In construction sites, when falling of lifted objects occur and the falling objects pass through underlying slabs, severe harm may be caused to persons under the slabs. Especially, when construction sites are located above public passages such as roads or railroad tracks, harms may be caused to not only construction workers but also unrelated third parties who use such passages. Therefore, it is important to ensure a sufficient safety for workers and third parties who are under the construction site in case a lifted object falls onto a reinforced concrete (RC) slab.
Significant studies on projectile penetrating RC slabs have been carried out. Those studies proposed some empirical formulae for penetration or perforation limit. Collision problem dealt with in this study has some different features as to the ones reported in those previous studies. Falling objects in construction sites tend to be heavier and have lower velocity than the projectiles of mentioned previous studies. Floor slabs which are treated as collision targets in this study are thinner than the slabs of those studies from the perspective of the ratio of slab thickness to diameter of projectile. Therefore, the behavior of RC floor slabs is not clear when they are subjected to impact loadings by falling objects during construction.
In this study, full-scale drop test and numerical simulations were conducted to examine the behavior of RC slabs subjected to collision of falling objects. Test specimens were made assuming generally used slabs in steel structure buildings in Japan. The specimens have 150mm thickness and constructed on steel deck plates which were considered as non-structural formworks. A falling object was made of a square tube and its mass was about 2.3t. The analytical model was made to replicate the shape of the specimens by finite element meshing. The numerical simulation was satisfactorily and validated by the experimental results. The numerical analysis could reproduce the state of damage of the slabs and time history responses observed in the experiment.
The experimental and analytical results showed that the falling objects could not perforate completely the slabs even when the assumed falling conditions were beyond the perforation limit predicted by the empirical formula proposed by Degen. The falling objects did not fully pass through the slabs when falling heights were 10m and 15m although the calculated perforation height limit was 8.3m considering similar condition as those of the experiment. N=0.72 was adopted in the empirical formula as the shape factor of the tip of the falling object. The diameter of the falling object was adjusted in order that the perimeter of the circle was equivalent to that of the falling object.
The empirical formula seemed able to predict the variation in the failure mode of the slabs. When falling heights were within the perforation limit, concrete at collision points didn't fail completely. On the contrary, concrete at collision points failed completely and reinforcement bars were exposed when falling heights were beyond the perforation limit. In addition, analytical results showed that strain energy of concrete did not significantly increase relative to the increasing of falling heights when falling conditions were beyond the perforation limit. In contrast, strain energy of reinforcement bars increased proportionally to the falling heights.
