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Title: Flexural behaviour of concrete slabs reinforced with GFRP rebar subjected to varying temperature histories
Author: El-Zaroug, Orner Ramadan
Awarding Body: University of Leeds
Current Institution: University of Leeds
Date of Award: 2008
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Abstract:
The use of non-metallic glass fibre reinforced polymer (GFRP) materials as an alternative to steel reinforcement in concrete is gaining acceptance mainly due to their high corrosion resistance. A high strength-to-weight ratio and ease of handling and . fabrication are added advantages. However, the thermal characteristics of GFRP rods . can be sUbstantially different from those of concrete and conventional steel bars. The difference in the transverse thermal expansion between concre'te and FRP rods may cause hoop stresses within the concrete which can adversely affect the bond between the concrete and the rods and, eventually, lead to the formation of cracks within the concrete cover when the temperature increases. This research is an experimental investigation of the influence of transverse thermal expansion of GFRP rod on the flexural performance of concrete slabs. Fourteen concrete slabs (divided into four series, A, 8, C and D) were constructed and tested. The slab specimens, 1S0xSOOx2800 mm, were reinforced longitudinally using GFRP rod of 13, 16 or 19 mm bar diameters. No shear reinforcement was provided. The reinforcement ratio, bar diameter, clear bar spacing, concrete cover and placement configurations of GFRP rods were all varied. Each slab was simply supported and subjected to a two-point incremental load to failure. Prior to these ultimate loading tests, some test slabs were either thermally cycled once (series A, 8 and C) or nine times (series D). One slab from each series (A, 8 and C) was tested as a control specimen at room temperature only (no imposed thermal history). The flexural behaviour of these slabs in terms of crack pattern, crack width, deflections, ultimate strength and mode of failure as well the thermal behaviour of GFRP reinforced slabs was investigated. In addition, an attempt has been made to examine the effect of temperature change (100°C) on the mechanical behaviour of GFRP materials. The properties evaluated included the tensile strength, bond behaviour and maximum bond stress. Finally, the experimental results were also compared with the theoretical predictions obtained from the ACI 440.1 R-06, analytical models and with numerical simulations obtained from nonlinear finite element analysis (DIANA-9, 200S). The experimental results showed that the control slabs performed better than the thermally cycled slabs in terms of: mid-span deflection, surface crack widths and ultimate capacity. A number of parameters: reinforcing placement configuration of GFRP bars, bar size, reinforcement ratio, and thermal actions were found to affect the flexural behaviour of the slabs. Due to the transverse thermal incompatibility between the concrete and GFRP, thermal action appears to influence the bond between the concrete and GFRP bars. It was found that the critical concrete cover for GFRP slabs using single or bundled bars depends on reinforcing placement configuration, the transverse thermal expansion of GFRP bars, bar diameter and the concrete tensile strength. To reduce the potential of thermally-induced transverse cracking in GFRP concrete slabs reinforced with a single bar (13, 16 and 19 mm) at a temperatur~ incr~.ase of up to 60°C, a vertical concrete. cover greater than 1.S times the bar diameter (at least 1.Sdb ), a horizontal concrete cover equal or greater than SO mm, and a higher tensile strength of the concrete (at least 2.4 MPa for 13 mm bars) are recommended. For slabs reinforced with bundled (two) bars (13 and 16 mm),the required concrete cover is 1.Sdb and 2.Sdb with tensile strength ler = 3.2 and 3.6 MPa, respectively.
Supervisor: Not available Sponsor: Not available
Qualification Name: Not available Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.491652  DOI: Not available
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