Study On Stress Behavior Of Unbonded Partially Prestressed Concrete Beams With High-Strength Steels

Unbonded partially prestressed concrete(UPPC)structures have the advantages of easy to operate, facilitate to replacement tendon,economic rationality,etc.And other excellent mechanical properties similar to bonded partially prestressed concrete structures.Compared with HRB400 steel,HRB500 grade high-strength steel has much more mechanical properties and process performance indicators,it had been included in design of Concrete Structures(2011).HRB500 grade high-strength steel will be applied in UPPC structure is trend of the times indeed.There are seven rectangular beams,include five UPPC beams configurated with HRB500 grade non-prestressed reinforcement beams and two UPPC beams common non-prestressed reinforcement.In the experiment,three UPPC beams configurated with HRB500 grade non-prestressed reinforcement beams and two UPPC beams common non-prestressed reinforcement used to static load test,and other two UPPC beams configurated with HRB500 grade non-prestressed reinforcement beams used to fatigue test.The main works listed as follows:1. Summary and analysis the beams’mechanical performance between the fatigue test and static load test.2.Put forward the factors impact on the bending capacity of the test beams which include strength of non-prestressed reinforcement,reinforcement ratio non-prestressed,different loading styles and integrated reinforcement index.3.Collect existing countries’specification and researchers’formulas on the ultimate stress,then substitute the data of test into equations,and determine whether each formula is applied to calculate ultimate stress of beams configurated with HRB500 grade non-prestressed reinforcement.The results show that the beams configured with HRB500 high strength non-prestressed longitudinal reinforcement improved the ultimate bearing capacity.With the increased of HRB500 high strength longitudinal reinforcement ratio,ultimate bearing capacity increased progressively.Fatigue loads reduced ultimate bearing capacity under static loading.When non-prestressed reinforcement ratio was different,limit stress increment of beams configured HRB500 high strength non-prestressed longitudinal reinforcement were lower than them configurated low intensity non-prestressing tendons.When loading methods was different,fatigue load improved beams’limit stress increment for 12.5%,So it is should not be ignored that repeat loads generated additional stress increment.Integrated reinforcement index is not the only factor associated with stress increment.Calculated on the ultimate stress in 《Unbonded prestressed concrete structures technical specification JGJ92-2004》 was applicable to calculate limit stress of unbonded partially prestressed structures that HRB500 rebar as a non-prestressing tendons.