Theoretical analysis of the flexural strength and behaviour of unbonded partially prestressed concrete beams and slabs with and without bonded reinforcement.

摘要

A modified version of the computer program written by Chan (1986) forthe analysis of unbonded prestressed concrete members under third pointloading was developed. The new program carries out the analysis more quicklyand efficiently while still maintaining the required accuracy level.The program was used to analyse twenty-two unbonded beams withbonded steel tested in China and twelve unbonded slabs with bonded steel anda futher six unbonded slabs without bonded steel tested at the University ofCanterbury. All analytical and experimental results were compared . Thecomparison revealed that the theoretical analyses gave good representation ofthe flexural behaviour of the unbonded concrete members both with andwithout bonded reinforcement.The report confirms the Chinese finding that the combinedreinforcement index has very significant effect on the ultimate tendon stressincrease and moment capacity for the unbonded members However, the effectof span-depth ratio on the flexural behaviour of unbonded partially prestressedconcrete members was not significant. It is also confirmed that the unbondedmembers with bonded reinforcement behave in a more effective way thanthose without bonded reinforcement. The report recommends that bondedreinforcement should be used in design practice.Two recommendations based on experimental results are proposed forthe determination of ultimate moment capacity of unbonded partiallyprestressed concrete members. The proposed expressions for member withoutbonded reinforcement is given just for comparison and it is not recommendedfor use in practical design.It is also recommended that the value of the combined reinforcementindex chosen should be greater than 0.06 to prevent the occurrence of flexuralinstability and less than 0.305 for efficient design of the unbonded system.Value greater than 0.305 lead to a compression failure resulting in a lowvalue of ultimate tendon stress increase and no increase in moment capacity.