Weight Dropping Impact Test

The weight dropping impact test was carried out by using the weight dropping machine as shown in Figure 8. The falling weight was set at W = 4.0 kN and the falling height was set at H = 0.25, 1.25 and 2.5 m (V = 2.21, 4.94 and 7.00 m/sec), that is, impact energy was set at E = 1.0, 5.0

Time (s)

(a) Rubber (R50 and R60) and LMF (b) R50 , LMF5, MM5 and HMF5

Fig. 9. Impact load ~ time relation (input energy Ei = 1.0 kN-m).

iMh

200 –

Time (s)

(a) Rubber (R50 and R60) and LMF (b) R50 , LMF5, MM5 and HMF5

Fig. 10. Impact load ~ time relation (input energy Ei = 5.0 kN-m).

and 10.0 kN-m. These mean that E = 1.0 kN-m is the energy that laminated fiber may never break, E = 10.0 kN-m is the energy that laminated fiber may break perfectly and E = 5.0 kN-m is the intermediate value between 1.0 and 10.0 kN-m. These energies are determined by the results of static compression test. The impact transmitted load is measured by using the 2,000 kN load cell attached at the steel plate under the specimen.

Figures 9, 10 and 11 illustrate the load-time relations obtained by weight dropping impact test. It can be seen from Figure 9 that the maximum impact transmitted load of LFRR is larger than the one of usual rubber and the impact duration time of LFRR is shorter than that of usual rubber in case of low input energy E = 1.0 kN-m. This may be the reason why the stiffness of LFRR in elastic region is larger than that of usual rubber. However, it should be noticed from Figures 10 and 11 that the maximum impact load of LFRR at large input energy becomes smaller than that of usual rubber.

Table 3. Maximum impact load.

I. OkN • m

5.0kN. m

lO. OkN * m

R50

120*6

497.7

987.7

R65

114*8

482.3

991,5

LMF5

203*8

326.3

687.1

LMF25

268.9

690.0

803.9

MMF5

167.5

414.4

670.9

HMF5

168.4

474.7

765.6

Table 4. Energy absorption ratio.

Specimen

Energy absorption ratio (%)

Ei=1.0kN m

Ei=10.0kN m

R65

72.1

85.0

LMF5

86.6

88.7

LMF25

88.9

90.4

MMF5

89.3

87.8

HMF5

86.5

85.5

The reason why the maximum load of LFRR is reduced may be due to that the LFRR can absorb the large kinetic energy by breaking the laminated fiber and decreasing the stiffness.

Table 3 shows the maximum impact load and the hatching figures mean that the laminated fiber breaks. For instance, the maximum loads of LMF5 in cases of E = 5.0 kN and 10.0 kN-m are 1/1.5 smaller those of usual rubber R65. Therefore, the LFRR is effective as a shock absorber rather than usual rubber from the viewpoint of the mitigation effect of impact load at high input energy.

Fig. 14. Indirect application of LFRR to bridge restrainer system.

Table 4 expresses the energy absorption ratio (AE) which is defined as follows:

E – E e

AE =————- x 100%, (1)

E W

in which E and E’ are the kinetic energy before and after collision, respectively. The velocity of weight is obtained by differentiating the traveling distance with respect to time as shown in Figure 12. It can be seen from Table 4 that the energy absorption ratio of LFRR is larger than that of natural rubber in every cases. Therefore, the LFRR can absorb the kinetic energy of weight, that is, the velocity of the weight (girder) after collision in case of LFRR becomes smaller than that of usual rubber. This means that the damage of girder using the LFRR may be smaller than that using usual rubber.