There is extensive experimental evidence of the decrease in shear stress at failure at increasing size in glass fiber-reinforced polymer (GFRP) reinforced concrete (RC) beams. An important practical implication is that extrapolating strength values from typical laboratory-scaled experiments to design larger members may be misleading. The complexity of the underlying mechanics is reflected in the lack of commercially available numerical tools that enable one to reliably estimate strength irrespective of beam size. This dissertation reports on research on a Lattice Discrete Particle Model (LDPM) based model to simulate the response of scaled slender GFRP RC beams without stirrups. The numerical model includes: (1) a calibrated and validated concrete LDPM; (2) orthotropic GFRP bar elements; and (3) a nonlinear bond-slip law for GFRP bar-concrete interface.

The first study, includes the calibration and validation of the concrete LDPM based on the typical provided information (i.e., cylinder compressive strength, and maximum aggregate size). Next, the proof of concept is achieved by accurately simulating the shear behavior of GRFP RC beams without stirrups having effective depth in the range 146-292 mm, which is significant for successfully predicting the size effect.

In the second study, LDPM-based numerical models are deployed to simulate the load-midspan displacement response, crack pattern, shear strength and associated size effect for GFRP RC beams without stirrups having effective depth in the range 146-883 mm. The numerical simulations yielded accurate predictions of load-deflection response, strength, and failure mode, irrespective of the size.

In the third study, the implications of variations in the concrete fracture energy and the maximum aggregate size are investigated numerically, in two cases, for which strength and failure mode of the GFRP RC beams without stirrups are significantly changed. Based on the simulation results, it is recommended that the fracture tests along with the compressive strength tests need to be performed on the concrete samples to improve the shear strength predictions and to avoid unrealistic failure modes.

The obtained results from this research are significant since, for the first time, they demonstrate the successful use of numerical simulations to accurately predict the shear behavior and the associated size effect of scaled GFRP RC beams without stirrups.