Month: December 2021

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Multiple earthquakes occur all over the world where challenging fault systems exist. A structure damaged by an earthquake is exposed to the risk of aftershocks within a short interval of time, which accumulates damage to the structure affecting its stiffness, strength and ductility. This study aims to investigate the response of reinforced concrete infilled frames subjected to multiple ground motion sequences. A two dimensional computational model of a mixed used RC building located in Karachi, Pakistan is developed as a bare and infilled frames for comprehensive comparative analyses. Initially, nonlinear static pushover analysis was used to estimate the capacities and damage patterns of frames. Finally, to track the complete response selected frames were subjected to three real seismic sequences (recorded at a short interval of time at same station with same direction) and four artificially generated repeated seismic sequences. Results are presented in the form of Engineering Demand Parameters (EDPs), which conforms the effects of multiple earthquakes particularly in the case of infilled frame.

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Seismic design methods based on the substitute equivalent linear elastic structure concept are based on the use of high-damping response spectra. They are being used also for the analysis of structures equipped with seismic isolation and energy dissipation systems. Damping is integrated in the response spectra using the so-called Damping Reduction Factors (DRF). It has been proposed in seismic codes to estimate high-damping response spectra from their 5% damping counterpart. The assessed structural damping value for a building over a ground motion may differ considerably from the value specified in the design. Due to the importance of damping in the structure’s seismic performance, the structural damping uncertainties should be taken on consideration in the design step.
In this paper, the damping uncertainties effects on DRFs for the estimation of high damping response spectra, are examined. Monte Carlo technique is used to describe the damping uncertainties as a lognormal probability distribution. Artificial Neural Networks (ANN) and nonlinear regression are then applied to integrate the damping uncertainties. 

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During the Northridge and Kobe earthquakes, many of steel moment-resisting frames at the beam-to-column connection were damaged due to excessive deformation.  As a solution, steel slit dampers were used in the connections to prevent the connections’ fracture and damage of the main members of the structure. In the present paper, a numerical investigation was carried out with ABAQUS software to investigate the parameters affecting the seismic performance of steel slit damper in beam-to-steel column connections. The damper specimen were simulated and verified with an experimental work under cyclic and monotonic loading. A reasonable agreement was obtained between the finite element analysis and the experimental test results. For easy expression of the damper performance criteria, monotonic loading were used by presenting the results in the form of moment-rotation.  The variables studied included the various proposed shapes for the damper, damper boosting effect, and damper thickness in the seismic performance of beam-to-steel column connection. The results show that with increasing the thickness and strengthening of the steel slit damper, the bending moment, stiffness and energy dissipation capacity of the connection, increases. Also, the new proposed slit damper had the best performance among the other dampers.

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We present a scalable approach to the design of a novel seismic isolator recently appeared in the literature, which features a unit cell composed of a central post that can slide against a base plate. Such a post carries the vertical load and is connected to four corner posts through stretchable “tendons” attached to rigid “limb” members. The bio-inspired, sliding-stretching isolator under examination is easily assembled in a fabrication lab making use of 3D-printed components and metallic parts manufactured by online and/or local suppliers. This article illustrates a scalable design approach that permits to size the components of the system according to the design values of the vertical load and the lateral displacement capacity. It is accompanied by a cost-analysis comparing the estimated cost of the proposed device with the costs of standard seismic isolators currently available on the market.

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