Citation

Brena SF, Morrison MC. ACI Struct. J. 2007; 104(3): 267-277.

Copyright

(Copyright © 2007, American Concrete Institute)

DOI

unavailable

PMID

unavailable

Abstract

Although strut-and-tie models can be useful in the design of concrete structures containing discontinuity regions, the existing margin of safety of a structure designed using strut-and-tie models is not currently known. This study provides experimental observations of four deep beams with openings designed using strut-and-tie models. Results indicate that measured strength of the laboratory specimens was significantly higher than calculated capacities from the design strut-and-tie models. Sources that contributed to the difference in anticipated and measured strengths are identified and quantified. All specimens failed at much higher loads that those associated with critical tie yielding, and no significant reorientation of principal strains occurred after yielding of critical ties in all specimens. Shrinkage and temperature reinforcement contributed significantly to strength in 2 of the specimens. Step-by-step nonlinear analyses were conducted for specimens designed using indeterminate strut-and-tie models to determine the sequence of tie yielding after stress redistribution and provide a more accurate estimate of specimen strength. The increase in calculated capacity obtained from this approach ranged between 15-17%, resulting in a decrease in the ratio of measured to calculated strength.