Theory Behind the Seismic Performance of Steel Frame Structures

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had to stay in the linear elastic range for wind and seismic loading. Modern codes design for inelastic behavior and are the basis of the capacity design procedures that are currently in place. The current building code of Canada has the principle of capacity design for structural steel systems that carry lateral loads. There is an element in the lateral force resisting system that is meant to dissipate energy by an inelastic response when subjected to seismic loading. All other members of the system are then designed to adequately resist the seismic loading, all while remaining elastic. The brace is designed to dissipate energy and to withstand major deformations by having tension ductility along the length and compression buckling.

This is the framework of a typical single story CBF building in Canada

In 1965, the NBCC design for lateral earthquake loading was calculated using the following equation:

V = KW

V = lateral loading due to earthquake

W = dead load

K = RCIFS

R = geographical earthquake factor

C = construction-type factor

I = importance factor

F = soil and foundation conditions

S = structural flexibility factor

The main difference between the old building code and the current code (NRCC 2010) is the geographical earthquake factor, R. Unique spectral acceleration ordinates are used in modern calculations and depend on the location of the building. The old code used a seismic zoning map that was created in 1953. This zoning map split the country of Canada into four zones. Each zone then had it’s own earthquake factor of R, which was then used for the calculations. These values of R were selected based on past earthquake activity However, this concept contained a large flaw in assuming that earthquakes on the eastern and western coasts were similar in accelerations, magnitudes, frequencies, and return periods when they were in fact not similar at all. Modern research and studies have concluded that there is a substantial difference between earthquakes that occur in the east and earthquakes that occur in the west.

In conclusion, steel frame structures are perhaps the safest buildings during an earthquake. Steel’s structural integrity and soundness has been known about for quite some time. But the 1960s were a time of revolutionary research and rewriting of the design codes. Professor Popov’s research findings at the University of California at Berkeley began this revolution and is still used and referenced in many codebooks and design manuals.

Works Cited

Caruso-Juliano, A., et al. "Seismic Performance Of Single-Storey Steel Concentrically Braced Frame Structures Constructed In The 1960S." Canadian Journal Of Civil Engineering 41.7 (2014): 579- 593. Computer Source. Web. 27 Apr. 2016

Hamburger, Ronald O., Krawinkler, Helmut, Malley, James O., and Adan, Scott M. (2009). "Seismic design of steel special moment frames: a guide for practicing engineers," NEHRP Seismic Design Technical Brief No. 2, produced by the NEHRP Consultants Joint Venture, a partnership of the Applied Technology Council and the Consortium of Universities for Research in Earthquake Engineering, for the National Institute of Standards and Technology, Gaithersburg, MD., NIST GCR 09-917-3

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