Punching Shear of Flat Slabs with Pultruded GFRP Stay-in-Place Structural Forms
Publication: Journal of Composites for Construction
Volume 27, Issue 4
Abstract
This paper examines the punching shear behavior of a new concrete flat slab design, incorporating a glass fiber-reinforced polymer (GFRP) stay-in-place (SIP) structural form system and orthogonal GFRP top rebar mesh. The SIP form system comprises I-beams supported on the four sides of a column and flat plates with T-up ribs supported by, and adhesively bonded to, the bottom flanges of the I-beams. The web and top flange of the I-beams are embedded in the slab, thereby providing flexural and shear reinforcement, while the SIP ribbed plates provide the bottom reinforcement. Four full-scale interior slab–column specimens, 2000 × 2000 × 200 mm3, were tested under axial compression applied to the column. The slabs have a central 300 × 300-mm square column extending 300 mm on either side of the slab. The study assessed the contributions to punching shear strength of different components of the GFRP system. The new design experienced a 29% higher punching shear strength than the control slab with GFRP rebar only, and was much more ductile. The load dropped gradually over a large range of deflection, increasing the ductility index from 1.6 in the control slab to 3.1 in the slab incorporating the new design. An analytical model is developed for punching shear strength, accounting for concrete contribution and flexural and web contributions of I-beams. Results agreed with experimental strength, within −6% to +13%. A parametric study examined a range of rebar reinforcement ratios, different GFRP I-beam sizes and a comparable steel I-beam.
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Acknowledgments
The authors wish to acknowledge the financial support provided by the Natural Sciences and Engineering Research Council of Canada (NSERC) and the kind support provided by Sika Canada Inc. and V-Rod/Pultral Inc.
Notation
The following symbols are used in this paper:
- Af
- cross-sectional area (FRP);
- Afs
- area of the SIP form within one side of the punching shear perimeter;
- Aw
- area of the I-beam web within one side of the punching shear perimeter;
- amax
- maximum aggregate size;
- bo
- punching shear perimeter;
- c
- column side length;
- d
- effective depth to reinforcement;
- Ec
- concrete modulus;
- Ef
- Young’s modulus of the flexural FRP reinforcement;
- Es
- steel modulus;
- Ew
- transverse Young’s modulus of the web of the GFRP section;
- ffu
- ultimate tensile strength (FRP);
- concrete compressive strength;
- concrete tensile strength;
- G
- shear modulus;
- Gf
- shear modulus of the web of the GFRP section;
- Gfs
- shear modulus of the SIP form;
- h
- sab thickness;
- I
- moment of inertia;
- Vc
- concrete contribution in punching shear;
- Vcr
- cracking load;
- Vf f
- shear contribution of the flange of the I-beam;
- Vf s
- shear contribution of the SIP form;
- Vf w
- shear contribution of the web of the I-beam;
- Vfb
- GFRP I-beam flexural contribution in punching shear;
- Vfw
- GFRP I-beam shear contribution in punching shear;
- VT
- total load;
- Vu
- peak load;
- Δ(cp+sh)
- long-term deflection due to creep and shrinkage;
- Δ80%
- displacement of specimen at 80% of peak load (postpeak);
- Δcr
- displacement at cracking load;
- Δmax
- displacement at 80% VT (postpeak);
- ΔPmax
- deflection at Pmax;
- Δu
- deflection at Pu;
- Δy
- displacement at yield;
- γ
- shear strain of I-beam flange;
- axial (vertical) strain in I-beam web;
- θ
- rotation of I-beam;
- ρf
- reinforcement ratio (FRP);
- ρf′
- compression reinforcement ratio;
- ρfb
- balanced reinforcement ratio;
- ρfv
- shear reinforcement ratio; and
- τc
- punching shear strength.
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Published In
Journal of Composites for Construction
Volume 27 • Issue 4 • August 2023
Copyright
© 2023 American Society of Civil Engineers.
History
Received: Jul 11, 2022
Accepted: Feb 25, 2023
Published online: Apr 18, 2023
Published in print: Aug 1, 2023
Discussion open until: Sep 18, 2023
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