There are two actions that cause earthquake damage: inter-story drift and floor acceleration. Together, these two actions cause damage to the structural frame, building contents, architectural facades, partitions, piping and ductwork, ceilings, building equipment and elevators. Our current codes specify drift limits but they do not require the structural engineer to investigate floor accelerations. Selection of the structural system is therefore based primarily on the system with the best drift performance. The structural system of a building represents approximately 20% of the total building cost, with the remaining 80% coming from the architectural, mechanical and electrical components. Generally the architectural, mechanical and electrical components are much more vulnerable to floor accelerations. Since these components are both more vulnerable and more valuable, an evaluation of the comparative performance of floor accelerations will become much more important as we head towards the use of performance based design. This paper provides a comparison of the maximum inter-story drifts and floor response spectra of both a three and nine building each with four different structural systems. Each of the building models were analyzed as fully nonlinear structures and subjected to a total of 10 time histories each. One set of five time histories was representative of a 50% in 50 year earthquake, while the other set was representative of a 10% in 50 year earthquake. Both sets were developed for the Los Angeles area. The results of each set of five were averaged and reported separately. The results of this comparative study are of significant benefit to practicing engineers who have a need to select an appropriate structural system without the resources to perform such a comprehensive study. The paper also discusses the importance of considering both floor accelerations and inter-story drift when selecting the structural framing system, especially as we move towards the implementation of performance-based design.
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