نشریه مهندسی سازه و ساخت
سال دهم شماره 11 (پیاپی 76، بهمن 1402)

The present research aimed to evaluate the effect of industrial steel fibers on the mechanical properties of reactive powder concrete (RPC). A series of reinforced RPC specimens containing different percentages of steel fibers having different diameters were built. By performing resistance tests on the samples, the mechanical properties (compressive, bending and tensile strengths) of RPC were determined. The results of the compressive tests showed that by increase in the curing age from 7 to 42 days, the strength of RPC containing group 2 steel fibers (medium fibers: diameter 0.6 mm) increases compared to the control concrete. This is attributed to the continued reactions between the cement paste and the interlocking of most of the quartz-silica sand aggregates and micro-silica powder in the RPC specimens with steel fibers. The highest compressive strength of RPC compared to the control concrete was obtained for the sample containing 2% group 1 steel fibers (small fibers: diameter 0.4 mm) equal to 421 MPa (29.11% growth compared to the control concrete). By reduce in the diameter of fibers, the number of fibers in the sample and subsequently the interlocking between aggregates and fibers increases and the replacement distribution of aggregates improves. Based on the flexural strength tests, 2% of groups 1 and 2 steel fibers and 3% of group 3 (large fibers: diameter of 0.8 mm) were determined as the optimal value of fibers to achieve the maximum flexural strength of RPC. Based on the tensile tests, it was found that with the addition of 1%, 2% and 3% of groups 1, 2 and 3 steel fibers, the growth of RPC tensile strength is completely upward. The reason was attributed to the bridging effect of steel fibers in the concrete matrix. Empirical equations obtained from regression analysis have high accuracy for estimating resistance properties.

Considering the increasing use of seismic isolators in the country, which reduce the force on structural members and increase the overall displacement of the structure during an earthquake, it is necessary to create an optimal method for using this system along with reducing the overall displacement of the structure. Also, the use of damper systems reduces the overall and inter-floor movement of the structure during an earthquake. Therefore, it is essential to investigate the effect of using damping systems to optimize seismic isolators. On the other hand, the optimal use of the combination of two damper and isolator systems can be effective in reducing construction costs and repair costs resulting from earthquakes and provides structures with optimal performance. Therefore, in this article, two viscous and frictional dampers as well as isolator were used in high-rise concrete structures with 15 and 20 floors and the combination of these two systems was evaluated in the behavior of the structure. The structures are separated by lead core rubber isolators. The results were studied under three earthquake records of the nearby area. The results showed the positive effect of dampers and separators on the behavior of the structure, and reasonable results were obtained depending on the seismic records used in the article. also, showed the positive effect of the combination of separators and dampers in reducing the amount of relative displacement, roof displacement and base shear. The simultaneous use of damper and isolator in the structures caused a 35% reduction in the base shear of the structures, 47% in the maximum relative displacement and 29% in the displacement of the roof point.

Earthquake wave transmission from the source to the site is modeled by the ground motion prediction equations (GMPEs or attenuation equations). Considering the high contribution of these equations in the variability of the ground motion in the site, the selection of the appropriate relations for the region is of particular importance. The number of prediction equations is large, but there is no specific relationship for many areas, so it is necessary to use criteria to determine the best equations for probabilistic seismic hazard analysis(PSHA). In this paper, 62 relationships used by analysts in Iran and Tehran region are introduced to the three criteria of Rennie divergence, Euclidean distance and likelihood method, are ranked based on similarity with actual occurrence data, and the most suitable relationships for Tehran are introduced. The results show that the relationship of Zare and Sabze Ali (2006) in all three methods has a very good match with the Tehran region earthquakes. Also, some global relations have a better match than the regional relations obtained in Tehran. The results of the sensitivity analysis show a decrease in the effectiveness of the regional PSHA using the ranking. It also shows that relying on the opinion of experts brings more than 90% confidence in the selection of GMPEs, which seems sufficient in some cases. .If this level of accuracy is not sufficient, it is necessary to use the appropriate weighted equations in the analysis based on the physics-based ranking results. Otherwise, the results of the probabilistic seismic hazard analysis will fluctuate and may not have the sufficient reliability.

Structures with large opening roofs are vulnerable to wind, in these structures due to the low dead load, the wind load has a greater effect on these types of structures. In the calculation of wind force, one of the coefficients related to the geometry of the structure is the pressure coefficient (Cp), which is provided for some common structures in the loading regulations. Arch opening of 0.1, 0.2 and 0.3 was done using wind tunnel test and numerical modeling based on Computational Fluid Dynamics (CFD) method using ANSYS software and wind pressure coefficients on these structures are presented, it can be seen that with increasing The ratio of the height to the opening of the arch of the maximum coefficients of negative wind pressure (suction), increased in such a way that on the middle axis of the structure in the state of α = 90o, the maximum negative pressure in the structure S-1, S-2, 3-S, is equal to -2 and It is -1.7 and -1.6. The pressure coefficients on the sides facing the wind show a positive number, which indicates the pressure on these surfaces, the maximum positive pressure occurs at α=90o (the state where the direction of the wind is perpendicular to the shed) and in this case the pressure coefficient is equal to +1. In structure S-1 (height-to-opening ratio 0.3), the maximum deformation created for the wind application angle is α=40o, which is 20% more than α=90 o.

The present research investigates the strain demand of boundary elements of concrete shear walls reinforced with hybrid steel-composite rebars. In this regard, the numerical model of an existing full-scale sample has been done in VecTor-2.0 software and the results has been validated. Then, parametric studies were carried out for different values of the hybridization ratio where the cyclic response, maximum force, secant stiffness, single-cycle energy, displacement recovery index and strain values of the rebars are extracted. The results show that the combination of steel and composite rebars improves the hysteresis response of shear walls, maintains the post-yield strength, and increases the secant stiffness for lateral drifts over 1.9%. Also, this technique leads to a self-centering behavior minimizing the seismic damage. Hybridization with the combination ratio rh≥0.2 provides strength and maintains the stability of the wall. Increasing the hybridization ratio higher than rh=0.3 only results in an increase in the strength with no residual displacement change. For walls with a low rebar hybridization ratio, the cyclic strain-displacement curves are asymmetric, but the behavior becomes symmetric and the maximum steel strain is reduced by 50% by increasing the ratio. The expansion in the steel strain cycles is insignificant for low hybridization ratios. However, it becomes more apparent with the increase of composite rebars. The effective straining height of the steel in the basic model is equal to half the length of the shear wall, but with the addition of composite rebars, this height increases up to 80% of the wall length, which indicates the yield distribution of the steel in a wider area of the member when it is hybridized with composite.

In this study, the seismic performance of the reduced beam section (RBS) steel moment-resisting frame (SMRF) equipped with composite steel plate shear wall (CSPSW) and high-performance fiber-reinforced cementitious composites (HPFRCC) is investigated using Abaqus software. The finite element model of HPFRCC-CSPSW was validated using experimental results. Then, the seismic performance of the six-story SMRF with common SPSW, as well as HPFRCC composite CSPSW systems under near-field (NF) and far-field (FF) earthquakes, was investigated and the results (bearing capacity, stress, deformation, and energy absorption) were compared. For this purpose, 5 NF and 5 FF seismic records were used. The results showed that the energy absorption and shear capacity of HPFRCC-CSPSW increased significantly but the maximum stress value decreased compared to common SPSW. The seismic performance of the investigated systems largely depends on the type of earthquake. However, in both SPSW and HPFRCC-CSPSW systems, the maximum displacement and the base shear under the NF earthquakes were higher than those of FF earthquakes. Besides, for all NF and FF earthquakes, maximum displacement in the SPSW system occurred in lower stories, but in the frame with CSPSW, the major displacement occurred in the upper stories. The highest increase in shear capacity and energy absorption of the system in FF earthquakes was for the Tabas accelerometer (75 and 128%, respectively) and the Imperial Vali earthquake (94 and 101%, respectively). Also, the maximum displacement in SPSW and HPFRCC-CSPSW systems occurred in Northridge (14.6 cm) and Tabas (16.2 cm) NF earthquakes, respectively; the Chichi earthquake also had the greatest damage to the structure under FF earthquakes.

One of the important issues in the vibration analysis of rail structures is to investigate the effect of train movement and the variable location of the load. This research introduces a new model to provide the ability to investigate 3D stress during analyzing a linear model. This model includes 6 degrees of independent transitional and rotational freedom, and one dependent degree of freedom as Warping to analysis the effect of moving loads. So, the interaction of the independent degrees of freedom has been considered due to the asymmetry of the cross section, especially in the earthquake load conditions. Finally, using a numerical Mathcad programing model, some of the parameters that are effective in modelling and vibrational analysis of rails have been examined. One of the important achievements of this study is to prove the effect of rail vibration acceleration on the characteristics of the analysis model as well as the need to determine the length of the computational model based on the results of the rail vibrational acceleration and its processing at the end of the rail. According to the formulation performed, stiffness and damping matrix are asymmetric, because of the velocity and acceleration vector effect of the load, however the mass matrix remains symmetrical. Also, by creating initial sinusoidal displacement conditions on the system, the conditions of corrugation phenomena can be expressed. The seismic acceleration applied to the model to evaluate the relevant freedom degrees and determinate the permanent deformation is considered in the model. It indicates the presence of permanent twisting and warping values in the rail-beam model, is about 40-50% of the maximum value. According to this investigation, the determination of the boundary conditions based on the damping of the acceleration at the end of the rail is very effective in calculating the results more accurately.

Buckling restrained braced frames (BRBFs) may have damage concentration in one or few stories during severe seismic excitations, because buckling restrained brace (BRB) yields in a certain story and the stiffness of that story is significantly reduced. Drift concentration is undesirable because it can lead to general instability resulting from the P-Δ effects or residual drift. For controlling damage concentration and achieving a uniform distribution of drift in all stories, a new system entitled rocking buckling restrained braced frame (RBRBF) is used. RBRBF system generates uniform story drifts over the height of structure and prevents the damage concentration in one or few stories. Unlike conventional braced frames, the braces on one side of the braced span along with the adjacent columns and ties are part of a vertical truss system that is hinged at the base and designed to remain elastic until the near collapse limit state is reached. This vertical truss system works as a strong support for preventing damage concentration in one or few stories of the braced frame. The braces on the other side of the braced span are BRBs and are designed to provide energy dissipation. The novelty of this paper is investigating the seismic collapse of this new structural system under the effect of subduction ground motion records, which have higher significant duration compared with crustal ground motion records. For this purpose, the considered structures are assumed to be located in Seattle, which is subjected to both subduction and crustal ground motions. The results indicate that RBRBFs can effectively reduce drift concentration using the displacement‐based design approach and under both crustal and subduction ground motion records have significantly better performance in terms of seismic collapse compared with BRBFs. In addition, all structures under subduction records have lower collapse capacity values compared with crustal records.

One of the future problems of humans is environmental pollution. Negligence and lack of management of greenhouse gas production threatens human life on the planet. Considering the emission of CO2 gas due to the production of cement, it is important to find a way to reduce the consumption of cement in concrete as the most consumed building material. The use of pozzolans to make strong and durable concretes has become very important in the past years. In this research, two widely used pozzolans, namely zeolite and bentonite, were tried to improve the behavior and durability of SCC concrete. Therefore, the combination of zeolite and bentonite in weight ratios of 2.5%, 5%, 7.5% and 10% was used instead of cement. The tests performed include slump flow, concrete viscosity, compressive strength, and durability of concrete against melting and freezing cycles at different ages. The results of this research showed that the use of these pozzolans will reduce the strength in the early ages of concrete, but this problem will be solved with the increase in the age of concrete. So that using a combination of 5% zeolite and 5% bentonite can increase the final compressive strength (90 days) of concrete up to 8.6%.

Buckling Restrained Braces (BRBs) show high ductility and energy dissipation capacity under seismic excitations. It is possible to improve these features by modifying the BRB configuration and the structural system including these braces. Buckling Restrained Braced Frames (BRBFs) may have drift concentration in one story, which leads to the instability of structure due to P-Delta effects and residual drift. To solve the problem of non-uniform damage distribution along the height of structure, which is a disadvantage of BRBFs, researchers have proposed the Rocking Buckling Restrained Braced Frame (RBRBF) system. Each braced bay in this system consists of a conventional brace on one side, a BRB on the other side and a connecting element at the middle of the bay. The conventional brace in one side of the braced bay with the side column and the connecting element form a pin-supported vertical truss system like a rocking wall that behaves elastically until near the collapse of structure. In this study, 4-, 8- and 12-story RBRBFs and BRBFs are considered. Then, by performing non-linear dynamic analyses, the effects of mainshock-aftershock sequences on the seismic collapse of the structures are evaluated, and the results obtained for the two structural systems are compared. The results show that the seismic collapse resistance of each RBRBF under mainshock-aftershock sequences is significantly higher than that of its corresponding BRBF.

Load transfer from beam to column in connections by a reliable path is one of the most important and critical issues that has been proposed and studied in various details by many researchers. The failure of the connection between the column and the beam is one of the main reasons that causes the failure and accelerates the collapse process of the structures. In the current research, it has been tried to increase the capacity and strength of the connection by proposing an innovative hybrid connection of reinforced concrete beam to steel column in two cases and provide the possibility of using these details in heavier sections. The innovative connection is proposed in two ways: 1- placing two steel shear web plates inside the concrete beam and connecting it with the end plate to the steel column 2- placing two steel shear web plates with upper and lower flange plates together inside the concrete beam and its connection with the end plate to the steel column. In this regard, after modeling and validating the prototype, the capacity and behavior of the proposed connections have been checked in Abaqus finite element software. The results of the analysis show that an increase in energy absorption with the addition of continues plate, and this effect is more visible with the increase in the dimensions of the beam and column in higher drifts. Also, the addition of flange plates to the steel part of the hybrid concrete beam is very effective in the overall ductility of the connection, and this has caused a 24% increase in the ductility coefficient and 13% in the maximum strength compared to the other proposed connections. At the same time, increasing the length of the steel part of the beam has increased the strength of the connection in all cases.

Maintenance is the possibility that maintenance conditions can be implemented in a certain period of time by using certain methods and resources. The importance of the level of maintenance of railway optical communication transmission networks and its repair and optimization (NET) is due to the need to maintain railway safety and prevent rail accidents. Today, the safe movement of trains is not possible without telecommunication networks. The interruption of optical transmission networks leads to the blocking of railway lines, and the blocking of the line leads to the reduction of traffic and productivity, damage to the rail network, and sometimes the occurrence of irreparable accidents in the railways. Also, the disconnection and failure of telecommunication transmission networks leads to the interruption of all train control telecommunication services, because all train control services are based on telecommunication networks. In the railway telecommunication department of J.A., as well as the railway infrastructure, unlike the maintenance and repair system based on reliability, the maintenance is basically done when the devices are out of service, which in addition to imposing heavy additional costs on the railways, causes It reduces productivity and increases the number of breakdowns. Therefore, the current research tries to provide a new model for increasing the level of maintainability by evaluating the current network capability of the railway telecommunication transmission system, which will lead to increasing productivity, safety and reducing the time intervals of blocking the railway network. The case study implemented in this research is Hormozgan railway area.