1、 General idea of construction survey and correction of steel structure engineering

 How to ensure the overall perpendicularity and structural elevation of the project is the focus of the project survey work.According to the construction characteristics and key points of steel structure engineering, the main work contents of measurement and correction are as follows: 

　　1  Acceptance of horizontal control baseline and elevation datum point.

 　　2  The establishment of horizontal control network: the construction range of Benxi steel structure project is wide, and the construction survey control area of steel structure engineering is large, so the quality and rationality of construction control network layout is very important.According to the site visibility conditions and engineering structure characteristics, the rectangular axis control network is established to control the installation accuracy of steel columns.

 　　3  Survey and correction of steel column, long-span truss and giant truss: the tracking measurement control method combining theodolite to correct verticality and total station to correct axis deviation is adopted.

 2、 Preparatory work 

 　　1  According to the measurement workload and operation difficulty of Benxi Steel Structure Engineering, Zhang Yunzhi, a survey engineer with many years of construction experience, is selected to be fully responsible for all the field survey work, and professional surveyor Zhang Jinguang is equipped to cooperate.

 　　2  The instruments (zts602s total station and DS32 level) used in the project shall be inspected and calibrated by the authoritative measurement and testing center, and the inspection results and personnel qualification shall be reported to the owner, supervision and other departments for record before the survey construction can be carried out.For the measuring equipment such as large scale for measuring length, error correction shall be carried out with the supervisor and the manufacturer.

 　　3  Be familiar with and check the size relationship of each part in the design drawing, and put forward and solve the problems found in the joint review of drawings in time.The construction of the project is carried out in strict accordance with code for construction quality and acceptance of steel structure engineering (GB 50205-2001) and code for engineering survey (GB 50026-93). 

　　4  Understand the construction sequence, determine the sequence and time requirements of Surveying and setting out, and formulate detailed setting out scheme from the aspects of division of construction flow, installation sequence of steel structure, construction schedule and plane layout of temporary facilities.

 　　5  According to the general layout of site construction and the needs of construction setting out, the appropriate point coordinates should be selected to make it convenient for large area control, the surrounding line of sight is unobstructed, and it is not easy to be damaged by mechanical rolling, which is conducive to long-term retention of application, preventing the obstruction of line of sight and damage of point position, so as to meet the measurement accuracy requirements and long-term use requirements of site horizontal control network and elevation control network.

 　　6  Sort out the office data, control network of construction axis, leveling base point and survey records of civil engineering survey, handle site handover, and make obvious marks for the mark points.

 3、 Construction of vertical transmission control network and steel structure

 　　3.1  Establishment of horizontal control network

 According to the building axis control points provided by the civil engineering unit, combined with the pre calculated control network coordinate data, the plane control network of steel structure is measured and set up according to the construction requirements and structural characteristics.The internal control method is adopted in the above ground construction stage, that is, to establish a rectangular control network in the plane, control the measurement and correction, and re survey the axis deviation.

 　　3.2  Establishment of elevation control network

 　　1  During the construction, the elevation datum point will be measured to the surrounding concrete structure which has been completed, and marks shall be marked for the measurement of steel column anchor bolt, steel column and embedded parts.

 　　2  The vertical elevation measurement is transmitted upward from the structural steel column, and the steel ruler is used to transfer upward. The level is used to check whether the elevation control point is in the same plane. If it is not more than ± 2mm, the average value is taken as the result. If it is more than ± 2mm, it is transferred again.

 　　3.3  Notes on steel structure engineering

 　　1  In order to ensure the measurement accuracy of steel structure engineering, strong wind, sunshine and other weather as well as construction impact, vertical transmission of horizontal control network is adopted at the same time period, and vertical transmission of horizontal control network is not allowed in Gale Weather above level 4.

 　　2  In the vertical transmission of elevation and horizontal control network, the point position must be retested and closed every time the point is transferred. The qualified self inspection report shall be submitted to the professional supervision engineer for acceptance, and it can be put into use after passing the acceptance.

 　　3  The angle and distance of the whole control network should be closed during the horizontal control network surveying and setting out.When the mean square error of angle measurement is ± 9 ‖, the mean square error of distance measurement is 1 / 24000, and the straightness is within ± 5 ‖, the whole survey control network can meet the requirements of specifications and construction accuracy.The completed survey control points are marked with marking pen and fenced with protective fence to avoid the damage of control points in the construction.

 　　5  When setting out the horizontal line, the instrument height of the level is directly adjusted to make the line of sight of the rear view align with the horizontal line, and the line of sight punctuation is directly marked with a red pencil when looking forward.This can improve the accuracy by 1-2mm.

 　　6  When measuring the elevation or horizontal line, the front and rear sight distance shall be equal as far as possible.

 　　7  When measuring the distance upward from ± 0.00m horizontal line, the steel ruler used shall be verified by metrology. When measuring the height difference, the ruler body shall be vertical and the standard tension shall be used. Meanwhile, the length and temperature of the ruler shall be corrected.

 　　8  In order to prevent the accumulated elevation deviation from exceeding the limit of the total height deviation, the elevation deviation of each node should be strictly controlled.The original starting point should be used to transmit the distance, the ruler body should be kept vertical, and the whole ruler should be transmitted. It is not allowed to transfer node by node to avoid accumulated error.

 4、 Survey control of steel structure engineering

 　　4.1  Survey control of steel structure engineering truss

 　　1  Projection of center line of bottom chord:

 During assembly, the lower chord control point is introduced to the laid construction jig frame, and the point position is marked. Then the total station is set up to close the angle and distance. The side length error is controlled within 1 / 15000 and the angle error is controlled within 6 “.After the accuracy of control points meets the requirements, the instruments are respectively set up at the main control node, and the center line is measured on the jig frame and marked with ink lines.

 　　2  Test of the control node of the lower chord:

 As each truss is assembled in sections, the node control must be done well in each section. According to the condition of truss segment, the node is used as the control basis.The positioning axis is selected as the control baseline. On this baseline, the intersection point between the projection of the control node and the baseline is found by analytic method, and intersects with the projection line of the center line of the bottom chord, which is to obtain the projection point of the control node on the horizontal plane.

 　　3  Truss elevation control:

 According to the truss segment, the intersection node of bottom chord and web member close to the segment point can be selected as the elevation control point.

 Measure the rear view elevation to a certain point on the jig frame one by one with a level gauge and mark it.This is taken as the basis of the rear view.According to the back view point of each elevation, the actual elevation of the corresponding lower chord control node mark point on the platform is measured respectively, and then compared with the design elevation of the corresponding control node, the height difference is obtained, which is clearly marked on the corresponding node mark point of the jig frame, which is used as the basis for truss sectional assembly elevation. The elevation control target is ± 5mm.

 　　4  Truss straightness measurement and control:

 According to the projection of the center line of the truss bottom chord on the horizontal plane as a straight line, the projection line of the outer edge of the truss is symmetrical to the center line of the bottom chord, so the control basis of straightness can start with the following chords.

 　　5Verticality observation of truss:

 After the adjustment of truss elevation and straightness, the translation method is used to control the truss perpendicularity.The specific survey and positioning axis is translated to the same side by about 0.7 ~ 1.2m (depending on the specific visibility). Two translation points are obtained. The theodolite is erected on one translation point, and the other translation point is viewed backward. Tower ruler is set up at the arch camber in the middle of truss. The vertical degree of truss span is determined by reading the longitudinal wire section of theodolite and comparing with the horizontal displacement value.The allowable perpendicularity deviation of midspan is 10 mm (relative error).

 　　6  Deformation observation of truss under deflection:

 After the installation of the steel truss in the steel structure engineering, the total station is set up at any position, and the height coordinate is obtained and recorded. After the truss is loaded with roof load, the height coordinate of the same position is observed with the same method, and the deflection value of the steel truss is obtained by comparing the height difference twice.And make records.

 　　4.3  Measurement control of steel column

 The measurement and correction of steel column is an important link in the process of steel structure installation, which is directly related to the construction quality of the whole building.In order to ensure the construction quality of the project, our company will adopt the construction method which has been mastered skillfully in the measurement and correction of the above ground structure.

 　　1  Measurement and correction of the first steel column

 　　1) Preparation before installation:

 　　(1) Firstly, according to the horizontal control network used in the basement, the center point of the steel column bottom plate is measured on the concrete bottom plate surface, and then the cross ink line is popped according to the midpoint line, and the elevation of the intersection point of the “cross” ink line is measured;

 　　(2) According to the axis, correct the bolts with large deviation of embedded parts, so as to facilitate the placement of column bottom after steel column installation;

 　　(3) The base surface is trimmed according to the elevation points on the foundation surface, and the thickness of the base plate is calculated according to the measured elevation of the foundation surface and the height of the bottom cylinder surface. When the base plate is placed, it is leveled with a level gauge to make it conform to the design elevation

 　　2) Positioning and correction of the first steel column:

 　　(1) Steel column in place: after the steel column is in place on the foundation, the center line of the column shall be aligned with the center line on the foundation surface. The position of the column bottom shall be in place as soon as possible during the installation of the steel column. A small amount of deviation can be corrected by Jack and crowbar. The axis deviation after the column bottom is in place shall not be greater than 2mm.

 　　(2) Steel column perpendicularity correction: after the steel column bottom is in place and the column bottom standard is completed, the verticality is checked by theodolite. In two directions perpendicular to each other, the theodolite is used to aim the side center point of the steel column top, and then the difference between the projection point of the center point and the corresponding column side center point at the bottom of the column is compared, which is the deviation value of the steel column perpendicularity in this direction.The value should not be greater than H / 1000 and the absolute deviation should be less than or equal to 10 mm.When the line of sight is blocked, the instrument can be set up at the position away from its axis, but the deviation angle should not be greater than 15 degrees.

 　　1  Measurement and correction of steel columns above ground

 　　1) Preliminary calibration: after the steel column is installed in place, the joint dislocation of the upper and lower steel columns and the alignment of the central axis are corrected.

 　　2) Steel column perpendicularity and elevation correction: after the initial calibration, when the steel column is in an independent state, two theodolites are used to calibrate the steel column perpendicularity.Two theodolites are used to observe the X and Y directions of the steel column respectively. The observation angle of the theodolite is not more than 15 degrees. Firstly, the verticality deviation value of a single steel column is obtained by observing the upper and lower central axis of the steel column, and then the corrector is instructed to correct the vertical deviation of the steel column by adjusting the expansion and contraction of the jack.The elevation adjustment value of the steel column is determined according to the elevation deviation of the top of the previous column, the manufacturing length deviation of the steel column in this section, and the weld shrinkage value of the steel column.The elevation deviation of steel column is adjusted by adjusting the expansion and contraction of four jacks fixed on the steel column connecting plate.If the height of the steel column needs to be adjusted, the elevation deviation of the steel column shall be adjusted by adjusting the expansion amount of the four jacks fixed on the temporary connecting plate of the steel column; if the column of this section needs to be lowered, the steel column shall be installed after the same amount of cutting treatment on the ground surface of the steel column lower opening before installation; the elevation adjustment of the steel column shall not exceed ± 3mm.When the two methods are adjusted, the temporary connecting plate ear plate at the butt joint of steel column shall be reamed. 

Steel column survey

　　3) Overall correction: after the steel column perpendicularity correction is completed, when the steel column and beam in a area are installed, the overall measurement and correction of steel column in this area shall be carried out, and the local deviation shall be corrected by using the guide chain and cable wind rope.For the overall deviation, the verticality of multiple steel columns is corrected by multiple instruments at the same time.

 　　4) Axis and elevation measurement before welding: after all the steel columns in the construction area are corrected, the plane control network is introduced upward to the construction floor, and the top axis and elevation of the steel column are measured after the total station is closed.When the axis and elevation measurement deviation meets the specification requirements, the high-strength bolt shall be finally screwed. After the construction, the deviation measurement of the column top axis and elevation shall be conducted again, and the deviation data shall be sorted out to determine the welding construction sequence.

 　　5) Measurement of front axis and elevation after welding: after welding, according to the floor plane control network after the completion of welding, use total station to measure the column top axis and elevation deviation value of the steel column in this section, sort out the deviation data and report it to the professional supervision engineer for acceptance, and provide the basis for the installation, measurement and correction of the next steel column.

 　　5  Precision control target and guarantee measures

 　　5.1  Installation allowable deviation control target 

Table measurement control objectives

name

Allowable deviation

Allowable deviation of project internal control

Overall verticality of buildings

50 mm outward and 50 mm inward

20 mm inward and 20 mm outward

Total building height deviation

-H/1000≤e≤H/1000

-30≤e≤30

-20≤e≤20

Single column inclination

H / 1000 and ≤ 10mm

H / 1000 and ≤ 8mm

Story height deviation

ΔH≤±5mm

ΔH≤±5mm

Vector bending of buildings

E ≤ L / 2500 and E ≤ 25mm

E ≤ L / 2500 and E ≤ 25mm

Torsion of upper and lower columns

e≤3

e≤3

Elevation difference of column top on the same floor

-5≤e≤5

-5≤e≤5

Column bottom elevation

-2≤e≤2

-2≤e≤2

　　5.2  Measurement accuracy control measures of steel structure engineering

 　　1  Therefore, according to the requirements of the steel structure, the measurement accuracy of ± 2 mm is higher than that of the steel structure.

 　　2  The manufacturing and testing tools used in the project can only be used with the label of qualified validity period and error range.The steel ruler and instrument used in the measurement shall be verified by measurement first, and then used after checking the error, and regular calibration shall be achieved.The manufacturing, installation, supervision and inspection standards should have the same accuracy.

 　　3  According to the floor plane shape and structural type and hoisting capacity of installation machinery, considering the symmetry and overall stability of steel structure installation, reasonably divide the construction area, control the overall installation size, and prevent the accumulation of welding and installation errors.

 　　4  To ensure the accuracy of the axis control point delivered by the laser theodolite, the instrument should be strictly aligned and leveled during the measurement. The full circle rotation should be adopted during the survey, and the survey should be conducted once every 900 and the center should be taken four times.And avoid lifting shaking, strong sunlight and wind speed and other adverse observation factors.

 　　5  The elevation and axis datum point must be measured from the starting datum point and form a geometric figure. Multiple points are closed to each other to meet the accuracy requirements and adjust the error.

 　　6  The revised spatial dimension of steel structure will be reviewed.If the local dimension has error, the construction sequence and direction should be adjusted, and the installation accuracy should be adjusted by using welding shrinkage.

 　　7  In addition to strengthening self inspection and providing special personnel for monitoring, the line inspection department should recheck and inspect the main control points, and conduct a certain proportion of sampling inspection on the measurement results before and after the welding of steel columns, so as to prevent the accumulation and transmission of errors and ensure that the measurement accuracy meets the requirements of construction acceptance.