異形鉄筋の交差溶接接合性能に及ぼす溶接条件の影響

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  • INFLUENCE OF WELDING CONDITIONS ON CROSS-WELDING JOINT PERFORMANCE OF DEFORMED REINFORCING BARS
  • イギョウ テッキン ノ コウサ ヨウセツ セツゴウ セイノウ ニ オヨボス ヨウセツ ジョウケン ノ エイキョウ

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<p> 1. INTRODUCTION</p><p> The authors have developed the footing beams in double layered main bars with cap-tie system and cross-welding joint between main bars and stirrups. However, welding conditions in cross-welding joint have not been sufficiently clear. The objectives of this study are to investigate the influence of welding conditions on welding strength and fracture patterns and to evaluate the structural performance of beam specimens with the parameters of welding conditions.</p><p> </p><p> 2. WELDING STRENGTH TEST OF CROSS-WELDING JOINT</p><p> The welding strength test using cross-shaped specimens is experimentally investigated. The test parameters are the combinations of reinforcing bars and the welding conditions. The bars of D16, D19 and D22 are selected as main bars, and D10, D13 correspond to stirrups. In the first series test, electric current (11,500 - 16,000A) and energization time (5 - 30cycle) are varied. As the results, three types of fracture patterns are observed (weld peeling, welding point breakage and breakage of base bar). In the case of D10 stirrup, the welding strength exceeds the yield strength of base bar by integrated current of over 4000A･s, and breakage of base bar is observed by integrated current of over 6500A･s. In the case of D13 stirrup, the welding strength exceeds the yield strength of base bar by integrated current of over 5000A･s.</p><p> In the second series, electric current (10,000 - 18,000A) and welding pressure (3 - 7kN) are varied. As the results, the welding pressure has little influence on welding strength and fracture patterns. The energization time of 20 or 26cycle is not enough to avoid weld peeling for the combinations of D16, D22 main bar and D13 stirrup.</p><p> </p><p> 3. LOADING TEST OF BEAM SPECIMEN</p><p> In order to confirm the structural performance of the footing beams (main bars and stirrups are welded), the anti-symmetrical cyclic loading test for actual-size beam specimens is conducted. The test parameters are conditions of welding and the target concretestrength. All specimens are designed to show shear failure before flexural yielding of main bars to evaluate the shear capacity. The electric current and energization time is set to 13,000A and 30cycle for specimens No. 1-1 and No. 1-4, respectively, to have enough welding strength (breakage of base bar, called A-Type). The electric current for specimens No. 3-3 and No. 3-4 is set to 7,000A to show weld peeling (called B-Type). As the results, the maximum load and initial stiffness of A-Type specimens show similar or higher ones comparing with those of conventional beam specimens. B-Type specimens show the remarkable decrement of shear force after the loading cycle of 1/33 rad. The maximum loads ofA-Type specimens can be evaluated by shear capacity calculated by the conventional method.</p><p> </p><p> 4. CONCLUSIONS</p><p> 1) The cross joint strength of reinforcing bars by flash butt welding increases as the integrated current also increases.</p><p> 2) The integrated current by which the sufficient joint strength can be obtained differs by the combinations of main bars and stirrups.</p><p> 3) The beam test results indicate that the maximum load and stiffness of A-Type specimens show similar or higher ones comparing with those of conventional beam specimens.</p><p> 4) B-Type specimens show smaller stiffness and the maximum load and remarkable decrement of shear force after the maximum.</p>

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