CN-121997661-A - Large-span prestressed concrete box Liang Gengye cracking tracing method

Abstract

The invention belongs to the field of bridge structure health detection, and discloses a method for tracing cracking of a large-span prestressed concrete box Liang Gengye, which comprises the following steps of (1) establishing a three-dimensional cracking stress model, (2) clarifying a rule that the maximum cracking stress direction changes along with a steel beam anchoring mode, (3) combining the trend of a peduncle crack with the steel beam anchoring, qualitatively judging whether the cracking stress is a main factor of cracking, and (4) solving a maximum three-dimensional cracking stress value, comparing with the tensile strength of concrete, and quantitatively identifying whether the cracking stress is a main factor of cracking. The method for tracing the cracking of the large-span prestressed concrete box Liang Gengye aims at the problem of cracking of the large-span prestressed concrete box Liang Gengye, rapidly completes qualitative judgment of main cause by combining the crack form and the steel beam anchoring mode, verifies by three-dimensional splitting stress calculation, builds a qualitative and quantitative dual-criterion tracing system, and has wide engineering application prospect.

Inventors

• YI TINGHUA
• Hou Shunteng
• LI WENJIE
• ZHENG XU
• YANG DONGHUI

Assignees

• 北京建筑大学
• 大连理工大学
• 中国交通建设集团有限公司

Dates

Publication Date

20260508

Application Date

20260127

Claims (1)

1. 1. A method for tracing cracking of a large-span prestressed concrete box Liang Gengye is characterized by comprising the following steps: The method comprises the steps of firstly, establishing a three-dimensional splitting stress calculation model of a post-tensioned prestressed concrete structure based on a compression diffusion model; the anchoring area of the post-tensioned prestressed concrete structure is filled with a plurality of longitudinal compressive stress contours, each longitudinal compressive stress contour represents a force flow, the pressure contour along the vertical direction, namely the beam height direction, is y (x), the pressure contour along the transverse direction, namely the beam width direction, is z (x), y (x) and z (x) are four-time polynomials containing x, the coordinate directions in a three-dimensional splitting stress model are as follows, wherein x, y and z respectively represent the longitudinal direction, namely the beam length direction, the vertical direction, namely the beam height direction and the transverse direction, namely the beam width direction, of the post-tensioned prestressed concrete structure, and the three-dimensional splitting stress calculation model adopts three basic assumptions: (1.1) geometric distribution presumes that the distribution of the force flow below the anchor plate and the stress uniformity region at the anchor section of the post-tensioned prestressed concrete structure follows a linear relationship, and if the ordinate of the longitudinal compressive stress contour line in the beam height direction and the beam width direction at the stress uniformity region section is y i 、z i , the starting point coordinate y 0 、z 0 of the longitudinal compressive stress contour line at the stress uniformity region section satisfies: ; wherein a represents the length of the anchor plate along the height of the beam, g represents the length of the anchor plate along the width of the beam, c represents the height of the anchor section of the post-tensioned prestressed concrete structure, and d represents the width of the anchor section of the post-tensioned prestressed concrete structure; (1.2) the direction of force flow presumes that at the anchoring section of the post-tensioned prestressed concrete structure and at the section of the stress uniform distribution area, the main compressive stress, i.e. the direction of the prestressing force, is perpendicular to the anchoring section of the post-tensioned prestressed concrete structure and at the section of the stress uniform distribution area, so that the tangential slope of the longitudinal compressive stress contour line at the anchoring section of the post-tensioned prestressed concrete structure and at the section of the stress uniform distribution area is zero: ; (1.3) transverse stress boundary assuming that at the section of the stress uniform distribution region, the stress is uniformly distributed, the transverse stress σ b is zero, and the transverse stress is proportional to the curvature d 2 y/d 2 x、d 2 z/d 2 x of the longitudinal compressive stress contour, thereby obtaining: ; (1.4) equations (1), (3), (5), (6), (7) represent five boundary conditions, the y (x) expression is determined, the z (x) expression is determined by equations (2), (4), (5), (6), (7), the vertical and horizontal splitting stresses sigma b,h (x)、σ b,t (x) are obtained by integrating the contributions of all longitudinal compressive stress contours passing through the section of the stress uniform distribution area at any position x in the longitudinal direction of the post-tensioned prestressed concrete structure, and the sigma b,h (x)、σ b,t (x) is solved as follows: ; Wherein, the In order to uniformly distribute the stress at the section of the region, And finally, calculating the maximum splitting stress of the post-tensioned prestressed concrete structure in the vertical direction and the horizontal direction by using the calculation models respectively as follows: ; Determining the maximum splitting stress direction of the prestressed steel beam during anchoring along the beam height and the beam width by using a finite element analysis method, wherein the maximum splitting stress direction comprises the following specific steps: The method comprises the steps of (2.1) establishing a finite element model of a three-dimensional post-tensioned pre-stressed concrete structure and an anchor plate, setting a plurality of groups of dimension parameters by considering the geometric dimension effect of the post-tensioned pre-stressed concrete structure and the anchor plate, and simulating different arrangement working conditions of the anchor plate along the beam height direction and the beam width direction in the finite element model; applying a prestress load on the anchoring plate, and exploring the direction of the maximum splitting stress of an anchoring area of the post-tensioned prestressed concrete structure when the prestress steel beam is anchored along the beam height direction and the beam width direction through numerical simulation calculation; Step three, qualitatively judging whether the maximum splitting stress is a dominant factor for causing splitting according to the actual trend of the peduncle and axillary cracks and the anchoring mode of the prestress steel bundles; (3.1) the cracks of the axillary region are divided into horizontal cracks and oblique cracks; When a horizontal crack appears in the peduncles and the prestress steel bundles of the peduncles are anchored along the beam width direction, the maximum splitting stress along the beam height direction is estimated as a leading factor for initiating the crack according to the consistency of the crack form and the space stress direction; (3.2) when the axillary region has oblique cracks, the morphological characteristics of the axillary region show that the superposition of multidimensional stress fields exists, and the oblique cracks are estimated to be commonly dominated by cleavage stress along the beam height direction and the beam width direction according to the superposition; Calculating the maximum splitting stress according to the qualitative judgment result, comparing the maximum splitting stress with the tensile strength of the concrete, and quantitatively judging whether the splitting is caused by the maximum splitting stress or not; (4.1) simplifying the peduncle axillary region into a regular cube structure in modeling analysis, and equivalently enabling the prestress steel beam anchoring function in the peduncle axillary region to be concentric anchoring load acting on the cube structure; (4.2) calculating the maximum splitting stress by adopting a formula (9) according to the condition that horizontal cracks appear in the axillary region and the prestress steel beam is anchored along the beam width direction, and comparing the maximum splitting stress with the tensile strength of concrete; And (4.3) aiming at the inclined cracks in the axillary region, calculating the maximum splitting stress along the beam height direction and the beam width direction simultaneously, and then calculating the main tensile stress to compare with the tensile strength of the concrete, wherein if the main tensile stress is larger than the tensile strength of the concrete, the cracking risk is proved.

Description

Large-span prestressed concrete box Liang Gengye cracking tracing method Technical Field The invention belongs to the field of bridge structure health detection, and relates to a method for tracing cracking of a large-span prestressed concrete box Liang Gengye. Background The large-span prestressed concrete box girder bridge plays an important role in modern bridge engineering. However, during long-term operation, prestressed concrete box girders are subject to more cracks. The existence of cracks accelerates the corrosion of the internal steel bars and significantly weakens the durability of the prestressed concrete structure. The axillary peduncles of the prestressed concrete box girder are used as key parts for connecting the top plate and the web plate, and cracks often appear in practical engineering. However, the analysis on the pre-stress box girder cracking mechanism is mainly concentrated in the box girder top plate, web plate and bottom plate areas, and the crack cause and evolution mechanism of the peduncle area are not systematically revealed. Therefore, a system is necessary to research the cracking mechanism of the part, and theoretical support is provided for the durability design and maintenance of the prestressed concrete box girder bridge. Although it has been considered that the overstress may cause cracking of the prestressed concrete structure, as Linyun Zhou and Shui Wan in "Full-range nonlinear analysis of post-tensioned anchorage zones based on modified strut-and-tie model", the overstress is considered to be one of the main causes of cracking of the post-tensioned prestressed concrete anchoring zone. However, the determination of whether the cracking of the Liang Gengye area of the prestressed concrete box is caused by the splitting stress still has two major difficulties, namely 1) the lack of a three-dimensional splitting stress calculation method facing the peduncles. The existing splitting stress calculation model has obvious limitations that firstly, in the analysis dimension, the two-dimensional distribution of the vertical splitting stress along the length of the beam (along the height of the beam) is considered, the three-dimensional space distribution essence of the vertical splitting stress and the horizontal splitting stress along the longitudinal direction (along the length of the beam) cannot be truly reflected, for example, a solution method for the vertical splitting stress distribution along the longitudinal direction in a two-dimensional prestressed concrete structure is researched in "Investigation of Bursting Forces in Anchorage Zones: Compression-Dispersion Models and Unified Design Equation" by Zhiqi He and Zhao Liu, and secondly, in the application scene, the existing method mainly aims at the anchoring situation of the prestressed steel beam along the height direction of the section, but the common anchoring characteristics along the width direction of the section of the beam in the axillary region cannot be considered, for example, zhiqi He, jiatong Chen, zhao Liu, zhongguo John Ma in ANALYTICAL APPROACH FOR BURSTING CRACKING ANALYSIS of post-tensioned anchorage zone are researched. This double limitation makes it difficult to accurately obtain the actual cleavage stress amplitude in the peduncle region, and thus it is impossible to determine from the quantitative level whether or not the cleavage is dominated by cleavage stress. 2) The direction of the action of the maximum splitting stress in different steel bundle anchoring modes is not clear. For example Joung Rae Kim, hyo-Gyoung Kwak and Byung-Suk Kim in Design equation to evaluate bursting forces at the end zone of post-tensioned members, it has been confirmed that the splitting stress is distributed in both the beam height and beam width directions, but the correspondence between the splitting stress direction and the steel beam anchoring mode has not been established. The influence of different anchoring arrangement modes on the maximum splitting stress direction cannot be fully considered in the existing research, so that whether the splitting at the axilla of the box girder is due to the splitting stress effect cannot be effectively judged in a qualitative level. Therefore, how to establish a three-dimensional splitting stress calculation method suitable for the box Liang Gengye area to determine the stress amplitude, and reveal the internal correlation between different steel bundle anchoring modes and the maximum splitting stress direction, so as to construct a splitting tracing judgment criterion combining qualitative and quantitative analysis, which has become the technical bottleneck to be broken through in the current urgent need. Disclosure of Invention The invention provides a method for tracing cracking of a large-span prestressed concrete box Liang Gengye. The method can accurately calculate the three-dimensional splitting stress of the box Liang Gengye area, and clarify the stress distrib