Flexural cracking member 1

[PowerRanger]

Hi Fellows

I am disigning the bearing pad support the bridge beam. And I have a question about the creep and shrinkage displacement at the bottom of the beam.

My case is, the prestress beam I designed is allow the cracking under the full loading, and my question is after the beam cracked at the bottome of the beam, will there be any more shrinkage and creep at the bottom of the beam, or the shrinkage and creep only affect the top of the beam to the neutral axis in a crack section?

Thank you

 

[apsix]

I'd like to know the answer myself PR, but you will get a better response if non-code-specific questions are posted elsewhere, 'structural eng. other topics' for example.

 

[rapt]

PowerRanger,

Shrinkage and creep will still affect the whole section. Shrinkage will cause the crack to widen more while creep may reduce the width of the crack. The final result will probably be a wider crack and significantly increased deflections.

By the way, how is this going to affect the bearing pad support? Is it the final slope/curvature at the support that you are interested in. This will definitely increase with shrinkage and creep.

 

[PowerRanger]

Hi Rapt

In my situation, the creep by prestress at the bottom of the beam is at the same way as the shrinkage before the section crack under the dead load itself.(member hog at this time, bottom stress act compressive, so the strain is toward each other at the support). After traffic loading, the section crack, this is what I am not understand the creep and shrinkage strain movement at the support after the concrete is flexure cracked.

For designing the bearing, I need to find out the shear strain due to tangential movements and forces.

Thank you.