Journal of Rehabilitation in Civil Engineering
Volume:7 Issue: 2, Spring 2019

Steel-concrete-steel (SCS) sandwich panels are composed of two steel plates with low thicknesses and high densities and strengths and one thick layer between both plates with low strength and density known as core that is composed of concrete. Cohesive material-epoxy resin or shear connectors are usually applied in order to connect the plates to the concrete core. SCS sandwich composites are being developed so they can be utilized in offshore structures and buildings. Stud bolt is one of the shear connectors and their interlayer shear behavior is examined in the present study. In order to inspect the effect of parameters on interlayer shear behavior of steel-concrete-steel sandwich structure with stud bolt connectors, push-out test is performed under progressive loading. Pursuant to the tests performed, relations are proposed to predict ultimate shear strength and load-slip behavior of samples with stud bolt shear connectors. Consequently, numerical model of push-out test is presented on the basic component of Steel-Concrete-Steel sandwich structure (SCS) with stud bolt connectors. The results indicated that finite element model is consistent with test results applying mass scaling in Explicit Solver with a suitable analysis speed. Applying the regression analysis on the results of 80 numerical models of push-out test,a relation was proposed for shear strength of push-out samples with stud bolt connectors.

In recent years, seismic design of structures has been undergoing significant changes as a result of increasing demand for optimization and minimizing the level of damage and reducing the cost of structural repairs, the development of analytical methods and the remarkable improvements of computer performance have been among the factors which influenced the design of structures. A lot of research has been conducted on the development of better braces with perfect elastoplastic behavior. The inventions and development of buckling restrained braces have been the results of these researches. In this study, the performance of Buckling Restrained Environmental Braces (BRB) in high-rise buildings were evaluated applying nonlinear time-history dynamics analysis with three pairs of acceleration and compared with conventional concentrically braced frame (CBF). The studied structures are 20, 40, and 60 stories building which braces were utilized peripherally. The acquired results reveal that the application of Buckling Restrained Brace Frames (BRB) instead of conventional braces frame (CBF) in high-rise steel buildings ameliorates hysteresis behavior of the braces and reduces lateral displacements and increase the capacity of base shear as well.

Cylindrical liquid storage tanks are contemplated as vital structures in industrial complex whose nonlinear dynamic behavior is of crucial importance. Some of these structures around the world have demonstrated poor seismic behavior over the last few decades; consonantly a major improvement is required to reach their level of applicability. There are several methods and techniques for rehabilitation and reducing damages in these structures which among them the devices for passive control, particularly base isolators, are perceptible. Friction Pendulum System (FPS) is the most popular base isolation system which its period does not depend on the structural weight. In this research work, the efficiency of FPS is examined on decreasing the seismic responses of base isolated steel storage tanks as well as the impact effect of slider to the side restrainer. To this end, the whole mass of liquid storage tank is contemplated as three lumped masses known as convective mass, impulsive mass which is connected to tanks with corresponding spring, and rigid mass which is connected rigidly. By means of state space method the time history analysis is done applying 60 earthquake records to acquire dynamic responses under the various hazard levels i.e. SLE, DBE and MCE ground motions. The results show that the normalized base shear force in squat tank decreased 59%, 62% and 33% respectively under SLE, DBE and MCE ground motions. The reduction of normalized base shear force in slender tank is 53%, 49% and 35% under the aforementioned hazard levels. Examining the effect of side restrainer’s stiffness on the maximum responses exhibit that the impact effect must be considered particularly when the system is excited by MCE’s ground motions.

Rock material is common in the construction of hydraulic structures. In the present study, to the aim is to examine the reactive solute relationships for transport and degradation processes through the rockfill media. By applying the analytical solution of reactive transport, the 1st to 3rd theoretical temporal moments have been extracted, consequently by applying two methods of curve fitting and temporal moment matching, the coefficients of dispersion and degradation have been exploited. Two rock diameter, two operating discharges and five instantly injection mass have been used as the variables of experiments. The EC sensors with operation software were installed inside the rockfill media and then the experimental breakthrough curves with intervals of 4 seconds have been extracted. It is concluded that both methods are suitable for application of transport and degradation processes inside the media. It was found that by increasing inflow discharges, pore velocity, and media diameters the dispersion coefficient decreases and with a decrease in media diameter or with increase in injection mass the decay rate decreases. The sensitivity analysis on the derived moment equation and also skewness coefficient equation indicated that the velocity and degradation are the most and less effective parameters on the moment equations respectively.

The seismic performance of elliptic braced moment resisting frame (ELBRF) is assessed here and is found that the structural behavior is improved and is of free of architectural space. The demand for seismic performance of ELBRF is estimated through conventional pushover methods of 3, 5, 7, and 10-story ELBRF frames and they are compared with special moment resisting frames (SMRF) and X-Braced CBF and Inverted V-Braced CBF concentrically braced frames. The effective parameters in the seismic design of structures, like the ductility, overstrength and response modification factors are evaluated. The response modification factor for ELBRF in the design by ultimate limit state and allowable stress methods is proposed as 10 and 14.4, respectively. Finally, the process of forming plastic hinges in ELBRF is assessed and it is found that an increase in height makes the plastic hinges to be transmitted to the upper stories, allowing the structure to collapse at higher stories.

In this paper, the seismic collapse probability of special steel moment-resisting frame (SSMRF) structures, designed to 4th edition of Iranian seismic design code, under near fault pulse-like and far fault ordinary ground motions is evaluated through fragility analysis. For this purpose, five sample frames with 3 to 15 stories are designed and imposed to the ground motion excitations with different characteristics. Fragility curves are derived for the sample frames using the results of incremental dynamic analyses. Three sets of near fault ground motion records with different range of pulse period and one set of far fault ordinary records are used in dynamic analyses. Each record set involves ten acceleration time histories on soil type III. Based on the obtained results, it was found that pulse-like motions with medium- and long-period pulses are significantly more destructive than other types of ground motions. Fragility analysis reveals that the average collapse probability for the case study frames under the far and near fault ground motions at the intensity of 0.35g equals to 4.3% and 10.3%, respectively. These values are 15.9%and 38.6%, for PGA of 0.53g. It is also found that the increase in the height, leads to increase in higher modes effect to transfer drift demands toward upper stories.

With growth the construction technologies, Cold-Formed Steel, CFS, sections are widely used in ordinary steel buildings because of some advantages such as light weight, ease of installation, decrease in cost, and increase in speed of operation. Using the bolted connections for CFS joist is one of the best details for steel structures.  The main objective of this study is to conduct an experimental research to evaluate the load carrying capacity of bolted connections based on various bolts arrangement. Ten full scale joist-beam connections are tested under the incremental gravity load. The variable parameters are the arrangement of bolts, and thickness of CFS sheets. The joist sections made of two C-shaped, which are back-to-back connected using self-drilling screw bolts in the web. The arrangement of bolts connection and steel sheet thickness are considered as two major factors to improve the load carrying capacity. Base on the obtained results, it was observed that increasing the number of the bolts and their spacing from the neutral axes led to the additional load carrying capacity. Furthermore, it can be concluded that the thickness of CFS sheets play an effective role for load carrying capacity of connections.

The massive construction in poor lands has encouraged engineers to use deep foundations in order to transfer superstructure loads to the subsoil. Since soil excavation, sampling, and laboratory testing as a part of site investigation are relatively difficult, in-situ tests such as cone penetration test (CPT) as a very informative test may be recommended. The CPT has been widely used in engineering as a part of site investigation, and its data has been used to determine the axial capacity of piles. In this paper, the prediction capability of three empirical widely famous old methods used to predict the axial pile capacity based on CPT data is evaluated by using field data obtained from direct field pile loading tests. In this evaluation, the direct pile load test results are used as measured data. Three popular famous statistical evaluation methods namely the best-fitted line, geometric mean, and geometric standard deviation have been used. The evaluation results indicate that generally although predicting methods based on CPT data have been widely used to determine the axial bearing capacity of piles, they need to be upgraded for the economic and relatively accurate design of piles. According to the statistical studies carried out in the current research, among three old empirical methods, although the Nottingham and Schmertmann Method (1975, 1978) (NSM) [7, 8] has the best agreement with test results, it is felt that the method needs to be upgraded. The modification of NSM has been done in the current paper using a comprehensive database.

This study based on free vibration analysis and study the behavior of framed structure under different frequency of vibration using ANSYS software and shaking table. A small scale uni-axial shaking table was prepared in laboratory, which can produce lower to moderate vibration, regarding frequency and velocity. Moment resisting framed structures constructed with connecting beam and column elements of mild steel wire of different dimensions were tested in shaking table and analyzed using ANSYS software. The effect of masses and stiffness of structures on its natural frequency and deflection under certain ground vibration also studied and discussed. The test results showed that, this shaking table is satisfying the general concept of free vibration. The height of structures has an inverse effect on its natural frequency for same lateral stiffness. After several shaking, structure’s natural frequency started to decreases with their decreasing stiffness. Therefore, the fabricated shaking table can used in free vibration analysis.

In recent years, it is considerably attempted to develop the concept of energy dissipation as an applicable technology to overcome the energy released by earthquakes. The passive control systems such as metallic dampers have been widely considered. Energy dissipating dampers are used to modify the response of structures as well as to reduce the damages in structure members. This study is conducted to investigate the seismic response of three normal concrete moment resisting frames with 4, 7 and 10 stories equipped with Triangular Added Damping and Stiffness (TADAS) metallic dampers. OpenSees software is employed for nonlinear time-history analysis using seven earthquke records to determine the structure response. The results showed the considerable modifed seismic responses. It is observed that the story drifts are constant and the maximum values in retrofitted 4, 7 and 10 story frames have been decreased 54%, 56% and 55%, respectively. Also, the maximum floor acceleration, the maximum roof displacement and the maximum story shears are lower in the frames equipped with damper and the lateral behavior of the majority of the retrofitted frame members has been upgraded to Immediate Occupancy (IO) and Live Saftey (LS) performance level.

Inclusion of steel fibers to concrete progresses the flexural and tensile capacities of concrete. Consequently the shear capacity of concrete flexural members improve. Predicting the shear capacity of concrete beams containing steel fiber is an important issue not only in structural design but also to retrofitting of existing structures. Since there are several variables to assess the shear capacity of steel fiber reinforced concrete (SFRC) beams, presenting a suitable equation is a complicated task. The aim of the present paper is to evaluate an empirical formulae based stepwise regression (SR) method for shear capacity of SFRC beams. A series of reliable experimental data has been provided from literatures for model development. The obtained results based SR model were compared with experimental data in training and testing state. A practical formulae based SR method has been developed for shear capacity assessment of SFRC beams. Besides, several equations based models also presented to compare with the equation based SR model. The comparison showed the SR formulae gives the most exact accuracy than others in terms of shear capacity assessment of SFRC beams.

In this study, the seismic inter-story drift of structures is estimated by a combination of mode-acceleration equations with the modelling of high-rise buildings with flexural and shear cantilever beams. In the equation presented for calculating the inter-story drift, having less knowledge of the building is adequate and this issue is of significance in estimating the nonstructural component forces, especially in high-rise buildings and also in the initial design of structures. Also, a comparison of inter-story drift estimated by the approximation method with an exact method indicates that the application of the mode-acceleration method compared to mode-displacement with a fewer number of modes comes close to the exact calculation, which facilitates and expedites the analysis. In order to carry out an exact evaluation of the presented equation, inter-story drift is calculated and compared in 10, 15 and 50 story buildings during three seismic records using approximate relations. Exact analysis of those structures is done in finite element Opensees software. The results of comparisons show that the presented equation provides an adequate estimation without the need for modelling and lengthy software analysis.