Size Effect Hidden in Excessive Dead Load Factor
Publication: Journal of Structural Engineering
Volume 128, Issue 1
Abstract
The paper shows that the excessive value of the dead load factor in the ultimate load requirements of the current structural design code implies a size effect. The size effect implied, however, does not have a rational form; it cannot distinguish among various types of failure in which very different size effects apply. This size effect partly compensates for the absence of the actual size effect, primarily the size effect due to energy release, from the current code specifications. Therefore, it would be dangerous to reduce the dead load factor without simultaneously introducing size effect provisions into the code. The question of a possible reduction in the dead load factor cannot be separated from the question of size effect, and so the fracture experts and reliability experts must collaborate. Further it is shown that a possible size effect is hidden in a reliability-based code due to the fact that the reliability implied in the code increases with the contribution of the dead load effect to the overall gravity load effect. The overreliability ratio defined in this study may be used to quantify the additional size effect that can be hidden in a reliability-based code.
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References
American Association of State Highway and Transportation Officials (AASHTO). (1994). LRFD bridge design specifications, 1st Ed., Washington, D.C.
American Concrete Institute (ACI). (1999). “Building code requirements for structural concrete,” ACI 318–99 and “Commentary” ACI 318–99, Farmington Hills, Michigan.
Ang, A. H.-S., and Tang, W. H. (1984). Probability concepts in engineering planning and design, Wiley, New York.
Bažant, Z. P.(1984). “Size effect in blunt fracture: Concrete, rock, metal,” J. Eng. Mech., 110(4), 518–535.
Bažant, Z. P.(1993). “Scaling laws in mechanics of failure,” J. Eng. Mech., 119(9), 1828–1844.
Bažant, Z. P.(1999a). “Size effect on structural strength: a review,” Arch. Appl. Mech., 69, 703–725.
Bažant, Z. P. (1999b). “Size effect in concrete structures: nuisance or necessity?” (plenary keynote lecture), in Structural Concrete: The Bridge Between People, Proc., fib Symp., Viacon Agency, Prague, 43–51.
Bažant, Z. P. (2000). “Lecture on Scale Effects,” presented at Politecnico di Milano (April 5).
Bažant, Z. P., and Chen, E.-P.(1997). “Scaling of structural failure,” Appl. Mech. Rev., 50(10), 593–627.
Bažant, Z. P., and Novák, D.(2000a). “Probabilistic nonlocal theory for quasibrittle fracture initiation and size effect. I. Theory,” J. Eng. Mech., 126(2), 166–174.
Bažant, Z. P., and Novák, D.(2000b). “Probabilistic nonlocal theory for quasibrittle fracture initiation and size effect. II. Application,” J. Eng. Mech., 126(2), 175–185.
Bažant, Z. P., and Novák, D.(2000c). “Energetic-statistical size effect in quasibrittle failure at crack initiation,” ACI Mater. J., 97(3), 381–392.
Bažant, Z. P., and Novák, D.(2001). “Proposal for standard test of modulus of rupture of concrete with its size dependence,” ACI Mater. J., 98(1), 79–87.
Bažant, Z. P., and Planas, J. (1998). Fracture and size effect in concrete and other quasibrittle materials. CRC Press, Boca Raton, Fla.
Cornell, C. A.(1969). “A probability-based structural code,” J. Am. Concr. Inst., 66(12), 974–985.
Ellingwood, B., Galambos, T. V., MacGregor, J. G., and Cornell, C. A. (1980). “Development of a probability-based load criterion for American National Standard A58.” NBS Special Publication No. 577, National Bureau of Standards, U.S. Dept. of Commerce, Washington, D.C.
Ellingwood, B. R.(1996). “Reliability-based condition assessment and LRFD for existing structures,” Struct. Safety, 18(2–3), 67–80.
Frangopol, D. M., ed. (1999). Bridge safety and reliability, ASCE, Reston, Virginia, 244 pages.
Frangopol, D. M., and Nakib, R.(1991). “Redundancy in highway bridges,” Eng. J., 28(1), 45–50.
Frangopol, D. M., Ghosn, M., Hearn, G., and Nowak, A.(1998). “Guest editorial: Structural reliability in bridge engineering,” J. Bridge Eng., 3(4), 151–154.
Ghosn, M., and Frangopol, D. M. (1999). “Bridge reliability: Components and systems,” Chapter 4 in Bridge Safety and Reliability, D. M. Frangopol, ed., ASCE, Reston, Virginia, 83–112.
Hasofer, A. M., and Lind, N. C.(1974). “Exact and invariant second-moment code format,” J. Eng. Mech. Div., 100(EM1), 111–121.
Jacobsen, R., and Rosendahl, F.(1994). “The Sleipner Platform accident,” Struct. Eng. Int. (IABSE, Zurich, Switzerland), 3, 190–193.
Levy, M., and Salvadori, M. (1992). Why buildings fall down. W. W. Norton, New York.
Madsen, H. O., Krenk, S., and Lind, N. C. (1986). Methods of structural safety. Prentice-Hall, Englewood Cliffs, NJ.
Nowak, A. S.(1995). “Calibration of LRFD Bridge Code,” J. Struct. Eng., 121(8), 1245–1252.
Pattison, K.(1998). “Why did the dam burst?” Invent. Technol.14(1), 23–31.
Swenson, D. V., and Ingraffea, A. R.(1991). “The collapse of the Schoharie Creek bridge: A case study in concrete fracture mechanics,” Int. J. Fract., 51(1), 73–92.
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Copyright © 2002 American Society of Civil Engineers.
History
Received: Jul 24, 2000
Accepted: Jun 27, 2001
Published online: Jan 1, 2002
Published in print: Jan 2002
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