Numerical Simulation Of Antiknock And Reinforcement Of Reinforced Concrete Beam With Initial Small Cracks Subjected To Air Blasting Loads

Recently, the disasters appear more frequently with the increasing of terrorist attacks and explosion accidents. Explosion may lead to severe damage to adjacent buildings, even catastrophic collapse. Anti-explosion and reinforcement of reinforce concrete(RC) structure is one of hot topics in safety problems of structures. As one of the important bearing components of building structures, the damage of RC beam may cause the collapse of the whole structure under blasting loads.At present, the studies of anti-explosion of RC beams are mainly limited the ideal models. The initial defects of RC beam, such as initial crack, indentation, and tiny gap are not considered. But these initial defects have adverse effect on the service life and antiknock performances of RC beam, and they can result in the existence of insecurity to some extend. As a novel reinforment technique, the structure or its components could be strengthened effectively by carbon fiber sheet(CFS), and static strength and fatigue strength could also be considerably increased. Therefore, the numerical studies on anti-explosion and reinforcement of RC beam with initial small cracks have important theoretical and engineering significance.Based on the reasons mentioned above, the following three aspects, such as pressure propagation process and dynamic response of RC beam; the influence of initial small cracks on the dynamic response and failure behaviors of RC beam, and antiknock ability for the RC beam with initial small cracks locally strengthened with CFRP sheet, are studied by the large nonlinear dynamics analysis software ANSYS/LS-DYNA. The main results are as follows:(1) After exploding of TNT above RC beam in the air, shock wave firstly spreads outward freely in the form of approximate spherical wave. When touching the RC beam, phenomena of reflection and transmission could be observed. Reaching the surface of RC beam, shock wave is reflected and the peak overpressure is significantly increased. When spreading to the bottom of RC beam, the shock wave is reflected and a strong tensile wave could be formed, which leads to the tensile failure of RC beam on the mid-span bottom. The mid-span top of RC beam is impacted by shock wave at the earliest and the bending deformation of the mid-span is greater than the other parts of RC beam. When the impact of shock wave nearly disappears, the maximum bending deformation of RC beam could be obtained. Different failure modes(such as bending failure mainly produced on simple supported beam, and bending shear failure mainly produced on clamped beam) can be produced under the same conditions of explosive mass and proportion distance. The antiknock ability of RC beam could be improved by increasing the ratio of longitudinal reinforcement of mid-span of beam and stirrup at the supports of beam and strength of the concrete and reinforcing steel bar, reinforcement of the local-easy cracking area(mid-span of beam and bearing point) with high stresses.(2) The presence of initial small crack makes the RC beam earlier broken and results in an evident concentration of strength failure at the pre-cracked sections under air blasting load. RC beam with initial small cracks subjected to air blasting load usually break at the cracked sections and the positions for blast loading begin to be loaded. A crack located at RC beam’s mid-span or the ends can lead RC beam much easier broken under air blasting load and a crack on the compression surface has a larger influence than that on the tensile-surface of RC beam. Influence of an initial small crack is strongly location-dependent and surface-dependent. Increasing the reinforcement ratio and reducing the stress of concrete and longitudinal reinforcement, the flexural capacity of RC beam is increased and the corresponding antiknock ability of RC beam could be enhanced.(3) When RC beam with initial small cracks is locally strengthened with CFS, the overall stiffness of RC beam could be improved, and both the damage and deformation of RC beam could be also reduced under blasting load. Also, the antiknock ability of the RC beam with initial small crack is enhanced. Studying the influence of reinforcement layers and size of CFS, resepcetively, the reinforcement effect of 4 layers CFS is found to be more improved. It is also found that the strengthening length of CFS is 300 mm and the higher antiknock performances of RC beam is obtained.