Design Method For Stress Increment Of Externally Prestressed Tendons In Corrugated Steel Web Composite Beam

The externally prestressed tendons corrugated steel web composite beam has the features of unique structural form,good stress performance,beautiful external appearance,and difficult to occurred web crack,makes its widely used in bridege engineering.At present,researchers have focused on the mechanical behavior of the corrugated steel web composite beam,few researches have been conducted on the stress increment of externally prestressed tendons.Considering the great influence of external prestressed tendons on the flexural capacity of bridge structures,it has profound theoretical and practical significance to study the stress increment of external prestressed tendons.In this paper,the stress increment of externally prestressed tendons in corrugated steel web composite beam is studied based on the research of Yusheng Yellow River Bridge.The main research and conclusions are summarized as follows:1)The research status of externally unbonded prestressed concrete box girder bridges at home and abroad is systematically expounded,and the research methods in this field and the calculation method of external prestressed tendons stress increments are summarized.2)The flexural capacity tests of external prestressed corrugated steel web composite beams were carried out,the deflection of the beam,the effective prestress under the anchor and the strain of the top and bottom plate and the web were collected and analyzed.The results show that the corrugated steel web box girder has good ductility.The beam failure has experienced elastic phase,the cracking phase and the plastic phase.When the beam enters the plastic phase,the structural stiffness of the beam decreases rapidly,the deflection increases,and the stress increment of external prestressed tendon increases fast.The development of the anchoring force of the fiber Bragg grating sensor and the vibrating wire pressure sensor is the same.The maximum error of the test data is 4.11%,which verifies the feasibility of the fiber grating technology and breaks the limitation of the vibrating wire sensor monitoring points.3)The formula for calculating the stress increment of external prestressed tendon in the composite beam with corrugated steel webs in the elastic stage under different loads and reinforcement forms is derived,witch based on the deformation theory and considering the influence of "shear deformation" and "secondary effect".Taking model test beam as the research object,parameter fitting analysis was carried out.The research shows that the effect of "second-order effect" on the stress increment of external prestressed tendons is 0.2%.which could be ignored.The stress increment of external prestressed tendons decreases linearly with the increase of elasticity modulus of concrete,while increases with the height of beam.The ratio of the corrugated steel webs thickness to the height of beams has negligible effect on the stress increment of external prestressed tendons.4)A nonlinear numerical model'was established using Abaqus to simulate the structural response of the test beam.The results show that in the elastic stage,the stress increment of the external prestressing tendons of the model beam is linear with the deflection and load respectively.As the load increases,the beam enters the cracking stage.At this time,the beam stiffness is reduced,but the steel bar in the tension zone of the bottom plate does not yield and is still in the linear elastic range.Therefore,the stress increment of external prestressed tendons is approximately linear with deflection and load,respectively.When the steel bar in the tension zone yields,the beam enters the plastic stage.At this time,the stiffness of the beam decreases rapidly,and the deflection and the stress increment of the external prestressed tendons increase sharply.The stress increment of the external prestressed tendons is approximately curve-dependent with the deflection and load.5)Parameter fitting analysis was carried out on 36 nonlinear numerical models.The results show that the influence of concrete strength on the stress increment of prestressed tendons is positively correlated.The area and strength of normal steel in the tension zone,the initial effective stress and the ratio of height to span have a negative correlation with the stress increment of prestressed tendons.The ratio of the ultimate stress increment at the mid-span loading and the three-point loading is 0.74.the average ratio of the length of the equivalent plastic hinge area to the height of the neutral axis is 19.53.6)Based on the Pannell model,the ratio of the length of the plastic hinge to the height of the neutral axis was obtained,the formula for the ultimate stress of externally prestressed tendons in corrugated steel web composite beam was proposed and verified by experiments.The proposed formula has good consistency with the experimental results,which indicates that it can be used for external prestress design of corrugated steel web composite beam.