The steel structure project is the easiest work to do. You know why? It will just start with anchor bolt installation, checking the distances of the anchor bolts and the critical distance. Ensuring the locations and level by providing survey report. Erecting the steel members start from column bracing, rafters, purlins, beam, joist etc. A tremendously easy and can be erected quickly.
Steel structure work is really different from concrete structure, concrete works are more complex, especially when the project is a high-rise concrete structure. Therefore, the foundation will be huge enough to carry all the load transferred from superstructure then follows the complexity of the construction of foundation towards superstructure.
In concrete structure, steel reinforcement holds the concrete elements that make it stand and firm, but in steel structure, it’s either the rivets or bolts that held it stand. So, I am going to write the most common method of checking the tightness of connection bolts in most practical and easiest way.
Actually, there are five methods of checking the tightness of connection bolts. There is “Direct Tension Indicator” or DTI. The direct tension indicator is usually written in the specification and one of the requirements to check the bolt for tightness. There is that called “Turn-of-Nut” method which is also easy to use but hugely tedious. Imagine that if you have 3,000 bolts in one “truss or floor beams” it is not practical. The other methods, we will discuss it later.
Now, in our projects we’ve used the most extremely simple and easy ways to checking the connection bolts tightness and you should be doing this in your project.
This is what we called “Calibrated Wrench Pre-tensioning.”
Here is the guide to check the connection bolts using calibrated wrench pre-tensioning or torque wrench.
1. Calibration Certificate
Maintain the calibration certificate of the torque wrench. If you have subcontractor require them to submit the calibration certificate and keep it in a file. Log it in your equipment calibration log to trace the date of expiration or validity of calibration. Make sure it is up to date.
2. Impact the bolts via impact machine
Before checking the bolts with torque, the bolts should have been tightened to snug-tight condition via impact machine. Make sure that all the bolts have been impacted.
Impacting to snug-tight condition
Snug-tight condition is defined as the tightness attained with a few impacts of an impact wrench or the full effort of an ironworker with an ordinary spud wrench to bring the connected plies into firm contact
3. Determine the torque value of bolts
There are standards that specify the torque values of the bolts like German Standard, British Standard, and American Standard. Some use the German Standard, but in our current project we are using American Standard which is ASTM A325 and ASTM A390. It is important to determine first the tightening torque requirement of bolt before checking the bolts with a torque wrench.
4. Bolt tightening inspection
Bolts shall be checked by calibrated torque wrench as per recommended tightening torque in the applied project standard. There are types of torque wrenches that you can use from, one is having the digital or dial gauge and the other has clicked type torque wrench. Click type is easy to use and very convenient. You are maybe asking “How to determine if the bolt being checked has passed to the required tightening torque value?” Because of the click type torque, once the torque has reached to tightening torque value a sound “Click” will come from the torque itself.
5. System of checking a group of bolts
This photo serves as a sample of system of tightening
If you are in the connection plate consists of a group of bolts shown in the above photo. Let us have an example to just explain how the system of checking. The tightening would start either from the bottom corners of the plate, let us say you would want to start at lower left corner and then cross in the upper right corner of the plate and vice-versa.
You should take extra care when the erection of steel structure, especially high-rise steel structure, hangars with 43.0-meter columns, space steel truss for pipe racks etc. If you will not consider the importance of connection bolts, those structures may fail. Because of bolts, that is why those structures I have mentioned are still standing rigidly and firm.