EXPERIMENTAL STUDY ON SHEAR PERFORMANCE OF STEEL-CONCRETE COMPOSITE BEAMS AFTER EXPERIENCING HIGH TEMPERATURES

To study the shear behaviors of steel-concrete composite beams after experiencing high temperatures, Material performance tests on normal concrete and steel after high temperature and static load tests on steel-concrete composite beams after high temperatures were carried out involving experimental parameters of heating temperature and cooling regime. The mechanical properties of concrete and steel after high temperatures and two cooling regimes were studied, and the microstructure of concrete after high temperatures was observed by using the scanning electron microscope. Then, seven steel-concrete composite beams were designed according to 'strong bending and weak shear'. The distribution of the section temperature field during temperature rise and fall was measured. Loading failure tests on composite beams at room temperature and after experiencing high temperatures were carried out. The ultimate bearing capacity, mid-span deflection and strain of composite beams at room temperature and after high temperatures were compared and analyzed. Furthermore, the effects of heating temperature and cooling regime on mechanical performance of composite beams were analyzed, and the calculation method for ultimate shear capacity of composite beams after high temperatures was discussed. The results show that the loose cement compound in concrete and the crack at the wrapping interface between cement and aggregate are the main factors causing the deterioration of macro mechanical properties of concrete after experiencing high temperatures. The failure modes of steel-concrete composite beams at room temperature and after high temperatures are penetrating oblique cracks in concrete slab. The bearing capacity, stiffness and ductility of composite beams decrease with the increasing heating temperature. When the temperature is lower than 400 ℃, the cooling regime has little effect on the bearing capacity. When the temperature is 600 ℃, the bearing capacity of composite beams after water spray cooling is greater than that of natural cooling. Compared with the natural cooling specimens, the stiffness of the specimens after water spray cooling is large and the ultimate deflection is small. Based on the experimental data and regression analysis, the calculation formulas between concrete compressive strength, steel yield strength and heating temperature are established. The calculated values of the revised AS/NZS 2327 specification formula are in good agreement with the test values.