Research on calculation of unbonded tendon stress increment in prestressed concrete two-way slab during service stage

The finite element analysis model of unbonded prestressed concrete two-way slab supported by four sides and columns was established by using ABAQUS finite element software. The stress growth law of unbonded tendon in prestressed concrete slab during service stage was researched. The results of finite element analysis show that the stress increment of unbonded tendon increases with the increase of the composite reinforcement index, increases with the increase of the tensile strength of the non-prestressed reinforcement, and decreases with the increase of the rotational constraint level of the boundary of the prestressed concrete slab. According to the analysis results, the formulas for calculating the stress increment of unbonded tendons in service stage were established considering the influence of the composite reinforcement index, the four sides support conditions, the relative position of the prestressed tendon in the slab and the steel type of the non-prestressed reinforcement. The unbonded prestressed concrete two-way slabs supported by columns were divided into upper slab belt and mid-span slab belt. The influence of composite reinforcement indexes and steel types of unprestressed reinforcements on the stress increment of unbonded tendons was investigated respectively. The calculation expressions of stress increment of unbonded tendons in service stage were established for upper slab belt and mid-span slab belt.