Experimental Study On The Flexural Behavior Of The Monolithic Joint Of New And Old Concrete Bridge

With the rapid development of economy,the traffic volume has grown rapidly,and it is particularly urgent to expand the old bridge.The monolithic joints of the new and old concrete bridges can affect the construction progress of the bridge widening,and it is also a weak part of the structural stress performance.At present,there are few research on the mechanical properties and transmission mechanism of the local internal structure of the joints,and the design of the joints between the new and old concrete bridges is often handled by experience,which lacking systematic experimental research and theoretical basis.Therefore,it is of great theoretical and practical significance to study the mechanical properties of the joints of new and old concrete bridges.Based on the new and old concrete bridge splicing project of the Fenghuangshan Tunnel section of the west extension line of Guanghui Expressway by the project "Development of high-performance concrete under driving vibration environment",and the test method is used to study the flexural failure mechanism of the monolithic joint of new and old concrete bridge.The main research contents include the following aspects:(1)A fast hardening and retarding low-alkalin sulphoaluminate cement concrete is developed,which can be used in practical engineering.The pre-test study on the flexural behavior of the monolitic joint of the new and old concrete bridge is carried out.(2)The major variables in this paper includes the type of concrete(F60,S60,UHPC),splice detail(straight bar,headed bar and U bar),the preparation of interface(smooth and rough),the joint width(150 mm,200 mm,300 mm).The flexural behavior of 15 new and old concrete bridge is studied.The failure mode,cracking load,ultimate load and deflection of panel are deeply studied.The force transmission mechanism and failure mechanism at the joint are also explored.(3)Comparing the experimental results with the theoretical calculation values of the flexural capacity of the new and old concrete bridge predicted by the Strut-and-Tie model,this study also provide theoretical references for the design of joints of new and old concrete bridge.Several important conclusions are extracted from the testing and analysis,and list in the following:(1)All the decks cracks at the interface first.The cracking load of the joint is related to the type of new and old concrete and the preparation of interface.However,it has nothing to do with splice detail,the joint width and the lap joint.(2)The mechanical properties and failure modes of the F60 and S60 decks are consistent,while the UHPC joints have higher load capacity,crack resistance and ductility.(3)The stiffness of the U bar and Headed bar deck is larger than that of the straight bar deck.The ductility of the straight bar,U bar and headed bar test deck increases sequentially.Compared with the straight bar,the U bar and the headed bar can impr ove the ultimate load of the joint,and the U bar has better bearing capacity of the joint than the headed bar,but it is not obvious.(4)The rough interface has improved the cracking load of the deck,but it has no effect on the bearing capacity and failure mode of the deck.(5)The joint width has little effect on the ultimate capacity of the UHPC joint of deck.In general,for the UHPC joint of deck,the joint width is recommended to be 200 mm.(6)The calculation formula derived from the Strut-and-Tie model can predict the flexural capacity of the joints of new and old concrete bridges conservatively.