Title:
Performance of Open Double Stirrups as Punching-Shear Reinforcement
Author(s):
Aaron Nzambi, Denio Oliveira, and Pedro Silva
Publication:
Structural Journal
Volume:
121
Issue:
6
Appears on pages(s):
145-159
Keywords:
anchoring; flat plate; open double stirrups; punching; shear reinforcement
DOI:
10.14359/51740870
Date:
11/1/2024
Abstract:
This study experimentally evaluated the mechanical performance
of a new type of punching-shear reinforcement in five bidirectional
reinforced concrete slabs subjected to symmetrical loading. The
proposed shear reinforcement model consists of double-layered
open stirrups anchored to the flexural reinforcement, installed
after the longitudinal bars have been positioned, simplifying the
construction process. The main variables were the transverse
reinforcement ratio and the inclination of shear reinforcements. It
was found that the higher the reinforcement ratio and the inclination angle, the higher the shear strength, as expected. The open double-stirrup shear reinforcement provided more displacements and increased the punching-shear capacity by up to 36% and 40%, respectively, for vertical and inclined stirrups. Although closed stirrups are still widely used in construction, the proposed solution with open double stirrups demonstrated clear gains in punching-shear resistance, indicating their potential for practical use as reinforcement in slab-column connections. In addition, a comparison with theoretical punching-shear strength predictions from ACI 318, Eurocode 2, and ABNT NBR 6118 codes revealed conservative estimates with ACI 318, while ABNT NBR 6118 showed better accuracy.
Related References:
1. ACI Committee 318, “Building Code Requirements for Structural Concrete (ACI 318-19) and Commentary (ACI 318R-19) (Reapproved 2022),” American Concrete Institute, Farmington Hills, MI, 2019, 624 pp.
2. EN 1992-1-1:2004, “Eurocode 2: Design of Concrete Structures - Part 1-1: General Rules and Rules for Buildings,” European Committee for Standardization, Brussels, Belgium, 2004, 227 pp.
3. ABNT NBR 6118:2023, “Design of Concrete Structures,” Brazilian Technical Standards Association, Rio de Janeiro, RJ, Brazil, 2023, 242 pp. (in Portuguese)
4. Broms, C. E., “Elimination of Flat Plate Punching Failure Mode,” ACI Structural Journal, V. 97, No. 1, Jan.-Feb. 2000, pp. 94-101.
5. Graf, O., “Versuche über die Widerstandsfähigkeit von Allseitig Aufliegenden Dicken Eisenbetonplatten unterb Einzellasten,” Deutscher Ausschuß für Eisenbeton, No. 88, Berlin, Germany, 1938. (in German)
6. Elstner, R. C., and Hognestad, E., “Shearing Strength of Reinforced Concrete Slabs,” ACI Journal Proceedings, V. 53, No. 7, July 1956, pp. 29-58.
7. Nzambi, A.; Gomes, L.; Amanajás, C.; Silva, F.; and Oliveira, D., “Pile Caps with Inclined Shear Reinforcement and Steel Fibers,” Scientific Reports, V. 12, No. 1, 2022, Article No. 10047. doi: 10.1038/s41598-022-14416-2
8. Melo, G. S. S.; Coelho, A. E. G.; and Oliveira, D. R. C., “RC Flat Slabs with Inclined Stirrups as Shear Reinforcement,” Proceedings of the International Workshop on Punching Shear Capacity of RC Slabs, J. Silfwerbrand, G. Hassanzadeh, and S. Kinnunen, eds., KTH Royal Institute of Technology, Stockholm, Sweden, June 2000, pp. 155-162.
9. Andrade, J. L. S., “Experimental Study of the Inclination of Open Stirrups in Reinforced Concrete Slabs,” MSc thesis, Universidade de Brasília, Brasília, Brazil, 2000, 142 pp. (in Portuguese)
10. Langohr, P. H.; Ghali, A.; and Dilger, W. H., “Special Shear Reinforcement for Concrete Flat Plates,” ACI Journal Proceedings, V. 73, No. 3, Mar. 1976, pp. 141-146.
11. Gomes, R. B., and Regan, P. E., “Punching Resistance of RC Flat Slabs with Shear Reinforcement,” Journal of Structural Engineering, ASCE, V. 125, No. 6, June 1999, pp. 684-692. doi: 10.1061/(ASCE)0733-9445(1999)125:6(684)
12. Regan, P. E., “Punching Tests of Concrete Slabs with Riss Star Shear Reinforcement for Riss AG,” School of Architecture & Engineering, University of Westminster, London, UK, 1993.
13. Andrä, H.-P.; Dilger, W. H.; and Ghali, A., “Durchstanzbewehrung für Flachdecken,” Beton- und Stahlbetonbau, V. 74, No. 5, May 1979, pp. 129-132. doi: 10.1002/best.197900230
14. Trautwein, L. M.; Bittencourt, T. N.; Gomes, R. B.; and Bella, J. C. D., “Punching Strength of Flat Slabs with Unbraced Shear Reinforcement,” ACI Structural Journal, V. 108, No. 2, Mar.-Apr. 2011, pp. 197-205.
15. Dilger, W. H., and Ghali, A., “Shear Reinforcement for Concrete Slabs,” Journal of the Structural Division, V. 107, No. 12, Dec. 1981, pp. 2403-2420.
16. Ferreira, M. P.; Melo, G. S.; Regan, P. E.; and Vollum, R. L., “Punching of Reinforced Concrete Flat Slabs with Double-Headed Shear Reinforcement,” ACI Structural Journal, V. 111, No. 2, Mar.-Apr. 2014, pp. 363-374.
17. Furche, J., “Elementdecken im Durchstanzbereich von Flachdecken,” Betonwerk + Fertigteil-Technik, V. 63, No. 6, 1997, pp. 96-104.
18. Siburg, C.; Hegger, J.; Furche, J.; and Bauermeister, U., “Durchstanzbewehrung für Elementdecken nach Eurocode 2,” Beton- und Stahlbetonbau, V. 109, No. 3, Mar. 2014, pp. 170-181. doi: 10.1002/best.201300075
19. Seible, F.; Ghali, A.; and Dilger, W. H., “Preassembled Shear Reinforcing Units for Flat Plates,” ACI Journal Proceedings, V. 77, No. 1, Jan.-Feb. 1980, pp. 28-35.
20. Chana, P. S., “A Prefabricated Shear Reinforcement System for Flat Slabs,” Proceedings of the Institution of Civil Engineers - Structures and Buildings, V. 99, No. 3, Aug. 1993, pp. 345-358. doi: 10.1680/istbu.1993.24355
21. Beutel, R., and Hegger, J., “The Effect of Anchorage on the Effectiveness of the Shear Reinforcement in the Punching Zone,” Cement and Concrete Composites, V. 24, No. 6, Dec. 2002, pp. 539-549. doi: 10.1016/S0958-9465(01)00070-1
22. Siqueira, J. P. A., and Melo, G. S., “Punching Shear in Flat Slabs with Open Stirrups as Shear Reinforcement,” Structural Concrete, V. 24, No. 2, Apr. 2023, pp. 2827-2843. doi: 10.1002/suco.202200050
23. Regan, P. E., and Samadian, F., “Shear Reinforcement Against Punching in Reinforced Concrete Flat Slabs,” The Structural Engineer, V. 79, No. 10, May 2001, pp. 24-31.
24. Bassurucu, M.; Turk, K.; and Turgut, P., “The Effect of Hybrid Fiber and Shear Stud on the Punching Performance of Flat-Slab Systems,” Journal of Building Engineering, V. 77, Oct. 2023, Article No. 107555. doi: 10.1016/j.jobe.2023.107555
25. Oliveira, D. R.; Melo, G. S.; and Regan, P. E., “Punching Strengths of Flat Plates with Vertical or Inclined Stirrups,” ACI Structural Journal, V. 97, No. 3, May-June 2000, pp. 485-491.
26. Leonhardt, F., and Mönnig, E., Concrete Constructions – Volume 2: Special Cases of Design of Reinforced Concrete Structures, Editora Interciência, Rio de Janeiro, Brazil, RJ, 1978, 162 pp. (in Portuguese)
27. ABNT NBR 7480:2024, “Steel for the Reinforcement of Concrete Structures — Specifications,” Brazilian Technical Standards Association, Rio de Janeiro, RJ, Brazil, 2024, 17 pp. (in Portuguese)
28. ABNT NBR ISO 6892-1:2024, “Metallic Materials — Tensile Testing: Part 1: Method of Test at Room Temperature,” Brazilian Technical Standards Association, Rio de Janeiro, RJ, Brazil, 2024, 79 pp. (in Portuguese)
29. ABNT NBR 16889:2020, “Fresh Concrete — Slump Test,” Brazilian Technical Standards Association, Rio de Janeiro, RJ, Brazil, 2020, 5 pp. (in Portuguese)
30. ABNT NBR 5739:2018, “Concrete — Compression Test of Cylindrical Specimens,” Brazilian Technical Standards Association, Rio de Janeiro, RJ, Brazil, 2018, 9 pp. (in Portuguese)
31. ABNT NBR 7222:2011, “Concrete and Mortar — Determination of the Tension Strength by Diametrical Compression of Cylindrical Test Specimens,” Brazilian Technical Standards Association, Rio de Janeiro, RJ, Brazil, 2011, 5 pp. (in Portuguese)
32. ABNT NBR 8522-1:2021, “Hardened Concrete — Determination of Elasticity and Deformation Modulus: Part 1: Static Modulus by Compression,” Brazilian Technical Standards Association, Rio de Janeiro, RJ, Brazil, 2021, 24 pp. (in Portuguese)
33. Moe, J., “Shearing Strength of Reinforced Concrete Slabs and Footings Under Concentrated Loads,” Bulletin D47, Portland Cement Association, Skokie, IL, 1961, 135 pp.
34. Oliveira, D. R. C.; Regan, P. E.; and Melo, G. S. S. A., “Punching Resistance of RC Slabs with Rectangular Columns,” Magazine of Concrete Research, V. 56, No. 3, Apr. 2004, pp. 123-138. doi: 10.1680/macr.2004.56.3.123
35. Regan, P. E., “Shear Reinforcement of Flat Slabs,” Proceedings of the International Workshop on Punching Shear Capacity of RC Slabs, J. Silfwerbrand, G. Hassanzadeh, and S. Kinnunen, eds., KTH Royal Institute of Technology, Stockholm, Sweden, TRITA/BKN Bulletin 57, June 2000, pp. 99-107.
36. Nzambi, A. K. L. L.; de Oliveira, D. R. C.; do Nascimento, H. M.; and Azevedo, E. P., “Effect of the Failure Surface Inclination of Punching with Studs as Shear Reinforcement,” Practice Periodical on Structural Design and Construction, V. 28, No. 2, May 2023, p. 05023002. doi: 10.1061/PPSCFX.SCENG-1199
37. Barreto, N. R., and Melo, G. S., “Punching in Reinforced Concrete Slabs with Open Inclined Stirrup Shear Reinforcement,” Anais da XXXI Jornadas Sud-Americanas de Ingenieria Estructural, Mendoza, Argentina, 2004, 16 pp. (in Portuguese)