MPC
Research Projects (1999-00)

Identifying Number

MPC-179

Project Title

Full-Scale Laboratory Testing of a Timber Railroad Bridge-Continuation

University

Colorado State University

Project Investigator

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

External Project Contact

Dr. Shakoor Uppal
Research Engineer
AAR - Transportation Test Center, Inc.
P.O. Box 11130
Pueblo, CO 81001
(719)584-0594

Project Objective

A need exists to examine the effectiveness of the methods being used by the railroads to accomplish strengthening and repair of its timber trestle bridges.

Since field load testing involves the difficult constraint of conducting testing with minimal or no interruption of train service, a complementary laboratory test program is essential to examining the benefits (to load capacity) of the types of repairs, retrofits and upgrades being employed. Also field expediency and site conditions can lead to deviations from intended repairs. This project involves controlled laboratory testing of a "tinker toy" type full-scale bridge superstructure to study the effects of different upgrade and retrofit methods. The objective is to examine these under controlled conditions and assess their structural effectiveness. Results will be used to improve strengthening methods and foster improved AREA design code provisions for such bridges.

Project Abstract

This continuation project is being conducted in the Structural Engineering Laboratory at Colorado State University (CSU). A full-scale laboratory test specimen will essentially replicate (in size) a chord of an existing three span bridge that was previously field load tested in the field before and after its strengthening. The specimen will involve fully connecting all the caps and all ties and the steel rail, as a stand-alone specimen fully replicating the field construction techniques, too. The laboratory specimen reduces some of the site specific support conditions that complicate understanding of the behavior of this type of bridge as compared to existing code design procedures. After load testing the specimen, it will be strengthened with an additional stringer ply and retested to examine the changes in response. Load tests will be conducted using existing (at CSU) load frame and hydraulic actuator capability. Displacement and strain will be measured at predetermined locations during load testing. These results will provide an improved understanding of the behavior of the timber trestle bridge and the consequences of strengthening and retrofit methods.

Task Descriptions

The tasks and time frames for this experimental test program are:

• Task 1 – Acquire the needed materials for the specimen. (R. Gutkowski - December 15, 1999)
• Task 2 – Construct the three span specimen. (R. Gutkowski - March 31, 2000)
• Task 3 – Plan and conduct the load tests. (R. Gutkowski - May 31, 2000)
• Task 4 – Strengthen the specimen with an additional stringer ply. (R. Gutkowski - June 30, 2000)
• Task 5 – Repeat the load tests. (R. Gutkowski - August 31, 2000)
• Task 6 – Reduce the data and assess the effectiveness of the strengthening method. (R. Gutkowski - September 30, 2000)
• Task 7 – After review of the results and findings with the AAR, prepare an MPC report. (R. Gutkowski - October 31, 2000)

Milestones, Dates

• Starting Data: November 1, 1999
• Complete Initial Tests: May 31, 2000
• Complete Second Tests: August 31, 2000
• MPC Report: October 31, 2000
• MS Thesis: Subsequent to the project
• Ending Date: October 31, 2000

Yearly and Total Budget

Student Involvement (e.g. Thesis, Assistantships, Paid Employment)

Funds are included for support of a graduate research assistant and hourly student labor.

Relationship to Other Research Projects

This project follows and complements a past joint MPC-AAR (AAR=Association of American Railroads) project on "Railroad Bridge Strengthening Needs." That two year effort involved load testing of three typical timber trestle bridges in the field in 1995. One bridge was retrofit in 1996 and retested in 1997. One outcome was the recommendation of the conduct of this laboratory load testing project. This project is a continuation of that MPC-AAR cooperative laboratory study. In the prior lab work, three specimens were constructed and tested. To limit material cost, a three span bridge chord specimen was constructed and tested. It was then disassembled and some of its materials used to construct a two-span specimen. In turn, that specimen was disassembled and some of its materials used to construct a one span specimen. A variety of planned load tests were conducted, and the specimens were altered by implementation of field type repairs and strengthening. To enable this sequence it was decided to not fully connect all components (e.g. ties to stringers) of the bridge, as to do so would pragmatically obviate the disassembly and material reuse process. While it was anticipated the behavior would not be markedly affected, that did not occur for the vital three span specimen. Consequently, to complete the study it is necessary to reassemble and fully connect the three span bridge chord specimen and retest it in a fully connected test set up.

Technology Transfer Activities

The AAR is involved in a strategic program to investigate the structural performance of existing timber trestle bridges via a program of field load tests. This project is the outcome of such field tests, whereby the need for a controlled laboratory test was deemed beneficial to better understanding behavior. The AAR has contributed materials and staff time to the determination of the details of this project. By its commitment of services and funds, the AAR anticipates usable outcomes and will implement them to improve its timber bridge inventory. Ultimately, the AAR plans to incorporate the findings in its strategic plans for the near and intermediate term retrofit needs. Upgrading of AREA design code provisions to reflect the studies and in-place assessment needs is also planned by the AAR.

Potential Benefits of the Project

This project promotes the maintenance of effective, efficient railroad services to small communities. The AAR is the national industry association representing the numerous member railroads. The research is part of a targeted program of research to address the distressed state of its timber railroad bridges, nationwide. The AAR's timber bridge research needs were determined by a team of about ten invited experts who conducted a 1994 research needs workshop for the AAR on the topic. Co-PI, Dr. Richard Gutkowski was one of the invited experts and was subsequently approached by the AAR to conduct research on timber trestle bridges. Nationally, the structural conditions of short span, timber trestle railroad bridges can be characterized as one of increasing concern. Numerous aged and aging timber trestle bridges exist in the national inventory. Many have been in service for 40-100 years, particularly on short lines in sparsely populated areas. Modern load demands necessitate that, on an as needed priority basis, that they be repaired or retrofitted. Reports by the AAR indicate that degradation has been occurring with material failure evident at some sites. Consequently, some existing bridges need to be strengthened to more safely carry these increased loads to avoid potential structural problems leading to costly replacements. The laboratory testing will allow assessment of current design code provisions, in the absence of field site-specific idiosyncrasies that cloud the findings of field tests. The aim is to determine the correctness of existing analytical procedures in the AREA code vis-a-vis measured behavior of the open desk timber trestle bridge. The AAR is implementing such research to develop strategic plans for the near and intermediate term retrofit needs for their large inventory of timber bridges.

Concern for viability of the railroad bridges is high as the safety issue adds to the concerns of a recent history of short line closures. The impact of railroad bridge failures or closures on intermodal freight movement can be devastating to local, state and regional agricultural and freight economies. By helping to upgrade railroad bridges on main lines and short lines, the programmed research will contribute to the effective transport of agricultural goods and freight throughout the region and country. Without attention to them, some timber trestle railroad bridges will remain possibly deficient for current actual trainloads and others, which are nominally safe will only worsen. The safety concerns are evident as are the potential negative economic consequences of potential railroad bridge closures or, worse, failures. Even one main line bridge failure could be a crisis situation locally and regionally and create national fears.

TRB Keywords

Bridges, full-scale laboratory, load testing, railroads, strengthening, trestle