Abdul Qadir Bhatti

Performance evaluation of retrofitting strategies for non-seismically designed RC buildings using steel braces

Recent major earthquakes around the world have evidenced that research in earthquake engineering must be directed to the vulnerability assessment of existing constructions lacking appropriate seismic resisting characteristics. Their retrofit or replacement should be made in order to reduce vulnerability, and consequent risk, to currently accepted levels. In this work, the efficiency of ductile steel eccentrically-braced systems in the seismic retrofitting of existing reinforced concrete (RC) buildings is studied. The retrofit technique studied consists in a bracing system with an energy dissipation device, designed to dissipate energy by shear deformation. The numerical model was calibrated with cyclic test results on a full-scale structure. The models used for the RC frame and masonry represent their real behavior and influence in the global structural response. The steel bracing system was modeled with strut rigid elements. The model for the energy dissipater device reproduces rigorously the behavior of the shear-link observed in the cyclic tests, namely in terms of shear, drift and energy dissipation. With the calibrated numerical model, a series of non-linear dynamic analyses were performed, for different earthquake input motions, intending to study: the influence of the retrofitting system in the response of bare and infilled structures; the influence of the location and strength of the retrofitting system.

Dynamic Response Analysis for a Large-scale RC Girder Under a Falling-weight Impact Loading

In order to establish a rational impact resistant design procedure for prototype reinforced concrete (RC) structures, not only experimental study but also numerical analysis study should be conducted. However, numerical analysis method on impact response analysis for those structures has not been established yet. Here, in order to establish a rational numerical analysis method for prototype RC structures under impact loading, a falling-weight impact test was conducted for prototype RC girder with 8 m clear span. Referring to the experimental response waves, numerical accuracy was investigated varying major parameters. From this study, following results were obtained as: (1) fine mesh should be used near supporting gigues; (2) Drucker-Prager yield criterion should be applied which gives better results than von Mises one; and (3) appropriate system damping constant should be set to h = 0.015.

Elasto-plastic dynamic response analysis of prototype RC girder under falling-weight impact loading considering mesh size effect

This paper focuses on an applicability of the proposed numerical analysis method to the large scale RC girder under falling-weight impact loading using effective finite element mesh size distribution by comparing with experimental results. The results obtained from this study are: (1) displacement wave can be accurately estimated with seven-division of stirrup interval. (2) The maximum impact force and reaction force can be roughly estimated by using the mesh geometry with one-division for the each interval. (3) Damping constant should be used as 1.5%. (4) Drucker-Prager yield criterion should be applied. (5) The crack patterns can be roughly estimated with seven divisions between intervals of stirrup.

Impact Response Analysis of Prototype RC Girders with Sand Cushion Using Equivalent Fracture Energy Concept

In order to establish a proper finite element model of prototype RC girder with sand element for impact response analysis, dynamic response analysis of RC girders with sand cushion subjected to impact force due to falling weight was performed to improve the state of the art of protective design for real scale rock-sheds using LS-DYNA code. Here, in order to establish a modification method for material properties of concrete so as to rationally analyze the prototype RC girder with sand cushion using coarse mesh, an equivalent fracture energy concept for concrete elements was proposed and the applicability was investigated comparing numerical analysis results with experimental results. From this study, it is confirmed that even though coarse mesh was used for prototype RC girder with sand cushion, similar results with those obtained using fine mesh can be assured.

Numerical study for impact resistant design of full scale arch type reinforced concrete structures under falling weight impact test

In this paper, a falling-weight impact test using full scale arch type reinforced concrete (RC) structures was conducted to verify a proposed impact response analysis method. The applicability of the numerical analysis method was confirmed by comparison with the experimental results. The validity of the current impact resistant design procedure to the performance based design procedure was investigated using the proposed numerical analysis method. From this study, it is confirmed that by applying the current impact resistant design procedure, a performance based impact resistant design with a sufficient safety margin may be obtained for the full scale arch type RC structures.