Assessing risk differently means building with protective design in mind
Building codes fall short of ensuring America's infrastructure is prepared to withstand severe natural and manmade disasters. The solution is to recognize why protective design is important, then use a proven risk-analysis approach to cost-effectively mitigate risks associated with extreme events.
Codes aren’t enoughBuilding codes haven’t caught up with the increasingly devastating effects of massive tornados, fires, floods and hurricanes, or with manmade catastrophes and industrial accidents that rip communities apart and cost billions of dollars. But developers fear that, if codes are adjusted to require property construction to withstand catastrophes that never may occur, the costs will make new projects virtually impossible to build.
Fortunately, risk-based analysis can dramatically reduce the potential of extreme-event damage without threatening projects financially.
The reality: Extreme events and socioeconomic havocBuilding codes are based on historical, location-specific probabilities that a natural disaster will occur in a given area. But increasingly, climate-related events — outside of what probabilities anticipate and more severe than codes were established to manage — are causing:
• Injuries, loss of life, and emergency response and recovery operations.
• Disrupted business continuity, occupancy, production, and movement of people and goods. When Super Storm Sandy struck the Northeast, for example, New York’s highway tunnels flooded, and railways and subways were rendered inoperable. The region’s residents were unable to get to work for at least a week, and businesses and workers experienced unrecoverable financial losses.
• Structural damage that requires costly, time-consuming repairs. The Gulf Coast and a number of Midwestern cities, for example, still are struggling to rebound from catastrophic hurricane or tornado damage, some of which occurred years ago.
Currently, the Federal Emergency Management Agency pays for disaster repairs and may retrofit assets to better withstand future catastrophes. But FEMA’s reserve fund is $20 billion in debt. With the increase in the number and severity of extreme events, there soon won’t be money to help.
Climate extremes and the threat of terrorism demand that society — and the development, owner and engineering communities, in particular — think proactively about how to cost-effectively evaluate, build and/or retrofit high-value infrastructure.
Risk-based analysis goes beyond codesA risk-assessment model evaluates structures’ individual components and calculates total risk based on each asset’s:
• Necessity. A crucial asset automatically receives a high-risk rating.
• Location. Analysis of structures in seismic zones, tornado alleys or adjacent to chemical plants considers the likelihood that they will experience extreme events, and whether design and construction should exceed code requirements.
• Vulnerability. Structures that will tend to suffer damage — such as a bridge built on shallow footings that could collapse when buffeted by storm surge — are considered high risk.
Risk can’t be eliminated. But strategic, innovative thinking can increase a structure’s ability to withstand extreme events without adding significantly to project costs. For example, risk-based analysis reveals how to sensibly:
Reduced risk without significantly greater cost
• Mitigate location risk. In a known tornado alley, building two smaller hospitals on opposite ends of town — rather than a single hospital — reduces risk for the entire community.
• Protect against vulnerability. Make it more difficult, for example, for terrorists to deliver explosives to structures that are attractive targets. Options include erecting barriers to traffic and nearby parking, limiting the number of entry points, screening people as they enter, and creating distance between the structures and parking lots.
• Plan for worst-case scenarios. During Hurricane Katrina, air trapped under Lake Pontchartrain’s twin I-10 bridges permitted the storm surge to shift the bridge deck segments off their piers. The bridges were impassable until emergency repairs allowed the westbound span to open to two-way traffic — more than a month and a half after the storm. Risk analysis, which would have considered storm surge and seismic possibilities during original construction, would have encouraged drilling vent holes in the bridge decks and using strong tie-down bearings to help ensure the bridges’ survival during a storm surge.
• Make infrastructure resilient. Current codes require building envelopes to withstand hurricane-force winds but not tornado-force winds. Using risk analysis, the strategy would be to control damage, limit the outage period and save lives by:
o Allowing the cladding to come off during a tornado to reduce pressure on the structure.
o Designing a sound frame and foundation to survive the event. That allows for rebuilding rather than demolition and replacement, which cost more and take longer.
Resiliency is the goalRisk assessment looks at how to strengthen structures and also to address cataclysmic events when they occur. The approach evaluates potential consequences and establishes relevant, rapid-recovery plans that focus on:
• Reducing casualties by placing priority on evacuating people. Preventing collapse until occupants can evacuate, preventing progressive collapse and providing safe refuge until rescue all are part of the plan.
• Reducing environmental impact with sensors that monitor crucial infrastructure, and by periodically inspecting safety systems and containment structures for signs of deterioration.
• Reducing property damage by maintaining redundant facilities and hardening essential facilities before extreme events strike.
• Reducing recovery time with prioritized plans and procedures to quickly restore critical infrastructure to operability
Rather than allowing codes to limit thinking and action, consider how to address the challenges of extreme events with protective design:
• Every community should commission a qualified engineering firm to assess and communicate with city leaders about how potential risks can be resolved before disaster strikes.
• Owners/operators of critical infrastructure — power plants, hospitals, manufacturing facilities — should invest in initial risk assessments. They take only a few days and are not expensive, especially in contrast to the cost of extreme-event damage.
The keys are to recognize why protective design is important to preserving both lives and property, and then to use a proven risk-analysis approach to cost-effectively mitigate risks associated with extreme events.