Under Rigid calculation assumptions, Hilti correctly applies psi_parallel = 2.0 per the ACI code. When I adjust the calculation type to CBFEM, the psi_parallel factor reduces to 1.0, and concrete edge failure in the parallel direction occurs. When comparing the two reports, the demands are within 1% of each other, while the capacity for CBFEM has been reduced by 50%. What is the purpose of not multiplying the 2.0 factor for parallel edge breakout for CBFEM calculations, but not Rigid?
This effect also happens when adding an eccentricity to the shear force along the plane of the wall. For example, with the shear load located as centered between two rows of anchors, Hilti calculates psi_parallel = 2.0. When I offset that load by a small amount (say 0.1"), psi_parallel = 1.0, and the parallel breakout utilization doubles despite the load on the anchor closest to the edge only increasing by ~1%.
Hi Brian,
The following may be applicable: Section 17.5.2.1 within the ACI 318-14 Chapter 17 anchoring-to-concrete provisions requires analyzing edges perpendicular to the direction of the shear force (17.5.2.1a or 17.5.2.1b) as well as edges parallel to the direction of the shear force (17.5.2.1c). Section 17.5.2.1c states that edges parallel to the direction of the shear force are permitted to be twice the value determined from either equation 17.5.2.1a or 17.5.2.1b as well as taking the modification factor for edge effect, Ψed,V, equal to 1.0. The PROFIS Engineering software represents the provisions of Section 17.5.2.1c through the modification factor Ψparallel,V. For edges perpendicular to the direction of the shear force, Ψparallel,V = 1.0. For edges parallel to the direction of the shear force, Ψparallel,V = 2.0.
If there is a slight angle produced as a resultant of shear and/or moments in different coordinate directions, PROFIS assumes there is no “true parallel” edge (Ψparallel,V = 1.0). The resultant force may be because when a nonrigid plate is assumed (CBFEM analysis), the shear load is calculated as acting eccentric with the centroid of the anchor group. This creates a torsion moment. The software assumes the resultant shear load acts towards the nearest fixed edge when a torsion moment acts on the anchor. The shear load may not distribute equally among the anchors. The PROFIS Engineering software is limited to a strict interpretation of the ACI 318-14 Chapter 17 anchoring-to-concrete provisions.
Regards,
Emily