Numerical Estimates of the Seismic Response of Building Structures Reinforced With High-Strength Steel

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Title: Numerical Estimates of the Seismic Response of Building Structures Reinforced With High-Strength Steel

Author(s): Jeffrey M. Rautenberg and Santiago Pujol

Publication: Special Publication

Volume: 293

Issue:

Appears on pages(s): 1-10

Keywords: Nonlinear dynamic analysis; ASTM A1035; steel congestion; seismic response.

Date: 10/4/2013

Abstract:
The use of high-strength longitudinal reinforcement—having a specified yield stress between 80 and 120 ksi—in concrete elements has been shown to allow for the use of lower reinforcement ratios leading to reductions in fabrication costs and congestion. This is especially relevant to structures built in seismically active regions in which reinforcement ratios are typically higher than in structures in regions with a lower seismic risk. Recent research initiatives related to the use of high-strength reinforcement have largely been focused on the response of isolated elements instead of the response of building frames. This paper presents results from a suite of numerical analyses designed to investigate the effects of high-strength longitudinal reinforcement on overall building frame response. Using steel with a higher yield stress allows for reductions in reinforcement ratio. Those reductions, in turn, cause a decrease in post-cracking stiffness. To investigate the effects of this relative softening, a series of multiple-degree-of-freedom models were proportioned to represent idealized frames reinforced with high-strength steel. Nonlinear dynamic analyses were conducted to estimate their response to a set of seven strong-motion accelerograms. It is shown that increases in drift demands related to the use of high-strength steel range from negligible to approximately 20 percent, depending on a number of factors including base shear strength, ground motion intensity, and extent of high-strength steel use. This increase in drift demand 1) is modest compared to the uncertainties associated with predicting ground motion intensities and 2) needs to be confirmed through experiments.