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CN-121994188-A - Method for measuring lowest point elevation of section of lower chord member of steel mesh frame

CN121994188ACN 121994188 ACN121994188 ACN 121994188ACN-121994188-A

Abstract

The invention discloses a steel mesh frame lower chord section lowest point elevation measurement method which comprises the following steps of S1, determining a measured section of a rod piece to be measured, S2, erecting a total station on the ground right below the lower chord piece to be measured, wherein the horizontal projection distance L between the total station and the measured section meets the following relation that L=k (H-i) (1.2 is less than or equal to k is less than or equal to 2.8), S3, fixing the vertical angle of a total station telescope, enabling a laser indication point to be located at the rightmost end of the rod piece section, recording a horizontal angle alpha start , enabling the laser indication point to be located at the leftmost end of the rod piece section, recording a horizontal angle alpha end , calculating a horizontal angle span, S4, equally dividing a horizontal angle interval [ alpha start ,α end ] into n, S5, sequentially measuring each measuring point elevation H k according to a measuring point horizontal angle sequence alpha k , S6, locating an elevation minimum measuring point index k_min, meeting H k_min =min(H k , and adopting a three-point quadratic interpolation formula to calculate a theoretical lowest point elevation H min .

Inventors

  • HU TIANWEI
  • LI GEN
  • FU LIQING
  • WANG WENHONG
  • Luo Cangjun
  • Zhong Haoqi
  • ZHOU PENG

Assignees

  • 甘肃省建筑设计研究院有限公司

Dates

Publication Date
20260508
Application Date
20260324

Claims (4)

  1. 1. The method for measuring the lowest point elevation of the section of the lower chord member of the steel mesh frame is characterized by comprising the following steps of: s1, determining a measured section of a rod piece to be measured, determining a projection point O and a height H of the section to be measured, referring to a design drawing, and determining the section diameter D of the rod piece; s2, erecting the total station on the ground right below the lower chord member to be tested, wherein the horizontal projection distance L between the total station and the section to be tested meets the following relation: L=k•(H-i)(1.2≤k≤2.8), wherein H is the height of the rod piece from the ground, k is a distance coefficient, and i is the instrument height of the total station; S3, fixing the vertical angle of the telescope of the total station, enabling the laser indicating point to be positioned at the rightmost end of the section of the rod piece, recording the horizontal angle alpha start , keeping the vertical angle unchanged, enabling the laser indicating point to be positioned at the leftmost end of the section of the rod piece, recording the horizontal angle alpha end , and calculating the horizontal angle span delta alpha= |alpha start -α end |; s4, equally dividing the horizontal angle interval [ alpha start ,α end ] into n parts to generate a measuring point horizontal angle sequence: (k=1,., n-1), wherein n is an odd number; S5, measuring the elevation H k of each measuring point in sequence according to the measuring point horizontal angle sequence alpha k to form a data pair (alpha k ,H k ); S6, positioning an index k_min of the minimum measuring point of the elevation, satisfying H k_min =min(H k ), and calculating a theoretical minimum point elevation H min by adopting a three-point quadratic interpolation formula: And outputting a result, namely the elevation H min of the lowest point of the cross section.
  2. 2. The method for measuring the lowest point elevation of the cross section of the steel mesh frame bottom chord member according to claim 1, wherein in the step S2, when k is not less than 1.2 and not more than 2.8, the elevation angle of the line of sight is not less than 19.7 degrees and not more than 39.8 degrees.
  3. 3. The method for measuring the lowest point elevation of the cross section of the steel mesh frame bottom chord member according to claim 1, wherein in the step S4, n is more than or equal to 9 and less than or equal to 17.
  4. 4. A method for measuring the lowest point elevation of a steel mesh frame bottom chord section according to claim 3, wherein when the diameter of the rod to be measured is 40-80mm, n=9; When the diameter of the rod to be measured is 80-150mm, n=13; When the diameter of the rod to be measured is 150-200mm, n=15.

Description

Method for measuring lowest point elevation of section of lower chord member of steel mesh frame Technical Field The invention relates to the technical field of building deformation measurement, in particular to a method for measuring the lowest point elevation of a steel mesh frame lower chord section. Background The steel net frame is used as a main bearing structure of a large-span building, and deflection deformation measurement is a key index for evaluating structural safety. According to the 7.3.6 of the technical standard for steel structure field detection (TCECS-2022), the steel mesh frame deflection calculation needs to take the lowest point elevation of the lower chord section at the span and the support as input data. However, the steel mesh frame bottom chord member is mostly of a circular section, and the lowest point elevation measurement has the following technical problems: 1. When the component deflection detection is carried out, the existing specification only prescribes that the observation points should be distributed along the axis or the side line of the component when the total station, the level gauge or the laser range finder is adopted, each component is not less than 3 points, the mid-span deflection of the component is determined through calculation by measuring the relative position difference between the two ends and the mid-span (TCECS 1009-2022, 7.3.6) but a specific measurement method of each point is not provided. For deflection detection of the steel net rack, the height of the lower chord member of the net rack from the ground is more than 10m, and the diameters of the lower chord members at the two ends and in the midspan are different, so that when the relative positions of the lower chord members are measured by adopting a total station, the axes or the side lines of the rod members are difficult to accurately position by manual visual inspection, and the error of the measured midspan deflection value of the net rack is larger. 2. The visual positioning error is large, namely when the lowest point of the circular section is manually visually detected, the visual positioning error is influenced by visual angles, light rays and experience of operators, and the error is large, so that the height measurement result is distorted; 3. The instrument erection is free of quantitative basis, wherein the total station erection position is more empirical, and quantitative parameters which are compatible with measurement accuracy and operation comfort are lacked. The above problems lead to the prior art directly affecting the reliability of the deflection calculation results. Disclosure of Invention Aiming at the technical problems, the invention provides a method for measuring the lowest point elevation of the section of a lower chord member of a steel mesh frame. In order to achieve the above purpose, the technical scheme of the invention is as follows: the method for measuring the lowest point elevation of the section of the lower chord member of the steel mesh frame comprises the following steps: s1, determining a measured section of a rod piece to be measured, determining a projection point O and a height H of the section to be measured, referring to a design drawing, and determining the section diameter D of the rod piece; s2, erecting the total station on the ground right below the lower chord member to be tested, wherein the horizontal projection distance L between the total station and the section to be tested meets the following relation: L=k•(H-i)(1.2≤k≤2.8), wherein H is the height of the rod piece from the ground, k is a distance coefficient, and i is the instrument height of the total station; S3, fixing the vertical angle of the telescope of the total station, enabling the laser indicating point to be positioned at the rightmost end of the section of the rod piece, recording the horizontal angle alpha start, keeping the vertical angle unchanged, enabling the laser indicating point to be positioned at the leftmost end of the section of the rod piece, recording the horizontal angle alpha end, and calculating the horizontal angle span delta alpha= |alpha start-αend |; s4, equally dividing the horizontal angle interval [ alpha start,αend ] into n parts to generate a measuring point horizontal angle sequence: (k=1,., n-1), wherein n is an odd number; S5, measuring the elevation H k of each measuring point in sequence according to the measuring point horizontal angle sequence alpha k to form a data pair (alpha k,Hk); S6, positioning an index k_min of the minimum measuring point of the elevation, satisfying H k_min=min(Hk), and calculating a theoretical minimum point elevation H min by adopting a three-point quadratic interpolation formula: And outputting a result, namely the elevation H min of the lowest point of the cross section. Wherein in the step S2, when k is more than or equal to 1.2 and less than or equal to 2.8, the elevation angle of the sight line is more than