Shear reinforced concrete

The main value of the counterforce technique is that it requires only half the explosive needed to accomplish the same result using standard formulas and placement. For example, a 14 inch diameter timber which requires 3% pounds of plastic explosive to cut conventionally can be sheared in two with counterforce charges of % pound each. Reinforced concrete piers 2 feet by 2 feet which can be broken conventionally by 17 pounds of explosive can be broken by counterforce charges of 4 pounds each. 

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... 

A comprehensive list of behavioral phenomena and physical attributes affecting the strength and stability of steel frames is compiled in White 1991. Some of the items listed include initial imperfections, residual stresses, initial strains, construction sequence, effects of simultaneous axial force, shear and moment on section capacities, P-dclta effect, local buckling and spread of inelastic zones in members. A similar list of items could be compiled for reinforced concrete and other structural materials. It is clear that a comprehensive advanced analysts can become quite... 

This type of construction may be totally reinforced concrete, or may be a combination of concrete or steel frames with cast-in-place or precast walls. Shear wall details should be developed using the seismic provisions of ACI 318, Chapter 21. Figures 8.10 and 8.11 are typical cast-in-placc details. 

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. 

A section though the reinforced concrete shear wall is shown on the following page. This section applies to each of the four sides of the building. 

Three types of jacketing methods using either reinforced concrete, steel or fiber as seismic retrofit to increase the flexural and shearing strength, and ductility of existing concrete piers are adopted. For steel jacketing method, liquid epoxy resin is effectively used for injection in the space between steel jacket and concrete piers. 

The secondary beams on the second floor had nibs at their ends which were supported on special corbels cast into the primary beams (Fig. 8.6). The shear and bond stresses in this connection were found to be greater than those normally adopted in reinforced concrete construction. The dowel used to locate the secondary beam was cast into the corbel and was to be surrounded by reinforce-... 

Similar to the design of flexural strengthening, the following states for the shear design of reinforced concrete (RC) members can be distinguished as the stmctural loads increase ... 

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

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 ... 

TTiantafillou, T. C. (1998). Shear strengthening of reinforced concrete beams using epoxy-bonded FRP composites. ACI Structural Journal 95(2) pp. 107-115. 

During the Itzmit earthquake some LNG tanks sustained by reinforced concrete columns were subject to important damages followed by the collapse of the basement, due to the insufficient shear strength of the columns (Figure 5b) (Sezen et al., 2007)... 

It is verified by an inspection that the bottom reinforcement consists of 7 bars of the diameter 25 mm and the reinforcement area is 3.44 x 10 m /m. Due to corrosion, the area is reduced to 3.26 x 10 m /m. In general three ultimate limit states of moment, shear and combined moment and shear are assumed to be important for deteriorating reinforced concrete bridges, Sarveswaran Roberts (1999). 

Midlands police car park soon after construction, as a result of a deficiency in conventional reinforcement, has been well publicised. Here again, additional bonded plate reinforcement was installed in order to control further cracking under live load. An 11 m span, 2 m deep reinforced concrete beam at a shop in Bootle was strengthened to provide a 10% increase in ultimate moment capacity. In so doing it was calculated that the mean horizontal shear stress resisted by the adhesive was 9.84 N/mm. ... 

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. 

According to the result in Fig. 8.10, a crack of which angle is over 60° could be classified as the tensile crack, because the shear ratio is less than 40%. Consequently, in one version of SiGMA (Ohtsu 2000), two vectors are always obtained and plotted. For the tensile crack, arrow symbol is employed. Results in a bending test of a reinforced concrete beam are given in Fig. 8.11 (Ohtsu 1995). 

Fig. 10.8. Located AE sources in reinforced concrete beams of (a) bending-mode failure and (b) shear-mode failure.

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