Experimental Study On RC Two-way Slabs Strengthened By External Prestressing

Among the numerous strengthening methods of concrete structure, because external prestressing method can actively control initial stress, avoid stress lag, increase bearing capacity, reduce crack width and deflection under the service load and improve the durability, it is considered one of the most powerful techniques for strengthening and rehabilitating. Many studies on it have been finished at home and abroad,however, the researches is nearly the ones about beams and one-way slabs , there are few ones on two-way slabs . In this paper, the research is mainly focused on the mechanical behaviors of the two-way slab strengthened by one-way external prestressing under vertical uniform loads. The main content is following:1. Through prototype test, the effect of different initial stresses and layouts of prestressing tendons on the stiffness, deformation, strain of tendons and bearing capacity of slabs is studied. Experimental study indicates, one-way external prestressing can notably reduce the deflection of slab, postpone the appearance of crack, increase the crack and yield load of slab. In addition, it is also found that higher initial stresses of tendons, reasonable tendon layout, and more prestressing tendons all can improve the stiffness of slab. But by comparison, reasonable tendon layout is most effective to the improvement of stiffness and bearing capacity of slab.2. Finite element analysis program ANSYS is used to analyze behaviors of test slabs in total procedure under vertical loads.The results of calculation indicate, the non-linear finite element model introduced in this paper can highly reflect real mechanical characters of strengthening slabs in all stages.3. Yield-Line method is used to calculate the bearing capacity of strengthening slabs. The calculation results show that Yield-Line method can be used to calculate the bearing capacity of the slab strengthened by one-way external prestressing after referring to the calculation of ordinary slab. But because dome effect is not considered in the plastic hinge theory, its results are often less than the one's of experiments, and it is safer to calculate the ultimate strength of strengthening slabs in practice.4. Several recommendations for design and construction of RC two-way slab strengthened by external prestressing are proposed.