AMIRKABIR JOURNAL OF CIVIL ENGINEERING (AMIRKABIR)
Year:2013 | Volume:44 | Issue:2|Papers Count:11

On recent fifty years, using pre-stressed concrete for construction of continuous bridges with constant or variable cross section has a large spread. One of important objects in design is the way of connecting deck to piers that is done mostly by means of bearings. In the case of using neoprene bearings, There are three kinds of deck-pier connection, Simple, semi-rigid and rigid connections. Desired performance against environmental conditions, possibility of sliding, and finite movement of deck are of important properties for neoprene bearings. Bearing lines’ number and the effect of connection construction in load transferring, stress distribution in bridge piers and the ratio of bending moment to axial force transferred, are surveying in this research. Models, contain four spans continuous pre-stressed concrete bridges with various span lengths, and are analyzed by Finite Element Method and using ABAQUS analyzer. After analysis performance, models with different kinds of connection are compared. With assuming smeared crack performance for concrete, elastic for neoprene and elastic-prefect plastic for steel, analysis is done and for each model, load transfer is surveyed. Results of analysis show the effective role of distance variation of two rows of bearings, in comparison with their thickness effect. In addition, analysis results insist on optimum design for bearings, to have a safe and controlled load transfer.

Infills have considerable effects on seismic behavior of buildings and should be considered in the analysis or be isolated from the containing frames. Despite, most types of infills cannot be regarded as engineered elements, specially for the lack of sufficient ductility and normally ignored in the analysis phase. Recently a new type of infill is proposed, that has a frictional fuse at the mid-height. High ductility of such infill has been confirmed through experimental studies. In this paper finite element analysis results of the fused infills are presented to study the relation between their ultimate capacities and the fuse sliding strengths. For this ABAQUS 6.8-1 was applied after being confirmed by the experimental results. The obtained results show that the infill ultimate strength rises by increasing the fuse sliding strength, however will remains constant after a certain amount, depending on the infill propertie. Moreover, infills and frames will behave in their optimum capacities when such infills are applied in the frame.

The most important function of structural diaphragms is to support and transmit gravity loads to vertical structural elements such as columns. In addition, diaphragms play an important role in collecting lateral loads at specific elevations and distributing them to the lateral resistance system. Thus, in-plane behaviour of diaphragms can be considered for structural analysis and design of structural elements and securing the optimum seismic performance of the structure. In order to investigate structural behaviour of composite steel-concrete diaphragms in low-rise steel structures, one to six storey steel structures with planar aspect ratios of one, three and five with different areas of openings have been analysed by the ETABS code. Results from response spectrum dynamic analysis indicate that the assumption of rigid diaphragms in the studied structures, in particular in the lower floors, is inappropriate. Diaphragms with openings of 20 to 50 percent of area have a flexible behaviour. An opening area of more than 20 percent increases the natural frequency of the structure, hence, necessity for an expansion joint.

The nature of fracture in reinforced high strength concrete (HSC) members is brittle and therefore in the seismic areas the ductility investigation of heavily reinforced HSC members is important. Six reinforced HSC beams with different percentage of tensile and high compression bars with attaching electrical strain gauges cast and loaded experimentally up to failure. During the test, the strains on the concrete middle face and on the tension and compression bars along with deflection at different points of the span length measured. Ductility of doubly reinforced members was compared with the singly reinforced members. The theoretical results based on ACI and CSA codes have been compared with the experimental results. In this paper, the displacement and curvature ductility of such members are also reported.

Seismic performance of steel moment frames with side-plate connections has been investigated with emphasis put on earthquake uncertainties. Based on experimental and finite element results, a connection model was proposed and calibrated to represent the side-plate connection behavior. Afterwards, some two-dimensional moment frames were adopted from the designed three-dimensional frame structures which were modeled incorporating the established connection model. To reflect the uncertainties associated with earthquakes, the incremental dynamic analysis procedure was performed. The procedure outcomes, which consist of more than 1500 nonlinear dynamic analyzes, were used to investigate the structures performance in terms such “limit-state frequencies” and “seismic demand hazard curve”. The quantified performances may be used in comparing the studied structures with similar other structures and also as a crisis to the prescriptions issued by design guidelines for the structures under consideration.

A critical state constitutive model for sands was previously developed with emphasis on capturing the main aspects of the behavior of loose liquefiable sands. The model, which was presented in detail in previous publications, was formulated and verified for various drained and undrained loadings of sands under monotonic conditions. However, in order to enable the model to predict the behavior of in-situ soils, which often exhibit strong inherent anisotropy, it was found important to extend the model formulation such that it will also be able to predict the behavior of sands with strong anisotropy.In this paper, it is shown that by adding a new anisotropy parameter to the model, it is possible to simulate the behavior of strongly anisotropic sands. The anisotropy parameter depends on sand fabric and loading condition. Ability of the modified model to account for soil inherent anisotropy is verified by comparing observed and predicted responses of inherently anisotropic sand subjected to various loadings.

Fiber reinforced concrete (FRC) has been used widely due to its advantages over plain concrete such as high energy absorption, post cracking behavior, flexural and impact strengths, arresting shrinkage crack.This research discusses the effect of increasing the percentage of polypropylene fiber on flexural toughness and strength of FRC. Three percentages of polypropylene fiber were substituted in 1% steel fiber reinforced concrete (SFRC). Finally, the mechanical properties of three types of hybrid fiber reinforced concretes were compared with each other and with steel fiber reinforced concrete by measuring their flexural toughness and flexural strength. A four-point bending test was adopted to determine the effect of hybrid fibers on crack arresting and post crack behavior.The research results show that the more the percentage of polypropylene fiber which is substituted in SFRC is, the less the amount of energy absorption and flexural toughness with FRC will be.

The nonlinear force-displacement curve of RC columns are presented in the current standards for seismic rehabilitation of existing buildings (such as ASCE41) by two displacement-based values of “a” and “b” that correspond to the loss of lateral and axial capacities, respectively. The ASCE41 presents the values of these two parameters as a function of the volumetric ratio of transverse reinforcement. A confinement index is proposed in this paper that accounts for the yield strength and arrangement of the transverse reinforcements as well. This index was used to predict the parameters “a” of 38 tested RC columns and the parameters “b” of 13 other columns. A table is proposed that gives the values of these two parameters based on the values of the proposed confinement index of the columns. It is shown that the proposed confinement index and table predicts more accurate values of the parameters “a” and “b”. Based on the results, maximum difference ratio to experimental values is reduced from 4.7 to 3.6 in comparison with those of update to ASCE41-06 while satisfying its specifications and regulations.

Quake isolation is a comparatively new method for designing earthquake-resisting buildings. Instead of increasing the resistance of the structure against lateral pressures, this method is based on reducing the pressures on it. Economic expenses comparing with other methods are against widespread application of this technology. Therefore, this paper, aiming at the economic aspects of this method, considering the present approach of the codes, focusing on this method’s applicatory and practical aspects, making changes in prevailing processes of designing structures, and using optimization technology of genetic algorithm, presents a program in FORTRAN environment. This program is, in fact, a combination of the programs of isolation designing and that of genetic algorithm optimization, and its main goal is to reduce the expenses of isolating structures, considering the applicatory and practical aspects of this technology. Based on the dimensions of a certain site, this program is able to examine the various plans of columniation while considering the matters related to superstructure and implementation and finally suggest a plan which leads to the production of an isolation system with lower expenses.