Would confining strain gauges inside a PVC cylinder (isolated from the concrete) work?
EDIT 1 :
Thanks a lot, for the answers.
In the absence of any external load, If one can measure the strains (stress independent) in a concrete wall using strain gauges (bonded directly to the concrete), what strain is it that we are measuring, the unrestrained component of the strain ? (Assume that thermal corrections to the strain gauge have been made)
If yes, Isn't the process of converting these strains to stresses flawed, since these "strains" cannot be used to compute the restrained stresses in say, concrete (since you will need to know the external restraint factor,R, as well).
εrestrained = R(εth + εsh) - εcr ...........(cannot be measured directly)
εfree = (1-R)(εth + εsh) ..........(measurable strain)
σrestrained= εrestrained * Ec
[If R=1.0, then free strains are 0,but restrained stress not 0]
If you bond the strain gauges directly to concrete you can measure shrinkage and thermal strains when no external load is applied. When you apply a load you will measure thermal+shrinkage+elastic+creep strains all toghether.
The solution you propose about confining gauges inside PVC cylinder does not work.
BR
GB
Yes it can be done. For thermal strain, you need to do compensation, since the strain gauge itself will undergo expansion/ contraction.
for analisys along time a perfect solution is put a gauge into structure, and another into similar material (and size) witthout loads.
The first take data of thermal+shrinkage+elastic
The second take data only of thermal.
Do the difference....
If a strain gauge is inserted in the concrete structure, it eill measure the strain due to loading , thermal and shrinkage. If you can determine the stresses due to loading theoretically using any software like SAAP . then subtact it from what is measured experimentally to get what is due shrinkage and temperature
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