在非地震区的多数建筑中，柱子中的纵向钢筋刚好在每层楼面的上方拼接。搭接的要求随钢筋在极限荷载下的应力状态而变化。通常，柱子中的所有钢筋具有相同的长度或接头，不管它们是处于受拉面还是受压面。这样做是为了减少现场错误的可能性。
                    Ties are provided in reinforced concrete columns for four reasons: 钢筋混凝土柱子中采用箍筋有四个原因：

（1）restrain the longitudinal bars from buckling out through the surface of the column.
            ACI Code gives limits on the size, spacing, and the arrangement（布置）of the ties so that they are adequate to restrain the bars. The minimum tie size is a No.3 bar for longitudinal bars up to （在..以内）No.10, and a No.4 bar for larger longitudinal bars, or for bundled bars（束筋）. The vertical spacing of ties shall not exceed 16 longitudinal bar diameters to limit the unsupported length of these bars, and shall not exceed 48 tie diameters to ensure that the cross-sectional area of the ties is adequate to develop the forces needed to restrain buckling of the longitudinal bars. The maximum spacing is also limited to the least dimension of the column. In seismic regions much closer spacings are required.
          （1）箍筋阻止了纵向钢筋向柱子表面的屈曲。
             ACI规范给出了对箍筋尺寸、间距和布置的限制，以使它们足以约束钢筋。对10号以内的纵筋其最小箍筋的尺寸是3号，对较大的纵筋或束筋其（最小箍筋的尺寸）为4号。箍筋的竖向间距不超过16倍的纵筋直径以限制这些纵筋未被支撑的长度，且不超过48倍的箍筋直径以确保箍筋的横截面面积足以形成为约束纵向筋屈曲所需要的力。（箍筋）最大的间距也被限制为柱子的最小尺寸。在地震区需要的间距要密得多。
    （2）Ties hold（固定）the reinforcement cage（笼）together during the construction process.
    （3）Properly detailed（布置）ties confine（约束）the concrete core, providing increased ductility.
（2）在施工过程中箍筋将钢筋笼固定在一起。
（3）适当布置的箍筋约束着核心混凝土，以增加延性。
         （4）Ties serve as shear reinforcement（抗剪钢筋）for columns.
            If shear governs, the smaller spacing (d/2, d = effective depth) must be used and the area of all legs（箍筋肢）parallel to the direction of the shear force must satisfy ACI Code. ACI Code requires that bar anchorage（锚固钢筋）in connections of beams and columns be enclosed（包围）by ties, spirals, or stirrups（钢筋箍）.
          （4）箍筋作为柱子的抗剪钢筋。
            如果由剪力控制，则必须采用较小的间距（即1/2d，d为有效深度），且所有平行于剪力方向的（箍筋）肢的面积必须满足ACI规范。ACI规范要求连接梁与柱的锚固钢筋应被普通箍筋、螺旋箍筋或钢筋箍包围。
             Finally, extra ties are required at the outside（外部）(lower) end of offset bends（迂回管弯头）at column splices to resist the horizontal force component in the sloping（倾斜）portion of the bar.

            最后，在柱子拼接处的迂回管弯头的外部较低端需要额外的箍筋，以抵抗钢筋倾斜部分的水平力分量。


UNIT 9

Action Under Overload-Cracking Load
超载（-开裂荷载）下的反应
           It has been shown that a variation in the external load acting on a prestressed beam results in a change in the location of the pressure line（压力线）for beams in the elastic range. This is a fundamental principle（规律）of prestressed construction. In a normal prestressed beam, this shift（移动）in the location of the pressure line continues at a relatively uniform rate（速度）, as（随着）the external load is increased, to the point where cracks develop in the tension fiber. After the cracking load has been exceeded, the rate of movement in the pressure line decreases as additional load is applied, and a significant（显著）increase in the stress in the prestressing tendon（预应力钢筋束）and the resultant concrete force begins to take place.
           This change in the action of the internal moment continues until all movement of the pressure line ceases（停止）. The moment caused by loads that are applied thereafter（其后）is offset（抵消）entirely by a corresponding and proportional change in the internal forces, just as in reinforced-concrete construction. This fact, that the load in the elastic range and the plastic range is carried by actions that are fundamentally different, is very significant（重要的） and renders（使..变得）strength computations essential for all designs in order to ensure that adequate safety factors exist. This is true even though the stresses in the elastic range may conform to（符合）a recognized（公认的）elastic design criterion.