Creep & Shrinkage Effects on Bearing Design

[PatsSuperfan]

All,

I am trying to design a steel-reinforced elastomeric bearing for a simply-supported prestressed box beam bridge. Per AASHTO Section 14.7.5.3.2, the max horizontal displacement of the bearing may be 65% the design thermal movement range combined with the movements caused by creep, shrinkage, and post-tensioning. I gathered the stress losses in prestressing from the CONSPAN program used to design the beams. I then assummed the stress loss due to shrinkage and creep are transferred to the concrete, and have applied Hooke's law to solve for displacement. Is this the right approach to find the horizontal displacement due to creep & shrinkage? I received displacements of 1.8" which seems high relative to the thermal movement range (.75"). The bridge is 85.5' in span and has 11 girders.

Thanks in advance.

 

[Franksta]

Are you taking all of the of the losses? I usually assume that half of the losses have occurred in the yard before erection. I feel this is safe because most of the losses over the life of the beam occur in the first weeks.

Also, I assume when you say you are using Hooke's law that you are using the modulus of elasticity the strand, right?