Test And FE Analysis On Bending Performance Of UHPC Waffle Deck

In order to solve the problems of heavy self-weight and cracking in concrete bridge panel that exist in the use of traditional steel-concrete composite girder,Prof.Shao Xudong of Hunan University proposed steel-UHPC lightweight composite structures innovatively.By utilizing the excellent mechanical properties of UHPC the cracking problems in concrete bridge panel can be solved effectively.Meanwhile,the reduced self-weight,which amounts to 30%-40%,is beneficial to enhance the span and to simplify the construction process of composite girder bridge.This paper conducted preliminary investigations on the flexural behavior of UHPC waffle bridge panel in transverse direction from three aspects:full-scale strip model test,nonlinear finite element analysis by ABAQUS and theoretical analysis.In addition,a segmental model is established by ANSYS to analyze the influence of the longitudinal and transverse rib spacing on the mechanical performance of the waffle bridge deck.The main completed works are as follows:(1)Four models with transverse ribs in full scale were developed for static bending test.The test results show that under the action of positive bending moment,the specimens underwent following typical stages:linear elastic phase,crack development stage and yield stage.The mechanical behaviour of the four models under flexural load is that,after the linear elastic stage,transverse cracks appear at the bottom of transverse rib and lead to the first decrease of structural stiffness.With the development of cracks,the redistribution of internal forces results in a continuous rise of stress in bottom reinforcements until yielding,which causes a second drop in stiffness.Then cracks propagate further upward till the top of flange,the full developed tensile zone leads to the rise of stress in top reinforcements until yielding,there appears a third drastic decline in stiffness and consequently the specimens trend to reach the bearing capacity.(2)A nonlinear finite element analysis was implemented by using the FEM software ABAQUS,in which the material nonlinearity,geometric nonlinearity and plastic damage model of UHPC were considered.The results from FEM simulation are consistent with those from experiments.On the basis of test and finite analysis,a theoretical analysis focusing on the load capacity or ultimate bearing capacity of typical stages is conducted,such as initial cracking load,the yielding load of bottom tension reinforcement,ultimate flexural capacity and shear bearing capacity.The deviation among theoretically analysis,tests and FEM simulation is small.(3)On the basis of results above,the influence of primary parameters on the transverse bending resistance of UHPC waffle deck panel is ascertained.These parameters include:the diameter of longitudinal reinforcement in the bottom,transverse rib height,top plane height and transverse rib spacing.The results indicate that the influence of the diameter of longitudinal reinforcement in the bottom on the initial cracking is negligible,whereas the development of cracks can be effectively restricted;the increase of rib height shows not only some inhibitory effect on the initial cracking,but also enhancement of the initial stiffness,the stiffness after cracking and ultimate bearing capacity of the T-beam;increasing the height of top plane can achieve a similar effect,but the rise of initial stiffness by increasing rib height is 5.4 times than by increasing top plane height.A larger rib spacing can bring higher initial stiffness,the stiffness after cracking as well as ultimate bearing capacity of a single transverse rib,though the global stiffness in transverse direction is impaired.(4)Base on Shengtian bridge,a segmental model is established by ANSYS to analyze the influence of the longitudinal and transverse rib spacing on the mechanical performance of the waffle bridge deck,the test results show:as far as this bridge is concerned,the decrease of spacing of transverse ribs(an increase in the number of transverse ribs)has little effect on the maximum transverse tensile stress on the bottom surface of transverse ribs,but has obvious improving effect on the transverse tension in negative moment area;the decrease of spacing of longitudinal ribs(an increase in the number of longitudinal ribs)can significantly reduce the longitudinal tensile stress on the top or bottom surface of waffle bridge panel,meanwhile it can also decrease the transverse tension on the top or bottom surface of waffle bridge panel in a certain degree.