Earthquake‐induced floor horizontal accelerations in buildings

Abstract

SUMMARYFloor horizontal accelerations are needed for obtaining forces for the design of diaphragms, for the design of their connections and for the design of non-structural components and equipment supported by structures. Large oor horizontal accelerations have been recorded in buildings during earthquakes. Such accelerations have been responsible for inertia forces causing damage to services and are a major reason for structural damage and even building collapse.This paper describes an analytical investigation into earthquake-induced oor horizontal accelerations that arise in regular buildings built with rigid diaphragms. The paper also describes several methods prescribed by design standards and proposes a new method. The method is based on modal superposition modiÿed to account for the inelastic response of the building's lateral force resisting system. Results obtained from time-history inelastic analysis are compared with the proposed method.

Dual‐plastic hinge design concept for reducing higher‐mode effects on high‐rise cantilever wall buildings

“…Figure 6 shows clearly that there are very large differences between the shapes of the bending moment envelopes obtained from the MRSA and the NDTHA, and the differences become more pronounced in the 20-and 40-story buildings. As pointed out by others [5,8,9,13,14], the second and other higher modes are not greatly affected by the base plasticity as inferred by the MRSA and this is the main reason for the differences in shapes. This figure also shows that the bending moment envelopes obtained from the NDTHA reaches or exceeds the EC8 linear design envelopes in all cases.…”

“…Elastic forces obtained from the modal combinations are reduced by a force reduction factor to obtain design forces. In 2002, Rodriguez et al [13] suggested that inelastic response at the base of cantilever walls reduces mainly the first mode of response. Consequently, the relative contribution of the higher modes to response quantities, such as bending moments and shear forces, increases with an increase in ground motion intensity augmenting the curvature ductility demand at the base.…”

Establishment of performance‐based seismic design factors for precast concrete floor diaphragms

“…The diaphragm design methodology [1], including design factors determined here and rational methods proposed by the research team [2,19], serves as the basis for comprehensive modifications to diaphragm design currently in the codification process [4,5].…”

“…The following trends are further identified in Figure 12: (i) maximum diaphragm force typically increases with number of stories, because of the importance of higher mode effects in these structures [19]; (ii) diaphragm force increases with aspect ratio (because the corresponding increase in diaphragm flexibility tends to amplify diaphragm motion relative to the LFRS) to a point where diaphragm flexibility becomes sufficiently high to partially isolate the diaphragm response from the LFRS, and thus tends toward lower diaphragm force amplification, as also seen in simpler models [18]; (iii) the effect of number of stories is more significant than that of diaphragm aspect ratio, implying that higher mode effects are more significant than the effect of diaphragm flexibility, particularly for elastic diaphragm response; (iv) moment frame structures show similar but slightly smaller diaphragm force amplification than shear wall structures; and, (v) the smaller diaphragm depth (d = 9.7 m) associated with hollow-core exhibits slightly smaller diaphragm force amplifications than comparable deeper diaphragm cases (d = 18.2 m) associated with double tees.…”

Earthquake-Induced Collapse Risk and Loss Assessment of Steel Concentrically Braced Frames

“…Such a mechanism may result in large residual drifts and structural collapse [1,2]. Steel CBFs is likely to experience high absolute floor acceleration demands even at low seismic intensities due to their high lateral stiffness [3,4]. Moreover, prior studies [5,6] indicated that steel brace flexural buckling is typically triggered at relatively small story drifts.…”