Shrinkage analysis
Shrinkage analysis
(OP)
Folks,
I need to study the shrinkage of a box girder and associated restraint forces. I have never done one before and I am unable to figure out a good starting point?
Can anyone give me good pointers? Design examples etc.?
I need to study the shrinkage of a box girder and associated restraint forces. I have never done one before and I am unable to figure out a good starting point?
Can anyone give me good pointers? Design examples etc.?






RE: Shrinkage analysis
RE: Shrinkage analysis
The restraint for my situation is a elastomeric bearing which I have modelled as a spring restraint. If you don't allow adequate movement, the built up stressed from these parameters will be very large.
RE: Shrinkage analysis
I am trying to do a similar process to yours. I am trying to compute a shrinkage strain and use that as a coefficient of thermal expansion and use a 1 degree temperature gradient to compute the restraint forces.
However, I am having difficulty computing the shrinkage strain. I have not been able to find good examples to do the same. Do you have any references that you don't mind sharing? I think the key for me is to get to a shrinkage strain value at different ages of concrete.
RE: Shrinkage analysis
RE: Shrinkage analysis
My girder was being installed after 4 months, so only 75% of the total shrinkage strain would occur (300 micro strain). So the free movement of the girder was 5mm (2"), of which there was very little restraint provided against movement so the girder was free to shrink that amount.
If you have a prestressed member you best check creep shortening as well because this can be of same magnitude to shrinkage.
RE: Shrinkage analysis
Your conversions from mm to feet and to inches are all wrong.
RE: Shrinkage analysis
your right, 18000 is more like 60'.
RE: Shrinkage analysis
RE: Shrinkage analysis
I'm don't work with the imperial units often but try to use both units on this forum.
The precast beam I mentioned above was only moving 5mm at the bearing which is 1/5".
RE: Shrinkage analysis
RE: Shrinkage analysis
Bridges may be understood to have less restriction to free shrinkage if upon free supports; without looking farther some more recent codes, the "Instrucción relativa a las acciones a considerar en el proyecto de puentes de carreteras", a code that stood about 5 decades ruling the construction of road bridges in Spain in the second half of the XX century, shrinkage should be taken between 150 and 400 microstrain, the first value for humid zones that have less shrinkage, and 400 for dry and desertic areas, that have more.