Shear reinforcement

Diagonal Tension. The allowable shear stress, v (psi), on a concrete section without shear reinforcement is ... 

Maximum acceptable values for ductility and support rotation are presented in Appendix 5.B. Predicted response must be compared to ductility ratio and support rotation limits to ensure that neither is exceeded. The engineer must determine if lower limits are appropriate. The values vary with material type, section type and protection category required. For reinforced concrete members, response limits are influenced by the shear reinforcing provided as well as the type of response (i.e., flexure, shear, compression). In general, for elements in which shear or compression... 

Shear reinforcing is not commonly used in wall and roof elements even though reinforced elements can undergo an extended plastic response. Shear reinforcing increases the diagonal shear capacity of the member, but more importantly, it... 

Usually, for shear design the well-known classical truss model is used. The shear strengthening design also requires knowledge and understanding of the cmcial failure modes of the externally bonded shear reinforcement (EBSR). 

State I Uncracked cross-section, i.e. no shear cracks exist, the concrete carries the whole load, virtually no stress in the shear reinforcement. 

State II Shear cracks exist, the internal shear reinforcement (ISR) is in the elastic region, the ISR and the EBSR carry the load in proportion to their stiffness. 

Figure 4.20 shows the principle of the three states. In the figure, the numbers 1 and 2 indicate the start of the yielding of internal shear reinforcement and the failure of externally bonded shear reinforcement, respectively. 

Several equations for the concrete contribution can be found in the relevant literature. However, this equation describes the design shear resistance of a RC member without shear reinforcement. It is important to note that this definition for the concrete contribution is different from the definition of State r given above in this section. To determine Erc, the load at the first shear crack should be calculated. Additionally, all the usual design verifications for RC (failure of the concrete struts, shift of moment line, etc.) have to be considered. For ductility reasons, the member should have a minimum internal shear reinforcement ratio, otherwise strengthening is not recommended. 

The ULS shear resistance of a member can be calculated using eqn 4.29. It is recommended that the concrete contribution (Fr c = 0) is neglected. The contribution of the internal steel stirrups, Fr, can be calculated using the truss model (assuming a shear reinforcement inclination of 90°) such that ... 

The contribution of the EBSR, Fr, , can also be calculated using the truss model (assuming a shear reinforcement inclination of 90°) such that ... 

Nominal design shear stress at perimeter Shear reinforcement required at perimeter ... 

Mitsui Y, Murakami K, Takeda K, Sakai H, Study on shear reinforcement of reinforced concrete beams externally bonded with carbon fiber sheets. Composite Interfaces, 5(4), 285-295, 1998. 

Area of concrete cross-section, net of steel reinforcement Area of FRP reinforcement Area of FRP shear reinforcement Area of one stirrup leg Area of steel reinforcement Young s modulus of elasticity of concrete Young s modulus of elasticity of FRP reinforcement Young s modulus of elasticity of the fiber itself Young s modulus of elasticity of steel reinforcement Design value of the maximum anchorage force transferred by the FRP reinforcement bonded on a masomy structure in the presence of a force perpendicular to the bonded surface area Shear modulus of adhesive Shear modulus of concrete Moment of inertia of transformed section... 

When the shear reinforcement runs parallel to the mortar joints, the above contributions can be calculated as follows ... 

Afw is the area of the shear reinforcement arranged parallel to the shear force, with a pace Pf orthogonally measured along the direction of the shear force... 

In the preliminary stage of the drawing up of the reinforcement plan, besides the evaluation of the mechanical properties of the members making up the structure, tests for the mechanical properties of the substrate should also be performed. The higher or lower incidence of the substrate characteristics is a function of the kind of application that is to be used either with reference to adherence applications (bending or shear reinforcement) or contact applications (passive confinement of masonry columns or pillars). In order to increase the mechanical properties of the substrate, it is possible to intervene in advance and apply composite materials by laying a suitable primer using special products. 

The shear reinforcement of concrete beams should not be performed with pultruded sheets, but, instead, with fabrics being impregnated on laying, because of the special geometry of the reinforcement, which, as underlined in the foregoing chapters, cannot be limited to the sides of the beams but it should be continuous, at least at the lower surface, if it is not possible to totally wrap the beam. 

Card 9.6 Stiuctuial shear reinforcement of concrete beams by carbon fiber fabrics... 

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