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Problems Existing in the Installation of Anchor Bolts and Solutions

The steel structure factory building has the advantages of saving steel, low cost, easy production and installation, short construction period, wide application range, beautiful appearance, and can be demolished, etc., which are recognized by users. For the construction unit, the most important task is to embed the anchor bolts. During the construction process, due to errors or errors in design drawings, measurements, operations, weak installation and fixation, or shock or vibration when pouring concrete, excessive deviations in some bolts are often caused.

The most common deviations in the construction process are as follows:

1. Deviation of plane position of anchor bolts

Plane position deviation refers to the installation error of anchor bolts in the plane. Mainly due to poor fixation, or shock or vibration during concrete construction, some bolts often have excessive plane position deviation.

The usual way to deal with this kind of deviation is: when the deviation between the bolt center and the designed center line is within 10mm, you can adjust the bolt hole position of the column base plate or cut holes to adjust, but be particularly careful to avoid damaging the base.

When the bolt diameter is within 36mm and the deviation distance is less than 36mm, the hot-bent bolt method is generally used. The so-called hot-bending bolt method is to dig a 150-200mm deep groove at the root of the anchor bolt, bake the root of the bolt with an oxygen acetylene gun, and bend the bolt into an S shape. Bending or deformation of the anchor bolt will cause the bolt to The working stress is several times greater than normal, so the rounded corner transition is used during hot bending, and the bent part is buried in concrete to prevent stress concentration at the corner. The heating temperature is controlled in the range of 700-800 ° C, and water cooling is avoided to prevent the bolts from becoming brittle. If the diameter of the bolt is equal to or greater than 36mm, hot bending can also be used, but anchors such as steel plates or steel bars need to be welded to the bending part. Its length should not be less than the distance between the upper and lower tangent points of the S-bend, and the length of the weld should be calculated to make the bolt pull Straight and breaking strength.

If the anchor bolt deviation is very large (larger than), the method of setting up a transition steel frame can be used, that is, cut the bolts first, weld the channel steel frame, and then weld new bolts to the channel steel. All channel steel welds must be calculated. The newly installed bolts are firmly welded together with the original bolts buried in the foundation with large deviations through channel steel or I-beam to transmit the horizontal and vertical forces on the superstructure. The frame design should ensure sufficient strength and rigidity to make it a reliable whole.

2. Elevation deviation of anchor bolts

Deviation in the height direction of anchor bolts is also common. The theoretical exposed length of the anchor bolt depends on the thickness of the grout, the thickness of the anchored equipment (plate, box, frame, etc.), and the length of the nut required to tighten the nut. After all the bolts are installed, take one of the upper left corner or upper right corner bolts as the horizontal elevation benchmark and fix it with a nut. Use the bolt elevation as the benchmark and then use a spirit level to adjust the level of other bolts. Generally, adjust the four ground bolts at the four corners first. Anchor bolts, and then the middle anchor bolts, use the cross adjustment method, and compound multiple times to ensure that all bolts are on the same level.

If the elevation deviation of the anchor bolts is -30~30mm, but the column foot installation can still ensure that the threads are 2 nut lengths, no treatment is required, or the nuts can be tightened and then welded to the backing plate and column foot plate. , to prevent the nut from loosening; if the thread is high, a steel pad can be added for adjustment.
If the bolt elevation deviation is greater than -30~30mm and cannot meet the installation requirements, the method of lengthening the bolts can be used. The specific steps are as follows:
First, cut the concrete around the bolt into a concave pit, use bolts of the same diameter, and weld the upper and lower grooves butt or butt each other, and then add welding steel bars on both sides. The steel bars will not expose the surface of the short column leveling layer to facilitate the steel column. Install. When the diameter of the bolt is within 36mm, weld 2 steel bars; when the diameter of the bolt is greater than 36mm, weld 3 steel bars. The cross-sectional area of the additional steel bars should not be less than twice the cross-sectional area of the original bolt, nor should it be used less than 16 mm. The length of steel bars and welds is generally taken from the upper and lower parts (d is the diameter of the bolt).

3. Treatment of anchor bolt “traps”

When tightening the anchor bolts, due to excessive force, the bolts were pulled out of the equipment foundation, making the equipment installation impossible. At this time, the concrete in the middle of the bolt needs to be chiseled away, and then two intersecting U-shaped steel bars need to be welded, and concrete can be refilled to re-fix the bolt.