Experimental and Analytical Forensic Investigation of Bridge Timber Piles under Eccentric Loads Daniel J. Borello 1 , Bassem Andrawes 2 , Jerome F. Hajjar 3 , Scott M. Olson 4 1 Newmark Civil Engineering Laboratory, Department of Civil and Environmental Engineering, University of Illinois at Urbana-Champaign, B112 Newmark Civil Engineering Lab, 205 North Matthews Ave, Urbana, IL, USA; PH (847) 877-6287; email: dborello@illinois.edu 2 Newmark Civil Engineering Laboratory, Department of Civil and Environmental Engineering, University of Illinois at Urbana-Champaign, 3122 Newmark Civil Engineering Lab, 205 North Matthews Ave, Urbana, IL, USA; PH (217) 244-4178; email: andrawes@illinois.edu 3 Newmark Civil Engineering Laboratory, Department of Civil and Environmental Engineering, University of Illinois at Urbana-Champaign, 2129b Newmark Civil Engineering Lab, 205 North Matthews Ave, Urbana, IL, USA; PH (217) 244-4027; email: jfhajjar@illinois.edu 4 Newmark Civil Engineering Laboratory, Department of Civil and Environmental Engineering, University of Illinois at Urbana-Champaign, 2230d Newmark Civil Engineering Lab, 205 North Matthews Ave, Urbana, IL, USA; PH (217) 265-2584; email: olsons@illinois.edu ABSTRACT This study examines the structural behavior of bridge timber piles under eccentric compression loading. A collapsed rural concrete bridge supported on timber piles was used as a prototype in this study. Samples of the collapsed piles were retrieved and experimentally tested under compression and combined compression and flexure. The experimental timber pile response was used to calibrate an numerical model of the full timber piles of the prototype bridge, including material and geometric nonlinearity as well as soil-structure interaction. The numerical results illustrated that the pile strength was significantly reduced under eccentric load compared to concentric load. It was concluded that the effect of compression-flexure interaction on bridge timber piles must be checked during design, especially in the case of simply-supported superstructures where loading on one span may lead to eccentric loading on a timber pile group. INTRODUCTION Timber piles have been commonly used as a foundation system since the middle of the 18th century (Timber Pile Council, 2002). The interaction of combined compression and flexure loads in wood was first investigated in 1924 by the Army and Navy for airplane construction (Newlin and Trayer, 1956). Experimental testing and analysis based on Euler buckling illustrated that the material capacity was a function of load eccentricity as well as the slenderness of the section. In 1982, Zahn 98 2010 Structures Congress © 2010 ASCE