علي ناجي عطية دعيبل

The cracking due to restrained shrinkage at early ages of concrete is one of the shortcomings of concrete, which may reduce its sustainability. Staged nonlinear static analysis adopted by SAP2000 software is used to analyze one-way slabs applied to restrained shrinkage. Staged nonlinear static analysis has been improved using the concept of cracked element and the proposed model showed good correlation with test results. Creep strain calculated by CEB-FIP cannot be used correctly with shrinkage at early ages of concrete (first three months), and a modification factor has been suggested in the present research. The modification factor is dependent on the steel ratio. Shrinkage relaxed due to creep has been found slightly affected by the steel ratio, which may be considered constant and equals to 60% approximately. Steel reinforcement will control crack width by reducing the restrained length of shortened concrete due to shrinkage, which is equal to the distance between multiple cracks

This study deals with the behavior of reinforced concrete structures subjected to external explosions by using a three dimensional nonlinear analysis program. The section design property is employed to model the reinforced concrete structural elements. The behavior of concrete is simulated by an elasto-plastic work. Numerical study is carried out to evaluate the current international blast design guidelines like the US General Service Administration (GSA 2003), and the United Facility Criteria (UFC 2005) of the US Department of Defense (DoD). It is found that the building designed according to the (GSA 2003) guidelines would not satisfy the (UFC 2005) requirements to mitigate progressive collapse, while a building designed according to the (UFC 2005) requirements could withstand a blast loads resulted from detonation of (250 Ibs) at (30 ft). A parametric study is carried out using SAP 2000 software to investigate the effects of column dimensions, beam depth, and reinforcing steel ratio on the safety of the structure. It is found that increasing column dimensions by (25%) to the (UFC 2005) design is enough to reduce the standoff distance, but increasing beam depth by (20%) is not enough

This paper is devoted to investigate the behavior of prestressed concrete beams under pure torsion using a non-linear three-dimensional finite element model. The 20-noded isoparametric brick elements have been used to model the concrete. The reinforcing bars are idealized as axial members embedded within the concrete element and perfect bond between the concrete and the reinforcement has been assumed to occur. The behavior of concrete in compression is simulated by an elasto-plastic work hardening model followed by a perfect plastic response, which is terminated at the onset of crushing. On the other hand the behavior in tension is simulated by implementing a smeared crack model in connection with using a tension-stiffening model that account for the retained post-cracking stresses, and a shear retention model that modifies the shear modulus of rigidity as the crack widens. Also a model to simulate the reduction in the concrete compressive strength in presence of tensile transverse straining has been implemented in this study. Two types of prestressed concrete beams under torsion have been analyzed and the finite element solutions were compared with the experimental data. Several parametric studies have been carried out to investigate the effect some important material parameters. In general, good agreement between the finite element solutions and the experimental results was obtained

The intention of modeling concrete walls subjected to shrinkage deformation. To achieve this goal, an analytical study is carried out using the finite element method (FEM) of analysis using program ANSYS. Element (solid 65) is used to model concrete and element (link 8) to model steel reinforcement, and shrinkage phenomenon is represented by converting the measured total shrinkage strain to an equivalent temperature to calculate cracks width depending on strain generated at nodes. The overall crack pattern and the estimated crack widths are shown to have good agreement with the experimental results

This research deals with the analysis of reinforced concrete horizontally curved deep beams, loaded transversely to its plane, using a three-dimensional nonlinear finite element model in the pre and post cracking levels and up to the ultimate load. The 20-node isoparametric brick element with sixty degrees of freedom is employed to model the concrete, while the reinforcing bars are modeled as axial members embedded within the concrete brick element. Perfect bond between the concrete and the reinforcing bars is assumed. The behavior of concrete in compression is simulated by an elasto-plastic work hardening model followed by a perfect plastic response, which is terminated at the onset of crushing. In tension, a fixed smeared crack model has been used with a tension-stiffening model to represent the retained post-cracking tensile stress. Also, a shear retention model that modifies the shear modulus after cracking is used. Numerical study is carried out to investigate the effect of the shear length to effective depth ratio (a/d) on the ultimate load resisted by curved beams. Numerical study is carried out to investigate the effect of the central subtended angle, boundary conditions, amount of transverse reinforcement, and using additional longitudinal bars (horizontal shear reinforcement) on the behavior of reinforced concrete horizontally curved beams with different shear length to effective depth ratios (a/d)

In this study, the effect of concrete compressive strength on its resistance to blast pressure has been studied. The efficiency of concrete to resist low, intermediate and high pressure ranges has been evaluated, when it has been exposed to a difference in compressive strength. It has been concluded that reduction in compressive strength due to faults in construction will decrease the diagonal shear capacity of concrete and the reduction is seen more evident in the direct shear capacity at the low and intermediate pressure ranges. Also, it has been concluded that an increase in the concrete strength will improve relatively both types of shear (diagonal and direct shear) at low and intermediate pressure ranges and the diagonal shear only at the high pressure range. But it has been seen that the use of high strength concrete will reduce the absorption capacity of blast energy of the structural element. So, it is not recommended to use such concrete at the high pressure ranges