| The internal forces of reinforced concrete structures are usually determined by the design value of loads, material strengths and other parameters with using simplified structural models and more suppositions, then to evaluate stresses in their control sections based on the known results above, which are approximate with unknown degree. In fact, the real internal forces and stresses are different incompletely with those by calculation because of more factors, such as the kind, the value, the distribution and the transfer of loads, the uncertainty of elastic modulus of concrete relative to extant stress and others, the supporting conditions of structural members, furthermore the temperature change, the cracks, the foundation settlement and so on.In safety evaluation, quality checkup, test research, accident analysis, reinforcing and rebuilding of existent concrete structures, it is often need to determine the real internal forces of structural members by their section stress to make exact estimations then to adopt correct measures. So developing the research of determine the real internal forces of reinforced concrete structures can not only enlarge the check or measure range, promote the technology development in this range, but also change the embarrassed situation that the real internal forces (including prestress effects) in building members can not be measured at present.Professor Panli, who is working in China Academy of Building Research, creates the new method which can solve the problem above and is briefly introduced as follows. Drill a small hole on surface of the measured steel bar, to force the impaired section has a strain increment△εs and measure it.Enlarge the hole at the same position more times to get the array [△εs,i]. In elastic area, based on deduced functions between real stressσs of steel bar and [△εs,i], sameσs values can be gained from calculations. By principle of coordinative deformation, the real concrete strainσc around the measure position of steel bar can be assured fromσs. At last, real axial force N0 and real moment M0 in measured members can be calculated byσc in different positions on the section with assumption "Plane sections before bending remain plane after bending."In the research, calculation analysis of 18 steel bars in different diameters and holes have been done in using Ansys finite element program, which affirms primarily the measure method of strain increment△εs,p around thesmall holes. According to tension tests of short steel bars and axial compression tests of concrete columns, the consistent results compared with Ansys analysis and the statistical function between△εs,p and△εs have beenacquired. Furthermore, the correctness and applicability of Pan' s method have been validated with more improvements as yet. |
