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Robustness of flexible endplate connections under fire conditions.

Hu, Ying (2010) Robustness of flexible endplate connections under fire conditions. PhD thesis, University of Sheffield.

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Abstract

Worldwide interest in how to prevent the progressive collapse for tall and large buildings under exceptional loading conditions was heightened by the collapse of the twin towers at the World Trade. The performance of steel-framed structures subjected to fire loading is heavily reliant on the interaction between structural members such as columns, slabs and beams. The implicit assumption in fire engineering design is that bolted connections are able to maintain the structural integrity for a large and tall building under fire conditions. Unfortunately, evidence from the collapse of the World Trade Centre towers and full scale fire tests at the BRE Cardington Laboratory indicates that connections may be particularly vulnerable during both heating and cooling. Hence, this PhD research is focused on structural performance of simple steel connections under fire conditions, particularly the interaction mechanism between non-ductile and ductile components in a connection and connection failure mechanism in a steel-framed structure subjected to fire loading. The research involved experimental testing of simple steel connections and components (structural 8.8 bolts) at elevated temperatures. High temperature tests on structural bolts demonstrated two modes of failure at elevated temperatures: bolt breakage and thread stripping. In order to prevent the thread stripping in a connection, the manufacturing process of bolts and nuts has been investigated and the 'overtapping' of nut threads to accommodate the (zinc) coating layer for corrosion resistance has been indentified as a primary reason resulting in this premature failure between bolts and nuts. Experimental tests on endplate connections revealed the ductility of these connections to decrease at high temperatures, which might hinder the development of catenary actions in fire if plastic hinges are attempted to be formed within the connection zones. Component-based modelling and finite element simulation have been utilized for investigation of the performance of these connections. An improved component-based model has been developed which includes nonductile (brittle) components (bolts and welds) into a connection model with a reasonable assumption of their failure displacements, based on experimental tests. This model also features vertical components for consideration of shear response of these connections in fire. The component-based connection model has been used in a sub-frame structure and a parametric study demonstrates that a connection may fail due to a lack of rotational capacity (failure of bolts or welds) in a structure exposed to a fire. Therefore, partial depth endplate connections are recommended to be fireprotected to prevent the failure of these brittle components. Alternatively, ensuring the strength of brittle components (bolts and welds) is higher than that of other components in each bolt row is necessary to achieve the ductile failure mechanism of simple connections. Based on the experimental tests, component-based connection modelling and finite element simulation, recommendations to improve the robustness of simple steel connections in fire have been presented.

Item Type: Thesis (PhD)
Academic Units: The University of Sheffield > Faculty of Engineering (Sheffield) > Civil and Structural Engineering (Sheffield)
Identification Number/EthosID: uk.bl.ethos.522409
Depositing User: EThOS Import Sheffield
Date Deposited: 14 Dec 2016 14:54
Last Modified: 14 Dec 2016 14:54
URI: http://etheses.whiterose.ac.uk/id/eprint/14969

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