Several Eurocodes are relevant for anchoring:
- EN 1993-1-8 (first and second generation)
- EN 1992-4
- EN 1992-1-1 (reinforcement design and concrete in compression
- EN 1994-1-1 (headed studs)
The following anchor/fastener types are
- Post-installed:
- Straight
- Cast-in:
- Washer plate - Circular
- Washer plate - Rectangle
- Headed stud
- Hook
- Reinforcement
IDEA StatiCa Connection enforces the design checks according to the anchor type:
- Post-installed:
- Straight - EN 1992-4
- Cast-in:
- Washer plate - EN 1993-1-8
- Headed stud - EN 1992-4
- Hook - EN 1993-1-8 + EN 1992-1-1 with halved bond strength
- Reinforcement - EN 1992-1-1 material model with an increased safety factor \(\gamma_{M2}=1.25\) for welds or threads at the reinforcement connecting to the base plate
IDEA StatiCa Detail allows for customization suitable for advanced users. The user should sufficiently explain their choice, and, if in doubt, choose the design code with the lower resistance.
Note that IDEA StatiCa Detail, to be aligned with SCI's The Design of Cast-in Plates, considers the safety factor of \(\gamma_s\ = 1.15) for reinforcement as opposed to Connection.
EN 1993-1-8:2024
The second generation Eurocode will become valid in 2027, but even now it contains the expert knowledge that European countries within the CEN organization have agreed upon. It makes a distinction between anchor bolts (traditional long anchors) and fasteners between steel and concrete (typically post-installed); however, without a clear definition. The distinction can be made based on governing failure mode – anchor bolts fail in a ductile manner (by steel failure in tension or in shear), and fasteners may fail in a brittle failure mode (concrete-related). The problem is that the resistance differs among the codes, e.g., steel resistance in tension and especially in shear between EN 1993-1-8 and EN 1992-4. Another option is to distinguish by the anchor or fastener type and application – long anchor with a washer plate is the anchor bolt, and short post-installed anchor is a fastener between steel and concrete. Ideally, both such conditions should be met – anchor type and governing failure mode.
Figures taken from EN 1993-1-8:2024 and EN 1992-4
EN 1993-1-8 provides the load resistances for:
- Anchor bolts in tension - steel failure mode (A.18.1)
- Anchor bolts in shear - steel failure mode (A.20)
For other failure modes, it refers to EN 1992-4:
- Steel failure of the fastener between steel and concrete
- Concrete cone failure
- Pull-out failure
- Combined pull-out and concrete failure
- Concrete splitting failure
- Concrete blow-out failure
- Steel failure of reinforcement
- Anchorage failure of reinforcement
Furthermore, EN 1993-1-8 provides the load resistances for bolts, anchor bolts, and, although not explicitly stated, also for fasteners between steel and concrete in Table 5.9 for:
- Bearing resistance of the base plate
- Punching shear resistance of the base plate
- Combined shear and tension of anchor bolt loading interaction
Note that at the moment, these checks are not provided by IDEA StatiCa Connection, because of the following reasons:
- The base plates are typically thick, and the resistance of anchors is rather low compared to the resistance of the base plates. Therefore, bearing resistance and punching shear resistance very rarely govern the design. However, when the user chooses a thin base plate, these failure modes should be verified manually.
- The interaction of tension and shear was determined for bolts by a great number of tests. The anchors have their shear failure limited to \(F_{vb,Rd} = \frac{(0.44-0.0003 \cdot f_{yb}) \cdot f_{ub} \cdot A_s}{\gamma_{M2}}\) as opposed to the bolt shear failure \(F_{v,Rd} = \frac{0.6 \cdot f_{ub} \cdot A_s}{\gamma_{M2}}\). The figure below shows the interaction diagram of an anchor made of grade 4.6 (\(f_y = 240\) MPa – the highest anchor shear strength to bolt shear strength ratio) underlayed by experiments in Eurocode background documentation [1]. For bolt design, three interaction diagrams are used across various codes:
- Eurocode interaction
- Quadratic interaction (e.g., EN 1992-4, alternative AISC, AS, CSA, IS)
- AISC interaction
It can be seen that the interaction check for anchors with limited shear strength is not strictly necessary, which is supported by Explanation at Steel support from the Netherlands:
For checking of normal bolts, Table 3.4 of EN 1993-1-8 includes a formula for the interaction of normal force and shear force. However, this formula only applies to bolts in a normal (steel-steel) connection and not to anchors in a column base plate connection. When checking the shear resistance of the anchor, a tensile force in the bolt equal to the resistance to yielding was already taken into account; see Eq. 6.2 of Cl. 6.2.2 (7) of EN 1993-1-8. The actual tensile stress that occurs in the anchor is therefore not relevant. This calculation method is based on tests carried out at the TU Delft. These calculation rules from the Eurocode are identical to the calculation rules from the TGB series. The explanation of the calculation rule is included in NEN 6772 but not in EN 1993-1-8. For column base plate connections, it is therefore sufficient to only carry out the separate checks for tension and shear.
This refers to experiments published in the Heron Journal that form the basis for Eurocode formulas.
At the CEN/TC 250/SC 3/WG 8 meeting in Oslo, the issue was discussed, and most working group members agreed that the interaction should be performed regardless. Since patch 26.0.3, the interaction of tension and shear will be performed for cast-in anchors in IDEA StatiCa Connection again.
EN 1992-4:2018
The scope of EN 1992-4 is severely limited in scope. It covers only a rectangular bolt layout with a base plate edge parallel to the concrete edge, where anchors are in holes with standard hole clearance. This Eurocode covers all the concrete-related failure modes for all anchor types:
- concrete cone breakout in tension
- concrete edge failure
- concrete side-face blowout failure
Figure taken from EN 1992-4
Slotted holes are not considered...
Combination of anchor types
Issues: stiffness - different for different load types - e.g., creep for sustained loading of bonded anchors, depending on temperature...
More base plates at one concrete block
Extremely difficult interactions - Connections directly giving red cross
Anchoring to different block surfaces
References
[1] H. H. Snijder, D. Ungermann, J. W. B. Stark, G. Sedlacek, F. S. K. Bijlaard, and A. Hemmert-Halswick, "Evaluation of test results on bolted connections in order to obtain strength functions and suitable model factors — Part A: Results," Eurocode 3 Editorial Group, Background Documentation to Eurocode No. 3 "Design of Steel Structures, Part 1: General Rules and Rules for Buildings," Chapter 6, Document 6.01, Rep. BI-88-087, IBBC-TNO, Delft, The Netherlands, Jun. 1988 (issued Mar. 1989).