Code References
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The shear resistance of precast concrete components must meet the following requirement (22.5):
(eq. here)
('where:' list in word doc or here?)
where:
Vc = nominal shear strength provided by concrete
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For simply supported horizontal members, 9.4.3.2 has defined the critical section for shear to be a distance d from the face of the support for non-prestressed members and h/2 for prestressed members. If a concentrated load is present between the critical section and the face of the support, then the face of support should become the critical section. For members that do not have the loads applied at the top of the section or are non-simply supported, then the critical section should conservatively be located at the face of the support.
If the user requests that If the non-composite section be is being used for shear resistance, then the non-composite height is used to calculate d and H. If the user requests that the composite section be is being used for shear resistance, then the composite height is use. The user must also make an affirmative response to move the critical section away from the support face.
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All values of f’c used in determining Vc are reduced by the appropriate factor if using lightweight concrete. Note that the analysis uses the base area of prestressing strand, ignoring development length, to determine if a member is prestressed or non-prestressed.
For For composite members, the shear area (and the depth thereof), is dependent on whether the composite topping is to be considered a part of the shear resisting section. The final strength of the precast section at all times to calculate the shear resistance, even when the user selects the use of the composite section. The full depth is also used in the calculation of d (with a lower limit of 0.8*H), except where d is used in the term V*d/M, then the actual d is used with the limit of 0.8*H.
For For all beams (both prestressed and non-prestressed), the minimum shear strength is 2 * sqrt(F’c).
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The shear area is calculated based on the polygons which make up the cross section, which are used in place of the bd term in the equations for Vc. These polygons encompass only the area of the non-composite section. Some sections (typically the sections which consist of webs and top/bottom flanges), only the polygon which encompasses the web is used (and extending this polygon into the top and bottom flanges, if present). This polygon is extended into the topping if the composite shear resistance section option is selected by the user.
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When no transverse reinforcement has been defined, the amount of shear required to be resisted by shear reinforcement, Vs, is calculated by:
(eq)
The strength of the provided transverse reinforcement, when applicable, is computed by summing all of the zones the location overlaps with. Eriksson Beam computes the total transverse provided based on the transverse inputs and use in ACI 318-14 Eq. 22.5.10.5.3.
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The cross section limits are checking against ACI 318-14 22.5.1.2. If the limits fail and error will be displayed in the analysis report.
Shear Options (show here or in program operation?)
Options | Description |
|---|---|
Treat as slab | |
Limit shear per ACI 318-14 9.4.3.2 | |
Composite Behavior |
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In the case of single and double tees, when they are simply supported, uniformly loaded, and when they require little or no shear reinforcing as calculated for Avcw, and approximately 0.04 in2/ft or less of shear reinforcing as calculated for Avci, the engineer may omit the leg mesh in the middle 80% (+/-) of the span.
For the case of hollow core slabs, if the untopped section depth is <= 12.5 in., then no minimum shear steel is required. If the untopped depth is > 12.5 in., then minimum shear reinforcement is not required where Vu <= 0.5φVcw. Currently, the analysis does not take this provision into account.
Note that required shear reinforcement does not include any suspension steel that may be required for ledges. A separate ledge analysis is required.
Critical section for shear. The critical section for shear is based on the depth of the resisting element, and assumes that the loads on the beam (including self-weight) between the critical section and the support go directly into the support without the mechanism of beam action (acting kind of like a small column). The depth used to calculate the critical section should be based on the cross section used to resist shear. This approach seems rational to me, as the loads will be relatively small (basically the weight of the composite beam and not much more). If there is an applied concentrated load between the critical section and the support, then the critical section is the face of the support.
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PCI Industry Handbook Committee, PCI Design Handbook, 8th Ed., PCI, Chicago, 2017.
(still need to add keywords)