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In the past decade design procedure changed to �performance-based design� from�force-based design�, by this mean many researchers focused on nonlinear static analysis (NSA)and the procedure named �PUSHOVER�. Advantages of this method are defining the inelasticbehavior of structure without nonlinear dynamic analysis (NDA) effort and also defining plastichinges formation in critical elements, and the order of formed plastic hinges. In spite of these goodadvantages NSA is limited to short and planar structures and application of that in tall andtorsionaly asymmetric structures may yield unreliable results.In this study reliability of NSA is investigated by performing both nonlinear static and dynamicanalysis on six 2D moment resisting concrete frames. Non linear dynamic analysis has been doneby the suggested method in FEMA356 guideline called �Target Displacement Method�. A groupof 4 different lateral increasing loads were used in pushover analysis and 3 different groundmotions were applied in NDA. Results indicate that same responses can be obtained by performingNSA, but errors will be increased by frames height increment.

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In this paper a general procedure for automated minimum weight design of twodimensional steel frames under seismic loading is proposed. The proposal comprises two parts: a) Formulation of automated design of frames under seismic loading and b) introduction of an optimization engine and the improvement made on it for the solution of optimal design. Seismic loading, that depends on dynamic characteristics of structure, is determined using "Equivalent static loading" scheme. The design automation is sought via formulation of the design problem in the form of a standard optimization problem in which the design requirements is treated as optimization constraints. The Optimality Criteria (OC) method has been modified/improved and used for solution of the optimization problem. The improvement in (OC) algorithm relates to simultaneous identification of active set of constraints and calculation of corresponding Lagrange multipliers. The modification has resulted in rapid convergence of the algorithm, which is promising for highly nonlinear optimal design problems. Two examples have been provided to show the procedure of automated design and optimization of seismic-resistant frames and the performance and capability of the proposed algorithm.

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The main aim of this paper is to extend the recently developed methods for calculating the buckling loads of planar symmetric frames to include the effect of semi-rigidity of the joints. This is achieved by decomposing a symmetric model into two submodels and then healing them in such a manner that the :::union::: of the eigenvalues of the healed submodels result in the eigenvalues of the entire model. Thus the critical load of the frame is obtained using the eigenvalues of its submodels.

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The objective of this paper is to present a new method for protecting the lives of residents in catastrophic earthquake failures of unreinforced masonry buildings by introducing some safe rooms within the buildings. The main idea is that occupants can seek refuge within the safe rooms as soon as the earthquake ground motions are felt. The information obtained from the historical ground motions happened in seismic zones around the globe expresses the lack of enough safety of masonry buildings against earthquake. For this potentially important reason, an attempt has been made to create some cost-effective seismic-resistant areas in some parts of the existing masonry buildings, which are called safe rooms. The practical method for creating these areas and increasing the occupant safety of the buildings is to install some prefabricated steel frames in some of their rooms or in their halls. These frames do not carry any service loads before earthquake. However, if a near field seismic event happens and the load bearing walls of the building destroy, some parts of its floors, which are in the safe areas, will fall on the roof of the installed frames consequently, the occupants who have sheltered in the safe rooms will survive. This paper expresses the experimental and theoretical work executed on the steel structures of the safe rooms for bearing the shock and impact loads. Finally, it was concluded that both the strength and displacement capacity of the steel frames were adequate to accommodate the distortions generated by seismic loads and aftershocks properly.

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Pullback test has no scrupulous theoretical establishment. It is based on the hypothesis that the response of

the structure can be related to the response of an equivalent single degree-of-freedom (SDOF) system. This implies that

the response is controlled by a single mode. In fact, the steel frame of each safe room, which is introduced within the

unreinforced masonry buildings for protecting the lives of residents in catastrophic earthquake failures, contains a

SDOF structural system. In pullback test, the steel frame carries its gravity load first, and then it will be pushed under

an incremental lateral roof displacement pattern, which is imposed to its center of mass. This paper expresses the

results of 13 pullback tests executed by the authors on the steel frames of safe rooms. The results show that pullback

test is a practical method for seismic performance evaluation of safe rooms. Also the performance of these frames

located in a collapsing three storey masonry building is presented with favorable conclusions. In fact, the results of

pullback test of the safe room located at the ground-floor level were compared with the requirements of Iranian code

for seismic resistant design and it was concluded that the steel frame had an acceptable performance against seismic

effects.

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In this paper, the problem of layout optimization for X-bracing of steel frames is studied using the ant system (AS). A new design method is employed to share the gravity and the lateral loads between the main frame and the bracings according to the requirements of the IBC2006 code. An algorithm is developed which is called optimum steel designer (OSD). An optimization method based on an approximate analysis is also developed for layout optimization of braced frames. This method is called the approximate optimum steel designer (AOSD) and uses a simple deterministic optimization algorithm leading to the optimum patterns and it is much faster than the OSD. Several numerical examples are treated by the proposed methods. Efficiency and accuracy of the methods are then discussed. A comparison is also made with Genetic algorithm for one of the frames.

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 From the time that civil engineers have used steel in building structures, they tried to increase its strength so as to produce more economic and lighter structures by using more elegant sections. Increase of steel strength is not always useful for all members of a steel structure. In some members under certain conditions, it is needed to reduce the strength as much as possible to improve the behavior of structure. By using very low strength steel according to the Easy-Going Steel (EGS) concept in this research, it is shown that the performance of diagonal Eccentrically Braced Frames (EBFs) improves substantially. For this purpose, a finite element analysis was used to simulate diagonal eccentrically braced frames. Fifteen diagonal eccentrically braced frames were designed through AISC2005. By substitutingvery low strength steelinstead of carbon steel with equal strength in the links, their performance improve fundamentally without any global or local instability in their links.

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Inelastic deformation of structural components is generally acceptable in seismic design. In such behavior, the strength of structures increases while plastic hinges are formed in members frequently. The strength revealed during the formation of plastic hinges is called "overstrength". Overstrength is one of the important parameters in the seismic design of structures. The present study tries to evaluate the overstrength of the concentrically steel braced frames (CBFs), considering reserved strength, because of members post-buckling. As such, a static nonlinear (pushover) analysis has been performed on the model buildings with single and double bracing bays, different stories and brace configurations (chevron V, invert Vand X-bracing). It has been realized that the number of bracing bays and the height of buildings have a low effect on reserve strength due to brace post-buckling. However, these parameters have a profound effect on the overstrength factor. These results indicate that the overstrength values for CBFs, proposed in seismic design codes, need to be modified.

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The objective of this paper is to determine the drift demand hazard curves of steel moment-resisting frames with different number
of stories in territory of Tehran this is done through the combination of the results obtained from probabilistic seismic hazard
analysis and the demand estimated through the best probabilistic seismic demand models. To select the best demand model, in
this paper, a Bayesian regression has been used for the statistical analysis of the results obtained from incremental dynamic
analysis in order to estimate the unknown parameters of model and to select the best Intensity Measure (IM) parameter also the
probability of overall collapse of structures has been computed. Considering the efficiency and sufficiency of the models, the
results indicate that the accuracy of models with one single IM is a function of the number of stories, consequently the current
widely used model with spectral acceleration in first period as IM is not suitable for all structural heights. Furthermore,
regarding the fact that it is difficult to prepare a seismic hazard curve for a combined IM, it seems that the best model can be
found among models with two single IMs. In other words, the best model to cover all structural heights is the one with linear
combination of spectral acceleration of the first and the second period. Furthermore, using different models to calculate the
curves shows that regardless of the number of IMs, estimated demands strongly depend on the standard deviation of model.
 

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This article presents the application of two algorithms: heuristic big bang-big crunch (HBB-BC) and a heuristic particle swarm

ant colony optimization (HPSACO) to discrete optimization of reinforced concrete planar frames subject to combinations of

gravity and lateral loads based on ACI 318-08 code. The objective function is the total cost of the frame which includes the cost

of concrete, formwork and reinforcing steel for all members of the frame. The heuristic big bang-big crunch (HBB-BC) is based

on BB-BC and a harmony search (HS) scheme to deal with the variable constraints. The HPSACO algorithm is a combination of

particle swarm with passive congregation (PSOPC), ant colony optimization (ACO), and harmony search scheme (HS)

algorithms. In this paper, by using the capacity of BB-BC in ACO stage of HPSACO, its performance is improved. Some design

examples are tested using these methods and the results are compared.

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In this paper a discrete Big Bang-Big Crunch algorithm is applied to optimal design of reinforced concrete planar frames under

the gravity and lateral loads. Optimization is based on ACI 318-08 code. Columns are assumed to resist axial loads and bending

moments, while beams resist only bending moments. Second-order effects are also considered for the compression members, and

columns are checked for their slenderness and their end moments are magnified when necessary. The main aim of the BB-BC

process is to minimize the cost of material and construction of the reinforced concrete frames under the applied loads such that

the strength requirements of the ACI 318 code are fulfilled. In the process of optimization, the cost per unit length of the sections

is used for the formation of the subsequent generation. Three bending frames are optimized using BB-BC and the results are

compared to those of the genetic algorithm.

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A new type of infilled frame has been recently proposed. It has a frictional sliding fuse, horizontally installed at the mid-height of the infill. It has already shown that such infilled frames have higher ductility, strength and damping ratio as well as more enhanced hysteresis cycles, compared with regular infilled frames. This experimental paper is focused on the influence of gravitational load on the behaviour of the fused infill panel. Furthermore, a repairing method in which damaged specimens are repaired by grout plasters is also studied. The results show that the gravitational load, applied to the surrounding frame of the infill for the dead or live loads, arises the ultimate strength of the fused infill specimens. It is also shown that repairing the failed specimen by grout was so efficient that the repaired specimen had greater strength than the original one. However, top gap, between the infill and the top beam of the enclosing frame should be absolutely avoided, because it decays the ultimate strength.

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The seismic behavior of frame bridges is generally evaluated using nonlinear static analysis with different plasticity models hence this paper tends to focus on the effectiveness of the two most common nonlinear modeling approaches comprising of concentrated and distributed plasticity models. A three-span prestressed concrete frame bridge in Tehran, Iran, including a pair of independent parallel bridge structures was selected as the model of the study. The parallel bridges were composed of identical decks with the total length of 215 meters supported on different regular and irregular substructures with non-prismatic piers. To calibrate the analytical modeling, a large-scale experimental and analytical seismic study on a two-span reinforced concrete bridge system carried out at the University of Nevada Reno was used. The comparison of the results shows the accuracy of analytical studies. In addition, close correlation between results obtained from two nonlinear modeling methods depicts that the lumped plasticity approach can be decisively considered as the useful tool for the nonlinear modeling of non-prismatic bridge piers with hollow sections due to its simple modeling assumption and less computational time.

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High performance and reliability of refurbish able knee braced steel frames has been confirmed in previous researches trying to get an optimal design for its configuration. Buckling of diagonal member which affects the hysteretic behavior of KBF under cyclic loadings has not been foreseen in previous evaluations of this system. This deficiency can be improved by utilization of adjustable rotary friction damper device (FDD) as knee element. Diagonal element buckling can be prevented considering a suitable value for FDD sliding threshold moment Mf. Lower values of Mf Lower energy dissipation rate in FDD and this leads to an optimization problem. Nonlinear time history analyses have been performed in addition to lateral cyclic loading analyses to evaluate the response of single story KBF subjected to seismic excitation. Optimal Mf in FDD has been chosen according to these analyses results. Roof displacement and acceleration, base shear and diagonal element’s buckling status have been compared in optimally designed KBF and FDD utilized KBF (FKBF) with different configurations. Nonlinear dynamic analyses have been performed for one, four, eight and twelve story frames under different seismic records with several PGAs. More than 60% displacement response reduction has been earned for the FKBF without considerable increase in base shear.

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Well-known seismic design codes have offered an alternative equivalent static procedure for practical purposes instead of verifying design trials with complicated step-y-step dynamic analyses. Such a pattern of base-shear distribution over the building height will enforce its special stiffness and strength distribution which is not necessarily best suited for seismic design. The present study, utilizes a hybrid optimization procedure to seek for the best stiffness distribution in moment-resistant building frames. Both continuous loading pattern and discrete sizing variables are treated as optimization design variables. The continuous part is sampled by Harmony Search algorithm while a variant of Ant Colony Optimization is utilized for the discrete part. Further search intensification is provided by Branch and Bound technique. In order to verify the design candidates, static, modal and time-history analyses are applied regarding the code-specific design spectra. Treating a number of building moment-frame examples, such a hyper optimization resulted in new lateral loading patterns different from that used in common code practice. It was verified that designing the moment frames due to the proposed loading pattern can result in more uniform story drifts. In addition, locations of the first failure of columns were transmitted to the upper/less-critical stories of the frame. This achievement is important to avoid progressive collapse under earthquake excitation.

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This paper describes experimental and numerical investigations on two specimens of frames composed of steel reinforced concrete beam and angle-steel concrete column under horizontal low cyclic loading. Based on the test results, the relationship curves of the horizontal load-displacement and the failure modes are acquired. Meanwhile the hysteretic behaviors, skeleton curves, stiffness degradation, energy dissipation, residential deformation of the two specimens are studied. Nonlinear structural analysis program OpenSEES is employed to predict the experimental curves. Using the verified numerical model, the influences of slenderness ratio, axial compression ratio, steel ratio of column, cross-section moment resistance of I-shaped steel in beam, ratio of longitudinal rebars of beam and prestressing level on skeleton curves are investigated. The results indicated that the two specimens exhibited the favorable ductility and energy dissipation capacity, and the beam depth could be reduced to improve service function because of the application of the prestress. The ultimate horizontal load decreases with the increase of column slenderness ratio, and firstly increases then decreases with the increase of axial compression ratio. In the meantime, the descent segment of skeleton curve is smooth with the increase of column slenderness ratio, and becomes steeper with the increase of axial compression ratio.

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The linear and nonlinear responses of steel buildings with perimeter moment resisting frames (PMRFs) are estimated and compared to those of equivalent buildings with spatial moment resisting frames (SMRFs). The equivalent models with SMRFs are designed by using an approximated procedure in such a way that, not only their fundamental period, total mass and lateral stiffness are fairly the same as those of the corresponding buildings with PMRFs, but also other characteristics to make the two structural "as equivalent" as possible. The numerical study indicates that the interstory shears of the PMRFs building may be significantly larger than those of the SMRFs building. The main reasons for this are that the buildings with PMRFs are stiffer and that the dynamics properties of the two types of structural systems are different. The interstory displacements are similar for both structural systems in many cases. For some other cases, however, they are larger for the model with SMRFs, depending upon the closeness between the earthquake corner periods and the periods of the buildings. The global ductility and story ductility demands are larger for the buildings with PMRFs, implying that, since larger ductility demands are imposed, the detailing of the connections will have to be more stringent than for the buildings with SMRFs. It can be concluded, that the seismic performance of the steel buildings with SMRFs may be superior to that of steel buildings with PMRFs. The findings of this paper are for the particular models used in the study. Much more research is needed to reach more general conclusions

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In this paper, an approximate method is proposed for determining sway of multistory RC buildings subjected to various types of lateral loads. The calculation of both fundamental period and stability index in RC building requires the sway term at each story level. Using approximate method design engineers can estimate sway terms at each story level. The developed analytical expressions are inserted into fundamental period and stability index equations to replace the sway terms, which yields modified equations for fundamental period and stability index without any sway terms. It is fairly easier to employ these equations developed by eliminating all sway terms. Results obtained from the equations are remarkably close to those generated by the related computer program. Consequently, design engineers can reliably use the simple equations to calculate stability index and fundamental period, which enables the determination of these parameters without referring to the complex sway terms. The capability and accuracy of the proposed equations are demonstrated by a numerical example in which computer program results are compared with the proposed methodology.

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The paper presents a parametric numerical study on the horizontal load-bearing capacitiy of timber framed wall elements coated with single fibre plaster boards (FPB) that can be used in the construction of single- or multi-storey prefabricated buildings. The research deals with both the full elements (without any opening) and with elements containing an opening. The key behaviour indicators like the racking stiffness and strength were determined and presented as ratios dependent on the opening area. A comparative study has proved that none of the methods from the literature that were previously developed for different types of wall elements can be accurately applied to the FPB-sheated panels. It has also been shown that the methods currently available in the European design codes underestimate the capacity of wall elements with openings. Based on the results some diagrams are proposed that enable quick and efficient determination of the essential properties of wall elements with arbitrary areas of openings and may thus represent a useful tool for the structural design process.

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Steel plate shear walls have long been used as a lateral load resisting system. It is composed of beam and column frame elements, to which infill plates are connected. This paper investigates the progressive collapse-resisting capacity of 50-story building 3D model of the strip model of steel plate shear wall comparing with X-braced and moment frame system based on the removing structural elements from a middle and corner of the exterior frame, in the story above the ground. The collapse behavior is evaluated by different nonlinear static and dynamic analyses using conventional analysis software. In this study, vulnerability of structures is also assessed by sensitivity index (SI) regarding the sensitivity of structures to dynamic effect induced by progressive collapse. To identify vulnerable members, resulting actions of nonlinear static analysis, considering load factor to account for dynamic effect, at the failure mode of structure at the specific performance level are compared by the factor of redundancy related to overall strength of structure, with the linear static analysis of damaged model without considering dynamic effect,. Comparing analysis results indicated that in the steel plate shear wall system, the progressive collapse resisting potential is more than X-braced and moment frame. Sensitive index of highly sensitive elements to dynamic effect stated that in the structural models, beams are more vulnerable in moment frame than X-braced frame and SPSW structure, significantly, and vulnerability of columns in X-braced frame and SPSW system is more than moment frame.