INTERNATIONAL JOURNAL OF ADVANCED STRUCTURAL ENGINEERING
Year:2016 | Volume:8 | Issue:1|Papers Count:7

Bridge damages during the past earthquakes caused several physical and economic impacts to transportation systems. Many of the existing bridges in earthquake prone areas are pre-1990 bridges and were designed with out of date regulation codes. The occurrences of strong motions in different parts of the world show every year the vulnerability of these structures. Nonlinear dynamic time history analyses were conducted to assess the seismic vulnerability of typical pre-1990 bridges. A family of existing concrete bridge representative of the most common bridges in the highway system in Iran is studied.The seismic demand consists in a set of far-field and near field strong motions to evaluate the likelihood of exceeding the seismic capacity of the mentioned bridges. The peak ground accelerations (PGAs) were scaled and applied incrementally to the 3D models to evaluate the seismic performance of the bridges. The superstructure was assumed to remain elastic and the nonlinear behavior in piers was modeled by assigning plastic hinges in columns.In this study the displacement ductility and the PGA are selected as a seismic performance indicator and intensity measure, respectively. The results show that pre-1990 bridges subjected to near-fault ground motions reach minor and moderate damage states.

The main purpose of this paper is to investigate the effect of bidirectional continuously graded nanocomposite materials on free vibration of thick shell panels rested on elastic foundations. The elastic foundation is considered as a Pasternak model after adding a shear layer to the Winkler model. The panels reinforced by randomly oriented straight single-walled carbon nanotubes are considered.The volume fractions of SWCNTs are assumed to be graded not only in the radial direction, but also in axial direction of the curved panel. This study presents a 2-D six parameter power-law distribution for CNTs volume fraction of 2-D continuously graded nano composite that gives designers a powerful tool for flexible designing of structures under multi-functional requirements. The benefit of using generalized power-law distribution is to illustrate and present useful results arising from symmetric, asymmetric and classic profiles. The material properties are determined in terms of local volume fractions and material properties by Mori–Tanaka scheme. The 2-D differential quadrature method as an efficient numerical tool is used to discretize governing equations and to implement boundary conditions.The fast rate of convergence of the method is shown and results are compared against existing results in literature.Some new results for natural frequencies of the shell are prepared, which include the effects of elastic coefficients of foundation, boundary conditions, material and geometrical parameters. The interesting results indicate that a graded nano composite volume fraction in two directions has a higher capability to reduce the natural frequency than conventional 1-D functionally graded nano composite materials.

One of the most important issues in tall buildings is lateral resistance of the load-bearing systems against applied loads such as earthquake, wind and blast. Dual systems comprising core wall systems (single or multi-cell core) and moment-resisting frames are used as resistance systems in tall buildings. In addition to adequate stiffness provided by the dual system, most tall buildings may have to rely on various control systems to reduce the level of unwanted motions stemming from severe dynamic loads.One of the main challenges to effectively control the motion of a structure is limitation in distributing the required control along the structure height optimally. In this paper, concrete shear walls are used as secondary resistance system at three different heights as well as actuators installed in the braces. The optimal actuator positions are found by using optimized PSO algorithm as well as arbitrarily. The control performance of buildings that are equipped and controlled using the PSO algorithm method placement is assessed and compared with arbitrary placement of controllers using both near- and far-field ground motions of Kobe and Chi–Chi earthquakes.

Steel built-up batten columns are common types of columns in Iran and some other parts of the world.They are economic and have acceptable performance due to gravity loads. Although several researches have been conducted on the behavior of the batten columns under axial loads, there are few available articles about their seismic performance. Experience of the past earthquakes, particularly the 2003 Bam earthquake in Iran, revealed that these structural members are seismically vulnerable. Thus, investigation on seismic performance of steel batten columns due to seismic loads and providing a method for retrofitting them are important task in seismic-prone areas.This study aims to investigate the behavior of concrete filled batten columns due to combined axial and lateral loads. To this end, nonlinear static analyses were performed using ANSYS software. Herein, the behaviors of the steel batten columns with and without concrete core were compared. The results of this study showed that concrete-filled steel batten columns, particularly those filled with high-strength concrete, may cause significant increases in energy absorption and capacity of the columns.Furthermore, concrete core may improve post-buckling behavior of steel batten columns.

In conventional design of an elevated aqueduct, apart from considering the weight of water inside the channels, hydrodynamic forces are generally neglected. In a few special cases involving high seismic zones, hydrodynamic forces have been modeled considering equivalent lumped-mass type idealization or other models. For support conditions, either the base is considered as fixed or in a few cases, equivalent spring-dashpot system is considered.However, during an intense seismic event, nonlinear soil structure interactions (SSI) may alter the response of the aqueduct significantly. This paper investigates the effect of hydrodynamic forces and SSI on seismic response of a representative elevated aqueduct model. Different modeling concepts of SSI has been adopted and the responses are compared. Frequency domain stochastic response analysis as well as time-history analysis with a series of ground motions of varying hazard levels have been performed.Demand parameters such as base shear and drift ratio are studied for varying heights of water in channels and different site conditions. From the frequency domain analysis, the effect of convective masses is found to be significant.From the time history analysis, the overall effect of increase in height of water is found to be negligible for nonlinear base case unlike the fixed and elastic base cases.For the nonlinear base condition, the base shear demand is found to decrease and the drift ratio is found to increase when compared to the results of linear base condition. The results of this study provide a better understanding of seismic behavior of an elevated aqueduct under various modeling assumptions and input excitations.

The variation of pressure at the faces of the octagonal plan shaped tall building due to interference of three square plan shaped tall building of same height is analysed by computational fluid dynamics module, namely ANSYS CFX for 0o wind incidence angle only. All the buildings are closely spaced (distance between two buildings varies from 0.4h to 2h, where h is the height of the building). Different cases depending upon the various positions of the square plan shaped buildings are analysed and compared with the octagonal plan shaped building in isolated condition. The comparison is presented in the form of interference factors (IF) and IF contours. Abnormal pressure distribution is observed in some cases. Shielding and channelling effect on the octagonal plan shaped building due to the presence of the interfering buildings are also noted. In the interfering condition the pressure distribution at the faces of the octagonal plan shaped building is not predictable. As the distance between the principal octagonal plan shaped building and the third square plan shaped interfering building increases the behaviour of faces becomes more systematic. The coefficient of pressure (Cp) for each face of the octagonal plan shaped building in each interfering case can be easily found if we multiply the IF with theCp in the isolated case.

Relatively little research has been reported on the time-dependent in-service behavior of composite concrete slabs with profiled steel decking as permanent formwork and little guidance is available for calculating long-term deflections. The drying shrinkage profile through the thickness of a composite slab is greatly affected by the impermeable steel deck at the slab soffit, and this has only recently been quantified. This paper presents the results of long-term laboratory tests on composite slabs subjected to both drying shrinkage and sustained loads. Based on laboratory measurements, a design model for the shrinkage strain profile through the thickness of a slab is proposed.The design model is based on some modifications to an existing creep and shrinkage prediction model B3. In addition, an analytical model is developed to calculate the time-dependent deflection of composite slabs taking into account the time-dependent effects of creep and shrinkage.The calculated deflections are shown to be in good agreement with the experimental measurements.