A Research On Fiber Reinforced Concrete And Its Application In Continuous Rigid-frame Bridge

Continuous rigid frame bridge,a kind of traditional and classical bridge,is still troubled by the crack problem.And an alternative to solve this problem is provided by the development of fiber reinforced concrete.Basalt fiber and polyacrylonitrile fiber are widely used,and their single addition type and hybridizing with other fiber are studied.But no study for their hybrid is publicly reported.In order to improve the situation,an experimental research on the mechanical properties and optimal fiber dosage of basalt-polyacrylonitrile hybrid fiber concrete was carried on.Based on the experimental result,taking Hongyanxi Bridge as the engineering background,the application of fiber reinforced concrete in continuous rigid frame bridge is discussed in the article.The main content is as follows:(1)Mechanical experiments including compression,bond splitting tensile,flexure,elasticity modulus were applied on 240 specimens with the concrete age of 28 d from 80 groups.With the raw material-C55 concrete-and the ratio of compounds was kept constant,the specimens were set in 16 variable basalt fiber and polyacrylonitrile fiber dosages,and with each dosage there were specimens in 3 different sizes.Through discussion and analysis,the results showed that the bond splitting tensile strength reached the highest increase of 18.6% when there were 0.15% basalt fiber and 0.11% polyacrylonitrile fiber in volume content;the flexural strength reached the highest increase of 24.5% when there were 0.10% basalt fiber and 0.09% polyacrylonitrile fiber in volume content.(2)Basic mechanical experiments of early age hybrid fiber concrete under the optimal fiber dosage were also conducted.Under the optimal fiber dosage,the strengths of cube compression,bond splitting tensile and flexure of the concrete age of 3d were respectively increased by 7.32%,20.56%,18.79%,compared to plain concrete in the same concrete age.As for the concrete age of 7d,the parallel increases were 3.35%,18.82%,22.09%.(3)Midas is used to give space stress analysis for the zero block of Hongyanxi Bridge,the result indicates that most area is in the compression state in the conditions of the largest cantilever stage and the completion stage.And different degrees of tensile stress,which value is allowable,are appeared in the local area of the top and bottom boards and webs.But the larger tensile stress is appeared in diaphragm plate hole location,and the max values in the two stages are 2.38 MPa and 2.50 MPa respectively with a local crack threat.(4)For the crack threat in diaphragm plate,a fiber reinforced concrete application,with low implementation difficulty,improved mechanical properties and little cost,is given in this article.