Evaluation of three‐dimensional modal pushover analysis for unsymmetric‐plan buildings subjected to two components of ground motion

Abstract

The accuracy of the three-dimensional modal pushover analysis (MPA) procedure in estimating seismic demands for unsymmetric-plan buildings due to two horizontal components of ground motion, simultaneously, is evaluated. Eight low-and medium-rise structures were considered. Four intended to represent older buildings were designed according to the 1985 Uniform Building Code, whereas four other designs intended to represent newer buildings were based on the 2006 International Building Code. The median seismic demands for these buildings to 39 two-component ground motions, scaled to two intensity levels, were computed by MPA and nonlinear response history analysis (RHA), and then compared. Even for these ground motions that deform the buildings significantly into the inelastic range, MPA offers sufficient degree of accuracy. It is demonstrated that PMPA, a variant of the MPA procedure, for nonlinear systems is almost as accurate as the well-known standard response spectrum analysis procedure is for linear systems. Thus, for practical applications, the PMPA procedure offers an attractive alternative to nonlinear RHA, whereby seismic demands can be estimated directly from the (elastic) design spectrum. In contrast, the nonlinear static procedure specified in the ASCE/SEI 41-06 Standard is demonstrated to grossly underestimate seismic demands for some of the unsymmetric-plan buildings considered. Figure 2. First triplet of periods and modes of vibration of the UBC85 buildings (only roof motion is shown).by the letters A, B, and C followed by the number of stories and the design code: plan A is rectangular with two axes of symmetry, plan B is symmetric about the y-axis, and plan C is unsymmetric about both x-and y-axes. The buildings have similar plan areas and floor weights, with a span length of 30 ft and a story height of 13 ft. Design code forces for the buildings, assumed to be located in Bell, CA (33.996 N, 118.162 W), were determined, but their member sizes were governed by drift instead of strength requirements [9]. Figure 3. First triplet of periods and modes of vibration of the IBC06 buildings (only roof motion is shown). ModelingNonlinear RHA, MPA, and code pushover analyses were implemented for these buildings using the PERFORM-3D computer program [10] modeled with the following features: (1) beams and columns were modeled by a linear element with tri-linear plastic hinges at the ends of the elements that include in-cycle strength deterioration, but not cyclic stiffness degradation. Axial load-moment interaction for the columns was represented by the plasticity theory;(2) panel zones were modeled as four rigid links hinged at the corners with a rotational spring that represents the strength and

Effect of Steel and Concrete Coupling Beam on Seismic Behavior of RC Frame Accompanied with Coupled Shear Walls

“…In TNSP, the inverted triangular pro le was used for displacement-based load pattern of storey masses, according to FEMA-356. For a high-rise structure whose force distribution changes continuously during seismic events due to higher mode contribution, the three main mode shapes in each direction were considered to perform Modal Pushover Analyses (MPA) in this research [45][46][47]. For control point of the displacement of structure in all analyses, the center of mass at the roof level is selected.…”

Errors caused by peak factor assumptions in response‐spectrum‐based analyses

“…that are defined relative to the peak factor p 0 associated with an SDOF oscillator having natural frequency ω 0 and damping ratio ζ 0 , where it is understood that p i and p 0 on the right hand side of (17) are computed for the same ω g , ζ g and τ. In the following derivation, we set ζ 0 = 5 % and define ω 0 as the frequency at which the ζ 0 = 5 % pseudo-acceleration response spectrum assumes its maximum value.…”

“…Additional information of the structural system is available in References [15] and [17]. We assume the damping ratio is 5% for all modes.…”

The modified and extended upper-bound (UB) pushover method for the multi-mode pushover analysis of unsymmetric-plan tall buildings

“…Over the past decade, several efforts have been made to extend pushover analysis methods to unsymmetric-plan 3D building structures taking torsional effects into account. Modal pushover analysis (MPA) [8,23,24], consecutive modal pushover (CMP) procedure [21,22], the extended N2 [17], adaptive modal pushover procedure [27] and generalized force vectors method [15] were extended to unsymmetric-plan building structures in which the effect of higher modes in both elevation and plan (torsion) was taken into consideration.…”