Dynamic Testing of Open Ground Story Structure and In Situ Evaluation of Displacement Demand Magnifier
01 Oct 2017-Journal of Performance of Constructed Facilities (American Society of Civil Engineers)-Vol. 31, Iss: 5, pp 04017055
TL;DR: The majority of housing tenements in developing countries constitute a class of structure termed open ground story (OGS) of medium rise and highly vulnerable to strong seismic motions as mentioned in this paper, which makes them vulnerable to earthquakes.
Abstract: The majority of housing tenements in developing countries constitute a class of structure termed open ground story (OGS) of medium rise and highly vulnerable to strong seismic motions. Eval...
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TL;DR: In this paper, the effect of soil flexibility on the seismic response of open ground storey buildings has been investigated and the column-side sway mechanism is developed due to the presence of soft storey between the stiff upper storey and rigid base by assuming the soil support is stiff enough.
Abstract: Bhuj earthquake in India, 2001 had witnessed spectacular failures of a class of reinforced concrete multi-storied buildings termed as Open Ground Storey (OGS) buildings, necessitated by a functional demand to provide a parking space within a building plan. Due to the absence of brick-infilled walls at the ground floor, a sudden reduction in the storey stiffness can cause enormous seismic displacement demand in the ground storey itself. Further, the column-side sway mechanism is developed due to the presence of soft storey between the stiff upper storey and rigid base by assuming the soil support is stiff enough. The present study focuses on the effect of soil flexibility on the seismic response of open ground storey buildings. Analytical studies on typical open ground storey building models considering the soil flexibility have been carried out in SAP2000 software and static nonlinear analysis (pushover analysis) has been used to study the lateral response. Variation in boundary conditions are incorporated by simulating three different soil conditions hard, medium and soft, classified as mentioned in IS 1893 (Part 1) 2016. It is observed from the present study that the soil flexibility increases the lateral displacement and secondary forces associated with the P-Delta effect. Further, a parametric study is carried out to study the influence of soil flexibility in OGS buildings of various slenderness ratios. The importance of considering the influence of soil-structure interaction has been highlighted for obtaining a realistic performance point of the building. In addition, for preliminary and quick seismic assessment of huge stock of existing OGS buildings in Indian urban regions, a simplified methodology for estimating the lateral behaviour of a flexible base open ground storey building has been developed. This methodology is useful to segregate the highly vulnerable OGS buildings that undergo a detailed assessment prior to retrofit. The developed methodology is validated with the detailed analytical studies made on open ground storey buildings.
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TL;DR: In this article, the authors have developed a retrofitting technique of seismically damaged building using Geopolymer concrete and Chevron steel bracing with passive energy dissipation devices Experimental studies are carried out using the 4m × 4m triaxial shake table test facility to evaluate the seismic performance of bare frame and open ground storey building.
Abstract: Retrofitting is a technique wherein the damaged structure is strengthened to original design requirements During 2001 Bhuj earthquake in Gujarat, India many open ground storey building damaged So there is an urgent need for retrofitting of damaged buildings This calls for techniques that are technically sound and economically feasible to upgrade deficient and damaged buildings Also, Portland cement (PC) production is under critical review due to high carbon dioxide gas released to the atmosphere and Portland cement is also one among the most energy-intensive construction materials So retrofitting of existing deficient building using eco-friendly material which could promise higher structural performance than the original building is required The main contributions is development of retrofitting technique of seismically damaged building using Geopolymer concrete and Chevron steel bracing with passive energy dissipation devices Experimental studies are carried out using the 4 m × 4 m tri-axial shake table test facility to evaluate the seismic performance of bare frame, Open ground storey building, X-plate retrofitted building, Shear wall retrofitted building Two three storied half scale model buildings, one open ground storey (OGS) building and a bare frame building are tested for different earthquake inputs in the shake table The acceleration spectrum of IS1893:2002, soft soil is used as seismic input for the above tests The failure modes and crack pattern of buildings after the seismic test are analysed The damaged OGS building after the shake table test is retrofitted The local retrofitting of columns and beam-column joints in the ground storey is carried out using Geopolymer concrete The global retrofitting of building is formulated with Chevron type steel bracing incorporating X-plate damper in the ground storey Sweep sine tests on OGS building before and after retrofitting with X-shaped metallic damper is carried out The natural frequencies and mode shapes of the models are evaluated The retrofitted OGS building is again subjected to shake table test to the study the seismic performance under varying amplitude as per IS 1893:2002 ground motion The same model buildings are analysed in SAP 2000 to predict the seismic performance of the retrofitted RC framesAn innovative technique of retrofitting the seismic damaged building using Geopolymer concrete and construction of shear wall is explored Two Reinforced Concrete shear walls are constructed inside the open ground storey building as global retrofitting technique Sweep sine test is carried out after retrofitting with shear wall The fundamental frequency of open ground storey building increased from 375 Hz to 725 Hz due to the addition of shear wall The pushover test on building is carried out The pushover analysis is carried out to study the seismic response of reinforced concrete building with local and global retrofitting using SAP 2000 software Comparison of experimental and analytical push over curves is plotted A significant improvement in the strength and stiffness of the open ground storey building after retrofitting with shear wall is observed
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TL;DR: In this paper, a stress-strain model for concrete subjected to uniaxial compressive loading and confined by transverse reinforcement is developed for concrete sections with either spiral or circular hoops, or rectangular hoops with or without supplementary cross ties.
Abstract: A stress‐strain model is developed for concrete subjected to uniaxial compressive loading and confined by transverse reinforcement. The concrete section may contain any general type of confining steel: either spiral or circular hoops; or rectangular hoops with or without supplementary cross ties. These cross ties can have either equal or unequal confining stresses along each of the transverse axes. A single equation is used for the stress‐strain equation. The model allows for cyclic loading and includes the effect of strain rate. The influence of various types of confinement is taken into account by defining an effective lateral confining stress, which is dependent on the configuration of the transverse and longitudinal reinforcement. An energy balance approach is used to predict the longitudinal compressive strain in the concrete corresponding to first fracture of the transverse reinforcement by equating the strain energy capacity of the transverse reinforcement to the strain energy stored in the concret...
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TL;DR: In this paper, the authors developed expressions for the ultimate deformation capacity and for the deformation at yielding of reinforced concrete (RC) members in terms of their geometric and mechanical characteristics, which are essential for the application of displacement-based procedures for earthquake resistant design of new RC structures and for seismic evaluation of old ones.
Abstract: The inelastic deformation capacity of reinforced concrete (RC) members is important for the resistance of RC structures to imposed deformations, and especially so for seismic loads as earthquake-resistant design relies on the ability of RC members to develop (cyclic) deformations well beyond elastic limits without significant loss of load-carrying capacity. This study develops expressions for the ultimate deformation capacity and for the deformation at yielding of RC members in terms of their geometric and mechanical characteristics. Such expressions are essential for the application of displacement-based procedures for earthquake-resistant design of new RC structures and for seismic evaluation of old ones. They are also essential for a realistic estimation of the effective elastic stiffness of cracked RC members and structures, which is important for the calculation of seismic force and deformation demands.
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TL;DR: In this paper, the column stiffness and drift concentration within a frame based on pushover and dynamic analyses is investigated, and it is shown that continuous seismic and gravity columns in a structure significantly decrease the possibility of large drift concentrations.
Abstract: Steel concentrically braced frames are generally designed to resist lateral force by means of truss action. Design consider- ations for columns in these frames are therefore governed by the column axial force while column bending moment demands are generally ignored. However, if the columns cannot carry moments, then dynamic inelastic time-history analyses show that a soft-story mechanism is likely to occur causing large concentrated deformations in only one story. Such large concentrations of damage are not generally seen in real frames since columns are generally continuous and they possess some flexural stiffness and strength. This paper develops relationships for column stiffness and drift concentration within a frame based on pushover and dynamic analyses. It is shown that continuous seismic and gravity columns in a structure significantly decrease the possibility of large drift concentrations. An assessment method and example to determine the required column stiffness necessary to limit the concentration of story drift is provided.
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TL;DR: In this paper, the authors examined the seismic collapse safety of reinforced concrete frame buildings and examined nonductile moment frames that are representative of those built before the mid-1970s in California.
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