نشریه مهندسی عمران مدرس
سال بیست و دوم شماره 6 (بهمن و اسفند 1401)

In geotechnical and geo-environmental projects such as thermal stabilization, thermal remediation of contaminated soils and nuclear waste disposal, clays are always exposed to heat and heavy metal contamination. The study of the effect of heavy metal contaminants and thermal treatment on the geo-environmental engineering properties of clayey soils has long been considered by many researchers. Calcium carbonate as a major component of clay soils and as a non-plastic material reduces the plasticity properties of the soil. Calcium carbonate affects the process of heavy metal adsorption by clay particles. Accordingly, the presence or absence of calcium carbonate in the soil can have a secondary effect on the plasticity properties of clay. Generally, clayey soils retain the heavy metal contaminants by four phases. These phases include retention by cation exchange, precipitation by hydroxide carbonates (oxide and hydroxide), organic fraction and residual retention. A review of the literature studies has shown that little attention has been paid to the effect of retention phases of heavy metal contaminant on the plasticity properties of bentonite in thermal improvement from a micro-structural point of view. For this reason, this study is aimed to investigate the influence of retention phases of heavy metal contaminant on the behaviour of bentonite in thermal process. A natural bentonite soil is used in this study. The soil has been decarbonated by the use of hydrochloric acid.  To achieve the above mentioned objective, carbonated and decarbonated bentonite was prepared in a non-contaminated state and laboratory contaminated with heavy metal zinc (Zn) at concentrations of 5, 10, 20, 70 and 120 cmol/kg-soil. Contaminated and non-contaminated samples are first ground and then subjected to a temperature of 20, 110, 300, 400 and 500 °C for two hours. Then, by the use of Atterberg limit, XRD, pH and SSE experiments, micro-structural and macro-structural analysis of changes in carbonated and decarbonated bentonite plasticity properties has been investigated. According to the achieved results, in low concentrations of zinc heavy metals, calcium carbonate phase of heavy metal retention is the dominant phase in soil contaminant interaction process which prevents the change of bentonite structure. Therefore, the reason for the reduction of the Liquid limit is the reduction of the electrical charge of the clay particles, which is the result of lowering the pH. By an increase in contaminant content, all of the soil retention phases contribute to soil contaminant interaction process. Therefore, the role of calcium carbonate reduces in soil plasticity behaviour changes. As the temperature rises, Zinc metal as an accelerating agent has further reduced the Liquid limit in carbonated bentonite and decarbonated bentonite. In decarbonated bentonite, due to the absence of calcium carbonate, the clay particles adsorb more zinc. As a result, the effect of lowering the Liquid limit during increasing temperature by the heavy metal zinc in decarbonated bentonite is greater than in carbonated bentonite. Bentonite with its predominant sodium and zinc exchange cations loses its plasticity properties at temperatures of 400 and 500 °C, respectively, and the plastic limit for them is not measurable.

The importance of some factors, including providing temporary and permanent habitation, construction speed, increasing the material strength and decreasing the construction cost, have made the attention to choice of vertical and lateral load-bearing systems as one of the necessities of the construction industry in the event of natural disasters such as floods and earthquakes. The need for any building in any area depends on a variety of conditions that may arise at one time and disappear at another. In this study, for the first time in Iran, firstly, a rapid-fabricated steel structure with both temporary and permanent habitation ability, and the capability of moving, assembling and disassembling is introduced, and then the seismic behavior of it’s beam-to-column connection is evaluated for using in ordinary steel moment frames. In order to evaluate the three characteristics of stiffness, strength and ductility of the proposed connection, nonlinear analysis is done using ABAQUS/6.14.2 software, and the evaluation of the seismic behavior of the connection is conducted in accordance with the criterias of chapter B of ANSI/AISC 360-16. According to the results, section properties and length of the beam, end-plate thickness, location and diameter of the bolts, and the location of the stiffeners on the end-plate are the effective parameters on the stiffness and strength of the proposed connection. Among all parameters, end-plate thickness and diameter of the bolts are two important factors that mostly affect the stiffness of the connection. Investigations show that the proposed connection, by having the sufficient stiffness and strength, is able to withstand the entire plastic moment capacity of the beam. Also, the plastic hinge is occurred outside of the connection region and the final failure mode of the system is the plastic local buckling of the compression flange of the beam. The mentioned abilities make it possible to use the proposed beam-to-column connection in ordinary moment frames as a fully restrained and fully strength connection.

Due to the increasing population and lack of construction space, the use of high-rise buildings around the world is inevitable, so the use of sections with high strength to weight ratio that take up less space has been considered by researchers. One of the sections that has been considered by researchers and engineers to achieve this goal is composite columns, especially steel filled with concrete (CFT). These columns use the advantages of steel and concrete both and also have advantages such as eliminating column formwork in construction, providing complete enclosure conditions for concrete, preventing concrete parts from collapsing and tearing from the steel profile of the column and delay. The buckling of steel sheaths due to the presence of concrete is more common than other composite columns. CFTs also have higher strength, lateral stiffness and ductility than reinforced concrete columns of the same dimensions. The use of external stiffeners for replacement with continuity plates has been considered by researchers and design engineers and various forms have been proposed so far. The results of previous research have shown that external stiffeners are a good alternative to continuity plates.In the present study, the behavior of steel frames with Hollow Steel Sections(HSS) and Concrete Filled Tube(CFT) Columns has been investigated. After launching the test setup and locating the displacement meters and dynamometers, the structure is subjected to cyclic loads according to the defined loading protocol. Three samples of two-opening and two-story frames with hollow box columns (HSS), concrete filled box (CFT) and concrete filled box with horizontal reinforcement nets have been evaluated experimentally and different parameters Their strength, ductility, hardness, energy absorption and cyclic behavior have been studied. In addition, the impact of the presence of concrete and horizontal reinforcement nets has been evaluated. On the other hand, in order to investigate the effect of using external stiffeners and horizontal bar mats in the frame, all connections of the two-story frame of the present study selected of this type. The results show that the use of concrete has improved the strength of connection due to the reduction of the buckling of the column plates, but the ductility has decreased. External stiffeners are used in all specimens, and as expected, the plastic hinge is moved into the beam, providing the idea of strong column-weak beam. In another part of the research, the behavior of the CFT frame and The presence of horizontal bar networks of the panel zone, which shows its effect of it in improving the behavior of the frame. The use of concrete in steel sections increases the strength of the frame, but since it is used in frames with CFT columns, beams with weaker sections show little reduction or little increase due to the use of concrete properties in pressure and Steel is in tension. On the other hand, the presence of concrete reduces the buckling of the column plate. In addition, the box-shaped sections around the concrete cause the concrete to be enclosed and ultimately increase the strength and energy absorption of the structure.

In the present study, the results of two numerical finite element models prepared for the dynamic behavior of a concrete bridge in the rail transport network have been modified using the GP algorithm compared to the field data. In this research, taking into account the logical error for the data obtained from the two numerical models and field survey, in addition to modifying the results of models in the field of frequency, acceleration and displacement, the assumed values in the analyses in the error range should be corrected. The results of the GP algorithm showed the success of the algorithm in reducing errors between numerical and field results; so that the errors are limited in the range of %. The bridge studied in this paper is the Arroyo Bracea Bridge in Spain that is made of concrete beams and slabs. This is a bridge with two 15.25 m spans and a 45-degree angle with I-shaped beams crossing two railways. This bridge is modeled with two finite element methods and then is measured via a field survey to evaluate the results of the both models. Then, the difference between the results of the two numerical models and field survey is reduced by proposing the GP algorithm. This bridge is modeled by SAP2000 using orthotropic plate, isotropic plate and beams model. In both models, 6 degrees of freedom are considered for each point, and the interaction between the train and the bridge is neglected. The values of mass, modulus of elasticity, cross-sectional specifications, and degree of stiffness of the support are determined for each model. Accuracy of dynamic parameters was obtained from the studied bridge and experimental samplings are conducted from two finite element models. In addition to surveying the dynamic specifications of the soil around the bridge, in this study, the natural frequency of the bridge is obtained with analysis of modals and values of acceleration and displacement in traffic load conditions by installing the piezoelectric accelerometers at 11 points of the bridge. In this study, the soil characteristics around the bridge were also examined. First, by explaining the basics of the GP algorithm, the algorithm prepared in this article was introduced. The data on cross-sectional values, modulus of elasticity, and mass were selected as effective parameters from the initial data of the models and were randomly recorded along with field data in the error range of 1000. For having data with the same level, the values of parameters were normally distributed. Then, by implementing the algorithm proposed for the initial data of each model, a mathematical equation was presented per field data. These equations, in addition to reducing the error of the results of the model, also modify the initial data by providing correction coefficients. The proposed algorithm reduces the error data by 20.31% for acceleration on the part of the bridge deck.  Given the importance of dynamic behavior of the bridges in high-speed or heavy-load lines, the high accuracy of the results of the analyses related to this behavior is very important. However, the use of GP algorithm for calibration in analysis of bridge dynamic behavior is very restricted and there is still a possibility of development and improvement. One of the achievements of this paper is that it can be used in similar issues by providing mathematical equations, modifying initial parameters with correction coefficients, and significant reduction in error values. For further research, it is also suggested to investigate the matching factor in specific vectors in the modal analysis via this method. Determining the optimal values of the proposed algorithm parameters using the other methods and sensitivity analysis of GP algorithm compared to the changes in parameters are among the other proper suggestions for subsequent research.

One of the most important problems in downstream hydraulic structures is the destructive kinetic energy of the flow. Experts always try to properly design and reduce the effect of this destructive force on the downstream of hydraulic structures in rectangular channel. The aim of this study was to investigate the effect of sudden contraction with the rough bed of contracted section on the relative energy dissipation in the supercritical flow. Three types of constrictions with widths of 5, 10 and 15 cm and three roughnesses with average diameters of D50=0.8, 1.28 and 2.08 cm and range of Froude number 2.5 to 7.5 and relative contracting 0.5 to 0.83 was examined. Experimental results showed that with increasing the upstream Froude number, the upstream relative energy dissipation (ΔE/EA) increases. Also, by applying roughness to the bed of all three sections of contracting, it was observed that energy dissipation increased significantly so that the highest energy dissipation with 78.35% increase related to 15 cm contracting and the lowest energy dissipation with 43.35% increase related to the contracting of 5 cm. The relationships extracted to estimate the relative energy dissipation showed that the results are in good agreement with the experimental data with a correlation coefficient of 0.927 and a normalized square absorption line of 0.02.

The performance of steel rebars in reinforced concrete is always complicated and important. Each reinforced concrete element contains two parts, including concrete and steel rebars. Under severe forces, the behavior of reinforced concrete structures and their elements is dependent on the interaction between steel and concrete.  Due to the composite nature of these structures, their performance is complex and might be studied in different aspects. Incorrect evaluation of this item will lead to the wrong design. Although this performance affects all parts of a concrete structure, development length and lap splice are the most significant parts. One of the common tests, in evaluating the steel reinforcing bars' performance, is the pullout test, however, there are deficiencies in different investigations. In this research, five pullout specimens were tested, containing four specimens with confined and one with unconfined concrete, which had three different bar sizes including 20, 22, and 25 mm. Tests were conducted on 300 mm cube specimens and 250 mm development length of steel rebars which was insufficient. Rebars with sufficient development length have a different performance. The testing method was monotonic and the compressive strength of concrete was 23 MPa. Normally two cracking and damaging mechanism is observed. It is pullout of rebar or splitting of concrete. In confined concrete pullout occurs, while in an unconfined specimen, splitting of the concrete takes place so the bonding strength and axial force tend to zero much faster. Using these results and results from other researches, some important parameters in the field of bonding and slippage of rebars, including compressive strength of concrete, rebar size, force direction (pulling or pushing), and confinement of concrete were investigated and some equations with high accuracy were proposed to generalize available results to desired results. For verifying and increasing the range of results, three valid kinds of research are used, which confirm the accuracy of results and equations. This study showed that the bonding strength would increase 20 percent by 50 percent increase in compressive strength of concrete. Moreover, by changing the bar diameter from 20 to 22 and 25 mm, for a constant compressive strength of concrete, bonding strength decreases 4.3 and 10.6 percent respectively. By using the proposed equation, maximum bond strength for different bar sizes may be evaluated. Besides, maximum bond strength is reduced up to 40 percent of a confined specimen, and the slippage corresponding to maximum bond strength is reduced 15 to 30 percent as the result of using unconfined concrete. In the same way, for the same bar diameter, pullout force reduced up to 40 percent. The slippage corresponded to maximum bonding strength is about 1.4 to 2 mm for confined concrete and 0.25 to 0.45 mm for unconfined concrete. Bond strength and slippage of rebars vary in compressive and pulling forces. This is due to the axial behavior of the rebar's head in compression. The compressive axial force of the bar may increase the bonding strength up to 10 percent, comparing to pulling axial force.

Damages caused by the impact of adjacent structures in past major earthquakes have shown the importance of structural control systems to reduce the seismic risk of the impact of structures. Connecting energy dissipation devices to adjacent buildings is a practical and effective approach to prevent collisions as well as reduce the seismic responses of structures, and this issue has been an active research field in recent years. One of the semi-active control methods is the use of MR dampers. These dampers use a magnetic fluid that produces large damping forces in a piston-cylinder system that can be controlled instantly by changing the applied voltage to the damper. The Bouc-wen model has been used to take advantage of the unique properties of MR damper as well as to consider its inherent nonlinear behavior. In this study, to evaluate the performance of MR dampers using a fuzzy control system, three- and nine-story standard structures under seismic excitation of two near-field earthquakes including Kobe (1995) and Northridge (1994) and two far-field earthquakes including El centro (1940) and Kern county (1952) with maximum accelerations of 0.1g to 1g are investigated.The MR damper is connected to the third floor level of the two structures and can produce a controlled force equivalent to 1000 kN. The fuzzy system is designed based on the displacement of the third floor of two structures to reduce the risk of collision of structures as well as reduce seismic responses. the benchmark buildings have been modeled in OpenSees and the fuzzy control system was implemented in MATLAB software. The displacement responses of the third floor of structures are considered as the input value of the fuzzy system and the required voltage of MR damper is considered as the output value of the fuzzy system. In addition, triangular membership functions have been used to determine the degree of membership of input values. In general, the control system designed under far-field earthquakes has shown better performance in reducing the responses of two structures compared to near-field earthquakes. According to the results obtained from the dynamical analysis, the fuzzy system used under far-field earthquakes compared to near-field earthquakes and based on evaluation criteria of J1 (maximum roof displacement), J2 (maximum roof acceleration), J3 (maximum Base shear) and J4 (maximum relative displacement of floors) in three-story building 17.35, 4.94, 3.58, 12.17% and in nine-story building 7.93, 7.05, 0.67, 9.13%  showed better performance, respectively. Also, according to the evaluation criterion of J5, which is related to the minimum required gap between two buildings, the fuzzy system used under far-field earthquakes has shown 9.71% better performance than near-field earthquakes.

Cementitious composites are mainly used in the construction industry due to their good characteristics such as low cost, acceptable compressive strength, and easy access. However, there are many weaknesses in these materials, including low tensile strength, brittle behavior, and unacceptable durability (service life), which need to be improved to achieve more sustainable constructions. Nowadays, the using of nanotechnology have been growing and nanomaterials have been widely used in compound with a multitude of conventional materials. The outstanding chemical and physical properties of nanomaterials enable them to play a key role in various applications, such as modifying the material structure, ameliorating the properties of the material, and manufacturing modern multifunctional products. Recent advances in nanotechnology have led to produce nano-sized particles that can improve the durability performance of construction materials. Nanoparticles such as nano-silica, nano-Fe2O3, nano-clay, carbon nanotube (CNT), nano-Al2O3, nano-TiO2, and graphene oxide have been used to enhance the properties of cementitious composites. The performance of halloysite nanotube on the characteristics of cementitious composites has been studied less than other nanomaterials. Although the positive effects of nanomaterials such as halloysite nanotube (HNT) on the properties of cementitious composites have been proven, the very important issue of the correct and proper dispersion of nanomaterials in the cementitious environment has not been studied acceptably. The high surface energy and interparticle forces, including van der Waals, hydrogen bonding, and electrostatic interactions, make the nanomaterials highly susceptible to agglomeration. The aggregates of nanomaterials not only decrease their benefit but also act as potential weak spots in cementitious composites that can cause stress concentration, therewith diminishing the mechanical properties of cementitious composites. In this regard, the current paper investigated the effective factors on the agglomeration of halloysite nanotube (HNT) in the cementitious alkaline environment. Finally, this paper presented an approach for solving the problem of HNT agglomeration. Results showed that Ca2+, K+, and Na+ ions as alkaline agents of cement environment are the main factors to provide a state for HNT agglomeration. Among them, Ca2+ has more effect in agglomeration of halloysite nanotube due to the bridging effect between halloysite particles. From the results, the dispersion of HNT made better with increasing the alkalinity of cement environment until pH=11, while after this pH, the agglomeration of HNT started and the intense of agglomeration raised with the increase of pH, where it reached a maximum value at pH=13.5. Common approaches to nanoparticle dispersion are through physical methods (e.g., ultrasonic, high shear mixing, ball milling, etc.) and chemical methods (e.g., chemical modification of nanoparticle surfaces, use of dispersants such as surfactants, etc.). For the cementitious systems, a combination of ultrasonic and surfactant is mostly suggested. In this research, the effect of various surfactants on overcoming the agglomeration of halloysite nanotube in the cementitious environment was studied. The results indicated that the Polycarboxylate-based surfactant has better performance on improving the dispersion of HNT compared to that of other surfactants. Furthermore, incorporation of 3 wt% HNT enhanced the compressive, flexural and sorptivity of plain mortar up to 26, 22, and approximately 28%, respectively. The outcomes of the current paper display the fact that it is necessary to have special attention on the subject of the proper dispersion of nanomaterials in the cementitious environment for achieving the maximum efficiency of nanomaterials.

 The removal and treatment of sludge from municipal wastewater treatment plants is important due to environmental factors, so there is a significant incentive to discover and develop strategic plans to reduce excess sludge production in sewage treatment processes. Activated sludge system is used as the main biological process for municipal and industrial wastewater treatment and an excess sludge production rate in this process is between 15-100 liters per kilogram of removed BOD5. One of The usages an anaerobic reactor in the activated sludge system known as the Cannibal process that is one of the conventional methods used to reduce the sludge production rate at the sewage treatment line, which has low operating costs and relative simplicity to process design. The system's overall reducing efficiency is generally up to 50%. The purpose of this process is less production of sludge and also improvement of wastewater quality. In order to achieve reduction in excess sludge production, different mechanisms are considered which include microbial predation, uncoupling metabolism, endogenous metabolism and lysis-cryptic growth. The microbial predation mechanism is one of the important mechanisms in the cannibal process that is a suitable choice for reduction of excess sludge because of its low strategic cost and environmental compatibility. The objective of this research is the applicability of Quorum quenching (QQ) phenomenon in a conventional Cannibal process for enhancing the microbial predation mechanism to improve the efficiency of reducing sludge and other effective sludge parameters. Quorum sensing system is a new method of managing social behavior of microbial Population. The decomposition of Acyl Homosserine Lactones (AHL) is the most usable and practical way for creating disturbance in Quorum sensing system. For increasing the free bacteria population, Quorum quenching agent is used in the aerobic tank. These enhance microbial predation and show decrease in Extracellular Polymeric Substances (EPS). So far many bacteria with QQ feature are reported in biological wastewater treatment reactors. The basis of this project was designed in two laboratory phases and the reactors were operated with synthetic wastewater. In the first phase, the cannibal process was used in the form of a laboratory reactor, and in the second phase, by installing a separate aeration reactor and adding the Rhodococcus sp.BH4 bacteria, a quorum quenching bacteria, in a polymeric structure of alginate and introduced as QQ beads. The modified Cannibal process was designed. Microbial predation mechanism is one the methods that increase population of eukaryotic predators by changing the microbial structure of activated sludge system; by this method, efficiency of reduction of excess sludge production is increased. The results showed that the presence of QQ grains led to an increase in the number of eukaryotic species. The yield coefficient (Yobs) in the modified Cannibal and the control Cannibal was 0.389 and 0.092, respectively, with a significant decrease of 77%. Also, the results of EPS, which indicates the proper functioning of this system, has been analyzed and investigated. The applied QQ primary treatment enhances the Microbial predation mechanism in Cannibal system, significantly improve the efficiency of this system, and biological excess sludge notably is decreased.

In recent years, many studies have been conducted on the mechanical properties and durability of fiber concrete. These types of concretes are used in the reinforcement and repair of high-rise structures. In this study, the effect of mixing fiber concrete with 1 to 6% of additives including E207 and polycarboxylate ether separately with polypropylene fibers using durability tests including bulky water absorption tests, electrical resistance, rapide chloride penetration (RCPT) as well as compressive strength of concrete have been investigated. In addition, to study the microstructure of cement paste containing polypropylene fibers and polycarboxylate ether additives and E207 additive, X-ray diffraction (XRD) spectroscopy scanning electron microscopy (SEM) and X-ray chemistry tests were used. The results show that with the addition of polycarboxylate ether and polypropylene fibers (sample A) the permeability of chlorine ion in the samples was reduced uniformly so that the maximum reduction in chloride permeability in sample A was 51% while The addition of E207 additive and polypropylene fibers (sample B) reduced the permeability of chloride in concrete by 35% compared to the control sample. On the other hand, by adding additives A and B in the mixing design, the water absorption of concrete in samples A decreased by 27% and in samples B, 21% compared to the control sample. Also, the addition of polypropylene fibers in the amount of 0.6 kg/m3 reduced the electrical resistance of concrete in the samples by 5% compared to the control sample. The electrical resistivity in samples A increased by 213% and in samples B by 268% compared to the control sample. Compressive strength in samples A increased by 134% and 56% compared to the control sample of 7 and 28 days, respectively. And the highest compressive strength in B samples at 7 and 28 days of age increased by 38% and 39% compared to the control sample, respectively. In addition, by adding E207 to sample B, the compressive strength of the samples was reduced by more than 4%. Also, the results of SEM experiment showed that by adding polycarboxylate ether additive and E207 additive to the concrete microstructure concrete mix design, both samples were more homogeneous and dense than the control sample. The water apsorbtion less aligned .The results of XRD and XRF experiments on the samples showed that by adding polycarboxylate ether and E207 additives to the samples, more calcium silicate gel was formed and the aggregate pores were more cohesive and cohesive than the control sample, which confirms the results. Compressive strength test of concrete. According to the mentioned results, it can be concluded that with the addition of polycarboxylate ether and E207 additives, the durability and compressive strength of fiber reinforced concrete with polypropylene fibers are significantly increased against aggressive factors and concrete structures in the design. Mix concrete using additives according to this research. They will have a longer life and greater resistance to the aggressive agents of concrete structures, especially chloride, which will be economically viable in large projects

Deep beams are members considered to have span to depth ratio less than 4. These beams are widely used in different sorts of structures including dams, reservoirs, silos, caissons and high-rise buildings. The cracking mode of deep beams is mainly dependent on their boundary conditions. Due to the rule of shear failure, deep beams are designed against shear. So, strengthening and repairing these beams has always been important to improve shear resistance. One of the applied methods is the use of CFRP fibers for repairing and strengthening deep beams. These fibers can be fabricated in the form of strips, sheets and rebars. Due to the constructional limitations, CFRP strips are frequently installed on the external surface of beams. For this reason, the failure of strengthened beams coincides with debonding of CFRP strips. The former experiments indicate that strengthening deep beams with CFRP strips is useful for improving their behavior. These experiments also indicated that parameters including strengthening angle, shear span to depth ratio and the method of CFRP installation can affect the strength increment due to CFRP. One of the other remarkable parameters that affects the behavior of reinforced concrete beams is size effect. This parameter matters when the geometry of struts and nodal zones remains slender in deep beams. To assess the intensity of size effect in deep beams, the force strength of beam must be normalized based on the compressive strength of concrete and the beams sections area. This study was conducted to investigate the effect of CFRP strengthening on the size effect on deep beams. It was aimed to use explicit dynamic analysis method in Abaqus software so as to model and analyze 53 CFRP-strengthened deep beams with evaluation of previous experiments. In this method, due to the absence of excessive iterations within each analysis step, the number of analysis steps is increased. The so-called method is also appropriate for simulating quasi static models. To reach the purpose of study, the specimens of three different experiments were modeled and analyzed to evaluate the assumptions of numerical modeling. After the evaluation conditions were satisfied, 53 deep beams were modeled in Abaqus software. The specimens were subjected to two incremental point loads and were divided into four-member groups with depths of 400 mm, 600 mm, 800 mm and 1000 mm. The beams shear span to effective depth ratios are 0.5, 1 and 1.5; The compressive strength of concrete also varied from 24.8 MPa to 35 MPa. Since changing the width of deep beams does not affect the intensity of size effect, the beams width was considered constant and equal to 80 mm.The results of the study indicate that strengthening deep beams with CFRP strip or sheet is suitable for reducing the size effect; In addition, increasing compressive strength of concrete and keeping the loading plate constant can amplify size effect of deep beam. Increasing shear span to effective depth ratio of beam caused the size effect to be decreased. Strengthening deep beams with both angles of 45 and 90 degrees was appropriate for decreasing deep beams size effect.

In the present study, the feasibility of ensuring uniform deformations in the lateral bearing system of thin steel shear walls has been investigated. For this purpose, using ABAQUSTM finite element software, a 3-story concrete frame was modeled and analyzed by the nonlinear time history analysis method. Due to the lower weight, speed of execution and consequently the reduction of construction costs in steel shear walls compared to reinforced concrete shear walls, they have been significantly developed. In important buildings in North America and Japan, this type of lateral bearing system has shown very good behavior against strongly earthquakes. Also, due to the good performance of steel shear wall systems, the use of steel shear wall in seismic countries during earthquakes in North Ridge, USA, Kobe and Japan has greatly increased. The system of steel shear walls is similar in performance to plate girder. In steel shear walls, the columns act like flanges, the filler steel plate acts as the web and beam similar to the stiffeners in the plate girder system. In general, the performance of steel shear walls is based on the creation of a diagonal tensile field in the steel plate that occurs after buckling. In 2003, the Canadian Steel Structures FEMA 450 proposed guidelines for the design of steel shear walls. In 2005, the design requirements for steel shear walls with special details were added to the steel structures section of the AISC Regulation. According to ASSHTO 2018 regulations, steel plates are divided into three behavioral ranges slender, moderate, and stocky according to their thickness. In 2021, during research, a new method for evaluating the behavior of steel shear walls with the relationship of part of the plate height to the vertical boundary elements was reviewed. In this type of connection, the middle of the filler plate was not connected to the vertical boundary elements. In this type of connection, reducing the connection length between the filler plate and the vertical elements leads to a reduction in stiffness and bending on the vertical boundary elements. In this paper, three different thicknesses were selected in the behavioral range of slender plates and how to connect them to the surrounding elements was defined in whole and in partial. In this evaluation, the effect of changing the connection length of the steel plate for the range of slender plates is investigated. The connection of steel shear walls to the surrounding members (beams and columns) is based on the percentage of the shear plate and the connection length ratio of steel plates are examined on the maximum relative in-plane displacement (drift) and the displacement of all stories. Uniform distribution of live and dead loads for the roof floor 1 and 5.3 (KNm2) respectively and for the other floors equal to 2.5 and 5.5 (KNm2) respectively is assumed. The behavior of the frame in the first stage is evaluated by the record of the Kobe earthquake. The results showed that in general, reducing the length of the plate connection leads to an increase in the maximum relative in-plane displacement (drift) of the stories and it is possible to control the ductility of the structure. 0. 6  is the critical area for a sender plate 5 mm. Because due to the early buckling and the occurrence of resistance after buckling, the maximum relative in-plane displacement (drift) has decreased. Also, 0.6 and CLR≥0 / 75 introduced as critical areas for 2 mm and 8 mm plates, respectively. In slender plates with very small thicknesses, the shear strength is very low and can be ignored, and the plate enters the post-buckling resistance immediately after loading. For this reason, the results of these plates determine the behavior of the structure. By reducing the thickness, the non-uniformity in the maximum relative in-plane displacement (drift) of the stories was seen, which was significantly improved by using suitable partial connections of the shear steel plate to the surrounding elements.

During the construction of steel structures, the executive groups often fabricate some stories and tighten the connection bolts, defined as the snug-tightened bolt in this research. The lower stories, in which the connection bolts are snug-tightened, will be pre-tensioned at least to the level of preloading based on design codes, called pre-tensioned bolts, in this paper. The connections will be complete, while some upper stories will have snug-tightened bolts. As a result, the stiffness of the bolted connections varies throughout construction, and the structural characteristics change with time. So it is necessary to investigate the seismic behavior of bolted extended end-plate moment connections in both snug-tightened and pre-tensioned bolts while constructing high-rise structures. Bolted unstiffened end plate moment connections are one of the most usable connections used as prequalified connections in special steel moment frames. According to the AISC design code, this connection can be considered one of the most important parts of moment-resisting frames with enough bolt pre-tension levels. In this paper, using three full-scale bolted unstiffened end plate moment connections designed according to AISC, the effects of bolt pre-tension levels have been examined experimentally under SAC cyclic loading protocol. Bolt pre-tension level has been defined as α coefficient to show the pre-tensioning level in three specimens. The bolts of the first specimen are not pre-tensioned, called snug-tightened bolts, and is reference connection. The bolt pre-tension levels of the second and third specimens were created in accordance with AISC and Iranian National design code and more to Fu of bolts, called pre-tensioned and fully pre-tensioned, respectively. The bolts' moment capacity, total energy absorption, initial rotational stiffness, ductility of connection, and stress and strain variation are investigated. According to the results, an increase in bolt pre-tension level would significantly improve the cyclic behavior of connections. Further, an increase in bolt pre-tension led to the initiation of the inelastic deformation from a minor rotation, and the ductility of the connection improved. The results show that the increase in moment capacity and energy dissipation in the pre-tensioned compared to snug-tightened is 27 and 23%, respectively. However, In comparison with the pre-tensioned, the fully pre-tensioned specimen has increased by 11 and 9%, respectively. As a result, the connection with bolt pre-tension level, under design regulations in comparison with the reference connection, can be considered a connection of a special moment resisting frames. So bolt pre-tension level higher than the value mentioned in the design code is better but not needed.

In many construction projects, it is necessary to excavate the land so that its walls are vertical or close to vertical. Lateral pressure is exerted on these walls due to the movement of the soil behind it. In order to prevent the collapse of the walls of the excavated site and its possible consequences, temporary or permanent structures are implemented, which is called stabilization. Excavations are secured for various reasons. They may be stabilized to protect personnel entering and working in the excavation or to protect buildings or municipal services adjacent to excavation. Over the past years, there have been a large number of excavations in large cities, including Tehran, which were abandoned due to some problems. Furthermore, while some excavations need to be designed for a long time, long-term design basics are not observed during such processes. Stabilization of most of these excavations has been done using anchors. In this method, after placing and implementing the anchors, they are prestressed by applying force. Observations and long-term surveys of these excavations show that in some cases, locking force of anchors decreases, leading to dangers. Therefore, it is very important to know the long-term behavior of anchors in excavations to investigate the stability of these excavations that are prolonged or abandoned for a long time. In this study, field data of the long-term behavior of a excavation in Tehran is used and numerical modeling is done based on this case study. Verification and calibration of the numerical model has been done based on field measurements. Also in this article, relationships based on the results of the numerical model have been proposed to predict the anchor load in the long term in cohesive coarse-grained soil. The proposed relationships predict well the anchors load at one year after the end of excavation. These relationships are separated to three categories of five strands anchors, six strands anchors and six strands anchors with short length. In the following, the variables affecting the long-term behavior of the anchor loads embedded in the excavation have been studied. These variables include soil properties, depth of the excavation and neighbor surcharge of the excavation. The results of this article, in addition to presenting the relationship for anchor load prediction, include the introduction of variables that affecting long-term behavior. The parametric study shows that with the increase of the angle of internal friction or the increase of soil cohesion, the amount of anchors load decreases over the time. Also, by increasing the depth of the excavation or increasing the neighbor surcharge of the excavation, the load of the anchors decreases less over time. Of course, the impact of excavation depth occurs mostly in the lower anchors and does not affect the anchors of the first row and close to the ground. Studies showed that anchors close to the earth surface have a greater rate of load reduction over time among anchors with the same length and number of strands. Also, among the same anchors, anchors with shorter length experience more load reduction over time.