PROFIS ENGINEERING
Extrapolating ACI 318 Provisions for Shear – Nonuniform Square or Rectangular Anchor Layouts
Figure 4.
Reference Figure 4 [ 9 ]. It illustrates an anchorage consisting of sixteen anchors with a shear load( V ua) acting towards the x- edge on the anchor columns. The anchor spacing in the x direction between columns varies. The anchor spacing in the y direction between rows also varies, but s y12, s y23 and s y34 are less than 3c a1, col 1 so the anchors in each column will be assumed to act as a group. The shear load( V ua) acts at the centroid of the plate; however, the irregular anchor spacing between rows and columns creates a torsion moment on the anchorage. The magnitude of shear load assumed to act on a particular column will be influenced by this torsion moment.
A resultant shear load will act towards the one fixed edge in the x- direction. The unequal spacing between columns means that concrete breakout in shear for some columns may be defined by Case 1 / Case 2, while concrete breakout in shear for other columns may be defined by Case 3.
Determining whether Case 1, Case 2 or Case 3 controls for a particular column in Figure 4 [ 9 ] requires consideration of the following parameters:
• Anchor columns assumed to resist shear load( e. g. col 1 and / or col 2, 3, 4)
• Distance of the near column anchors( anchors in col 1) to the fixed edge( e. g. c a1, col 1).
• Spacing between columns in the direction of the applied shear load( e. g. s x12, s x23, s x34).
• Check s xnn for any two adjacent columns versus c a1, col 1.
• For any two adjacent columns, determine whether Case 1 / Case 2 or Case 3 are applicable
• Based on which case is applicable, determine the magnitude of shear load( V ua, col n) assumed to act on each relevant column.
• Calculate the design concrete breakout strength( ϕV cbg, col n) for each relevant column using the edge distance in the direction of the shear load for that column( c a1, col n).
• Check the utilization for each relevant column( V ua, col n / ϕV cbg, col n).
• Design is satisfied if( V ua, col n / ϕV cbg, col n) ≤ 1.0 for each column being considered.
• MAX { V ua, col n / ϕV cbg, col n } controls the anchorage design with respect to concrete breakout in shear.
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