Precast supported by composite steel beams problem 1

[tw]

We recently had a problem whereby some precast spandrel panels were erected by attaching to the steel floor beams prior to the concrete floor slab being poured. The floor beams are all design as composite steel beams. In one particularly heavy panel, the weight caused excessive deflection in the supporting steel and erection was halted. After looking at it, we told them to pour the concrete slab and allow at least 7 days cure prior to erecting panel.

They are claiming delay and extra cost due to situation. I can't find anywhere where this situation is specifically addressed in our specs. Has anyone else had this problem?

I guess we need a note to tell steel erectors how steel buildings work? Should the precast specification have something about this?

tw

 

[JAE]

You, as the Engineer of record, need to either:

1. Design the composite beam to account for all anticipated pre-composite dead loads on the beam alone (including the precast) and ensure that it is strong and stiff enough (i.e. serviceable), or
2. Design the composite beam for all anticipated pre-composite dead loads on the beam alone (without the precast) and ensure that it is strong and stiff enough AND note on your plans your assumption that the precast must be installed after the deck is cured out.

You normally don't dictate on your plans the means and methods of construction, however, you should be cognizant of the probable means and methods, thinking through the constructability of your design.

If structural stability and safety involves a particular SEQUENCE then that sequence should be spelled out for the benefit of the contractor.

 

[dik]

I don't think it's a one way thing... If the contractor was skilled, the existence of shear connectors should have flagged that the construction was composite or there may be information in the drawing notes that indicates composite construction.

It's common construction to construct the superstructure and then add cladding elements... The contractor should have asked about his sequence, perhaps.

Was there any site review? or was it flagged as a consequence of the excessive deflection?

 

[jheidt2543]

Putting precast cladding on a building without making sure the framing system is braced in SOME way, either poured slabs at each level or temporary bracing, is asking for trouble from those CONSTRUCTION GREMLINS.

I agree with JAE that the designer should have notes on the drawings regarding necessary bracing or sequencing during construction. But hopefully it isn't the first time the contractor has been to the dance. He should know the basics of putting a building together too.

It sounds like the finger pointing has started because a problem popped up. Preconstruction and pre-installation conferences should be required at the start of each major phase on all your projects. They resolve a lot of questions and prevent most major problems.