Meaaurement of Residual Stress in Pre-stressed Concrete Structure
by Stress-relief Method combined with Flat Jack
By H. Asai, M. Fujita, Thomas Le Diouron and N. Miyamoto
Concrete Journal, Vol.42, No.4, Apr. 2004
- Synopsis
- The direct measurement of residual stress provides essential information on the health condition of existing structures: it allows to investigate the extent of the deterioration and to devise appropriate reinforcing solutions (re-stressing). A technique has been developed for this purpose and is now commercially available in the market. The proposed technique consists of a stress relief-method combined with a flat-jack: first a slot is cut in the concrete, and then a flat-jack is inserted and inflated so that the original condition can be restored. The residual stress is derived from the pressure in the flat-jack when the original condition is restored. This technique therefore overcomes the necessity of estimating the Young Modulus. This paper describes the "stress relief-method combined with a flat-jack" technique, the unique shape of the slot, and the verifiaction testing that have been conducted to verify applicability and accuracy of the method. The testing have confirmed that this method gives a level of accuracy comparable to the strain gages, and that the results are not largely affected by varying stress profiles, concrete cracking or the presence of steel reinforcement.
- Keywords:
- Stress Relief Method, Residual Stress in Concrete, Flat Jack, Accuracy of measurement
