I'm wondering if Hilti is doing the calculations incorrectly for the concrete breakout strength of anchors in shear. If an anchor group close to an edge is subject to a shear load in one direction only, PROFIS seems to apply the psi_parallel factor correctly depending whether the shear force is perpendicular or parallel to the edge. If the anchor group is subject to shear forces in both directions at the same time, the factor defaults to 1.0 which is the case when the shear load is perpendicular to the edge. However, it always uses this lower factor to determine the capacity and then compares it to the highest applied shear load without considering whether this load is being applied perpendicular or parallel to the edge. In my opinion, and when comparing to other programs, the concrete edge failure check should be done for each edge condition and compared to the corresponding shear load in that direction. Otherwise, there are connections where even if 0.001kips of shear is applied in a direction perpendicular to an edge will result in the connection capacity being reduced by half when it's resisting a shear load in the other axis that is several orders of magnitude higher.
Hi Santiago,
See the following information regarding how the software calculates parallel and perpendicular edges which discusses torsion moments. 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. PE 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.
Respectfully,
Emily