为什么光束柱关节是特殊的

在RC建筑物中，在其交叉点处的横梁共同的列的一部分称为梁柱关节（图1）。由于它们的构成材料具有有限的优点，因此关节具有有新利客户限的力量承载能力。当在地震期间施加大于这些力的力时，关节受到严重损坏。修复损坏的关节是困难的，因此必须避免损坏。因此，必须设计光束柱接头以抵抗地震效应。

关节的地震行为

Under earthquake shaking, the beams adjoining a joint are subjected to moments in the same (clockwise or counter-clockwise) direction (Figure 1). Under these moments, the top bars in the beam-column joint are pulled in one direction and the bottom ones in the opposite direction (Figure 2a). These forces are balanced by bond stress developed between concrete and steel in the joint region. If the column is not wide enough or if the strength of concrete in the joint is low, there is insufficient grip of concrete on the steel bars. In such circumstances, the bar slips inside the joint region, and beams loose their capacity to carry load.

Further, under the action of the above pull-push forces at top and bottom ends, joints undergo geometric distortion; one diagonal length of the joint elongates and the other compresses (Figure 2b). If the column cross-sectional size is insufficient, the concrete in the joint develops diagonal cracks.

Reinforcing the Beam-Column Joint

Diagonal cracking & crushing of concrete in joint region should be prevented to ensure good earthquake performance of RC frame buildings. Using large column sizes is the most effective way of achieving this. In addition, closely spaced closed-loop steel ties are required around column bars (Figure 3) to hold together concrete in joint region and to resist shear forces. Intermediate column bars also are effective in confining the joint concrete and resisting horizontal shear forces.

Providing closed-loop ties in the joint requires some extra effort. Indian Standard IS:13920-1993 recommends continuing the transverse loops around the column bars through the joint region. In practice, this is achieved by preparing the cage of the reinforcement (both longitudinal bars and stirrups) of all beams at a floor level to be prepared on top of the beam formwork of that level and lowered into the cage (Figures 4a and 4b). However, this may not always be possible particularly when the beams are long and the entire reinforcement cage becomes heavy.

锚定梁杆

The gripping of beam bars in the joint region is improved first by using columns of reasonably large cross-sectional size.Indian Standard IS:13920-1993 requires building columns in seismic zones III, IV and V to be at least 300 mm wide in each direction of the cross-section when they support beams that are longer than 5m or when these columns are taller than 4m between floors (or beams). The American Concrete Institute recommends a column width of at least相邻梁中使用的最大纵杆直径的20倍。

In exterior joints where beams terminate at columns (Figure 5), longitudinal beam bars need to be anchored into the column to ensure proper gripping of bar in joint. The length of anchorage for a bar of grade Fe415 (characteristic tensile strength of 415MPa) is about直径50倍。从柱的面向锚杆的柱子的末端测量该长度。在小宽度的柱中，当梁杆具有大直径（图5A）时，梁顶杆的一部分嵌入到灯柱上铸造的柱中，并且其一部分悬垂的柱子。

It is difficult to hold such an overhanging beam top bar in position while casting the column up to the soffit of the beam. Moreover, the vertical distance beyond the 90º bend in beam bars is not very effective in providing anchorage. On the other hand, if column width is large, beam bars may not extend below soffit of the beam (Figure 5b). Thus, it is preferable to have columns with sufficient width. Such an approach is used in many codes [e.g., ACI318, 2005]. In interior joints, the beam bars (both top and bottom) need to go through the joint without any cut in the joint region. Also, these bars must be placed within the column bars and with no bends (Figure 6).

文章由以下方式编写：

c.v.r.murty.

Indian Institute of Technology Kanpur

Kanpur, India

由...赞助：

Building Materials and Technology Promotion

Council, New Delhi, India

Originally Published

BMTPC.地震提示