Sharif Digital Repository

The earthquake engineering is the meeting of knowledge and techniques in studying, designing, implementing, controlling and strengthening various structures against seismic loads. The assessment of the performance of structures through previous earthquakes has shown that one of the major causes of damage to the existing buildings is the excessive displacements caused by the asymmetric load distribution, stiffness or resistance. Such irregularities, lead to severe dynamic reactions, especially torsion ones. Today, many structures can be considered as irregularity in plan and height. For this reason, it is expected that these structures will be highly vulnerable to seismic loads as compared to... 

Recent research in the field of earthquake engineering has seen the development of a number of different displacement-based seismic design (DBD) methods. Such methods aim to overcome limitations with the force-based design methods incorporated in current codes, and the most developed DBD method currently available is the Direct DBD approach, presented by Priestley. The objective of this work is to investigate the performance of the Direct DBD design procedure for steel moment-resisting frame structures. For this purpose, a series of regular steel MRF frames, varying from 4 to 20 stories in height are designed based on DDBD approach and utilizing displacement design spectrum of the Iranian... 

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... 

Application of Shape Memory Alloys (SMAs) as a means for vibration suppression of structural systems has extensively been explored in recent years. Recovering the applied residual strain upon unloading (super-elasticity) or by heating (shape memory effect) at different temperature ranges are two inherent features of SMA materials that have gained most attention. In this work, the seismic behavior of a proposed beam-column semi-rigid end-plate connection that has been equipped with both steel and SMA studs in austenite phase is investigated. A number of 3-D steel MRF structural models with 6,9 and 12 number of stories are considered. These structural models are subjected to bi-directional... 

With increasing population and lack of habitable spaces, the building heights increased in cities around the world. Placing components of a structure in tandem may cause a permanent failure of the members due to strength reduction. During recent years, this kind of failure occurred in different places of the world, and is called progressive collapse. There are some various samples of the progressive collapse which all are good samples of failures such as building failure in Ronan Point in the UK, Twin Towers or the world trade center in NY, and Pentagon building. According to these issues, different institutions codified guidelines and codes in this field such as Department of Defense as DoD... 

For many years of tall buildings with regard to the development and progress towns are necessary for the urbanite of the city and are considered as progress of the symbols societies. These buildings because of high wore their features special treatment under the influence lateral loads like the earthquake. In a way that today is an important issue in seismology and Earthquake Engineering all the powerful movements of the earth and its effect on the performance of the workforce special buildings as tall. Two points in this important subject. First modeling and simulations of the Most Powerful Earthquakes that in general occur in the field of near source earthquake generator. The earthquake of... 

Reduced beam section connection was one of the connections that were introduced and prequalified by SAC project to replace pre-northridge connections. This connection reduces both flanges of the beam at appropriate distances from beam to column connection to make a fuse protecting welds from brittle fracture. The RBS is prequalified in limited span-to-depth ratio, for designing this connection for short and deep beams may effect its performance. Since these limitations are based on limited experiments, forty three numerical models were analysed to recheck them in this study. These models are verified based on two published experiments and are capable of predicting all known yield mechanisms... 

In new method of performance-based design, the behavior of structure during earthquake is considered more realistically, and applying damage parameters like plastic ductility and inter-story drift to determine the seismic performance of structures is suggested. Damage indexes, the contribution of damage parameters to damage capacity of structural members, are defined to specify damage level of each element. In addition, damage spectrum which is the diagram of values of certain damage index versus natural period of single-degree-of-freedom system will be useful to seismic assessment of existing structures and seismic design of new ones. By the way, endurance time (ET) method can be... 

The main purpose of this research is to investigate the possibility of using piezoelectric patches for active control of a number of steel moment resisting frames (MRF) structures under seismic loading. For this purpose, the response parameters of 3 structural models with different numbers of stories and bays are considered. Piezoelectric patches which are connected to different parts of beams and columns are used to apply the calculated control forces. For this purpose, Sap2000 software is used for preparing the structural models and the MATLAB software is utilized to compute the required control forces and optimal placement of the piezoelectric patches. Furthermore, the nonlinear behavior... 

In this thesis behavior of intermediate steel moment frames and intermediate steel moment frames equipped with knee element are investigated. The knee element attaches to the beam element by inverted-V type concentric braces. The knee element acts as a fuse to dissipate input energy during an earthquake by the formation of plastic hinges. On the other hand, brace elements remain in the elastic range without buckling and provide suitable lateral stiffness. Main object of this investigation is reducing deteriorations in the main frame in intermediate and sever earthquake by concentrating deteriorations in knee element. Whereas knee element is not a main element of the frame, retrofitting of the... 

Various types of passive energy dissipating systems have been introduced for controlling the seismic response of structures during the last few decades. A number of these control devices have been practically implemented in different structures all over the world. Shape Memory Alloy (SMA) is among those passive control systems that have attracted a large attention due to its innate features, i.e., recovering the induced residual strains upon unloading (superelastic effect) or by heating (shape memory effect).This study investigates the seismic behavior of a set of steel structural models with different number of stories and eccentricities equipped with a type of fixed SMA connections. In the... 

This thesis presents the results of three tests to evaluate cyclic behavior of special moment resisting frames (SMRFs) with slitted web section. Typically, in SMRFs energy is dissipated by formation of plastic hinges at the beam ends. Nevertheless, based on the codes, the span-to-depth ratio of beams in SMRFs should be larger than a minimum value to assure the development of plastic hinges with sufficient length at beam ends, reducing application of short span beams. Reduced beam section (RBS) was developed to improve the performance of steel moment frame connections by weakening the flanges at a short distance from the columns. In this thesis, an alternative approach is proposed for short... 

This thesis presents the seismic performance evaluation of steel MRFs with nonlinear replaceable links. Although existing MRFs can provide life safety during a design level earthquake, they are expected to sustain significant damage at the locations of flexural yielding fuses in the beams .These drawbacks can be mitigated by introducing replaceable links at the locations of expected inelastic action. Codes require that the span-to-depth ratio of the beams in moment resisting frames (MRF) should be limited to guarantee the development of plastic hinges with a sufficient length at beam ends. To overcome the abovementioned limits, in this paper a new replaceable shear structural fuse is... 

The purposeof this study isto findthe propertiesof an equivalent linear Multiple Degrees of Freedom (MDOF) system, or so-called substitute structure, that its response is an approximation ofthe target actualnonlinearMDOF structure’s response (Shodja, 2013). In that regard,thestiffness anddampingmatricesofthe substitutestructure are considered as functions ofthe stiffnessand dampingmatrices ofthe actualnonlinear structure. Inthisway,the substitute structurescan be constructedthroughtrial and errorfor structures with different fundamentalperiods, damping ratios and number of floors.Inthat regard, a number of multi-story steel moment resisting frames are considered. The ductilities of these... 

The use of shape memory alloys (SMAs) has been seriously considered in earthquake engineering due to their unique capabilities, such as the ability to tolerate cyclic deformations, recentering, and dissipating energy. Consequently, the effect of hybrid connections (SMA and steel based beam-column connection) in asymmetric structures is investigated in this research.A 4 story steel special moment resisting frame with 0%, 10%, and 20% eccentricities have been considered to find out the performance of a novel beam-column connection in reducing the seismic response of structures such as maximum drift ratio and residual displacement. In order to find out this issue first, the symmetric model has... 

The purpose of this thesis is the optimal retrofitting of the moment resisting frames with telescopic dampers, using the adaptive approach. In this regard, numerical modeling of the telescopic behavior has been presented firstly. Also, a 3,9,20 story (sac) 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 exceed 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,... 

Considering connections as ideally rigid or pinned is a common assumption during design and analysis of steel moment frames. However, in real world, steel connections show a non-linear behavior between these two ideal states. The aim of this research is to investigate the effect of partially restrained connections on the design and performance of two-dimensional steel moment frames under vertical and horizontal loads that are applied statically. For this aim, nonlinear finite element modeling is used in probabilistic evaluation process to assess the performance of existing structures. To capture the real behavior of structure in models, geometric and material sources of nonlinearity are... 

This study evaluated post-tensioned system’s behavior in the steel structure. The post-tensioned system includes post-tensioned frame and gravity system (gravity frame and floor diaphragm) and considers the interaction of post-tensioned frame with gravity frame. Post-tensioned frame is the moment frame that has post-tensioned connections instead of ordinary connections. Bolted top and seat angles are used in the connection, along with post-tensioned high strength strands that run parallel to the beam. The strands compress the beam flanges against the column flange to develop a resisting moment and the friction between the beam and column and the two angles resist shear. Studies showed that... 

In Endurance Time method structures are subjected a set of predesigned intensifying excitations. These excitations are produced in a way that their response spectrum, while complying with a specified spectrum, intensifies with time. So they can be used approximately to simulate the average effects of several ground motions scaled to different intensities. In this study applicability of Endurance Time method for evaluating collapse potential of buildings is investigated. A set of steel moment frames is used for collapse assessment. The process of using Endurance Time method in collapse evaluation is explained with consideration of uncertainty effects. collapse fragility curves and collapse... 

Fire is one of the permanent threats due to earthquakes, however in spite of the attention drawn towards design and retrofitting of structures in recent years in our country, no effective steps have been taken for examining design methods and control of the structures’ reactions in case of a fire. One of the reasons for this, is lack of observations and data and also lack of a standard for design of structures that are resistant to fire. Since the connections of beams and columns play an important role in performance of the structures, in this research the behavior of a structure having a semi-rigid connection to an end plate has been investigated by performing an experiment on a scaled...