مهدی قاسمیه

So far, various elements have been introduced for modeling concrete shear walls, which are classified into two general categories: microscopic and macroscopic. Compared to microscopic elements, macroscopic elements have less degrees of freedom and therefore require less time for analysis. This is the main advantage of these elements. In this article, a special type of macroscopic elements called Multiple-Vertical-Line-Element-Model (MVLEM) is used to model the concrete shear wall. These elements simulate the behavior of simple shear walls well, but when the opening is embedded in the wall, it does not work satisfactory. In this article, the modified MVLEM is used to model the concrete shear wall with asymmetric openings. For this purpose, an experimental concrete shear wall with asymmetric openings was selected and verified using the microscopic finite element method in Abaqus software. After validation, the shear wall was subjected to macroscopic modeling in Abaqus software. In this model, a method for macroscopic modeling of the coupling beam was proposed, which is based on the moment distribution diagram in the beam. When the wall is subjected to lateral loading, due to its geometric shape, the amount of moment on one side of the beam is almost zero and on the other side it is maximum. In simple concrete shear walls under lateral load, the amount of moment at the top of the wall is zero and at the bottom is maximum too. Therefore, the coupling beam can be considered as a simple shear wall. In the shear wall with asymmetric openings, the coupling beams are modeled as simple shear wall whose base is connected to the main wall. After modeling the coupling beam, three different methods were proposed to connect this beam to the main body of the wall. This research includes a microscopic wall with asymmetric openings, three macroscopic walls. The main difference between the macroscopic walls is in the way of connecting the beam to the shear wall, which is based on the difference in the stiffness of the connection. In order to check the accuracy of the proposed models, macroscopic and microscopic walls were subjected to static and quasi-dynamic loading. Based on the results of the aforementioned analyses, the models showed acceptable behavior. The amount of connection stiffness caused the behavior of macroscopic models to be different from each other. Based on the results, as the stiffness of the beam to the wall increases, the bearing capacity and elastic stiffness of the model increases and the ductility decreases. The degree of stiffness of the connection also affects the cyclic behavior of the wall. In such a way that the higher the stiffness of the connection, the greater the loss of carrying capacity is observed in cyclic loading. In the model whose stiffness is higher than the other models, it experiments a large resistance drop in the ninth and tenth cycles. In the model whose stiffness is less than the others, less drop is observed and it shows a soft behavior. The model in which the connection stiffness was in the middle level showed the most accuracy compared to other models.

BRBs are a new type of seismic resistance system that is being used extensively nowadays due to their enhanced seismic performance than conventional braces. In BRB braces, because the buckling of the steel core is prevented, the structure shows more stable behavior. In this type of bracing, the hysteresis performance of the bracing is similar to the hysteresis performance of the core material. Another feature of these braces is that the ductility of the steel material occurs over a considerable length of the brace. Although BRB braces are capable of dissipating large amounts of energy, they are unable to eliminate their residual strains. In other words, they do not have the property of self-centering. This leads to the non-return of the structure and to its original configuration after the seismic excitations; in the absence of a return mechanism. There may arise many permanent deformations in the structure during an earthquake. To overcome these permanent deformations, various innovative solutions have been developed in the construction of steel frames, including the use of shape memory alloys (SMA) that have two prominent features of shape memory and superelastic behavior and can return to their original position after subjected to the various loadings condition. In recent years, beside the Nitinol shape memory alloy (NiTi), Iron-based shape memory alloys (SMA-Fe), which have many advantages over previous SMAs and particularly due to their lower cost, have been introduced and being used in many construction projects. In this research, the seismic behavior of structures braced with BRB, and iron-based shape memory alloy and Nitinol shape memory alloys has been investigated. Seismostruct finite element software has been used to model these systems. Incremental dynamic analysis (IDA) has been performed on seven story structures equipped with X braces with different materials. The results of this study show that braced structures with iron-base shape memory alloys undergo less maximum displacement and permanent displacement compared to nitinol-braced structures. However, these structures experience more maximum displacement than BRB braced structure. The more the structures enter the nonlinear stage (in the maximum values of the relative inter-floor displacement demand) the more the dispersion of the results increases and the structure is more affected by the input accelerometers. The structure with buckling bracing will reach instability later than the two structures with shape memory alloy bracing.It is also observed that the elastic stiffness (slope of the linear behavior region) in all 3 braced frames is equal to each other. And finally, the IDA curve of the BRB structure is higher than the two shape memory alloy structures, and at equal acceleration, it is clear that the displacement of the shape memory alloy structures is more than the buckling structure, and it can also be seen that the iron-based shape memory alloy brace has a favorable performance and its curve is slightly higher than the NiTi shape memory alloy. Also, two shape memory alloy structures move almost together and reach instability at one point. According to the curves, it seems that the braced structures with shape memory alloys have performed well and until these structures reach instability.

In the 1994 Northridge and 1995 Kobe earthquakes, a large number of conventional bending frames suffered brittle fractures at the beam-to-column joint. Researchers have found that structural components of structural systems are very effective in controlling the energy caused by dynamic loads, especially earthquake and explosion loads. In recent years, Iron-based shape memory alloys, which have two important properties of superelasticity and shape memory behavior, have been used to improve the seismic performance of structural systems. This study investigates the energy dissipation capability and other properties of moment connection with expanded end-plate and bolts made of super-elastic ferrous based memory alloys. The 3D connectivity models are built using ABAQUS finite element software. By applying cyclic loads to the end of the beam, its behavior has been studied. In this research, two types of four-bolt connections, one with the behavior of a thick plate and the other with the behavior of a thin plate, have been modeled, and in each case, the connection behavior with and without the use of shape memory materials has been evaluated and compared. The use of these materials in connection with thick plate behavior has increased the ductility of the connection by 35%, and the connection has compensated 93% of the deformation and returned to its original state. In connection with thin plate behavior, the increase in ductility of the connection is 54% and 85% of the endured deformation has returned to the initial state.

Considerable age of numerous concrete structures and due to some reasons like changes in design philosophy, increase in applied loads, etc., have made strengthening and maintenance compulsory. Shear failure in reinforced concrete beams is frequently sudden and brittle. For this reason, efforts are made to avoid this type of failure by strengthening them, especially in structures that were made with engineering mistakes and damaged structures. Steel, fiber-reinforced polymers, and carbon fiber-reinforced polymers are used as conventional solutions, but these methods have some drawbacks. For instance, prestressing them is hardly applicable, and the prestressing force decreases over time. Therefore, nowadays, as an alternative, shape memory alloys (SMAs) are investigated as new strengthening methods owing to their unique features. Shape memory alloys are novel and smart material groups that have been considered in civil engineering for many purposes, including active and passive control of structures, dampers, and strengthening of structures like reinforced concrete structures and bridges, etc., due to unique features such as pseudo-elasticity and shape memory effect. They have the particular property of returning to their initial shape by heating which is called the shape memory effect. If the SMAs prevented from returning to their initial shape by using mechanical fixation, a prestress force develops owning to the shape memory effect property. NiTi or Nitinol has been used for damping applications in civil engineering, and it has been investigated in the literature. Iron-based shape memory alloys (Fe-SMAs) have attracted much attention in civil engineering applications due to their shape memory effect. Particularly for strengthening applications, iron-based shape memory alloys have some benefits such as wide transformation hysteresis, high elastic modulus, and lower cost compared to conventional NiTi alloys. The advantage of shape memory alloys over fiber-reinforced polymer is that they can be prestressed more easily than FRP, and the prestressing force will not reduce over time. In addition, it does not require any mechanical and hydraulic jacks. Prestressing these materials has some advantages in strengthening. For example, cracks and deformations can be reduced or at least prevented from further growing, and the stresses in internal stirrups are reduced. The usage of prestressing for shear strengthening is rare because it is very complex from a practical standpoint. This study aims to assess the behavior of RC beams strengthened in shear with iron-based shape memory alloys. For this purpose, based on experiments in the literature, T-beams with 5.2-meter long are investigated numerically by using finite-element analysis software, ABAQUS. Three-dimensional finite element models were developed using the concrete damage plasticity and were verified with experimental results. Comparison between the results from the FE models and experimental test results confirmed the accuracy of the proposed models. Furthermore, the effects of parameters such as shape memory alloy diameters, prestressing force, and shotcrete thickness on beams' shear behavior are also investigated. The results of the analysis indicate a notable increase in the final shear strength of the strengthened beams and a reduction in stirrups' stresses. The prestressing ability of shape memory alloys delays the yielding of stirrups and the appearance of shear cracks and reduces the thickness of the cracks.

Buckling restrained braces have been shown to exhibit favorable energy dissipating characteristics in steel structures during an earthquake and are therefore widely used in passive control of structures. However, they face the problem that they do not return to their original shape upon unloading, and consequently, the structure experiences large permanent deformations after the earthquake which usually makes the structure impossible or uneconomical to repair. In recent years, to solve this problem, researchers have used Iron-based shape memory alloys which have two essential properties of superelasticity and shape memory behavior. These alloys have been considered due to their high energy dissipation capacity, their ability to withstand large strains, recentering and not leaving permanent deformations upon unloading, and their much lower cost than other shape memory alloys. In this research, the seismic behavior of three-story structures braced with buckling restrained braces, iron-based shape memory alloy, and nitinol shape memory alloy, which is one of the most famous shape memory alloys, is investigated. Modeling and Nonlinear dynamic analysis for these structures have been performed in Seismostruct software. Maximum displacements, residual strains, and force-displacement diagrams of these structures have been studied due to the application of different accelerometers of large earthquakes of recent years with different intensities. The results of this study show that braced structures with Iron-based shape memory alloys experience more maximum displacements than Buckling restrained braces, although unlike BRBF they do not leave any permanent displacement. Also, these structures undergo fewer maximum displacements and permanent displacements compared to nitinol-braced structures, and in general, show better performance.

In the welded joints, residual stresses appear in the areas around the melting pool and the areas that are affected themselves by the welding heat after the completion of heating and cooling welding cycle. The residual stresses reduce the integrity of the metal’s mechanical properties and also the serviceability of the made parts. Recognition and investigation of these stresses is a complicated and pricey process in operation. One can use numerical methods such as finite element for recognizing and investigating the tensions and unwanted welding deformations in order to solve the problem. In this research, regarding the importance of these stresses in construction fittings, a thorough numeric research on the stresses in welding joints has been conducted using Abaqus software. To this purpose, GOLDAK double ellipsoid model has been considered for heating source primitively to ensure the reliability of this evaluating method. Using this technique, the outcome of this model has been compared with the existing technical literature. The heat flux has been encoded in Fortran programming environment with the help of DFLUX subroutine and applied to the original model. Once the temperature history of all thermal analysis groups obtained, mechanical loading analysis will start to identify the residual stress in the fragment. The results demonstrated large amounts of residual stress at the joint site. The amounts of these stresses in some parts of the joint were as much as the yield stress of metal; i.e. to say the metal was formed as plastic at the end of the welding process.

Based on the past experience of engineers, welded connections usually do not perform well during earthquakes. Nevertheless, welding is used in all prequalified moment connections in chapter 10 of the National Building Code of Iran and as a result, there is a need for a fully-bolted prequalified moment connection for use in intermediate moment frames (IMF) and special moment frames (SMF). Thus, in this paper, a novel type of fully-bolted connection was investigated using T-shaped sections and web angles. First, the finite element model of the connection was developed in Abaqus software and validated with respect to experimental results. Next, using the concepts of Eurocode 3, section 1-8, a method for calculating the stiffness and strength of the connection was presented and was validated with the help of several experimental tests and finite element modeling. The results confirmed the proper performance of this method in predicting the stiffness of the connection. Since finite element modeling and experimental tests require a lot of cost and time, the proposed method can be a good option for engineers. Next, with the aim of parametric study on the connection, a large number of connections were designed based on capacity. Based on the component method, the connections stiffness was calculated using supervised machine learning techniques and multiple linear regression learning algorithm. Next, using the data obtained from the design and component method, a parametric study was performed on the connection and a simple formula was presented to calculate the initial stiffness of the connection. The results of this study show excellent regression performance in predicting connection stiffness. In addition, according to the obtained formula, the depth of the beam and diameter of the bolts connecting the T-shape flanges to the column flange have the most impact on the connection stiffness. Finally, the studied connection was classified according to its rigidity. The results showed that the studied connection acted as a fully-restrained connection and can be used in IMF and SMF systems.

Due to the relatively high use of steel buildings in Iran and the importance of rigid steel beam-to-column connections, which are among the vital components in this type of buildings, the need to better understand the behavior of these connections against earthquakes has been noted. Also due to the special characteristics of the near-field earthquakes, which is different than far-field earthquakes and it has its own characteristics; and the fact that some catastrophic earthquakes occurred in Iran, such as the Bam earthquake (2003) and the Tabas earthquake (1978) had the characteristics of the near-field earthquakes, which can show the importance of the near-field ground motions; the purpose of this study was to propose a loading protocol for special steel moment- resisting frames under near-field earthquakes for Iran. Therefore, first, by examining the earthquakes that have occurred in Iran during several years, near-field earthquakes have been selected. Steel buildings of 3, 5, 7, 9, 12 and 20 floors were designed and analyzed according to the rules and regulations of Iran, then for each of the designed steel buildings a critical frame was determined; the values of the scale factors are also specified. After performing nonlinear time‐history analysis and applying the proposed near-field ground motions to all of the critical frames, inter-story drift angles for all frames was obtained and compared. The third floor of the 3-story critical frame was selected as the critical floor; which is a story whose results will be used to construct a loading protocol; The basic rainflow counting and simplified rainflow counting were performed for the critical inter-story drift angles results; The proposed loading protocol are derived based on the MCE-level seismic hazard and 84th percentile values of key seismic demand parameters. These parameters are number of damaging cycles, maximum inter-story drift, sum of inter-story drift range, inter-story drift range and residual inter-story. The rationality of the proposed loading protocol was justified by showing the cumulative distribution function. The proposed loading protocol has 23 damage half-cycles, including 3 pulse half-cycles with inter-story drift ranges of 0.060, 0.100 and 0.078 radians; which are calculated by the basic rainflow counting method. The maximum inter-story drift was obtained 0.065 radians. In the final half cycle, the mean value is the same as the residual inter-story drift of 0.03 radians. Also, the sum of the inter-story drift ranges is equal to 0.684 radians. The proposed loading protocol was compared with the SAC near-field earthquake protocol, the maximum inter-story drifts in the proposed protocol is 0.065 radians and in the SAC protocol is 0.06 radians. Furthermore the pulse cycles in the proposed protocol have inter-story drift ranges equal to 0.060, 0.100 and 0.078 radians; while the three pulse half-cycles at the beginning of the SAC loading protocol have inter-story drifts of 0.08, 0.05 and 0.04; respectively. Therefore, the proposed loading protocol has a higher inter-story drift and stronger pulse cycles than the SAC near-field earthquake protocol; but the total number of cycles defined in the SAC protocol is greater than the proposed protocol.

Residual displacement after an earthquake disrupts the performance of the structure and leads to local stress. There has been special important in development and the using of self-centering lateral resisting systems that reduces residual drift after a large earthquake. Self-centering lateral resisting systems often include a restoring force component that dissipates seismic energy. Eccentrically braced frame with vertical link (V-EBF) is one of seismic system based on shear yielding of link beams. If link beam has short length and supplies seismic requirements, link will be able to tolerate significant rotation without strength degradation. Shear link beam has a fat hysteresis curve and height potential of energy dissipation; for this reason the use of short link beam in eccentrically braced frame was modeled by using experimental models which were provided by other researchers and compared with laboratory results. After validation, 8 and 12 story V-EBF and equipped with SMA rods were designed and their performance were compared with similar structures without SMA rods. In order to compare the structures, pushover, time history and Incremental Dynamic Analysis (IDA) were performed. The results of seismic analysis indicate that the using of SMA rods improves seismic performance and provides excellent reversibility capacity so reduces residual displacement of structure considerably.

Today, there is an increasing interest in use of seismic isolation to protect the structures against earthquakes. The most common type of seismic isolation is called base isolation, in which the isolation layer is installed under foundations to separate the structures from the ground and reduce the earthquake forces. However, the use of this type of seismic isolation faces some difficulties such as construction in congested urban areas or construction of near sea structures. Furthermore, for seismic retrofitting of existing buildings, the installation of the isolation under foundations is difficult or even impossible; so, it needs to be located on the middle floors of the buildings. The method of isolation design is called floor or middle story isolation. Despite the advantages of seismic isolations, they have some limitations such as instability in large deformations, residual displacement, and the need for replacement after severe earthquakes. The use of Shape Memory Alloys (SMA) regarding their unique properties is considered as an appropriate solution to overcome the above problems. These smart materials show high strength and strain capacity, high recentering ability, and high resistance to corrosion and to fatigue. The purpose of this study is to investigate the effect of combination of middle story isolation utilized by Natural Rubber Bearing (NRB) and iron-based shape memory alloys in steel structures and to compare the performance of such structures with and without the presence of the shape memory alloy in the middle-story isolation system. Then, a three-story steel structure has been modeled and evaluated. For this purpose, a structure with floor isolation and iron-based shape memory alloy was modeled in OpenSees computer program. The structures were then subjected to seismic loading. The results were presented in the form of story drift, floor acceleration, floor shear forces, and base shear. The outcome of this research showed that the use of these alloys in the middle-story isolation reduced the overall base shear and floor shear forces. The overall story drift, floor acceleration and displacement are reduced; with the exception at the isolation level. Thus, utilizing the natural rubber bearing isolator along with the iron-based shape memory alloy can be considered as a desirable system for the seismic protective design of buildings.

This paper focused on the behavior of steel plate shear walls (SPSW) in high-rise buildings. The influence of essential parameters including number of stories, stress angles and openings and investigated. Comparison with moment resistant frame and alternative method of modeling the shear walls with Strip elements is investigated. Using finite element method, a four story steel plated shear wall which has been tested before was modeled and the results obtained were compared with the test data. Comparison of the results approved the numerical modeling. Then the 20-story, 15-Story and 10-story steel plated shear walls were designed in accordance with AISC-Seismic Provisions to make results more practical. Comparing steel pated shear walls with different heights with each other, it is noticed that with lowering SPSWs, its initial stiffness improves and its ultimate strength decreases; but the overall ductile behavior was maintained. Also to make it useful and practical, moment resistant frames were modeled similar to SPSWs but without infilling panels. This research showed that with lowering the SPSW height, its behavior gets closer to moment resistant frames. Also behavior of SPSWs with openings was studied. Four openings in a same position, same width and different height were modeled to see the effect of openings on the overall SPSWbehavior. Generally, it was observed that an opening in infilling panels reduces SPSW initial stiffness and final strength.

In this study, to develop the Iranian loading protocol in the region, the detailed seismic, numerical, statistical, finite element and laboratory studies were conducted according to the region’s conditions. Finally, a loading protocol was proposed that provided a proper simulation of the region’s seismic demand. It also complied with the construction and design conditions of structures in the region and can apply to structural moment components, especially moment connections in the laboratory conditions. It is noteworthy that the region’s proposed loading protocol provided some criteria for evaluating the performance of moment connections in the target values level, qualifying conditions, and collapse threshold control of moment connections. To achieve the objectives of this study and to evaluate and match the proposed loading protocol’s performance conditions, two pairs of identical specimens of WUF-W and RBS welded moment connections were examined and evaluated in the laboratory subjected to the proposed loading protocol of the region and SAC loading protocol. It should be noted in the laboratory and numerical studies that the damage parameters and applied demand resulting from both loading protocols were evaluated and compared while matching and controlling the conditions and criteria presented in the proposed loading protocol of the region. It is noteworthy that the present study’s welded moment connections well satisfied the performance conditions and criteria of the proposed and SAC loading protocols.

Seismic loading in seismic prone countries is very important and the lack of enough attention can make a irreparable damages to structures and non-structural elements. Dissipating earthquake energy just by using elastic capacity of structure, will increase the dimension and weight of structural elements like column, beam, walls and the cost of building will increases. Incoming seismic energy should be dissipated in plastic process and in this process, structure must remain stable. Shearwall is using widely because of its suitable behavior against seismic loading and good ability of energy dissipation. Sometimes it is inevitable to avoid openings in shear walls due to architectural considerations. Providing enough ductility in these shear walls is a difficult job because of stress concentration around of voids. The other problem of using shear walls is plastic deformations that make the structures useless. One way of improving ductility and self-centering ability of shear walls is using smart materials. Shape memory alloys are one of the newest smart materials that have two important behaviors, called shape memory effect and superelasticity. Removing the residual deflection after unloading of elements made by shape memory alloys by heating called shape memory effect. Superelasticity in SMAs is returning the elements to their initial shape after unloading by them. Good corrosion resistance, good fatigue behavior and weldability are the other positive behaviors of shape memory alloys. In this paper the improvement of the shear walls ductility and self-centering ability with using shape memory alloys in superelastic phase is investigated. Shape memory alloys can withstand up to 7 percent of strain without any residual deformation. In this paper shear walls modeled by shear-flexure interaction multi-vertical-line-element-model (SFI-MVLEM). This model was implemented in the Open System for Earthquake Engineering software (OpenSees). Considering interaction between shear and flexural response in shear walls has made this element superior. Superelastic reinforcement bars were embedded in plastic hinge of boundary elements, coupled beam and walls web separately. Shear wall modeled by using SMA in boundary element, coupled beam and walls web called SMAB, SMAC and SMAW respectively. To examine the effects of these alloys on energy dissipation capacity and self-centering ability of the shear walls, structure were evaluated in cyclic analysis. Place of using SMAs on shear wall in very important and can influence widely on shear wall so most optimized place of using SMAs in shear wall should recognized. Two case of optimization considered in this analyze. In first one, best place is a place that using SMAs on it causes minimum energy dissipation reduction and maximum residual displacement removing. In second one, best place is the place that causes maximum residual displacement removing with minimum usage of SMAs. In order to find the influence of SMAs on ductility of shear wall, pushover analyse was used. Using SMAs in boundary elements of shear walls made maximum increasing in ductility of shear wall but the best place for using SMAs for optimization of usage of SMAs is walls web. Based on the results, with using shape memory alloys, ductility of shear walls was increased and its residual deformation and energy dissipation capacity was decreased. The best place of using SMAs in shear wall is coupled beam for optimization of energy dissipation and residual displacement and for optimization SMA usage is walls web.

The 1994 Northridge earthquake motivated the researchers to overview the conventional design philosophies. At that point, one of the safest lateral load resisting systems was the fully restrained welded steel moment frame and it had been the dominant design choice in the seismic regions. The confidence in the fully restrained frames has been decreased by brittle failures of welded connections. Thus, the researchers introduced the new seismic structural systems; braced frames and hybrid frame.
Hybrid steel frame is a new lateral resistant steel moment frame that is designed based on introducing the new energy dissipating mechanism. In order to enhance frame’s seismic performance, selected rigid connections are replaced with the ductile energy dissipating semi-rigid connections. This concept at the first glance is similar to the eccentrically braced frame. In the eccentrically braced frames, structural fuses are isolated links distributed throughout the frame, while in the hybrid frames fuses are semi-rigid connections placed at the selected locations with particular patterns. The seismic performance of hybrid frame is in such a way that story drift results in the rotation of the semi-rigid connections. Thus, for a properly designed connection that behaves in a ductile manner, the rotation is absorbed by angle or plate yielding without bolt or weld fracture. It would lead to excessive end plate or angle distortion at ultimate rotation that can be retrofitted after earthquake.
In this research, the ductile semi-rigid connection is used in hybrid frames. Finite element modelling of the hybrid frame is conducted in OpenSees computer program. The semi rigid connections are implemented in OpenSees by nonlinear plastic rotation ends. The nonlinear hinges are modelled by using Ibarra Krawinkler deterioration model. The panel zone is also modelled by Krawinkler model proposed in the FEMA 355C. Then, several different patterns and locations of semi-rigid replacements within 3 story benchmark SAC frame are selected. All the frames are subjected to nonlinear static analysis as well as cyclic displacement analysis. For the assessment of the frames subjected to seismic excitations, nonlinear dynamic history analyses are conducted subjected to 40 Los Angeles records. The finite element numerical model of the SAC frame is also verified by comparing the results with the technical literature. Normalized base shear, energy dissipation capacity, and maximum story drift angle under 40 Los Angeles records are obtained for each frame. Finally, based on the mentioned parameters and design criteria the frame with desirable performance is selected.
In general, hybrid frames have less base shear, less energy absorption, and more drift compared to frames with rigid joints (SAC frames). The lower energy absorption of these frames is due to the fact that in beams that are connected to the column in a rigid manner, the plastic joint of the beam is not activated and the semi-rigid connection is responsible for energy absorption. The geometric characteristics and cyclic behavior of semi-rigid joints are such that they absorb less energy than plastic beam joints. The data obtained from different analyzes on hybrid frames are slightly different and this shows that the effect of semi-rigid joints in short-term frames is not significant.

Following Northridge earthquake, wide spread brittle cracking had been observed in steel moment connection, and this, was in contrast with the philosophy of designing steel moment frames which accounts for dissipating energy by forming plastic hinges at beams. This situation led to the development of improved connections to make them less prone to brittle fracture. However, studies have shown that these new connections, typically known as post-Northridge connections, can still have the tendency to fracture but in a ductile manner when subjected to ultra low cycle fatigue loading. Ultra low cycle fatigue loading consists of limited cycles of loading with large amplitude which induce strains that are several times greater than yielding. Searching the literature, varied methods have been proposed to predict cracking in ductile steel for both monotonic and cyclic loading. In this research, a micro mechanical model called cyclic void growth model has been applied to predict the instance and location of cracking in the steel structure. For the purpose of predicting the low cycle fatigue failure, finger shaped steel moment type connections with top and bottom cover plates which their experimental data were available, used as a benchmark study. A micro mechanical model is integrated into the ABAQUS finite element program in order to simulate crack initiations in the cover plate welded beam to column connection. For this purpose, a Fortran code is linked with the ABAQUS software for simulating the crack and specifically to predict when and where the crack initiates. By understanding the crack initiation and the location of this crack, a trend line for low cycle fatigue under various constant drift angels are put together. The trend line provides a number of cycles for the crack to initiate by applying the specific drift angle. Therefore, a finite element model of a cover plate welded moment connection was developed and was used in order to simulate cracking in the connection model. Thus, each crack location and the number of cycles to initiate the crack were detected. Utilizing cyclic void micro mechanical model of growth analysis, which is a technique to predict fracture in a ductile material, different cover plate connections were modeled in the steel moment frame, and then their critical points to trigger the crack were identified. Finally, for the finger shaped cover plate moment connection, considering different loading curves data and in order to present the low cycle fatigue life prediction, displacement versus the number of half cycles diagram is produced. Finite element results demonstrated acceptable agreement with the experimental data. Furthermore, the low cycle fatigue life of connections under loading with constant amplitude is estimated, and S-N curves are proposed. These curves can be applicable for engineering purposes, such as performance based design. Also it is demonstrated that the finger plate joint revealed a good performance against soft cracking in low cycle fatigue compared to a number of previously tested joints. The results of the S-N curve for a constant displacement loading averaged 73% of the lifetime of the initial cracking. Sensitivity analysis with 20% tolerance on the intrinsic parameters of the micro mechanical model showed a maximum change of 15% in the responses.

In this research, numerical modeling and evaluation of the using new smart alloys in concrete shear wall structures is investigated via finite element method. For this purpose, two 5-story concrete shear walls, one of which is without opening and the other is with openings, are modeled in Abaqus software. In these shear walls, steel and shape memory reinforcement with different percentages were installed in these walls. Then, the results of seismic behavior analysis after installing members made of shaped-memory alloys in reinforced concrete shear wall with interface joint beams are presented. The obtained results are compared with the response of shear wall structures without these members. There are no shape memory bars in the reference shear wall and all its reinforcement is made of steel. The finite element method is a technique which widely used in this field of study. Utilizing this type of analysis and comparing the behavior between single shear wall and shear wall by using shaped-memory alloys, improving seismic behavior and dramatically reducing final and lasting deformation in shear wall structure with shape memory alloy are monitored. In static loading, similar results were observed, indicating the elimination of permanent deformation by these alloys

Nowadays, Steel Plate Shear Wall (SPSW) is considered as a suitable alternative to conventional lateral load resisting systems that used for earthquake resistant design of structures, because of high post buckling strength, significant ductility, stable hysteresis characteristics and high initial stiffness. Also, steel plate shear wall has lighter weight of structures, increased floor area, quicker speed of construction, significant economically affordable and high quality control compared to a traditional reinforced concrete shear walls. Study on behavior of steel plate shear wall was began in 1970s with the aim of providing an easy method for the analysis and design. The initial experimental and analytical researches clarified varies aspects of seismic behavior of steel plate shear wall, but it is still unknown, because of its complex behavior and design. Although some researches on steel plate shear wall has been done since the early 1980s, the appropriate performance of structures that had steel plate shear wall as lateral load resisting systems in the Northridge, USA (1994) and Kobe, Japan (1995) earthquakes caused researchers and working engineers to investigate and implement the steel plate shear wall system to a greater extent. Analytical and experimental research works and studies, provided primarily in Canadian, US and UK universities on steel plate shear wall considered different facets of the seismic behavior of steel plate shear wall and flourished the essential procedures for its application as an effective lateral load resisting system. However, in order to investigate the performance of steel plate shear wall comprehensively, wide range of nonlinear behavior has to be assessed and predicted and it requires hysteresis models that are capable to consider all deterioration modes. One of the comprehensive analytical hysteresis models is the modified Ibarra-Krawinkler (IK) deterioration model that provides four deterioration models including basic strength deterioration, post-cap strength deterioration, unloading stiffness deterioration and accelerated reloading stiffness deterioration for systems with bilinear, peak oriented and pinching behavior. In this study, by calibrating the modified Ibarra-Krawinkler deterioration model parameters for steel plate shear walls with different properties, some equations are proposed to determine modified Ibarra-Krawinkler deterioration model parameters. First, one of the experimental specimens was modeled and analyzed in ABAQUS software and accuracy of results was measured. Then, 60 number of pinned joints-one story steel plate shear walls with different infill plate thickness and bay length, using two types of steel for infill plate are numerically modeled and analyzed by ABAQUS software. Also, the height of steel plate shear walls was kept constant equal to 3500 mm. Using OpenSees software numerical analysis results, the modified Ibarra-Krawinkler deterioration model parameters are calibrated. Then, by identifying the effective factors, some statistics equations are suggested. According to the results, effective parameters on lateral load resisting capacity, elastic stiffness and post capping stiffness were thickness of infill plate and its steel type and ratio of bay length to height of steel plate shear wall. Also according to the results, the and ratio of bay length to height of steel plate shear wall had more influence on modified Ibarra-Krawinkler deterioration model parameters.

In order to provide a comprehensive assessment of the structural components, behavior of structures should be traced and predicted far into inelastic region. For this purpose, analytical hysteresis models are needed which are capable of representing all modes of deterioration. In order to utilize these models,a database is required to calibrate models. In this paper relationships are proposed to predict modified Ibarra-Krawinkler model parameters for welded flange plate steel connections. To provide the database, a number of welded flange plate connections are designed based on Iran Steel Code. The designed connections have been modeled and analyzed numerically in a finite element software. Prior to proceed the investigation, finite element numerical model of the connection was created in the ABAQUS computer program in order to predict the micro-mechanical behavior of the welded flange plate steel connection. Using the nonlinear method of analysis, the cyclic behavior of such moment resisting connection was obtained. The numerical results were verified by comparing the results obtained experimentally and specifically for the steel welded flange plate moment connection. Simulation of several numerical models and in comparison with the laboratory results indicate the accuracy of the finite element model. Once the finite element micro behavior was verified, then fifty three different welded flange plate moment connections were designed for different number of steel moment frame with various heights and floor numbers. All the connections are modeled in the ABAQUS computer program and the cyclic behavior of such connections such as the hysteresis behavior are obtained. The hysteresis behavior of the connections were included in the moment frame connections by utilizing the rotation behavior in the connection. The steel frames are modeled in a customized version of OPENSEES computer program. The numerical model consists of nonlinear beam column elements with the rotational spring element at the end in which the rotational behavior of the spring were the hysteresis behavior of the connection obtained from ABAQUS computer program. These springs simulate the hysteretic response a steel component (beam or olumn) subjected to cyclic loading including strength and stiffness deterioration based on the modified Ibarra-Krawinkler deterioration model. Panel zones are modeled in such away that the shear distortions were explicitly included with the possibility of nonlinear behavior during an earthquake. The numerical results show that most numerical specimens predict the plastic hing location to be right after the top flange plate. Using numerical results as a database, the model parameters are calibrated and effective geometrical properties of connections are determined. The most effective parameters are beam depth, beam span to beam depth ratio, beam web depth to web thickness ratio, top plate length to top plate thickness ratio, bottom plate length to bottom thickness ratio, and beam flange width to beam flange thickness ratio. Finally, using nonlinear regression equations, relationships for predicting the model and deterioration parameters are proposed. Also different rotational capacity such as maximum plastic rotation, plastic rotation spectrum and cumulative plastic rotation are predicted. From the regression analysis the pertinent parameters effecting the detioration of the connection are identified.

The strength and deformation capacities of the structural elements are affected by the cumulative damage of that component. For this purpose the loading protocols used for investigating the performance of the connections should give an accurate estimation of the structural components capacities and yield appropriate simulation of the reality. It is essential to investigate the differences and features of the loading protocols. On the other hand, regarding the widespread use of the moment connections of I-shaped beam sections in the box-section columns, investigating the seismic performance of these moment connections is of vital importance. Meanwhile, the majority of code details for accepting moment connections are presented for H-shaped columns. For this purpose 12 types of RBS and WUF-W moment connections with box-section columns were designed and examined as analytical models in the study. The seismic behavior and difference in performance of these two types of moment connections were investigated and compared at the level of the relative displacement acceptance in the codes and also the collapse threshold under SAC and ATC-24 loading protocols. In continuation, while investigating the demand and applied energy, and the features and differences between the loading protocols, the conditions for strength loss at the collapse threshold of moment connections in the special moment resisting frame are also proposed.

This study investigated the effect of combined loading on end-plate moment connection considering the interaction of bending moments, axial forces and twisting moments. In some cases, beam-to-column joints can be subjected to the simultaneous action of bending moments, axial forces and twisting moments. Current specifications for steel joints do not take into account the presence of axial forces (tension and/or compression) or twisting moments in the joints. Although the axial force or twisting moments transferred from the beam is usually low, it may, in some situations attain values which can lead to a considerable effect on the connections behaviour and significantly reduce the joint flexural capacity. Unfortunately, few studies considering the bending moment versus axial force interactions have been reported and there aren’t any reports considering bending moments versus twisting moments interactions or combination of all the mentioned cases of loads at the same time. The lack of knowledge for understanding the performance of end-plate moment connection under combined loads may lead to unreasonable or even unsafe design. Thus in this study a combination of different loads being applied simultaneously on the end-plate moment connection have been examined. Therefore two extended End-Plate connections with different behaviour modeled using finite element method of analysis. The interactions between connection components (bolts, members and endplate) were accurately modelled to simulate the actual behaviour of connections. Material nonlinearity as well geometric nonlinearity were considered in the analysis including the effect of contact. At first the behavior of the end-plate models are investigated in pure bending application. The numerical results were validated against experimental data. Due to the lateral loads and because of the existence of axial force in the moment resisting frames, the combination of bending and axial force in beams should be considered. An example of having bending and axial action is when the structures are subjected to fire which the effects of beam thermal expansion and membrane action can induce significant axial forces in the connection is a common condition. The results show that even in small amount of axial force the mode of failure and moment capacity of connection can change. Axial tensile forces decrease the initial stiffness of connection and axial compressive forces increase the stiffness. In many applications beams are eccentrically loaded and as a result experience twisting loads in combination with bending. The interaction effects due to torsion acting in combination with bending can reduce the capacity of the beam and initial stiffness of connection. Finally axial forces were added to the previous models so they experienced a combination of axial force, bending and twisting moment. The results indicated that the level and direction of axial force significantly modified the connection response. It was observed that compression forces significantly decrease the bending capacity of the models and lateral-torsional buckling of beam occures in all models. Tension forces can reduce the effect of torsion and in many cases they caused the bolts ruptured. Moreover, interaction diagram for predicting the bending capacity considering interaction of bending, torsion and axial forces are proposed based on the results from finite element analysis.

In this study, a comprehensive experimental and numerical investigation concerning with structural performance of butted joints constructed with wood-polymer members (poly (furfuryl alcohol)) was carried out under combined stresses in comparison with control specimens. The aim of this research was to enhance performance of these joints in outdoor applications especially under combined stress. For investigation of this joints performance, specimens with two different values of furfurylation at 20% and 65% in comparison with control specimens were evaluated. Mechanical properties of specimens were determined according to ASTM D-143 and materials properties were defined by this properties for modeling. Proportional limit of loading value from experimental was compared with result of FEM model. Result of FEM model completely confirmed experimental results and the validation of model was performed well. To understand about joint behavior at FEM model and to predict the fracture reasons, some properties of fracture mechanics related to wood polymer were used.

In regions that are susceptible to earthquake occurrence, designing large and engineering developed structures such as tall buildings, dams and bridges most often requires quantitative dynamic analysis. Engineers discuss important questions on possible magnitude of earthquake in the zones under construction and require knowledge on the movements or the spectrums enforces and/or defining parameters. Time history analysis is the most natural analytical method compatible with the physical behaviors in the course of earthquake in a way that structures are performed by including the effects of earth acceleration as a function of time being applied in the structural base. The accelerograms which are used in analyzing the chronological history in determining the impacts of earth movement must reveal the actual movements of earth in the construction site of the structure during earthquake; As a result, selecting accelerogram is very important in analyzing the chronology. Unfortunately, the point that suitable records must be selected with respect to the conditions that govern seismic source, the geological characteristics, tectonic distance from fault and the largeness of the zone is usually neglected. Our country is located in one of the most active seismic regions in the world. According to the scientific information and documents, Iran is one of the riskiest regions of the world and is exposed to serious damage from earthquake. In the recent years, there has been an earthquake with large physical and financial casualties in one of the regions of the country once every five years in average. Presently, Iran is on top of the list of countries where earthquake is associated with life casualties. It is very difficult to fully prevent damages caused by high magnitude earthquakes. This is especially important in the city of Tehran with the very large population that lives in it, and is encircled by several active faults. The main goal of this research is to prepare a suitable list of remote range strong motion accelerograms to be used in nonlinear analysis in Tehran. The main focus of this research is to study all parameters that are effective in selecting suitable strong motion accelerogram in Tehran and for this purpose, 1000 strong motion accelerograms from earthquakes that occurred in Iran between 1978 through 2007 were studied and the entire parameters effective in selecting suitable strong motion accelerograms for the city of Tehran including distance, magnitude, frequency contents, earthquake mechanism, soil and specifications of earth strata were reviewed. Ultimately, a suitable list of strong motion accelerograms is presented to be used in nonlinear three-dimensional analysis. To achieve this goal, the geological and geotechnique features of the region were studied. In addition, the mechanism of active faults in the region were studied as well and by considering the parameters of magnitude, the focal depth, the distance of registry stations to the earthquake place, the geology studies of the records registry stations, mechanism and the frequency contents of a series of the accelerograms are suggested to reveal the actual movement of earth in Tehran as much as possible; if modeling and chronological history analysis are bi-dimensional, it will be possible to use 28 categories alongside and orthogonal with the faults in the suggested list. It should be noted that to analyze the chronology, only those accelerograms were used which could be scaled with the spectrum of the standard plan of the region and prove compatible with the frequency period of the structure. Minimum moment magnitude in the mentioned list is equal to 5.6 and maximum moment magnitude is 7.4. The mean magnitude in this list is 6.45. The mean maximum earth acceleration for the list was equal to 0.191g. The dominant mean period in the list is 0.64 seconds. The dominant frequency in this collection of accelerogram includes a large frequency range; therefore, suitable stimulation could be anticipated from this list for various structures.

Premature rupture of steel structures in seismic Northridge connections led to investigate the connection performance against the forces of earthquake, many researchers are studied. The performance of these joints and connections against forces caused by various kinds of earthquakes, accurate determination of the used parameters and bearing capacity parameters of connections. The fact that no two earthquakes are similar adds emphasis to adopting a coordinated approach for testing different structural elements. These requirements results in developing standard loading histories called loading protocols. Today, the ever-increasing development of using steel in the construction industry in Iran has become clearly evident. Considering the fact that Iran is an earthquake-prone country, identifying the behavior of these structures against earthquake forces assumed importance. Seven, twelve and twenty-story steel moment frames were selected as research models, and after preparing a proper list of accelerograms recorded in the course of earthquakes occurred in Iran during 1978-2007 , the seismic demands applied to structural components were estimated. Regarding the catastrophic aftermath of earthquakes, having a reliable approach to assess the seismic demands proper to the region of interest seems inevitable. The scope of this study is to provide a list of far-field seismic records applicable to 2-D nonlinear time history analyses in Iran. To do that a set of 2000 seismic records from Iran's seismic records database has been investigated based-on their characteristics, amongst are focal distance, magnitude, rupture mechanism, frequency content, and soil profile, resulting in compilation of a list of 20 accelerograms for the purposes of the two dimensional and non-linear analyses in Iran. The proposed accelerograms portray as a true area’s seismic movement as possible. In continuation of study, the final coefficient of scale for the accelerograms for the steel moment frames is calculated with a point to point differentiation method in periodic intervals corresponding to each frame. For the coefficient of scale, an operation conducted in a way that for each accelerogram in the average spectrum, an appropriate response is determined. Time-history dynamic analysis has been carried out by using the list of proposed accelerogram records aiming at preparing the loading protocol of steel moment connections, and the rainflow cycle counting technique has been employed to determine damage parameters for research models. Considering the fact that strength and deformation capacities depends on cumulative damage in earthquake engineering, every component has a permanent memory of past damaging events and at any instance in time it will remember all the past excursions (or cycles) that have contributed to the deterioration in its state of health. A loading protocol is developed specifically for this purpose.For developing the loading protocol of moment-resisting connections, the time history is analyzed using the proposed set of accelerograms recorded, and by applying the method of rainflow cycle counting, damage parameters are determined for the research models. The number of damaging cycles, total deformation range, deformation range and peak of deformation range are the employed parameters, which will be evaluated and compared for all the layers of the research models. Afterwards, statistical estimations are performed on damage parameters and target values are established. Finally, a loading protocol is recommended for moment-resisting joints commonly used in Iran which has the capacity of being applied to the considered structural elements under one general state.

Major earthquakes that have occurred in recent years have shown that beam to column connections are the main focus in lateral force transference in steel moment frame structures. Over the past years, much research on the seismic behavior of steel moment connections has been performed in order to determine the behavior of joints. Studies agree that in frame analysis, joint rotational behavior should be considered. This is usually done using the moment-rotation curve. Models, such as analytical, experimental, mechanical and numerical, can be used to determine joint mechanical behavior. The most common is the mechanical model, with several variances. In this study, a summary is given on each model characteristic.In this paper, the seismic performance of an I-shaped beam to box-column steel connection with top and seat plates was studied using the component method. In the context of the component method, whereby a joint is modeled as an assembly of components and rigid links, concentrating on beam-to-column and beam-to-beam joints, several components contribute to the overall response of the connection. Despite the complexity of the various connection types, the proposed model is able to provide analytical solutions for the moment-rotation response of a steel connection using appropriate transformation criteria for the assembly of components in series and/or in parallel. Also, in order to evaluate the behavior of the connection in a vast range of nonlinear behavior, a modified Ibarra-Krawinkler deterioration model is used. The correctness of results was examined by comparing the moment-rotation and force-drift curves of the beam to column connection with the top and seat plates, which were obtained by the component and experimental methods.Results show that moment-rotation and force-drift curves obtained by the component and experimental methods are reasonably close to each other; proving the correctness of the above method in evaluating the seismic performance of the connection.

Shape Memory Alloys (SMA) are smart and novel materials that exhibit variable stiffness and strength associated with their different polycrystalline phases. The Shape Memory Effect (SME) and Superelastic Effect (SE) are two distinct properties that make SMA a smart material. Shape memory effect (free recovery effect) means that a large (pseudo-) plastic deformation can be reversed by heating. If the going back is prevented by, e.g., concrete, a stress in the SMA results (constrained recovery effect) [1]. A Superelastic SMA can restore its initial shape spontaneously even from its inelastic range upon unloading.
The specific objective of this study is to investigate the effect of ordinary and pretension SMAs with memory effect behavior in concrete shear walls separately. For this purpose, we analyzed concrete shear walls with different percent of SMAs and steels under monotonic loading in ABAQUS Finite element. Two different concrete shear walls, one reinforced with ordinary SMA together with steel rebars and the other with pretension SMA with steel rebars, have been analyzed. The seismic behavior of the two concrete structure models has been compared in terms of their load against displacement.