Resilience-based retrofitting of existing urban RC-frame buildings using seismic isolation

The improvement of the seismic resilience of existing reinforced-concrete(RC) frame buildings, which is essential for the seismic resilience of a city, has become a critical issue. Although seismic isolation is an effective method for improving the resilient performance of such buildings, target-oriented quantitative improvements of the resilient performance of these buildings have been reported rarely. To address this gap, the seismic resilience of two existing RC frame buildings located in a high seismic intensity region of China were assessed based on the Chinese Standard for Seismic Resilience Assessment of Buildings. The critical engineering demand parameters(EDPs) affecting the seismic resilience of such buildings were identified. Subsequently, the seismic resilience of buildings retrofitted with different isolation schemes(i.e., yield ratios) were evaluated and compared, with emphasis on the relationships among yield ratios, EDPs, and levels of seismic resilience. Accordingly, to achieve the highest level of seismic resilience with respect to the Chinese standard, a yield ratio of 3% was recommended and successfully applied to the target-oriented design for the seismic-resilience improvement of an existing RC frame building. The research outcome can provide an important reference for the resilience-based retrofitting of existing RC frame buildings using seismic isolation in urban cities.

OPTIMUM PARAMETERS AND DESIGN OF TUNED MASS DAMPER FOR BUILDING FRAMES UNDER GROUND ACCELERATION

For the purpose of comparison and applications, two criteria for the optimum searching are considered, which are the minimization of the minimum of the maximum dynamic magnification factor(Min. Min. Max. DMF) and the minimization of the minimum dynamic reduction factor (Min.Min.DRF). A study is carried out to investigate the applicability of designing TMD utilizing the unit modal participation factor. In addition, the design steps for the building frame with TMD are suggested. It is demonstrated that significant reduction in the response can be achieved by adopting the optimum TMD parameters in the present paper.

Effect of URM infills on seismic vulnerability of Indian code designed RC frame buildings

Unreinforced Masonry (URM) is the most common partitioning material in framed buildings in India and many other countries. Although it is well-known that under lateral loading the behavior and modes of failure of the frame buildings change significantly due to infill-frame interaction, the general design practice is to treat infills as nonstructural elements and their stiffness, strength and interaction with the frame is often ignored, primarily because of difficulties in simulation and lack of modeling guidelines in design codes. The Indian Standard, like many other national codes, does not provide explicit insight into the anticipated performance and associated vulnerability of infilled frames. This paper presents an analytical study on the seismic performance and fragility analysis of Indian code-designed RC frame buildings with and without URM infills. Infills are modeled as diagonal struts as per ASCE 41 guidelines and various modes of failure are considered. HAZUS methodology along with nonlinear static analysis is used to compare the seismic vulnerability of bare and infilled frames. The comparative study suggests that URM infills result in a significant increase in the seismic vulnerability of RC frames and their effect needs to be properly incorporated in design codes.

Response of a 2-story test-bed structure for the seismic evaluation of nonstructural systems

A full-scale, two-story, two-by-one bay, steel braced-frame was subjected to a number of unidirectional ground motions using three shake tables at the UNR-NEES site. The test-bed frame was designed to study the seismic performance of nonstructural systems including steel-framed gypsum partition walls, suspended ceilings and fire sprinkler systems. The frame can be configured to perform as an elastic or inelastic system to generate large floor accelerations or large inter story drift, respectively. In this study, the dynamic performance of the linear and nonlinear test-beds was comprehensively studied. The seismic performance of nonstructural systems installed in the linear and nonlinear test-beds were assessed during extreme excitations. In addition, the dynamic interactions of the test-bed and installed nonstructural systems are investigated.

Static and Dynamic Analyses of Spliced Column

The analysis of spliced column has been carried out to detect optimum location of providing splices in the column.In the present work,static and dynamic(free vibration)analyses of spliced column have been done by randomising the location of splicing.A symmetrical four storey steel framed building has been modelled,analysed and designed for loads(dead,live and earthquake loads)recommended by Indian Codal provisions using Staad.Pro.The critical column at each floor level is identified based on axial force(AF),bending moment(BM)and shear force(SF).The total 16 models of spliced columns have been designed and then modelled in a 3D CAD Design tool(SOLIDWORKS)and then imported in the finite element tool(ANSYSWorkbench 14.0)for detailed analysis.The variation of stress,strain and deflection of the spliced column are shown in the form of contour.Further,the modal analysis is performed to determine the natural frequencies.The results of static and dynamic analyses are compared for each modelled spliced column to obtain the optimum location for providing splices in the column.The dynamic analysis of spliced column is of utmost importance in the region where dynamic loadings like earthquake,cyclones etc.are more frequent,and mere static analysis does not account for the safety of the structure.This study will help the engineers to select directly the optimum size and location of the splices in the column of a steel framed building.

Experimental study on seismic characteristics of typical mortisetenon joints of Chinese southern traditional timber frame buildings

The seismic characteristics of four typical mortise-tenon joints of Chinese southern traditional timber frame buildings were researched, including Yanwei mortise-tenon joint （including dropping Yanwei mortise-tenon joint）, Shizigutou mortise-tenon joint, Ban mortise-tenon joint and Mantou mortise-tenon joint. Experiments on thirteen specimens were carried out. Failure modes, hysteresis curves, skeleton curves and rotational stiffness were studied. The results provided a theoretical basis for seismic research, protection and maintenance of Chinese southern traditional timber flame buildings.