Several reinforced concrete bent caps (deep beams) in Texas have developed
significant diagonal cracks in service. The cracking in two bent caps was so extensive
that costly retrofits were implemented to strengthen the structures. Strut-and-tie
modeling is currently recommended in most U.S. design specifications for the design of
reinforced concrete bent caps and deep beams. Designers have expressed concerns with
the lack of clarity and serviceability-related considerations in strut-and-tie model design
provisions.
Due to concerns with strut-and-tie modeling design provisions and field problems
of in-service bent caps, TxDOT Project 5253 was funded. Several tasks conducted
within Project 5253 are addressed in this dissertation. The effects of minimum web
reinforcement and member depth on the strength and serviceability behavior of deep
beams are presented. The transition between deep beam shear capacity and sectional
shear capacity near a shear-span-to-depth (a/d) ratio of 2 is addressed. A service-load
shear check to limit diagonal cracking in service is outlined. Lastly, a simple chart that
correlates the maximum width of diagonal cracks in a deep beam to its residual capacity
is developed.
To accomplish the objectives of Project 5253, thirty-seven tests were conducted
on reinforced concrete beams with the following cross-sectional dimensions: 21”x23”,
21”x42”, 21”x44”, 21”x75”, and 36”x48.” The specimens were loaded with a/d ratios of 1.2, 1.85, and 2.5. The test specimens are among the largest reinforced concrete deep
beams in the literature.
To supplement the findings of the experimental program, a database of deep beam
test results was compiled. Entries in the database that lacked sufficient information and
that did not meet established cross-sectional size or web reinforcement criteria were
filtered from the database. The use of the database in conjunction with the experimental
program enabled each objective to be addressed from both broad and specific viewpoints.
Several recommendations for improving the strength and serviceability design of
deep beams are presented including a minimum web reinforcement requirement,
provisions to ease the transition between calculated deep beam and sectional shear
capacity, and a design check to limit diagonal cracking in service. / text
| Identifer | oai:union.ndltd.org:UTEXAS/oai:repositories.lib.utexas.edu:2152/7559 |
| Date | 01 June 2010 |
| Creators | Birrcher, David Barra |
| Source Sets | University of Texas |
| Language | English |
| Detected Language | English |
| Format | electronic |
| Rights | Copyright is held by the author. Presentation of this material on the Libraries' web site by University Libraries, The University of Texas at Austin was made possible under a limited license grant from the author who has retained all copyrights in the works. |
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