Elastic Gains for Service III check

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Jkw
Elastic Gains for Service III check

Version 2.7.1 added a method for controlling elastic gains and losses. This was done by allowing the user to specify the percentage of each load to be used. Can anyone tell me what percent was used in previous versions of the code? I am specifically interested in live load.

Thanks in advance.

Rick Brice
The LRFD specification does

The LRFD specification does not prescribe what percentage of each load type to use. Presumably, 100% of all the loads would be used as they influence the effective prestress and the stress in the girders.

In versions of PGSuper prior to 2.7.1 the elastic gains due to slab shrinkage was considered when computing effective prestress, however slab shrinkage was completely ignored when computing girder stresses. This didn't make any sense. When the slab shrinks and causes tension in the strands, thereby increasing the effective prestress, the corresponding increase in tensile stress in the bottom fiber of the girders should be accounted for as well. In other words, you can't take the benefit of slab shrinkage without taking the negative effect as well.

There is a lot of uncertainty about how much slab shrinkage really affects the girder stress and effective prestress. The PCI BDM recommends it be ignored and then goes on to say that if you feel it be taken into account that you should use about 50% of the predicted value.

It is my understanding that some DOTs do not permit their engineers to take advantage of elastic gains for design. In this case, using 0% would satisfy their requirements.

I guess that is a long winded answer.

Rick

Richard Brice, PE
Software Applications Engineer
WSDOT Bridge and Structures Office

Jkw
Thank you for your response.

Thank you for your response.

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