Sharif Digital Repository

The purpose of this research is to study the behavior of some kind of conventional and retrofitted Khorjini connections, such as stress and strain concentration and eventually strain-jumping phenomenon. Thus the software ABAQUS 2019 was used to fabricate the FEM models of the connections with experimental prototypes. In analytical studies, 21 specimens with different sizes of the connection components were analyzed. True stress-strain curves for steel and weld materials were used and damage initiation and revolution were considered in the weld material. Also cracking of the welds was considered by a micromechanical method. The main defects of the connection are severe initial stiffness... 

Masonry buildings are wide spread in Iran and some other countries . These buildings are highly vulnerable to seismic excitations if not constructed in accordance with engineering fundamentals . Thus it is necessary to retrofit these structures to flee from humanitarian and economical damages inflicted by earthquakes. One of the critical vulnerabilities of masonry buildings is due to transverse instability of it’s infills . Therefore to study out of plane behavior of these elements , an infilled frame is modeled and analyzed with ABAQUS , the results of which is in good congruence with the experimental one . In this model , stress distribution due to one way arching action in the confined... 

In this study, HSS and double angle braces subjected to cyclic loading in order to study the buckling and post buckling behavior have been investigated by Finite Element method. The results of FE analysis are fairly in good agreement with experiments. Analysis demonstrate that when local buckling occurs in middle span, subsequently, strain rises severely. Accordingly, this strain jumping causes early fracture in braces. Therefore, local buckling can be one of the primary reasons of fracture in braces. As a result, local buckling must be considered one of the primary limit state of Performance-Based design of steel braces. In addition, finding a way to predict local buckling can help us to... 

Considering the role of fluid storage tanks within or after an earthquake and the irreparable damages from their destruction that arise from the nature of the fluids of flammable or toxic nature stored in those tanks, it is very important to ensure stability and durability of the tanks when an earthquake is occurring. One of the most important damages to storage tanks within the past earthquakes has been lack of stability of their walls taking place in the form of elephant buckling. A certain storage tank was subject to a case study in this research and the tank's body, foundation, anchorages, the tread between the fluid and tank's body and between the bottom sheet and foundation were... 

The paper presents the results nonlinear analysis of steel base plates subjected to different combinations of axial and bending forces. The bending forces range from small moments representing small eccentricities to large moments from seismic actions. The results of analyses proved to be in good agreement with experiments. The parameters investigated in this study are as follows: distribution of strain and stresses in the concrete foundation and the steel plate, the strains and stresses in the tensile anchorage bolts, the location of neutral curve under the base plate, the centre of compressional reaction forces in concrete, the flextural rigidity of the base plate connection, and the axial... 

Since 1906, after the earthquake of Messina in Italy, Italian engineers start developing a new method for increasing the resistance of a structure during an earthquake. With the limitation of time and technology, this method was acceptable for the time period. By developing the accelerographs and seismographs and the methods to process big data, new methods are developed and are being used in designing structures; new technologies allow engineers to analyze the performance of structures with ease. The studies in this research indicates that achieving the safety indices in any design require utilizing all dynamic properties of a structure such as period, stiffness and damping. In this... 

In order to reduce structural and nonstructural damages and associated financial losses during intense seismic events such as Bam earthquake, seismic retrofitting of existing structures should be considered as a special issue. In this regard, for quantifying the seismic performance of structures a guideline termed “instruction for seismic rehabilitation of existing building No.360” is issued which is mainly borrowed from performance-based assessment procedures FEMA 356. In contrast to conventional seismic design methods which are based on controlling stress ratio for different load combinations, in performance-based earthquake engineering methodology, the displacement control of structural... 

Steel structure with saddle connections constitutes a portion of the old steel structures in Iran. During past strong ground motions such as Manjil and Bam earthquakes, these structures were vulnerable and experienced significant damages. These structures were widely used due to their easy installation. However, according to their unpromising behavior, they need an appropriate lateral force-resisting system. A concrete shear wall is one of the suitable lateral force resisting systems that can improve the behavior of steel frames with saddle connections. To find the coefficients of seismic performance factors including response modification factor, overstrength factor, and deflection... 

In recent years a large number of passive energy dissipating systems developed in accordance with pioneering work on friction dampers which was firstly reported by pall(1979). Uusing Friction dampers reduce the inelastic demand of the structure during severe earthquake motions by sliping and a large portion of input energy dissipated mechanically in friction instead of yielding the main components of the structure. Based on economical purposes, it is valuable to know in which storey and slip force should be employ the friction devices to have an optimized performance of the structure. Due to kinematic conditions of slip and stick stages, as well as transition zones between them in friction... 

This thesis presents an extension of an analytical method previously introduced for evaluation of the deformation capacity of RC columns. The method utilizes fiber elements to arrive at nonlinear moment-curvature relationship for each segment. An existing stress-strain model has been modified and used in this study. This model considers the crushing failure of confined concrete, buckling of longitudinal reinforcements in compression, and their fracture in tension. It also accounts for the spiral fracture. This method was employed to determine the force-displacement diagrams for circular RC columns dominated by flexural mode of failure, and was calibrated against a number of relevant... 

By investigating reports of severe and destructive earthquakes of the past years we have realized that shear-wall structures most of the times had better seismic performance and more reliability than moment resistance frames. Asymmetrical arrangement of shear walls due to architectural limitations caused distortions in the structure. On the other hand, seismic regulation don’t compliance existence of twisting moment in the structures. What was said are all the most important reasons for not employing asymmetric shear wall sets in the structures by designers. The purpose of this study is to compare the seismic behavior of symmetric moment frame structures with seismic behavior of symmetric... 

It is more than a century to study qualitative and quantitative behavior of structures against earthquakes will be benefited from laboratory studies. In fact, the best method for observing the behavior of a structure during an earthquake is earthquake simulation on the structure. Today, the most effective way to do these tests is simulating of earthquake by using of Shaking Table. The shaking table consists of three main parts: electronic, hydraulic and mechanical. The accuracy of earthquake simulation’s results are very important. In recent years, numerous studies on the dynamic behavior of the above components and the interactions between these components are performed. In this study, we... 

Masonry infills are vastly used as surrounding walls and partitions. Presence of infill in a building causes some change in strength, stiffness, period and generally seismic behavior of the structure.Mainly there are 5 modes of failure including 1- interface cracking 2- sliding along bed joint 3- diagonal cracking 4- corner crushing and 5- ultimate failure. According to these failures, three stages of strength as shear strength, corner strength and ultimate strength can be defined.Diagonal crack can be calculated by slip surface method grown in Sharif university of Technology. Based on this method the strength of infill wall falls down as the cohesive strength of mortar loses and so the slip... 

The present study looks into the fracture of perforated steel plates and their sensitivity in ductile fracture. It also examines the effects of strain rise phenomenon in these specimens. The main employed fracture model is VGM, which was first introduced by Rice and Tracey, and later enhanced by Kanvinde et al.. The general methodology includes finite element simulation and lab experiments on perforated plates, to determine ductility, strain concentration in hole periphery and model sensitivity. Fot thid purpose 86 steel sheet specimen with different holes and cuts were manufactured and tested. With the acquired data, the impact of strain concentration on the load carrying capabilities and... 

This thesis presents the results of an experimental and analytical study on the application of the strapping technique for seismic retrofit of reinforced concrete columns. In this technique, the columns are externally confined by post-tensioned metal strips. In the first phase of the experiments, the compressive stress-strain behavior of strapped cylindrical and prismatic specimens was studied. Effects of several parameters were studied including shape and size of specimens, strength of plain concrete, mechanical characteristics of confining strips and the level of pre-tensioning of the strips. The second phase of the tests included studying the lateral performance of strapped RC columns.... 

In this thesis, the strain rise phenomenon and its adverse effect on the deformation capacity of steel elements, members, and connectors were investigated. The high-rate increase in plastic strains was termed strain rise. In this study, the sharp increase in plastic strains and its causes were investigated through conducting experiments and extensive numerical analyses. The causes of strain rise were fallen into two categories as primary and secondary. To limit the adverse effect of strain rise two methods of decreasing the initial stress concentration and expanding the plastic volume were proposed. The strain rise in the saddle and pre-Northridge connections as a result of primary effects... 

For the preliminary design of isolated structures, it is necessary to select the appropriate damping ratios in each mode. The inherent modal damping in this type of structures is small. On the contrary, a significant value of damping is induced by dampers in isolator system into structural modes. The purpose of this study is to determine the Modal damping ratios in isolated structures. In this regard, shear structures of 2 to 10 floors with linear behavior in both superstructure and isolation level have been analyzed. The Structures have been modeled taking advantage of OpenSees. Samples are analyzed under sinusoidal loading applied to each floor. In order to achieve modal damping, an... 

The paper presents the results of nonlinear analysis of steel base plates subjected to different combinations of axial and bending forces. The bending forces range from small moments representing small eccentricities to large moments from seismic actions. The results of nonlinear analysis are done on three samples of the column base plate with large moment, small moment and compression axial force are compared to the results of the code. The parameters investigated in this study are as follows: distribution of strain and stresses in the concrete foundation and the steel plate, the strains and stresses in the tensile anchorage bolts, the location of neutral curve under the base plate, the... 

Over the last years, terrorist attacks and accidental explosions have brought on a need for research in the field of structural engineering to study the response of a building subjected to blast loading conditions. An explosion within or surrounding a building, not only can have disastrous effects causing both structural damage or failure, but may also lead to the death of human beings.In order to prevent these catastrophes and gain a better understanding of responses of the buildings and lateral resisting systems with different characteristics, the study of the behavior of the lateral resisting systems under blast loading conditions is essential. This research will also aid in the... 

In this thesis, finite element (FE) models were developed to study hysteresis behavior of pipe braces subjected to cyclic loading. Thus steel braces previously tested by other investigators are used. The results of the analysis are in good agreement with the experiments. Besides, the FE analysis could also simulate both the overall and local buckling. As a result, a sharp growth in plastic strains is followed by geometric changes at the mid-span due to local buckling. The sharp growth of plastic strains is entitled as strain rises. In fact, the local buckling triggers rupture of braces at the mid-span. The local buckling initiation is identified by the sharp growth in plastic strains....