Report Tests Seismic Performance of Materials

TUESDAY, JUNE 28, 2022


The United States Resiliency Council (USRC) recently prepared a report evaluating the comparative seismic performance of four commonly used construction types in typical multifamily developments for the National Ready Mixed Concrete Association (NRMCA) and the RMC Research & Education Foundation.

Earthquake Performance Comparison of Multifamily, Multistory Apartment Building Constructed of Various Materials compared concrete framing using insulated concrete forms (ICF), traditional wood framing, cross laminated timber (CLT) and steel framing. The materials were tested for seismic performance found in Los Angeles, Seattle and Memphis, Tennessee.

The template applied to each method/material entailed a four-level apartment, 360 feet by 68 feet, totaling 98,000 square feet, and was assumed to have been designed to the most current edition of the International Building Code without any special seismic features beyond code requirements.

For the research, NRMCA provided funding to construct each building based on RS Means data. According to the report, the estimated baseline cost of the ICF configuration ranged between $15.6 million and $20.5 million, depending on location. Traditional wood construction was estimated to cost $14.1 million and $20 million, depending on lumber prices, CLT ranged between $15.1 million and $12.7 million and steel ranged between $16.3 million and $21.5 million.

The RMC Research & Education Foundation was also reported to provide grants to USRC for the research.

With this data, USRC calculated the net benefits and net construction cost differences of ICF relative to the other three configurations. USRC also estimated the potential return on investment considering earthquakes that might occur over a 50-year building life and what repair costs and recovery time might look like regarding the associated damage to the materials and range of earthquake intensity at each location.

Key findings from the study included:

  • The cost differential among the various material systems considered is relatively minor, typically 6% or less, particularly considering the volatility of lumber and, to a lesser extent, steel;
  • The ICF configuration produced an 18% to 80% higher lateral force strength and four to five times higher building stiffness than the other configurations;
  • Property losses in a Design Level Event were approximately 170% to 270% higher for the wood, CLT and steel configurations than the ICF configuration in Los Angeles and Seattle, and 40% to 85% higher in Memphis;
  • Estimated recovery times in a Design Level Event for the ICF configuration were typically less than two weeks. Recovery times for the other configurations ranged from approximately 6.5 to 9.5 months in Los Angeles and Seattle, and 1.5 to 5.5 months in Memphis;
  • Total losses, considering property and rent were approximately 270% to 530% higher for the wood, CLT and steel configurations than the ICF configuration in Los Angeles and Seattle, and 85% to 130% higher in Memphis; and
  • The net benefit in a Design Level Event of the ICF configuration, considering the difference in estimated construction cost, ranged from $1.0 million to $5.3 million in Los Angeles and Seattle. In Memphis, the range was between -$1.5 million (negative benefit) to $800,000 net benefit.

Another point the report touched on was the USRC earthquake building performance rating system, which communicates the performance of a building using one to five stars across the three dimensions of safety, damage and recovery time for an earthquake equivalent to the design level event (DLE).

As outlined by the USRC earthquake rating definitions chart, a modern code-compliant building might expect to receive three to four stars in safety and two or three stars in damage and recovery. This rating would represent a building that would be safe for its occupants, not necessarily quickly repairable.

A USRC Gold or Platinum Rating (four and five stars in all three dimensions) would ordinarily be limited to essential or critical facilities, perhaps 5%-10% of the building stock. A well-designed ordinary building might be expected to achieve a Silver Rating (a minimum of three stars in each dimension). 

According to the report findings, an ICF building might be expected to receive a USRC Gold or Platinum Rating in each location considered. Similar wood and steel framed structures may or may not achieve a USRC Silver Rating based on location.

Several other conclusions drawn from the results of the study include:

  • The cost differential among the various material systems considered is relatively minor, typically 6% or less, particularly considering the variability of lumber and, to a lesser extent, steel;
  • While the design of each building option was targeted to basic conformance to the International Building Code, the performance of ICF showed both higher strength and higher building stiffness compared to the traditional wood frame, CLT and steel frame configurations;
  • In a Code Design Level Event, the ICF configurations showed significantly less building drift than the other configurations, with roof deflections of the former on the order of 20-25% of the latter;
  • Property losses in a Design Level Event were approximately 170% to 270% higher for the wood, CLT and steel configurations than the ICF configuration in Los Angeles and Seattle, and from 40% to 85% higher in Memphis;
  • The additional strength and stiffness of the ICF configurations resulted in substantially reduced recovery time relative to the other configurations, primarily because minimal structural damage is caused, and nonstructural damage to partitions, cladding, utilities and egress routes is likely to be significantly less as a result of the lower building drifts. Estimated recovery times in a Design Level Event for the ICF configuration were typically less than two weeks. Recovery times for the other configurations ranged from approximately 6.5 to 9.5 months in Los Angeles and Seattle, and 1.5 to 5.5 months in Memphis;
  • Total losses, considering property and rent, were approximately 270% to 530% higher for the wood, CLT and steel configurations than the ICF configuration in Los Angeles and Seattle, and 85% to 130% higher in Memphis;
  • The net benefit in terms of the reduced losses considered in a Design Level Event, which included direct property damage and lost rental revenue, accounting for the difference in estimated construction cost of ICF construction relative to other materials, ranges from $2.6 million to $5.3 million in Los Angeles and from $1.0 million to $3.2 million in Seattle. In Memphis, where the seismicity is substantially lower than on the west coast, the net benefits are less, between -$1.5 million net cost of the ICF system relative to wood, and $800 thousand net benefit relative to steel;
  • Considering the annual benefit of reduced losses over time relative to additional construction costs, in Los Angeles the 50-year ROI ranges from 2% to 8% and in Seattle from -1% to 16%. In Memphis, the return on investment was generally negative from -8% to -5%;
  • Not all potential benefits have been included in this analysis. Avoided casualties, shelter costs, debris impacts, and the social and economic impacts to a community due to lost housing and workforce are examples of the additional benefits achieved with higher-performing buildings. Therefore, the net benefits associated with ICF construction are a lower bound estimate of the return on investment;
  • An ICF building might be expected to receive a USRC Gold or Platinum Rating where egress from the building is not hindered following a Design Level Event, repair costs would be less than 5% of the building replacement cost, and functional recovery could be restored within one to two weeks; and
  • Similar wood and steel framed structures may or may not achieve a USRC Silver Rating, implying that because of larger building drifts occupants may be hindered in using stairs or elevators to exit, and functional recovery time might be on the order of several months to a year.

“We’re proud to work with our partners at NRMCA to release this illuminating USRC report,” said Foundation Chairman Rodney Grogan (Dunn Investment Co./MMC Materials). “It’s important to understand the true costs of building material selection, especially in areas subject to natural disasters.”

“Our industry has long recognized the benefits of resilient construction,” added NRMCA Vice President, Fire Codes & Standards Shamim Rashid-Sumar, P.E. “The USRC study quantifies these benefits beyond first construction costs to include the impacts of damage, repair, and recovery time.”

A full copy of the report can be viewed here.

   

Tagged categories: Building materials; Color + Design; concrete; Condominiums/High-Rise Residential; cross-laminated timber; Disasters; Good Technical Practice; Government; Hazards; Health & Safety; Health and safety; NA; North America; Program/Project Management; Projects - Commercial; Research; Research and development; Residential; Safety; Stainless steel; Steel; Structural steel; timber; United States Resiliency Council

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