BULLETIN OF EARTHQUAKE SCIENCE AND ENGINEERING
Year:2016 | Volume:13 | Issue:2|Papers Count:9

In structures with brace, one major problem is the great hardness of the bracings frames which are efficient to improve the seismic performance and to reduce the size of the hardness. A highly stiff braced frame cannot adequately dissipate the energy exerted by earthquake, so it causes the structure to absorb a large portion of this energy. As a result, designers always look for viable strategies that allow the steel structure to move along earthquake motions and dissipate this energy. This paper sought to evaluate one of such strategies, which is the use of rubber and lrad rings in the bolted connections between braces and gusset plates. Finite element software (Abaqus / 6.13) was used to perform a dynamics analysis on a frame by subjecting it to the seismic records of Bam, Kobe and San Fernando earthquakes. This procedure was then repeated for the frame whose bolted connections contain rubber and lead rings and the values of base shear, drift, maximum stress in the structural members and the internal energy of the structure were compared. The results showed that the adding rubber rings to the connections of braced frame decreases its maximum base shear and energy absorption.

Measurements of the speed of passing ultrasonic waves are used to determine the quality and strength of materials. Velocity of ultrasonic waves of solids depends on the density and elasticity characteristics. The quality of material depends on the firmness and elasticity of the, so measurement of the speed of passing waves can be used to determine the quality of and elastic properties. According to the application of cement based grout to bridge the gap between the members and the concrete foundation and the ability to absorb and transmit static and dynamic loads by grout into the foundation, structural engineers need to grout with high quality, strength and durability that has a strong internal structure and with minimal pores and cavities inside. Ultrasound waves passing speed test is done to check these features and its results are presented based on dynamic modulus of elasticity. The results show that the modified grout mix with nano-silica, silica fume, and dynamic modulus of elasticity increased so that by replacing 1% nano-silica powder and 20% micro silica powder in grout combination with cement, dynamic modulus of elasticity increased to 64%.

Significant growth of buildings in different shapes and heights in urban areas and lack of attention to their dependence being adjacent to each other during earthquakes has increased devastating effects of seismic loads. Existing buildings have been designed and constructed separately against earthquakes. However, to pounding of adjacent buildings has been less paid attention. Since different buildings are designed independently thus their floor levels are not at the same height and probable sudden poundings during earthquakes can damage and collapse the weaker building. There are two kinds of such poundings: floor to floor and floor to column that 1st case is investigated in this research.In this paper, in order to determineand reduce the pounding forces between adjacent buildings, two 2 and 3-story RC buildings are considered in which floor to floor pounding is studied. To prevent or reduce pounding damage, the effect of gap distance between two adjacent buildings and using viscoelastic damper in their bracingon reducing seismic impact and related pounding are investigated. SAP2000 and ANSYS are used for numerical study.Analyses results show that using viscoelastic dampers and increasing distance between two buildings would reduce their lateral displacements and related pounding. For example, 3cm distance between two adjacent buildings would create 7 impacts while increasing the distance to 4.5cm would reduce the impacts to 2. Also, placement of viscoelastic dampers between building floors would control their lateral displacements and reduce the impacts to just one.

In recent years, the idea of using durable materials which are capable of absorbing energy and have high ductility are highlighted in structural engineering. One example of these materials is shape memory alloys which show predefined physical properties in different conditions. These materials show little residual strain under loading and unloading cycles even when passing through the yield area. In fact, they create regenerative forces in structures. In this study, the effect of shape memory alloys on energy dissipation and reducing vibration amplitude of multi-story steel frame is investigated. For the present purpose, shape memory alloy rebars are used in the middle of the diagonal elements of braces. ABAQUS software is used in the present study. To validate models, first, two-story braced frame with shape memory alloy used in the laboratory studies of Han et al (2003) is modeled and analyzed in the software. The results obtained by the two laboratory and analytical methods are in acceptable agreement. To investigate the effect of height on the seismic performance of the buildings equipped with this type of dampers, 3- and 12-story buildings were considered and reciprocating nonlinear analysis and nonlinear dynamic time history analysis using Tabas accelerogram were performed. Results show that using this type of dampers cause quick energy dissipation and a significant reduction in the vibration amplitude and base shear so that the existence of shape memory alloy in 3-story building makes the ability of the structural system in dissipating energy and the initial stiffness of the system increase 2.5 and 2 times respectively. Moreover, with an increase in height, its effectiveness in controlling the seismic response of structure is reduced between 10-15 percent.

Using additional dampers for reducing input energy of structures is an effective way for dissipating input energy of structures. Including appropriate tools in dissipating the input energy of structures is viscoelastic damper. Generally, according to the structural analysis, the soil under structures is assumed to be rigid and the effect of soil structure interaction has been ignored. However, in reality, this soil is not rigid and the soil beneath the structures changes the dynamic specifications of structures and thus response of it. Structural response and damper performance depend on various components including type of earth movement and soil specifications. In this research, a few two-dimensional special concrete frames were examined. For frame modeling of additional damper, we used Kelvin method and for modeling of soil structure interaction effects with additional damper we used spring and damper equivalent method in the OpenSees app. Studied frames after rehabilitation with damper have been analyzed under dynamic nonlinear time history analysis. This analysis was done in three damping 5%, 10% and 15%. And at the end the results of soil-structure interaction impact with viscoelastic damper under different damping are studied.

Today, the process of seismic improvement and resistance has been accelerated in our country due to this fact that most current buildings has an old and non-standard context in our country. Studying the resistance is inevitable case especially in the columns which is the most important and critical structural components. So, this study is conducted to investigation the column's behavior of reinforced concrete under cycle loading before and after the improvement with polymer fibers. In this regard, one laboratory study was used in order to modeling verification. Then, the appropriate approach was examined in order to study the. Arrangement of resistance of Polymer fibers in Abaqus finite element software with simulation with several various models. After studying the hysteresis –bar curves transformation, load-displacement curve cover – transformation, ultimate load and the contribution of polymer fibers of models was found that samples those have polymer fibers have a greater ability to more loading bearing and also, have more absorb property and more energy amortization than samples without fiber.

The main purpose of the current research is to develop a new mechanism that makes PSO to work better. Optimization is a tool to find the best solution of a multi-modal problem. Nowadays engineers and designers are looking for optimal designs due to restriction of resources. Recently many optimization algorithms have been developed to takle complex problems, such as Particle Swarm Optimization (PSO). This algorithm is known as a strong explorer but weak exploiter. The main problem is many internal parameters to be tuned. So that users should achive a set of sensitivity analyses to adjust them for the problem at hand, but in the mean time the obtainded values may not proper for other problems.In the present work, in order to overcome this shortcoming, a mutation mechanism as an important element of genetic algorithm is implemented in PSO. Each particle in the optimization proccess is assigned with a random number, then, as the procedure goes on, the random number of each individual is compared with a treshhold and if it is smaller than the treshhold, the particle gets mutated. This new algorithm entitled as modified particle swarm optimization (PSO). Three reinforced concrete MRF optimum design problems are solved by MPSO, PSO and results compared together with another research results based on HS algorithm. Studying the results show that MPSO compared with adjusted PSO by sensitivity analysis and HS, not only brings to better solutions, but it also does not need to any manual adjustment by sensitivity analysis.