Dissertation

Effect of Bolt Assembly on the Robustness of Steel End Plate Connections at Elevated Temperatures

Shaheen, Mohamed Abdelrasoul Ahmed

2022

Overview

The ability to withstand accidental loads without disproportionate collapse, i.e. robustness, is a necessary characteristic of any structure. Previous studies have demonstrated that the robustness of steel frames during fire is controlled primarily by the rotational capacity of beam to column connections. Higher values of rotational capacity allow the beam to develop catenary action which enhances the survivability of the steel frame during fire. Over the last two decades several inroads have been made to increase the rotational capacity of beam to column connections during fire. The previous methods improved the rotational capacity by either changing the connection types or topology while overlooking the contribution of the bolt assembly (bolt and nut) to the behaviour, despite the fact that the frequent failure mode of connections reported in the literature is the bolt failure.In this study, the rotational capacity is enhanced by improving the contribution of bolts. One feasible method is to eliminate the brittle failure mode of the bolt assembly i.e. stripping. A detailed FE study is initially presented investigating the factors affecting the failure modes of high strength and stainless steel bolt assemblies under tensile force. It was concluded that the stripping failure is primarily controlled by the thread length in the grip, the further the nut distance from the shank, the higher the resistance to stripping. The effect of stripping failure on the ductility of end plate beam to column connections was also numerically investigated at ambient and elevated temperatures. It was concluded that the rotational capacity of a connection can be 5.0 times higher if stripping failure is avoided, particularly at elevated temperatures.Another feasible method to improve the rotational capacity of connections is to increase the deformation capacity of the bolt assembly, the higher the bolt's elongation, the higher the rotational capacity that can be achieved. By inserting a steel sleeve with a designated length, thickness and wall curvature between the end plate and the washer, the load path between the end plate and the bolts can be interrupted, promoting a more ductile response. End plate connections with various sleeve geometries were numerically investigated using a validated FE model at ambient and elevated temperatures. The proposed system substantially enhances the rotational capacity up to 3.46 times that of the standard connection. An elastic response consistent with standard connections is maintained indicating that the proposed system is compatible with existing codified elastic design approaches without modification. An analytical solution was also proposed to predict the geometric parameter of a sleeve with a circular waveform. The sleeve is mathematically represented using shell of revolution theories under axisymmetric load. The comparison between the proposed analytical solution with validated FE models show that the predicted rotational capacity based on the analytical solution is very conservative, however with a significantly higher rotation capacity than that of the standard configuration.

• Publisher: ProQuest Dissertations & Theses
• Subject: Boundary conditions / Crack propagation / Deformation / Design / Ductility / Failure / Friction / Geometry / Grain boundaries / High strength steel / Materials science / Mathematics / Mechanics / Physics / Shear strength / Stainless steel / Tensile strength
• ISBN: 9798352997987