Experimental Overview

1.1. Dimensions and Static Design Values ofRC Girder

In this study, a RC girder, which is for designing roof of real RC rock-sheds, was taken for falling – weight impact test of prototype RC structures. The girder is of rectangular cross section and the dimensions are of 1 m x 1m and clear span is 8 m long, which is similar to the width of real RC rock-sheds. Figure 1 shows dimensions of the RC girder, distribution of rebar, and measuring points for each response wave. In this figure, it is confirmed that 7#D32 rebars are arranged as main rebar assuming 0.65% of main rebar ratio corresponding to designing of real RC rock-sheds and 4#D32 rebars are arranged as the upper axial rebar to be about a half of main rebar ratio. Thickness of concrete cover is assumed to be 150 mm as well as real rock-sheds. D16 stirrups are arranged with intervals of 250 mm, which is less than a half of an effective height of the girder. In this study, arranging interlayer stirrups and upgrading in shear load-carrying capacity, the RC girder was designed to be collapsed with flexural failure mode. Axial rebars were welded to 12 mm steel-plates at the ends to save the anchoring length of the rebars.

The displacements of the girder were measured at mid-span (D — 1) and the other five points (D — 2 to D — 6) with the intervals of 750 mm from the mid-span. Impact force P was estimated using deceleration of the heavy weight, which is measured using accelerometer set at its top surface. Reaction force R (= R1 + R2) was also measured using load-cells installed in the supporting gigues. The detailed static design parameters of the RC girder are listed in Table 1. Static flexural and shear load-carrying capacities Pusc and Vusc were calculated based on Japanese concrete standards (JSCE, 1996). From this table, it is confirmed that the RC girder designed here will collapse with flexural

Table 1. Static design parameters of RC girder.

Shear rebar

Static shear

Static shear

Static bending

Shear-bending

ratio

depth ratio

capacity

capacity

capacity ratio

Pt

aid

Vusc (kN)

Pusc (kN)

a

0.0065

4.71

1651

892

1.85

Table 2. Material properties of concrete.

Age

Compressive strength

Young’s modulus

Poisson’s ratio

(days)

fC (MPa)

Ec (GPa)

Vc

36

30.4

27.6

0.186

failure mode under static loading because shear-bending capacity ratio a is larger than unity. The static material properties of concrete and rebars during experiment are listed in Tables 2 and 3, respectively.