What is SOFA Method?

The basis for anchor design in Europe is the design approach given in EN 1992-4. However, there are many cases where solutions cannot be found by strictly following this standard. Therefore, in addition to the design provisions of EN 1992-4, Hilti offers a design approach per the so-called “SOFA method”. SOFA stands for “Solution for Fasteners” which is a design method which goes beyond existing codes. The provisions in SOFA are based on state-of-the-art industry research and undergo extensive review by technical key experts before implementation into PROFIS Engineering.

Both for static and dynamic (seismic and fatigue) loading, EN 1992-4 covers a limited range of anchor layouts as shown in Figure 1. The individual anchor spacing in one direction must be the same, and the maximum possible anchor layout is restricted to a 3x3 rectangular configuration when not bound by an edge. Other shapes (e.g., circular or free location of anchors within the steel plate) are outside of the scope of EN 1992-4. The allowed anchor layout depends on the following parameters:

• Hole clearance between steel plate and fastening: Depending on the location of the fastening relative to the clearance hole in the steel plate, not all anchors are assumed to evenly resist the shear load. The maximum possible clearance hole is defined in Table 1.
• Load direction: According to EN 1992-4, the fastening can be loaded in tension, shear or a combination between tension and shear.
• Location of the fastening relative to the edge of a concrete member: EN 1992-4 distinguishes between fastenings located close to the edge and far away from the edge. If the edge distance, ci, of the fastening in all directions (i = 1 and 2) is the larger of 10hef and 60dnom, the fastenings is considered far away from the edge. If not, then the influence of the edge distance on the concrete related failure modes needs to be considered.

Table 1 – Hole clearance (table taken from EN 1992-4)

a)    Fastenings without hole clearance for all edge distances and for all load directions, and fastenings with hole clearance according to Table 1 situated far from edges for all load directions and fastenings with hole clearance according to Table 1 situated near to an edge loaded in tension only

b)    Fastenings with hole clearance according to Table 1 situated near to an edge for all load directions

Figure 1 – Anchor configurations covered in EN 1992-4 (picture taken from EN 1992-4)

The SOFA design method offers three main features:

1.   Design provisions for tension, shear, and combined tension and shear for anchor layouts beyond the scope of EN 1992-4, allowing design coverage up to 99 anchors in a group.

2.   Improved shear design provisions to better utilize the fastening for the failure mode “concrete edge failure”.

3.   Design provisions for loading scenarios and anchor configurations not covered in EN 1992-4 (e.g., stand-off close to the edge of a concrete member)

Both for 1) and 2) Profis Engineering (PE) requires filling the gap between fastener and steel plate to guarantee that all fasteners are loaded equally.

This article provides first information on what SOFA stands for and what advantages this method provides to a designer. The article is followed by three additional articles providing more in-depth information about the main features of SOFA.

1)   Anchor configurations according to EN 1992-4 arranged close to the edge of a concrete member: How to optimize the design in PE?

2)   Rectangular and irregular anchor configurations beyond EN 1992-4: How does PE design such anchor configurations?

3)     SOFA stand-off design: Improved design provisions and calculation