نشریه مهندسی سازه و ساخت
سال هشتم شماره 12 (پیاپی 52، اسفند 1400)

This paper investigates the importance of super-structure modeling in estimating soil’s contribution to the seismic response of soil-structure systems. For this purpose, soil-structure systems with different lateral resisting systems are studied and the values for the main parameters of the system, including parameters determining the soil-structure-interaction (SSI) and the contribution of flexural and shear deformation to the total response of the system are determined. To this end, a one-bay frame with flexural-shear behavior is utilized to model the super-structure in the soil-structure system. In this research, different soil-structure systems are studied using artificial and real acceleration floor responses. The results from investigating different soil-structure systems showed that the proposed method to identify the system can estimate the main parameters of the soil-structure system with acceptable accuracy. Moreover, the results showed that two different systems with different lateral resisting systems and the amount of soil’s contribution can be identified with almost the same floor acceleration responses. For an instant, a moment-frame system located on soft soil with relatively high soil-structure-interaction may have the same floor acceleration responses as a shear-wall located on firm soil with less soil contribution. This observation shows the importance of using more realistic modeling for the super-structure in soil-structure systems to achieve more reliable estimates of soil’s contribution to the system’s response.

Diagnosing type and amount of deficits in beams and structure is highly important in terms of performance and impact. Despite of paramount studies on CFRP application, its usage as Strips can be mentioned as one of the most important ways. Using Half Scale in building structure and lab beams would provide more adducible results. Considering type of breakdown and its progress, the growth cracks on the surface of beams is different. In all constructions, the manner of implementation and the quality of materials are two important principles in terms of performance and efficiency of the structure. In present study, type breakdown in the beam of reinforce concrete is addressed in a nondestructive manner. In this technique, by using finite element method in identifying beam breakdown without creating an unstable condition, one can achieve a nondestructive situation in experiments which is significantly cost – effective. Hence, 16 250mm × 250mm × 2100mm concrete beams were built and divided into two groups with and without FRP composite. Each group has a control beam and remained samples have breakdown in concrete and rebar. Prepared beams were put in a 4 – point experiment and, upon gathering and analyzing relevant data, beams prototyping was begun. By using finite element method, all beams were prototyped in lab. The findings from prototyping and lab analyses are compared in the format of load – location change graph. One can consider the results of prototyping as a proper approximation of lab samples.

Nowadays, finding ways to reduce earthquake force due to its damages is one of the most important challenges in the field of earthquake engineering. As a result, the selection of passive Viscouz damper is preferable due to its low cost advantage, more appropriate technology and commen use in country. In this research, the effect of Viscouz damper on seismic performance of concrete moment resisting frame has been investigated. For this purpose, three medium concrete moment resisting frames, which have3, 6 and 10-floors, are designed by the Sap2000 software without damper effect. Then, the damper has been analyzed by siesmo struct software. these frames have been designed by common methods, and then have been studied under the acceleration of selected earthquake mappings by using static pushover and dynamic time history analysis, with and without supplemental viscous dampers. Based on these studies, a value is suggested for the behavior factor of the damper added to the structure and compared with the values contained in the 2800 regulations. Also, this factor is investigated in structures equipped with this damper in far field and near field earthquakes. by including viscous damper, damping increases 20% .the suggested values of the behaviour factor for the static pushover and dynamic time history analysis are 6.29 and 6.23 respectively.

In general, masonry structures are divided into two categories in terms of the connection between components: mortar-free masonry, which is called dry joint, and structures that use mortar to connect the components. Due to environmental conditions, when the mortar loses its adhesion over time, the components of the wall can be considered as discrete elements. The poor performance of masonry structures leads to the failure of a significant number of these structures even in moderate earthquakes. In particular, in-plane failure in the walls of masonry structures is very common. The results of laboratory research show that shear failure is very likely in lateral loading. One of the characteristics of this failure mode is its ability to resist high shear force and low ductility, which leads to brittle failure in the wall. Previous numerical studies on masonry structures have been mainly based on the finite element method in which the wall components are considered as continuous elements and the local behavior of the constituent parts of the walls is ignored and causes their real function to be misunderstood. In this paper, first, the specifications of unreinforced masonry wall specimens were determined based on the results obtained from previous experiments, and then numerical models were calibrated and analyzed using two software ABAQUS (finite element software) and 3DEC (discrete element software). Then, behavioral diagrams of walls with different characteristics were extracted under different loading conditions. Finally, a comprehensive comparison between the results obtained from the discrete element and finite element methods was presented. Finally, it was concluded that the discrete element approach provides a more accurate prediction of unreinforced masonry walls than finite element one.

The main goal of the 2030 sustainable development plan is to develop access to renewable, sustainable, reliable and cost-effective energy. One of the renewable energy sources is wind energy, which is produced using wind turbines. These turbines are mainly used in coastal or offshore areas that are seismic and liquefied. The development of these turbines in areas with high seismic potential and liquefied soils has necessitated the use of piles and other deep foundations. In this paper, the effect of liquefied soil layer characteristics on the soil-mono pile interaction under the effects of far and near field earthquake records has been investigated. Dynamic nonlinear time history analyses were performed by considering four types of liquefied sand with a thickness of 5 m, under 2 kW turbine load and the effect of 14 earthquake records. Nonlinear analyses are performed in OpenSees software by considering the appropriate behavioral model for soil layers and the interaction between the pile and the soil. The results showed that in earthquakes with a PGA less than 0.4 g and in sandy soils with a density of more than 70% liquefaction does not occur. The highest displacement is related to the pile located in T1 soil, which has the lowest internal friction angle (ɸ = 30) and the lowest soil compaction percentage. With the occurrence of liquefaction in the middle layer, the support level of the monopile is transferred from ground to the end of the liquefiable layer. Based on the results the values of maximum pore pressure, flexural moment and shear force of the soil under near and far-field records decrease with increasing soil density that is more evident for far-field earthquakes.

Seismic isolation research was largely predicated on the observation that most strong-motion records recorded up to that time had very low spectral acceleration values (~2 sec.) in the long-period range. In recent years, however, a number of records from near-source sites have been obtained, raising serious questions about the viability of seismic isolation in near-fault locations. In this study, various analytical models of base-isolated structures have been simulated in a nonlinear platform. The used base isolation systems have been the Lead Rubber Bearing (LRB) and the Friction Pendulum (FP). Arrays of far-field and near-fault strong ground motions have been considered for performance evaluation. The main issue is that increasing the bearing damping in isolators beyond a certain value, may decrease the bearing displacement; however, it may transmit higher accelerations into the superstructure. Considering all these, the seismic performance of the investigated structure and the BI systems have been assessed considering a probabilistic approach utilizing fragility curves. The results indicated that the BI systems have very adequate seismic performance in far-field regions; however, their efficiency may significantly decrease in near-fault regions.

Towers and tall buildings have been considered since the beginning of human civilization and providing the suitable stiffness and especially the lateral stiffness is one of the basic factors in the design of these structures. In this matter outrigger systems are very effective in reducing the response of the structure to lateral loads. Also, the occurrence of earthquakes and its destructive effects in recent years has increased the importance of applying the behavior and performance criteria to control the distribution of resistance and deformation in structural components. Therefore, it is necessary to provide an optimal design with economic justification capability, the main purpose of which is to achieve a reliable level of safety and performance against natural hazards. In this research, in two structures with 24 and 36 floors, using modified dolphin echolocation metaheuristic algorithm (MDE), the performance based design of steel structures equipped with outrigger system while layout optimization of the brace has been done. All performance design constraints are considered in accordance with FEMA regulations. The results indicate the appropriate behavior of structures with outrigger, the effect of outrigger position on its performance and the process of achieving optimal structure. as the 36-story structure in the optimal position of the outrigger installation, the weight of the structure has decreased by about 3.9% compared to the installation position at equal height distances. In both structures, the criterion of story drift and axial length change of bracing members prevails and the necessity to consider the effects of higher modes in studying the behavior of the structure is emphasized so that by increasing the number of floors and higher modes influence, the optimal position of outrigger is shifted to the upper floors.

The continuous growth of the population will guarantee a massive demand for cement in the near future. Using pozzolanic materials in concrete manufacturing is intended as an optimal solution to lower the rate of greenhouse gas emission, and diminish energy resources and cement consumption. This research is aimed at evaluating Semnan Bentonite as partial replacement of cement. Seven bentonite mixes and control mix (CM) were examined. The main variable is the proportion of bentonite (5%, 10%, 15%, 20%, 25%, 30% and 35% by weight of cement) in replacement mode while the amount of cementitious material, water to cementitious material ratio, fine aggregate content were kept constant. To study properties of hardened concrete, compressive strength, splitting tensile strength tests and prediction of the modulus of rupture were performed. According to the results of compressive strength test, using 5% bentonite as partial replacement of cement, results in 8% increase in compressive strength 28 days as compared with the control mix. By replacing 35% of bentonite with the weight of cement, the compressive strength 28 days is reduced by 21%. According to the results in mixtures containing bentonite, if the amount of bentonite is more than 20% by weight of cement, the tensile strength 28 days is reduced by 45% compared to CM. According to the results, replacing 5% and 10% (by weight) of cement with bentonite, the predicted rupture modulus will increase by 3.7% and 3.1% compared to the CM, respectively

According to design criteria, site specifications, and required height, different dimensional options are considered for geometric parameters, while design gravity dams. Among options, an option that provides sustainability and low costs is considered as an executive option. In this study, the Koyna concrete gravity dam section in India and the Kalat Zavin concrete gravity dam in Khorasan Razavi province were optimized using the election meta-heuristic algorithm (EA) concerning the stability conditions. In this model, geometric parameters were considered as decision variables and dam weight as an objective function. The model obtains geometric parameters in such a way that the dam weight is minimized. To evaluate the proposed method, the Koyna dam and Kalat Zavin dam data set were used and the results were compared with Genetic (GA), Honey Bee Mating Optimization (HBMO), and Imperialist Competitive (ICA) algorithms. The results of the EA method indicate a 9.87% and 10.40% decrease in the volume of concrete consumption and a reduction in area for Koyna and Kalat Zavin dams. Based on the comparisons, the EA algorithm showed better performance in optimizing the dam section than the genetic algorithm (GA), honey bee mating algorithm (HBMO), and imperialist competitive algorithm (ICA) optimization models. optimization models. Also, the improvement rate of the EA algorithm in comparison with ICA, HBMO, and GA algorithms is equal to 8%, 6%, and 11%, respectively.

Self-compacting concrete is an innovation in the field of concrete that has resolved one of the main problems in the construction of concrete structures, namely the problem of concrete compaction. This type of concrete has caused a uniform composition in concrete with a new composition and the invention of superplasticizer. In the present study, the effect of introducing the additives of zeolite and micro silica and their replacement with a part of cement has been evaluated by testing the mechanical properties including compressive, tensile, flexural and ultrasonic waves tests on the control specimen of self-compacting concrete and expansive self-compacting concrete. Also, the short-term deformation due to shrinkage of self-compacting concrete caused by drying for a period of 210 days after the fabrication of specimens has been investigated. Experimental results have shown that micro silica and zeolite pozzolans improve the microstructure of the evaluated concrete, which improves the mechanical properties. In fact, the replacement of cement with pozzolans has made the parts of the transition zone of the specimens better and condensed. Shrinkage test results also show that zeolite and micro silica pozzolans lead to a significant reduction in drying shrinkage. Drying shrinkage of the concrete containing 15% zeolite and 7.5% micro silica decreased by 32% and 15% compared to the control concrete containing expansive materials at the age of 210 days, respectively.

Bridges are counted as one of the most important and vulnerable structures in the vital veins of every country. The abundance of the concrete box deck bridges with concrete arches on the one hand, and the complex dynamic behavior resulted from special geometric conditions of this class of bridges which have made them more vulnerable on the other hand, were aimed to be studied in this research. In this study, a model of a concrete box deck bridge with concrete arches and the appropriateness of using lead-rubber bearing system were examined, and ultimately, two states of the bridge with and without seismic isolation were assessed by fragility curves, and the amount of possible seismic damage have been obtained. The study results were analyzed by modeling the bridge in the CSi Bridge finite-element software in three dimensions and under the excitation of 100 pairs of real accelerogram and under nonlinear time-history analysis, and the responses of the elements were extracted. So that, compared to the state without seismic isolator, the maximum relative displacement in the model with seismic isolator has decreased by 55 and 28 percent in the longitudinal and transverse directions; respectively. Also , based on the result of modal analysis and comparison of t the vibration period, the results show a significant increase in the first to third period of vibration of bridges in the state with seismic isolation compared to the without seismic isolation. The results of studies indicate that In this bridges with seismic isolation have reduced the drift of columns significantly so that the seismic fragility of the bridge system has been reduced at different levels of damage.

Diagonal lattice systems are extensively structured systems of tubular and frame structures and can drastically reduce the weight of the structure and significantly improve the behavior of high-rise buildings by significantly reducing shear lameness. In this paper, the number of partitions, the angle and the optimal structure of single and double layer diagonal grid systems in tall buildings are determined. For this purpose, a computer program and meta-innovative solutions based on genetic algorithm and Caramba have been used as the engine of structural analysis. In these analyzes, the relationship between input factors including distance between two layers, angle and number of elements and number of vertical and horizontal divisions with output factors obtained from structural analysis using Caramba engine, including maximum deformations, weight and Pi delta effect were obtained. Based on the results obtained from genetic algorithms and meta-heuristic solutions, the weights obtained for diagonal lattice systems are more than one layer compared to two-layer systems. In addition, due to lower weight, simpler geometric structure, higher execution speed, no need for highly skilled technical force, lower energy consumption, less architectural space, creating more open spaces and better exposure in single-layer systems than two-layer, These systems are recommended for use in high-rise buildings.

Today, information and knowledge are so intertwined with human life that the present age has been called the information era. In this situation, the role of human in the organization and the way of looking at him/her will have a significant contribution to the success or failure of the organization. The role of human resources is becoming more and more prominent and it is now mentioned as the only factor in gaining a sustainable competitive advantage. Furthermore, due to dramatic developments in the field of human resource management, competency-based human resource planning has found a special place. In this study, a project scheduling problem considering multi-skilled resource and manpower competency is investigated. To do this end, an integrated multi-objective optimization model of project scheduling and human resource assignment including total completion time and execution cost minimization and project quality maximization is presented. To solve problem exactly, a mixed-integer programming model is developed and then solved by ε-constraint method in GAMS software. As the proposed model is NP-hard, a non-dominated sorting genetic (NSGA-II) algorithm is developed to solve the large scale problem. Furthermore, in order to validate the proposed algorithm, its results compare with exact method for instance problem in small scale. Results indicate that the proposed algorithm is outperformed and it can be used for real case problems.

In this research, consider to the importance of the effect of concrete strength on dynamic behavior of concrete dams, the effect of body concrete stiffness on seismic performance of roller compacted concrete (RCC) dams is investigated using Monte Carlo simulation which is the effective method for evaluation of different parameters on dynamic responses. For implementation of concrete stiffness, the modus of elasticity is considered as input parameter and its effect on output parameters including maximum response of dam crest displacement, 1st principle stress at heel, 3rd principle stress at toe and hydrodynamic pressure at heel of dam selected as critical responses is investigated. Ansys software, based on finite element method, was selected for dam modeling and seismic analysis and Nemark method has been used to solve the dynamic equation. Watana dam has been selected as case study and has been modeled in the 2-dimensional form and dam-reservoir-foundation interaction considered in model. Finally, to show the effect of modulus of elasticity of dam concrete, the responses were obtained as sensitivity curves. Obtained curves show the trend of responses to variation of modulus of elasticity obviously. According to results, one can select the optimum value of modulus of elasticity of concrete and concluded about the safety of dam consider to design criteria.

Increasing demands for the use of lightweight concrete as well as blast-induced hazards in all over the world have led to performing extensive studies to achieve a better understanding of the behavior of the impact and heat-resistant lightweight concrete. In fact, the plastic concrete is of high ductility and low permeability whose compressive strength is much lower than that of the ordinary concrete. This type of concrete is obtained by mixing cement, sand, water and bentonite. Bentonite in this mixture is a type of clay that promotes its formation and stability. In this paper, the effect of steel, polypropylene and glass fibers on the post-heat strength (both tensile and compressive) of the plastic lightweight concrete has been investigated. To do so, after the process of heating on the specimens (exposure temperatures of 25, 100, 250, 500 and 700 °C), the compressive and tensile strength tests were conducted on the specimens. Accordingly, the results indicate that the addition of the steel fibers greatly affects the concrete strengths such that in some cases, the post-heat strengths of the concrete was enhanced by more than 40%. However, it was found that in contrast to the steel fibers, polypropylene and glass fibers leave insignificant effects on the post-heat performance, which is attributed to their physical and visual characteristics.

Excavating tunnels in soft urban land has its own limitations. One of the most important limitations is the control of surface settlements to prevent damage to surface structures. Accordingly, choosing the best method for tunnel excavation is very significant. Among the existing methods for digging urban tunnels, step drilling methods are very widely used. Typically, these methods are not comparable to the mechanized drilling method for long tunnels. However, step drilling methods are used to drill short tunnels, large sections such as subway stations, non-circular sections, and complex structures such as intersections. Among the most important executive parts of step drilling are the length of the drilling step and the distance between the work fronts. Although these two parameters are very influential factors on the technical and economic aspects of the step drilling method, but there is no coherent process to determine these two parameters. In this research, the drilling stages of the tunnel of line A of Qom metro have been investigated in order to determine the length of the drilling step and the distance between the work fronts. The method of excavating this tunnel is pre support method. Using three-dimensional finite element modeling (Praxis 3D Tunnel), tunnel drilling is simulated in different progress modes. Eight progressive modes are provided for step length and six modes for spacing between fronts. The length of the drilling step and the distance between the work fronts are selected by examining the effect of different forward modes on the transverse diagrams of surface settlement, settlement values and soil displacement around the tunnel. Studies show that the same drilling step of 1 meter for the upper and lower parts with a distance of 25 meters between the fronts (a distance of more than one diameter of the tunnel), has the best performance for tunneling.

Today the use of concrete and steel columns is expanding rapidly. Therefore, the importance of studying these types of columns and providing solutions to improve the performance of these columns, is considered very important. Elastic modulus is a key parameter employed to estimate the deformation of structures and structural members and is typically expressed in terms of the compressive strength. Understanding the modulus of elasticity of reinforced concrete steel columns (SRCs) containing steel fibers and especially their behavioral changes during axial load application is an important issue. This paper tries to evaluate four moduli of elasticity of reinforced concrete columns containing steel fibers (SRFC). To achieve this goal, 36 SRFC specimens were constructed and various types of modulus of elasticity including the initial modulus, the sequential modulus, the yield point modulus, and the peak point modulus were examined. The research variables include the shape of steel section (H-shaped and C-shaped volume ratio of steel fibers (0, 0.75, and 1.25%), and stirrup spacing (40, 65, and 130 mm). The results showed that the modulus of elasticity of the SRFC columns was affected by the shape. Thus, the modulus of elasticity of columns with H-shaped cross-section was higher than columns with C-shaped cross-section due to more confinement in this type of cross-section. Also, increasing the percentage of steel fibers in the concrete of these types of columns can, in addition to increasing the ductility, increase the modulus of elasticity of the column by an average of up to 6%. In addition, the distance of the arches has a very significant effect on the modulus of elasticity of this type of columns, so that with increasing the distance of the arches, the modulus of elasticity of the columns decreases (about 35%) sharply.

This paper presents the results of an experimental investigation on the flexural performance of concrete beams containing recycled aggregates concrete (RCA) and reinforced with a variety of fibers. In this research, 5 concrete beams with a length of 150, width 20 and height 30 cm were made. One beam containing natural aggregate (NA) and fiber-free as control specimen, one beam containing RCA and fiber-free and the other three beams containing RCA and reinforced with 0.5% of each of the steel, polypropylene and korrta fibers. The performance of the beams were investigated under four-point bending test in two elastic and plastic zones. The parameters of limit of proportionality, modulus of resilience, flexural modulus of elasticity and yield moment in the elastic zone and the parameters of the ultimate moment, ductility, energy absorption and flexural toughness in the plastic zone were investigated. Beams containing NA and RCA had a slight difference (less than 10%) in all the mentioned parameters. On the other hand, the fibers used improved the flexural performance of the recycled beams in both elastic and plastic zones, which the effect of steel fiber was more significant than polypropylene and korrta fibers. Finally, the experimental results obtained in this study were compared with the results of Iranian Concrete Code (ABA), ACI 318, EuroCode 2 and CSA. The results of this comparison indicated that the lowest difference with the experimental results is related to ACI 318 and the highest difference is related to EuroCode 2.