نشریه مهندسی سازه و ساخت
سال هشتم شماره 5 (پیاپی 43، امرداد 1400)

By reviewing the literature on steel slit yield dampers (SSD), this study investigated and compared the effect of new strip shapes and geometric patterns on the behavior of this type of dampers. This study investigated a reference slit-less sample (solid) along with nine samples with a single row of blades or slits and three different shapes and geometric patterns, namely simple or constant cross-section, linearly tapered cross-section, and parabolic tapered cross-section with an elliptical slit at three different heights. These samples were subjected to cyclic loading in the laboratory. After determining force-displacement hysteresis curves, the important behavioral parameters of the investigated SSDs were calculated and compared. Effective stiffness, effective damping, force capacity, and displacement under cyclic loading were among the considered parameters in the current study. Results showed that dampers with simple blades and elliptical slits exhibited the poorest and best performances, respectively. Findings also indicated that the elliptical damper offered the highest effective stiffness, greatest energy absorption, and specifically the longest durability to cyclic loads. At displacements larger than 5 mm, the increase in effective stiffness of samples with an elliptical slit was roughly 1.6 times greater than that of samples with linearly tapered cross-sections. The equivalent viscous damping within the aforementioned displacement range at the optimal dimensions for a sample with an elliptical slit was roughly 1.1 times greater than that in a sample with linearly tapered cross-section.

Steel shear wall with corrugated plate is a lateral load resistant system. In recent years, researchers have made investigations in this Field. In this study, the behavior of this system under pushover loading has been evaluated. For this purpose, 20 samples of steel shear wall system with corrugated plate with bay to height ratio of 0.85,1.4,2,2.5 And in 1,2,4,6,10 Stories has been designed. Then these samples with finite element software (Abaqus) were analyzed. Results of this study show that the initial stiffness of this type of shear walls is high And it's resistance in drift about 0.1 percent reaches to the highest amount. But when the plate is subjected to interaction buckling it's stiffness and resistance has been decreased significantly. Also, Results of this study shows that before the plate reaches to buckling limit; a greater percentage of shear force is resisted by plate but after plate's buckling frame has more contribution in resisting shear force. In this study mechanism of creation of tension Field in this type of systems has been evaluated and relation for determination of tension Field's angle was proposed. In the end, in this study, a method for estimating pushover diagram of shear wall system with corrugated plate for one and several story structures has been presented. This solution was founded on the interaction between frame and corrugated Plate and by results of experimental and numerical samples was verified.

Considering the differences that exist between the laboratory and site conditions, the in-situ estimation of bond strength of repair mortars is important. Therefore, in this paper, the results obtained from the use of two methods, “Friction-transfer” and “Pull-off”, for measuring the shear and tensile bond strength of repair mortars applied to substrate concrete, are presented. Since the drying shrinkage of the repair mortar has considerable effect on their adhesion, the shrinkage of the mortars is considered. In order to increase the accuracy of the measured bond strength of the repair mortars, substrate concrete with saw cut surface was employed to minimize the interferences occurring between the pure adhesion and the mechanical keying effects of the rough surfaces. The age of the substrate concrete at the time of the application of repair mortar was 90 days and after curing under different conditions, the repair/concrete bond strength was measured at different ages. For measuring the shrinkages of the repair mortars, nine standard shrinkage samples were prepared and their shrinkages were measured. Regarding the effect of the curing process on the drying shrinkage of the repair mortars, two different curing systems of “covering with wet hessian and polythene sheet” and “stored in the laboratory”, for 7 and 90 days were considered. The results tend to show that, the amount of the aggregates and the associated cement paste have substantial effects the shrinkage of the repair mortars. It was also seen that the shrinkage causes reduction on the shear and tensile bond strength at the repair/concrete interface. Furthermore, the reduction of the shear bond strength seemed to be slightly more than the corresponding reduction of the tensile bond strength. A very high correlation was also observed between the related shear and tensile bond strength of the repair mortars.

As the population grew, cities expanded rapidly, requiring Super structures for residents to live in, as well as heavy structures such as bridges for faster population access to various locations. Also in big cities, tunnels are needed for various purposes, such as moving facilities, car lanes and subway tunnels, which is one of the concerns of engineers. On the other hand, most of these tunnels are built in cities in the vicinity of heavy structures that deliberately have deep and semi-deep foundations. Tunnel excavation has caused long-term and short-term displacements at the ground surface, which is more pronounced in piles adjacent to the tunnel excavation site. In such a way that the displacements formed in the ground are transferred to the piles and cause axial force in the piles. All these studies on the effects of drilling on adjacent structures and piles are very important in terms of drilling safety factor. Accordingly, in the present study, a three-dimensional analysis has been performed using ABAQUS finite element software. The effects of tunnel drilling with different diameters and locations on the deep foundation in the bridge near the drilling site have been investigated. The results showed that tunnel location, if improperly selected, has destructive effects on pile tip settlements, axial force changes of piles and tunnel surface settlements. Similarly, as the diameter of the tunnel increases, the number of piles in the pile increases sharply when the tunnel is located just below the tunnel site. Also, as the diameter of the tunnel increases, the number of piles in the pile group increases by about 29% when the tunnel is located just below the pile group. When the construction site of the tunnel is located between the group of piles and at a greater depth than the tip of the piles, the amount of settlements changes to a critical state and with increasing the diameter of the tunnel, the rate of subsidence of the pile tip increases by 48.9% and the amount of subsidence Increases by 54%.

Geometric nonlinear analyses are used in many structural problems, such as the determination of failure load, as well as the study of buckling mechanism. Nevertheless, due to the complex nature of this type of problems and the absence of a comprehensive analytical solution for them, numerical methods are utilized in practice to approximate the exact response of these systems. In the application of numerical methods, there are also some difficulties such as divergence or finding the correct path of equilibrium, especially in the case of bifurcation points. Hence, the main purpose of this research is to apply the modified energy method (introduced in the dynamics of structures) in quasi-static problems with geometric nonlinearity and bifurcation points so that the efficiency of this method can be compared to others, such as Newtonian numerical techniques and force-displacement-constraint approaches. To achieve the objectives of this research, after briefly reviewing the current force-based computational methods in practice, the energy method is described for such problems, and then the step-by-step process of its computer implementation will be presented. Afterward, by coding in MATLAB software and applying the method to numerical examples employed by other researchers such as truss and frame structures, the numerical results are verified by analytical solution as well as those obtained by other methods, such as Newton-Raphson and Arc Length techniques. Generally, the interpretation of the results obtained from performed simulations has shown that the presented numerical method in analyzing nonlinear geometric problems has better accuracy compared to the Arc Length method; moreover, it can well pass through bifurcation points in the force-displacement curve without divergence in comparison with the Newton-Raphson method.

Nowadays terrorist attacks on civilian facilities have increased.Paying attention to the design of construction sites against the impact loads due to the explosion is important. Identifying the nature of explosive loads and their impact on the structure is one of the important issues to be studied. The explosion is one of the complex phenomena including high strain rate which highly affects the structural elements behavior. Regarding the fact that existing steel structures are typically designed based on conventional gravity and seismic loads, it is required that the performance of these structures be investigated under the explosion load. In this study, the evaluation of simple steel frame behavior with different dampers against explosive load and earthquake is investigated. Nonlinear dynamics analysis is performed on models with 3, 5 and 10 floor structures and in accordance with UFC 3-340-02 at two different levels of explosive charge, in the SAP 2000 software. The results show that between XADAS, friction dampers, Viscose in diagonal system, in the seesaw system, U-shaped with flexural and shear performance and proposed pipe dampers, The displacement dampers have the greatest impact in reducing the structure response. From this Friction damper and pipe and U-shaped with flexural function is more effective.

Uncertainties are inevitable in the estimation of structural engineering issues and increase the cost of retrofitting. In the presence of uncertainties, the results of seismic evaluation are incorrect and create conservatism in acceptance criteria at structural performance levels. Considering and quantification of uncertainties in design and rehabilitation of structures reduces the existing conservatism and can lead to the economic design and rehabilitation of structures. In the seismic rehabilitation of structures, uncertainties have been studied on existing structures and have been applied by coefficients in guidelines. Adding a secondary system to rehabilitate of existing structure can enter uncertainties into the computation and can be effective for results of reliability. Therefore, in this study, reliability of rehabilitated steel moment frame with steel shear wall has been discussed in order to quantify the uncertainty of the steel shear wall. The selected structure is a nine-storey steel moment frame of SAC project, which was rehabilitated by steel shear wall. The studied structures were analyzed pre- and post-rehabilitation, with probabilistic variables considered for steel shear wall by OpenSees software. Based on results of incremental dynamic analysis and obtained fragility curves, the values of the reliability index have been obtained for the rehabilitated structure in the presence of uncertainties. Results showed that considering of uncertainties and reducing them can reduce the existing conservatism and the cost of rehabilitation.

Bridges are one of the major infrastructures of a country, which, in the event of severe seismic activity and the occurrence of collapse, can cause severe damage in different regions and create a severe crisis. Bridges with very long spans have always been a great challenge for engineers throughout history. Cable-stayed types of bridges are becoming more and more popular in the construction of long span bridges due to their advantages. A great number of cable stayed bridges in the world are located in the seismic zone and also near active faults so the effect of near field excitations on the seismic vulnerability of cable stayed bridges should be investigated probabilistically in accordance with far field excitations. Generation of vulnerability functions in the form of fragility curves is a common approach for assessing bridges seismic vulnerability. In this article, a set of analytical fragility curves for a case study cable stayed bridge (the Bill Emerson Bridge) are developed based on Incremental nonlinear dynamic analysis (IDA). The findings represent the effect of near fault excitations on the vulnerability of this long span bridge model. For example, the probability of a complete and extensive damage state for the considered cable stayed bridge in 1.5g for far field is 10 and 32 percent respectively, while in the near field, this value increases to about 19 and 44 percent, that indicates increase vulnerability of bridge in near field. The median values of seismic fragility for the considered bridge model decreased significantly in near field excitation in the Extensive and Complete damage states. The results can guide future regional risk assessments regarding the importance of including or neglecting near field excitations impacts on cable stayed bridge’s vulnerability.

Many studies have been conducted showing that the mass damper improves the performance of structures against wind loads and seismic loads. This paper presents a model for passive tuned mass damper with softening stiffness; the Newton−Raphson method and state space were used to solve nonlinear equations of motion. To evaluate the performance of the proposed mass damper, an 11-storied steel structure subjected to the Northridge and Zarand earthquakes was evaluated. This structure was initially modelled and analysed without a damper and with the softening PTMD. Then the effect of varying angles of the mass damper was investigated; eventually the damper was converted into a non-linear semi-active tuned mass damper. To reduce the displacements of the damper, fuzzy control was used for the controller. The results show that the proposed mass damper with a 60-degree angle could reduce the displacement in the earthquakes of Northridge and Zarand by 48.8 and 36.2% on an average. The results of using different angles suggest that a 45-degree angle makes for the most favourable performance for the structure and mass damper. It points out that in the use of an isolator for the 11th floor, this floor has the potential for higher displacement than any other floor, but, in this article, using the controller and the proposed semi-active damper, it has been shown that this floor can also experience lower displacement.

There are a number of reasons for considering web openings in steel structures with I-sections. Design of these structural members is always a practical challenge in steel construction. There are several design methods available in the literature for design of these components. Most of these methods rely on the moment-shear-axial interaction curves. However, the preliminary studies have shown that the real performance of these reduced sections is in the form of diagonal struts. The objective of this study is to present a new model based on the tensile and compressive action of diagonal struts at reduced web region to calculate shear strength of the perforated section.For this purpose, the geometry and dimensions of the diagonal struts are described and the shear strength of reduced section is calculated accordingly. To assess the accuracy of proposed geometry and dimensions for diagonal struts, a topology optimization is conducted for two finite element models and results are compared to the proposed values based on which a good agreement is found between optimized and proposed geometries. Next, design curves are presented for calculation of shear strength followed by comparison of proposed model and its predictions with the ones obtained from numerical analysis. Comparing the predictions of the proposed model with the results of 120 finite element samples, the absolute mean error and standard deviation of absolute error were calculated to be 6% and 3.7%, respectively. This comparison shows that, although the presented model is simple and easy to use, it has acceptable accuracy and can be utilized for calculation of shear strength in perforated steel I-beams.

Damage occurrence is always inevitable in structures. So far, many examples of damage types in engineering structures have been recorded with many losses of human and financial. For this reason, the detecting of structural damages during its exploitation to provide safety with the lowest cost has been the subject of many researchers in the last two decades. In this regard, the wavelet transform is a powerful mathematical tool for signal processing, has attracted the attention of many researchers in the field of health monitoring of structures. In this paper, due to the increase of steel plate shear wall in the building industry, it was considered the problem of detecting the location of the damage in steel plates. In this paper, due to the increase of steel plate shear wall in the building industry, it was considered the problem of detecting the location of the damage in steel plates. At first, the steel plate was modeled in ABAQUS finite element software with free support conditions, and then the healthy and damaged first eight mode shape was extracted. The primary and secondary modes shape was analyzed using discrete two-dimensional wavelet transform as a two-dimensional spatial signal. The results of the diagonal details of the wavelet analysis of secondary modes shape show the turbulence of the wavelet coefficients, compared with primary modes shape in damage locations; so that, wavelet analysis of the modes shape of the first mode, show damage location with the better equivalence of wavelet coefficients and the error of less than 6%.

Buildings are always affected by a variety of natural and abnormal forces during their operation. Impact of vehicle collision is an abnormal load which is not usually considered in the design of structures. With the spread of terrorist attacks in many parts of the world, investigation the behavior of structures against unusual loadings, such as blast or vehicle collision has been considered. In this study, steel moment frames with knee braces (2, 5 and 8 story) were designed by SAP 2000 software in two-dimensional according to codes guidelines, and then time history analysis of them was performed by SeismoStruct software subjected to impact of light vehicle collision. The responses such as displacement, drift, acceleration of the stories and the base shear of the frames were compared under the effect of light vehicle collision impact with different velocity (from 10 to 120 km/hr). The results show that the velocity 90, 120 and 100 km/hr causes dynamic instability state in frames with 2, 5 and 8 story respectively. The results also show that the performance level of the mentioned frames based on the maximum stories drift and for the different velocities of impact. For example, in the range of impact velocity of 50 to 80 km/hr, the performance level of 2-story frame was "Life Safety" and regarding to 8-story frame, the performance level was "Immediate Occupancy" for velocities 10 and 20 km/hr.

In this paper, the influence of Winkler type elastic foundation on the free vibration behavior of non-local Euler-Bernoulli beam with varying cross-section is semi-analytically investigated. For this purpose, the governing equation of motion is derived based on nonlocal elasticity Eringen’s model and Hamilton’s principle. The power series approximation is applied to solve the fourth order differential equation, since in the presence of variable cross-section, stiffness quantities are not constant. Based on this semi-analytical methodology, displacement component and cross-section properties should be expanded in terms of power series of a known degree. The natural frequencies of non-local beam with variable cross-section are then derived by imposing the boundary conditions and solving the eigenvalue problem. The results of this research are compared with the obtained results by other researchers and there is a good agreement. At the end, the effects of different parameters such as: end conditions, nonlocal Eringen’s parameter, tapering ratio and Winkler spring constant on non-dimensional natural frequency of nano-beam are studied in detail. The outcomes of this study indicate that the increase of nonlocal parameter and non-uniformity ratio causes to decrease the dimensionless natural frequency. However, with increasing the Winkler elastic constant, the non-local frequencies increase. Furthermore, it is shown that the effect of Winkler elastic foundation is predominate than the tapering ratio and Eringen’s parameter on the natural frequency of nano-beams.

There are numerous old arch bridges in Iran that have been used as railway bridges for more than eighty years. In Iran's railway network, there are about 3,700 bridges which all of these have been designed based on service load in that time (low-speed trains) and are still serving for trains at maximum speed of 100 km/h. Using of high-speed trains has been spread all over the world in the last two decades. In recent years, the use of high-speed trains is necessary in the Iran. It is not possible at all to replace old masonry arch bridges due to field and economic constraints, so it is necessary to evaluate the dynamic behaviour of these bridges under the high-speed trains. To evaluate complex behavior of these bridges, results of field tests are required. Since it is not possible to perform field tests for all arch bridges, these structures should be simulated correctly by computers for structural assessment. The present study investigates two plain concrete arch bridge which are located in kilometer 23 and 24 of the old Tehran-Qom railway. The numerical model of the bridge is established in accordance with detailed geometrical properties of the bridges. The numerical model has been validated based on the existing experimental results. In the model updating procedure, the vertical deflection at the crown under static loading and the movement of the six-axle train by 60 and 80 km/h, as well as the first three modes of the bridges were selected as a calibration criterion. In the second step, different geometrical of Pardis high-speed train are used and totally 13 geometrical models have been detected and investigated. By using the finite element method and the macro-modelling approach, the km-23 and km-24 bridges were simulated and totally 26-time history dynamic analyses have been conducted. Dynamic behaviour of the bridge under moving load model of Pardis trains at speeds of 150km/h have been assessed. Finally, deflection and acceleration responses for all 26 dynamic analyses at the crown of the bridges have been extracted and compared. These analyses are conducted to the aim of finding opportunities and constraints in using railway masonry arch bridges in the Iran as it is necessary to use existing rail lines on the rail network, due to the high cost of the construction of new ones and the need to know the existing structures such as bridges and their properties under the impact of high-speed trains. A realistic prediction of the structure's response helps a rational operation of the bridges in the service, that’s why the correct understanding of the dynamic behaviour of railway bridges is essential. The results of present study indicate that these bridges have good behaviour under high-speed trains.

Past studies have shown that aftershocks can increase structural damage, especially for structures damaged in the mainshock and experienced nonlinear behavior. This damage is generally the result of increased lateral displacement of the structure and thus, it is necessary to estimate the lateral displacement of the structure under seismic evaluation accurately. Although the target displacement in the nonlinear static analysis method is calculated by means of relationships presented in performance-based design codes, the effect of the aftershock is not taken into account. In this study, the impact of aftershock on inelastic displacement ratio is considered as the most effective factor in determining the target displacement. The results showed that this ratio increases significantly due to aftershocks. The dispersion of the results led to the investigation of the hazard levels of the input earthquakes and subsequently using the scaling method of the accelerograms. For this purpose, a target aftershock spectrum was generated by a statistical study on the maximum acceleration ratio of the mainshock and its corresponding aftershocks, thereby the aftershocks scale to an independent target acceleration spectrum. Comparison of the responses from scaling revealed that dispersion in results are an inherent issue and cannot be resolved. Finally, by modifying in the current relationship of the code, a new formula has been proposed for the inelastic displacement ratio such that the mean error values were reduced as much as possible.

Discrete singular convolution is a new numerical method that its ability to vibrational analysis has been demonstrated in the last decade. A lot of research on how to apply the complex boundary conditions of the different issues using this method is carried out and a variety of solutions have been proposed in this regard. Applying the boundary conditions in the governing equations of coupled shear walls, is a challenging issue. This paper proposes a new algorithm for applying the boundary conditions in the vibration analysis of coupled shear walls using the DSC method. In order to validate the proposed method, several samples were analyzed using this algorithm and the results were compared with the values obtained from three conventional numerical methods of Finite element (FEM), Differential quadrature (DQM) and Finite difference (FDM) methods. The great conformity was found between the results which emphasized the validity and integrity of the proposed method. In addition, the ability of the DSC algorithm was explored in terms of the computational speed, computational effort and the amount of computer memory required aspect and compared with the other conventional numerical approaches. It is concluded that the DSC is more efficient than the compared numerical methods from the results of this study.

According to the Eurocode, the partial safety factor (γM) is a coefficient related to the material properties considering the uncertainties in geometry and modeling, which design value for the material properties are determined by dividing the actual value of the material properties by this coefficient. In this paper, determination of γM considering uncertainties for the Persian historical masonry shear wall was studied. To this aim, behavior of different specimens of masonry shear walls (with constant thickness) under in-plane shear loading and constant pre-compression with four different aspect ratios (height to length) and six different boundary constraints (under the effect of lateral walls and ceiling), by considering the uncertainty effect for two parameters of modulus of elasticity and thickness of wall were studied by the nonlinear pushover analyses. The results showed that by increasing the aspect ratio, the lateral shear strength of the walls decreases and γM is increased, whilst by increasing the boundary constraints, shear strength of the walls increases and γM decreases. The more impact of the horizontal component (ceiling) was observed, as compared to the vertical component in one direction, increases the boundary constraints and the lateral load-bearing capacity. It was also observed that the decrease in the initial shear stiffness of the walls was characterized by an increase in the wall aspect ratio, although this parameter changed slightly with changes in boundary constraints. In conclusion, the value of γM for the Persian historical masonry shear wall materials is proposed between 1.1 to 1.8.

Self-compacting concrete is a special concrete that flows with its weight in the form and does not need to shake. based on experimental findings, its compressive strength decreases with an increase in the specimen size; this phenomenon is called “size effect and its beginning is a nonlinear failure in concrete and other fragile materials. The purpose of this study was to investigate the size effect on compressive strength of cubic and cylindrical specimens in self-compacting concrete containing pozzolanic materials of microsilica and Taftan Pumice. To this end, the least squares (LSM) method and Bezant’s Size effect rule have been used to analyze the data. Seven designs consist of 3 different mixing designs of 2.5, 5 and 10% cement weight replaced by micro silica also 3 mixing designs containing 15, 20 and 25% weight of cement replaced by Pumice. An additional design was also made as a reference mix design. All Mix designs were cast in various size-cubic molds and also in standard cylindrical molds. According to the results, Mixes with 5% micro-silicon (M5) and 20% Pumice (P20) showed the highest compressive strength. The compressive strength ratio of cubic to cylindrical specimens was studied in all mixing designs. The results of the experiments show that self-compacting concrete cube specimens have a higher compressive strength than standard cylindrical specimens, and the compressive strength ratio of cubic specimens to standard cylindrical specimens with increasing cubic sizes from 5 to 15 centimeters decrease. On the other hand, the results show that the effect of size has decreased in designs with 5% microsilica and 15% pumice.