Title:
Enhancing Punching Strength and Deformation Capacity of Flat Slabs
Author(s):
Raffaele Cantone, Miguel Fernández Ruiz, Jan Bujnak, and Aurelio Muttoni
Publication:
Structural Journal
Volume:
116
Issue:
5
Appears on pages(s):
261-274
Keywords:
Critical Shear Crack Theory; dowel action; experimental tests; flat slabs; punching; shear reinforcement
DOI:
10.14359/51716842
Date:
9/1/2019
Abstract:
Punching reinforcement systems have significantly developed in recent years as they allow enhancing the punching resistance of slab-column connections as well as their deformation capacity. These systems, with varying geometry and layout, normally consist of vertical or inclined shear reinforcement with both ends anchored on the compression and tension side of the slab. For very high levels of load, when even common punching reinforcement systems cannot safely ensure the transfer of loads, steel shear heads are usually embedded in the slab to enhance the resistance of the connection. Yet, shear heads might be expensive and difficult to place in construction sites. Following the principle of the dowel action of the compression reinforcement, this paper introduces a novel system to efficiently reinforce slabs against punching shear by using large-diameter double-headed studs acting as shear dowels. This system enhances the performance of shear-reinforced slabs with respect to conventional solutions and might be an efficient alternative to shear heads for a large number of practical situations. The system is validated by means of a specific experimental program including 11 axisymmetric punching tests on interior slab-column connections. The results demonstrate not only the increase of the punching strength but also the deformation capacity of the connection. It is also shown that the system can be consistently designed accounting for the doweling forces by making use of the theoretical frame of the
Critical Shear Crack Theory (CSCT), allowing to understand the activation of the shear dowels on the basis of the deformation of the member.
Related References:
1. Kinnunen, S., and Nylander, H., Punching of Concrete Slabs without Shear Reinforcement, Elanders Boktryckeri Aktiebolag, 1960, 122 pp.
2. fib Bulletin 81, “Punching Shear of Structural Concrete Slabs: Honoring Neil M. Hawkins,” ACI- fib Symposium Proceedings 378, 2017.
3. Einpaul, J.; Fernández Ruiz, M.; and Muttoni, A., “Influence of Moment Redistribution and Compressive Membrane Action on Punching Strength of Flat Slabs,” Engineering Structures, V. 86, 2015, pp. 43-57. doi: 10.1016/j.engstruct.2014.12.032
4. Einpaul, J.; Ospina, C. E.; Fernández Ruiz, M.; and Muttoni, A., “Punching Shear Capacity of Continuous Slabs,” ACI Structural Journal, V. 113, No. 4, July-Aug. 2016, pp. 861-872. doi: 10.14359/51688758
5. Einpaul, J.; Brantschen, F.; Fernández Ruiz, M.; and Muttoni, A., “Performance of Punching Shear Reinforcement under Gravity Loading : Influence of Type and Detailing,” ACI Structural Journal, V. 113, No. 4, July-Aug. 2016. doi: 10.14359/51688630
6. Mirzaei, Y., “Post-Punching Behavior of Reinforced Concrete Slabs,” PhD dissertation, École Polytechnique Fédérale de Lausanne École Polytechnique Fédérale de Lausanne, Lausanne, Switzerland, 2010, 230 pp.
7. Fernández Ruiz, M.; Mirzaei, Y.; and Muttoni, A., “Post-Punching Behavior of Flat Slabs,” ACI Structural Journal, V. 110, No. 5, Sept.-Oct. 2013, pp. 801-812.
8. Habibi, F.; Cook, W. D.; and Mitchell, D., “Predicting Post-Punching Shear Response of Slab-Column Connections,” ACI Structural Journal, V. 111, No. 1, Jan.-Feb. 2014, pp. 123-134.
9. Cavagnis, F.; Fernández Ruiz, M.; and Muttoni, A., “An Analysis of the Shear-Transfer Actions in Reinforced Concrete Members without Transverse Reinforcement Based on Refined Experimental Measurements,” Structural Concrete, V. 19, No. 1, 2017, pp. 1-16. doi: 10.1002/suco.201700145
10. Cavagnis, F.; Fernández Ruiz, M.; and Muttoni, A., “A Mechanical Model for Failures in Shear of Members without Transverse Reinforcement Based on Development of a Critical Shear Crack,” Engineering Structures, V. 157, 2018, pp. 300-315. doi: 10.1016/j.engstruct.2017.12.004
11. Muttoni, A., “Punching Shear Strength of Reinforced Concrete Slabs without Transverse Reinforcement,” ACI Structural Journal, V. 105, No. 4, July-Aug. 2008, pp. 440-450.
12. Fernández Ruiz, M.; and Muttoni, A., “Applications of Critical Shear Crack Theory to Punching of Reinforced Concrete Slabs with Transverse Reinforcement,” ACI Structural Journal, V. 106, No. 4, July-Aug. 2009, pp. 485-494.
13. Lips, S.; Fernández Ruiz, M.; and Muttoni, A., “Experimental Investigation on Punching Strength and Deformation Capacity of Shear-Reinforced Slabs,” ACI Structural Journal, V. 109, No. 6, Nov.-Dec. 2013, pp. 889-900.
14. CEN 10080:2005, “Steel for the Reinforcement of Concrete – Weldable Reinforcing Steel – General,” European Committee for Standardization, Brussels, Belgium, 2005.
15. Einpaul, J.; Bujnak, J.; Fernández Ruiz, M.; and Muttoni, A., “Study on Influence of Column Size and Slab Slenderness on Punching Strength,” ACI Structural Journal, V. 113, No. 1, Jan.-Feb. 2016, pp. 135-145.
16. Simões, J. T.; Fernández Ruiz, M.; and Muttoni, A., “Validation of the Critical Shear Crack Theory for Punching of Slabs without Transverse Reinforcement by Means of a Refined Mechanical Model,” Structural Concrete, V. 19, No. 1, 2018, pp. 191-216. doi: 10.1002/suco.201700280
17. Muttoni, A.; Fernández Ruiz, M.; and Simões, J. T., “The Theoretical Principles of the Critical Shear Crack Theory for Punching Shear Failures and Derivation of Consistent Closed-Form Design Expressions,” Structural Concrete, 2017, pp. 1-17.
18. Fernández Ruiz, M.; Muttoni, A.; and Kunz, J., “Strengthening of Flat Slabs against Punching Shear Using Post-Installed Shear Reinforcement,” ACI Structural Journal, V. 107, No. 4, July-Aug. 2010, pp. 434-442.
19. Fernández Ruiz, M., and Muttoni, A., “Performance and Design of Punching Shear Reinforcing Systems,” 3rd International fib Congress 15, 2010.
20. Sørensen, J. H.; Herfelt, M. A.; Hoang, L. C.; and Muttoni, A., “Test and Lower Bound Modeling of Keyed Shear Connections in RC Shear Walls,” Engineering Structures, V. 155, 2018, pp. 115-126. doi: 10.1016/j.engstruct.2017.11.004
21. Mises, R. V., “Mechanics of Plastic Deformation in Crystals,” Math Mech, V. 8, 1928, pp. 161-185.
22. Rasmussen, B. H., Betonindstobte Tvaerbelastede Boltes og Dornes Baereevne, Bygningstatiske Meddelser, 1963.
23. Nielsen, M. P., and Hoang, L. C., Limit Analysis and Concrete Plasticity, CRC Press, Boca Raton, FL, 2016.
24. Muttoni, A.; Fernández Ruiz, M.; Bentz, E. C.; Foster, S. J.; and Sigrist, V., “Background to the Model Code 2010 Shear Provisions—Part II Punching Shear,” Structural Concrete, V. 14, No. 3, 2013, pp. 195-203. doi: 10.1002/suco.201200064
25. Belletti, B.; Scolari, M.; Muttoni, A.; and Cantone, R., “Shear Strength Evaluation of RC Bridge Deck Slabs According to CSCT with Multi-Layered Shell Elements and PARC_CL Crack Model,” IABSE Conference, Geneva, Switzerland, 2015, pp. 1158-1165.
26. Cantone, R.; Belletti, B.; Muttoni, A.; and Fernández Ruiz, M., “Approaches for Suitable Modelling and Strength Prediction of Reinforced Concrete Slabs,” fib Symposium, 2016.