Curved Beam vas Cambering a Beam

[Arun4567777]

Dear Members,

1. Will curving a beam have the same effect as cambering a beam in terms of achieving the desired structural performance and deflection characteristics?

2. When calculating the elastic deflection of a steel beam with a natural mill camber of 10mm due to fabrication tolerances, should the natural mill camber deflection be added to the computed elastic deflection to obtain the total deflection, especially when designing for stringent deflection limits?

 

[Tomfh]

Camber can have some effect on slab thickness, eg if the camber means the beam is poking up slightly above an otherwise level deck, vs the beam hanging slightly below the top of the formwork.

 

[Arun4567777]

I'm in the initial stages of my career, and a specialist is handling this task. The concrete's self-weight is 4.5 kN/m², while the remaining 25 kN/m² load is due to uniformly distributed racking loads which will come after slab has set. I'm assuming a downward camber to explore a hypothetical scenario: if there's a 1% chance the beam is erected with a downward camber. After the slab is poured and achieves flatness, it will be subjected to a 25 kN/m² load, causing the non-composite beam to deflect by 7mm. Considering the 1% probability of a 6mm natural mill camber in the downward direction, should I add this to the 7mm deflection?"


From the outset, I've been seeking clarification on this specific point. I concur that erecting the beam with a downward camber is impractica with no logic. However, for theoretical purposes and to gain a deeper understanding, I'm exploring a hypothetical scenario where, due to a lack of knowledge or oversight, the beam might be erected with a downward camber. This thought experiment allows me to better comprehend the implications and potential consequences of such an action.

 

[EngDM]

A lot of beam connections are installed such that the connection is towards the top of the beam. For the beam to be installed incorrectly, the holes for the connection (assuming a knife plate or some other bolted connection) would also need to be fabricated in the wrong place. There would have to be quite a lot of mistakes for that to even happen. You're going to waste a lot of time if you dig too deep into hypotheticals.

 

[Smoulder]

@Arun Your question has been answered several times already but people also explained details so you can figure it out yourself next time. Using latest numbers of 6mm beam camber and 7mm deflection:

- Bottom of the beam will be 13mm out of straight.

- Top of beam also 13mm out of straight.

- Slab is cast on top of the beam (?) so slab soffit also 13mm out because it follows the top of beam. The slab will be 200mm thick at beam ends and 206mm thick at beam midspan.

- Top of slab will be 7mm out of straight. Sounds like this is the number you are interested in.

BUT also take account of slab construction tolerance. It won't be perfectly flat. Safest to add the whole tolerance to calculated deflection and check the total < 10mm.

 

[HDStructural]

I'm jumping into this late, sorry if this has already been discussed. Why can't you just use grout pads under the robotics equipment to ensure it is perfectly level. As long as the LL deflection of your structure meets their system requirements, it shouldn't matter if the structure deflects too much under dead load because the grout pads will ensure that the robotic equipment will start at "perfectly level" and the only other deflections it would see are the live load deflections which meet their requirements.

 

[Arun4567777]

@ Smoulder To confirm, my question was specifically about the steel beam's deflection. I now understand that if the camber is hypothetically downward, I should indeed add it to the theoretical deflection of the steel beam as calculated by the analysis model. This validates my initial assumption, and I'm glad I have clarity on this matter. Thanks for making it more clear.

For the concrete it will do the rest of the job to maintain that flatness and giving me a value less than 10mm. Btw this value of 10mm is achieved considering those tolerances as well.

Thanks everyone for your help.