| The concrete cable-stayed bridges in China are in the forefront of the world both in terms of number and span.Under the action of long-term heavy traffic and other factors,the PC cable-stayed bridges are prone to crack and deformation,which seriously threaten the service safety of bridge structures.The cracking problem of the PC cable-stayed bridge is inevitable even under the combined action of cable and prestress.It has been proved that the concrete cable-stayed bridge designed according to the theory of partially prestressed can theoretically improve the limitations of the original fully prestressed concrete design.In addition,with the more and more extensive application of the UHPC material in the field of bridge engineering,and the deficiency of traditional bridge reinforcement technology,it is particularly important to find new reinforcement materials and methods for the concrete cable-stayed bridge system Therefore,it is of great theoretical significance and engineering application value to study the mechanical behavior of the PC and the partial prestressed concrete(PPC)cable-stayed bridge system and to strengthen its main beams based on the UHPC.The main contents of this paper are as follows:(1)The static performance and the grouting reinforcement test of main beam of the PC cable-stayed bridge segment scale model were carried out.The PC cable-stayed bridge segment scale model was designed and fabricated,the static load tests were carried out under elastic stage,different crack width conditions and failure load conditions,and the pre-damaged main beam with 0.5 mm level over-limit crack was reinforced by grouting.The results show that the PC main beam showed good working performance with cracks.Under the condition of different crack widths,the main beam cracks developed smoothly.In the process of repeated loading and unloading for the same working condition,the repeatability of the cracks distributions were good,and the cracks were basically closed after unloading.The stiffness and crack resistance of the cracked the PC girder of the cable-stayed bridge can be effectively restored greatly by grouting reinforcement.(2)The static performance and grouting reinforcement of main girder test of the PPC cable-stayed bridge segment scale model after fatigue were carried out.A reduced-scale model of the PPC cable-stayed bridge was designed and manufactured.For the structure with fatigue damage,the equivalent lane load was applied until the main crack width reached 0.5 mm.The static properties of the PPC girder after fatigue damage were then studied.Furthermore,the cracks in the main beam were reinforced by grouting,and the recovery degrees of girder stiffness and crack resistance were studied.It is found that that the main girder still has large residual bearing capacity and good crack resistance after fatigue damage,and the grouting treatment of a few cracks in the main girder can also greatly restore the stiffness of the main girder with excessive cracks,which further reveals the engineering feasibility of the PPC cable-stayed bridge.(3)The model test of the UHPC reinforced concrete cable-stayed bridge girder was carried out.Based on the excellent mechanical properties of the UHPC,the basic mix proportion was determined and the basic mechanical properties test was completed.Then,the bottom edge of the main girder of the damaged concrete cable-stayed bridge was strengthened with the UHPC,and the static performance,failure mode and ultimate bearing capacity of the structure were studied.The results showed that the UHPC reinforced concrete cable-stayed bridge girder greatly improved the stiffness,crack resistance and bearing capacity,and the final failure mode was the fracture of ordinary steel in the UHPC layer,and increasing the reinforcement ratio of the UHPC layer can effectively improve the ultimate bearing capacity of the reinforced girder.(4)Based on the test results,the optimization design method of the UHPC reinforced the PC cable-stayed bridge was proposed.The stiffness distribution law of the PC cable-stayed bridge model under different crack widths was summarized;the influence law of the UHPC layer thickness on the stiffness of main girder of the PC cable-stayed bridge was revealed based on numerical analysis method.Based on an actual PC cable-stayed bridge and the test results of the scaled model,the damage state of the main beam with 0.1mm level cracks was simulated.The improvement of the system stiffness and the main beam stress of the PC cable-stayed bridge strengthened by the UHPC were discussed.On this basis,the optimization design method of the main girder of the PC cable-stayed bridge strengthened by the UHPC was proposed. |
