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由于无粘结预应力筋能够在混凝土中滑动,受弯构件中无粘结筋的应变始终在其锚固长度内不断自行调整,而趋于均匀分布。因此,在某些情况下,最大弯矩截面处的无粘结预应力筋的应力始终低于相应有粘结预应力筋的应力,而不能充分发挥预应力筋钢材的强度。此外,在无粘结预应力混凝土受弯构件中如不配有普通钢筋(有粘结非预应力筋),在使用荷载下会出现裂缝过宽,裂缝条数少,间距过大的不利现象。为此,目前国内外均在这类构件中配一定数量的普通钢筋,以补偿由于无粘结预应力筋极限应力降低造成的抗弯强度损失,并改善使用荷载下不利的裂缝状态。许多国家在自己相应的规
Because the unbonded prestressed tendons can slide in the concrete, the strain of the unbonded tendons in the flexural member always adjusts itself within the anchorage length and tends to be evenly distributed. Therefore, in some cases, the stress of the unbonded prestressed tendons at the maximum moment cross section is always lower than that of the corresponding bonded prestressed tendons, and the strength of the prestressed tendons steel cannot be fully exerted. In addition, in the unbonded prestressed concrete flexural members, if there is no ordinary steel (bonded non-prestressed tendons), there will be unfavorable phenomena such as too wide cracks, small number of cracks, and large gaps under the applied load. To this end, at home and abroad, a certain number of ordinary steel bars are used in such components to compensate for the loss of bending strength due to the reduction of ultimate stress of unbonded prestressed tendons, and to improve the unfavorable state of cracks under the use of loads. Many countries in their own regulations