Experimental and Numerical Investigations of the Behavior of Flush End Plate Connections at Elevated Temperatures Hongxia Yu, Ph.D. 1 ; I. W. Burgess 2 ; J. B. Davison, Ph.D. 3 ; and R. J. Plank 4 Abstract: This paper reports on a set of test results on flush end plate connections at ambient and elevated temperatures. The experiments aimed to investigate the behavior of connections at the ends of unprotected beams in fire situations, when they may be subjected to significant tying forces and large rotations at elevated temperatures, as a consequence of high beam deflection. A change in first fracture mode was observed with increasing temperature as the failing component became the bolts rather than the end plate as the strength of bolts reduces faster than that of steel in fire. At elevated temperatures, the use of thicker end plates can enhance the peak resistance, but reduces the rotational capacity of the connection. Finite-element analyses were performed to simulate the tested connections, and gave predictions very close to the observed behavior of the connections in both the loading and the postpeak resistance phases for all the tests at high temperatures. Via these simulations, minor cracks in the end plate, which were widely observed during the tests, were found to have little effect on the overall resistance. Development of the forces in each bolt row showed that, at the peak resistance of the connection force, their distribution can be far from uniform, which emphasizes the need for the full load-displacement-temperature relationships of bolt rows in simplified component-based analysis methods. DOI: 10.1061/ASCEST.1943-541X.0000277 CE Database subject headings: Connections; Fires; Finite element method; Simulation; Failures; Temperature effects. Author keywords: Flush end plate connection; Fire; Finite-element simulation; Failure. Introduction A recent trend in the performance-based design of composite framed structures has been to fire-protect composite beams on the main column grid, while leaving other beams unprotected. The unprotected composite beams tend to deflect greatly and may de- velop some catenary action at very high temperatures. This re- quires the connections at the beam ends to be able to resist significant tying forces. Simultaneously, large deflection of the beam causes the connections to rotate; connections then must either have high capacity in both rotation and separation to ac- commodate the deformation, or be very strong in order to force the rotation into a hogging curvature of the beam end. Therefore, depending on the type of connection adopted, various levels of moment may be transferred through it to the supporting member. Flush end plate connections are widely used in construction practice in the U.K., and their moment-rotation characteristics have been investigated previously, both at ambient temperature by Aggarwal 1994 and at elevated temperatures by Al-Jabri et al. 2005. However, calculation of the tying capacity, as specified by the U.K. design recommendations The Steel Construction Insti- tute and The British Constructional Steelwork Association Lim- ited SCI & BCSA 2002, is based on the assumptions: • That the connection is subjected to pure tension; and • That each bolt row contributes fully to its total tying resistance. This situation is impossible in practice, as the coexistence of other actions reduces the resistance of individual fasteners. For the whole connection, all the bolt rows may not reach their maxi- mum resistance simultaneously unless their behavior is ductile. If this is not the case an “unzipping” failure may occur as the most heavily deformed components fail before sufficient redistribution to less loaded areas is achieved. From 2005–2008 the University of Sheffield and University of Manchester conducted a joint research program with the aim of investigating the tying capacity and ductility of steel connections at elevated temperatures. Previous tests by Ding 2007 had shown that connections could be subjected to tying forces up to 1.6 times the magnitude of the coincident shear force at high temperatures. Various levels of moment may be transferred through a connection, depending mainly on the connection type. Hence, the investigation adopted a test setup in which the con- nections were subjected to combinations of tying and shear forces. Moments were generated at the connection from the lever arm of the applied force. In total, four types of connection were studied; flush end plates, flexible end plates, fin plates, and web cleats. This paper reports the test results on flush end plate con- nections. The behavior of the connections at various temperatures, and subjected to different load combinations, are given. Different failure modes are described, and their effects on the behavior of the connections are illustrated. Finite-element simulations of the tests have also been per- 1 Lecturer, Dept. of Civil Engineering, Tsinghua Univ., China. E-mail: yuhx@mail.tsinghua.edu.cn 2 Professor, Dept. of Civil and Structural Engineering, Univ. of Shef- field, U.K. E-mail: ian.burgess@sheffield.ac.uk 3 Senior Lecturer, Dept. of Civil and Structural Engineering, Univ. of Sheffield, U.K. E-mail: j.davison@sheffield.ac.uk 4 Professor, School of Architecture, Univ. of Sheffield, U.K. E-mail: r.j.plank@sheffield.ac.uk Note. This manuscript was submitted on June 1, 2009; approved on June 30, 2010; published online on July 15, 2010. Discussion period open until June 1, 2011; separate discussions must be submitted for individual papers. This paper is part of the Journal of Structural Engineering, Vol. 137, No. 1, January 1, 2011. ©ASCE, ISSN 0733-9445/2011/1-80–87/ $25.00. 80 / JOURNAL OF STRUCTURAL ENGINEERING © ASCE / JANUARY 2011 Downloaded 10 Oct 2011 to 166.111.44.246. Redistribution subject to ASCE license or copyright. Visit http://www.ascelibrary.org