MPC
Research Projects (2001-02)

Identifying Number

MPC-215

Project Title

Structural Modeling of Substructure Resistance for Timber Trestle Railroad Bridges, Year 1

University

Colorado State University

Project Investigator

Dr. Richard M. Gutkowski, Professor
Department of Civil Engineering
Colorado State University
(970)491-8291 or Fax (970)491-2788
gutkowsk@engr.colostate.edu

External Project Contact

N/A

Project Objective

The objective of the project is to empirically quantify the substructure spring constants for incorporation into rigorous computer models of timber trestle railroad bridges.

Project Abstract

Ordinary structural modeling of bridges does not account for the presence of "discontinuities" such as loosened connections, gaps due to shrinkage to due moisture/drying cycles; support movement, differential bearing of members etc. These alter load capacity and stiffness from the original condition and significantly affect behavior. A need exists to reflect the aspects into an improved structural analysis and design process for timber trestle railroad bridges. Software features (e.g. gap elements; interface element etc.) exist in an available commercial software to include the above "discontinuities" and free displacement. This is proving successful for the lab specimen. A need exists to better represent the substructure resistance that exist in the field compared to laboratory support conditions.

Task Descriptions

Computer modeling of the resistance of the substructure supports requires inclusion of gap and/or empirical spring stiffness components. For a laboratory specimen, this is proceeding successfully. However a need exists to empirically quantify the substructure spring constants in a manner representative of field response. "Spring stiffness" implies the vertical load-displacement characteristics provided by the cap-piles-ground to the end support of each stringer of a chord =. Two main task are proposed: 1) to examine data from past field tests to see if they provide the necessary measurements to quantify the spring stiffness, and 2) if necessary, to conduct a direct load test of the substructures of an actual bridge. The latter might be in cooperation with the Association of American Railroads (AAR), using a bridge in Colorado. AAR support would be sought, if this need materializes.

CSU has an extensive data base from its past field tests of 3 timber trestle railroad bridges. The work plan for those tests did not include determination of spring constants for use in structural modeling. However, some measurements of displacements were taken near or at supports in each bridge. It is unknown of this data would be sufficient for the purpose. Hence the first step is to examine that data in detail. If it is consistent with the need (locations of data, accuracy, completeness) it can be incorporated in the computer modeling. Predicted response will be verified by comparison with the measured response of the entire bridge, as available from the prior field tests. Modeling improvements will be made to optimize the simulation. If the substructure field data is inadequate or questionable in regard to quantifying substructure stiffness, then a load test in the field is necessary. The need for and feasibility of that test would be addressed either later in Year 14 or in Year 15 by communication with the AAR. If possible, such a test would be planned and proposed for Year 2 of this project.

Milestones, Dates

• Starting Date: July 1, 2001
• Examine existing data base: November 1, 2001
• Determine stiffness constants: January 15, 2002
• Incorporate into computer model: April 1, 2002
• Compare analytical predictions with field test results: June 1, 2002
• Recommendations for Year 2: June 30, 2002
• Ending Date: June 30, 2002

Yearly and Total Budget

This is a possible two year project. The attached budget is for July 1, 2001-June 30, 2002. The amount requested is $17,850 USDOT and is augmented by $17,346 as a CSU match. The total budget is $35,196.

Student Involvement

Support for a graduate research assistant for 7.5 months is included.

Relationship to Other Research Projects

In a Year 10, an MPC project was conducted to field test three timber trestle railroad bridges. In Year 11 a project was conducted to strengthen one of these bridges and retest it. In a Year 12 MPC project, a full-scale chord of three span timber trestle bridge was subjected to laboratory load testing. It replicated the chord of an existing bridge previously field tested before and after strengthening. The purpose was to compare field vs. laboratory behavior. An ongoing Year 13 project has the objective utilizing available commercial 3-D finite element software to rigorously model this specimen.

Technology Transfer Activities

Technology transfer will be via an MPC summary technical report, including input to and review by the AAR. If warranted in Year 1, a technical journal and/or conference paper will be prepared for submittal and an MPC Research Seminar over the TEL8 telecommunications network after completion of the two year project. Publicity about all of the MPC projects is available through the MPC web site maintained at NDSU.

Potential Benefits of the Project

Structural condition of timber trestle railroad bridges is of national concern. Railway car weights and train loads have increased considerably in recent decades. Loosened connections, gaps due to shrinkage to due moisture/drying cycles; support movement, differential bearing of members etc. develop over time and are present in older bridges. These alter load capacity and stiffness from the original condition and significantly affect structural behavior. Security of these bridges is imperative and improved structural modeling contributes to better understanding of response to these increasing loads and field conditions.

TRB Keywords

Bridge, computer model, railroad, substructure, timber, trestle