Scientia Iranica
Volume:22 Issue: 4, 2015

In this study a nonlinear procedure for analysis of a membrane element of a FRP strengthened concrete beam-column joint is proposed based on softened truss model. The procedure employs three equations for equilibrium, three for compatibility and six equations for the constitutive laws of materials. The model is capable of analysing nonlinear behaviour of RC beam-column joints under cyclic loading and has three major attributes including nonlinear association of stress and strain in the presence of FRP, contribution of concrete damage by means of softening coefficient and consideration of the bond effect between steel, FRP and concrete. The proposed model is applied to some previously tested, strengthened beam-column joints and shows good predictions of shear strength of these joints. The effect of various parameters on response of reinforced concrete beam-column joint, such as column axial load, FRP reinforcement amount and FRP properties has been studied on parametric manner. It is observed that even a low quantity of FRP can enhance the shear capacity of the joint significantly. Also, it is observed that the axial load increases the confinement of the joint care, which in turn increases the shear capacity of the joint.

Integrating the rate form equations governing the behavior of material is an important step in solving every plasticity problem. Providing a compromise between accuracy and computational effort demands the combination of low order elements with efficient integration algorithms. First and second order accurate integration algorithms are well established in the realm of infinitesimal theory. However for large deformation plasticity models, second order integration algorithms are not given much attention in the literature. Inspired by midpoint rule algorithms conventionally used in small deformations, a new integration algorithm is proposed for finite strain J2 plasticity that outperforms the classical backward Euler method. Algorithmic setup as well as the derivation of tangent operator which is crucial for quadratic rate of convergence of the Newton-Raphson algorithm is discussed in detail. Employing four node quadrilateral elements in solving benchmark examples it is shown that the proposed algorithm is very stable from numerical standpoint and has outstanding convergence properties.

The load carrying capacity in a damaged steel beam can be substantially increased through repairing by attaching fiber-reinforced-polymer (FRP) plates to tension flange. Such a repaired beam is generally failed by either debonding of the FRP plates from the steel flange or FRP rupture at the damage location due to the stress concentration. In this case, the effectiveness of repair significantly depends on the repairing materials properties, i.e. FRP and adhesive. This paper developed a Finite Element (FE) modeling of damaged steel beams repaired with FRP plates, aimed to clarify the FRP and adhesive properties effects on beam recovery. The primary defect was simulated by inserting a notch through the tension flange at mid-span. To ensure the validity of the proposed numerical model, the results of numerical models compared with those existing experimental works. A parametric study performed to achieve a better understanding on the sensitivity of parameters which are responsible for flexural behavior of the repaired beams. Studies showed that influence of the most investigated parameters on the response of the repaired beam is very notable, and considering influential parameters in choosing the material for a FRP-repair, leads to promising results in design consideration.

This paper presents the results of an experimental study which was carried outto identify the vulnerabilities of existing multicolumn bridge bents constructed in Iran and to develop an appropriate retrofit measure to alleviate such vulnerabilities. In this study a three column reinforced concrete bridge bent which was designed for gravity load with inadequate seismic detailing is considered.Two identical specimensscaled to 30% of prototype dimensions were tested under in-plane cyclic loading condition. One of the specimens simulated as-built condition while the other specimen was retrofitted by external prestressing along the cap beam as well as transverse prestressing of an exterior joint. The test results on the as-built specimen indicate that joint shear distress and bond failure of longitudinal column reinforcement within the joints are the predominant failure modes. Such failure modes adversely affected the behavior and energy absorbing capacity of the as-built specimen. Seismic behavior and energy absorbing capacity of the retrofitted specimen improved significantly. The improved behavior of the retrofitted specimen was mainly due to better performance of the joints.

Soils reinforced by geogrids exhibit different behavior, compared to unreinforced soils, due to having high tensile strength elements. In this paper, the main factors influencing the behavior of such reinforced soil under a strip footing are investigated and discussed. A numerical model for the reinforced soil is developed using FLAC-2D finite difference software. The model is calibrated, and then different important factors such as width, number, distance and depth of the first layer of geogrid are studied and evaluated. The qualitative behavior of the reinforced soil under different conditions of reinforcement elements is also studied in this work. The results of several analyses show that the optimum depth of the first layer of geogrid is one fourth of the footing width, and the other layers would have effective role up to 1.75 times of the width. Also, the distance between geogrid layers needs to be decreased in case of increasing their number, whose optimum value is less than half of the footing width. The geogrid width and its tensile strength have considerable effect on the behavior of the reinforced soil, when geogrid layers are in optimum position.

This numerical study aims to evaluate the seismic performance of bridges retrofitted with a new compound restrainer and the sensitivity of their responses to likely changes in the characteristics of the restrainer’s components. Compound restrainer was introduced as a retrofit tool for improving seismic response of multi-span bridges in terms of forces and displacements. The compound restrainer is mechanically an assembly of several elastic and plastic springs. To this end a real 2-span and a real 3-span simply supported plate girder bridge have been used for case study. Nonlinear time history analyses of detailed three-dimensional models have been performed under seismic excitations in order to assess the performance of the existing and retrofitted bridges restrained by conventional restrainers and compound restrainers, numerically. The results show that the compound restrainer is very sensitive to the characteristics of its components. Moreover, while past earthquakes have shown the deficiencies of the conventional restrainers, the compound restrainer seems to be successful in dissipating hysteresis energy in bridges as well as in reducing the internal forces imposed on the substructures.

The impact of solar radiation on the uncoupled transient thermo-structural behavior of an arch dam is investigated under the earthquake loading. Temperature distribution within the dam body is determined by solving the governing differential equations taking into account the water and air temperature and the solar radiation. Finite element model of the dam-reservoir-foundation system including joint nonlinearity is excited using three-component ground motion. Results of the thermal transient analysis with and without solar radiation effects are used as an initial boundary condition for the seismic analysis. Results show that considering solar radiation leads to non-uniform temperature distribution on the exposed faces and increasing the tensile stresses within the dam body.

Due to the high rigidity and strength of bracings, they are widely employed in seismic design of steel buildings. Bracing plays a fundamental role in the absorption and dissipation of earthquake forces. Failures of braced steel buildings are often due to the shortage of compressive strength and out-of-plane buckling of bracing connections. One of the factors contributes to the buckling behavior of gusset plates is position and type of connection of bracing to the gusset plate. In this paper, the pre- and post-buckling behavior of gusset plates is studied considering the presence or absence of longitudinal and transverse stiffener on the bracing splice plates as well as the arrangement of edge stiffener on gusset plates. To this purpose, a nonlinear static analysis is performed, the results of which are compared to the results obtained from the laboratory model. Results of the research show that application of longitudinal stiffeners leads to an increase in the buckling and post-buckling behavior of gusset plate while transverse stiffeners only influence the post-buckling behavior of gusset plate. In addition, implementation of double stiffeners on a gusset plate somewhat adds to the buckling capacity of the gusset plate, but affects post-buckling behavior of gusset plate better.

This study presents a new hybrid algorithm for treating solid walls in the context of weakly–compressibleSPH model. The basic concept is to fill an impervious region with some layers of dummy particles for improving the solution accuracy and a single layer of repulsive particles for imposing no-penetration condition along the solid–fluid interface. The latter consists of a new repulsion mechanism that, unlike the well known Lennard–Jones model, induces no pressure oscillation close to the wall. This hybrid boundary treatment technique is implemented in conjunction with a parameter–free SPH scheme to provide a Lagrangian solver for 2D Navier–Stokes equations. The accuracy of the model is verified by recourse to challenging numerical tests in free surface hydraulics, including dam break surging over dry bed with and without obstacle as well as free falling water jet from a sharp-crested weir. Comparison with relevant numerical and/or experimental data from the literature shows fair agreement in each case.

Special Moment Resisting Frame (SMRF) is one of the most well-known and practical Seismic Force Resisting Systems (SFRSs) with a high range of ductility and energy dissipation as well as with the capability of providing enough space for the architectural design purpose of buildings or other structures. One of the most important deficiencies of this system is the matter of controlling its maximum drift against the lateral force of earthquakes. So, it results in a non-economical design especially in tall buildings. Eccentrically Braced Frame with Vertical link beam (V-EBF) is almost a new Seismic Force Resisting System in which the vertical link beam has the role of the ductile member with a wide range of ductility and energy dissipation capacity. In this paper, the ductility and energy dissipation capacity of the SMRF and V-EBF systems are compared. For this purpose, a number of one-story one-bay frames with these two systems with different characteristics are analysed by non-linear finite element method under quasi-static cyclic loading and the results are compared.

Waste tire is increasingly becoming an environmental, health, and aesthetic problem. Used tires are of category of waste whose recycling is extensively difficult because of highly complex structure, the diverse composition of the raw material. Concrete is a versatile construction material due to easy to fabrication, locally available material, and high mechanical strength. The use of waste tires as a concrete additive is a possible disposal solution. Rubberized concrete may thus contribute in sustainable construction by use of industrial waste, minimizing the natural resources and produce a more efficient material. In this paper experimental investigation is carried out to evaluate the flexural strength, compressive strength, abrasion resistance and carbonation of concrete containing waste rubber tire fibers as partial replacement of fine aggregates. Fibers from mechanical grinding of used rubber tire have been incorporated with three water–binder ratio and six levels of rubber fibers contents (0-25%). It has also been shown that with increasing replacement level of rubber fibers, flexural strength and abrasion resistance is increased. Further, it has been also observed that compressive strength and carbonation depth changes with the increasing of the replacement level of waste rubber content.

In suspension bridges both inclined and vertical hangers have their advantages and disadvantages. The inclined hangers are more prone to fatigue in comparison with vertical ones, but inclined hangers when encountering lateral loads (such as wind and earthquake loads) react better than vertical hangers. In some cases, some of the inclined hangers show slackness and some get too stressed. In this paper by using a new modification of the hangers system; while keeping the advantages of both systems, the disadvantages of both systems were resolved and slackness phenomenon was completely removed. The new arrangement of the hangers was formulated. Three different hangers systems were analyzed under nonlinear static analysis for symmetrical and asymmetrical live loads plus dead load. Results showed that the modified hangers system was improved considerably in comparison with vertical or inclined hangers.

In this paper, modeling and control of a rotary missile which uses the proportional navigation law is purposed, applying Quantitative Feedback Theory (QFT) technique. Dynamics of missile are highly uncertain; thus application of robust control methods for high precise control of missiles is inevitable. In the modeling section, a new coordinate system has been introduced which simplifies the analysis of rotary missile’s dynamics equations. In the controlling part,applicationofQFTmethod leads to the design of robust PID controller for highly uncertain dynamics of missile. Since the missile’s dynamics have multivariable nonlinear transfer functions, in order to apply QFT technique, these functions are converted to a family of linear time invariant processes with uncertainty. Next, in the loop shaping phase, an optimal robust PID controller for thelinear process is designed. Lastly, analysis of design procedure shows that robust PID controller is superior to the commonly used PID scheme and multiple sliding surface schemes in terms of both tracking accuracy and robustness.