5TH International Congress on Technology - Engineering & Science - Kuala Lumpur - Malaysia (2018-02-01)

Numerical Evaluation Of One-way Reinforced Concrete Slab Subjected To Air Blast Loading

The number of explosive events are growing due to terrorist attacks and accidental explosions all over the world, so important structures must be assessed under explosive loading. The explosion is known as a sudden release of energy phenomenon [1]. This phenomenon is often analyzed by two factors of maximum pressure and pressure increase rate. Reinforced concrete (RC) is the main material in military structures and nuclear power plants, and the dynamic response of a concrete structure is more complex under explosive loading [2]. RC walls are often used as a shield to protect contents in structures against explosive loads. Overall, when the RC wall is subjected to blast loading, the stresses of a specific region of the wall are increased, and this will cause severe damage to this area. The surface under blast waves is compressed, and it may be damaged under high compression [3]. To evaluate concrete damage under free air blast loading, McVay has conducted extensive experimental and numerical researches in 1998. Many different researches has been established in this field such as experimental and numerical assessment of the stiffened plates response subjected to gas explosions [4], experimental and numerical investigation on the RC pavement under blast loading [5], Evaluation of blast loading and its effects on buildings [6], numerical investigation of the two-way RC slab dynamic response under explosive loading [2], assessment of the one-way slab dynamic response under close-in explosive loading [1], investigation of numerical and experimental damage of RC slab with normal and high strength concrete under contact explosion [7] and numerical evaluation of RC slab damage under contact explosion in air and underwater [8]. In recent years, numerical methods have extensively developed, and researchers have utilized many different softwares (ABAQUS\CAE, LS-DYNA, ANSYS AUTODYNE, etc.) to simulate the RC slab responses under blast loading. In the present study, the behavior of RC slabs under close-in explosive loading in the air are assessed by numerical simulations with finite element methods and by using ConWep equation in ABAQUS\CAE focusing on impact damage. This study uses the experimental model of Wang et al. (Figure 1) to verify the numerical method and to select the best element sizes (Figure 2). By comparing the experimental and numerical results, it is observed that there is a very good correspondence between numerical and experimental results (Figure 3). The simulation of central displacement rate of the RC slab has a relative error of 2.8%, and this shows that the numerical method has a good accuracy for simulating central displacement (Table 1). Then RC slab response is simulated when it is subjected to 200, 310, 460 and 550 gr of trinitrotoluene (TNT) at a distance of 20 cm from point 1 (Figure 1), and the peak pressure in points 1 and 2 under 4 explosive weights are extracted (Figure 4). To calculate the peak pressure (Ps0), an exponential function is fitted to the results at point 1 based on a scaled distance (Z). This equation for Z<1 (m/〖kg〗^(1/3) ) is as follow: P_s0=336509.17e^(-4.86Z) R^2=0.997 (1) For small charge weight, when one-way RC slab is under close-in blast, the displacement at point 1 is not maximum, but the slab edge (point 3) has maximum displacement (Figure 5). However, when the charge weight increases, the maximum displacement will occur in point 1, and it happens 4-6 millisecond after the explosion. Figure 6 shows that if the charge weight increases, the change of pressure rate increases significantly in point 1, and the other three points do not have such an intensive change.
Maziar Fahimi-Farzam, Saeid Pourhosein