An Evaluation Method for Effective Prestress of Simply Supported Prestressed Concrete Beams with Breathing Cracks

Wenlong Guo,Xiaojin Zhao,Hexu Liu,Peng Liang,Y Frank Chen,Dan Ma

doi:10.1155/2021/8876093

Abstract

Loss of effective prestress and accurate detection of actual stress in existing precast prestressed concrete bridges are two major challenges in the bridge industry. In this respect, this research aims at an improved method for the critical decompression moment (DM) test of cracked sections depending on the stress change rate of tensile rebars. A calculation method for total effective prestress of prestressing strands in the tensile region is derived with the assumption of the plane section and pre-decompression elastomer. The proposed method is verified by laboratory tests on beams and numerical analysis and by addressing effective prestress issues of existing simply supported beams. The determination results of the critical decompression state show that the proposed method (i.e., the stress change rate of tensile rebars-load curve) is more sensitive and reasonable than the traditional stress increment, i.e., load curve method. The evaluation results of the total effective prestress are more reasonable than the traditional method based on the steel stress relief hole technique or frequency test results. Compared with the existing methods for estimating the prestress using the mid-span deflection or crack width, the proposed method is more reasonable in theory and calculation. It provides a guide for the evaluation and reinforcement of aging bridges.

Highlights

Prestressed concrete bridges occupy a relative majority position in bridge engineering because of their advantages, such as simple construction, convenient mold casting, and low cost
In order to more clearly show the re-opening of the crack in the main beam with a closed crack element under the critical decompression state, the first two columns in Figure 11 present the concrete stress distribution within the full height range of the main beam, while the third column only shows the development of the crack at the lowest edge of the beam element
It is shown that the numerical analysis results are consistent with the theoretical calculation in Section 3 when the test load-stress change rate of the rebar in the tensile zone curve method proposed in this paper is used to determine the critical decompression state of the section

Summary

Introduction

Prestressed concrete bridges occupy a relative majority position in bridge engineering because of their advantages, such as simple construction, convenient mold casting, and low cost. Due to issues such as low design load, long servicing time, indeterminate estimation of effective prestressing decay effect, and overloading, most of the prestressing concrete bridges in service are cracked at varying degrees. Most of the cracks are in the closed state under dead loads while remaining open under live loads. Karayannis and Chalioris [2] introduced the design method of partially prestressed concrete structure based on crack width and proposed the design program and useful chart. Karayannis and Chalioris [2] introduced the design method of partially prestressed concrete structure based on crack width and proposed the design program and useful chart. e direct design method of partially prestressed concrete beams based on plastic mechanics theory was proposed by Alnuaimi and Bhatt [3] verified on indoor model beams

Objectives

Methods

Results

Discussion

Conclusion