Composite Steel Structures
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Jones, R.A. and Peiris, R.S.A., "Load Distribution Analysis Of A Continuous Two-Span Multi-Beam Bridge Deck", ARRB (Australia Road Research Board) Proceedings, Vol. II, Part 2,1982. 16. "Distribution Of Wheel Loads On Highway Bridges", NCHRP Project 20-5, Topic 14-22, February, 1984 17. Hays, C.O. and Hackey, J.E., "Lateral Distribution Of Wheel Loads On Highway Bridges using The Finite Element Method", Structures And Materials Research Report No. 84-3, University of Florida, Department of Civil Engineering, December, 1984. 18. Newmark, N.M., Seiss, C.P. and Penman, R.R., "Studies of Slab And Beam Highway Bridges - Part I Tests Of Simple Span Right I-Beam Bridges", University of Illinois, Bulletin, March, 1946. 19 Burdette, E.G. and Goodpasture, D.W., "Full-Scale Bridge Testing - An Evaluation of Bridge Design Criteria", Final Report. The University of Tennessee, Department of Civil Engineering, Dec. 1971. 20. King, J.P.C. and Csagoly, P.F., "Field Testing of Aguasabon River Bridge in Ontario", Transportation Research Record 579, 1976. 21. Dorton, R.A., Holowka, M., and King, J.P.C., "The Conestogo River Bridge - Design and Testing", Canadian Journal of Civil Engineering, Vo). Heins, C.P., "Highway Bridge Field Tests In The United States, 1948-70', pulbic Roads, 1972. 25. Gangarao, H.V.S., "Survey Of Field And Laboratory Tests On Bridge Systems", Transportation Research Record 645, 1977.
variety of span lengths, widths, number of grlders and slab thickness were analyzed. For two 50 ft. spans with seven girders (slab aspect ratio of 0.12) the value of D in the S/D formula varies between 6.1 and 7.96 for midspan center girder depending on the slab to girder stiffness ratio. This is in lieu of the 5.5 specified in AASHTO Standard Specification. Perhaps more representative are results for a 100 ft., two span continuous bridge with five girders spaced at 9 ft, where D varies between 8.4 and 10.8. Another Interesting result in Walker's report is regarding the structural idealization of the bridge. It has been found that the simple grid model can represent the essential behavior of the bridge as the more exact models do. The grid model was constructed such that the transverse beams represent the equivalent slab and diaphragms (if present) and the longitudinal beams represent the longitudinal composite girders. The fact that the grid model gives good representation of the essential behavior of the bridge can not be generalized. The grid model has certain limitations, however it gives a better representation of the bridge behavior than does a simple two-value S/D rule. A simple micro computer implementation of a grid model is seen by Walker as a better method than the S/D formula to predict lateral load distribution. Recently Hays, Sessions and Berry (8), have demonstrated that the effect of span length, which is neglected in AASHTO can be considerable. They found that AASHTO results are slightly unconservative for short spans and quite conservative for longer spans. Furthermore they compared the results of a finite element analysis with field test results and concluded that the comparison showed generally good agreement. A wide range of load distribution methods are available in the technical literature (9-17). These methods range from empirical methods, as the one recommended by AASHTO and described above, to sophisticated computer-based solution techniques which take into consideration the three-dimensional response of the bridge. The computer methods utilize a wide rang of structural idealization. Some use a simple equivalent anisotropic plate or grid work while others use sophisticated finite element models that consider detailed aspects of the interaction between the components of the bridge superstructure. The parameters which influence the load distribution most are; the number of girders and their spacing, the span length, and the girder moment of Inertia and slab thickness.
Trucks were used later in various positions and strains were measured due to these truck loads. Stresses were calculated from measured strains and compared with analytical stresses calculated based on the design assumptions which are according to AASHTO Standard Specifications. Reasonable agreement between the analytical and experimental results was obtained for dead loads where the steel girders were acting alone without the concrete composite action. Furthermore the diaphragms connecting girder 5 (the instrumented girder) to girder 4 were only loosely connected under the dead loading. Differences in magnitude and distribution pattern, however, were observed for the live loading. These differences are basically due to the conservatism in AASHTO load distribution method as well as the inability of the two dimensional composite beam approach in depicting the actual three dimensional behavior of the bridge system The testing of the bridge was sponsored by Maine Department Of Transportantion, James Chandler is the Bridge Design Engineer. The analytical results presented in this paper were calculated by Steve Abbott of MODT. The interest and support of Jim and Steve as well as Karel Jacobs, also of MDOT, Is greatly appreciated. American Association of State Highway Transportation Officials, Standard Specification for Highway Bridges 2. Newmark, N., "Design of I-Beam Bridges", Transactions ASCE, Vol. 74, No. 3, Part I, March, 1948. 3. Heins, C.P. and Kuo, J.T.C., "Live Load Distribution on Simple Span Steel I-Beam Composite Highway Bridges At Ultimate Load", CE Report No. 53, University of Maryland, College Park, MD., April, 1973. 4. Heins, C.P. and Kuo, J.T.C., "Ultimate Live Load Distribution Factor For Bridges", Journal Of The Structural Division, ASCE, Vol. 101, No. ST7, Proc. Paper 11443, July 1975.