Research on Ultimate Stress Increment of Unbonded Prestressed Steel Bars Based on Reliability

Unbonded tendons have been widely used in practical engineering worldwide, and scholars from various countries have conducted extensive research on the ultimate stress increment of unbonded tendons. However, the current calculation methods usually calculate the ultimate stress increment of unbonded prestressed tendons which is smaller than the actual increment, and most of them tend to be unsafe. Therefore, this article is based on the ultimate state equation of the normal section bearing capacity of unbonded prestressed concrete beams, sorting out the statistical parameters and distribution types of each random variable in the ultimate state equation, and using the first order second moment method to solve the structural reliability. Based on the target reliability index, the main factors and calculation formulas that affect the ultimate stress increment of unbonded reinforcement were analyzed, and a correction coefficient was introduced to consider the impact of reliability on the ultimate stress increment. By calculating the uncertainty coefficients of resistance calculation modes corresponding to different correction coefficients, the value of the correction coefficient was determined, and a reliability based calculation formula was established.