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The University of Southampton

Research project: An investigation into strong and ductile glass–GFRP composites

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Despite the great potential of glass as a construction material, its brittle material behaviour poses major challenges when designing load-bearing glass structural members. Our research shows that float glass–glass fibre reinforced polymer (GFRP) hybrid beams, in which a layer of GFRP bonded between two horizontal glass sheets (Fig. 1a), are stronger and ductile compared to conventional laminated glass. The results demonstrate that the hybrid beams behaved elastically until the failure of the tension glass layer, and once cracked, the GFRP layer carried the tensile force enabling the load carrying of the cracked beam. Broken glass pieces remained stuck and interlocked on the GFRP layer, consequently ensured a significant post-breakage strength and prevented total failure.


Glass–GFRP beams were fabricated from two sheets of float glass (600 mm x 40 mm x 6 mm (thickness)) and a pre-cured GFRP sheet (650 mm x 40 mm x 1.35 mm (thickness)) that was adhesively bonded in between the glass layers. A second set of hybrid beams in which the GFRP layer was initially tensioned to a pre-determined load to ensure a uniform compressive prestress of magnitude ~7 MPa in the glass sheets were also tested. All beams were tested in four-point bending as shown in Fig. 1b. The load response and the failure behaviour of the hybrid beams were compared with the reference beams of single-layer and adhesively bonded double-layer beams made from the same 6 mm thick float glass.

Fig.1 (a)
Fig.1 (b)

Fig. 1 (a) Layout of float glass–GFRP hybrid beams (b) Four-point bending test configuration

Fig. 2a shows the load–midspan deflection relationships of the all types of beams tested in the study. As expected, the single and double-layer glass beam failed in a brittle manner due to a major crack originated in the tension side in the constant moment zone. Results shown in Fig. 2a suggest that the hybrid beams did not lose the load carrying capacity and the stiffness completely after the formation of the first major crack. The reported maximum loads of the two types of hybrid beams are about 5 times and 1.3 times stronger than the single-layer and the double-layer glass beams respectively. The all hybrid beams and the double-layer beams were about 7-8 times stiffer than the single layer beam in the pre-crack regime.

Fig.2 (a)
Fig.2 (b)

Fig. 2 (a) Load–midspan deflection relationships of different types of glass beams (b) Mid-span stresses at the tension and compression surfaces of the glass–GFRP hybrid beams

The degree to which the strength and stiffness of hybrid beams can be modelled by using finite element (FE) models was also investigated in the study. The FE models were validated by comparing the predicted stresses in the glass beams with the experimental data obtain from strain gauges and the stresses measured using a Scattered-Light-Polariscope (SCALP). For example, Fig. 2b shows the agreement between the predicted midspan surface stresses and that determined from the strain gauge data and SCALP for one of the hybrid beams.



Failure Behaviour and Ductility of Hybrid Beams

The hybrid beams continued to take load after the first major crack, albeit a drop in the stiffness. Once the tension glass layer has cracked the combination of the GFRP and the compression glass layer carried the applied load whilst the stiffness of the beam gradually decreased due to the development of new cracks. Fig. 3 shows the disturbed crack pattern observed in the hybrid beams compared to the single major crack that caused the failure of single and double-layer glass beams.



Fig. 3 (a) (b) (c) (d)
Fig. 4

Fig. 3 Crack pattern of (a) Single-layer float glass, (b) Double-layer float glass, (c) Glass–GFRP hybrids (no prestress), and (d) Glass–GFRP (pre-stressed) hybrids

Fig. 4 Recovery of the displacement of hybrid beams upon unloading

Ductility index, the ratio of the additional midspan deflection after the first major crack in the beam to the midspan deflection at the first major crack, may be used to quantify the ductility of the hybrid beams. The ductility indices of the hybrid beams are greater than about seven compared to zero ductility indices of single and double-layer glass beams. The experiments also showed that despite heavy cracking, the hybrid beams recovered almost the total deflection upon unloading (Fig. 4).



Benefits to structural engineering


  • Innovative use of float glass to build strong and ductile structural members
  • Safe post-breakage behaviour of glass structural elements
  • Glass members with improved performance against extreme loads


Funding sources


  1. The Institution of Structural Engineers
  2. University of Southampton



Relevant publications

Achintha, M and Balan, B (2016) Characterisation of the Mechanical Behaviour of Annealed Glass–GFRP Hybrid Beams. Construction and Building Materials (Under review)

Balan, B and Achintha, M (2016). ‘Experimental and numerical investigation of float glass– GFRP hybrid beams’. Challenging Glass Conference 5 – International Conference on the Architectural and Structural Application of Glass, Ghent, Belgium, 16–17 June.


Further information

Please contact Dr Mithila Achintha (E-mail: or 02380 59 2924)









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