第4章 受弯构件的斜截面承载力（3-英）.ppt

4.6 Detailing Requirements to Ensure the Bending Capacity of Diagonal Section(保证斜截面受弯承载力的构造措施) Contents Requirements for bent-up position: In order to ensure that the bending capacity in a diagonal section is adequate, bent-up position must be extended beyond its fully developed point by a distance h0/2 . (弯起点距离”充分利用点”的距离≥h0/2,以保证斜截面受弯承载力) In order to ensure that the bending capacity in a normal section is adequate, the ultimate moment diagram must envelop design moment diagram when bent-up. (弯起后抵抗弯矩图Mu必须包住设计弯矩图M, 以保证正截面受弯承载力) 华南理工大学土木工程系\ 1.Ultimate Moment Diagram or Moment of Resistance Diagram 正截面受弯承载力图 （抵抗弯矩图） 2. Bent-up of longitudinal bars 纵筋的弯起 3. Cut-off of longitudinal bars 纵筋的截断 4. Anchorage of longitudinal bars 纵筋的锚固 4.6 Detailing Requirements to Ensure the Bending Capacity of Diagonal Section Question? J C C J V fy(As-Asb) fy Asb z zsb Mc Mmax Bending capacity in diagonal section JC If the longitudinal bars (As) are not bent-up alone the beam, the bending capacity in diagonal section is certainly ensured. The design moment subjected by section CC’ and JC are both equal to Mc However, when part of the longitudinal bars are bent-up or cut-off alone the beam, the bending capacity in diagonal section may be smaller than that in normal section. Thus the bending capacity in diagonal section should be considered in design. Bending capacity in normal section CC’ 1.Ultimate Moment Diagram or Resistant Moment Diagram 正截面受弯承载力图(抵抗弯矩图) The ultimate moment diagram gives the maximum resistant moment of the normal sections along the beam, it depends on member dimensions and material properties only, independent of the load. The ultimate moment diagram without bent-up bars. a c b d 1 2 3 4 A B 跨中最大弯矩计算，需配 纵筋2Φ25+ 2Φ22 If the longitudinal bar is designed for the maximum moment Mmax and is maintained along the span wthout being bent-up, the ultimate moment of any section should be adequate. Th