Experimental and Theoretical Investigations of a New Flat Slab System Incorporating GFRP Stay-In-Place Structural Forms and Embedded I-Beams

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Authors
Boules, Philopateer
Keyword
Stay-in-place forms , Reinforced Concrete , Finite Element Analysis , Digital Image Correlation , Punching Shear , GFRP , Two-way slabs , Structural form , Bond , Embedded beams , Flat slab , Connections , Shear reinforcement
Abstract
A novel steel-free concrete flat-slab design for floors is introduced. It includes embedded glass fiber-reinforced polymer (GFRP) I-sections as primary and secondary beams, with columns supporting the primary beams. GFRP stay-in-place (SIP) structural forms span the spacing between, and are bonded to, the lower flanges of the I-beams. Different components of the floor were investigated. Flexural behaviour in the direction transverse to the I-beams was investigated in the positive and negative moment regions using 2,575×610×225 mm slab segments, incorporating bonded connections and away from connections. A design-oriented analytical model was developed to predict connection strength based on bond failure. A case study of a floor design was presented and met the strength requirement. A nonlinear finite element analysis with emphasis on the flexural behaviour in the two orthogonal directions, namely transverse and parallel to the I-beam was also carried out. It incorporates appropriate interfacial and contact relations and robust failure criteria of the constituents. The model was verified against experimental results and used in a comprehensive parametric study. Punching shear behaviour of the slab was investigated using four full-scale interior slab-column specimens, 2000x2000x200 mm, tested under axial compression applied to the column. The study assessed the contributions of different components of the GFRP system. The new design experienced a 29% higher punching shear strength than a control slab with GFRP top rebar only, and an increase in ductility index from 1.6 to 3.1. An analytical model was developed, accounting for concrete contribution and flexural and web contributions of I-beams. Results agreed with experimental punching shear strength, within -6 to +13%, and a parametric study was carried out. A special emphasis was placed on the bonded connection between SIP forms and I-beams, being the weakest link in the system. Bonded connections of different types and configurations were examined through 48 bond specimens tested in tension. Digital Image Correlation (DIC) was used to capture strain and slip profiles along the interfaces, from which shear and peeling stress distributions were established. The connections reached 80-100% of the full capacity of the member, governed by the transverse tensile strength of the I-beam. The two highest occurrences were fiber-tear of the SIP form and adhesive failure. The combined test data was used to establish the shear-peeling stress interaction failure envelope and a bond-slip relationship.
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