Determination of a strength parameter for In Situ evaluation of timber railroad bridge piles subject to decay and fatigue damage accumulation

Abstract

The objective of this thesis is to devise a method to determine the residual strength of used creosote treated timber railroad bridge piles of various dimensions that have been subjected to varying degrees of environmental and mechanical deterioration. A total of 37 timber piles from three different locations were used for experimentation. Upon receipt, the piles were assigned an identification number and then stripped of any extraneous material such as wood blocks, drift pins, metal strapping, erection spikes, and metal bolts. The piles were then inspected for any form of pretest damage including, but not limited to, longitudinal cracking, fire damage, rot, decay, adequacy of creosote penetration, and general fitness of the wood. The piles were tested in uniaxial compression parallel to the grain in a custom built frame with a capacity of 1.8 million pounds. Data taken from the testing included the applied load and three separate measurements of axial deformation. Testing for each specimen was terminated when any of the following occurred: longitudinal splitting along the length of the specimen, longitudinal splitting along the length of the specimen through bolt holes, localized barreling of the cross-section, lateral buckling, mushrooming of the butt or tip end, and/or manual termination due to failure to sustain load. A correlation was discovered between a two part pile strength parameter, [], and the ultimate test load, P[max]. The pile strength parameter consists of the axial stiffness as determined from a plot of load vs. deflection for each pile and a slenderness parameter obtainable from simple measurements as the square of the pile tip diameter divided by length. A least squares linear regression analysis was performed on a plot of the ultimate load from each test, P[max], vs. the pile strength parameter, [], for each test. Uniaxial compression tests of small clearwood samples of different species were similarly tested to determine potential limits of the pile strength parameter approach. This method of determining residual pile capacity is simple in concept and can be used in the field to determine remaining axial strength of in-service piles.