Field tests of timber railroad bridge piles



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Texas A&M University


The objective of this thesis is to explore the possibility of a non-destructive method of improving the dependability and economy of timber railroad bridges that have been exposed to environmental and service conditions. With railway companies increasing the load of trains in return for larger profit, maintenance and replacement of timber bridges has risen throughout recent years. Once chosen for its low cost and ease of construction, timber bridges are being replaced by more efficient concrete and steel trestles. The load path of a passing train through the elements of a bridge pier can be affected for several reasons. One focus of this report is how the load is distributed among the piles or supporting elements. Through recent research at Texas A&M University (2003), a relationship between the ultimate test load, Pmax, and the strength parameter, Lambda, was derived from 33 destructively tested specimens. Piles used in the testing were accumulated from three different locations in the United States and subjected to uniaxial compression along the length of the pile in a steel test frame. Instrumentation along the length of the piles provided data for plots of load versus deflection. Analysis of the plots showed that the tendency of the strength parameter, Lambda, to predict the ultimate test load was consistent but a computer generated model representing a typical service train revealed significantly lower loads on the piles than those used in the destructive tests. Further analysis of the test specimens at lower load levels led to a service level strength parameter that was derived with levels comparable to typical train loads. Guidelines for the service strength parameter, Beta, were based upon hypothetical loads from the computer generated model and previous test data. Field testing involved consent from a railroad company to install load cells and string potentiometers on an in-situ timber bridge. While simultaneously taking load and deflection measurements for bridges under the dynamic load of a passing train, the axial stiffness of the piles was determined and used in the calculation of the service level strength parameter,Beta. Future research includes removing the piles that were tested in the field and assessing them in the original method of axial compression in the steel test frame. This method can be used universally in the field to examine load path of passing trains and assess the amount of remaining axial strength of in-situ piles without interrupting daily flow and traffic of the railroad bridge. Ultimately, this research could lead to the railroad industry saving money and time due to the quick and convenient installation process.