Adaptive Modal Combination Procedure for Nonlinear Static Analysis of Building Structures

ASCE, Journal of Structural Engineering, Vol. 132, No. 11, pp. 1721-1732, Nov. 2006

( AWARD WINNER PAPER: ASCE Raymond Reese Research Price in Structural Engineering)

Erol Kalkan, U.S. Geological Survey, Menlo Park,
Sashi K. Kunnath, University of California, Davis,

A new pushover analysis procedure derived through adaptive modal combinations (AMC) is proposed for evaluating the seismic performance of building structures. The methodology offers a direct multimode technique to estimate seismic demands and attempts to integrate concepts built into the capacity spectrum method recommended in ATC-40 (1996), the adaptive method originally proposed by Gupta and Kunnath (2000) and the modal pushover analysis advocated by Chopra and Goel (2002). The AMC procedure accounts for higher mode effects by combining the response of individual modal pushover analyses and incorporates the effects of varying dynamic characteristics during the inelastic response via its adaptive feature. The applied lateral forces used in the progressive pushover analysis are based on instantaneous inertia force distributions across the height of the building for each mode. A novel feature of the procedure is that the target displacement is estimated and updated dynamically during the analysis by incorporating energy-based modal capacity curves in conjunction with constant-ductility capacity spectra. Hence it eliminates the need to approximate the target displace- ment prior to commencing the pushover analysis. The methodology is applied to two existing steel moment-frame buildings and it is demonstrated that the AMC procedure can reasonably estimate critical demand parameters such as roof displacement and interstory drift for both far-fault and near-fault records, and consequently provides a reliable tool for performance assessment of building structures.

Predicted foor displacement and interstory drift ratios by nonlinear static procedures compared to the nonlinear response history analyses (RHA) of select impulsive near-fault records for 6- and 13-story SMRF buildings; Adaptive Modal Combination procedure is more accurate in predicting the "exact" responses obtained by nonlinear RHAs as compared to the MMPA (Modified Modal Pushover Analysis) and simple nonlinear static procedure based on Mode-1 proportional load vector.

Download an example OpenSees model of 6-story building with MatLAB post-processing codes for adaptive pushover analysis.

Related Journal Papers and Presentations

1 Kalkan, E. and Kunnath, S.K. (2006). “Adaptive Modal Combination Procedure for Nonlinear Static Analysis of Building Structures”, ASCE Journal of Structural Engineering, 132(11): 1721-1732.
2. Kalkan, E. and Kunnath, S.K. (2006). “Adaptive Modal Combination Procedure for Predicting Seismic Response of Vertically Irregular Structural Systems”, Proc. of the Eight National Earthquake Engineering Conference: Paper No. 700, San Francisco, April 18 - 22.
3. Kalkan, E. (2006). Predicting Seismic Demands of Building Structures, Ph.D. Dissertation, University of California, Davis.
4. Kalkan E. (2008) Adaptive Nonlinear Analysis as Applied to Performance based Earthquake Engineering, Tuft University Seminar Series.