Generalized Strength Prediction Model for Timber Beams Strengthened Using NSM FRP Bars and FRP Sheets

Area of Science:

• Structural Engineering
• Materials Science
• Civil Engineering

Background:

• Existing analytical models for Fiber-Reinforced Polymer (FRP)-strengthened timber beams are limited to single reinforcement techniques.
• There is a need for a unified model accommodating hybrid reinforcement systems for timber beams.

Purpose of the Study:

• To develop a generalized analytical model for predicting the flexural capacity of timber beams strengthened with near-surface-mounted (NSM) FRP bars, externally bonded FRP sheets, or hybrid combinations.
• To validate the proposed model against experimental data and assess the performance of hybrid strengthening systems.

Main Methods:

• Formulation based on internal force equilibrium and strain compatibility.
• Incorporation of a constitutive model for timber, including linear elastic tension and bilinear compression with softening.
• Validation through four-point bending tests on timber beams strengthened with Glass Fiber-Reinforced Polymer (GFRP) and externally bonded GFRP sheets.

Main Results:

• The generalized analytical model demonstrated good agreement with experimental results (2-23% difference).
• Hybrid strengthening increased timber beam flexural capacity by up to 84% compared to control beams.
• Improved stiffness, ductility, and overall structural response were observed with hybrid systems, with GFRP reinforcement remaining effective.

Conclusions:

• The proposed generalized analytical model is a practical and reliable tool for predicting the flexural strength of FRP-strengthened timber beams.
• The study supports the structural rehabilitation and sustainable retrofitting of timber structures using advanced FRP reinforcement techniques.
• Hybrid FRP strengthening is effective in enhancing the performance of timber beams, with efficient utilization of reinforcement materials.