Handover axis control points and elevation datum points, layout truss axis and positioning elevation; Re-measure the position and elevation of the bearing and make records. If the error exceeds the allowable range of the specification, it should be corrected in time.

Truss positioning control

According to the positioning axis, measure the lower chord elevation, and adjust the lower chord elevation and positioning dimension error within the control range. Before hoisting the truss, according to the design drawings, determine the spatial position of the support point of the lower chord of the truss, mark it well, and put it in place according to the mark when hoisting.

Upper chord plane control

According to the elevation of the control point of the upper chord near the bearing, the elevation of several points is measured by using instruments such as level and spirit level, so as to control the elevation of the upper chord plane of the whole truss to be consistent with the elevation of two points of the section. After the temporary fixation of steel truss connection is completed, under the supervision of surveyors, the axis deviation and elevation deviation are corrected with jacks, chains and wedges.

Measuring method of steel structure:

Installation survey of roof steel structure is a very important survey work. How to use advanced measurement technology to accurately install the structure in place according to the design drawings will directly affect the quality and progress of the project. The embedment of anchor bolts and the installation and measurement of the structure are introduced below.

4. 1 Embedding of anchor bolts

1) Plane position measurement: use high-precision total station (or theodolite) to determine the normal line (longitudinal center line) of each column by polar coordinate method, use total station to measure the distance, determine the center of anchor bolt, and then make a vertical line through the center point to determine the transverse center line. The relative accuracy of the positioning line is 1/40000, the median error of the angle measurement of the positioning direction line is 5 ",the longitudinal distance error between the corresponding two points is 1.5mm, and the transverse distance error between adjacent two points is 2.0 mm ..

2) Measurement method: an angle steel frame with the same height as the anchor bolt positioning plate is embedded in the lower concrete, and the vertical and horizontal center lines are measured on the frame, marked with a red triangle, and compared with the vertical and horizontal column positioning axes on the positioning plate. According to the deviation, adjust the positioning plate so that the vertical and horizontal axes of the positioning plate are completely coincident with the measuring axis. The allowable error between the vertical and horizontal axis of the positioning plate and the design position is 0.3 mm. Before the initial setting after concrete pouring, the center line of the positioning plate should be tested again. If there is any deviation, it should be corrected immediately until it meets the accuracy requirements.

3) Elevation measurement method: DS 1 is used for elevation measurement of anchor bolts. Directly putt the level from the elevation control point to the angle steel shelf for auxiliary installation, mark it with red paint, and adjust the height of the positioning plate to the design position according to the elevation point of putt to avoid the allowable error of elevation measurement.

Phase difference1mm.

4.2 Structural Installation Measurement

During the installation of steel structure, due to the influence of structure and scaffolding, the measuring line of sight will be blocked to a considerable extent. Solution: First, determine the plane projection of the main stressed members of the steel structure at the construction site, and project the main points (directions) onto the construction surface with a laser straightener; The second is to set up two or three observation platforms higher than the roof structure, and use high-precision total station to measure and control the three-dimensional coordinates. During installation, use laser plumb instrument or theodolite to control the approximate position of steel structure. Then use the total station to control its precise position. Stick the self-adhesive reflective target special for total station on the steel structure node in advance. After aiming at the target, the three-dimensional coordinates of the node are transferred from the total station by coordinate lofting (input by the computer in advance), and the total station automatically calculates the actual coordinates of the point and the difference between the actual coordinates and the installation position, thus regulating the installation process and completing the final installation measurement control.