposure areas, use of exterior cladding that is susceptible to hail damage should be limited.

Regions susceptible to wildland fires

For wildfire damage resistance, buildings should meet the requirements of the International Wildland-Urban Interface Code.
SEI Sustainability Committee © 2011 & Main Blogger. Supported by Makeityourring Diamond Engagement Rings

You can add link or short description here