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目前国内外生产的打桩机在打砼预制桩时为了减少施工过程中的吊装应力,较多采用双点或多点起吊法。如图1所示,设桩架顶部两起桩定滑轮之间的距离为A,绑在桩身上两起桩动滑轮之间的距离为B,动定滑轮之间的垂直距离为H,显而易见在桩吊起的过程中,滑轮组与中心铅垂线之夹角α始终是随桩的升高,即H的减小而增大。随着α的增大,钢丝绳对轮缘的水平力N值也增大。由图2可知,(?),因(?)值和(?)方向一定,随着α增大,钢丝绳与滑轮的相对运动方向改变,(?)值增大。
At present, domestic and foreign pile drivers have adopted double or multi-point lifting methods in order to reduce the lifting stress during the construction of precast piles. As shown in Fig. 1, the distance between two fixed pile pulleys at the top of the pile carrier is A, and the distance between the two fixed pulleys on the pile body is B, and the vertical distance between the movable pulleys is H. It is obvious that During the pile lifting process, the angle α between the pulley block and the central plumb line is always increased with the pile, that is, H decreases. With the increase of α, the horizontal force N of the wire rope to the rim also increases. From Figure 2, we can see that (?), due to the (?) value and (?) Direction is certain, with the increase of α, the direction of relative movement of the wire rope and the pulley changes, (?) Increased value.