torque-twist curve(Fig.4-2),which at the cracking torque shows continued twist at constant torque until the reinforcement has picked up the portion of the torque no longer carried by concrete. Any further increase of applied torque must then be carried by the reinforcement. Failure occurs when somewhere along the member the concrete crushes along a line such as a-d in Fig.4-1. In a well-designed member such crushing occurs only after the stirrups have started to yield.如图4-1a所示，构件充分配筋时，混凝土在受到大于等于未配筋构件强度的扭矩处的开裂。裂缝呈螺旋状，事实上，许多这样螺旋状的裂缝相距很近地发展。一旦开裂，混凝土的抗扭能力下降到未开裂混凝土构件的一半。剩余部分从扭矩由钢筋承担。这种内力重分布在弯矩曲线上得到体现。（如图4-2），图表明在开裂扭矩作用下，扭矩不变，弯曲持续增长，直到钢筋承担承担部分不再由混凝土承担的扭矩，任何增加的作用扭矩都由钢筋来承担。当沿构件的某处的混凝土沿一条直线压碎如图4-1中的a-d线是，构件达到破坏，在设计合理的构件中，只有箍筋达到屈服，这种压碎破坏才会发生。
The torsional strength can be analyzed by considering the equilibrium of the internal forces which are transmitted across the potential failure surface, shown shaded in Fig.4-1.This surface is seen to be bounded by a 45°tension crack across one wider face, two cracks across the narrower faces of inclination Φ, an angle generally between 45°and 90°, and the zone of concrete crushing along line a-d. The failure is basically flexural,
as for plain beams, with a concrete compression zone developing adjacent to a-d.通过考虑，传播通过可能破坏面的内力的平衡可以来分析扭转强度，如图4-1的阴影所示。这个破坏面由宽面上的45°张拉，裂缝和窄面上的通常45°和90°之间的倾角Φ的两条裂缝构成，而且混凝土压碎区沿着直线a到d。与平梁相似，这种破坏基本是弯曲型的，有沿a-d发展的混凝土压应力区的。
第五单元The role of shear stress is easily visualized by the performance under load of the laminated beam of Fig5-1; it consists of two rectangular pieces bonded together along their contact surface. If the adhesive is strong enough, the member will deform as one single-beam, as show in Fig5-1a. On the other hand, if the adhesive is weak, the two pieces will separate and slide relative to each other, as show in Fig5-1b. Evidently, then, when the adhesive is effective, there are forces or stresses acting in it which prevent this sliding or shearing. These horizontal shear stresses are shown in Fig5-1c as they act, separately, on the top and bottom pieces. The same stresses occur in horizontal planes in single-piece beam; they are different in intensity at different distances from the neutral axis.通过如图5-1，用薄片叠成的梁在荷载作用下的性能可以很容易的观测到剪应力的作用。它由两个长方形构件在它们的接触面粘合组成。如果这个粘合足够强，构件变形与单梁变形相似，如图5-1a所示，另一方面，如果这个粘合很弱，这两个部分会分开，且彼此相对滑动，如图5-1b所示，明显可以看出，当粘合有效，有阻止其滑动成受剪的
力或应力产生。这些水平剪应力如图5-1c所示，它们单独作用在顶部或底部。同样的应力产生在单梁的水平面上。它们随着与中性轴距离的不同，其强度大小不同。
Fig. 5-1d shows a differential length of a single-piece rectangular beam acted upon by a shear force of magnitude V. Upward translation is prevented, i.e., vertical equilibrium is provided, by the vertical shear stresses v. Their average value is equal to the shear force divided by the cross-sectional area, Vav=V/ab, but their intensity varies over the depth of the section. As is easily computed from Eq. 1, the shear stress is zero at the outer fiber and has a maximum of 1.5 Vav at the neutral axis, the variation being parabolic as show. Other values and distributions are found for other shapes of the cross-section, the shear tress always being zero at the outer fibers and of maximum value at the neutral axis. 图5-1d表明了整块矩形梁在大小为V的剪力下，不同长度的剪力大小。没有向上的位移，也就是说，通过竖向剪应力V达到了垂直方向上的平衡。它们的均值等于剪力除以横截面积。VAB=V/AB.但是他们的强度随着高度不同而不同，如式1中简单算出，外层纤维的剪应力应为O，中性轴有最大剪应力1.5V，如图所示，这种变化成抛物线形。其他不同截面形状的值和分布发现最外层纤维的剪力应为O，最大值在中性轴上。
If a small square element located at the neutral axis of such a beam is isolated as in Fig. 5-2b, the vertical shear stresses on it, equal and
opposite on the two faces for reasons of equilibrium, act as shown. However, if these were the only stresses present, the element would not be in equilibrium; it would spin. Therefore, on the two horizontal faces there exist equilibrium horizontal shear stresses of the same magnitude. That is, at any point in the beam, the horizontal shear stresses of Fig. 5-2b are equal in magnitude to the vertical shear stresses of Fig. 5-2d. .如果，从如图 5.26所示梁中的中性轴处取出一个小的立方体V，根据平衡原理，它的竖向剪应力大小相等，方向相反。然而，如果仅有这两个应力存在，构件将不会平衡，而会旋转，因此，在两水平面上存在着相同数量的以保持平衡的水平向剪应力，也就是说，梁内的任一点，如图5-26所示的水平向剪应力等于如图5-26所示的竖向剪应力。
第六单元 Since external load is very rarely applied directly to the reinforcement steel can receive its share of the load only from the surrounding concrete. “Bond stress” is the name assigned to the shear stress at the bar-concrete interface which, by transferring load between the bar and the surrounding concrete, modifies the steel stresses. This bond, when efficiently, developed, enables the two materials to form a composite structure. The attainment of satisfactory performance in bond is the most important aim of the detailing of reinforcement in structural components.因为外部荷载很少直接作用，加强筋只承受了周围混凝土的部分荷载“粘结应力”是分布在钢筋混凝土内表面的剪力。他将荷
载传递到钢筋以及它周围的混凝土，改变钢筋的压力，这种粘结应力，可以高效地深度地使这两种材料成为组合结构粘结应力这一令人满意的作用，是加强结构构件细部的最主要的目的。
Bond strength was a more serious problem when only plain reinforcing bars were used. Bars with a deformed surface provide an extra element of bond strength and safety. On the other hand, the, behavior, of deformed bars, in particular the introduction of high-strength steels and large diameter bars, presented some new problems. This has necessitated a reex-ination of the conventional considerations of bond.
当仅仅使用光面钢筋时，粘结力是一个更重要的问题。表面不光滑的钢筋提供了更多的粘结应力，因此更加安全。然而，另一方面，变形钢筋，尤其是高强钢筋和大直径钢筋的使用也带来了一些新的问题。这就使对传统的需要考虑的粘结力的复查成为一种必要。
This equation indicates that when the rate of change of external bending moment (i.e., the shear force ）is high, the flexural bond stress can also exhibit high intensity. However, Eq.3 grossly oversimplifies the-situation, and it does not even approximately predict the magnitude of the actual bond stress. This is because the presence of cracks in the concrete at discrete intervals along a member results in additional bond stresses due to the tension carried by the concrete between the cracks. Even when the shear force is zero (region of constant bending moment ),bond stress will be developed. It has been observed, however,