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TEST RESULTS Typical shape of ruptured cone of concrete is shown in Figure 2. Due to the observation during test and the measurement of ruptured cone, the failure process was summarized as the following steps: (1) initiation of crack at a steeper inclination (40-55 degree) just around the bottom end of bolt; (2) propagation of crack at a slower angle (20-35 degree); and (3) rupture of concrete with scaling at a shallow angle near the outskirts of cone. The last stage, however, appeared after passing the peak load. The portion of concrete near the surface could not contribute to the ultimate capacity [1]. Since the second stage was considered to determine the ultimate capacity, the crack inclination at this stage was measured in details and the results were summarized in Table 2. Here, the measured crack angles in the four directions are shown, and the section 1 and 2 indicate the or­ thogonal direction to each other. The ruptured cone shape was not necessarily the same in each specimen, but the average angle of 28.4 degree was similar in any case despite of the difference of embed­ ment length. Figure 2. Ruptured cone TABLE 2 Test results Bolt fcf ft P max e (degree) 0 ave. d le * kgf/cm2 kgf/cm2 tonf sec,. 1 sec. 2 40 M10 196 17.9 2.11 28 20 48 25 28.6 2.12 24 30 27 27 14 60 M10 395 29.0 4.50 26 20 27 45 5.62 29 27 27 25 25.4 3.92 15 18 21 25 18 80 M12 320 22.9 6.32 30 30 25 30 395 29.0 6.70 24 35 21 29 31.6 381 25.7 5.6-1 21 26 23 22 22 100 M16 381 25.7 9.24 37 28 24 38 8.80 30 30 31 16 30.0 11.10 34 32 ----160 24 280 21.0 17.90 22 34 13 22 18.70 37 30 26 30 27.2 18.10 31 29 26 26 240 30 280 21.0 35.40 29 34 22 31 29.4 35.30 32 30 26 31