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I am using strut-and-tie method to design a corbel. I noticed that Eurocode mentions strut-and-tie only in section 6, which is ultimate limit state design. How do I perform serviceability limit state design for the corbel using strut-and-tie method?

Jordan
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One important thing to remember about the strut-and-tie method is that as a lower-bound method it is based on the plasticity theory. That is, the principle is to find a safe and statically admissible stress distribution, and if any such distribution is possible the structure will not collapse at this load. This principle only makes sense for the ultimate limit state. However, if the assumed load path is close to what linear elasticity theory would give, the stresses will be a decent approximation to a detailed finite element calculation and may very well be sufficiently accurate. Therefore, the difficult part of the calculation is knowing how well your strut-and-tie model aligns with elasticity theory.

There is a bit more on this in EN 1992-1-1 section 5.6.4.

But if you do your SLS check with a strut-and-tie model, the actual calculations are quite straightforward. Calculate the stress in concrete and reinforcement and check them against the SLS limits in section 7.2. Use the reinforcement stress to calculate a crack width and check that against the limit from section 7.3. And you're done. The strut-and-tie approach will not give you a way to calculate a deflection but for a typical corbel that wouldn't be very interesting anyway.

Wasabi
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ingenørd
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  • How do I derive the neutral axis depth for crack width check using STM? – Jordan Jan 22 '19 at 01:42
  • You can use the distance to the strut. – ingenørd Jan 22 '19 at 07:39
  • It seems arbitrary to do that. For beam method, we can calculate the neutral axis precisely. Do you have a worked example for this? – Jordan Jan 23 '19 at 04:28
  • That's not really the arbitrary part — the exact location of the neutral axis will usually have little influence on the crack width calculation. The arbitrary part is the stress calculation as I explained above. You have chosen a calculation method which is only an approximation, so you should not expect precise results. And sorry, no, I don't have a worked example that I can publish. – ingenørd Jan 23 '19 at 08:39