Composite Steel Structures : Advances, design and construction

Name: Composite Steel Structures:Advances, design and construction
ISBN: 9780429180415

doi:10.1201/9781482286359

Book

ABSTRACT

The constant need for cost-effective structural forms has led to the increasing use of composite construction, and a substantial amount of research effort is currently being spent in developing techniques for combining concrete and steel effectively. Significant economies in this form of construction have been observed, especially in bridges and building floors. Codes of Practice on composite construction are being revised in the UK and in Europe, in the light of the substantial amount of knowledge that has been generated in recent years. An International Conference organised by the Department of Civil and Structural Engineering, University College, Cardiff, UK, with the specific objective of discussing all types of metal structures in an integrated way, provided a forum for the dissemination of new concepts and for reviewing developments; the expectations of the organisers have been amply justified and exceeded by the level of international response to the call for papers. This volume contains 17 papers on composite steel structures, presented at the Conference, many of which were by well-known experts in their respective fields.

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.

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Field and laboratory tests were conducted (18-23), survey and review of the tests have been reported (24-26). Some correlation of theoretical and experimental data can be found in reference (27). The aforementioned brief review is limited to right (not skewed) straight (not curved) composite concrete slab on more than two steel girders type bridges. Distribution of loads for other types is being investigated under the NCHRP Project 12-26, which includes literature review and evaluation of available information. This will eventually lead to a recommended load distribution method (to replace the one that exists now) for consideration by AASHTO subcommittee on bridges and structures. The continuous portion of the bridge is about 1320 feet long, along its center line, and is composed of 6 continuous spans. The longest span is 300 feet (span 4) and it is the second continuous span from west to east (Bangor to Brewer). The spans west (span 3) and east (span 5) of the longest span are 199 feet and 247 feet respectively. The bridge is slightly curved in plan in spans 3 and 4. The bridge has 8 steel girders which are spaced at 14.0 ft. minimum to about 21 ft. maximum spacings. The girders are welded plate girders made of ASTM A588 unpainted weathering steel. The total depth of the girders in span 4 is about 10 ft. The webs are reinforced by single sided intermediate vertical stiffeners spaced at 10 to 13 ft apart. Intermediate cross-bracing diaphragms are provided between the girders at spacings vary between 17.5 and 25 feet. The bridge deck is composed of a 12 inch reinforced concrete slab which acts compositly with the steel girders (using shear connectors), and a 3 inch bituminous wearing surface. The top flange of the steel girders are embeded in the concrete and the depth of the slab over the top flange is 16 inches at the haunch. The haunch is rectangular and has a width equals the width of the steel flange plus 8 inches; 4 inches on each side of the steel flange. of the two middle girders (girder 5) was instrumented by 30 strain gages. The strain gages were Installed within span 4 (the longest span) as described in the following. Eighteen gages were installed at the location of one of the four bolted splices within the span; Six at the top flange, six

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at the bottom flange and six on the web. Eight gages were installed at the approximate locations of the maximum positive and maximum negative moments. At each location four gages were installed; one at the top flange, one at the bottom flange and two equally spaced on the web. Finally, four gages were installed on two cross-bracing diaphragms between girders 5 and 6 one at about mid-span and the other over the support. The gages at each cross-bracing were located one on a chord member and the other on a diagonal. The weldable strain gages used are constantan alloy gages with backing and encapsulation of polyimide film. The gages are bonded to stainless steel carriers, 0.005 in. thick, and have exposed copper coated integral solder tabs to which wire cables were soldered directly. The cables were connected to three switch and balance units (10 channels each unit) thus providing a method of sequentially reading the strain gage information on a single strain indicator. As mentioned earlier the bridge was tested during construction; hence strain measurements were taken due to the weight of the wet concrete before and after three placements. After the deck slab has reached its design strength, and before placing the bituminous wearing surface, strain measurements were taken due to truck loads positioned at sixteen different positions on the bridge deck. Eight 3-axel trucks weighting about 60 kips each were used. The overall length of each truck is 24'-8" and the overall width is 8' 6". The aforementioned sixteen positions of the trucks consist of the following, In twelve positions the trucks were forming a line about 200 ft long at mid-span A between pier 3 and pier A,

or centered over pier 3. These two positions were repeated six times each by having the trucks over girder 5, 6 or 7 and between girders 5 and 6, 6 and 7, and 7 and 8; see figure (3) which shows one of these positons. ............................................................. lllll

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Furthermore, the line of trucks was positioned in additional three positions over girder 5; one east of the instrumented splice towards pier 4, the second west of pier 3 towards pier 2 and the third east of pier 4 towards pier 5. In the final position the trucks were side by side across the width of the bridge at the middle of span 4, as shown in Figure (4). Stresses calculated from measured strains agree reasonably well with those analytically calculated due to the weight of the wet concrete. The stresses given in Table (1) are basically due to the weight of the eist bound lanes' wet concrete and are calculated assuming no composite action between steel and concrete; as was the case. Furthermore, under the weight of the wet concrete the diaphragms connecting girder 5 to girder 4 were only loosely connected. Under the truck loads, the deck slab acts compositly with the steel girders. In this case the stresses calculated from measured strains differ from those analytically calculated in distribution and magnitude, as can be noted from Table (2). The calculated stresses were based on AASHTO load distribution method; and composite-beam action was considered using an effective slab width as recommended by AASHTO Standard Specification. The analytical stresses in load cases 4, 5 and 6 are all zero since according to AASHTO girder 5 will be subjected to loads only when the wheels are within the two adjacent slab spans, i.e. between girders 4 and

FIGURE (4 ) - TRUCKS ACROSS THE BRIDGE

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The calculated and measured stresses due to eight trucks positioned side-by-side across the width of the bridge at the middle of span A, are

given in Table (3). As can be noted the differences are not as much as those of the results in Table (2). The differences in this case are only due to the inadequacy of the two-dimensional composite beam idealization in depicting the actual three-dimensional behavior.

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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.

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Fu, C.C. and Colville, J., "Inelastic Analysis of Continuous Composite Highway Bridges", CE Report No. 62, University of Maryland, College Park, MD., Dec. 1975. 6. Heins, C.P., "LFD Criteria For Composite Steel I-Beam Bridges", ASCE Journal Of The Structural Division, November 1980. 7. Walker, W.H., "Lateral Load Distribution In Multi-Girder Bridges", Proceedings of the AISC National Engineering Conference, Nashville, Tennessee - June 12-14, 1986. 8. Hays, C.O., Sessions, L.M. and Berry, A.J., "Further Studies On Lateral Load Distribution Using a Finite Element Method", Transportation Research Record 1072, Transportation Research Board (TRB), Washington, D.C. 1986. 9. Arendts, J., "Study Of Experimental and Theoretical Load Distribution In Highway Bridges”, M.S. Thesis, Iowa State University, December, 1967. 10. Gurbuz, Orhan, Theories of Transverse Load Distribution On Simple-Span (non-skewed) Beam-And-Slab Bridges", M.S. Thesis, Iowa State University, 1968. 11. Sanders, W.W., Jr. and Elleby, H.A., "Distribution of Wheel Loads On Highway Bridges", NCHRP Report 83, 1970 12. Jones, R.A., "A Simple Alogorithm for Computing Load Distribution In Multi-Beam Bridge Decks", ARRB (Australia Road Research Board) proceedings, Vol. 8, 1976. 13. McDougle, E.A., Bryan, R.H., Burdette, E.G. and Goodpasture, D.W., "Lateral Load Distribution For Two Continuous Steel Girder Highway Bridges", Transportation Research Record 607, 1976. 14. Culham, G.A. and Ghali, A. "Distribution Of Wheel Loads on Bridge Girders", Canadian Journal of Civil Engineering, Vol. 4,1977.

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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.

1977. 22. Bakht, B. and Csagoly, P.F., "Bridge Testing", Ontario Ministry of Transportation And Communiction, August, 1979. 23. Bakht, B., and Csagoly, P.F., "Diagnostic Testing of A Bridge", ASCE Journal Of The Structural Division, July 1980.