Probable Maximum Loss assessments (PMLs) are utilized by property owners, investors, lenders, and others to understand and control seismic-related risks. Seismic risk assessments evaluate how a property would fare in an earthquake. Not all clients view risks the same way, which means that the evaluation of earthquake risks takes on different forms for different clients.
In this blog, we’ll delve a little more into earthquake assessments of buildings and facilities in order to achieve client-desired levels of performance.
How Do Earthquakes Affect Buildings?
Beyond death and injury, earthquakes can result in damage to buildings, loss of inventory, disrupted operations and cash flow, interruption of utility and public services, and more. Ground shaking is the primary cause of earthquake damage, particularly in relation to unrestrained or inadequately braced non-structural systems. The strength of earthquake shaking depends on the earthquake’s magnitude, the property’s proximity to the fault, the local geology, the soil type, and more.
Current building codes are prescriptive, intended to produce buildings that meet a life-safety level of protection at a specified level of ground shaking. During these design-level earthquakes, code-designed buildings can achieve the intended goal of preventing loss of life or life-threatening injury, but could sustain extensive structural and nonstructural damage and be out of service for extended periods of time. In some cases, the damage may be too costly to repair, leaving demolition as the only option.
Because there is no way to predict earthquakes with certainty, the goal of seismic assessments is to create probable loss estimates, hence why they are called Probable Maximum Loss reports, instead of maximum loss reports. These enable people to understand the probable losses properties may face and what actions can be taken to mitigate them.
About Earthquake Assessments of Buildings and Facilities
Seismic risk assessments evaluate buildings as they exist currently and estimate potential earthquake losses for several different earthquake levels and different performance levels. These levels vary, and may focus on areas like collapse prevention, life safety, and immediate occupancy.
VIE estimates the current expected performance of facilities for the earthquake levels we are studying it for. From there, our engineers estimate what it would take to elevate that to what the facility owner would like to achieve. These earthquake levels are identified in ASCE 41, and the performance goals are identified by the client.
Different clients may have different performance goals, like life safety over collapse prevention. Some clients may worry more about business interruption and continuous operation of facilities after an earthquake while others may prioritize life safety over collapse prevention.
Earthquake risk assessments evaluate approaches, cost estimates, and procedures needed to achieve those goals. For example, your building for lower level earthquakes may fall down, but you want to achieve collapse prevention.
In earthquake assessments, our engineers look at buildings as they are now, estimate, and evaluate if they will achieve the client-specific goals already or what it would take to achieve desired levels of performance. VIE works with each client to understand their specific desired levels of performance and perceived risks.
Determining When Seismic Risk Assessments Are Necessary
Not all properties require seismic risk assessments. To determine if a seismic risk assessment is necessary, two main screening criteria are utilized: seismic zones and peak ground acceleration.
If a property is located in seismic zones 3 or 4, defined by the Seismic Zone Map in the ASTM, a seismic risk assessment is likely necessary. Now, Peak Ground Acceleration (PGA) is a commonly used screening tool. Properties can be brought up to better standards and work can be done to resolve stability issues, like seismic reinforcement.
Do You Need Earthquake Assessments of Buildings and Facilities?
VIE has over 40 years of experience in providing clients across the United States with seismic engineering services. VIE has performed these analyses using numerous techniques, such as expert database methods (as in ATC 13 and Thiel/Zsutty) and more detailed methods, such as those in ASCE 41 and FEMA P-58. Our engineers have also developed customized seismic risk assessment methods, which have been utilized in client-specific evaluations. VIE has performed private and government sector seismic evaluations, conforming to project-specific criteria.
To learn more about our seismic assessment services and other engineering services we provide, contact us today. We look forward to hearing from you.
