A concrete anchor bolt is used for bolting concrete structures together. One of the most common usage of bolts is for bolting the foundation of a masonic structure with it’s body. Therefore, anchor bolts play a very crucial role in determining the structural robustness of a building. In absence of proper quality of bolts or a flawless installation of the bolts, a building will collapse like a pack of cards in the event of even minor adversity such as heavy rain or storm. If you are getting a house or a building structure constructed and know nothing about bolts, following know how about concrete bolts can assist you in making your choices.
A concrete anchor bolt will work in one of two ways:
Hold the cement by expanding against the sides of the hole.
Hold the cement by the friction against the sides of the hole.
Based on the mechanism of work, anchor bolts are essentially of two types: “Friction” concrete anchors and “J” bolts. Friction concrete anchors have a ring around their threaded bottom that is kept in place by a tightening the screw which is fixed in the foundation by drilling a hole in it. The other type of concrete anchor bolts are “J” hooks that can be seated in the wet concrete.
The spacing between bolts ought to be carefully calculated. If two anchors are placed very far they might not hold the structure very well and if they are placed very near to each other or very near to the edge of the concrete then the force generated by two bolts can break the concrete.
The total load of the building must be divided equally amongst the number of anchors used. However, the load on each anchor should be less than it’s maximum load bearing capacity. The rule of the thumb is that bolt you choose should be certified for four times the weight it will carry if it is expected to bear static load and should be certified for eight times the weight it will carry if it is expected to bear dynamic load.
The size of the opening is very important .To drill down the holes for fixing the bolts prefer using hammer drill over masonry drill. This is because masonry drills chip away concrete while drilling the opening and as a result the opening is larger than the size intended. There are special drills for anchors for which hole size precision ought to be very high. For best results blow out any excess dust from the holes before placing the bolt in it.
Most importantly, the fastening power of a bolt is directly proportional to the quality of concrete. Where on one hand good quality concrete holds up well and results in strong buildings, on the other hand flaky and crumbly concrete does not tend to hold up very well and results in weak structures.