08 مبادرة #تواصل_تطوير - "Punching Shear Reinforcement for Flat Slabs"
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This document discusses punching shear reinforcement in reinforced concrete flat slabs, highlighting its advantages like architectural flexibility and ease of construction, alongside the primary disadvantage of brittle punching failure. It details methods for increasing punching shear resistance, types of reinforcement, seismic behavior, and relevant code provisions, with an emphasis on the need for shear reinforcement to enhance ductility. Additionally, an example is provided to illustrate the application of these principles using design codes.
08 مبادرة #تواصل_تطوير - "Punching Shear Reinforcement for Flat Slabs"
- 1. Punching Shear Reinforcement in Reinforced Concrete Flat Slabs Prof. Dr. Alaa Sherif Faculty of Engineering – Mataria Helwan University
- 2. Outline 1. Introduction 2. Means of Increasing the Punching Shear Resistance 3. Seismic Behaviour 4. Types of Punching Shear Reinforcement 5. Codes Provisions 6. Example Prof. Dr. Alaa Sherif
- 3. 1. Introduction Definition: Slab is directly supported on columns (no beams) Prof. Dr. Alaa Sherif
- 4. 1. Introduction (cont’d) Main Advantages of Flat Slabs • Architectural flexibility of spaces • Maximizing clear height of floor • No obstructions to ducts …etc • Ease of formwork • Speedy and ease of construction
- 5. 1. Introduction (cont’d) Main Disadvantage • Brittle punching failure!
- 6. 2. Means of Increasing the Punching Shear Resistance Increase thickness of slab (drop panel) Increase dimension of column (column head) Increase compressive strength of concrete (fcu) Brittle Behaviour Use of Shear Reinforcement Ductile Behaviour !!! Prof. Dr. Alaa Sherif
- 7. 3. Seismic Behaviour • Even if slab is not part of the horizontal loading resisting system, slab column connection will undergo the deformations under seismic loading • Ductility requirements – Interstory drift ratio Dru requirement Δ H DRu= Δ/H
- 8. 3. Seismic Behaviour (cont’d) • Shear Reinforcement increases the ductility and lateral drift ratio capacity Prof. Dr. Alaa Sherif
- 9. 3. Seismic Behaviour (cont’d) Prof. Dr. Alaa Sherif
- 10. 4. Types of Punching Shear Reinforcement
- 11. 5. Codes Provisions (a) Critical Sections (b) Provisions for Shear Reinforcement (c) Design Provisions Prof. Dr. Alaa Sherif
- 12. Code ACI 318-19 CSA 23.3-94 ECP 203-2018 EC2 DIN 1045-1 BS8110 No Shear RFT With Shear RFT Succesive perimeters Loaded area Shear stress for shaded zone checked on this perimeter Zone 1 2 3 4 0.75 d d/2 d/2 a b (a) Critical Sections Prof. Dr. Alaa Sherif
- 13. (b) Provisions for Shear Reinforcement (Stirrups) Min Slab Thickness Max Steel Stress Layout Spacing Limits In Radial Direction Spacing Limits In Tangential Direction ACI 318-19 152 mm, not less than 16 shear rft diameter 414 MPa, 496 MPa (Committee 421 for studs) Orthogonal CSA 23.3-94 -300 mm for stirrups - no restrictions for studs Orthogonal Not specified EC 2 Not Specified Radial/ Orthogonal Taken care of in the definition of the critical section DIN 1045-1 (stirrups) 200 mm Radial BS 8110 (stirrups) 200 mm Not Specified Not specified s d s do 05 05. , . s dt 2 0. Stirrups s d s do 025 05. , . Studs for for s d s d v f s d v f o u c c u c c 04 075 056 05 056 . . . ' . . ' 0 3 05 075. . , .d s d s do f d f d ywd ef ywd, . 250 0 25 in mm fy s f f MPa s d s y y, . . . . 500 07 03 400 400 07 10 s d s do 05 075. , . s dt 15. fy s d 075.
- 14. (c) Design Provisions Without Shear Reinforcement a b Punching Resistance of Concrete > Punching Shear Stress Resistance at Critical Section vr = vc Vc = punching resistance of concrete Prof. Dr. Alaa Sherif
- 15. With Shear Reinforcement Resistance for Section Inside Shear Reinforced Zone vr = vcs + vs ≤ vmax V P V T T V P V (c) Design Provisions (cont’d) vcs = resistance of concrete inside shear rft zone vs = resistance of shear reinforcement vmax = maximum allowed punching stress (diagonal compression resistance)
- 16. (c) Design Provisions (cont’d) With Shear Reinforcement Resistance for Section Outside Shear Reinforced Zone vr = vc-outside Vc-outside = resistance of concrete outside shear rft zone
- 17. 6. Example (ECP 203-2018) MPa db Q q u up 38.1 2702680 101000 3 0 d/2 d/2 a=b=400m b d = 270 mm, Qu = 1000kN fcu = 25 MPa, fy = 360MPa bo = 2680 mm necessaryisrftpunching governing29.1 5.1 25 316.07.1316.0 94.1 5.1 25 0.15.0316.05.0316.0 97.1 5.1 25 2.0 2680 2704 8.02.08.0 :oflessertheis cupup c cu cup c cu cup c cu o cup cup qq MPaMPa f q MPa f b a q MPa f b d q q Prof. Dr. Alaa Sherif
- 18. maxsup zonerftshearinsideSection upcrackedcupup qqqq mm100schoose 115 15.12680 350904 49.038.1 branches)8stiruups,12(No.9041138 350350 135mm 2 270 2 where 49.012.0 ..84.145.0 38.1 sup 2 sup max mms sbs fA q mmA MPaMPaf d s bs fA q MPa f q KOqMPa f q MPaq so yst st y so yst c cu crackedcup up c cu up up Prof.. Dr. Alaa Sherif
- 19. MPa q q cup up 65.0 2 7.1 2 zonerftshearoutsideSection .. 2 7.1 2 59.0 2706324 101000 6324118140044 11812,400 835 2 270 1007 2 7For 49.012.0 ..84.145.0 38.1 3 0 210 21 max KO q MPa db Q q mmxxb mmLxmmx mm d sL MPa f q KOqMPa f q MPaq cupu up c cu crackedcup up c cu up up L x1 x2 Prof.. Dr. Alaa Sherif
- 20. Thank you very much for your attention ! Prof.. Dr. Alaa Sherif