Bolted and screwed connections of thin sheet steels at elevated temperatures

Abstract

The structural behaviour of single shear bolted connections, double shear bolted

connections and single shear screwed connections of thin sheet steels at elevated

temperatures has been investigated in this study. The current design rules on bolted

and screwed connections of thin sheet steels for cold-formed steel structures are

applicable for ambient temperature condition only. These design rules may not be

applicable for elevated temperature conditions. Therefore, design guidelines should

be prepared for bolted and screwed connections of cold-formed steel structures at

elevated temperatures.

A total of 30 tensile coupon tests were conducted to investigate the material

deterioration of the thin sheet steels at elevated temperatures, and also to determine

the critical temperatures for connection tests. A total of 510 tests on single shear

bolted connections, double shear bolted connections and single shear screwed

connections of thin sheet steels at elevated temperatures was performed in the

temperature ranged from 22 to 900?C using both steady state and transient state test

methods. The test results were compared with the predicted values calculated from

the North American, Australian/New Zealand and European specifications for coldformed

steel structures. In calculating the nominal strengths of the connections, the

reduced material properties of the thin sheet steels were used due to the deterioration

of material at elevated temperatures. It is shown that the design strengths predicted

by these specifications are generally conservative at elevated temperatures.

Finite element models for single shear bolted connections, double shear bolted

connections and single shear screwed connections were developed and verified

against the experimental results. Explicit dynamic analysis technique was used in the

numerical analyses. Extensive parametric studies that included 490 finite element

specimens were carried out using the verified finite element models to evaluate the

bearing strengths of bolted connections as well as the tilting and bearing strengths of

screwed connections of thin sheet steels at elevated temperatures.

Design equations for bearing strengths of bolted connections as well as design

equations for tilting and bearing strengths of screwed connections were proposed

based on both the experimental and the numerical results in the temperature ranged

from 22 to 900?C. The bearing strengths of bolted connections as well as the tilting

and bearing strengths of screwed connections obtained from the test specimens and

the finite element analyses were compared with the predicted strengths calculated

using the proposed design equations and also compared with the design strengths

calculated using the current North American, Australian/New Zealand and European

specifications with consideration of the reduced material properties at elevated

temperatures. It is shown that the proposed design equations are generally more

accurate and reliable in predicting the bearing strengths of bolted connections as well

as the tilting and bearing strengths of screwed connections of thin sheet steels at

elevated temperatures than the current design rules. The reliability of the current and

proposed design rules was evaluated using reliability analysis. The proposed design

equations are suitable for bolted and screwed connections assembled using thin sheet

steels of thickness ranged from 0.35 to 3.20mm.