Improved of the Pull Out Force of the Concrete Anchor Bolt

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Many structures, that is a building, a dam, a bridge, and so on, are made of concrete because the concrete is very cheap and rich.Many instruments, that is a machine tool, a sign board, a slot vending machine, and so on, are attached to the wall and the floor of these structures. In order to attach these instruments to the wall and the floor , many kinds of concrete anchors are used. In general, a metal anchor is used. A metal anchor is made of steel. The metal anchor consists of an anchor bolt and a cone. When the instruments are attached to the concrete wall and floor using the metal anchor, the metal anchor is inserted to the drilled hole and the head of the concrete anchor is hammered. Then, the bottom end of the anchor bolt is expanded in the drilled hole by the cone and the anchor bolt is fixed in the drilled hole. On the other hand, a great many concrete anchor bolts are happen to be pulled out from the concrete walls and floors easily when the Hanshin-Awaji Earthquake has been occurred at 17th, January, 1995. Many machine tools and instruments are fallen down. So, it is demanded to increase the pull out force of the concrete anchor bolt.Therefore, in this study, a method for improvement of the pull out force of the concrete anchor bolt has been studied. In this method, the concrete anchor bolt is fixed to wall and the floor using inverse tapered hole, that is the diameter of the hole increases with the depth. In this study, a new tool has been developed in order to make a inverse tapered hole and the pull out force has been measured.As the result, the following conclusions are obtained.(1) The new tool to make an inverse tapered hole has been developed. Its inverse taper angle is 10 degree and the depth of the inverse tapered hole is 12 mm.(2) When the metal anchor is fixed in the inverse tapered hole, the pull out force is approximately 2.8 times larger than that of general drilled hole.