نشریه مهندسی سازه و ساخت
سال هشتم شماره 10 (پیاپی 50، دی 1400)

Following abnormal events, identification of load redistribution pattern in the load-bearing elements is an important issue in the field of structural engineering. As a possible event, one can imply to initiation of excavation-induced large differential settlements under the columns of common reinforced concrete (RC) moment frames. A large portion of existing literature have studied the effect of single-column settlement scenarios or tunnel-induced ground movements on 2D frames, however. Using two series of real ground surface settlement profiles (called medium and large) representing deep excavation adjacent to the construction site, 8 analysis cases were defined to gradually impose differential settlements under the columns in this paper. Apart from different 3D settlement profiles, the structure was assumed to be located on the corner or center of excavation edge, and two directions were also considered for the building plan. Based on the findings of the numerical models, the axial compressive force significantly decreased in a series of highly settled columns. Also the columns which were relatively far from the location of maximum settlement made key contribution to redistribution of loads. Moreover, a large number of columns experienced tensile axial forces in some of the cases with larger surface settlement imposed. The change in the direction of beam flexural moments in conjunction with some columns (not limited to the column having the largest settlement) shed light on possibility of damage in an extensive area of the building plan.

Buckling is one of the important issues in determining the mechanical behavior of cylindrical shells, especially composite shells. What makes the buckling matter important in composite cylindrical shells is the complexity of the behavior of these structures under the influence of a variety of special loads such as buckling under external pressure load. Uniform lateral loading in tanks occurs when tanks are in the state of liquid discharge. Moreover, if special contrivances such as the drainage valves do not work or properly, then buckling phenomenon and will cause an overall failure in the tank. In this research, the air suction system is used in order to apply external pressure and study the buckling behavior of specimens. As the buckling occurs, tiny cracks are created with a mild sound in the shell wall and in the extreme stage the loading process stops when it collapses. In this paper, the effect of geometric parameters, such as the R/t and L/R of a composite tank under external pressure, on buckling behavior is investigated. Obtained results are compared with software and theoretical results. The results showed in specimen of the same length, by increasing the geometric parameter R / t, the buckling capacity of the shells decreases and the number of buckling modes increases and by increasing the geometric parameter L / R, the buckling capacity of the shells increases and the number of buckling modes decreases.

Plates are one of the most important structural elements in which failure can be progressively transferred to other elements and cause overall damage. Therefore, identification of damage in these components plays an important role in the control of structural health. Damage detection and locating systems have a critical role in retrofitting and improving of structures and preventing the financial and human damages caused by the collapse of structures and would increase theirs service life .The main purpose of this thesis is to study how to identify and evaluate damage in plate-like structures using nondestructive methods, and improving this operation process.. In this study, the effect of torsion in addition to bending on the plate element is considered in the damage identification process by analyzing the shape data and their derivatives and by developing finite element numerical codes, calculating the slope and curvature of the plate based on the central finite difference method, Efficiency and performance of this method has been studies by different scenarios of damage in plate with different characteristics and an improved index has been introduced. Comparison of the results in both healthy and damaged structures showed increased robustness and accuracy of identifying the location of individual and multi-step injuries, especially at the edges of the plate and also Improved indicator performance validation with experimental data indicates appropriate accuracy of this index.

Nowadays researchers are trying to simultaneously enhance the mechanical properties and durability of concrete using additives. In this study, the experimental results of the effect of admixture concrete with different percentages of polycarboxylate ether and E205 additives were investigated separately on fiber reinforced concrete with polypropylene fibers. In this regard, durability tests including electrical resistivity tests, water absorption, rapid choloride permeability test (RCPT) and compressive strength of concrete have been investigated. In addition, to study the microstructure of cement paste containing polypropylene fibers and polycarboxylate ether additives and E205 additives were used, X-ray diffraction spectroscopy (XRD) experiments, scanning electron microscopy (SEM) images and XRF chemical composition test. The results show that adding additives to the concrete admixture, reduced compared to the control sample 51% chlorine ion penetration in concrete with polycarboxylate ether and polypropylene fibers (sample A) and 36% chlorine ion penetration with E205 additive. Water absorption was reduced in samples A 27% and in samples B, 16% compared to the control sample, also the increase in specific electrical resistivity compared to the control sample was 525% in samples A and 619% in samples B. Also, the compressive strength of samples at 7 and 28 days of age increased by 134% and 56%, respectively, and the highest compressive strength in samples B at 7 and 28 days were 43% and 29%, respectively. Control sample increased. According to the results, it can be concluded that the durability and compressive strength of fibers reinforced with polypropylene fibers is increased by adding polycarboxylate ether and E205 additives.

Today, conventional force based structural design (FBD) approach due to the weakness in controlling the expected performance level during an earthquake, do not meet the performance expectations of the designer. Direct displacement based design approach (DDBD) is recognized as one of the new main tools for satisfaction designer expected performance level. The effectiveness of DDBD approach has been evaluated in controlling the expected performance level of many structural systems so far, while the least attention has been paid to the effects of geophysical and site effect studies. In this study, seismic performance of RC frames designed with DDBD approach considering soil–structure interaction effects has been investigated. For this purpose, 4 RC frames with different heights that are placed on a 20 meters layer of soil were designed based on mentioned approaches. In the design process, the design displacement profile has been corrected according to the effect of soil-flexibility. The results of the study of frames with flexible bases show an increase in the displacement response of frames up to 8.22% compared to models with fixed bases. While the effects of soil-structure interaction did not have much effect on the story drift, so that in none of the frames the average maximum story drift did not exceed the expected performance level. In order to comprehensively investigate the soil–structure interaction effects, the performance evaluation of the RC frames in low-, medium-, and high-risk has also been examined. The results show minor changes in the maximum story drift at three different risk levels, considering soil–structure interaction effects.

Restricting resources and maintaining environmental quality has inevitably required the recycling of materials. Concrete is one of the most attractive building materials for recycling. The waste concrete can be crushed again, used as aggregate in the manufacture of concrete. In this study, for the modeling of compressive strength of concrete containing recycled aggregate, two formula-based regression methods named multivariate adaptive regression splines (MARS) was used. Mixing data from the research background to create suggested models, 239 laboratory data was compiled to estimate tensile strength of recycled concrete for parametric investigation. Then, two scenarios based on volumetric/weighted and ratio variables were defined to determine the best input parameters for the model using mallow’s technique. Among which a scenario including volumetric/weighted content, based on three statistical error indices including correlation coefficient (R), Root mean square error (RMSE) and mean absolute error (MAE) were selected as the best scenario. In this study, to determine the best model for estimating the compressive strength of recycled concrete by means of error statistics, it was determined that the correlation coefficient (R) in the training stage for MARS 0.973 and 0.903. Also. The RMSE statistical value for the proposed model MARS this stage was 16.176. In the testing phase, the MARS method was better than the M5p method. The results of uncertainty analysis indicated that the proposed method had a predicted mean error with very little distance in the semester. In addition, among the proposed smart methods, the MARS base on volumetric/weighted content approach was chosen for parametric analysis.

In many optimization studies, the goal is to minimize the costs which is necessary due to the limited resources and energy and the constantly increasing costs. However, this reduction in costs must be to some extent so that the expected performance of the structure is not impaired. In this study, the aim is to optimize the seismic performance and the weight of the structure simultaneously. In order to demonstrate the seismic performance of the structure, a criterion is needed to represent the seismic performance of the structure, for which the behavior coefficient parameter is used. In this paper, the optimal design of a special moment resisting frame is performed using the island genetic algorithm, once under a single-objective, objective function with the aim of minimizing the weight and again under a multi-objective, objective function with the aim of minimizing weight and maximizing behavior coefficient simultaneously. For this purpose, the design of 3 frames of 3, 6 and 9 stories with one span with a story height of 3 meters and span length of 18 meters is presented. In this research, truss arrangement, cross section of truss members, truss height and length of special zone of the truss moment resisting frame are optimized. The optimization code is written in Matlab software environment and OpenSees software is used for structural analysis. The constraints of optimization problem are based on the regulations and restrictions of AISC341-16. Finally, the results of the single-objective and multi-objective optimization are compared. The results show the efficiency and performance of the two-objective, objective function method in comparison with the single-objective, objective method.

In this numerical investigation, the effect of upstream and downstream interference of two identical tall buildings was evaluated using the computational wind engineering (CWE) method. In order to simulate three-dimensional turbulent wind flow with Reynolds numbers in the range of 1.4×〖10〗^4<Re<8×〖10〗^4, the Large Eddy Simulation (LES) model was used. Mean and fluctuating coefficients of drag and lift and pressure distribution were used as the main criteria to evaluate the aerodynamic response of the principal building in different conditions of interference. Streamlines and vorticity contours were presented and their relationship to aerodynamic results was interpreted to provide a better understanding of the physics of the problem. According to the results, the shielding effect of the interfering building in most interference cases led to a reduction of the mean drag coefficient of the principal building compared to the isolated case. Compared to the isolated building, depending on the location of the interfering building, the fluctuating lift coefficient either increases or decreases.Upstream interfering buildings with sufficient distance to the principal building lead to an increase in the fluctuating lift coefficient of approximately about 50 percent. While, the fluctuating lift coefficient of the principal building decreases up to 37 percent, due to the closely spaced tandem interference states. While the mean pressure coefficient at the windward surface is not significantly sensitive to the interference states, it is strongly influenced by the different states of the interference at the lateral and leeward surfaces. Aerodynamic parameters were less sensitive to Reynolds number variations due to the fixed position of the flow separation in the sharp corners of the rectangular section and the zero angle of attack in this study. Changes in the Reynolds number resulted in variations of about 4 to 10% in the drag and lift coefficients of the principal building.

In this paper, seismic behavior of corrugated steel shear walls arranged in different configurations is studied using fragility curves. Due to the advantages of steel shear walls, the use of this system has been of interest to the executives and designers and its use as a lateral resisting system in practical projects is rapidly expanding. Therefore, consideration of the unknown aspects of this system is important. In the present study, the effect of configuration of corrugated steel shear wall with cold rolled steel in structures with 3, 5 and 7 stories have been investigated. The number of bays in the direction of the shear wall is five, in the first type arrangement, the walls were in the first and the end of the bays, in the second type arrangement of the walls in the middle bays and in the third type arrangement, in the two spans of the first and the end they are staggered. For modelling the behavior of corrugated steel shear walls, previous experimental results have been used. Using static nonlinear analysis and increasing dynamic analysis, Fragility curves, which play an important role in assessing the seismic damage of buildings, are presented for these frames. The results of this study show that in type 2 layouts, the median intensity is higher than the two other arrangements in the structures with different stories. In addition, the corrugated shear walls in low-rise structures are more effective in decreasing the probability of failure subjected to far field earthquakes

Isogeometric analysis of forced vibration of continuous systems was investigated in this paper. The basis of this method is the use of NURBS functions, which provide an integrated mathematical basis to display the analytical models. The most important advantage of this method compared to conventional methods such as finite element is the accurate geometric modeling and almost no approximation with a new and easy method. The NURBS and B-Spline functions can have a higher continuity of derivatives in comparison with Lagrangian functions used in the finite element method. The forced vibration of Euler-Bernoulli and Timoshenko beams was studied in this paper. Using the Galerkin method and the principle of virtual work, the stiffness and mass matrix of these continuous systems were obtained considering the effects of shear deformation and rotational moment. Also, displacement functions were determined based on NURBS functions. Numerical examples of forced vibration of continuous systems are provided to prove the validity and efficiency of the proposed method. The natural frequencies of the members were obtained using MATLAB software and applying specific boundary conditions. furthermore, the results of the isogeometric analysis were compared with the exact solution of the Dynamic Stiffness Method. The results showed that the isogeometric method provides more accurate results due to the use of NURBS functions instead of approximate selective functions of the element.

Improving the mechanical properties of concrete with the help of fibers is considered as one of the common methods of concrete processing. Addition of fibers to concrete increases the energy absorption and ductility of concrete and prevents the spread of cracks. Steel, polypropylene and glass fibers are the most widely used fibers. In addition, new types of macro-synthetic fibers have been introduced. In this research, in order to improve the mechanical properties of concrete, a new type of macro-synthetic fibers has been used. Samples reinforced with 2, 4, 6 and 8% of fibers were evaluated using various compressive, flexural, tensile tests as well as elastic coefficient determination tests and their optimal consumption was selected. In this research, it has been tried that the test conditions are as compatible as possible with the industry conditions so that the final results of the research are in good agreement with the current situation of the concrete industry and can be used. Comparison of test results showed that, as expected, fiber-reinforced concretes have higher compressive, flexural, tensile strength and tensile strength than conventional concretes. In addition, between different percentages of fibers in concrete, in samples with percentages greater than 2%, the rate of increase of different strengths is lower than in the case without fibers. Therefore, considering the cost of macro synthetic fibers, the most suitable percentage for reinforcing concrete with them was introduced as 2%.

It is unavoidable to prevent serious damage to the structure and to reduce the casualties and damage caused to it. For this purpose, structural control systems can be used. The study used a viscous damper. The Endurance Time method (ET) is a simple method of analyzing history when the structure is exposed to a gradual accelerating function. The advantage of this method is that with only one analysis of the structure under the acceleration function of endurance time, the performance of the structure can be evaluated at different functional levels. In this study, the application of endurance time method in nonlinear seismic analysis of steel structures equipped with viscous dampers has been investigated. The parameter of engineering demand is the maximum drift of the floors, which is calculated in structures with and without viscose damper. Finally, using curves of endurance time, it was found that the use of viscous dampers reduced the maximum drift of the floors. Non-linear time history analysis (NTH) has also been used to validate the results of the (ET), which showed that the (ET) results are well matched to the nonlinear time history analysis. Finally, the results demonstrated that utilizing of ET method can be replaced in structural building which the viscous damper was utilized.

Due to adverse effect of lap splice on the ductility of shear walls, ACI 318-19 does not allows use of lap splice in stories with probable nonlinear excursions. However, due to lack of capacity design in ACI design approach for shear walls, in fact there are high probability of nonlinear deformation in all stories. This means possible nonlinear ABSTRACTDue to adverse effect of lap splice on the ductility of shear walls, ACI 318-19 does not allows use of lap splice in stories with probable nonlinear excursions. However, due to lack of capacity design in ACI design approach for shear walls, in fact there are high probability of nonlinear deformation in all stories. This means possible nonlinear demand in stories with lap spliced bars. This paper investigates performance of lap spliced boundary elements of lightly reinforced shear walls, where boundary elements subjected to mainly tensile loadings. Two specimens with continuous rebars and three specimens with lap splice of different lengths are included in the experimental program. The specimens are subjected to asymmetric cyclic axial loading. Test results reveals that lap splice increases deformation demand on the portions of the specimen out side of lap splice length, leading to rebar fracture at lateral drifts much smaller than that excepted for specimens with continuous rebars. Presence of lap splice could substantially decrease lateral drift capacity from 0.04 to about 0.013. Also out of plane buckling for specimens with lap splice occurs at smaller tensile strains.

The perforated steel plate shear wall is one of the different lateral load resisting systems. The steel plate shear wall system contains two rectangular openings, the middle panel between two openings has a major role in the energy absorption. In this paper, considering the middle panel similar to the link-beam of EBF and reviewing the existing theoretical formulas for anticipating the middle panel behavior, a new condition related to the stiffness of web plate and stiffeners, which are located on the surrounding opening is added. The results show that the new added condition helps better identify the behavior of the middle panel and to separate the boundaries of behavior type. In addition, a formula with high accuracy is determined to calculate the shape factor of a section with box-shaped flanges. Furthermore, in accordance with obtained diagrams from triple conditions, the effects of six dimension parameters on the behavior of the middle panel are investigated and the bounds of changing the behavior type of the middle panel are determined. The results of the theoretical study show that the 64% increase in width, 47%, and 32% decrease in height and plate thickness of middle panel respectively and 100%, 14%, and 122% increase in height of web, flange width, and thickness of box stiffeners respectively changed the behavior type of middle panel from flexural-dominant to shear-dominant. These obtained results were calculated only in the case of examining the relevant parameters.

During the past earthquakes, the formation of plastic hinges in columns has given rise to global structural damage in moment resisting frame structures. If the plastic hinges are formed in the beams, the most suitable energy dissipating mechanism in structure will happen. The kinked rebar has locally curved regions (usually near the inflection points in beams) which can be gradually straightened under tension. Due to lower initial yielding flexural capacity compared with that of a cross section reinforced with traditional straight bars, the beam section reinforced with kinked rebars will yield first when the RC frame is subjected to seismic loading, and thus, the strong column-weak beam hierarchy can be realized. In this study, first the load-deflection behavior of a reinforced concrete beam was numerically simulated by ABAQUS software, and the reliability of the finite element model was verified by comparing with the experimental results of other researchers. Then, the load-deflection response of the RC beams with kinked bars which has two-step behavior were investigated and described in steps by using finite element modeling results. Finally, the control beam was used for further analyses to investigate the effect of important parameters including: concrete compressive strength, reinforcement ratio, and the ratio of beam span to depth on load-deflection curve of beams. Results showed that the ultimate bearing capacity of RC beam increases as the reinforcement ratio increases, however, it doesn’t have an important effect on the first yielding point. The increase of concrete compressive strength also contributes to greater initial yielding. In addition, the increase of beam span can have negative effects on the flexural behavior of RC beams with kinked bars, and reduce initial strength and stiffness of beams.Finally, the behavior of an internal connection including a beam with kinked rebar to the column was evaluated.

Due to population growth in large cities and the growth of cities vertically, in order to facilitate serviceability and provide low-cost and easier access to the needed resources, engineers are forced to build high-rise buildings on less desirable soils. Given the seismic conditions of our dear country Iran and the variety in thickness of soil in different places, it is important to know the structure suffers the most damage under which conditions. In this study, a nonlinear three-dimensional model of soil-structure interaction in tall buildings with finite element method by Abacus software in the time domain is investigated to evaluate the effect of soil-structure interaction. the dynamic implicit used to calculate the problem. Thickness effect with considering soil-structure interaction for 4 different thicknesses by Drucker-Prager modeling method which also considers soil hardening properties under the effect of Lomaprita earthquake which is considered as an earthquake with low frequency content ( Earthquakes with low frequency content have more destructive effects), has been calculated. infinite boundaries used to absorb the reflect of waves. the boundaries The research results show that changes in thickness have significant effects on the analysis results. In this study, for each model, lateral displacement , acceleration, subsidence, acceleration spectrum and stress contours are investigated.

The most important form of structural ductility, known as global ductility, depends on the base shear force and the displacement of the roof of the structure. If the global ductility of the structure can be calculated by local ductility, the volume of calculations will be significantly reduced. Therefore, it is logical to obtain an acceptable estimate of these two requirements using a simple method during the seismic design process of the building. In this paper, using a database consisting of 12,960 structural frames with 3, 6, 9, 12, 15 and 20 floors, 3 types of column stiffness and 3 degrees of bracing slenderness and using the advantages of Particle Swarm Optimization (PSO) and Simulated Annealing (SA) algorithms present an empirical relationship between global and local ductility. All models have been analyzed under 20 pulse-like near-fault earthquakes considering 4 different performance levels. The results of validation show 81.26% and 69.07% correlation of the proposed relationships from PSO and SA algorithms. Therefore, the coefficients obtained from the particle swarm algorithm were introduced as the final result to apply in the proposed relation the coefficient of behavior of divergently braced steel structures. A comparison of the structural deformation demands resulting from the proposed relationships and an analysis of time history, confirm the existence of an acceptable agreement.

Cement production has always been associated with environmental challenges due to carbon dioxide emissions. On the other hand, cement production is an energy-intensive process and leads to the consumption of abundant fossil fuels. In order to solve this problem, the production of geopolymer concrete is on the agenda. The researchers decided to reduce the negative effects of cement production and have superior properties than ordinary concrete . Geopolymer cement matrix, due to the production of abundant hydrated gels, has a higher density and cohesion than the Portland cement matrix, and this is the main reason for increasing the resistance of this type of concrete to high heat compared to ordinary concrete. In this study, the effect of heat on the mechanical properties of slag geopolymer concrete containing 0 to 8% nanosilica and 1 to 2% polyolefin fibers at 90 days of processing age was investigated and XRF, XRD and SEM experiments were used to study the microstructure. In the optimal design of slag geopolymer concrete (containing 8% nanosilica and free of fibers), we saw a decrease of 8 and 44% in the values after and before heating in compressive strength tests and determination of ultrasonic pulse speed of concrete, while in control concrete, the results decreased Reached 38 and 37 percent. In slag geopolymer concrete containing 8% nanosilica and 2% fibers, tensile strength and modulus of elasticity equal to 14 and 34% showed results after and before heating, for control concrete these figures decreased by 51 and 59% in the results. Received, the results of the falling hammer impact test also had a reduction in the resistance of heat-exposed concrete to hammer blows. In the end, the microstructural studies were in overlap and in coordination with the results of the tests of this study.

In the present study, an effective method for damage detecting in beam to column connections and column to the ground connections is presented. Rotational springs are used to model the joints (beam to column and column to the ground) of the steel frame. After finite element modeling of the studied frames in Matlab software environment, modal analysis was performed. To identification of joint damages, an optimization problem formulated to identify location and severity of damages. A new optimization algorithm called moth-flame algorithm with high accuracy and speed is used to solve this problem. The joint damages modeled through the reduction of the rotational stiffness factors. To show the performance of presented approach, two frames consist of a four-story steel frame and a nine-story steel frame have been investigated. In the studied frames, damage was assumed at the beam to column connections and column to the ground connections and then the severity and location of damage at the assumed joint were identified by the proposed method. The results indicated that the proposed method is robust to detect damage in beam to column connections and column to the ground connections that can accurately identify the location and severity of damage at the joints.