Requirements for setting the construction datum point and positioning the cable for prestressed steel composite support:

Before installing enclosing purlin, it is necessary to determine the axis datum point, and use the total station or theodolite to calculate and measure the base point of the inner side of the two adjacent corners of the foundation pit through coordinate calculation. Through this base point, the plane installation and positioning is carried out by the method of connecting cables. The deviation of the actual installation axis shall not exceed5mm.

The thread used for pulling is usually string or cotton thread, diameterIn order to0.8～1.0mmAs appropriate, the site is determined by the distance of the wire; The pendant is used to set the center, the size is variable, the diameter is usually25～50mmAs appropriate, the tip of the line drop should be accurate in order to align with the center point.

A gallows is securely placed beyond the center point of the reference, string or cotton thread is hung and straightened using a tension force(The tension force should be the wire breaking force30％～0％)After positioning, mark on the triangular bracket for controlling the position of enclosing purlin installation.

The unilateral positioning line of enclosing purlin in the inner side of foundation pit should meet the basic requirement of being in a straight line, so as to ensure the uniform force of the outer envelope after applying prestress.

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