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American University of Sharjah
College of Engineering
Civil Engineering Department
Semester: Spring 2008
CVE411: Structural Concrete Design
ACI Provisions for Design of Shear Walls
1- The factored beam shear must be equal to or less than the design shear strength of the wall.
2- The Design shear strength of a wall is equal to the design shear strength of the concrete plus that of the shear reinforcing
3- The shear strength at any horizontal section in the plane of the wall may not be taken greater than (ACI section 11.10.3)
4- In designing for the horizontal shear forces in the plane of a wall, d is to be taken as equal to where is the horizontal wall length between faces of the supports, unless it can be proved to be larger by a strain compatibility analysis (ACI section 11.10.4)
5- ACI Section 11.10.5 states that unless a more detailed calculation is made (as described in the next paragraph), the value of the nominal shear strength used may not be larger than for walls subject to a factored axial compressive load , the value of may not be larger than the value obtained with the following equation:
(ACI Equation 11-8)
6- Using a more detailed analysis, the value of is to be taken as the smaller value obtained by substituting into the two equations that follow, in which is the factored axial load normal to the cross section occurring simultaneously with , is to be considered positive for compression and negative for tension (ACI section 11.10.6)
(ACI Equation 11-29)
(ACI Equation 11-30)
The first of these equations was developed to predict the inclined cracking strength at any section through a shear wall corresponding to a principal tensile stress of about at the centroid of the wall cross section. The second equation was developed to correspond to an occurrence of a flexural tensile stress of
at a section above the section being investigated. Should
Be negative, the second equation will have no significance and will not be used.
7- The values of computed by the two preceding equations at a distance from the base equal to (whichever is less) are applicable for all sections between this section and one at the wall base (ACI section 11.10.7).
8- Should the factored shear be less than computed as described in the preceding two paragraphs, it will not be necessary to provide a minimum amount of both horizontal and vertical reinforcing, as described in ACI section 11.10.9 or chapter 14 of the Code.
9- Should be greater than , shear wall reinforcing must be designed as described in section 11.10.9 of the Code.
10- If the factored shear force exceeds the shear strength , the value of is to be determined from the following expression, in which is the area of the horizontal shear reinforcement and is the spacing of the shear or torsional reinforcing in a direction perpendicular to the horizontal reinforcing (ACI section 22.214.171.124)
(ACI Equation 11-31)
11- The amount of horizontal shear reinforcing (as a percent of the gross vertical concrete area) shall not be less than 0.0025 (ACI section 126.96.36.199)
12- The Maximum spacing of horizontal shear reinforcing shall not be greater than or 18 in. (ACI section 188.8.131.52).
13- The amount of vertical shear reinforcing (as a percent of the gross horizontal concrete area) shall not be less than the value given by the following equation, in which is the total height of the wall (ACI section 184.108.40.206).
(ACI Section 11-32)
It shall not be less than 0.0025 but need not be greater than the required horizontal shear reinforcing .
For high walls the vertical reinforcing is much less effective than it is in low walls. This fact is reflected in the preceding equation, where for walls with a height/length ratio less than 0.5, the amount of vertical reinforcing required equals the horizontal reinforcing required. If the ratio is larger than 2.5, only a minimum amount of vertical reinforcing is required (that is).
14- The maximum spacing of vertical shear reinforcing shall not be greater than or 18 in. (ACI 220.127.116.11).
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