The Research On Stress Transfer Mechanism Of Slowly Bonded Prestressed Concrete Beams

As a new type of prestressing concrete construction technology,slow bonding prestressing concrete overcomes various problems in the construction and use of traditional post-tensioning prestressing concrete,and draws on its strengths to make up for its weaknesses.At present,more and more prestressing concrete has appeared in practical projects all over the country.On the basis of full reading of the research status of retarded bonding prestressing concrete structures by scholars at home and abroad,this paper,relying on the case of the Second Phase Project of the Library of China University of Petroleum(East China),monitors the concrete stress of experimental beams in tension stage,bond hardening stage of retarded bonding agent and embedded vibrating string strain gauge by arranging concrete surface strain gauges on experimental beams in situ.The stress transfer law of concrete is analyzed and summarized.Through theoretical calculation and finite element analysis,the stress transfer mechanism of retarded bonded prestressed concrete beams is obtained.The main conclusions are as follows:(1)During the tension process of slow-bonding tendons,the concrete stress mainly comes from the extrusion force of the anchorage at the tension end and anchorage end to the concrete at the beam end.The stress transfers inward from both ends,and the stress value of the concrete decreases gradually from the tension end to the mid-span position.(2)During the bond hardening stage of retarder,part of the prestressing force is transferred through the bond property between steel strand and concrete.With the increase of the bond hardening degree of retarder,the bond property between the prestressing tendon and concrete increases continuously,and the stress value of the concrete of the experimental beam increases gradually.(3)The closer the concrete is to the prestressing tendons,the greater the stress value of concrete.That is,the stress value transferred from the prestressing tendons to the concrete through bonding has distance property.With the increase of distance,the transfer effect gradually weakens.(4)During the bond hardening period with retarding binder,the stress growth of concrete in the experimental beam is not greatly assisted by the concrete at the end of the anchorage through extrusion.The stress growth of concrete in the experimental beam is mainly due to the remarkable improvement of the bond between the prestressing tendons and the concrete.