Precautions for the installation of anchor bolts

Summary:The application of anchor bolts in our lives is ve...

The application of anchor bolts in our lives is very common, and many construction facilities are fixed with them. For some newcomers, they must have many doubts about its installation work.

1. Verticality of anchor bolts
The anchor bolts should be installed vertically without tilting. If the installation is not vertical, it will inevitably cause errors in the installation coordinates of the bolts, and cause certain difficulties in installation. If the base of the bolt holes is very thick, the installation cannot even be carried out. Because the bolt is not vertical, its ability to withstand external forces is reduced. The specific analysis of its force is as follows: Suppose the pressure required to install the equipment is F (that is, the vertical tension of the anchor bolt is F), and the cross-sectional area of ​​the bolt is A. Then: ①The tensile force of the bolt when installed vertically is: F, the stress of the bolt is σ=F/A; ②The tensile force of the anchor bolt when installed obliquely is: F1, the tensile stress is: σ1= F1 F1 /A=F /Acosa ; At the same time, a horizontal component force F2 is produced. The bending stress generated by the force acting on point O is σ2= F2 L/W=FLtga/W (W is the bending section modulus); the total stress is σ =σ1 +σ2.

Obviously, F1 >F, relatively speaking, under this kind of force, the capacity of the anchor bolt becomes smaller and it is more likely to be damaged or broken. At the same time, the horizontal force component will cause the machine base to rotate in the horizontal direction, so the equipment is not easy to fix. Sometimes the installed equipment may change its position due to this component of force before the secondary grouting, causing rework or quality accidents. At the same time, due to the horizontal component of force, once it encounters an external force, it may cause errors in the aligned equipment, which is not allowed. Therefore, when installing the anchor bolts, they must be installed vertically to avoid tilting.

2. Laying of anchor bolts
①In the construction process, the secondary grouting of the dead anchor bolts is often encountered, that is, when the foundation is poured, the reserved holes for the anchor bolts are reserved in the foundation in advance, and the anchor bolts are put on when installing the equipment. Then use concrete or cement mortar to pour the anchor bolts.

②Before laying the anchor bolts, the rust and oil on the anchor bolts should be cleaned, but the threaded part should be coated with grease, and then check whether the fit with the nut is good. During the laying of the anchor bolts, Prevent debris from falling into the bolt holes to ensure the quality of grouting. When preparing for the secondary irrigation of hook type anchor bolts, it should be noted that the lower hook must not touch the bottom, and a gap of at least 100mm should be left. The distance between the bolt and each side of the hole wall should not be less than 15mm. If the gap is too small, it is not easy to fill up during grouting, and holes will appear in the concrete. If the equipment is installed in the basement or the concrete floor on the foundation, the hook end of the anchor bolt should be hooked on the steel bar; if there is no steel bar, a round steel should be used to cross the hook.

3. Tighten
The anchor bolts can be tightened only when the concrete in the reserved hole reaches more than 75% of its design strength. The tightening force of each bolt should be even; after tightening, the bolt should be exposed to the nut, and the exposed length should be 1/ of the bolt diameter. 3~2/3.

4. Make corresponding construction records
The corresponding construction records should be made in detail during the installation process to truly reflect the type and specifications of the anchor bolts, and provide effective technical data for future maintenance and replacement. Precautions for concrete pouring: Before pouring concrete, the screws and nuts on the upper part of the bolt sleeve must be greased with plastic sheet and tied with iron wire. When pouring concrete, especially when pumping concrete is adopted, the squeezing of the concrete must be avoided, which may cause the anchor bolts to go out of place. The concrete pump pipe should avoid pouring directly against the anchor bolts, and use artificial cloth within 30cm of the anchor bolts and the surrounding area as much as possible. When using a vibrator, do not over-vibrate in the above-mentioned area. When pouring concrete, the construction personnel must strengthen the monitoring of the anchor bolts, and use the level and theodolite to check each group of anchor bolts (especially the anchor bolts where concrete is being poured around) at any time. Once a deviation is found, it should be corrected immediately.


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