Q1.1
EN 1992-4, Clauses 7.2.1.2(2)(a) and 7.2.2.2(3)(a), limits the diameter of supplementary reinforcement for concrete cone failure in tension and concrete edge failure in shear to 16mm. How does IDEA StatiCa enforce this limitation when larger-diameter bars are present in the model?
Answer
The reinforcement definition will take place in the next section. What differentiates our solution is that we can model all reinforcement not only supplementary.
Also note that in EN 1992–4:2018, §7.1(10) it is stated that: “In the calculation of the area of supplementary reinforcement, the area of any underutilized reinforcement provided in the member for other purposes may be included provided such reinforcement meets the detailing requirements in this document.”
There is no solution I know of that can do that other than Detail 3D (next section).
Q1.2 (follow-up to Q1.1)
My only concern relates to the final condition of Clause 7.1(10): “provided such reinforcement meets the detailing requirements in this document.” This would appear to mean that reinforcement originally provided for other purposes must still comply with the detailing requirements for supplementary reinforcement, including the maximum bar diameter of 16 mm. Do you mean that the 16 mm diameter limitation and the associated detailing requirements are not applicable when using the Detail 3D methodology?
Answer
As you will see shortly, the user defines the reinforcement, so it is up to the user to respect the detailing rules or omit any reinforcement. However the method is validated and due to the non-linear underlying methodology it will naturally mobilize only reinforcement close to the fasteners as it accounts for the local effects.
Let me clarify that by “omit any reinforcement” I mean “omit any reinforcement you don’t want to be accounted”. You can also experiment by activating and deactivating reinforcement on the same model in case you have any doubts.
Q1.3 (follow-up to Q1.1)
I am already familiar with Detail 3D. My question was mainly about the normative justification, as I was looking for a defensible argument to present to clients when bars larger than 16 mm contribute to the load-transfer mechanism. Is there any normative basis or validation document supporting their consideration despite the 16 mm limitation specified in EN 1992-4?
Answer
The main source of this limitation is a pair of papers in Der Prüfingenieur (2016, 2018) by Eligehausen, Asmus and Sharma (University of Stuttgart / IEA). Eligehausen is the convenor of CEN/TC 250/SC 2/WG 2, the working group responsible EN 1992-4.
In this paper it is noted that with a large cross-section of supplementary reinforcement, failure can occur by crushing of the concrete struts. The CEN/TS and EN models do not cover this mode and it is meant to be avoided by limiting the diameter to 16 mm. The authors add that this is adequate in usual applications, but with many stirrups the failure load can be overestimated. The 2016 paper says the same for shear: strut failure is not treated and is supposed to be prevented by the φ ≤ 16 mm limit. The strut in question forms between the head of the headed stud and the bend of the stirrup.
ACI 318 gives a parallel limit with a geometric justification. The commentary (R17.5.2.1, ACI 318-25) writes:
- the test data behind the provisions were limited to bars of about No. 5 diameter (≈16 mm)
- the larger bend radii of larger bars can significantly reduce the effectiveness of the reinforcement for shear, so bars larger than No. 6 are not recommended
Also note that a dense cage of Æ16 legs can still reach failure.
However, in Detail 3D we are using the CSFM method, and the stress and strain of concrete is meticulously checked. As such, the crushing of concrete is one of the modes of failure checked by our method. In any case, it is up to the user to respect the detailing rules and we rarely see stirrups larger that 16mm.
Q1.4
As we are doing the embed design in IDEA StatiCa Detail, what checks are performed and how are they helpful in IDEA StatiCa Connection? In ACI code, supplementary reinforcement is only considered in case the concrete fails, but IDEA StatiCa covers both concrete and steel capacity based on the stress, so we are deviating from the code recommendation. Please clarify.
Answer
A cast-in or embedded plate requires checking of both the steel and concrete elements. This separation of concerns is shown in this picture by the dashed line, reflecting the separation of design responsibilities for the two types of elements. The steel elements — steel member, steel plates, bolts and welds — are all checked in IDEA StatiCa Connection.
The model is then transferred to IDEA StatiCa Detail for an accurate check of the fasteners (anchors and studs), concrete and reinforcement. This is an essential step, as a different methodology is used for these entities. In addition, Detail 3D can handle accurate concrete geometry, accurate reinforcement definition, additional loads on the concrete elements and, of course, different boundary conditions.
Q1.5
Within the combined check under both shear and tension, what safety factor do we use here?
Answer
Our solution is design oriented. This means that the standard code safety factors are used.
