---

A parametric study is performed to assess the influence of the tension reinforcement index, ( ω = ρ fy /f Bc), and the bending moment distribution (loading type) on the ultimate deformation characteristics of reinforced concrete (RC) beams. The analytical results for 15 simply supported beams with different amounts of tension reinforcement ratio under three different loading conditions are presented and compared with the predictions of the various formulations and the experimental data, where available. The plastic hinge rotation capacity increases as the loading is changed from the concentrated load at the middle to the third-point loading, and it is a maximum for the case of the uniformly distributed load. The effect of the loading type on the plastic rotation capacity of the heavily reinforced beams is not as significant as that for the lightly reinforced beams. Based on the analytical results obtained using the nonlinear finite element method, new simple equations as a function of the tension reinforcement index, ω, and the loading type are proposed. The analytical results indicate that the proposed equations can be used for analysis of ultimate capacity and the associated deformations of RC beams with sufficient accuracy.

---

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 the

flanged 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.

---

Steel-concrete hybrid systems are used in buildings, in which a steel structure has been placed on a concrete structure to make a lighter structure and have a faster construction. Dynamic analysis of hybrid structures is usually a complex procedure due to various dynamic characteristics of each part, i.e. stiffness, mass and especially damping. Dynamic response of hybrid structures has some complications. One of the reasons is the different stiffness of the two parts of structure and another reason is non-uniform distribution of materials and their different features such as damping in main modes of vibration. The available software is not able to calculate damping matrices and analyze these structures because the damping matrix of these irregular structures is non-classical. Also an equivalent damping should be devoted to the whole structure and using the available software. In the hybrid structures, one or more transitional stories are used for better transition of lateral and gravity forces. In this study, an equation has been proposed to determining the equivalent uniform damping ratio for hybrid steel-concrete buildings with transitional storey(s). In the proposed method, hybrid buildings are considered to have three structural systems, reinforced concrete, transitional storey and steel. Equivalent uniform damping ratio is derived by means of a semi-empirical error minimization procedure.

---

Steel plate shear walls have long been used as a lateral load resisting system. It is composed of beam and column frame elements, to which infill plates are connected. This paper investigates the progressive collapse-resisting capacity of 50-story building 3D model of the strip model of steel plate shear wall comparing with X-braced and moment frame system based on the removing structural elements from a middle and corner of the exterior frame, in the story above the ground. The collapse behavior is evaluated by different nonlinear static and dynamic analyses using conventional analysis software. In this study, vulnerability of structures is also assessed by sensitivity index (SI) regarding the sensitivity of structures to dynamic effect induced by progressive collapse. To identify vulnerable members, resulting actions of nonlinear static analysis, considering load factor to account for dynamic effect, at the failure mode of structure at the specific performance level are compared by the factor of redundancy related to overall strength of structure, with the linear static analysis of damaged model without considering dynamic effect,. Comparing analysis results indicated that in the steel plate shear wall system, the progressive collapse resisting potential is more than X-braced and moment frame. Sensitive index of highly sensitive elements to dynamic effect stated that in the structural models, beams are more vulnerable in moment frame than X-braced frame and SPSW structure, significantly, and vulnerability of columns in X-braced frame and SPSW system is more than moment frame.

---

Concrete filled steel tube is constructed using various tube shapes to obtain most efficient properties of concrete core and steel tube. The compressive strength of concrete is considerably increased by the lateral confined steel tube in circular concrete filled steel tube (CCFT). The aim of this study was to present an integrated approach for predicting the steel-confined compressive strength of concrete in CCFT columns under axial loading based on large number of experimental data using artificial neural networks. Neural networks process information in a similar way the human brain does. Neural networks learn by example. The main parameters investigated in this study include the compressive strength of unconfined concrete (f'c), outer diameter (D) and length (L) of column, wall thickness (t) and tensile yield stress (fy) of steel tube. Subsequently, using the reliable network, empirical equations are developed for the confinement effect. The results of proposed model are compared with recently existing model on the basis of the experimental results. The findings demonstrate the precision and applicability of the empirical approach to determine capacity of CCFT columns.