International Journal of Civil Engineering
Volume:7 Issue: 1, Mar2009

Concentric bracing is one of the most common lateral load resistant systems in building frames, and areapplied to many structures due to their manufacturing simplicity and economics. An important deficiency in thebracing members is their irregular hysteretic loops under cyclic loading. In order to overcome this problem, it isadvised to restrain braces against buckling under compression, since buckling restrained frames dissipate a largeamount of energy. One method to restrain braces against buckling is to cover them with concrete. Aproper coveringcan prevent the core from buckling and provide similar capacities whether in tension or compression which wouldproduce regular hysteric curves. In this study, the behavior of buckling restrained braces (BRB) has been investigatedby considering different types of surrounding covers. The steel core is encased in concrete with different coverings. Thecovering types include steel tubes, PVC pipes, and FRProlled sheets. Experimental and numerical analyses wereimplemented. According to the results, PVC pipes and FRPsheets are suitable alternatives to steel pipes. Furthermore,the behavior of several types of steel cores was assessed; since, applying steel with high ductility promotes the energydissipation of the brace. Finally, the effect of the separating layer between the steel core and the concrete on theperformance of bracing was evaluated.

A meshless approach, collocation discrete least square (CDLS) method, is extended in this paper, for solving elasticity problems. In the present CDLS method, the problem domain is discretized by distributed field nodes. The field nodes are used to construct the trial functions. The moving least-squares interpolant is employed to construct the trial functions. Some collocation points that are independent of the field nodes are used to form the total residuals of the problem. The least-squares technique is used to obtain the solution of the problem by minimizing the summation of the residuals for the collocation points. The final stiffness matrix is symmetric and therefore can be solved via efficient solvers. The boundary conditions are easily enforced by the penalty method. The present method does not require any mesh so it is a truly meshless method. Numerical examples are studied in detail, which show that the present method is stable and possesses good accuracy, high convergence rate and high efficiency.

Limit to the tension reinforcement ratio in flexural high strength reinforced concrete (HSRC) members isbased on the requirement that tension failure as sufficient rotation capacity are ensured at ultimate limit state. However, the provisions for the total amount of longitudinal reinforcement ratio (and) are not associated with any rational derivation. In this paper, a quantitative measure to evaluate an upper limit to the compression reinforcement ratio of flexural HSRC members is proposed. The quantitative criterion to can be derived from i) steel congestion and ii) considerations that are related to the diagonal compression bearing capacity of the members. In this paper it is shown that, when shear loading is dominant, the limit to is set by the diagonal compression criterion. Parameters that affect this limit are deeply investigated and the expressions were derived for different end conditions, to provide an additional tool for a better design and assessment of the flexural capacity of HSRC members.

The work presented in this paper investigates the causes of size effects in structural-concrete members. It is based on the use of a finite-element model found to yield realistic predictions of structural-concrete behavior in all cases investigated to date. In fact, the previous use of this model in investigations of size effects in reinforced-concrete beams indicated that such effects reflect the dependence of load-carrying capacity on small unintended eccentricities of the applied load and/or load-induced anisotropy, rather than, as widely considered, on fracture-mechanics characteristics. The present work extends the scope of the above investigation so as to include the case of reinforced concrete flanged shear walls, the behavior of which is already established experimentally. It is found that, unlike theflanged shear walls with a height-to-length ratio larger than 2, the shear walls investigated in the present work, in contrast with the interpretation given to recently published experimental findings, are size-effect independent.

This paper presents a hybrid approach to developing a short-term traffic flow prediction model. In this approach a primary model is synthesized based on Neural Networks and then the model structure is optimized through Genetic Algorithm. The proposed approach is applied to a rural highway, Ghazvin-Rasht Road in Iran. The obtained results are acceptable and indicate that the proposed approach can improve model accuracy while reducing model structure complexity. Minimum achieved prediction r2 is 0.73 and number of connection links at least reduced 20% as a result of optimization.

Confined masonry buildings are used in rural and urban areas of Iran. They performed almost satisfactory during past moderate earthquakes of Iran. There is not a methodology in Iranian Seismic Code (Standard 2800-3rd edition) to estimate their capacities quantitatively. In line with removing this constraint, an attempt is made to study in-plane behavior of two squared confined masonry walls with and without opening by using a numerical approach. These walls are considered based on Iranian Seismic Code requirements. Finite element 2D models of the walls aredeveloped and a pushover analysis is carried out. To model the non-linear behavior of the confined masonry walls, the following criteria are used: (1) The Rankine-Hill yield criterion with low orthotropic factor to model the masonry panel; (2) The Rankine yield criterion to model reinforced concrete bond-beams and tie-columns; (3) The Coulomb friction criterion with tension cutoff mode to model the interface zone between the masonry panel and reinforced concrete members. For this purpose, the unknown parameters are determined by testing of masonry and concrete samples; and by finite element analysis. Comparing the results show that the initial stiffness, the maximum lateral strength and the ductility factor of walls with and without opening are different. Also, the severe compressed zones of the masonry panels within the confining elements are found different from what are reported for the masonry panels of infilled frames by other researchers. This study shows that a further investigation is needed for estimating capacity of confined masonry walls with and without opening analytically and experimentally. Also where openings, with medium size are existed, the confining elements should be added around them. These issues can be considered in theKeywords: Confined Masonry, Bond-Beams, Tie-Columns, In-Plane Behavior, Capacity Curves, Interface Modeling next revisions of Iranian Seismic Code.

There are limitations in experimental studies on sand-gravel mixtures due to the small size of testingspecimens. Due to this problem, many researchers have worked on prediction of the shear strength of mixture by testing the sandy fraction of soil alone and developed empirical relationships. Most of the previous relationships have been determined for low surcharge pressures in which particle breakage does not affect the shear strength parameters. However, the particle breakage affects the relationships in higher confinements. At the present study, the results of large scale direct shear tests on sand and sand-gravel mixtures was used to investigate the shear behavior and dilatancy characteristics in a wider range of surcharge pressures. The gravel content, relative density, surcharge pressure and gravel grain size were considered as variables in testing program. The relationships between shear strength characteristics of sand and sand-gravel mixtures were determined considering dilation characteristics of the soil. In this regard, the minimum void ratio was found as a useful indirect index that relates uniquely to the critical state friction angle independent of soil gradation. The relations between critical state or peak friction angles of the mixture with minimum void ratio were determined as a function of surcharge pressure. The correlations could be useful for determination of the strength parameters of sand-gravel composites by testing sandy fraction of mixture.