Sharif Digital Repository

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... 

Digital image processing techniques are widely used in many areas of research and application such as astronomic monitoring, medical diagnosis, product quality control and weather forecasting. The captured film by camera, is converted into displacement data by using Matlab software and image processing methods. This study intends to provide “proof-of-concept” for the techniques, applying them to identification problems involving the simple pendulum, pendulum in-water, the car suspension system. Studies further illustrate that the digital imaging procedure and algorithms developed for the simple problems can be extended for identification of modal properties and structural characteristics.... 

The observed response of medium rise buildings during sever earthquakes worldwide has indicated that RC buildings with shear walls behave considerably better than other buildings. The conviction that shear walls are inherently brittle still prevails amongst engineers, and therefore, they usually prefer to choose moment resisting RC frames without shear walls. In this study, a number of RC frames, with and without shear walls are designed in accordance with the seismic codes, and are then subjected to an assemble of severe earthquakes. The results of timehistory nonlinear analyses of these models are then used to investigate the effect of the presence of shear walls within the framework of... 

With occurring severe earthquakes, damages of columns in RC buildings can lead to overall failure and collapse. So retrofitting of such columns that do not comply with the design requirements is necessary to prevent such phenomena. A variety of methods has been introduced so far for retrofitting. The key factors in determining the retrofitting methods are being economic and easily implemented in the design. Confining concrete columns with pre-stressed steel strips is a new technique that is simple and economic. Previous experimental experiments have shown that this method can enhance ductility and overall seismic behavior of such columns.
In the present study three and six story frames... 

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.... 

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... 

In this Thesis, the behaviour of stell brace was studied in finite element models. In this section, a comparison between the results of these models and the results of experimental models which were done in past years, was carried out. It shows that these result is in good agreement with each other, Moreover it has been found that the primary cause of failure in the sample is local bucking and then change in the geometry of sample which will be followed by strain jumping in next cycles which shows the importance of local buckling due to the proximity of this event to strain jumps and can be accepted as braces limit state design.Finally, we try to predict the time of failure of samples with... 

In this study the behavior of steel bracings under cyclic loading, is modeled with finite element method. Analysis have shown that after local buckling in plastic mid-span position, due to the severe geometry change, the strain grows rapidly, The sharp growth of plastic strains is entitled as strain rises. Geometry change created will cause the collapse brace speeding up. In fact, the main local buckling can be used as a determinative factor in performance base design for steel braces. So the thesis has been investigated, using the parameters fracture life to quantify local buckling and fracture. Also with using the CVGM model, the fracture of the brace could be predicted. The analytical... 

In evaluating the damage observed in the structures can be seen that the beam to the wall connection in the walls with openings has severe damage and repair and reconstruction of the beams at the connection is very expensive and difficult. One way to improve seismic behavior and reduce damage in the beams are using steel fibers. Hence in the present study the effect of different fibers in seismic behavior of coupling beams with different length to depth ratio are investigated. The concrete used in the beams of high strength concrete (C60). Therefore, nine model with length to depth ratio of 1.75, 2.25 and 2.75 first without fiber and then with 1.5 and 3 percent made in ABAQUS software. This... 

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... 

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... 

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... 

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... 

The purpose of this thesis is the optimal retrofitting of the moment resisting frames with friction dampers, using the adaptive approach. In this regard, numerical modeling of the frictional behavior has been presented firstly. Also a 6-story moment resisting frame has been modeled in the OpenSees environment and the time history analysis has been carried out under a specific earthquake record. It is shown that inter-story drifts of the frame exceeds the acceptance criteria which has been assumed 2.5% according to the Life Safety limit. Then, the optimal retrofitting of the frame has been done. It is demonstrated that the maximum inter-story drift of all stories is 2.5% or less, while the... 

The preliminary design of building structures is normally based on the equivalent lateral forces provided in seismic design guidelines. The height-wise distribution of these loads is predominantly based on elastic vibration modes. However, as structures exceed their elastic limits in severe earthquakes, these design load patterns may not necessarily lead to efficient distribution of strength within the structures. To address this issue, several alternative load patterns have been proposed for the seismic design of non-linear structures. However, due to the simplifications involved in the development of these design load patterns, their adequacy needs to be assessed for different structural... 

The purpose of this study was to find the optimal position and slip force of friction dampers, for improving the seismic performance of regular and irregular steel structures and comparison of dampers final pattern of these buildings.In this regard, one to six floor regular and irregular buildings were designed. These buildings were modeled three-dimensionally in the OpenSees Software, and were subjected to horizontal components of seven far field accelerogram in order to investigate the need for their rehabilitation. The results of the time history analysis of these buildings showed that inter-story drifts exceeds the acceptance criteria which has been assumed 2.5% according to the Life... 

Today, Stability review of existing structures is one of the most important problems that have underperformed in our country. Base of doing this important project is Instruction for Seismic Rehabilitation of Existing Buildings No.360. In these Criteria, Nonlinear Static Procedure (NSP) is the most popular analytical method. In this procedure, a building shall be modeled, analyzed, and evaluated as an assembly of elements and components. For modeling of components, in lieu of relationships derived from experiment or analysis, the generalized load-deformation with parameters a, b, c, shall be used for members of structure. These parameters were defined in Tables 5-6 and 5-7 for steel moment... 

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... 

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... 

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....