STUDY ON CONFINE CONDITIONS' INFLUENCE ON VIBRATING STRING STRESS METER MEASURING CONCRETE STRESS

Through the comparison tests of embedding vibrating string stress meter in concrete,which is wrapped with and without plasticine at the measuring area,the confine conditions' influence on the outcomes of the stress meter was studied when it's measuring the stress of concrete.The results showed that: based on the assumption that on any cross section the strain of concrete and stress meter are the same,vibrating string stress meter can relatively accurately measure the stress of concrete,but the measured value is a little smaller than the real one; wrapped with plasticine at the measuring area,the stress meter's confine condition is laterally flexible which is more similar to the free boundary condition on which it's calibrated,thus it can measure the stress of concrete more accurately,but its accuracy decreases with the increase of load; when the stress meter is directly embedded in concrete,its nominal axial stiffness will be increased because of the lateral constraint of concrete,thus its measured value will be correspondingly smaller.