Shear Strength

This section discusses the shear checks that are implemented within RAM Concrete Wall and the assumptions made by the program when performing the necessary calculations. The table below provides a summary of the sections of ACI 318-11 covering shear evaluation that have been implemented within the program.

Table 1. Summary of implemented ACI 318-11 sections covering shear strength. ACI 318-11 Shear Strength Checks
Code Section	Referenced Code Sections
14.2.3	11.9.1 - 11.9.7
14.3.1	11.9.9.1
21.9.4.1	-
21.9.4.2	-
21.9.4.5	-

The program performs the shear evaluation on Section Cut Segments. This is in contrast to the axial-flexural evaluation, which is performed on Section Cuts. The value of d as described in ACI 11.9.4 is taken as 0.8 multiplied by the length of the Section Cut Segment for in-plane shear evaluations. The design forces used are those acting on the Section Cut Segment. Since a Section Cut Segment is a planar entity, there will be only a single component of shear and a single component of flexure (in addition to axial load), both acting in the plane of the segment.

Figure below shows an example of two Section Cut Segments in a Wall Panel (the Wall Panel is highlighted in orange). Wall Panel 86 contains two Section Cut Segments. Section Cut Segment "SC1H:1C" is one segment within Section Cut "SC1H:1," which forms three segments that wrap around the wall core. A separate shear check will be performed for this segment, as well as the two other segments that comprise the Section Cut. Section Cut "SC1H:3" contains only one segment and thus the Section Cut Segment label is the same as the Section Cut label. A separate shear check will be performed for this segment as well.

Horizontal Section Cut Segments within a Wall Panel.

The In-plane and Out-of-plane shear capacity calculations use net thickness of the section cut segment, that means that when reveal depths are assigned to a wall panel (See Assign Wall Panel Reveal Depth), the shear capacity will not consider the concrete section of the reveals.

Chapter 11

This section references Sections 11.9.1 through 11.9.7. Section 11.9.2 specifies that the in-plane shear evaluation of walls shall be based on ACI equations (11-1) and (11-2). Out-of-plane shear evaluation is also checked by the program under those requirements.

ϕV_n ≥ V_u

ACI (11-1)

V_n = V_c + V_s

ACI (11-2)

In-plane Shear For walls subject to axial compression, V_c is calculated in accordance with 11.9.5.

V_{c} = 2 λ \sqrt{{f^{'}}_{c}} h d

where

h	=	thickness of the Wall Panel being evaluated
d	=	0.8l_w (per Section 11.9.4)

For walls subject to axial tension, V_c is calculated in accordance with 11.2.2.3.

V_{c} = 2 (1 + \frac{N_{u}}{500 A_{g}}) λ \sqrt{{f^{'}}_{c}} b_{w} d

ACI (11-8)

where

N_u	=	Combined axial load acting on the Section Cut being evaluated
A_g	=	Gross concrete area of the Section Cut Segment being evaluated

V_s is calculated according to Section 11.9.9.1.

V_{s} = \frac{A_{v} f_{y} d}{s}

ACI (11-29)

where

A_v

Area of horizontal shear reinforcement within spacing, s. RAM Concrete Wall uses the bar area and nominal spacing associated with the Bar Pattern used for the Wall Panel that the Section Cut Segment intersects. Thus, even if you change individual bars within the Wall Panel, the patterned bar will still be used for this calculation.

Out-of-plane Shear

For walls subject to axial compression, Vc is calculated in accordance with 11.2.1.2:

V_{c} = 2 (1 + \frac{N_{u}}{2,000 A_{g}}) λ \sqrt{{f'}_{c}} b_{w} d

ACI (11-4)

For walls subject to axial tension, Vc is calculated in accordance with 11.2.2.3 Check Eq ACI (11-8) where, for both cases:

where

Effective depth. The program considers the minimum effective depth calculated for the primary and secondary face of the wall without considering reveals and assuming that the bar in tension is orthogonal to the section cut.

V_s = 0

Chapter 21

The shear strength specified in 21.9.4.1 is calculated as:

V_{n} = A_{c v} (α_{c} \sqrt{{f^{'}}_{c}} + ρ_{t} f_{y})

ACI (21-7)

A_cv is calculated with the net thickness (without considering reveals).

The parameter α _c is a function of the length and height of the wall segment. RAM Concrete Wall uses the length of the Section Cut Segment to determine l_w, and uses the transverse distance associated with the Section Cut Segment to determine h_w. For example, for the Wall Panel shown in Figure below, Section Cut Segments SC1H:79 and SC1H:80 will have an h_w value equal to the height of the door. Whereas Section Cut Segments SC1H:19B and SC1H:81 will have an h_w value equal to the height of the entire Wall Panel.

Horizontal Section Cut Segments within a Wall Panel.

The parameter ρ_t is calculated as the reinforcing ratio of the Bar Pattern parallel to the Section Cut Segment being evaluated considering the gross thickness.