نشریه مهندسی سازه و ساخت
سال هشتم شماره 3 (پیاپی 41، خرداد 1400)

Space structures, especially double-layer caskets, have been widely used to cover large spaces. Due to the large number of members and joints in space structures, choosing the appropriate form and modulation has a great impact on weight loss and thus reduce the cost of the structure. On the other hand, the minimum weight does not always mean that the structure is economical, and other parameters such as the number of connection nodes, the number of members and also the amount of material wasted will have a significant impact on the final cost of the structure. The purpose of this paper is the economically optimal design of two-layer cast iron space structures based on the study of various parameters such as the weight of the structure, the best shape and the ratio to the opening of the cast iron. For this purpose, 28 models in common forms of this type of structures with two-way and oblique networking in different modulations of 2 and 3 meters and in the ratio of openings between 0.2 to 0.5 in Formian software and then models under different combinations of code loading regulations , Analyzed and designed in SAP2000 software. In the following, the forms that have violated the constraint of resistance or displacement have been discarded and the economic comparison of the approved forms with considering the number of nodes and excess members in each model has been discussed in order to influence the form, member modulation and span ratio in Optimize the weight and how it is distributed between the columns and members of the network and the cost of this type of structures to be shown and the best model with the most economical to be determined as an engineering design. The results show that the two-way form on the two-way with a modulation of 3 meters and a ratio of 0.3 span compared to other forms studied, significantly reduces the cost of the design and is the most economical design.

The purpose of this study is to investigate the effects of adding nanosilica and microsilica on the mechanical properties of cementitious composites containing polypropylene fibers. For this purpose, 13 composite mixes with the water to cement ratio of 0.28 were considered. One mix without microsilica and nanosilica, 4 mixtures with 0.5%, 1%, 3% and 5% nanosilica replacement levels, 4 mixes with 5%, 7%, 10%, 15% of microsilica, and 4 mixtures with the combination of microsilica and nanosilica were investigated. According to the results of the experiments, the composite samples containing microsilica and nanosilica had better results than the samples containing only one of these particles. In fact, the results of 28-day tests showed that the combination of 10% microsilica and 1% nanosilica produced the best cementitious composite according to compressive, tensile and flexural tests.The compressive strength was 61.32 MPa, which was 44.69 percent higher than the control mix, the tensile strength was 4.319 MPa with 34.88 percent improvement, and the flexural strength was 6.971 MPa with 30.37 percent improvement from the control mix. Using more than 3 percent of microsilica had negative effects in all circumstances comparing to the control mix. For example, the ones containing 5 percent of nanosilica and without microsilica had the compressive strength of 37.41 MPa, which was 11.72 percent lower than the control mix.

Plastic waste control has always been a major concern in many countries. The amount of these substances increases every year due to continued public consumption. Given the high cost of plastic recycling in developing countries, returning these materials to the industry for the production of building materials can be a viable solution to protect the environment. Since concrete is one of the most widely used composite materials in the building industry, it, therefore, provides a suitable base for the utilization of plastic waste. In this research, different plastic granules are replaced with a certain amount of fine natural aggregates, and the physical and mechanical properties of the concrete made from these materials are evaluated by necessary tests. The target plastics are Polypropylene, High Impact Polystyrene, and Polyethylene terephthalate. The size and aggregation of the mentioned fine plastic particles are similar, replacing the sand with 15% and 30% by weight. The results show that the mechanical properties of the concrete decrease as the amount of substituted plastic aggregates increases. However, among the concrete made with plastic aggregates, the one which contains High Impact Polystyrene, has the best performance. In addition, the workability of the concrete was improved by increasing the amount of plastic aggregate present in the concrete. However, in the concrete containing Polyethylene terephthalate, this index declined. Also, among the physical and mechanical properties of concrete, flexural strength and ultrasonic pulse velocity of concrete were the most varied, but the compressive and tensile strength and workability have undergone fewer changes.

In this investigation, the Al sheet metals Al3105, Ck45 and St12 with layers under impact drop test free loading are tested experimentally and numerically. The sheets are tested with 3-layers under impact free loading numerically. for comparing, the experimental test is tested. The height is 12 cm with free impact loading. The dimention of specimens are 220*230 cm2. with screw the specimens are tied. The fixure are maded with steel and the specimens are fixed on the ficture freely. The screew has Din933 standard. The acceleration data are repoted with accelareation sensor. The deformation are reported with hammer test. Also with theoretical method, the shells are invetigated with the dynamic equations. For numerical modeling, the ABAQUS is used. The resualts are shown that two method are the same resulats. Also the resualts are shown that the energy absorption is more for Al3105-St12-Al3105 to other sheets. Also the acceleration is more for Ck45-St12-Ck45 to other sheets. The acceleration data are repoted with accelareation sensor. The deformation are reported with hammer test. Also with theoretical method, the shells are invetigated with the dynamic equations. For numerical modeling, the ABAQUS is used. The resualts are shown that two method are the same resulats. Also the resualts are shown that the energy absorption is more for Al3105-St12-Al3105 to other sheets. Also the acceleration is more for Ck45-St12-Ck45 to other sheets.

Self-compacting concrete is one of the most High potential Concrete Currently available due to its wonderful fresh and hardened properties. fresh properties of concrete include the ability to pass, flow and stability, and with these properties will increase the efficiency of self-compacting concrete in all stages from making to utilization. One of the most important wastes in the steel industry is the electric arc furnace slag and one of its applications is the use as aggregate in concrete .The steel slag of Khuzestan Steel Company consists of fine and coarse aggregates, and in this research we first seek to design a suitable mix of self-compacting concrete And then we replace the amounts of coarse and fine slag by 10% incrementally as long as the concrete remains self-compacting. Replacement of coarse and fine slag has been possible up to 30%. fresh concrete tests include slump flow, V Funnel, J-ring and L-box which is evaluated according to the EFNARC guideline.. Hardened concrete tests include compressive and Split tensile strength performed on standard cubic and cylindrical specimens after curing saturation of concrete at 3,7,28 days. Replacement of coarse slag up to 30% improves hardened concrete properties, But slight decrease in fresh properties. By modifying the mix design and the use of super plasticizer to 3% by weight of cement The coarse slag has been 100% replaced by coarse aggregate and has achieved good fresh and hardened results. Replacement of fine slag by 10% of fine particle is the most optimal condition for fresh and hardened concrete properties, And replacing more than this percentage will greatly reduce the fresh and hardened properties.

In most structural codes, the drift capacity of masonry walls is an estimated of the structural behavior and the aspect ratio. In this paper, the determination of the drift capacity considering the effect of parameters such as lateral constraints, geometries, dimensions, and pre-compression for the Persian historic brick masonry was studied. Hence, the behavior of 64 different specimens of masonry walls under in-plane loading with four different modes of lateral constraints (under the effect of lateral walls and ceiling), four different aspect ratios (height to length) and six different boundary conditions (under the effect of lateral walls and ceiling), three values for the wall thickness and two values for the pre-compression (According to the load applied by one or two ceilings) were studied by nonlinear numerical analysis. After preparing the force-displacement curves, in order to obtain simplified parameters that are easily comparable and usable for design purposes, bilinear behaviors were idealized (linear elastic, perfectly plastic). The results showed that by increasing the lateral constraints, wall thickness and pre-compression, the drift capacity of the walls decreased, whilst the drift capacity increases by increasing the height-to-length aspect ratio. In addition, it was observed that the lateral walls (vertical components) were more effective in reducing the displacement capacity than the ceiling (horizontal component). In conclusion, according to numerical calculations, the value of drift capacity for the Persian historic brick masonry was found to be 1.33% to 2.63%.

Among the weaknesses of moment connections in large earthquakes were the damage of the connection’s elements and main components of the structure, such as the column, prior to the failure of other members, which causes the total collapse of the structure. Therefore, it is necessary to introduce a moment connection system which dampens the earthquake induction energy well, without damaging the main elements of connection and main structural members. Also, another reason for the low resistance of structures against large earthquakes is the inappropriate function of materials under stress. Therefore, in this study, the seismic performance of steel beam-column end-plate connection using corrugated sheets in I-section and nanotechnology in materials is investigated. The variables studied consist of three types of sheets in the web section (plan, corrugated), three types of sheet’s thicknesses and two types of material properties (St 37 and nanoparticles). Thus, 18 numerical models with similar dimensions, properties and lengths are simulated with the finite element method using Abaqus software. In most of the cases studied, increasing the thickness of the web’s sheet leading to an increase in the energy absorption of the investigated samples. Also, by increasing the thickness, the values of stresses in most samples decreased, However, in the samples with trapezoidal geometries by increasing the thickness from 10 mm to 20 mm, the stress values were increased. According to the results of this study, increasing the thickness of structural elements does not always lead to a decrease in the stress values applied to the structure and the geometrical shape of the element is very effective in the stress values.

The effect of masonry walls on the behavior of steel frames is one of the important issues of seismic response of structures. In this experimental study, the behavior of steel frames with masonry infill walls has been investigated and the effect of brick type, wall thickness, and wall openings has been evaluated. Seven 1:3, single-span and one-floor steel frame specimens were tested under the influence of quasi-static loading. All specimens except one had an infill wall. In these samples, three types of brick materials, two types of thickness and two types of openings were tested and evaluated. The bricks used in the infill walls were non-perforated clay bricks, perforated clay bricks and common lightweight clay blocks in Iran. The type and dimensions of openings were also adjusted according to the common dimensions used in a variety of buildings. The results show that the type of materials used in the infill walls, the wall thickness and the presence of openings have a significant effect on the seismic behavior of the structures. The infill wall significantly reduces structural ductility, while increasing its stiffness and ultimate strength. Therefore, in moderate to strong earthquakes, the infill wall has a negative effect on the structural behavior. In addition, the infill wall increases strain due to the imposed of localized deformation in the frame members. However, it reduces the strain on the panel zone.

Investigating the potential of soil liquefaction plays an important role in reducing earthquake damages. Prediction of this phenomenon is difficult due to the complexity of the nature of soil and earthquakes. Previous studies had many errors that include inaccurate modeling, inadequate databases and disregarding the uncertainties that are caused by soil and earthquake complexity. In this research Bayesian inference method is used as a probabilistic modeling method. This method used a comprehensive database of standard penetration test (SPT). For the first time, first-order reliability method (FORM) and importance sampling method were used to estimate the probability of failure and the reliability index of the limit state function of liquefaction. Then with the help histogram sampling, probability density function (PDF) and cumulative probability function (CDF) were obtained to investigate the probability of transgression. A sensitivity analysis of the model was also performed to estimate the most effective parameters. As a result of this study, a robust and efficient probabilistic model was developed to evaluate the liquefaction potential of soils. Comparing the results of this probabilistic model with other deterministic and probabilistic models showed a significant reduction in model uncertainty and standard deviation, increased accuracy and a better understanding of the relationship between failure probability and safety factor of liquefaction. Monte Carlo sampling and importance sampling methods were closed to each other. In the sensitivity analysis of the proposed model, the uncertainty of the magnitude of the earthquake parameter was identified as the most important uncertainty of the model.

Today, the importance of construction costs in construction projects is increasing day by day and it is necessary to study the estimation of construction costs and the factors affecting construction costs.This research has been done around the subject of estimate the construction costs by intelligence data driven methods named Artificial Neural Network (ANN), Support Vector Machine (SVM) and Gene Expression Programming (GEP) determine the effective factors on cost and cost optimization in east of Tehran. To estimate the costs of residential buildings, in this research it's used from 46 residential buildings which were implemented in west of Tehran and it's used from the artificial intelligence method to estimate the construction costs that is used from ANN, artificial neural network method, GEP, SVM and it was used from questionnaire and Friedman test method to diagnosis the effective factors on costs to prioritize factors that can optimize the costs by possessing these two factors, the effective factors on costs and construction costs estimation . After reviews and studies we resulted that costs estimation had been done by ANN, GEP, SVM methods and by comparing these methods, GEP cause of its less errors and more predictability, was the best method than others. The effective factors on costs were determined by Friedman test method that after reviews these factors, construction costs had been optimized.

These days a lot of dangers threaten the construction structures. Many abnormal loads are not considered in the design of structures. The column sudden removal can occur due to the errors during construction, explosion, shock or any other abnormal causes in the structure. If the structural response leads to a rebalance during the sudden column removal, this causes the structure to remain safe, and if the force balance is not created in the structure, it can cause Progressive Collapse (PC) in the structures. Structures are not designed toward PC scenarios, such as the sudden column removal. The assessment of structures behavior in PC scenario lead to a correct understanding about the resistance of structures in these scenarios. This research investigated the behavior and response of braced steel structures to the sudden column removal using the alternate load path method and nonlinear static and dynamic analysis. For this purpose, the 10 and 20-story structures were modeled nonlinearly by OpenSees software after the initial design and they are subjected under sudden column removal. Static and dynamic pushdown curves of the structures are considered as a criterion to assess the behavior of structures. The results showed that not only the type of braces is effective on the behavior and response of the structures during the PC scenario, but also the geometry of bracing in this scenario is.

Concrete shear walls has improved stiffness and ductility of moment frame systems in tall buildings,but high weight acheaved system can produce foundation engineering problems in loos coastal soils;An appropriate choise is substituting this shear walls with buckling restrained braces (BRB),have less weight and provide appropriate ductility and stiffness.In seismic design of structures3 models of 15, 25 and 35 floors in two systems Special reinforced concrete momment frame and special reinforced concrete momment frame equipped with buckling restrained brace ,also has lighter sections,desinged In accordance with the norms of Iranian design codes. After the sections are finalized in etabs 2016,3d models has been dane in opensees And by choosing a number of appropriate accelerometers compatibled with the region incremental Nonlinear Dynamic Analysis done. most of the floors drift Was considered As a demand parameter. By selecting the HAZUS relative displacement capacity Quadruple seismic performance damage levels (slight, moderate, extensive and complete) fragility curves produced. In higher rise models Fragility is more evident and median fragility difference increases from 0 in slighe damage level up to 0.13g in complete damage level in 3 type of building models that shows better Seismic performance in special brb moment systems than ordinary special moment frame systems.

Implementing as the key phase of a construction project is always at risk that contractors execute an important role in managing them. The process of evaluating and selecting contractors are important, and considering the various and sometimes intricate and complex criteria, the challenges of entrepreneurs must be addressed. In current methods, selection is done on the basis of price bids and other qualitative and quantitative criteria do not influence this choice, which is causing problems in choosing the right contractor. The aim of this research is to improve and provide a method for selecting contractors in the South Zagros Oil and Gas Production Company by identifying and presenting a model using a multi-criteria decision making method for simultaneous use of all criteria in contractor selection. For this purpose, the effective criteria in the selection of construction contractors were identified through a literature review and interviews with experts. The study population consisted 125 staff members of engineering and construction, contracts, business, legal, technical departments and operations. In this research we used SWARA method to weighting the identified criteria. The selection of the contractor was also done using the proposed model and the COPRAS method. In the proposed model, the proposed price criterion was negative and other criteria were positive, and the best contractor has been selected. It is hoped that the proposed model and research results to help in the selection of the contractor of the proper at South Zagros.

Due to occurrence of plastic deformations in horizontal link beam in Eccentrically Braced Frames (EBF), Performance of structure after Earthquake is disrupted and replacement of horizontal link beam is time consuming and need to cost. Using vertical link beam is one of the solutions to expedite structural performance after earthquake. Double vertical links are one of the new methods in EBFs that have been considered by the researchers. The aim of this paper is assessment of EBFs with longer links with flexural-shear interaction and flexural response and improvement of behavior with adding infill plate between two vertical link beams. For this reasons, after verification of modeling using finite element software, 6 specimens have been modeled in software with different specifications like vertical link beam length, infill plate and yield stress of infill plates. Initial assessments of models are carried out using nonlinear static analysis to more insight of response and changes in behavior. Thickness of infill plate is selected based in occurrence of plastic deformations in vertical link beams and avoid brace buckling during static nonlinear analysis. After nonlinear static analysis, cyclic loading is applied to 6 model based on AISC loading protocol. From cyclic loading of structures some crucial curve and parameters is extracted in different drift ratio like cyclic force, push curve, dissipated energy, secant stiffness, equivalent damping ratio. The results show in the frames with flexural-shear interaction response of link beams and infill plate, stable force displacement is observed under cyclic loading until drift ratio between 0.05 and 0.06 and for frames with flexural response of link beams and infill plate, stable force displacement is observed under cyclic loading until drift ratio between 0.06 and 0.07.

Effects of dynamic interaction between substation equipment in multi-connected systems on seismic response has been investigated. Also, influence of record to record and intensity variability on interaction results is studied. Three dimensional models of four vulnerable types of equipment including surge arrester, current transformer, circuit breaker and disconnect switch are developed and verified. Six different systems of equipment connected through rigid bus bars comprising of two, three and four equipment are considered. Incremental dynamic analysis is carried out on models using three-component records. Ratio of maximum responses in connected condition to those in unconnected condition has been utilized as interaction measure. Considering more than two-connected equipment and using three dimensional models are novelties of this paper. Importance of considering more than two-connected equipment has been demonstrated. It is found that for equipment in which contribution of higher modes on responses are notable, variation of ground motion features such as frequency content have more effect on interaction results than equipment in which natural frequency is dominant on responses. It is concluded that variability of record has more significant influence on interaction results than variation of seismic intensity. Differences in response ratios were higher at low intensities as compared to high intensity levels. High stiffness of connector at low intensities is the main reason for this result.

The use of FRP and other composite materials as bar or sheets is one of the most technically and economically viable options in the construction, refurbishment, and reinforcement of structures such as concrete structures. One of the most important issues to consider when using such materials is their bond strength to structural concrete. In this paper, the effect of combining ensemble prediction models with single estimation models on improving the results of single models is estimated to estimate the bond strength of GFRP bars to concrete. To this end, neural networks with predictive results inputs are first used to estimate the bond strength of GFRP to improve the best model result from the two previous models- Be. Then, by considering the prediction outputs of the first neural network model and the best single model above mentioned as input, the neural networks are again used to present a better model than the first ANN model. The final results show the reduction of the prediction error of the ANN model combined with single and ensemble methods compared to the single models previously presented, the weighted average output model of the two single models above and the ANN model. The combination of the two models usefulness a single.

In structural engineering, it is vital to design structures by providing pre-defined performance objectives economically. Reliability-based design optimization (RBDO) is looking for the best balance between safety and cost, by considering uncertainties in structural parameters and loading conditions. In recent decades, several methods have been used to solve RBDO problem. However, most of these methods suffer from high computational cost of solving the problem as a big challenge.In this paper, weighted simulation method, one of the newest and most effective methods for simulation-based reliability assessment methods, has been used for reliability analysis and evaluation of probabilistic constraints. The advantages of this method are a significant reduction in the computational cost and the proper accuracy of the final results.For minimizing the objective function, which is the weight of structure in this paper, Firefly algorithm (FA) is utilized. The FA is a stochastic metaheuristic approach based on the idealized behavior of the flashing characteristics of fireflies. In FA, the flashing light can be formulated in way that it is associated with the objective function to be minimized. The numerical example results indicate that using the proposed method leads to the optimum design solutions better than other methods in the literature without violating reliability constraints.

Liquid storage tanks are vital and have great importance in industrial facilities. One of the best ways to protect the fluid storage tanks against earthquake forces is the use of seismic isolation systems. These systems protect such structures against possible damage during an earthquake by allowing acceptable displacements at the base of the superstructures while preventing the superstructure from entering the nonlinear phases. One of the common methods for computer modeling of these structures is the use of equivalent mechanical models. It should be noted that, the mentioned equivalent mechanical models, are suggested for design of tanks by Standards and Codes. However, they are appropriate for rigid-wall tanks. On the other hand, the recent studies show that the seismic response of a rigid tank may be considerably less than that of a similar flexible tank. In this study, by using a state-of-the-art equivalent mechanical model of cylindrical concrete containers, that considers the issue of wall flexibility, the seismic responses of ground-supported and elevated concrete containers affected by the bi-directional horizontal motion of the earthquake is investigated. The results show that, by selecting the best mechanical properties of seismic base isolation systems, the seismic responses of these tanks can be greatly improved.

Concrete is the most widely used building material in recent decades, and researchers are innovating in the production of this material to improve some of it’s properties such as strength and durability. A part of these innovative efforts has led to the production of a new class of concrete called ultra-high performance concrete (UHPC). UHPC has the unique mechanical features that provide opportunities for the development of new techniques of construction, repairs and renovation of concrete structures. While most of the recommended relationships in the standards are based on normal strength concrete (NSC), it is necessary to know more about ultra-high performance concrete behavior. This study aimed to investigate bond behavior (the interaction between rebar and concrete) because it directly affects the performance of concrete structures. 24 cubic concrete specimens (20 cm and 25cm wide) with a centered rebar and two bond lengths, using UHPC and NSC, were subjected to pull-out tests. Concrete’s compressive strength and relative cover, bond length, and yield stress of the rebar significantly influence the failure mode. UHPC reduces the embedded length of rebars by increasing bond strength up to 5 times that in NSC. Regarding to the bond-slip curves, plain UHPC (used in this study) had less ductility than NSC. In NSC, increasing the bond length increases the maximum bond stress, while in UHPC, for increasing bond length, the maximum bond stress decreases. New relationships have been proposed to predict bond-slip behavior.

One of the most important challenges facing civil engineering community besides cost, performance problems such as vibration, especially in thin sections, the smooth and concrete movement of reinforced and complex sections, is increased resistance with reducing or not using cement. The purpose of this research is to innovate in Portland cementless concrete industry, which is inspired by geopolymer technology and its incorporation in self-compacting concrete (SCC) to produce sustainable concrete, in order to reduce carbon emission from Portland cement (PC) production. In this regard, the furnaces slag as amorphous (cement replacement) and alkaline actuators are used and laboratory study was performed on the fresh properties (slump Flow, T50, L-Box, hopper V and J rings) and hardened properties (compressive and tensile strength). Results indicate easy filling in narrow sections, improved compression, good bonding strength, reduced maintenance, faster construction speed, about 70% increase in 28-day resistance and 86% in 90-day resistance of Type III geopolymer concrete with respect to Portland cement concrete (reference concrete) with constant grade of 400 kg / m3, Use of industrial waste and reduction of air pollution, Improve mechanical properties (according to statistical results of compressive strengths up to 65 MPa), Reduce the overall construction cost of self-compacting geopolymer concrete in comparison to the rate of acquisition of resistance of conventional self-compacting concrete, self-compacting concrete with different slag percentages, conventional geopolymer concrete and ordinary concrete. Due to the high cost of alkaline activators in the country, lack of equipment and infrastructure for slag powder, insufficient information on the durability of geopolymer concrete is predicted and thereby create new opportunities for the construction industry.

The adequate solution for protecting main structural members and reducing the destructive effects of earthquakes use of structural systems combined with the replaceable fuse members, which due to the ductile behavior and seismic energy dissipation are next to the main members of the structure. Relatively low cost and easy repair process in these systems leads to rapid return to occupancy after an earthquake. In this study presents the response modification factor ‘R’ of the RC frame retrofitted with the linked column frame system with the number of floors 3- and 6-story with three different lengths of link beam. Based on the results of modeling the force-displacement curve, the R factor and related parameters are calculated based on the equivalent energy method. The results of the nonlinear static analysis, using the linked column frame system for retrofitting RC frame Can be increased the load bearing capacity and the capability of absorption and dissipation energy than a model of the RC frame without retrofitting about 3.5 times. The R factor in the Limit state method is about 8.95 which is more about 71% than a model of the RC frame without retrofitting. Also, the distance the corresponding displacement for the first plastic hinges formed in link beam and the corresponding displacement for the first plastic hinge formed in the RC frame for the model of LCF-0.8-0.45 is more than other models. This causes the damage to the replaceable link beam and the main structure is remained elastic phase and at a high risk level, this system will achieve to reach the rapid return to occupancy performance level.

Buildings may be subject to various external threats throughout their lives. These threats can cause progressive Collapse to the structure by damaging the critical structural elements. Studies on structural systems failure in recent years highlight the importance of the progressive collapse phenomenon caused by abnormal loading like crashes, terrorist attacks, explosions, earthquakes, and so on. In this study, the performance of 6-story masonry infilled reinforced concrete frames with varying percentages of openings in progressive failure due to varying span length and floor height is investigated. The frames examined have RC moment-resisting frames that are designed by the Iranian Building code. Progressive collapse simulation by alternative path method by removing the middle column of frames in OpenSees software with nonlinear static analysis. According to the results, In the case frames with 10%, 20%, and 30% openings in the infilled masonry wall, their maximum strength reduced by about 23%, 31%, and 39%. Also, the frame with openings reduces about 62% of the maximum force against the without openings frame. The results show that increasing every 0.5 m of span length from 4 to 6 m, on average, increases the force by about 9%. Also, increasing the height of the floor from 3 to 4 meters, on average, increase the strength of the frames by 13%. The results of this study showed the positive effect of infill, increased span length from 4 to 6 meters and height from 3 to 4 meters, the class is in the process of progressive collapse of RC frames.

Steel shear walls are one of the most commonly used systems for resistance and stability of structures to lateral loads, which are used to rehabilitate and improve the seismicity of structures in seismic zones.Among the advantages of this lateral load resistance system, similar to high-performance systems, high ductility, high absorption capacity and energy depreciation, high initial hardness, light weight relative to similar concrete, saving materials, reduced time and the cost of conruction pointed out.Recent research has shown that the buckling of these plates before the submission of environmental elements would produce a better performance of this kind of lateral load system.This leads to the expansion of the use of thin-walled plates that lead to emerging executive problems and affect the economic benefits of the plan.In order to overcome the dilemmas and accelerate the buckling of these sheets, the idea of using a perforated steel plate was introduced.In this paper, the behavior of steel shear walls with perforated plates is investigated.To perform a parametric study of the effects of holes with different geometric shapes on the shear wall, the method of laying and placing holes in the shear wall on structural performance, in terms of energy absorption, the total load bearing capacity of the system was investigated.For modeling the samples, Abaqus finite element software was used.Parametric results on 60 finite element models under cyclic loading of displacement type showed that if using the same hole percentage, the maximum bearing capacity was attributed to the shear wall model with holes with circular geometry It shows the best seismic behavior.

A new formula based on strut and tie model to determine the shear strength of exterior beam-column joints without transverse reinforcement (stirrup) in the joint region under monotonic and seismic lateral loading is proposed in this paper. Based on the accomplished topology optimization to determine directions of the principal stresses of the joint region, the main shear transfer mechanism in beam-column joints without transverse reinforcement in the joint region is diagonal strut mechanism; therefore, the proposed strut and tie model is made up of a concrete bottle-shaped diagonal strut. Formulae available in published literature for calculating the diagonal strut angle of inclination was checked by finite element analysis results of two exterior joints, the results indicate that all formulae have good agreement. Various experimental data set of this kind of joints are collected from previous literature based on consistent and specified criteria for data selection. The accuracy of the proposed procedure and two approaches of determining the diagonal strut width was checked by comparing calculated shear strengths with experimental data. Based on the two introduced approaches for calculating the diagonal strut width, approach 1 which does not take into account the column axial load, has the best performance in the proposed model. The proposed formula, in addition to the specified compressive strength of concrete which is included in Iranian and American concrete codes, considers other effective parameters on exterior joints behavior such as the beam longitudinal tension reinforcement ratio and its strength, the intermediate column bars and the joint aspect ratio. Therefore, the proposed formula is able to estimate accurately the shear strength of exterior beam-column joints without transverse reinforcement in the joint region.

This research deals with the buckling analysis of cracked column with fixed-fixed conditions. The crack is modelled with a unilateral elastic bending-stiffness behaviour, represented by a unilateral rotational spring. This model takes into account the crack closure effect on buckling behaviour of column. The governing equation of the problem is introduced by the variational approach based on energy arguments. Using the variational approach, the governing equation can be formulated as a function of damage index. Damage index is the stiffness of the equivalent rotational spring associated with the crack. A one-crack and a tow-crack are theoretically investigated to illustrate the effects of the crack on the buckling load. For the one crack column, the buckling load increases with the stiffness of the crack section. When the crack-stiffness parameter tends towards an infinite value, the structural model is reduced to the classical Euler column. It is observed that the buckling load increases as the crack get closer to the supports, for constant damage value of the crack parameter (constant crack depth). For the two crack column, the crack closure phenomenon is investigated. In order to two cases are considered. In the first case, the two-crack are located on the same side of column, and in the second case, the cracks are located on the opposite side of the columns. Comparison between two cases show that the crack closure influence on the buckling load. In other words the crack-closure phenomenon tends to increase the buckling load.