Research On The Deflection Of Pre-stressed Concrete Continuous Rigid Frame Bridge

Pre-stressed concrete continuous rigid frame bridge is widely used in long-span bridge. Continuous rigid frame bridge has many advantages, such as driving comfort, facilitate the construction, good overall performance and big structure stiffness. Because of that it has rapid development in 20th century even by now. But after putting into use, excessive deflection at the mid of span and box severely cracking become two problems that must be solved.Experts have different opinions on the reason of the excessive deflection at the mid of span. Firstly the paper introduces two methods that to solve excessive deflection at the mid of span-Pre-camber Method and Zero Moment Method.Pre-camber Method thinks it is caused by the deficiency estimation of the shrinkage and creep of concrete, which can be solved by setting pre-camber. However, Zero Moment Method feels pre-camber can not solve the problem fundamentally, because it can not change the state of stress, only changes the state of geometry. Excessive deflection at the mid of span for continuous rigid frame bridge is caused by unbalanced moment M in the program of construction because of design factors. Before closure the cross-section has initial slope 0 because of M, after closure the concrete has deflection alongθby the effect of the shrinkage and creep of concrete. So the reasonable way to solve the deflection of continuous rigid frame bridge is realizing moment equilibrium in the program of construction-Zero Moment Method.Secondly the paper verifies the reasonableness of the Zero Moment Method by building a simply supported beam model, deems that articles support pre-camber can solve the excessive deflection at the mid-span, just ascribe the reason to the long-term and uncertainty of the shrinkage and creep of concrete, and the motivation to set pre-camber is just because they have to, or knuckles will be formed in the shape of dead load state. So to solve excessive deflection at the mid of span by setting pre-camber is unreasonable. Zero Moment Method analyzes the mechanics of the excessive deflection at the mid of span, and expounds the influence mechanism of the shrinkage and creep of concrete, which is reasonable.Finally this paper taking guan shi he continuous rigid frame bridge which is under construction as engineering background, reasons lead to the excessive deflection at the mid of span and box severely cracking are expounded. Furthermore the paper analyzes factors of box cracking and discusses how vertical crack and deficiency calculation of pre-stress loss influence excessive deflection at the mid of span.