Direct shear, reinforced concrete

Direct Shear. For type I cross-sections (0 < 2°) the concrete between the flexural reinforcement Is capable of resisting direct shear. However, because cracking at the support yield line reduces the shear capacity, diagonal bars must be provided to at least resist the shear capacity of the concrete, v. For type II and III cross-sections (0 > 2 ), with little or no concrete shear resistance, The diagonal reinforcing bars must be designed to resist the entire shear load at the support. 

The primary failure mechanisms encountered in reinforced concrete buildings arc flexure, diagonal tension, and direct shear. Of these three mechanisms,. flexure is preferred under blast loading because an extended plastic response is provider prior to failure. To assure a ductile response, sections are designed so that the flexural capacity is less than the capacity of non-ductile mechanisms. 

M. Valle and 0. Buyukozturk, Behavior of fiber reinforced high-strength concrete under direct shear . Ad Mater. J. 90,1993,122-133. 

Carbon/Aramid Fiber Sheet Jacketing Method. The application of carbon/aramid fiber sheet for the reinforcement of concrete pier is adopted when restricted conditions are present on site, such as no permit of sectional increase due to clearance limit or weight increase on the foundation. The sheet in longitudinal direction is effective to increase the flexural strength and the sheet in transverse direction acts as lateral reinforcement to raise the shear strength. Particularly the fiber sheet is concentrically bonded at the termination of longitudinal rebar at the mid-height. 

In the last few years, dispersed steel fibres were successfully used in prestressed concrete bridge beams where they replaced mild steel reinforcement. As one of many examples, in Figure 14.1 the cross-section of the bridge deck for Saint-Pierre-la-Cour (France) is shown. Ten prestressed concrete beams form the main structure of the bridge deck. Additional plates are used as the lost shuttering for ordinary concrete cast in situ with ordinary reinforcement and covered with road pavement. The prestressed beams and plates are made with Ductal. Thanks to 3% volume of dispersed steel microfibres in Ductal matrix, there were neither stirrups nor other mild steel reinforcement needed against shearing and local stresses in the beams and considerable economy was obtained in time and the cost of labour. This is certainly a new and important direction for the future application of fibres in structural elements without any other reinforcement. 

Shear strength contribution carried by concrete depends on concrete compressive strength, (Q shear span, Ly), section depth, (d) axial load, (P) and gross area section, (Ag), while shear strength contribution carried by reinforcements depends on transverse reinforcement area (Ajv ) within a spacing (s) in the loading direction. 

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