Experimental & Analytical study on Tee beams reinforced Concrete using FRP composites analysis

Abstract

This study deals with experimental investigation for enhancing and strengthening structurally deficient T-beams by using an externally bonded fiber reinforced polymer (FRP). The rehabilitation of existing reinforced concrete (RC) bridges and building becomes necessary due to ageing, corrosion of steel reinforcement, defects in construction/design, demand in the increased service Loads, and damage in case of seismic events and improvement in the design guidelines. Fiber-reinforced polymers (FRP) have emerged as promising material for rehabilitation of existing reinforced concrete structures. The rehabilitation of structures can be in the form of strengthening, repairing or retrofitting for seismic deficiencies. RC T-section is the most common shape of beams and girders in buildings and bridges. Shear failure of RC T-beams is identified as the most disastrous failure mode as it does not give any advance warning before failure. The shear strengthening of RC T-beams using externally bonded (EB) FRP composites has become a popular structural strengthening technique, due to the well-known advantages of FRP composites such as their high strength-to-weight ratio and excellent corrosion resistance. This study assimilates the experimental works of glass fiber reinforced polymer (GFRP) retrofitted RC T-beams under symmetrical four-point static loading system. An innovative method of anchorage technique has been used to prevent these premature failures, which as a result ensure full utilization of the strength of FRP. Shear collapse of reinforced concrete (RC) members is catastrophic and occur suddenly with no advance warning of distress. In several occasions existing RC beams have been found to be deficient in shear and in need of strengthening. Conventional shear strengthening method such as external post tensioning, member enlargement along with internal transverse steel, and bonded steel plates are very costly, requiring extensive equipment, time, and significant labour. Conversely, the relatively new alternative strengthening technique using advanced composite materials, known as fiber reinforced polymer (FRP), offers significant advantages such as flexibility in design, ease of installation, reduced construction time, and improved durability. The overall objective of this study was to investigate the shear performance and failure modes of RC T-beams strengthened with externally bonded GFRP sheets. In order to achieve these objectives, an extensive experimental program consisting of testing eleven, full scale RC beams was carried out. The variables investigated in this study included steel stirrups, shear span-to-depth ratio, GFRP amount. The experimental results indicated that the contribution of externally bonded GFRP to the shear capacity is significant and depends on the variable investigated. The failures of strengthened beams are initiated with the deboning failure of FRP sheets followed by brittle shear failure. However, the shear capacity of these beams has increased as compared to the control beam which can be further improved if the deboning failure is prevented. An innovative method of anchorage technique by using GFRP plates has been used to prevent.

Introduction

As understanding of earthquakes improves, structural design codes are evolving, rendering many older structures inadequate by current seismic standards. Retrofitting is increasingly used to upgrade such structures, especially with innovative materials like GFRP (Glass Fiber Reinforced Polymer), which help improve the durability and seismic performance of buildings.

Experimental Study

An experimental program was conducted on nine RC T-beams to evaluate the effectiveness of GFRP strengthening:

• Beams were cast using M20 concrete and Fe415 steel.

• Beams were grouped based on flange widths (250mm, 350mm, 450mm).

• Some beams remained unstrengthened (control beams), while others were retrofitted using GFRP in different wrapping patterns: fully wrapped at 90°, U-wrapped, and at 45° angles.

• Epoxy resin (Araldite LY 556 with HY 951 hardener) was used for bonding GFRP to the beams.

Testing Method

• Beams were tested under four-point loading after 28 days of curing.

• Some beams had no stirrups (Group-A), while others had stirrups at 200mm spacing (Group-B).

• Beams were strengthened in critical shear zones using GFRP U-wraps, and flange anchorage systems were applied in some cases.

Results

• Group-A: Solid beams without GFRP had a shear capacity increase of 17.3% over the control beam. Beams with GFRP showed further improvements, with the best reaching a 33% increase in shear capacity.

• Group-B: Solid beam without transverse holes had a 41.67% higher shear capacity than the control. GFRP-retrofitted beams had up to a 53% improvement in strength.

Failure Modes

• Control beams generally failed in shear.

• GFRP-strengthened beams exhibited failure due to GFRP tearing, debonding, or combined shear failure, depending on the wrapping technique and anchorage used.

Conclusion

In this experimental investigation the shear behaviour of RC T-beams strengthened by GFRP sheets are studied. The test results illustrated in the present study showed that the external strengthening with GFRP composites can be used to increase the shear capacity of RC T-beams, but the efficiency varies depending on the test variables such as fiber orientations, wrapping schemes, number of layers and anchorage scheme. The present experimental program consisting of nine numbers of reinforced concrete T- beams with three different flange widths tested under torsion. The main objective is to exam line the effectiveness of epoxy-bonded GFRP fabrics used as external transverse reinforcement to resist torsion. Based on presented experimental results and analytical editions, the Following conclusions are drawn: 1) Experimental results show that the effect of flange width on torsional capacity of GFRP strengthened RC T-beams is significant. 2) Torsional strength increases with increase in flange area irrespective of beam strengthening with GFRP following different configurations schemes. 3) With 250 mm wide flange width increase in strength was 13%, with 350mm wide flange was 29% and for 450mm wide flange was found to be 69%. This is due to increase in area enclosed inside the critical shear path.

References

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Copyright

Copyright © 2025 Chandan Kumar , Ankita Singhai , Rahul Kumar Sathbaiya . This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.