Abstract：In order to study crack width distribution and calculation method of flexural member with ultra-high strength reinforcement of 600MPa, tests were carried out for the flexural properties of 18 concrete beams with ultra-high strength steel bar of 600MPa and 1 concrete beam with HRB400 reinforcement. Based on the tests, the influences of ultrahigh strength reinforcement of 600MPa under short-term loading on crack distribution, bearing capacity, average crack spacing and maximum crack width were analyzed. The results show that the cracking bending moment and ultimate bending moment of flexural members with such type of reinforcement can still be calculated according to the formula in current code; the calculated values of those parameters such as average crack spacing and maximum crack width under short-term load are different to some extent from those calculated according to the formula in the design code of current concrete structure. More specifically, the calculated values of average crack spacing are relatively large, and the calculated values of maximum crack width are smaller compared to the test values. Based on the test data, the formulas for calculating crack width of flexural members with such type of reinforcement were modified. In the first method, the formula of crack width is modified based on the calculation formula of the current code by introducing the comprehensive adjustment coefficient; In the second method, the average crack spacing in the current formula for calculating crack width is replaced with a modified formula, and a modified value for the short-term crack width enlargement coefficient is used. The results show that the calculation values obtained by the first modification method are in good agreement with the test values. Hence, in view of the continuity of the codes, the first method is recommended for modifying the crack width.
