Seismic Response of Vertically Irregular Frames: Response History and Modal Pushover Analyses

274

165

SUMMARYIncremental dynamic analysis (IDA) has been extended by introducing a set of structural models in addition to the set of ground motion records which is employed in IDA analysis in order to capture record-to-record variability. The set of structural models reflects epistemic (modeling) uncertainties, and is determined by utilizing the latin hypercube sampling (LHS) method. The effects of both aleatory and epistemic uncertainty on seismic response parameters are therefore considered in extended IDA analysis. The proposed method has been applied to an example of the four-storey-reinforced concrete frame, for which pseudo-dynamic tests were performed at the ELSA Laboratory, Ispra. The influence of epistemic uncertainty on the seismic response parameters is presented in terms of summarized IDA curves and dispersion measures. The results of extended IDA analysis are compared with the results of IDA analysis, and the sensitivity of the seismic response parameters to the input random variable using the LHS method is discussed. It is shown that epistemic uncertainty does not have significant influence on the seismic response parameters in the range far from collapse, but could have a significant influence on collapse capacity.

Section: Dispersion Measures and The Sensitivity Of A Gc To Random Vmentioning

confidence: 51%

Incremental dynamic analysis with consideration of modeling uncertainties

Dolšek

2008

274

165

“…Chintanapakdee and Chopra [10] performed a similar study as Al-Ali and Krawinkler [9]. The significant difference was that they used a beam hinge model, which discouraged soft-storey mechanisms.…”

Section: Previous Research On Vertical Stiffness-strength Irregularitymentioning

confidence: 99%

Seismic response of structures with coupled vertical stiffness–strength irregularities

Sadashiva

MacRae

Deam

2011

SUMMARYSeveral seismic design codes around the world restrict the use of the Equivalent Lateral Force analysis method to structures satisfying structural regularity limits. These regularity limits are based on engineering judgement and lack quantitative justification. One common irregularity is that of a change in vertical stiffness over the building height. This stiffness irregularity is almost always associated with a change in vertical strength over the building height. For this reason, the effect of various realistic combinations of stiffness-strength irregularity in shear-type buildings is evaluated to quantify regularity limits.Structures analysed had 3, 5, 9 and 15 storeys, and the floor mass at all the levels were kept the same. Both regular and irregular structures were designed in accordance with the Equivalent Lateral Force procedure to produce the same engineering demand parameter. Structural ductility factors of 1, 2, 3, 4 and 6, and target (design) interstorey drift ratios ranging between 0.5 and 3%, were used in this study. The irregular structures were created by modifying specific storey lateral stiffnesses from that of the regular structure. Strengths at these storeys were also modified to ensure realistic relationships between stiffness and strength. The modified structures were then redesigned until the target interstorey drift ratio was achieved at the critical storey. Inelastic dynamic time-history analysis was conducted to compare the maximum interstorey drift ratio demands of the regular and irregular structures. Simple equations were developed to estimate possible variations in demand due to vertical stiffness-strength irregularity applied at critical locations in structures.

“…This procedure will be described later. Introducing the n-th mode inelastic SDF system permitted extension of the well-established concepts for elastic systems to inelastic systems; compare Equations (10) to (17), Equations (12) to (19), and note that Equation (11) applies to both systems. Solution of the non-linear Equation (19) provides D n (t), which when substituted into Equations (13) and (14) gives oor displacements and story drifts.…”

Section: Inelastic Systemsmentioning

confidence: 99%

A modal pushover analysis procedure to estimate seismic demands for unsymmetric‐plan buildings

Chopra¹,

Goel²

2004

Self Cite

400

256

SUMMARYBased on structural dynamics theory, the modal pushover analysis (MPA) procedure retains the conceptual simplicity of current procedures with invariant force distribution, now common in structural engineering practice. The MPA procedure for estimating seismic demands is extended to unsymmetric-plan buildings. In the MPA procedure, the seismic demand due to individual terms in the modal expansion of the e ective earthquake forces is determined by non-linear static analysis using the inertia force distribution for each mode, which for unsymmetric buildings includes two lateral forces and torque at each oor level. These 'modal' demands due to the ÿrst few terms of the modal expansion are then combined by the CQC rule to obtain an estimate of the total seismic demand for inelastic systems. When applied to elastic systems, the MPA procedure is equivalent to standard response spectrum analysis (RSA). The MPA estimates of seismic demand for torsionally-sti and torsionally-exible unsymmetric systems are shown to be similarly accurate as they are for the symmetric building; however, the results deteriorate for a torsionally-similarly-sti unsymmetric-plan system and the ground motion considered because (a) elastic modes are strongly coupled, and (b) roof displacement is underestimated by the CQC modal combination rule (which would also limit accuracy of RSA for linearly elastic systems).