نشریه مهندسی سازه و ساخت
سال هشتم شماره 1 (پیاپی 38، فروردین 1400)

Hollow structural sections (HSS) have been used in many structural applications, owing to their efficient structural performance and suitable appearance. However, due to the lack of access inside the HSS column for bolting purposes, it has been difficult to develop a practical bolted moment connection. Thus, field welded beam-to-HSS column connections have been the only viable method. Recently some blind fasteners are developed to be used in application which access for installation is only from one side of the connection. At the moment different blind bolts were designed for use in one side connections. In this project, comparison of the test result of an article and three dimensional finite element modeling of the blind bolted end plate joint with concrete-filled square hollow section columns to steel beam and Lindapter blind bolt (Hollo-Bolt) under monotonic loading indicates that the finite element analyses can be used to predict the connection behavior with sufficient accuracy. After that studied parametric investigation under cyclic loading into the end plates thickness, bolt diameter and bolt pretension force for the blind bolted extended and flush end plate connections of steel beams to hollow section column with ABAQUS and got moment-rotation hysteretic curve of each ones. Results have shown that the end plates thickness, bolt diameter and bolt pretension force have influenced on the connection behavior.

Nowadays, nonlinear static and dynamic analyses methods are rapidly expanding to evaluate the seismic performance of structures. Nonlinear dynamic analyses methods require a large amount of computations and are relatively time consuming. This fact has led to the emergence of novel methods based on the concepts of nonlinear static and dynamic analyses. One of the most widely used structures in tall buildings is a combination of the two popular building structures: Bundled tube frame and belt truss. This structural form is effective in reducing the structure responses to lateral loadings. In this paper, two 20-story Steel buildings with different arrangement of resistant rigid belt truss in the 19th and 20th stories have been evaluated under 7 pairs of far and near-field scaled ground motion. Incremental dynamic (IDA), Incremental modified Pushover (IMPA), modal pushover (MPA), and dynamic time history analyses have been conducted to evaluate the seismic response of the structures. The accuracy of the IMPA method has been compared to that of the Incremental Dynamic Analysis (IDA), and a comparison has been also made between nonlinear behavior of the studied models, with and without the belt truss. Results indicate the significant difference in the story drift in the three aforementioned structural configurations under high-amplitude speed pulses. Structures stiffened with belt truss at higher levels of PGA have collapsed and the seismic capacity of the frame has been increased in the upper floors. Maximum relative displacement has been occurred in the inelastic response area near the middle stories.

In this study, the effect of isolators positioning at three Levels and different arrangements on seismic response of RC buildings are investigated. For this purpose 18 RC building of 4, 8 and 12 story with and without lead rubber bearing (LRB) isolators were selected. The LRB isolators positioned at three Levels and five different arrangements were modeled in Opensees software. The near field and far fault earthquakes were added to the frames and incremental dynamic analysis was performed. The fragility curves base on inter-story drift ratio as well as the IDA curves base on maximum inter-story drift ratio, maximum base shear, maximum roof displacement and acceleration versus peak ground accelerations (PGA) were plotted and compared. The results showed that among the isolated structures, the isolator positioning at the level of below the first floor (type 1 and type 2) had the best performance in reducing responses. The positioning type 1 (MSI-1) resulted the best decreasing in inter-story drift ratio and base shear. In addition, this type of isolator had the best increasing the PGA according to median fragility between the different types of the positioning levels. The recommended type of isolator had the best performance, especially in high rise buildings in severe damage levels.

Traditional earthquake-resistant systems are dependent on the inelastic response of the building members. These systems experience significant residual displacements after major earthquakes due to seismic energy distribution all over the building and make their repair uneconomical. Self-Centering systems in steel frame buildings omit residual displacements and concentrate building damage on Self-Centering connection and reduce the cost of repair. Due to the dispersion of the response of Self-Centering systems against different earthquakes, it is necessary to determine an index to control sensitivity of these systems against various records. In this paper, developing an efficiency index of steel moment frame systems with Self-Centering connections using the dispersion index's methodology is discussed. After performing the time history dynamic analyses of two steel buildings with 3 and 9 floors, six types of self-centering connections for each frame with seven dispersion indices were evaluated. Decreased dispersion of responses indicate that the system is more efficient. Among these, under the optimization of indices, it is tried to select an index with a better performance which resulted to CV index (coefficient of variation). Finally, the structure with the least dispersion of responses is selected from the viewpoint of efficiency. The selected model of this research for 3 and 9 story buildings is model M5 which is the fifth model of Moradi models.*

Today, it is quite clear that the speed of development of infrastructure in developing countries has led to much damage to the environment. Concrete is one of the products that plays an important role in the use of non-renewable resources. Today, the vision of sustainable development in the manufacturing industry is growing and increasing, and concrete is at the forefront of this as one of the most widely used construction products. The present study investigates the effect of the use of silica-fume (SF) pozzolan powder on the mechanical properties of recycled concrete made from fine recycled aggregates. Recycled concretes consists of different levels of replacement of fine recycled concrete with natural fines. In order to improve the quality of recycled concrete, Pozzolan was introduced at various levels with cement. To determine and compare the mechanical properties of concrete, 12 mixing designs were made and compressive strength tests at 7, 28 and 91 days, tensile strength, and ultrasound velocity at 28 days of age were performed. The results showed that, generally speaking, in the 28-day period, the use of SF can cause 25% recycled concretes to achieve a desirable 40 MPa strength. The use of 10% SF replacement rate, especially in concrete containing 25% recycled aggregates, made the mechanical properties of recyclable concretes significantly closer to conventional concrete.

In this paper, factors affecting the mechanical properties of polymeric granite artificial stone have been investigated. Epoxy resin and three types of additives called Poly ether ether ketone, Silicon rubber, and Nanoclay have been used to make the artificial stone. Unlike previous research on resin alone, this study has been conducted on artificial stone and samples made using these materials. These samples are compared with the control sample and the sample with optimal mechanical characteristics. The method of making artificial stone is that crushed stone blend with resin, and is molded into molds that are defined according to the American Association of Materials and Testing. Samples were made with two percentages of 7.5 and 15 percent to determine the optimum amount of additive. After curing, the sample is subjected to testing. The results obtained from these experiments for artificial stone show that the addition of polyether ether ketone to epoxy resin compressive strength by more than 30%. 7.5wt% of Nanoclay increases more than 6% in compressive strength in epoxy resin. Therefore, the amount of 7.5% by weight of the additive has been selected as the optimum percentage and only this percent is considered in the manufacture of flexural and tensile strength samples. Adding Silicon rubber to the epoxy resin, increases the flexural strength by 7%. Contrary to expectation, Nanoclay reduces flexural strength significantly. By examining the results of the tensile test, it was determined that the addition of silicon to the epoxy resin increased the resistance to 46% . It is concluded that the addition of silicon rubber has been effective in increasing the compressive strength and in increasing the flexural and tensile strength and adding polyether ether ketone.

Assessment and investigation of soil and bedrock properties is of an essence for construction of residential, commercial as well as industrial complexes. In order for the foundation system of such projects to be opted, it is necessary to assess the geotechnical characteristics of the site. In many projects where the site is located on problematic soils or non-engineered fills, if the accumulation of the soil is done with no specific consideration of controlling the fill thickness and compaction, the soil will experience some major problems regarding volumetric changes, bearing deficiencies, and internal instability. Therefore, it is crucial in such fills to employ some soil improvement and preservation measures in accordance with their materials, time and circumstance of the fill formation. In construction procedure of a complex near Tehran, due to non-engineered accumulation of debris and inappropriate compaction, it was recognized that the project was prone to unallowable differential settlement and instability, and for this reason, it was required to improve the subsoil properties by means of ground improvement techniques. Moreover, owing to the significant depth of problematic soils, the shallow improvement approaches would not suffice, and consequently, using semi-deep or deep improvement techniques were mandatory. In this paper, the geological characteristics of the site in line with assessment of the soil geotechnical properties after improvement were analyses in order to select the more appropriate improvement methods. Among different alternatives, the combination of earth works, shallow compaction, jet grouting and employing micropiles was shown to be the more optimum option from economical, technical, and feasibility perspectives, and therefore, was employed in the project.

The nature of dynamic loading is different due to the high force in a few milliseconds with static loading. The amount of energy absorption and energy loss in composite materials is a suitable measurement to evaluate the performance against impact loads. On the other hand, the use of self-compacting composites due to its unique properties has attracted the attention of researchers. High compressive and tensile strength, high flexural strength, has attracted more attention from researchers to this kind of cement composites. In this research, in the form of a comprehensive laboratory work, using four basement mixing designs, 64 rectangular composite panels were constructed in two groups of 100*100 mm with four thicknesses of 30, 45, 60 and 75 mm and tested under dynamic loading. Tensile and flexural strength tests were made on all four mixing designs. Steel fibers with percentages of 0, 0.25, 0.5 and 0.75 with length of 25 mm were used for the construction of cement composites. The drop hammer test machine with weighs 180 kg and the power of 7500 J is used. According to laboratory results, the combined use of steel and fiber reinforced steel sheets increased the energy absorption considerably. Also, the initial peak force increased and the deformation length decreased.

The earthquake is one of the natural phenomena, this is due to the impossibility to predict the time of the occurrence and impossibility prevention of earthquakes and then followed many physical's and financial Damage and Iran with the particular structure of the quake there, active and Seism tectonics in granite is among the areas with high risk of earthquakes in the world. One of the tools to control the behavior of the structures is the use of the Dampers .Structural control means that the characteristics of the dynamic behavior of structures to be set up in a way that the structural response under the effect of external irritation about not allowed outside .TADAS Yielding plate damper for loses of energy from controlled the speed and relative displacement of frame structures using classes ,Be aware of the performance and impact of the damper efficiency, engineers use them to help reduce the damage caused by the earthquake. Structural models consist of a four-story structure model, one span and three spans, and a two-story, one-and three-span structures, which were completely non-linear in sap software. And then same structure check with TADAS Damper on far from and near fault. The results show that the presence of this type of damper, the structural responses including drift and shear in the far-off faults are 20.85 and 21.12 respectively, and in the near-fault state, decreases by 23.30 and 26.84%, respectively

By reviewing previous studies in the field of roof’s collapse, an efficient analytical method is required to simulate the impact mechanism and failure procedure. Hence, the purpose of present study is mainly to analyze the beams' impact. Consequently, upper and lower beams are considered to survey the collision effects of upper beam’s equivalent concentrated mass to the lower beam’s midspan in a way that an initial impact caused by mass is taken into account. At first, the maximum bending moment at the midspan is calculated by assuming linear behavior and employing the relations which involves the kinetic energy of concentrated mass and potential energy of the lower beam. Then, studying a conventional steel frame demonstrates that the bending moment is about eight times greater than the bending moment capacity of lower beam, therefore it would lead to formation of a plastic hinge at the midspan. In continue, the mentioned relations are solved by using the equations of motion including inertial effect. The results are used to calculate velocity in different sections of lower beam. Subsequently, the equilibrium equation is employed in the middle of lower beam and a virtual hinge at an arbitrary section which is tending in a wave form to supports is considered. Due to mentioned assumptions by investigating hinge formation behavior, the time of hinge tendency to the supports is calculated. Additionally, displacement values along the lower beam are obtained. Finally, the diagrams and tables are represented by using the obtained equations and compared with the lower beam's displacement capacity. The results demonstrate that the lower beams will collapse due to the collision of concentrated mass of upper beam and progressive collapse occurs in lower stories. Finally, for more accuracy of present study, the effect of secondary impact of upper beam on the lower beam is considered.

One of the simplified methods, which is progressing and completing every day, is a nonlinear static analysis that can directly evaluate the performance of a structure in any limit state and provide information about the nonlinear behavior of the structure, and it also does not have the complexity of nonlinear dynamic analysis. In this study, the structural responses of nonlinear static procedure (NSP) based on standard 2800 were compared with ASCE 41-13 code and displacement -based adaptive pushover (DAP) method in three models of reinforced concrete structures including the 3, 7 and 10 story with medium ductility. In order to study the accuracy of nonlinear static analysis and seismic behavior of structures, nonlinear time history analysis (NTHA) which is the most accurate method in seismic assessment of structures was conducted.The results show that in 3 and 10 story the NSP according to standard 2800 with forces distribution obtained from the spectral dynamical analysis is more accurate than other NSPs in evaluating of story drifts ratio and maximum displacement along the height of buildings. In 7 story, displacement -based adaptive pushover (DAP) method can be estimated story drift ratio more precisely. In 3 and 10 story, the NSP based on 2800 with forces distribution obtained from the spectral dynamical analysis, can estimate the mean story drifts with a lower percentage error. According to the results, in each three model the uniform distribution of nonlinear static procedure (NSP) based on standard 2800 estimates the story drifts with less accuracy and high error. As a suggestion, nonlinear static analysis based on uniform distribution can be eliminated from the standard 2800.

Due to the fact that common structures are designed only against gravity and seismic loads, the performance of these structures must be investigated against impact loading, in order to protect against this damage if necessary. In this paper, the effect of the arrangement of different shape of transverse bars and their spacing on the performance of beam-column element against blast loading has been studied. In this study, 13 model of concrete beam-column element with different transverse bar arrangement has been explored to examine their performance against explosions with 25 kg TNT. The finite element modeling was performed in Autodyn software and the parameters of explosion modeling, behavioral models of concrete elements and rebar, air meshing dimensions and concrete elements were determined with the results of the field test of explosion in previous studies. In this research, five type of transverse bars shape were modeled proportional to the three spacing of transverse bars. The degree of deformation and the mode of failure of the elements were compared as a measure of the performance of different states of each other. The results showed that for constant area of rebar, the element with one square tie and one link has best performance comparing to other arrangements. The maximum deformation rate in the A-1 (with one square tie ) model was 65 mm and in the D-2 model (one square tie and one link), it was 26 mm, showing a decrease of 60%.

The linked column frame (LCF) as a seismic resistant system with the ductile behavior using shear fuse will reduce the damage to other members of the structure at different hazard levels. In this paper, the seismic behavior of the LCF systems designed by Shoaib and Malakoutian procedures has been evaluated. In order to improve the seismic performance of the designed samples, a new and optimal system with the pattern of the double linked columns has been proposed. For this purpose, a 3-story model of SAC buildings with two linked beam bays and four- moment frame bays has been designed by the procedures. The studied models include: 1-The model designed by Malakoutian procedure (MaM), 2- The model designed by Shoaib procedure (ShM) and 3- The LCF with double-linked column pattern (DLCF). Models have been evaluated using incremental dynamic analyses according to FEMAP695 instructions in OPENSEES. The results show that the model designed by Shoaib procedure (ShM) has “50%” and 14% more capacity than the model designed by Malakoutian procedure and the DLCF model respectively. Also the average link beam capacity in the ShM model is “50%” higher than the MaM model. Finally the results show that compared to the MaM model the new pattern of the linked column in the DLCF model has considerably increased the structure’s capacity, the link beam capacity in energy absorption and base shear capacity by an average of 30%.

In this study, the influence of different kinds of nanomaterials such as Nano oxides of Silica (NS), Aluminum (NA) and Copper (NC) on compressive strength (f’c), static elastic modulus (Ee), relationship between f’c and Ee and the relationship between static and dynamic elastic modulus (Ed) of self-compacted concrete are examined. The nanomaterials are used as the binder in replacement of Portland cement. For this purpose, standard cylindrical samples containing NS, NA and NC with amounts of 1.5, 0.25 and 0.25%, respectively, were tested between 3 and 90 days. The f’c, Ee and Ed are evaluated according to ASTM C39/39M-16b, ASTM C469/C469M-14 and ASTM C597-16, respectively. Results indicate that adding Nanomaterials lead to improvement of f’c and elasticity module. New relations between f’c and Ee and, also, linear relation between Ee and Ed defined for this kind of self-compacted concretes, and it was observed that type and quantity of the Nanomaterials have impact on these relations. The experimental data of Ee at early ages are smaller than the calculated values of Ee from recommended equations by ACI 318-14, ACI 363-10, and CSA A23.3-14. The difference between experimental data and calculated values of Ee is decreased when f’c increases. when the f’c is higher than 45 MPa, the experimental data of Ee are higher than the calculated values of ACI 363-10. The study indicate that the Ed is always greater than the Ee and the difference between Ed and Ee is decreased when f’c increases. It was found that the differences between Ed and Ee in this study are greater than the differences between Ed and Ee in BS 8110: 2 and the other studies.

Using viscoelastic (VE) dampers is one of the most effective tools for seismic retrofitting of steel structures. The results of many experimental studies demonstrated that using fractional derivative terms for modelling viscoelastic dampers offers an acceptable level of accuracy. Unlike viscous dampers the damping force is not linearly dependent to velocity and it is also highly affected by excitation frequency and ambient temperature. For this reason, solving the dynamic equation and calculating the seismic response of the structures equipped with VE dampers have many complexities. In this paper, the responses of a viscoelastically damped structure are calculated and the seismic performance of the building is evaluated while considering the effects ambient temperature as well as the inherent uncertainties related to ground motion excitation. The proposed relationships were used to calculate the structural responses and assess the seismic performance of a 5-story steel structure retrofitted with fractional viscoelastic dampers. The maximum relative displacement of the controlled structural at the operation, design, and maximum considered expected hazard levels were compared to those of the initial structure (without damper). Furthermore, fragility curves were used to compare responses and exceedance probabilities of performance limit states. The results show great improvement in structural seismic performance related to the reduction of both structural responses and exceedance probabilities of limit states. The effect of temperature changes in results has been also demonstrated.

Observations from past earthquakes in reinforced concrete buildings show that the masonry partitions can endanger the life of buildings occupants and lead to significant damage and loss. The most present codes of practice do not consider the effects of nonlinearity and higher modes of the structure and three-dimensional behavior of partitions on the out-of-plane seismic demands of these components simultaneously and the main purpose of this study is to investigate the effect of these cases together. This research involves assessing the seismic performance of partitions made of the hollow brick located in different stories of 3-, 7- and 11-story buildings containing 3D reinforced concrete special moment frames and subjected to a suite of 7 appropriate earthquakes. A finite element program, OpenSees, has been used for nonlinear seismic response history analysis. The average of the peak of responses of partition, under the seismic excitations, was computed for any model and the forces obtained using the analytical method, which some of them verified with existing studies results, were compared with the values from the code. For the majority of the models, the results show that the analytical seismic demands on partitions, in the lower half, are higher than those calculated using the code provisions because of the effect of higher modes of the structures and the peak values is even up to 1.54 times the computed value based on the code. The code provisions are conservative for the partitions in the upper half of the buildings.

Because of non-linear and settlement dependent behavior of soil and effect of the interactions, understanding the behavior of piles and raft and the load sharing mechanism in piled rafts is a key issue. Recently, researchers have introduced few normalized hyperbolic models according to numerical analysis to estimate the load-sharing ratio of piles in piled raft foundations. These models are based on experimental results and considering different interaction effects between pile-raft-soil, raft, and pile dimensions and the amount of settlement. The aim of this research is to investigate the behavior of piled raft foundation and to estimate the load-sharing ratio of piles experimentally. So, various tests have been conducted on piled rafts, group piles, and unpiled rafts under vertical loading by changing the number and length of piles and density of bed sand. For this purpose, an innovative combined loading system, instrumented by measuring devices, is designed and constructed; then the load-sharing ratio of piles from the total load with a novel method is estimated by measuring soil pressure underneath the raft at any settlement. According to the results, bearing capacity of piled raft foundation in analogous conditions is more than unpiled raft and twice group piles approximately. Also increasing the number of piles in piled rafts and group piles increases bearing capacity and reduces raft settlement. The load sharing ratio of piles shows downward trend by increasing settlement and it increases with increasing the number of piles in the same conditions. In this study, the ultimate bearing capacity of group piles which have been experimentally obtained is compared with the ultimate criterion of the hyperbolic model proposed by other researchers. Then, the model is modified by mathematical analysis methods indicating good agreement between experimental and analytical results.

Nowadays, the using of steel moment frames has been considered as an effective lateral load-resisting system against seismic forces. In this research, the effect of plastic hinges modelling of fully restrained connections has been evaluated on the strength of steel moment frame structures against progressive collapse. In order to assessment of the progressive collapse performance of sample structures, two structural models of 3 and 5-story buildings were designed and then the definition and modelling of plastic hinges have been done in two different modes. In the first mode, plastic hinges were modelled only for the beam and column members. In the second mode, plastic hinges were considered for the connections in addition to the beam and column members. The Five different types of investigated connections included WFP, WBH, WCPinWUF, WUF-B, Welded top and bottom haunch. The progressive collapse resistance of these buildings against sudden removal of internal and external column was separately studied using nonlinear static alternate path method presented in the UFC standard. The results of analysis indicated that if the plastic hinges of connections are separately defined in addition to the plastic hinges of beams and columns, the structure will have lower progressive collapse strength, and the resistance of the structure tends to its actual value. Simultaneous modelling of plastic hinges for connections and members at least 20% and maximum 37% affects the reduction of structural strength against progreive collapse. Therefore, the modelling of plastic hinges for connections and members simultaneously should be considered as a important regulation. According to the comparative results, the WCPinWUF and WUF-B connection respectively demonstrated that the most desirable behaviour and the weakest performance against the progressive collapses.