نشریه مهندسی عمران مدرس
سال بیست و دوم شماره 2 (خرداد و تیر 1401)

The displacement-based design method in structural design codes, in which displacement is considered a criterion for evaluating the structure, has been accepted due to the dependence of failure on displacement more than forces, overcoming the inherent shortcomings of force-based design methods. On the other hand, different levels and states can be defined concerning structures' performance. In the functional state of immediate occupancy, the relative lateral displacement due to cracking or plastic behavior does not remain in the structure. The structural members' stiffness and strength do not change fundamentally, and microscopic cracks are created in the structural members and façade. In the second case, i.e., life safety, some stiffness, and strength will be lost in all classes, relative deformation due to plastic behavior in the structure will be observed, and the risk of loss of life will be slightly higher. At the performance level, the collapse threshold remains in the members of structures of low stiffness and strength to withstand lateral loads, but the columns and load-bearing walls maintain their function, the relative deformations are high, and the structure is likely to collapse due to aftershocks. Due to decreased energy caused by earthquakes, dampers with passive control systems are installed in certain parts of the structure and absorb a relatively large part of the energy entering the structure under different mechanisms, and as a result, the structure does not suffer severe damage. After the Northridge and Kobe earthquakes, extensive laboratory studies were conducted to strengthen and increase the joints' ductility, and many modified joints were proposed. Extensive applied structural studies have been conducted on dampers' seismic behavior as one of the advanced tools of passive structural control systems due to earthquake energy dissipation. This work compares the effects of linear and nonlinear viscous dampers on the seismic behavior of 3, 9, and 20-stories steel moment frames, and the structural seismic responses are discussed. In linear dampers, the axial force is obtained by multiplying the damping coefficient ratio at the relative speed of the damper's two ends, and in the nonlinear state, the relative speed of the damper is between 0.2 and 1, in which 0.25 is used in the current study. The results showed that viscous dampers' implementation generally reduced the responses and decreased the structural damage during the earthquake. Absolute displacement of structural models in nonlinear dampers compared to linear ones has decreased with an increasing number of stories, but for maximum relative displacement with the increasing number of stories, nonlinear dampers had a more negligible effect. Due to the hysteresis extracted, nonlinear dampers in short and intermediate structures have more energy loss, which is significantly reduced in high damping structures. The plastic hinge distribution for these dampers has eliminated the failure LS at the life safety performance level. The base shear of 3, 9, and 20 story frames with a nonlinear damper is significantly reduced compared to a linear damper and shows the nonlinear damper's positive effect, especially on high-rise structural frame models.

In this paper, a simple numerical model is presented for analyzing trapezoidal alluvial valleys subjected to propagating obliquely incident plane SH-waves. As the literature review shows, the scattering effect of transient SH-waves on the surface of trapezoidal alluvial valleys has not yet been directly analyzed in the time-domain by half-plane BEM. In previous researches, the models were limited to the homogeneous single-material subsurface problems. Although in some researches, the mathematical formulation, numerical implementation, and transient analysis of two-dimensional non-homogeneous solids were presented as well, they were established to obtain the time-domain responses by the inverse Fourier/Laplace-transform from a mechanical problem point of view. Additionally, some researchers were used a full-plane time-domain BEM approach to present the time-domain responses for an alluvial valley. But in this study, based on an advanced half-plane time-domain BEM, the surface responses of a linear elastic trapezoidal alluvial valley are obtained due to propagating obliquely incident anti-plane SH-waves. In the use of half-plane time-domain BEM, the meshes are only concentrated around the interface of the basin. First, the problem is decomposed into two parts including a half-plane valley-shaped feature and closed filled alluvium. Then, the influence coefficients of the matrices are obtained by applying the method to each part. Finally, by satisfying the boundary/continuity conditions on the interfaces, a coupled equation is formed to determine unknown boundary values in each time-step. Then, all ground surface responses are also obtained in a secondary solution as internal points. After implementing the method in a general algorithm previously named DASBEM, several practical examples are analyzed to authenticate the obtained results beside prior published responses by other researchers. The main aims of this study are to present some applicable diagrams for use in engineering/operational projects, present a better view of alluvial valleys’ seismic behavior, and reveal the power of the developed algorithm in the analysis of complicated geotechnical problems. Thus, an advanced numerical study is performed to sensitize the surface motion of trapezoidal alluvial valleys with the variable of shape/impedance ratios as synthetic seismograms and three-dimensional (3D) amplification patterns. In the following, to complete the time-domain results, the transient response of the internal domain of the alluvium as well as the surrounding bedrock is shown by the snapshots’ views. Moreover, the sensitivity analysis is carried out to obtain the seismic amplification pattern of the surface by considering the key parameters including impedance and shape ratios, incident wave angle, and response frequency. Lastly, by collecting the maximum amplification of different scenarios and applying linear fit on the obtained values, the responses are summarized as a series of linear equations and tables. The results showed that the mentioned factors are very effective on the seismic response of the surface. The results of the present study can be used to complete the accuracy of existing codes around the subject of near-filed site effects.

In recent years, the use of supplemental damping devices to increase the capacity of structures against progressive failure due to explosion has received less attention. The main purpose of this research is to investigate the effect of using Triangular yielding metal damper called TADAS. in order to increase the capacity of an irregular three and nine-story steel moment frame buildings against pulse like seismic excitations and progressive collapse effect. For this purpose, seismic performance level of this structure has been evaluated and rehabilitated by TADAS damper. The seismic performance level of damper-equipped building was evaluated by nonlinear static analysis (pushover) and also nonlinear time history analysis under various pulse-like ground motions. In order to assess the performance of TADAS damper under progressive collapse phenomenon, 12 critical columns considering side and corner locations proposed by GSA code were selected to remove. Then considering the seismic nonlinear response of these columns under selected ground motions, four critical scenarios were selected for each building. According to irregularity of the structural plan the capacity of the rehabilitated structure was evaluated using nonlinear time history analysis. To simulate the progressive collapse phenomenon at first the internal column forces are evaluated before it is removed. These forces are dynamically applied to the structure as a nodal point load in addition to existed dead and live loads in five seconds after removing the column. After completing the amount of loading they kept unchanged for two second and finally the nodal point loads would be removed over a fraction of second and therefor the dynamic sudden column removal was simulated.  The nonlinear response of the irregular TADAS-equipped building was computed through the step by step numerical integration method known as the Newmark’s β-method integration procedure using SAP2000 software. A fiber element model was employed to take into account the non-linear behavior of columns while for beam elements it is used plastic hinge model considering ASCE41 code. The dampers are also modeled using the link element in the software and the nonlinear plastic Wen model is assigned to simulate the nonlinear behavior of this element . The presented results include comparison of roof displacement diagrams, inter story drift and center mass acceleration for the structure with and without dampers in different failure scenarios. The seismic results show the ability of TADAS damper to improve seismic performance of irregular building. This control system could reduce the inter story drift of buildings at least 40% while the center mass acceleration increase 5.0%  While the hysteresis diagram of dampers indicates their ability to suppress the response of this structure. These results indicate the success of the damping system in the simultaneous control of acceleration and displacement and indicate another result of this study. On the other hands the progressive collapse analysis results show the ability of TADAS damper to improve the capacity of the structure against four types of progressive failure scenario especially in scenario 2. The results showed that the vertical displacement was reduced at least 15%.

Zoning and seismic hazard analysis is a powerful tool with useful and valuable information for decision-making. In this study, seismic zoning of Ardabil city on the seismic bedrock level was studied using deterministic hazard analysis method, and fuzzy inference system. The purpose of earthquake hazard analysis is to estimate the strong ground motion parameters in a time period and in a specific site. In all steps of seismic hazard analysis, there are uncertainties that make inevitable use of appropriate methods in seismic hazard assessment. Fuzzy logic is known as a reliable method to evaluate seismic hazards with reliable results in a short time with a simple and flexible process. Iran is one of the most earthquake-prone countries in the world where cities severely suffered during this natural phenomenon. The city of Ardabil with the coordinates of 38.25 North and 48.30 East, is the center of Ardabil province and is located in the northwestern part of Iran. Due to its location among several important active faults with a background of numerous historical destructive earthquakes, its seismicity and hazard analysis seems to be necessary. For this purpose, all the active faults located within a radius of 150 km from the city center along with their seismic history were studied and 20 potential seismic sources were selected for seismic hazard analysis. In the present study, seismic hazard zoning analysis of the Ardabil city is first performed by the conventional deterministic method by meshing the whole area under study with dimensions of 1000 × 1000 meters; then it is performed using the fuzzy inference system for the centers of each mesh, and the results are compared. In deterministic seismic hazard analysis (DSHA), 5 attenuation relationships were used to determine the peak ground acceleration (PGA) and the site-specific response spectrum for the center of each mesh. According to the results obtained by DSHA method, the value of horizontal PGA varies between 0.24g and 0.43g, while using the fuzzy inference system it varies between 0.25g and 0.43g. As a result, the maximum horizontal PGA in this area can be suggested about 0.43g. According to the results obtained from both methods, source No. 3, for which the Bozqoush fault is its main active fault, can be considered the main source potentially causing destructive earthquakes in the future compared to the other sources. Moreover, this source is located at a very close distance to Ardabil city. As well, in general, it can be concluded that the western parts of the city are more prone of sever earthquakes compared to the other parts of the city, and therefore, it is better to build important buildings and infrastructures in areas with lower PGA (eastern parts of the city) and encourage the politicians to urban development to this direction in the future. This study clearly confirms that new techniques such as fuzzy methods can be used to improve and develop the seismic hazards analysis.

Having a long history of seismicity and experienced destructive and deadliest earthquakes make Iran one of the vulnerable countries against earthquakes. Based on the seismic hazard zoning map presented in the Iranian seismic code (2800 provisions), more than 90% of Iranian cities are located in areas with high or very high seismic hazard zones. On the other hand expansion of urbanization in recent decades almost comprises reinforced concrete (RC) buildings. Many of these RC structures constructed in accordance with codes that did not mandate adequate detailing and reinforcement for seismic protection, may have already suffered damage since their erection, due to insufficient maintenance, earthquake activity, or other natural hazards. Therefore providing appropriate solutions for the rehabilitation of such structures has always been considered essential. Metallic energy dissipators have been grown experimentally and theoretically almost for steel structures. U-shaped metallic-yielding damper as one of the most well-known metallic energy dissipators has also developed as a lateral-load resisting system for strengthening existing steel frames. Experimental and theoretical results showed that U-shaped metallic dampers can operate with large displacements in the inelastic range and dissipate energy through the plastic deformation of the steel. The purpose of this study is to take potential advantages of this system to strengthen deficient RC structures. To the best of the authors’ knowledge, this issue has rarely been considered, most of which are limited to small experimental studies. Therefore, it can be useful to study this issue numerically at the real size structural level. In this regard, three RC intermediate moment frames in 4, 6, and 8 stories and irregular in elevation are considered. Irregularity is considered by a setback in elevation of the frames as a special type of irregularity with considerable effect on seismic performance. Frames were first designed deficiently by SAP2000 software according to the provisions of the Iranian national building code and Iranian seismic code for the intermediate reinforced concrete moment-resisting frames. Then the frames strengthen by adding U-shaped metallic-yielding dampers together with inverted V-braces. The nonlinear dynamic time-history analysis is performed on all frames subjected to three far source input motions utilizing PERFORM 3D software. Nonlinear specifications of beams and columns are considered by assigning plastic hinges to them in addition to defining nonlinearity for the dampers. The results of roof displacement, base shear, inter-story drifts, and performance of frames at the life safety structural performance level are monitored for both cases with and without dampers. The use of U-shaped metallic dampers has always reduced significantly the maximum lateral displacement of the buildings. On average, under the three records of Imperial Valley, Manjil, and Tabas, the reduction is obtained as 32, 33, and 22 for 4, 6, and 8 story frames, respectively. Such a significant reduction is also visible in the inter-story drifts.  . No major effect on the maximum base shear force is observed and even in some cases, it is increased up to 10%. Failure of frames reduced by transferring nonlinearity of elements to the dampers and seismic performance assessment indicates that dampers strengthen frames to almost satisfy the requirements of the life safety level.

Nowadays, the use of recycled concrete has increased significantly for economic and environmental reasons. Increasing the replacement percentages of recycled aggregates change the mechanical properties of concrete. In this research, the mechanical properties of concrete containing recycled aggregates with different percentages of steel fibers and polypropylene fiber has been investigated in the structural laboratory. A total of 36 cylindrical compression specimens, 36 cylindrical tensile specimens with dimensions of 20 * 10 cm and 36 flexural specimens with dimensions of 10 * 10 * 35 cm were tested. Recycled aggregates (coarse aggregates) in ratios of 25 and 50% (weight ratio) replaced with natural materials (coarse aggregates). Also, steel and polypropylene fibers were added to recycled concrete samples in ratios of 0%, 0.5%, 1% and 0%, 0.4%, respectively. Fiber concrete samples containing recycled aggregates under compressive force, indirect tension and three-point bending are tested and factors such as compressive strength, tensile fracture toughness, modulus of elasticity, flexural strength and fracture energy were investigated. The results show that the increase in porosity in recycled concrete is affected by the increase in the percentage of replacement of recycled aggregates and reduces the specific gravity of concrete. Increasing the composition of 1% steel fibers with polypropylene fibers without the presence of recycled aggregate has a greater effect on increasing the specific gravity of concrete than polypropylene fibers (alone). By increasing 25 and 50% replacement of recycled aggregate, 0.8% and 2.5% of specific gravity of concrete were reduced, respectively. Compressive strength decreases with increasing replacement percentage of recycled aggregate. Increasing the percentage of replacement of recycled aggregate due to poor transmission area reduces the amount of energy absorption. So that by replacing 25% and 50% of recycled aggregate, the energy absorption rate decreases by 21.7% and 26%, respectively, compared to the control samples. Polypropylene fibers have a positive effect on increasing compressive strength and combination of polypropylene fibers with 0.5 and 1% steel fibers increases the energy absorption. Also, increasing the replacement percentage of recycled aggregates reduces the hardness. Maximum tensile strength decreases by 3% and 13% with 25 and 50% increase in replacement of recycled aggregate, respectively. The results of flexural strength test show that increasing the replacement percentage of recycled aggregate has a negative effect on reducing the final load and reduces the final load in flexural specimens. Also, polypropylene fibers have a positive effect on increasing the loads and preventing the collapse of concrete, and combining polypropylene fibers with 0.5 and 1% steel fibers, respectively, increases the final load by 20% and 95% in 25%, replacing recycled aggregates and increasing 19% and 21% of rainfall in 50% recycled aggregate replacement. Increasing the percentage of steel fibers, the amount of deformation in the area after cracking and the amount of energy absorption increases, so that by increasing the amount of steel fibers to 0.5% and 1% by volume of concrete, the amount of energy absorption to 2 and it increases 3 times. The use of polypropylene fibers in the area after cracking has little effect and increases the load capacity.

Although cement stabilization is used extensively to modify the soft clays, it may show limited success in some applications. Hence, this paper presents a multiscale investigation on the viability of employing zeolite and fiber to enhance the durability of cement treated soil against the freezing-thawing (F-T) cycles. In so doing, a wide range (0 to 30%) of additives including sole cement and cement-zeolite mixture (CZ) with different cement replacement were separately added to a soft soil sample and then mixed with the optimal fiber content of 0.75% (by weight), which was determined by the indirect tensile strength test. A set of experiments at various curing days (up to 90 days) were performed to study the mechanical and microstructural changes of the stabilized soils. The results indicated that while a low level of cement can modify the geo-mechanical parameters of soil sample, the compressive strength of cemented soil could decay up to 60% when the specimens exposure to the successive F-T cycles. Such changes may be ascribe to the F-T-induced particles rearrangement and degradation of the cementation structure-bonding, forming many new voids and cracks subsequently decreasing the interlocking of matrix. As a result, to get the strength guidelines threshold and make the composite water proofing a high dosage of sole cement and a long time of curing (at least 28-day) are needed, which may be uneconomical and lade to the brittle behavior. Adding zeolite (≤ 25% proportion) to supplant part of cement could effectively enhance the engineering properties of cement-mixed soil, due to an increase in the cementitious products [e.g. Calcium-aluminate-hydrate (CAH) and Calcium-silicate-hydrate (CSH)] induced by the pozzolanic activity, subsequent reduction of the inter pore-spaces and eventually a more compacted microstructure, as confirmed by the X-ray diffraction (XRD) patterns and scanning electron microscope (SEM) images. It should be emphasized that the zeolite/cement ratio is a very influential factor on the behavior of cement-zeolite mixture. Therefore, the cemented soil mixes with Zopt showed a further (up to 1.3 folds) resistance relative to the mere cemented soil as well as a greater tensile strength; however, the binary system was still vulnerable under the F-T action. In this case, the insertion of fiber could significantly enhance the soil durability (decrease the degree of damage by an average value of 50%), which was more evident at the small binder dosage and early stage of curing time. Incorporating fiber into the system also led to a higher tensile strength (nearly 1.5 times) than those deduced from the stabilization alone. Moreover, this strategy was effective to overcome the brittle nature of stabilized mixes, resulting an increase the post-strength up to 270%. These observations can be justified by the extended cementing gels formation and the enhanced interlocking of matrix through the CZ-fiber application. Overall, the combination of CZ blend and fiber can be considered as an effective technique for the soft soil modification with the fact that triggered a prominent reduction (~ 30%) in the needed amount of cement an time of curing (up to 3 folds) for the successful treatment against the F-T cycles.

The conventional bracing frame (CBF) systems show a limited drift capacity before buckling subjected to seismic loads. So, the induced damage in the structure reduces the strength and stiffness. In the last two decades, self-centering (SC) systems have been developed to resolve the deficiencies of the conventional seismic-resistant systems. In SC systems, the structural damage and residual drift are negligible, while they provide sufficient strength and stiffness. In these systems, prestressed elements are used to provide the initial stiffness. On the other hand, the steel plate shear wall, bracing, beam connection to the column provide energy dissipation mechanism. These elements are used as replaceable fuses after sever earthquakes. When the force applied to the structure is greater than the initial prestressing force, the gap created in the structure causes the energy dissipating elements to work. The main feature of SC systems is that they return to zero deformation after each load cycle. So, the post tensioned elements must remain elastic to be able to reduce the residual displacement. This property of the systems represents flag-shaped hysteresis lateral load-deformation curves. Among the engineering community, three methods of equivalent lateral forces (ELF), dynamic spectral analysis and dynamic time history analysis are commonly used for seismic analysis of structures. The endurance time (ET) method is a new method for seismic analysis and also for performance-based design of structures. In this method, the structure is subjected to special ET accelerations in which the dynamic response of the structure increases with time. The time needed for the structural failure index (such as the maximum drift of stories) to reach a certain level of performance or failure is defined as the structural ET. As a result, a structure that has a longer ET, has better performance against earthquakes. The main advantages of the ET method include: 1) by providing a suitable estimate of the structural response in each time history analysis, saves a lot of computational time for seismic evaluation, 2) the nonlinear properties of the structures may be considered which can be used for a variety of structures and complex behavior, 3) this method has a simple concept and principles for engineering applications, and 4) this method has a high capability for experimental work with a shake table. In the current research, the self-centering buckling restraining column braced frame (SC-BRC-BF) system was examined. This system not only increases the drift capacity, it also reduces damage and residual drift in the system. The SC-BRC-BF system consists of two rigid cores connected by buckling resistance columns (BRC) between tha adjacent floors. The BRCs are used as replaceable fuses to dissipate the input energy and to reduce the seismic responses. Vertical post tensioned cable is used to restore the system. For this purpose, a preliminary design approach was introduced for SC-BRC-BF systems with 3, 6 and 9 stories via SAP 2000 software. The simulation of structures under time history analysis and ET method was done via OpenSees software fin a 2D framework. Different seismic responses were investigated including: 1) roof drift, 2) the maximum strain of core elements, 3) drift concentration factor (DCF), and 4) Inter-story drift. The response of structures was examined at both DBE (Design Base Earthquake) and MCE (Maximum Considered Earthquake) levels. Comparing the responses from ET method and the conventional time-history method, the error rate does not exceed 10 and 15 % at the DBE and the MCE levels, respectively. The results obtained from seismic evaluation using the two mentioned approaches, corroborated the high efficiency of ET method with a few number of time history analyzes.

Since most of the soils in their natural state are unsaturated, therefore understanding and description of the compression and failure behavior of unsaturated soils are essential. The compression and failure behavior of unsaturated soils are affected by the interaction of the solid, liquid, and gas phases of the soil. Most of unsaturated soils exhibit a sudden change in their volume due to saturation that is called collapse phenomenon. The compression and collapse behavior of collapsible soils are so complex that can not be explained in the total or net stress spaces. Wetting induced collapse of the collapsible soil has a discontinuous response in net stress space and needs to be described using the matric suction. Calculations of the effective stress using the matric suction shows that the wetting induced collapse response of unsaturated soils is a continuous but a highly non-linear behavior. On the other hand, the compression characteristics of dry and saturated soils are different and change as the moisture content or the degree of the saturation of the soil change. In this research the compression and the wetting induced collapse behavior of unsaturated CL-ML soil have been investigated in the laboratory. Laboratory tests have been conducted by oedometer test device. Compression and wetting induced collapse behavior of unsaturated soil in dry state before collapse, during saturation and collapse state, and fully saturated after collapse state were studied. Pressure plate device was employed to obtain the soil water characteristic curve of the soil. Based on the laboratory results a compression and collapse model has been proposed to capture the compression and collapse behavior of the soil before, during and after wetting induced collapse. Using the soil water characteristic curve, the compression and collapse response of the soil was transferred to effective stress space. The binary-medium model was employed to describe the compression and the collapse behavior of the unsaturated soil based on its responses in two dry and fully saturated states as two reference states. Based on the binary-medium model, soil mass was considered as binary medium including two states of 0 and 1. The state of the soil in dry condition was considered as binary 0 and its state in fully saturated state was considered as binary 1. The state of the soil at any particular state between these two states was interpolated using a state function. An exponential form state function in terms of matric suction and the effective stress was introduced to relate the volume change of the unsaturated soil during the collapse state to its compression behavior in two dry and fully saturated states The state function was derived based on the laboratory experiments. The compression behavior of the soil in dry state was. Using the proposed model, the compression and collapse behavior of unsaturated soil in dry state, collapse state, and saturated state could be described in a single generalized model. The proposed model was verified by the laboratory tests conducted in this study and the available published in the literature. Verifications illustrated the ability of the proposed model in capturing the compression and collapse behavior of unsaturated collapsible soils.

Seismic design codes provide different equations for estimating displacement demands in various buildings and structures. Such equations were usually obtained by performing regression analysis over the obtained data from numerical models under different nonlinear analyzes. On the other hand, the application of artificial earthquakes is allowed to be considered for design and demand assessment in structures when there is a lack of suitable ground motions for a specific region and site. Since the accuracy of such relations affects the reliability of demand estimating in structures, it is required to assess the efficiency of such predictive relations. Moreover, it is essential to assess the efficiency of those relations for artificially generated earthquakes. Hence, in this study, the estimated demands from the design and assessment codes relations are evaluated for artificially generated ground motions. In this regard, regulations in the fourth edition of the Iranian seismic design code (also known as Standard 2800) and the last revision of the Iranian seismic evaluation code of practice (also known as Code-360) are considered. Estimated demands from these codes are compared to the results from the nonlinear time-history analysis of a group of single degree of freedom (SDOF) systems. Although an SDOF system can not represent the complete behavior of a complex building, for the low to medium-rise buildings with a fundamental vibration first mode, such an idealization is acceptable. In this regard, a group of SDOF systems with the elastic-perfectly-plastic (EPP) nonlinear behavior was considered. SDOF systems have vibration periods between 0.1s to 2.0s (as low to medium-rise buildings) with strength reduction factors (Rμ) of 2 to 8 to cover most of the common lateral resisting systems. These systems were analyzed under the action of 24 artificially generated ground motion records. Earthquake records were generated based on three different envelop shapes including compound shape, exponential shape, and Saragoni and Hart shape. These envelop shapes are representing the general form of an earthquake accelerogram and try to impose the real characteristics of an earthquake on the generated record. After employing the time-history analysis on each SDOF system, the mean of the maximum displacement demands of SDOF systems was obtained and compared to those from the estimating equations in Standard 2800 and Code-360. It is observed that estimated demands from Standard 2800 are closer to those from time-history analysis when compared with the obtained results from Code-360. Among the considered strength reduction factors, it was observed that SDOF systems with larger Rμ lead to a higher difference between the time-history results and those from codes. This is more predominant over the period range of 0.1s to 0.8s. So, relations in both codes are required to be modified for better demand estimating. In this regard, a method is proposed for modifying the available equations in the prementioned codes to accurately predict the displacement demands in systems under the action of artificially generated ground motions. A comparison between the results from the modified equations and those from the nonlinear time-history analysis shows the efficiency of the proposed method.

This paper investigates the mitigation of vibrations in grounds subjected to dynamic loads using soft and hard wave barriers. In order to consider the real problems, layered grounds are also modeled in addition to homogenous grounds. One of the important factors that needs to be considered in the groud vibration analysis is the effect of the groundwater table. Within this context, different levels of groundwater level are considered. Due to the difference between the impedance values at the interface of the dry and saturated parts of the ground, the upcoming incident waves experience refraction phenomenon, in which part of the wave reflects back to the medium from which it is propagated, while the other part transmits to the medium on which it impinges on. The amplitude of the applied loadings is small and therefore, the assumption of linear material behavior holds on. Biotchr('39')s poroelastodynamic theory and advanced finite element models are used for simulation of the wave propagation phenomenon in the saturated soil. Soft wave barriers are considered to be as open trenches while hard barriers are filled with concrete. Considering the very large number of solution space for finding the position and geometry of the soft and hard barriers, CMA-ES optimization algorithm is used. To find the optimization function, the poroelastodynamic finite element model is coupled to the optimization algorithm. This is performed using developed robust scripts by which the whole finite element model including the geometry, loading, boundary conditions, and assigning poroelastodynamic constitutive relation parameters are defined, at each step of optimization, without implementing graphic user interface (GUI). The soil domain is considered as homogeneous and layered unbounded half spaces. To model the unbounded soil medium in finite element simulations, low reflecting boundary conditions are applied around the model. One of the important parameters that affects the properties of the wave barriers is the frequency of loading. This is related to the dimension of the wavelength generated by the dynamic loading at a specific frequency. To consider this effect, the optimizations are performed for dynamic loadings with two different frequency values of 10 and 20 Hz. The obtained results indicate that open trenches are more effective than the concrete barriers. This is attributed to the very large impedance mismatch between the soil and air. The shape of optimal barriers is different in homogeneous and layered grounds and also water level table has a significant effect on the optimal barrierschr('39') shape. In addition, in the homogenous ground, optimal trenches sometimes take a slab-like geometry while in the layered ground, these barriers have a vertical column geometry and intersect the boundary between the two upper soil layers. All of the optimizations are performed by assigning a constraint for the maximum allowable volume to the barrier. This is performed by defining an appropriate penalty function. It is found that optimal barriers do not necessarily occupy the whole allowable barrier volume and in some cases their volume is less than the defined maximum constraint. This observation indicates that there is always no need to make the barriers as large as possible, which helps saving construction material and reducing the amount of earthwork.

In the past, fiber reinforced concretes (FRC) was used mainly in pavements and industrial floors however, FRC has a number of other uses as well, with recent uses including bridges, hydraulic structures, tunnels, pipes, canal linings and safety vaults. On the other hand, the resistance of FRC against to penetration of chloride ions, especially bonded chloride, has received less attention. In addition, the prior literature's results on chloride ions bound in different concretes have always been varied. This study analyses the mechanical characteristics of fibrous and normal concretes (NC) containing two pozzolans of metakaolin and pumice using microstructural investigation. Also, the chloride isothermal under marine environment was studied by simulating the immersion and tidal conditions. This study can be beneficial for use in different applications such as paving and bridges which are under the influence of chloride ion penetration. The first goal of this study is to increase the flexural strength of the pavement layer in order to reduce its thickness which can be economical, and the second goal is to study the durability performance of NC and FRC containing of cementitious material (pumice and metakaolin) with respect to the aggressive medium that is a determining factor in the lifetime of concrete structures. It is generally acknowledged that blocking the paths of chloride penetration by densifying the microstructures of the concrete can be a fundamental solution using pozzolanic reaction produced by pozzolans to enhance the durability of concrete. In the last years, metakaolin and pumice has been introduced as a highly active and effective pozzolan for the partial replacement of cement in concrete. Metakaolin and pumice consumes the Ca(OH)2 that is produced from the cement hydration process rapidly and effectively and in addition to CSH, phases like C2ASH8 (stratlingite), C4AH13 and C3ASH6 (hydrogarnet) are produced. These pozzolanic products enhance the structural properties of concrete and also contribute to total pore refinement. In this study, six concrete mixtures with a control mixture without any addition are prepared and tested in hardened states. Afterwards, the resistance to chloride penetration both in immersion and tidal conditions is investigated. Accordingly, first, the compressive strength and flexural strength test were performed on hardened states to assess the mechanical resistance of the different prepared mixtures at early ages and up to 365 days. Then, the microstructure study of six prepared mixtures were investigated by using Scanning Electron Microscope (SEM), EDX spectrum and CT scan test. Finally, the chloride penetration resistance of the different concrete mixtures was evaluated by measuring water-soluble chloride profile, bonding and total chloride in immersion and tidal conditions. In both the immersion and the tidal conditions, durability results show that metakaolin and pumice have a significant effect on the increasing chloride penetration resistance. This impact was far more apparent in pumice-containing samples. However, the concretes containing pozzolans have a porous structure, according to computed tomography scan (CT scan) analysis and microstructure results in this study, and the Ca / Si ratio is considerably lowered owing to decalcification. Also, the results showed that despite the structural porosity in concretes containing pozzolans, factors such as Ca / Si ratio and pore solution concentration play a very important role in their durability against chloride ion in the simulated marine environment.

Petroleum products and their derivatives cause severe soil pollution through transportation, leaks in pipelines or improper storage. These contaminants may affect the physical or chemical parameters of the soil. Nowadays, due to the increase in construction projects and consequently the need for suitable lands, the construction of structures on lands with contaminated soils is necessary. To determine the optimal methods for rehabilitation of contaminated soils, it is necessary to recognize the contaminated soil behavior and characteristics. There are several methods for stabilization of contaminated soils depending on the type of soils and their pollution. In selecting the appropriate method and materials, various aspects such as environmental issues, availability and cost-effectiveness of the method should be considered. In this study, the effect of oil pollutants on the geomechanical parameters of the sandy soil has been investigated and on the other hand, the performance of different environmentally friendly materials as adsorbents of pollutants and also their effect on the contaminated soil behavior was studied.  The studied soil is poorly graded sand that has been sampled from Qazvin district. The petroleum pollutants studied in this study are kerosene and gasoil. Three different materials incuding zeolite, perlite, and produced magnesite were used as sorbent in this study. In this study, the carbon dioxide emissions from industry were utilized to produce magnesium carbonate minerals. In the first step, the percentage of pollutant absorption for studied materials including the sand and sorbents was investigated. The results showed that the magnesite had the highest capability to absorb petroleum contaminants.  The percentage of pollutant absorption in magnesite was about 91% for gasoil and 85% for kerosene, while in studied sand it was 26% and 21% for gasoil and kerosene, respectively. The other sorbents including perlite and zeolite also showed high percentages of pollutant absorption. In order to investigate the effect of petroleum pollutants in the shear strength of sand, the direct shear tests was conducted on pure and polluted sample. The soil specimens with dimension of 10x10x3 cm and dry density of 18.35 kN/m3 were prepared by dry air pluviation method. After installing the sample in the device and before performing the test, the sample was saturated with contaminant. The specimens were sheared under different vertical stresses of 50, 100 and 200 kPa. The results showed a decrease in shear strength and more than 10 degrees decrease in internal friction angle of contaminated samples with respect to pure sand. The direct shear tests were conducted on the contaminated samples, treated by different sorbents. The results demonstrated an increase in shear strength for samples treated with perlite, but a loss in shear strength for samples treated with zeolite. The difference in shear strength between the magnesite-treated samples and the untreated samples was not significant. The study confirmed that perlite, zeolite, and magnesite have a capability to absorb petroleum contaminants in soils.  Carbon dioxide is one of the most influential factors in global warming in the coming decades, so the magnesite produced by capturing CO2 and its application as a pollutant absorbent can be an encouraging finding of this study.

Surface fault rupture is very dangerous for critical buildings and infrastructures located in or near active faults and can cause irreparable damages. These structures must be designed by considering the undesirable effects of surface faulting. In this case, geotechnical measures, especially the construction of reinforced earth foundations are very effective in reducing the adverse effects of surface faults. The ASTM designation primarily recommends avoiding constructions to the adjacent of active faults probable of causing rupture at ground surface during an earthquake, although it is hard to determine the exact location of surface faulting. The increasing growth of population and the need to develop cities, particularly in metropolitan areas with economic limitations or land restrictions, have attracted the attention of the engineering community more than before to carry out feasibility studies on the construction of buildings in active fault zones. Such a consideration does not negate that the primary recommendation to avoid construction of buildings over active fault zones is the most convenient solution; it rather aims at examining and making engineering arrangements for the construction of buildings in zones with surface faulting potential governable by engineering methods. In addition to buildings, linear projects such as roads, highways, and tunnels must cross regions probable of surface faulting. Therefore, geotechnical measures, particularly designing reinforced soil foundations, contribute significantly to the reduction of undesirable effects of surface faulting. This research is conducted based on a series of tests on foundations reinforced with geogrid, geocell, and a combination of both, subject to normal faulting, to reduce surface faulting ruptures. The tests simulate the behavior of a 1.5 m wide strip foundation, placed over 6 m thick alluvium, subjected to a displacement of 60 cm. Seven tests were performed by different types and numbers of reinforcement, which were scaled to 10. The image analysis was carried out to examine the ground settlement profile, angular distortion, and fault propagation path. The results showed that the geotextiles used in the reinforced soil foundation could effectively reduce the angular distortion, cause uniform settlement, and divert fault propagation path, all protecting the structure against faulting. In a foundation reinforced with one layer of geogrid, a uniform settlement occurred at fault-induced displacement. In particular, the geogrid largely affected fault distribution, angular distortion reduction, and uniform ground settlement. Also, the settlement occurred at a wider zone and reduced the angular distortion by 60%. It means that the geocell affected the reduction of angular distortion and creation of uniform settlement by about 30%; however, it did not affect faulting diversion. The results indicate that the foundation reinforced with a combination of geocell and geogrid reduces angular distortion by 70% acted almost the same as the foundation reinforced with one layer of geogrid. Due to the increased stiffness and compressive strength of geocell, the shear band was more diverted toward the left side, compared to the foundation reinforced with one layer of geogrid. The right boundary of the shear band was also moved to the left corner of the structure. Likewise, the foundation reinforced with a combination of two layers of geogrid and three layers of geogrid reduces angular distortion by 80%. The results also reveal that adding more than two layers of geogrid had no effect on angular distortion reduction and the fault propagation path was more diverted as the number of geogrid layers increased.

Hydraulic fracturing is a new and widely used method for extracting reserves and energy resources in the depths of the earth. In the near future, due to increase in energy consumption on the one hand and depletion of energy reserves on the other, using of this method will become a necessity. One of the most important and effective parameters in this process is the pressure and how it is applied in order to create fractures and fracture progression in rock layers. Another important parameter is the interaction between pre-existing natural fractures with different angles and hydraulic fracture. Due to the high costs of this process, the purpose of this study is to achieve the optimal state for the maximum progress of hydraulic fracture and the lowest amount of breakdown pressure at the same time. Numerical modeling was performed in two dimensions by Particle Flow Code ( PFC ) software from Itasca company on samples of Pocheon granite rocks with brittle behavior using distinct element method. PFC software uses circular disks in two dimensions to construct and make the sample using distinct element method. These particles are in contact with each other through bonds. In this program there are walls that interact with these disks to apply load on the sample. The flat joint model is used in order to create contacts between particles, and discrete fracture network is uded to to create pre-existing natural fractures for interacting with hydraulic fracture. Given that in the distinct element method (PFC software) our sample consists of a large number of particles in two dimensions that the general characteristics of the sample are formed based on the interaction between these particles, so we need parameters as input data to our software, existing disks and the link between them, to finally obtain the specifications of the same laboratory sample after modeling. These specifications and input data are referred to as micro parameters, and the final specifications, which are the same as our mechanical parameters in the laboratory, are referred to as macro parameters. To find the micro parameters of the sample we use the trial and error method. Here, our modeling is based on Brazilian and uniaxial compression experiments and … performed by Zhuang et al. laboratory investigations. Due to the limitations of PFC software for fluid flow modeling and limitations for using of CFD relationships, pressure equals to fluid pressure can be used as a new solution. In this way, by modeling a number of walls that form a complete circle with overlapping each other, and by considering the servo control mechanism, we move them in the opposite direction of their normal vectors and off-center, creating a comprehensive pressure Which is actually same as the fluid pressure. From the obtained results, it was found that with increasing the loading rate, the sample reaches the breakdown pressure and breaks in less time, but the amount of breakdown pressure increases. Also, by increasing the natural fracture angle relative to the horizon (clockwise), the specimen breaks at a lower breakdown pressure. Finally, by increasing the natural fracture distance from the center of the sample, the effect of the presence of the joint in the sample decreases and the breakdown pressure approaches the seamless state.

Fragility curves are powerful tools to assess and control of possible damages to the existing structures and estimate the exceedance probability from the seismic behavior of the structures under the influence of different earthquake levels. these curves present the probability of damage as a function of the ground motion characteristics. The main goal of the current study is to examine the existing methods and the presentation of a suitable method for the production of analytical seismic fragility curves and propose appropriate relationships for the exceedance probability from different performance levels. For this purpose, three high-rise building with 20, 25, and 30 stories with a slimming ratio greater than π, according to the standard 2800 and the sixth issues and tenth issues of the national building regulations of Iran, were designed. Then after extracting the perimeter frame, by using appropriate software, their analytical model was defined and validated. To evaluate the seismic response demand of frames, incremental nonlinear dynamic analysis (IDA) was performed. For IDA analysis, the 22 recommended records in the FEMAP695 guideline and two earthquakes in Iran were used. Spectral acceleration of the first mode of the structure with damping of 5 Percentage (Sa (T1.5%)) was used to introduce the intensity of the earthquake (IM) and the inter story drift ratio was used to introduce the engineering demand parameter (EDP) Or damage measure (DM). To find the appropriate function of the exceedance probability from limit states and use them in the production of fragility curves, the results of IDA analysis and nineteen different probability functions using the suitable program were used. in order that the used distribution describes the sample data in the best manner, the goodness of fit tests was used. the results obtained from the goodness of fit tests show that The probability distribution rank used by researchers (log normal) versus other probability distribution functions varies in ranking the best fitted probability distribution. and selecting the appropriate probability distribution is effective in the conclusions and determining the probability exceedance of the structure from the desired limit states. Therefore, in order to reduce the uncertainty related to the mathematical model (epistemic uncertainty) in the template of a comprehensive view and according to accuracy and the required seismic target, a suitable method for developing fragility curves for types of structural systems with different heights here called “intelligent seismic fragility curve (ISFC)” is introduced and presented. Such that if among the probability functions examined in this paper, the use of only one distribution is desired to compare several options, including deciding how to reinforce or comparing the seismic performance of several structures with duel system of special steel moment resisting frames with eccentric lateral bracings to plot the fragility curve, it is recommended: to use the probability distribution "Generalized Extreme Value", due to the ability to fit better than the distribution "log normal", but for more sensitive structures, such as nuclear power plants and hospitals that are of great importance and require high precision or in order to achieve the most accurate fitted possible to decide on about the vulnerability estimation for types of structural systems with different heights, It is then recommended: to estimate the exceedance probability from performance levels at the structure, before fragility analysis, by probabilistic evaluation and using the goodness of fit tests on suitable probability functions, at first, a best fitted probability distribution should be selected at all performance levels and then the vulnerability of structures is estimated by fragility curves.

Fine-grained soils, especially those consist of high content clay minerals, generally have high strength in dry state, but they loss their strength when subjected to absorb water as well as they may be swell. These phenomenon may lead to damage the structures located on them and it is required to stabilize them with different additive materials. Common additives for stabilization of problematic soils are cement, lime, fly ash, etc., which are almost costly and have environmental consequences. Nowadays, non-traditional material such as polymeric materials were added to the soils in order to their stabilization. In this research, the effect of polyester polymer resin on the physical and mechanical properties of fine-grained bentonite soil, with liquid limit and plasticity index of 226% and 179% respectively, was studied by performing Atterberg limits and unconfined strength tests. For this purpose, a polyester polymer resin were added to bentonite soil with various amount of 1.0, 2.5, 5.0, and 7.5 percent in dry weight. Soil mixtures were cured about 7 days and Atterberg tests were performed on them. Moreover, cylindrical specimens with 50 mm in diameter and 100 mm in height were prepared and cured during 7, 14 and 28 days. Soil specimens compacted in a splitted steel mold at four equal thickness layers. Then, the unconfined compression tests were carried out on these specimens with loading rate of 0.5 mm/min. The results of Atterberg tests indicated that the addition of polyester resin reduces liquid limit and increases plastic limit of bentonite and consequently it is led to decrease in plasticity index of the soil. Maximum decrements in liquid limit and plasticity index observed in treated soil with 7.5 percent polyester, which are about 41.0 and 65.0 percent respectively. In addition, the polyester resin improves the unconfined compressive strength of the soil and the rate of increment is high when the polyester amount rises from 0 to 7.5%. It was revealed that the polyester resin influences the unconfined strength considerably in a short time, and the rate of improvement gradually decreases with passing time. For example, adding 5.0 percent polyester polymer resin to bentonite soil improves the strength up to 2.05, 2.11 and 2.58 times respectively after curing times of 7, 14 and 28 days. It also means that after 7 day curing time the improvement effect of stabilizer is considerable and by passing time its effect diminishes. Moreover, adding polyester polymer resin to the soil decreases deformability of soil; it means that this additive cause the treated soil exhibits more brittle behavior rather than the pure soil. The photos of specimen after failure explain that failure surface of pure bentonite is inclined in relation with horizontal, while it tends to vertical direction in treated specimens. Analysis of SEM images, results of XRD analysis and FTIR spectroscopy suggest that polyester stabilizer penetrates into the layers of soil particles and, by inducing effective interaction makes the layers closer or sticks them together. These phenomena decrease water absorbing tendency in soil minerals and improve the plastic characteristics and shear strength of the soil.

Nowadays, the use of composite sections has become a common practice in the construction industry. Concrete is inherently a brittle material, with high stiffness and compressive strength. On the other hand, steel is a material with high tensile strength and ductility. The simultaneous use of steel and concrete in composite sections improves the performance and leads to optimum exploitation of the properties of both steel and concrete materials. Concrete-filled steel tube (CFST) is a type of section often used in high-rise buildings. In addition, the composite action of steel and concrete in CFST columns gives some advantages to these sections during fire incidents. On the one hand, the concrete core prevents the local buckling of the steel tube, and on the other, the steel tube prevents the spalling of concrete at elevated temperatures. The behavior of CFST sections at elevated temperatures is complicated due to interactions between the steel tube and concrete core. Therefore, achieving a correct understanding of the behavior and material properties in CFST columns is required for design and strengthening purposes. In this research, with the help of the gene expression programming (GEP) technique, a formula was developed to estimate the ultimate load-carrying capacity of CFST columns after exposure to elevated temperatures. To that end, the experimental data of 94 groups of CFST stub columns were employed, of which 80% were used to train the model and the remaining 20% to validate the model. Input variables included the compressive strength of the concrete core ( ), cross-sectional area of the concrete core ( ), yielding stress of steel ( ), cross-sectional area of steel tube ( ), normalized temperature ( ), and the confinement index ( ). The validity of the developed model was assessed using a portion of the data that had not been employed in the training phase. To ensure the correct prediction of the ultimate load-carrying capacity of CFST stub columns by the developed model, a sensitivity analysis and parametric studies were conducted on the model and revealed the complete compatibility of the model with physical facts. The results of this research indicate that increasing the compressive strength of the concrete core, cross-sectional area of the steel tube, yield stress of steel tube, cross-sectional area of the concrete core and the confinement index increases the ultimate load-carrying capacity of the CFST section, while increasing the exposure temperature lowers this parameter.