9. Observations and Conclusions

9.1 Observations

The focus of this research was to investigate the effects of the support motion observed in past research. The incorporation of the soil foundation and driven wood piles were intended to provide the support motions. Constructing a complete timber trestle bridge model created the small gaps between the stringers and crossties that were excluded from previous research of modeling only bridge chords. In addition to simulating realistic bridge behavior it was shown that the AxisVM software is capable of modeling the deflections of a timber trestle laboratory bridge specimen with the inclusion of support motions and initial small gaps between the stringers and crossties along with the semi-continuous bridge behavior.

The AxisVM model used to predict the behavior of the test specimen was very intricate and required extensive input, specifically the measured gap distances between the cross ties and the stringers and the empirical soil stiffness values. The extensive detail of specimen measurement and computer modeling that was used provided the opportunity to make many observations about physically and analytically modeling a timber trestle bridge system in a laboratory. These include:

• Two empirical methods were investigated to estimate the substructure stiffness of the physical specimen. The first method evaluated the stiffness of each group of piles and the soil around them with physical load testing. The second method used physical testing of the complete specimen and analytical modeling of the superstructure of the specimen using AxisVM software to estimate the stiffness of each pile group. The two methods resulted in substructure stiffness values within 5% of each other.
• The specimen was observed to deflect in linear increments under linearly increasing load increments. Linear load vs. deflection behavior suggests the load path through the structure did not noticeably change between the load levels of 4448 N (1000 lb) and 13344 N (3000 lb).
• Comparisons of the observed behavior of the specimen and the Axis VM predictions from the AxisVM model resulted in very similar deflected shapes. Numerical comparisons between the AxisVM model and the physical specimen showed that the model was able to predict the deflections of the specimen well within an accuracy of 5% to 10%.

9.2 Conclusions

After considering the observations from the load testing and AxisVM model the following conclusions are made:

• Including a soil condition in laboratory research can produce support motions that appear to be similar to those observed in field testing.
• Two methods of estimating the substructure stiffness were investigated and proved to provide similar stiffness values. The second method investigated involved physical testing of the completed specimen which, with further development, could yield a method to estimate the substructure stiffness of in-situ bridges with pile foundations.
• The analytical model created using AxisVM software successfully predicted the behavior of the physical specimen under the three load tests.

References

• American Forest and Paper Association. 2001. National Design Specification. Washington, DC.
• American Institute of Timber Construction. 1994 Timber Construction Manual, 4th ed. Englewood, CO.
• American Railway Engineering and Maintenance Association, 1995. Timber Structures, Chapter 7, 1995 Manual for Railway Engineering. AREMA. Washington, DC.
• Balogh, J., and R.M. Gutkowski. Full-Scale Laboratory Testing of a Timber Trestle Railroad Bridge (Phase 2). Report in preparation. Mountain Plains Consortium. Colorado State University, Fort Collins, CO.
• Babcock, S. 2005. Analysis and Testing of Support Motion Effects in Timber Trestle Bridge Specimen, M.S. Thesis, Fall 2005. Colorado State University, Ft. Collins, CO.
• Bowles, J. E. 1996. Foundation Analysis and Design, 5th ed. McGraw-Hill Companies, Inc.
• Byers, W.G. 1996. Service Life of Timber Trestles, Probabilistic Mechanics and Structural and Geotechnical Reliability, Proceedings of the Special Conference Proceedings of the 1996 7th Special Conference on Probabilistic Mechanics and Structural Reliability. Worcester, MA.
• Criswell M., 1982. Properties of Materials. Department of Civil Engineering, Colorado State University, Fort Collins, CO.
• Gutkowski, R.M., M. Peterson, M. Peterson, S. Uppal, D. Oliva-Maal, and D. Otter. 1999. Field Studies of Timber Railroad Bridges, AAR Report No. R-933. Association of American Railroads, Pueblo CO.
• Doyle, K.R., R.M. Gutkowski, M.E. Criswell, P.J. Pellicane, and J. Balogh. 2000. Test and Analysis of Full-Scale Open-Deck Timber Trestle Railroad Bridge Chords, Structural Research Report No. 82. Department of Civil Engineering, Colorado State University, Fort Collins, CO.
• Gutkowski, R.M., G.C. Robinson, and A. Shigidi. 2001. Field Tests of Open-Deck Timber Trestle Railroad Bridges, MPC Report No. 01-125. Mountain Plains Consortium, Colorado State University, Fort Collins, CO.
• Inter-CAD Kft. 2004. AxisVM Finite Element Program User's Manual Version 7.1. Budapest, Hungary
• International Code Council. 2003. Section 1808, Pier and Pile Foundations, International Building Code 2003. Whittier, CA.
• Moses, F., J. Lebet, R. P.Bez. 1994. Applications of Field Testing to Bridge Evaluation, Journal of Structural Engineering, 120, 6: 1745-1762.
• Naval Facilities Engineering Command. 1986. Foundations & Earth Structures, Design Manual 7.02. Alexandria, VA.
• Oommen, G., A. Lim, and S. Tselios. 1996. Evaluation and Rehabilitation of Victoria Bridge, Structures Congress - Proceedings Building an International Community of Structural Engineers Proceedings of the 14th Structures Congress. (Part 1 of 2 ) Vol. 1, Chicago, IL, ASCE, New York, NY.
• Poulos, H.G. and E.H. Davis. 1980. Pile Foundation Analysis and Design, John Wiley & Sons, New York.
• Reid, J.S., M.J. Chajes, D.R. Mertz, and G.H. Reichelt. 1996. Bridge Strength Evaluation Based on Field Tests, Probabilistic Mechanics and Structural and Geotechnical Reliability, Proceedings of the Special Conference Proceedings of the 7th Special Conference on Probabilistic Mechanics and Structural Reliability, Worcester, MA.
• Ritter, M.A. 1992. Timber Bridges: Design, Construction, Inspection, and Maintenance. United States Department of Agriculture, Forest Service, Engineering Staff, Washington D.C.
• Robinson, G.C., R.M. Gutkowski, M.L. Peterson, and M.E. Criswell. 1998. Field Testing of Open-Deck Timber Trestle Railroad Bridges, Structural Research Report No. 80. Department of Civil Engineering, Colorado State University, Fort Collins, CO.
• Rosenkrantz, W.A. 1997. Introduction to Probability and Statistics for Scientists and Engineers. McGraw-Hill Companies, Inc. New York, NY
• Shahawy, M.A. 1995. Nondestructive Strength Evaluation of Florida Bridges, Proceedings of SPIE - The International Society of Optical Engineering Nondestructive Evaluation of Aging Bridges and Highways. Oakland, CA.
• Smith, W.B. 1999. 1997 RPA Assessment, The United States Forest Resources Current Situation, Review Draft. USDA Forest Service, Washington, DC.
• Thomson, W.T., and M.D. Dahleh. 1998. Theory of Vibration with Application, 5th ed. Prentice Hall, Upper Saddle River, NJ.
• Tran, A.V. 1998. Study of an Open-Deck Timber Railroad Bridge, Department of Civil Engineering, Colorado State University, Fort Collins, CO.
• Troitsky, D.Sc. 1994. Planning and Design of Bridges. John Wiley & Sons, New York, NY.
• Uppal, A.S., D.E. Otter, R.M. Gutkowski, and A. Shigidi. 2002. Field Study of a Strengthened Timber Railroad Bridge, AAR Report No. R-956. Association of American Railroads, Pueblo, CO.
• Uppal, A.S. 2001. Compendium of Recent Research on Railroad Timber Bridges and Their Components, AAR Report No. R-947. Association of American Railroads Transportation Technology Center, Pueblo, CO.