Overloaded precast Ts

[JMASE]

If precast Ts are overloaded (significantly) and their loaded deflections measured, does the failure of these Ts to rebound when unloaded imply that they have lost structural capacity? Or, is it possible that some yielding and permanent deflection has occured, but if reloaded with a smaller load could behave in a linear way? Any references to technical literature that addresses the capacity of previously overloaded Ts would be appreciated.

 

[ANE91]

In the building world, the "worst" state of stress is commonly in the plant, at strand release, because the concrete is usually 1 day old and the prestress is maximal. Most are designed to be tension-controlled, so you'll see a lot of plastic deformation of bottom-fiber steel before the top crushes at ultimate. It follows that loss of structural capacity from flexural overload will be apparent at the top. How the beam behaves thereafter is anyone's guess. Deflections in prestressed beams are a tricky business, what with creep and steel relaxation and such.

 

[HTURKAK]

If precast Ts are overloaded (significantly) and their loaded deflections measured, does the failure of these Ts to rebound when unloaded imply that they have lost structural capacity?

The failure to rebound implies steel is yielded to a certain extent. How much overloaded when compared with strength design combination?

 

[JMASE]

The failure to rebound implies steel is yielded to a certain extent. How much overloaded when compared with strength design combination?

Hard to say, but approx. 50% increase in factored LL

 

[JAE]

When you say "failure to rebound" are you saying the load is removed and the DT doesn't move up at all?
Or doesn't move up to some flat line level configuration?

If the latter, how do you know where the original zero datum is for the deflection?
You don't really know where the member "started" in terms of its initial geometry do you?

If the former - doesn't spring back up at all - I'd be amazed if no rebound occurred - which puts you back in the latter condition of needing the original position.

 

[HTURKAK]

Hard to say, but approx. 50% increase in factored LL

You did not provide alot of information here. What about ( if any) cracks, what is the amount of deflection ?
The common practice is to provide rounded figure, amount of steel more than calculated . Use your engineering judgement and deflection limits allowed .
Probably the tension steel yielded to a certain extent then after unloading there is a permanent set that is strain hardening.