Numerical Simulation Of Concrete Slab Cracks In Negative Moment Region Of Prestressed Double Composite Continuous Box-girder Bridge

Compared with single steel-concrete composite beam, continuous double steel-concrete composite beam has gotten greater stiffness and carrying capacity but the tension cracks problem in top concrete slab is still inevitable in negative moment region. The appearance of cracks affects stiffness and durability of the structure. This dissertation does the research on the influence of pre-stressed degree and longitudinal reinforcement ratio to upper concrete slab tension cracks in negative moment region of double steel-concrete composite continuous box-girder structure by pre-stressed concrete method.This dissertation discusses and summarizes the bond-slip theory between reinforcement bar and concrete and the existing crack computational theory of composite beams. Determine feasible modeling methods via comparative analysis of different numerical simulation methods and then use finite element software ANSYS to establish plane finite element model of negative moment region including two situations of considering and not considering bond-slip between concrete and reinforcement bar. Use the equivalent load method to apply pre-stressing force. Choose separate model and double spring element to simulate reinforced concrete slab and the bond-slip between reinforcement bar and concrete. Use smeared model to simulate cracks.Element birth and death technology are used to simulate the crack appearance and expansion then cracking load, fracture interval and load-crack width curves are obtained under different pre-stressing degree and longitudinal reinforcement ratio. The simulation results show that cracking load are improved and fracture interval and crack widths are restricted by lifting pre-stressing degree and reinforcement ratio, which reach the purpose of inhibiting the appearance and propagation of negative moment region cracks. Calculation results identify that the design of selected engineering example meets the requirements of strength, stiffness and crack width also the section designing needs further optimization.The study in this dissertation is referential to crack calculation and further theory research of double steel-concrete composite beam.