The influence of drop hammer head type on dynamic response of reinforced concrete slab and theoretical analysis

It is commonly understood that the shape of the hammer head has a significant effect on the dynamic response of reinforced concrete (RC) slabs under impact loads, but few have conducted detailed analysis on it. This article focuses on the influence of different hammer head types which include square, rectangle, cylinder and hemisphere on the impact resistance of RC slabs. Then, residual displacement ratio and section damage rate are used to jointly evaluate the damage state of RC slabs under impact load. Finally, based on Hertz contact theory and Thornton elastoplastic assumption theory, the functional expression between the deformation and impact force of RC slab is derived under impact loads. The research results indicate that under the same contact area, the damage range of squares is larger than that of circles, the damage range of rectangles are larger than that of squares, and the damage range increases with the increase of the aspect ratio of rectangles hammer head. As the radius of the hemisphere hammer head increases, the maximum impact force gradually increases, and the shape of the impact force curve changes from the third type to the first type. Compared to Hemisphere-R50, the maximum impact force of Hemisphere-R60 increases by 33 %. As for the rectangular, square and circular flat hammer heads with the same contact area, the peak displacement of the circular hammer head is the largest, and it shows a trend of first increasing and then decreasing with the increase of radius. In addition, this article classifies the damage state of the slab into mild, moderate and severe damage based on joint indicators, which can provide reference for the performance design of reinforced concrete slabs. Finally, based on the comparison of theoretical formulas and numerical solutions, it is found that the maximum impact force of reinforced concrete slab subjected to planar hammer head impact can be calculated according to the theoretical formula.