Abstract

In the aftermath of earthquakes, hospital buildings are expected to remain occupiable to treat the injured. For the purpose, firstly, an appropriate structural system that ensures no or limited structural damage should be provided in such buildings; wall-frames are the recommended structural systems in hospital buildings. Secondly, it is also essential to adequately design wall-frames to help meet the preferred Occupiability seismic performance. The work presented in this paper examines the contributing factors for failure of structural elements in hospital buildings and explores structural configuration and design strategies for mitigating these failures. Nonlinear analyses studies of a typical hospital building in high seismic region in India are carried out to help provide quantitative guidelines for: (a) Structural Plan Density (SPD) of structural walls, and (b) design parameters, for achieving the preferred performance. Displacement-based limit state of structural damage adopted from traditional displacement demand estimation rules is proposed. Lateral stiffness, strength, and ductility are evaluated of study buildings, and efficacy of results obtained from nonlinear static analyses confirmed by performing nonlinear time history analyses in commercial software PERFORM 3D. Results demonstrate inadequacy of moment frame structural system in hospital buildings under strong earthquake shaking, identifies optimum overall SPD of structural walls and relative column-to-beam strength ratio of frame members, required to achieve Occupiability. A minimum 3% SPD of structural walls in Wall – Special Moment Resisting Frame (WSMRF), 4% SPD in Wall – Ordinary moment resisting frame (WOMRF) hospital buildings, and a minimum column-to-beam strength ratio (CBSR) of 2 is required in hospital buildings to attain Occupiability performance.

Abstract

This study considers simple acceleration sensitive Non-structural elements (NSEs) with fundamental period TS ≤ 0.07seconds, modelled as a rigid cantilever with lumped mass at the top (stick model). Numerical modelling of building and NSE together (complete model) and nonlinear time history analyses using 11 natural ground motions are performed in commercial software PERFORM 3D. Parametric studies of NSEs with lumped mass of 1-10 percent total seismic weight of building (in increments of 1 percent) for each fundamental period of NSE (in increments of 0.01s) is carried out, using spectrally scaled ground motions. Variations in: (a) lateral force demand on NSE, (b) Component Amplification Factor (CAF), and (c) Floor Amplification Factor (FAF), are monitored. Results are compared with the values of above parameters estimated as per EAK (2000), Eurocode 8 (1998 (1):2004), ASCE 07 (2016), NZS 4219 (2009), and NZS 1170 (5) (2004). It is observed that FAF varies nonlinearly across the floors (and significantly in the lower floors), as against linear variation stipulated in the above codes. The average CAF for the ground motions considered ranged between 1 and 2 up to Ts ≤ 0.06s. However, it increased significantly for Ts = 0.07s, thereby complementing ASCE 07 stipulation of 0.06s limit for rigid NSEs. The value of 2 is consistent with NZS 1170(5):2004 and 1 with ASCE 07 and EAK (2000). Further, as the NSE weight increased, the fundamental period of the building increased, and the average CAF marginally decreased. And, seismic force demand imposed on all NSEs during nonlinear time history analysis exceeded code recommended seismic design force under most ground motions.

Abstract

Wall-Frames, the recommended structural system for lifeline buildings is expected to have satisfactory and desirable seismic performance, especially if located in high seismic regions. In this work, fiber modeling approach is used to model inelasticity in walls and moment frames in a 6 storey-3-bay 2D wall-frame system. Displacement-controlled nonlinear static pushover analyses results from commercial software PERFORM3D suggest, the fiber type inelasticity in numerical models help predict nonlinear static behavior of study wall-frames reasonably well, compared to behavior of wall-frames with lumped inelasticity. In particular, increasing wall plan-aspect ratio enhances earthquake resistant virtues of wall-frames, namely stiffness, strength, and ductility. Further, early yielding is observed in stiffer wall-frames and reasonable ductility achieved in all study wall-frames. Alongside, limit states of structural damages are also monitored to grade the damages and in turn the seismic performance of wall-frames. In addition, results obtained from nonlinear static analyses are confirmed by performing nonlinear time history analyses of study wall-frames, towards quantifying the critical earthquake resistant virtues — results and investigations from the study is a precursor towards recommending design measures to ensure post-earthquake functionality of lifeline buildings. Keywords: Fiber modeling, Nonlinear static analysis, Limit states, Structural damages

Abstract

Wall-Frames, the recommended structural system for lifeline buildings is expected to have satisfactory and desirable seismic performance, especially if located in high seismic regions. In this work, fiber modeling approach is used to model inelasticity in walls and moment frames in a 6 storey-3-bay 2D wall-frame system. Displacement-controlled nonlinear static pushover analyses results from commercial software PERFORM3D suggest, the fiber type inelasticity in numerical models help predict nonlinear static behavior of study wall-frames reasonably well, compared to behavior of wall-frames with lumped inelasticity. In particular, increasing wall plan-aspect ratio enhances earthquake resistant virtues of wallframes, namely stiffness, strength, and ductility. Further, early yielding is observed in stiffer wall-frames and reasonable ductility achieved in all study wall-frames. Alongside, limit states of structural damages are also monitored to grade the damages and in turn the seismic performance of wall-frames. In addition, results obtained from nonlinear static analyses are confirmed by performing nonlinear time history analyses of study wall-frames, towards quantifying the critical earthquake resistant virtues—results and investigations from the study is a precursor towards recommending design measures to ensure postearthquake functionality of lifeline buildings.

Abstract

Earthquake Resistant Design Philosophy seeks (a) no damage, (b) no significant structural damage, and (c) significant structural damage but no collapse of normal buildings, under minor, moderate and severe levels of earthquake shaking, respectively. A procedure is proposed for seismic design of low-rise reinforced concrete special moment frame buildings, which is consistent with this philosophy; buildings are designed to be ductile through appropriate sizing and reinforcement detailing, such that they resist severe level of earthquake shaking without collapse. Nonlinear analyses of study buildings are used to determine quantitatively (a) ranges of design parameters required to assure the required deformability in normal buildings to resist the severe level of earthquake shaking, (b) four specific limit states that represent the start of different structural damage states, and (c) levels of minor and moderate earthquake shakings stated in the philosophy along with an extreme level of earthquake shaking associated with the structural damage state of no collapse. The four limits of structural damage states and the three levels of earthquake shaking identified are shown to be consistent with the performance-based design guidelines available in literature. Finally, nonlinear analyses results are used to confirm the efficacy of the proposed procedure.

Abstract

Artificial Bee Colony (ABC)method optimization procedure for design of RC moment frames​. Cross-section properties of frame members are optimized considering constraints specified by design codes.​Structural design provisions enunciated in Indian Standards IS456 (2000), IS1893 (2016) and IS13920 (2016) are used as system of design rules, to interact with Finite Element Method of analysis of frames developed for the study. Cross-sectional properties of structural members are chosen from a set of pre-defined sectional properties from the database developed to form design variables compliant with Indian Standards. The optimized design & detailing of frame elements are obtained after the frame structure is analyzed under the action of multiple load combinations ​ ABC method can then be applied, to improve the Nonlinear Response of the frame​