Through bolt installation errors h1>
EJOT offers various through bolts:
- BA-V, made of galvanic zinc-plated steel
- BA-F, made of hot dip zinc plated steel
- BA-E, made of A4 stainless steel
- (The through bolt BA-E-HCR, made of HCR stainless steel for highly-corrosive environments, is available upon request.)
Through bolts work by driving a steel bolt into the substrate. When the bolt is tightened, a metal ring is expanded, which in turn clamps the bolt into the substrate.
Caution on edgesThis concept of load transfer over the expansion pressure is also the reason that the through bolt has its limits as a fastener for certain applications. This is mainly the case when the fixing points are close to the edge of concrete surfaces. If the concrete has not enough mass to absorb the expansion pressure, the result may be spalling of the substrate material and in the end even complete failure of the fixing point.
In the following you can see some negative examples for the assembly of through bolts:
Mistake no. 1: Fixing point too close to the edge
This example shows a metal handrail that has been fastened to concrete steps with through bolts. The attachment points are at the outer edge of the steps. The occurring expansion pressure has damaged the surface of the concrete. In some parts the complete corners of the concrete have spalled.
The corner of the step is chipped - this is not going to hold!
Mistake no. 2 - Inclined bolt anchors
It seems that the installer knew that the edges are critical, because he tried to prevent the spalling by installing the through bolts at an angle. This second installation error is the reason that the through bolt could not be mounted flush with the attachment.
Mistake no. 3
Out of four possible installation points, the two most unfavourable ones at the edge were chosen.
What could have prevented the damage?The minimum edge distance for through bolts in concrete should have been observed and the drill holes should have been perpendicular.
As a rule of thumb for the edge distance, a minimum of 6 times the through bolt diameter (6 * d) should be used. Example: through bolt M10 = min. 60 mm edge distance. The currently valid approvals of the manufacturer and the included centre distance needs to be observed as well. The respective European Technical Approval ETA-18/0219 contains information about the min. edges distances.