Title:
Combined Beam-Slab Collapse Mechanism in Isolated Reinforced Concrete Beam-Slabs—Strength Design and Load Testing
Author(s):
Anurag Singh, Bijily Balakrishnan, and Devdas Menon
Publication:
Structural Journal
Volume:
118
Issue:
3
Appears on pages(s):
223-240
Keywords:
beam-slab system; combined beam-slab failure; rational design methodology; slab alone failure; yield line analysis
DOI:
10.14359/51730527
Date:
5/1/2021
Abstract:
In the conventional method of strength design of reinforced concrete (RC) beam-slab systems, it is assumed that if the beams are adequately stiff, the slab and beams can be analyzed and designed separately under factored gravity loads. This paper demonstrates, through yield line analysis and load testing of isolated beam-slab systems, that such a design, which tacitly assumes a ‘slab alone failure’ mechanism, is irrational and overconservative (failing at a load level much higher than expected). The actual collapse of the conventionally designed beam-slab system invariably involves a combined beam-slab failure mechanism. It is therefore more rational and economical to design explicitly for such a collapse mechanism, accounting for plastic hinge formation in the beams along with yield lines in the slab. The proposed method suggests provision of minimum slab steel (as prescribed by the design code), and then designing the beams aiming for a combined two-way beam-slab failure. Experimental load testing establishes that the collapse occurs as planned and that the proposed economical design has the desired code-specified safety margins.
Related References:
1. Balakrishnan, B., and Menon, D., “Collapse Load Estimation of Rectangular Reinforced Concrete Beam-Slab Systems—New Insights,” ACI Structural Journal, V. 115, No. 5, Sept. 2018, pp. 1279-1294. doi: 10.14359/51702246
2. Balakrishnan, B., and Menon, D., “Yield Line Analysis and Testing of Reinforced Concrete Rectangular Slabs with Primary and Secondary Beams,” ACI Structural Journal, V. 116, No. 5, Sept. 2019, pp. 187-200. doi: 10.14359/51716760
3. Hayes, B., and Taylor, R., “Some Tests on Reinforced Concrete Beam-Slab Panels,” Magazine of Concrete Research, V. 21, No. 67, 1969, pp. 113-120. doi: 10.1680/macr.1969.21.67.113
4. Park, R., “The Behaviour of a Model Slab and Beam Floor Designed by Limit Design,” Civil Engineering Trans., Inst. Eng., Aust, V. 12, No. 1, April 1970, pp. 1-6.
5. Singh, H.; Kwatra, N.; and Maneek, K., “Behavior of Shallow-Beam Supported Reinforced Concrete Rectangular Slabs: Analytical and Experimental Investigations,” Advances in Structural Engineering, V. 13, No. 6, 2010, pp. 1183-1198. doi: 10.1260/1369-4332.13.6.1183
6. Bailey, C. G., “Membrane Action of Unrestrained Lightly Reinforced Concrete Slabs at Large Displacements,” Engineering Structures, V. 23, No. 5, 2001, pp. 470-483. doi: 10.1016/S0141-0296(00)00064-X
7. ACI Committee 318, “Building Code Requirements for Structural Concrete (ACI 318-19) and Commentary (ACI 318R-19),” American Concrete Institute, Farmington Hills, MI, 2019, 624 pp.
8. IS 456, “Indian Standard Plain and Reinforced Concrete Code of Practice,” Bureau of Indian Standards, New Delhi, India, 2000.
9. Reynolds, C. E.; Steedman, J. C.; and Threlfall, A. J., Reynolds’s Reinforced Concrete Designer’s Handbook, Taylor and Francis, Boca Raton, FL, 2007
10. Pillai, U., and Menon, D., Reinforced Concrete Design, third edition, Tata McGraw Hill Publication Co. Ltd., New Delhi, India, 2011.
11. Singh, A., “Experimental Validation of an Improved Design Procedure for the Design of Isolated Rectangular RC Beam-Slab Systems,” MS thesis, Indian Institute of Technology Madras, Chennai, India, 2020.
12. Singh, A.; Balakrishnan, B.; and Menon, D., “Economical and Rational Design of ‘One-way’ RC Beam-Slab Systems,” Indian Concrete Journal, V. 94, No. 3, pp. 12-22.
13. Eurocode 2, “Design of Concrete Structures: Part 1-1: General Rules and Rules for Buildings,” British Standards Institution, London, UK, 2004.
14. Bailey, C. G.; Toh, W. S.; and Chan, B. M., “Simplified and Advanced Analysis of Membrane Action of Concrete Slabs,” ACI Structural Journal, V. 105, No. 1, Jan.-Feb. 2008, pp. 30-40.
15. Foster, S. J.; Bailey, C. G.; Burgess, I. W.; and Plank, R. J., “Experimental Behaviour of Concrete Floor Slabs at Large Displacements,” Engineering Structures, V. 26, No. 9, 2004, pp. 1231-1247. doi: 10.1016/j.engstruct.2004.04.002