نشریه مهندسی عمران مدرس
سال بیست و سوم شماره 1 (فروردین و اردیبهشت 1402)

Advancements in tunnelling technologies and ease of implementation of drilling methods in addition of other political and security issues made the construction of underground structures as an important alternative for answering the demands of population growth and the limitations of surface spaces in urban areas. Underground roads and highways, various types of tunnels and urban subway networks are the examples of underground structures being constructed and rapidly implemented in different countries. Meanwhile, for reducing negative effects to the environment, shortening the routes and improving traffic efficiency, urban tunnels should have high level of safety standards in design, construction and operation. Tunnels are considered major national projects and infrastructure investments, and huge costs are incurred around the world to build these structures. In countries located in highly active seismic zone, such as Iran, seismic researches for such important underground structures should not be ignored. The safety of such structures should be provided with respect to all loading demands and hazards issues associated with the site, including seismic loads. Reviewing seismic events in the past shows that underground structures have suffered less damage than above ground structures against seismic loads. However, in recent years, major earthquakes such as the 1995 Kobe earthquake in Japan, the 1999 Chi-Chi earthquake in Taiwan, the 1999 Kocaeli earthquake in Turkey, and the 2008 Wenchuan earthquake in China have caused underground structures to experience significant damage. There is evidence to conclude that the structural vulnerability of a tunnel in seismically active areas is an important issue but is either not yet well understood or not well assessed at the time of construction, emphasising that dynamic analysis of these structures against seismic loads is necessary. Earthquakes are likely to significantly affect tunnel performance by causing severe damage or excessive deformation of the tunnel structure. To understand the seismic-induced behaviour and performance of urban tunnels, this paper provides the state of the art in modelling studies of seismic design and assessment of tunnels. The review includes an investigation in seismic responses of real tunnels reported during past seismic events, the probable mechanisms caused damages in tunnels and physical and numerical methods used until now to either investigate those mechanisms or implemented in new designs. As an introduction, the seismic performance of tunnels affected by previous seismic events discusses first, emphasising the effective parameters in evaluation of tunnel seismic response and the relationship between the parameters, and the damage levels caused during earthquakes. Subsequently, the paper continues with a comprehensive literature review on the experimental methods used to investigate seismic-induced response in tunnels including physical testing, centrifuge tests, shaking table tests, and static tests. Analytical, quasi-static and numerical methods of dynamic analysis of tunnels and the accuracy of these methods are discussed then in details referring to some examples. The paper also reviews the effects of soil heterogeneity in the seismic response of tunnel and application of the random field for dynamic analysis of underground structures.  Examining the achievements and challenges remained in the field, the paper concludes with the existing gaps in the field to stimulate readers for doing more relevant researches.

Concrete Filled steel Tubes (CFT) have several advantages when used as columns in buildings. These advantages include efficient structural section benefiting from combined action of concrete and steel , drastic reduction of the need for steel rebars, confinement of concrete by steel tube permitting higher compressive strains, increasing resistance of steel tube against local buckling, eliminating a separate formwork for concrete and reduction of construction time. On the other hand, connection of steel beam to round steel columns including CFT has been a major challenge.The main complexity arises from difficulty of accessing the inside of tubular columns for installing continuity plates to transfer tension or compression between opposing beam flanges. Different methods have been proposed in the past to alleviate this problem. Solutions presented so far include external collar stiffener plates connecting opposing beam flanges, extending only the web of beam through steel tube column, extending beam flanges through column, using steel rebars embedded in concrete core and attached to beam flanges and finally, complete passage of steel beam through steel tube. Cyclic behavior of beam-column connection plays a vital role in seismic response of moment frame structures. Literature survey shows that despite numerous methods proposed for steel beam-CFT column connection, not any organized attempt has been undertaken to explore the cyclic behavior of these connections. In this paper, numerical modeling has been utilized to investigate the cyclic behavior of continuous steel girder and circular CFT connection. Before achieving the main analyzes, the modeling and analysis assumptions and techniques were verified using available pushover experiments on typical connections of similar arrangement. In current study, effect of column diameter, thickness of steel tube and thickness of girder flange and girder web have been considered. Fourteen samples with different values of column to beam moment capacity ratios ranging from 0.78 to 1.95 have been analyzed. Actual dimensions of specimens were selected to be compatible with production of steel tubes and have reasonable lateral load bearing strength. Beam and column dimensions were checked to comply with AISC360 compact section limitations. Two diameters of 405 and 505 mm were specified for columns while beams had a fixed depth of 428 mm. Thickness of St37 grade steel tube ranged between 4.5 to 8.5mm. Beams were considered to be of St52 grade with flanges of 12.5 to 16.5mm thickness and webs between 7 to 11mm thick. Some specimens slightly violated seismic compact section regulations of column and girder. Meanwhile, all specimens showed stable and large load-drift cycles and could tolerate 0.04 story drift ratio as stipulated by AISC code for special moment connections. Specimens which fully complied with code reqirements could undergo 0.05 story drift ratio while still maintaining at least 80 percent of their maximum strength. Analysis results show that in specimens with same columns, increasing girder flange or web thickness is accompanied with increased energy absorption. The fraction of energy absorbed by elastic deformation increased more than the energy dissipated through hysteretic nonlinear deformations. As a result, a reduction in hysteretic damping accompanied the increase in beam flange or web thickness.

The durability of a concrete structure is highly dependent on the strength and permeability of the surface layer, as it is the surface layer that must prevent the entry of materials that can initiate or enhance the harmful effects on concrete. Sulfates are one of the most common destructive factors in concrete in most parts of Iran, especially in the southern regions of the country where concrete is exposed to seawater (which contains sulfate compounds). Also, the lack of compaction of the surface layer, due to the difficulty of vibration in limited spaces between molds and rebars and other accessories, is one of the main reasons for the poor durability of reinforced concrete structures exposed to environmental factors. Naturally, incorrect vibration results (worming, detachment, dehydration) have stronger negative effects on permeability and therefore durability. Self-compacting concrete with suitable properties is free from these defects and as a result, materials with less inconsistency and uniform permeability have less weaknesses for environmental harmful factors and, therefore, have better durability. Therefore, considering that the "torsion" test shows good sensitivity to surface changes of concrete, so in this study, using the "torsion" test, the effect of magnesium sulfate on the surface strength of self-compacting concretes has been investigated. In the "twist" test, a 5 cm diameter metal cylinder is glued to the surface of the test site using epoxy resin adhesive. Then, using a conventional hand-held tachometer, a torsion anchor is inserted into the metal cylinder to break the test object. The equipment used in the "twist" test is very cheap, simple and accessible compared to other corresponding tests. The damage from the "torsion" test is very superficial and minor, and by causing failure in the test object itself, it directly determines its strength. Self-compacting concrete mixing designs were studied by replacing 25, 35 and 45% cement with fly ash filler, and a conventional concrete mixing design as a control to study the effect of magnesium sulfate on the strength of self-compacting concrete. Self-compacting concrete tests including slump flow test, slump flow time of 50 cm, V-shaped funnel, V-shaped funnel increase time (5 minutes) and L-shaped mold were performed on self-compacting concrete acceptance criteria on self-compacting concrete mixing designs. . The results indicate that sulfated water not only does not have a negative effect on the surface strength of self-compacting concrete containing fly ash, but also provides better curing conditions for these samples. The use of fly ash also makes the magnesium sulfate solution a more suitable medium than ordinary water for the surface strength of self-compacting concretes. The process of obtaining surface strength in almost all self-compacting samples treated in magnesium sulfate solution is more than that in ordinary water. However, in the case of ordinary concrete, the process of obtaining the surface strength of all samples placed in magnesium sulfate solution is less. For self-compacting samples treated in magnesium sulfate solution, with increasing the percentage of fly ash, the surface resistance of 3 and 7 days decreases. But the 28-day surface resistance increases.

Recycling of concrete has been the focus of researchers owing to the large volume of concrete waste and the limited resources of valuable materials. Recycled aggregate concrete (RAC) contains aggregates of various types of concrete and building materials that have been destroyed due to their shelf life or as a result of war and natural disasters. In order to use different types of recycled aggregates (RA), it is necessary to conduct more detailed and sensitive research on the behavior of RAC in order to reach the highest possible level of quality and cost in the construction process. On the other hand, RA are made of concrete with different properties and its aggregates have been subjected to different form of loading, hence it is important to carefully examine their behavior and properties. Therefore, in this study, the strength and the durability of RAC after freeze and thaw cycles were compared with natural concrete while different water/cement ratios are used.
In this study, RA were extracted from demolished waste concrete specimens and used to produce three mixtures named RC, RN and NC while 100, 50 and 0 percent of RA were replaced respectively. Water to cement ratio were kept as 45 and 55 percent of cement. A total number of 57 samples for flexural, compressive, tensile strength and ultrasonic tests were made. 24 samples were placed in the refrigerator and freeze and thaw cycles were applied on. 18 and 15 specimens were prepared for testing at 28 and 120 days of age, respectively. According to ASTM C666, the relative dynamic modulus of the specimens was tested using ultrasonic test after each 40 cycle’s period. After the test was finished, compressive strength, single point bending, indirect tensile tests and elastic modulus were determined for each specimens. Finally, the behavior of recycled and natural concrete was compared.
The results showed that the freeze and thaw cycles reduced the resistance of both RAC and NAC. Recycled aggregates have 2.5 times more water absorption than Natural aggregates. RAC has lost 41%, 18%, 10% and 28% of its compressive, flexural, tensile strength and modulus of elasticity, after the freeze and thaw cycle, respectively. The 100% replacement of RA reduced even more the mechanical behavior of samples. The relative dynamic modulus at the end of the cycles for RAC was 2% higher than that of NAC, indicating its better durability properties against freeze and thaw cycles. Concrete with 50% replacement of recycled aggregate has almost the same durability and strength as NAC, hence is recommended to be use in similar condition

Non-destructive damage detection methods analyze the output data collected from sensors to track the changes in the dynamic characteristics of the structure and detect the occurrence of damages. continuous recording and analysis of data to be aware of its safety and serviceability requires a network of sensors that are selected optimally and intelligently. Saving the cost of equipping the structure with this optimal sensor network, along with reducing damage detection error, has turned the issue of selecting the number and location of sensors into an optimization problem from an economic and functional point of view. Model order reduction methods along with optimization tools can play an effective role in selecting the master degrees of freedom. These methods divide the degrees of freedom of the structure into two groups of master and slave degrees of freedom. The master degrees of freedom appear in the process of calculating the mode shapes and natural frequencies, and the slave degrees of freedom are excluded from the equations. Finally, using the transfer matrix, the complete mode shapes are calculated using the mode shapes of the master degrees of freedom. In this paper, considering the key role of modal parameter recognition in structural damage detection, the performance and accuracy of different methods of dynamical model order reduction in the optimal sensor placement problem was studied. The 2d truss stucture and two-dimensional shear frame are modeled and analyzed. The sensor placement should be considered in such a way that the mode shape identification is done with sufficient accuracy and proper recognition. One of the effective tools in order to achieve this goal is to use the capabilities of metaheuristic optimization algorithms along with the capability of dynamic model reduction methods in the stage of identifying the mode shapes and before identifying the damages of structure. Combining model order reduction methods with metaheuristic optimization algorithms so that the selection of appropriate degrees of freedom for sensor installation (master degrees of freedom) leads to the most accurate identification of structural modes shapes is one of the main objectives of this study. The objective functions selected based on modal assurance criteria (MAC) and Fisher information matrix (FIM) and the capabilities of multi objective particle swarm optimization algorithm (MOPSO) to achieve the optimal number and proper arrangement of sensors are used to better identify the structural mode shapes and proper arrangement of sensors and obtained for system identification purposes. The results report better performance of SEREP and IDC methods in selection of master degrees of freedom and identifying the mode shapes of 2d truss and shear frame structures. According to the modeling and analysis performed for optimal placement of sensors using different model reduction methods, it can be concluded that the improved dynamic condensation (IDC) method is more accurate than other methods in identifying shear frame mode shapes and gives a smaller maximum non-diagonal MAC matrix element. Also, as the number of sensors increases due to the addition of information to the Fisher matrix, the Fisher matrix determinant increases and second objective function decreases. On the other hand, by reducing the number of available sensors, a limited number of modes can be detected. In this case, the best way to receive the structural modal information would be to place more available sensors on the lower and upper floors of the shear frame. Eventually, it can be concluded that the use of IDC and SEREP methods to select master degrees of freedom for sensor installation leads to better identification of modal parameters of the structure. Therefore, the capabilities of these methods can be used to identify damage in structures with a limited number of sensors.

Based on the seismic design, energy absorption by plastic deformation is necessary to prevent structures from collapsing during a severe earthquake. Therefore, estimating the behavior of structures to understand their response to earthquakes is particularly important. Seismic loads applied to structures are more significant than forces applied during design. This reduction in design applied loads is accomplished using a behavior factor. It is necessary to employ a behavior factor when evaluating the behavior of structures using linear analysis.
The behavior coefficient depends on ductility coefficient, structural damping coefficient, soil characteristics, earthquake characteristics, over strength coefficient, and design reliability coefficient. While in seismic code, this coefficient is entirely dependent on the type of lateral strength system used. At the same time, the behavior coefficient depends on the structural geometric properties which are investigated in this paper. Since nonlinear analysis is required to determine the effect of earthquake forces during design and nonlinear dynamic analysis is time-consuming, designers typically use nonlinear static analysis. Nonlinear static analysis is one of the nonlinear analysis methods that use the lateral load to represent the earthquake load on the structure statically and increasingly.
Estimating the behavior factor before starting the design process is a vital aid to designers. In this paper, we have examined the behavior factor of the reinforced concrete (RC) frame using gene expression programming. Gene expression programming is highly effective in this instance. Its effectiveness largely determines the success of the method. Gene expression programming is a class of genetic algorithms that utilizes a population of individuals, selects them based on their fit, and introduces genetic changes via one or more genetic operators.
Numerous inputs are required for this purpose, including the number of stories, the span length, the seismicity of the construction site, and the ratio of the compressive strength of concrete to the yield stress of longitudinal reinforcements. Afterward, 168 RC frames were designed via SAP2000 software, and the behavior factor value was obtained using nonlinear static analysis for each frame and subsequently transferred to the GeneXpro Tools software. The sixth and ninth national building regulations, Iran's seismic code, with the American Concrete Institute Code (ACI318-14), were used to analyze and design the structures examined. In the designed frames, the number of stories is 2, 4, 6, 8, 10, 12, and 15, and the ratio of span length to story height is 1, 15, 2, and 2.5, respectively.
The design base accelerations were 0.35, 0.3, and 0.25 in this study, and the longitudinal reinforcements' yield stress was initially set to 340 MPa and then increased to 400 MPa. The obtained results demonstrate that employing the gene expression programming method makes it possible to estimate the reinforced concrete frame's behavior factor with an acceptable degree of accuracy before initiating the design process.  Finally, the results show that the variations of the span length and the number of the stories significantly affect behavior factor. Furthermore, as the number of stories increases, the behavior factor decreases initially and then increases. Moreover, the impact of parameters, such as design base acceleration and yield stress of longitudinal reinforcements, is negligible in calculating the behavior coefficient.

The advantages of structures equipped with bracing systems such as high lateral stiffness, light weight of the skeleton compared to flexural frames plus the weakness of flexural frame connections as well as high risk of the performance of these connections during earthquakes always place the bracing lateral stiffness system at equal level of the other seismic-resistant systems in the minds of designers. However, Experiences gained from the concentric brace frames performance during earthquakes showed the undesirable function and hysteresis loops of the bracing system. The early buckling of the brace members causes joint failure, instability and unpredictable seismic behavior of the frame. Researchers tried to avoid the buckling phenomenon by making some changes in brace members structure. Using energy dissipation systems like buckling restrained braces, viscose dampers, friction dampers and yielding dampers were the methods which have been investigated during years. yielding dampers due to their benefits like economic aspects, easy construction, available material, flexible design, durability and significant impact on the seismic responses were one of the devices which has been considered. Many researchers worked on different types of yielding dampers. they used parallel plates yielding dampers on top of the chevron braces and slit dampers along diagonal brace. despite of many researches has been done, but it seems more efficient projects can be achieved in this field. the yielding dampers constructed so far have several considerable problems: i) the existence of one or two-level behavior against earthquakes, ii) the implementation of the welding process in energy-absorbing parts causing premature rupture of steel, and iii) the lack of support system in the event of severe earthquakes or unusual loads outside the design leading to frame instability. This research tries to design a two-level yielding damper with parallel fuse plates using finite element sensitivity analyses on an effective component of these types of dampers. After that to assessment of the damper function, an OpenSees code developed to analyze the nonlinear time history of the seven far-field selected ground motions. All the ground motions selected according to the FEMA P-695 suggested ground motions with the site class of C and the base shear, roof acceleration, story velocity and drift nonlinear time history responses of a three-story braced frame compared with and without damper. To prevent buckling of the brace members, dampers with the capacity of 90% of brace members capacity designed to use at any story brace and the maximum displacement capacity of dampers adjusted to the maximum allowable drift of the building stories. Results showed that, there are some effective and less effective parameters whose variation such as geometrical parameters can seriously change the total energy absorption level and improve the damper hysteresis loops. Also, According to the flexible design of the presented damper, if it needs to be designed with a force bearing capacity and energy absorption in accordance with the seismic design of the desired frame, it is possible to achieve the desired capacity by making changes in the overall dimensions and number of energy absorbing plates. time history responses assessment showed that using the new damper has a significant decreasing effect on the seismic responses of the building.

Natural soils pose an inter particle bonds that makes their compression and failure behavior different than the compression and failure behavior of remolded soils. Different reasons have been suggested for the creatin of inter   particle bonds, including natural cementation, carbonating agents, and aging. These classes of soils are called structured soil. Structured soils could also be produced from artificial cementation by cement, lime, and other chemical agents. Overconsolidated generally show different compression behavior in overconsolidated state and normally consolidated state and their compression index in both states are different. Structured materials show a highly nonlinear compression behavior after initial yielding in the normally consolidated state. Their compression index has a large value at the beginning of the virgin yielding and decreases as the structure of the soil crashes. This highly nonlinear behavior prevents from adapting the conventional linear compression models in both semilogarithmic or fully logarithmic scale in e-log(p) or ln(1+e)-ln(p) spaces. On the other hand, sampling disturbs the soil samples and destructs the soil structure. Although there are several new sampling methods and apparatuses to reduce the disturbance of the samples, however the disturbance could not be completely removed from sampling procedure. Disturbance of the samples makes the determination of the precompression pressure of the soil samples where the compression regime of the soil changes, very complicated. There are several methods for determination of the precompression pressure of disturbed samples that most of them are based on graphical procedures. This paper presents a contentious compression model for volumetric compression and yielding of structured soils considering the effect of the sample disturbance on the determination of the precompression pressure. The compression behavior of the structured soil in low stress levels where the structure of the soil is relatively intact (RI) is known and can be measured in the laboratory. Also, the compression behavior of a structured soil at very high stress level where in fully adjusted (FA) state is similar to the compression behavior of the same soil in remolded state. The compression behavior of the structured soil with some degree of the disturbance must lays between these two reference states. Based on the Disturbed State Concept (DSC) the behavior of any complex phenomenon between two reference states of RI and FA could be completely described using a coupling mechanism called the state function. In this paper, the compression curve of the soil in low stress levels at overconsolidated state was considered as RI state and the compression curve of the same soil in the remolded state was considered as FA state.  A continuous sigmoid form state function was proposed for description of the continuous change of the e-log(p) curve of the soil from overconsolidated state to normally consolidated states. The effect of the sample disturbance was introduced in the state function by an intactness parameter. High values of the intactness parameter produce distinctive changes from overconsolidated regime to normally consolidated regime that is the main character of intact samples. Based on the proposed model the precompression pressure could be determined minimizing the deviations of the predicted results from observed results in compression test. The proposed model was verified by data reported in the literature and also laboratory tests conducted by the authors. The verification of the model showed the ability of the model in determination of the precompression pressure of artificially overconsolidated samples with known precompression pressures more precise than the other methods.

The health of structures, provision of safety, and the sense of security are among constant requirements and perpetual challenges of engineering and managers in the field of crisis management. Erosion and occurrence of minor local damage to structures and structural members in the early stages of construction or during operation, especially in critical structures such as power plants, tall buildings, stairs, dams, airports, and hospitals, have always been among major problems. As time passes, Structures are affected by a variety of natural and non-natural destructive factors such as earthquakes, non-systematic excavations, dynamic vibrations resulting from explosions and heavy vehicle traffic. In addition, factors such as serviceability expectation beyond the design capacity of structural elements and failure to meet the latest expectations imposed by regulations, use of poor-quality materials and execution problems will reduce efficiency and, consequently the service life of structures. Also, the spread of local damages in structures can impair the overall health of the structure. Undoubtedly, knowledge of structural health and safety is of vital importance and structural health monitoring is recognized as one of the most important subjects that has received a lot of attention from researchers. Plates are one of the most important structural elements that can, when damaged, progressively transfer damages to other elements and lead to overall structural damage incurring irreparable social and economic costs. Due to the increasing applications of steel plates, especially in building structures (as steel plate shear walls) in the present study attempts were made to focus on damage detection and localization as one of the most important steps of health monitoring using modal dynamic data (natural frequencies and mode shapes) and a proposed diagnostic method based on two-dimensional discrete wavelet analysis. To this end, the modeled steel plate was subjected to frequency analysis in ABAQUS finite element analysis software and the modal data associated with damaged and non-damaged states were extracted. The results showed differences between the frequencies and lack of correlation between primary and secondary vibration mode shapes based on the modal assurance criterion (MAC) and the angle between the primary and secondary mode shape vectors. Using a propoed damage localization index (DLI) based on the wavelet coefficients obtained from the diameter details of the two-dimensional wavelet analysis of the primary and secondary vibration mode shapes, the damage zones were detected by creating a maximum relative jumps in the DLI diagram. Studies showed that DLI values are sensitive to the damage severity of the damage zone and with increasing the damage severity, these values increase in fixed spatial coordinates in the damaged zone. Also, the DLI of one damaged zone is independent of the damage severity of the other damaged zones, and this is a positive advantage in the damage determination process. Otherwise, failure to detect one damaged zone may affect the detection of other damaged zones, and consequently pose problems in the process of damage detection and localization in cases where we are dealing with multiple damage zones. According to the results of the present study, DLI can be proposed as an efficient and effective index in detection and localization of damages in steel plate elements.

Numerous studies have been devoted to the investigation of the deterioration and behavior of fiber-reinforced polymer (FRP) sheets (made from a variety of materials such as carbon, glass, or aramid) bonded onto the concrete substrate under a variety of adverse environments. Results indicate that environmental conditions might exercise significant and undesirable effects on FRP-concrete bond performance. In many corrosive environments, there are the potential risks of premature debonding and failure of the bonding interface in externally bonded FRP-strengthened concrete structures. The effects of freeze–thaw cycles on the fiber-reinforced polymer (FRP)-to-concrete bond strength were investigated using the particle image velocimetry (PIV) technique. For this purpose, 18 specimens were prepared, including 12 specimens strengthened with carbon FRP (CFRP) strips as well as six control specimens subjected to 200 and 500 freeze–thaw cycles, each consisting of four steps according to ASTM C 666. In the first stage, the temperature was held constant at 5°C for 4.2 h. The next step involved rapid freezing to ‒18°C for 2.4 h. In the third step, the temperature was held constant at ‒18°C for 2.4 h. Finally, the temperature was raised and maintained at 5°C for 3 h in the fourth step. The freeze–thaw under wet conditions was selected in order to create harsher conditions than the dry freeze–thaw conditions would. According to ASTM C 666, the specimens were stored in saturated lime water from the time of their removal from the molds until the time of freezing and thawing tests started. In addition, the nominal freezing and thawing cycle consisted of alternately lowering the temperature of the specimens from +5 to −18°C and raising it from −18 to +5°C in not less than 2 nor more than 5 h. The freezing and thawing chamber was equipped with a user defined program. The temperature range of the chamber was −30°C to +65°C. The temperature was controlled by a sensor, which can be immersed either into the sample or into the water in which the sample was placed. The specimens were strengthened via externally bonded reinforcement (EBR) and externally bonded reinforcement on grooves (EBROG) methods. After the concrete prisms had been subjected to 200 and 500 freeze–thaw cycles, they were placed in the single shear test machine. During each test run, a tensile force was applied to the FRP composite while the concrete block was restrained from movement. The single shear test machine consisted of a hydraulic jack with a capacity of 400 kN that provided the required force for the single shear test. Moreover, a load-cell with a capacity of 50 kN was used to measure the force applied to the specimens. In the current investigation, the specimens were subjected to a quasi-static loading of 2 mm/min in accordance with ASTM D3039/D3039M. The results of PIV measurements revealed that, compared with the specimens strengthened via the EBR method, the EBROG-strengthened specimens exhibited considerably enhanced bond performance. When subjected to 200 and 500 freeze–thaw cycles, the EBR-strengthened specimens experienced a 3% and 9% decrease in their bond strength, respectively; the EBROG-strengthened specimens experienced no decrease in bond strength and increases in the range of 7%–19% when subjected to 200 and 500 cycles, respectively.

The estimation of seismic demand that connects the ground motion intensity measure and the damage measure of structures is one of the most important components in the performance-based design. In the seismic demand model, the relationship between the structural response and a seismic parameter that expresses the random nature of earthquake is expressed in the mathematical form. Therefore, proper choice of earthquake intensity measure as a seismic parameter and identifying how it is related to structural damage can play an important role in reducing errors in seismic assessments. In many studies, the first mode spectral acceleration (Sa (t1)) or maximum ground acceleration (PGA) has been introduced as an appropriate intensity measure. However, some recent studies indicate that these IMs are insufficient in some circumstances. On the other hand, choosing a suitable method for measuring the sufficiency of intensity measures due to the existing uncertainties and also examining the performance of single-line demand model is of particular importance and should be considered. In this study, the suitability of different intensity measures of ground motion is quantified by using information theory and relative entropy concepts and    Sa (t1) is used as the base IM. For this purpose, several concrete moment frame structures with different number of floors and heights have been considered and time history dynamic analysis has been performed using pulse-like earthquake records by IDARC software. The Park-Ang damage index, which has many applications, especially in concrete structures, has been used for structural response. Given that there is a possibility of different behavior of intensity measures at different damage levels, the discussion of multilinear demand models is proposed and the performance of several multilinear models has been evaluated by statistical tests. The results show that velocity-based intensity measures are sufficient for moderate damage level under pulse liked records. At these damage levels, the use of first mode spectral acceleration or acceleration-based intensity measures such as maximum ground acceleration can cause errors. Also, studies conducted in this paper have shown that the use of single-linear model is not suitable for all damage levels and the use of a three linear model with respect to damage levels can reduce errors in seismic assessments.

With the advancement of technology in the world, industrial waste has become one of the most important environmental challenges. Deformation and reuse of these wastes is one of the ways to improve the sustainable state of the environment. Glass and rubber are among the most widely used materials in the world, which due to their nature have a lot of wastes. Waste tires cause a lot of environmental pollution due to their non-degradable materials. The use of waste glass and rubber in the construction industry can be a good solution in reusing waste materials. Concrete, on the other hand, is one of the most widely used materials in the construction industry, and the addition of rubber and glass crumb to concrete can improve some of its mechanical and dynamic properties. Of course, heat resistance of materials is one of the features that is effective in the type of application. Adding waste rubber and glass to concrete, of course, depending on their amount and size can increase the heat resistance of concrete to some extent.
In this research, the effect of replacing small and large aggregates with rubber and also glass powder with cement in concrete at ambient temperature and high temperature has been studied. The size of rubber used in concrete in two categories is 1 to 3 mm and 5 to 10 mm, which are replaced by fine-grained and coarse-grained, respectively, with replacement values ​​of 0, 5 and 10%. The size of the glass used is smaller than 75 microns and it can be replaced with cement with 0, 10, 15 and 20% replacement values. Shredded truck tires and powdered construction glass were used. In this study, cubic specimens were made into 15 x 15 x 15 cm specimens and cylindrical specimens with a diameter of 15 cm and a height of 30 cm were made according to the standards and processed for 28 days in optimal conditions. After processing, the number of cubic and cylindrical specimens was subjected to compressive and tensile tests. A number of other samples were placed in an electric furnace and heated to 600 ° C as standard. After removing the samples from the furnace, they were naturally placed at room temperature for 24 hours and then they were tested for the Residual compressive and tensile strength. The microstructure of concrete containing glass and rubber was examined by scanning electron microscope (SEM). The results of this study showed that adding rubber and glass to concrete causes a decreases compressive strength and increases tensile strength. The D10C10 design, which has the highest compressive strength, has a resistance reduction of about 12% compared to the reference design. The highest tensile strength of heated samples is related to D5C15 design, which is about 43% higher than the heated reference design. By comparing the sum of heated and unheated samples, it can be seen that heat at 600 ° C has reduced the compressive strength by an average of about 33%. In general, concrete made with 10% replacement of rubber instead of coarse in unheated samples and 15% glass instead of cement in heated samples showed better properties. Also, in the study of concrete microstructure, adhesion between rubber and concrete was appropriate.

The main purpose of this study is to provide a simple and efficient method for calculating the capacity of fillet welds subjected to in-plane eccentric loads. Various methods have been proposed to determine the capacity of fillet welds under such circumstances over time. The existing design methods, such as the conventional elastic method, are very conservative and do not match the test results well due to neglecting of ductility and strain compatibility of the weld group. On the other hand, the instantaneous center of rotation method (IC) considers the above parameters but requires complex calculations. Therefore, in the present study, a method for the design of the fillet welds is introduced which considers the inelastic properties of the welds in a simple manner, while provides a very good prediction of the weld group capacity. The proposed method is much more accurate than the conventional elastic method in the design of fillet welds and is much simpler than the IC method which has limitations in use and complexity in calculations. In this method, considering the ductility for welds, it is assumed that the stress distribution in welds is uniform when the weld reaches its maximum bearable deformation.
The performance of the proposed method which is called Plastic Design Method has been compared and evaluated in comparison with the prequalified IC method. To this end, 8 different configurations of weld groups from the AISC Manual were selected and their capacities were calculated for different amount of load eccentricity. Accordingly, despite the fact that the new method has almost the same computational cost of the elastic design method, it offers more accurate strength predictions of the weld groups. For all considered cases, the ultimate loads obtained from the proposed plastic method are just slightly different from those of the IC method and they are mainly on the safe side. To be more precise, the accuracy of the results calculated by the proposed method is within 90% of those of the IC method.
In accordance with the authors’ parametric studies on the factors affecting the results of the plastic design method (e.g., the angle of loading (θ), the weld length (l), the weld throat thickness (d), the secondary parameter (k) and the tensile strength of the welded metal), it was found that the angle of loading has the most profound effect. Therefore, the influence of loading angle on the predicted results was included. Accordingly, three different loading angles (i.e., zero, 45 and 75 degrees) were chosen and the weld groups capacities were calculated in each case. The corresponding results showed that as the loading angle increases, the accuracy of the results decreases and the most accurate predictions are obtained for the case of zero angle loading as compared with those of the IC method. Nevertheless, the predictions are still in an acceptable range for non-zero angles. It is also worth mentioning that irrespective of the loading angle, the new plastic method strength predictions are always far better than those of the conventional elastic design method.

In this research, the free vibration or natural frequency analyzes have been performed with the help of small-scale physical models. Laboratory modeling in the geotechnical engineering can be performed in the acceleration field of 1g.  In each of the physical modeling modes, the relationship between the model and prototype frequencies is very essential. In this paper, with the help of hammer impact pulse tests (HIPTs) -dynamic experiments- the optimal frequency ranges and the best geometric scales for physical modeling are investigated by a strongbox. The frequency range studied has been selected according to the study of shaking table models between 0.001Hz and 150Hz. To perform impact pulse tests, the physical models of dry sandy slope with different inclination angles from 25 to 60 degrees (and a constatnt slope height) have been instrumented by the piezoelectric acceleration sensors.  The relative density of the sandy slope models is medium dense and about 50% to 52%. In addition to 8 physical models of sandy slopes, two models of level-ground and empty box have also been investigated. The time-history of the acceleration function of the input excitation shock at the slope floor (base point) and the response acceleration at the slope crest are recorded by the acceleration sensors.  These acceleration time responses last for a short stroke (short impact) of less than 1.0 second duration. After extracting temporal responses, the frequency analyzes including transfer function (TF), Fourier response spectrum ratio (RFRS), and spectral energy density function (PSD-function) are derived from the temporal results. Using the transfer function or RFRS, quantitative values of natural frequencies of the physical model of the sandy slope and the storngbox are extracted in different vibration modes. According to the findings of the present study, for a constant slope model the frequencies at which the maximum seismic or dynamic energy is emitted are quite different from the frequencies with the maximum magnified response amplitude. The results of the present study prove the existence of a logic relationship between the sandy slope inclination angle (physical model natural frequencies) and the model response amplification frequency. So that by increasing the angle of inclination of the model slopes at a constant height, the magnification values of the impact acceleration response decrease. Because in general, the amount of sandy materials magnifies or weakens the amplitude of frequency responses. The presence of low sandy materials (on steep slope models) reduces the magnification range of the acceleration response and high sandy materials (on gentle slopes) increase the response range. Optimal frequencies in strong box modeling in the 1g acceleration field are frequencies that do not interfere with acceleration magnifications before or during seismic excitation (pre-seismic mode). Acceleration magnification causes resonance and premature failure in the physical model, which is generally undesirable and unmeasurable in laboratory studies. In this research, the optimal frequency range according to the measurements is proposed for the physical modeling of the 1g acceleration field. These ranges and frequency values are presented according to the various constraints such as the type of strong box, slope angle, relative density of sand, the actual frequency effect of the horizontal components of earthquakes, and so on.

Base isolation is an effective technology for reducing seismic damage to structural and non-structural components as well as building contents, allowing buildings to maintain their function during and after a rare, high-intensity earthquake. This makes it an ideal seismic response correction system for importance buildings. The main advantage of isolated structures is that seismic responses can be easily and effectively reduced by prolonging the period and increasing damping. Therefore, the natural period of the structure isolated from the base is longer. In this paper, a new energy balance method is used to design a lead rubber bearing (LRB) isolator. Energy balance method is an analysis method to evaluate seismic resistance based on the balance of seismic energy input to buildings due to ground motion and energy absorbed by the building. In other words, the energy balance method is a response prediction method to approximate the seismic response of buildings isolated from the foundation. This method is effective for determining the relationship between ground motion, seismic isolation period and the effect of reducing the reaction of dampers. In this method, the specifications of the isolation system, including stiffness, yield shear force and viscous damping ratio, are adjusted in such a way that the maximum shear and maximum displacement in the isolation system do not exceed a certain value determined by the designer. This allows the designer to limit the maximum displacement at the isolation level to a certain amount when there is a constraint on the supply of separation distance around the building and the isolated level. Also, by limiting the maximum shear of the isolators, it is possible to use the base isolation system for retrofitting the existing structures that have a certain lateral capacity.
This design method was first proposed and used in Japan. This method has been recently proposed in the Iranian regulations (which is being drafted) and has not been used much in this country so far. Its advantages include no need for trial and error in the design process, the possibility of designing a rubber and frictional type of seismic isolator, the possibility of using a viscous or hysteretic damper, or a combination of both at the isolator installation site. To evaluate the accuracy of this method, three 5, 10 and 15-story steel structures with an ordinary concentric braced frames in both directions for clinic usage have been modeled and under eight near and far-field earthquakes in the by the nonlinear time-history analysis method have been analyzed. The results obtained from the time-history analysis are in good agreement with the estimated results of the energy balance method. The error percentage related to the displacement of isolator compared to the value assumed at the beginning of the design for 5, 10 and 15-story structures is 3.4%, 2.57% and 2.12%, respectively. Also, the percentages of error related to the maximum shear of isolator compared to the value obtained from the performance curve for 5, 10 and 15-story structures are 11.08%, 12.61% and 13.98%, respectively.