Assessing the viability of implementing significantly oversized holes in high strength friction grip bolted connections

Abstract

The development towards a circular economy has many hurdles to overcome. For the construction sector an important step in this process is the transition towards reusing structural elements. Prefabrication of elements is a significant step towards achieving this concept. However, a case where both prefabrication and reuse are limited is the replacement of bridge decks. Headed bolts are welded to the steel supporting elements and encased in grout to connect them to the concrete deck elements. This method prevents reuse of the deck elements and hinders reuse of the steel supporting elements.

Research and literature exists on a number of alternative shear connectors that increase the modularity of these elements. The best alternatives have a single limitation in common: the allowed deviation for the placement of the shear connectors and bolt holes is smaller than is feasibly possible. The variances of element placement during construction add up to make it incredibly hard for these low tolerance connections to be made. The bolt hole diameter can be increased to increase the deviation tolerances. The large nominal hole clearance this results in needs to be considered. This can be done by using either resin injected bolts or High Strength Friction Grip (HSFG) bolted connections. Using HSFG bolted connections is preferred due to the shorter time spent on site and minimal waste, but research on the subject is sparse.

A proposed HSFG bolted connection that implements significantly oversized holes, defined as bolt holes with a nominal hole clearance roughly equal to the bolt diameter, and cover plates was designed together with both a control and regular connection to compare its behaviour with. The control connection is identical to the proposed connection with the exception of its holes which are normal sized. The regular connection has normal holes and does not include cover plates. Finite Element Models (FEM) were made of these connections that were subjected to static loading in a Finite Element Analysis (FEA). Test specimens of these connections were made and subjected to fatigue loading.

The numerical results of the static FEA showed that the use of cover plates reduced the stiffness and slip load of the connection. The second observation was the small impact that the hole size had on the slip load when using cover plates. This small impact becomes negligible at design preload.

The experimental results showed that the impact of larger bolt holes increased the loss of preload by roughly 1% during both short term relaxation and fatigue loading. The effect of the bolt hole size on the slip after fatigue loading was also concluded to be negligible, but the effect of the cover plates was concluded to be detrimental.

It was overall concluded that the use of significantly oversized holes in HSFG bolted connections with cover plates is viable. The negative effects caused by the cover plates and required longer bolt make it preferrable for large disc springs to be used instead of thick cover plates. The viability of the concept allows for further research on the subject.