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  • SEISMIC VULNERABILITY ASSESSMENT OF EXISTING RC STRUCTURES SUBJECTED TO MULTIPLE EARTHQUAKES.

    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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  • ESTIMATION OF STOCHASTIC DAMPING REDUCTION FACTOR USING MONTE CARLO SIMULATION AND ARTIFICIAL NEURAL NETWORK METHOD

    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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  • EVALUATION OF THE EFFECTIVE PARAMETERS IN SEISMIC PERFORMANCE OF SLIT DAMPER IN BEAM-TO-COLUMN CONNECTION

    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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  • A SCALABLE APPROACH TO THE DESIGN OF A 3D-PRINTABLE SLIDING- STRETCHING SEISMIC ISOLATOR

    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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  • SEISMIC ANALYSIS OF REINFORCED CONCRETE FRAME WITH BUCKLING RESTRAINED BRACE UNDER FAR AND NEAR FAULTS

    Today, Reinforced Concrete Frame with Buckling Restrained Brace (RCF-BRB) are commonly used as lateral resisting systems in seismic areas. Two characteristics of higher energy dissipation capacity and lack of buckling behaviour, has caused that RCF-BRB have a better alternative to conventional bracing. In this study, Seismic Analysis of RCF-BRB at far and near faults is investigated. Comparison of validation of BRB by ABAQUS software with laboratory model indicates acceptable agreement. In this paper, 3- and 5 story reinforced concrete frame with BRB were subjected to 6 earthquake scaled record, and roof displacement, base shear, force-displacement curve, and absorbed energy of the frame and its components were investigated. As well as stresses and plastic strain of frame components and BRB were also evaluated to find the causes of the weakness. The results showed that the far faults record has more destructive effects than the near faults record on the RCF-BRB and it was also found that the effective components in plastic deformation of BRB, are Core, and Gusset plate.

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  • NUMERICAL INVESTIGATION OF PERFORATED STEEL PLATE SHEAR WALL UNDER FIRE CONDITION

    The stability and lateral resistance of the Steel Plate Shear Wall (SPSW) is commonly used in earthquakes prone areas due to its high flexibility and energy absorption capacity in tall steel structures. Fire can significantly reduce the lateral resistance and stability of such structures. The purpose of this paper is to investigate the performance of Perforated Steel Plate Shear Wall (PSPSW) in the face of high temperatures. Therefore, 9 steel frames, each including one floor and one span, containing perforated steel plates, were numerically modelled and their behavioural characteristics were examined at high temperatures. Numerical results show that all seismic factors such as strength, stiffness and ductility in the lateral resistance and stability of Perforated Steel Plate Shear Wall (PSPSW) are reduced against high temperatures. Also, at high temperatures, it was found that before lateral loading, permanent plastic areas are formed, especially around the perforations, which increases the sensitivity of the system to the small earthquakes.

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  • OVER-STRENGTH DESIGN OF RC BEAMS ON FOUNDATIONS IN THE SEISMIC AREA

    A rigid plastic calculation method for predicting load versus maximum load pressures related to the formation of plastic hinges in the reinforced concrete (RC) beam on Winkler soil of foundation is proposed. The utility of the proposed method is to provide a simple calculation tool for hand calculation useful to predict the foundation’s bearing capacity and for verifying the over-strength of the soil-foundation complex. It is highlighted that the plastic resources of the soil-foundation complex depend not only on the characteristics of the soil, but also on the geometrical and mechanical characteristics of beam on foundation and the characteristics of the vertical load (intensity, eccentricity). The proposed method shows good agreement with numerical model developed with MIDAS Civil code. It is also shown that a maximum ratio of longitudinal steel bars should be adopted to ensure strength hierarchy with plasticization of RC beams before soil plasticization.

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  • A NEW MECHANICAL MODEL OF A LIQUID STORAGE TANK WITH BASE ISOLATION

    To reasonably predict the seismic response of the liquid storage tank under different earthquake records, a new mechanical model is proposed based on the equivalent principle of the base shear and the overturning moment. Firstly, the velocity potential of the liquid in the storage tank is introduced by resolving the Laplace equation. Thereafter, the governing equations of motion of a liquid storage tank with base isolation are derived on the basis of Hamilton’s principle. And finally, the dynamic response processes of the liquid storage tanks of different ratios of height to radius by using the existing mechanical models, proposed mechanical model, and three-dimensional finite element model in the software ANSYS are compared. The analysis results show that the proposed mechanical model is stable and reliable whilst the predicted results are highly accurate and effective. Given the high order convective modes, the liquid sloshing height has a delayed effect.

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