The recent ground motion results indicated that the RC buildings are required to be retrofitted by different strengthening techniques. Nowadays, the external strengthening gain interest since its easy, cost effective and not required redesign of buildings. The CFRP sheets are suitable solution and utilized by a number of researchers. However, the numerical cyclic performance of connection strengthened with different thicknesses of CFRP need to be well investigated. This study assessed the performance of RC exterior beam column connection strengthened with CFRP sheets First, two grades of concrete are utilized to be control specimens, normal concrete compressive strength (C20) and high concrete compressive strength (C50) then, the specimens are retrofitted with different thicknesses (1.2, 2.4, 3.6mm) of CFRP sheets. The stresses and damage states showed the importance of connection retrofitting. The CFRP shift the plastic hinge zone away from the panel zone. Furthermore, the results demonstrated that by increase of CFRP thickness the connection resistance will be improved. The comparison between the hysteresis curves demonstrated that the yield and ultimate loading were enhanced for strengthened connection for both concrete grades and the incremental in thicknesses also increase them. The outputs also exhibited that the stiffness and ductility has increased for retrofitted specimens indicating that the CFRP comprehensively overcome the applied cyclic loading and the beam column connection is able to resist such type of loading.
Recently, the bridge unseating prevention devices are widely used in active seismic zones. These devices are stiffness dependant, velocity dependant and energy dissipation devices. The energy dissipation devices are designed to overcome the energy that transfers from bridge substructure to superstructure. However, the current devices are not controlled to function with different ground motion intensities and should be replaced after yielding. Therefore, this research introduced a slotted plate energy dissipation device with three parts, each part function in known deformation range. The slotted plate behavior has been evaluated numerically by finite element method. Displacement control and load control analysis has been done, and then the effect of steel grade is studied to predict the suitable steel properties for designing the plate. Moreover, the slotted plate behavior is applied in 3D bridge seismic analysis to assess the multi-level performance and the ability to overcome the seismic effect on the bridge in longitudinal direction. The results approved the capability of the plate to dissipate energy in multi-stage of deformation. The lower steel grade is suitable for low to moderate earthquake zone and the high grade can be used in severe ground motion areas. Furthermore, the bridge longitudinal behavior has enhanced with different steel grades of the slotted plate.
The bridge bent is the most critical structural component of short span bridge that highly affected by different types of loadings. The bent failure has been observed due to in plane and out of plane loadings. Strengthening techniques are utilized for existing bridges. However, a replacement technique can be used for the new bridges to avoid bent failure. Moreover, the effect of combined loading on bent performance need to be evaluated. Therefore, this study assessed the performance of bridge bent under in plane, out of plane and combined loadings. Furthermore, replace the traditional flexural and shear steel reinforcement of the columns with CFRP bars. The performance of bent is assessed numerically by finite element analysis. For this purpose, six numerical bent models are developed. The first three models with traditional steel bars and the remaining models with CFRP rebars. The results demonstrated that out of plane loadings has more impact on the bent structural performance than other loading cases. Flexural and shear failures are observed in the columns for models with steel rebars. The failure started from lower side of the column for both in plane and out of plane loadings showing low resistance. The steel rebars yielded in early stage of loading indicating limited stiffness. However, the bent performance has been enhanced by replacing rebars with CFRP. The bent stiffness has slightly improved by replacing with less diameter of CFRP rods and stirrups. In addition, the CFRP bars showed considerable resistance and hardly showed plasticity during apply loading indicating that the CFRP is suitable material to replace steel reinforcement.
Recent seismic events showed the importance of understanding the structural performance of RC column that can be predicted numerically. The accuracy of column performance depends on type of the analysis and representation of seismic effect. Therefore, in this paper a nonlinear time history analysis has been performed to assess the seismic performance of bridge column using fiber hinge concept with time integration method using sap2000 software. A long bridge RC column is utilized and subjected to seismic excitation. The column has been divided into different size and numbers of fiber to assess the accuracy of the analysis and time consuming to analyze each case of fiber hinges. In addition, this paper used three-time integration methods, Newmark, Hilber-Hughes-Taylor, and Chung & Hulbert to predict the most suitable method to be used in column seismic analysis. The time history displacement and base shear in addition to moment rotation of the column are the most important factors to evaluate the column seismic performance. The analysis results demonstrated that the most suitable time integration method is Hilber-Hughes-Taylor for such type of the analysis since it gives more stable base shear result than other two methods. Furthermore, the results indicated that the accuracy of seismic performance increased by number of fibers incremental. Moreover, the number of steel fibers should be equal to the number of bars with same area and location. The unconfined and confined concrete should be divided into small areas to get accurate prediction of column seismic performance.
This paper presents a numerical and experimental assessment of a developed adjustable variable stiffness restrainer (AVSR) utilized for short span bridges. This restrainer has the ability to demonstrate multi stiffness capacity in different stages of bridge’s superstructure movement to mitigate the severe damage of bridge due to an earthquake. The multi-level stiffness behavior of developed AVSR is achieved by using multiple mechanical springs with different lengths and placed in parallel in proposed design. A small prototype of developed AVSR has been fabricated and tested under incremental and cyclic loading in order to assess the restrainer performance and the behavior has been validated using finite element analysis. Thereafter, the constitutive model of AVSR was derived for the proposed restrainer in order to implement it in numerical simulations. Furthermore, a parametric study has been conducted numerically to evaluate the effectiveness of different parameters on the restrainer capacity. Moreover, the efficiency of AVSR application in a single degree of freedom system has been assessed by performing seismic analysis on a frame equipped with AVSR subjected to different seismic excitations using Newmarkʼs method. The experimental and finite element results proved the efficiency of developed variable stiffness device to exhibit adjustable action against imposed loads in three designed stages. Furthermore, the parametric study results revealed that increasing the section area of the spring wire leads to increase the restrainer capacity. In contrast, the restrainer resistance is declined by an increase in the mean spring diameter and number of coils for each spring of AVSR. The time history analysis results also indicated that the frame response in terms of displacement, velocity and acceleration is improved by implementing the AVSR in the considered system.
This paper proposes a new multi-level spring restrainer (MLSR) that exhibits multi stiffness performance in different levels of movement of bridge superstructure to prevent unseating during applied dynamic loads. The analytical model of the proposed MLSR was formulated and the fabricated prototype was tested using dynamic actuator. Based on the developed analytical mode, the function of MLSR device relied on 12 parameters that further complicated the design process to achieve the best performance. However, the conventional optimization techniques utilized only one or a few factors for simple systems. Therefore, a multi-objective optimization method is proposed in this study by introducing the hybridization of Particle Swarm Optimization and Gravitational Search algorithm (PSOGSA) to optimize the restrainer parameters, as well as to improve the seismic performance of bridges using the optimum design. The optimized MLSR was implemented in the bridge subjected to multi-directional ground motion and its multi-level action to prevent unseating of bridge deck when the applied excitation was evaluated. The optimization process revealed girder displacement in three directions and the number of plastic hinges decreased from 44 to 99% for the optimized design. The time history analysis disclosed that the use of optimized MLSR device decreased the structural seismic response, such as the 3D deck movements, from 79 to 90%. Next, the base shear and drift ratio of bridge bent reduced to 75 and 85% in longitudinal direction and to 72 and 90% in transverse direction, correspondingly. The outcomes signify that the proposed MLSR device and the optimization algorithm have successfully improved the bridge structure resistance against severe ground motions.
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