• Coupled systems mechanics
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• v.11 no.1
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• pp.15-32
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• 2022

The comprehensive understanding of the fiber reinforced polymer behavior requires the use of advanced non-destructive testing methods due to its heterogeneous microstructure and anisotropic mechanical proprieties. In addition, the material response under load is strongly associated with manufacturing defects (e.g., voids, inclusions, fiber misalignment, debonds, improper cure and delamination). Such imperfections and microstructures induce various damage mechanisms arising at different scales before macrocracks are formed. The origin of damage phenomena can only be fully understood with the access to underlying microstructural features. This makes X-ray Computed Tomography an appropriate imaging tool to capture changes in the bulk of fibrous materials. Moreover, Digital Volume Correlation (DVC) can be used to measure kinematic fields induced by various loading histories. The correlation technique relies on image contrast induced by microstructures. Fibrous composites can be reinforced by different fiber architectures that may lead to poor natural contrast. Hence, a priori analyses need to be performed to assess the corresponding DVC measurement uncertainties. This study aimed to evaluate measurement resolutions of global and regularized DVC for glass fiber reinforced polymers with different fiber architectures. The measurement uncertainties were evaluated with respect to element size and regularization lengths. Even though FE-based DVC could not reach the recommended displacement uncertainty with low spatial resolution, regularized DVC enabled for the use of fine meshes when applying appropriate regularization.

• Structural Engineering and Mechanics
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• v.64 no.5
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• pp.557-566
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• 2017

Fiber reinforced polymer (FRP) sheets are the most efficient structural materials in terms of strength to weight ratio and its application in strengthening and retrofitting of a structure or structural elements are inevitable. The performance enhancement of structural elements without increasing the cross sectional area and flexible nature are the major advantages of FRP in retrofitting/strengthening work. This research article presents a detailed study on the inelastic response of conventional and retrofitted Reinforced Concrete (RC) frames using Carbon Fibre Reinforced Polymers (CFRP) and Glass Fiber Reinforced Polymers (GFRP) subjected to quasi-static loading. The hysteretic behaviour, stiffness degradation, energy dissipation and damage index are the parameters employed to analyse the efficacy of FRP strengthening of brick in-filled RC frames. Repair and retrofitting of brick infilled RC frame shows an improved load carrying and damage tolerance capacity than control frame.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.32 no.6
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• pp.349-357
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• 2019

Finite element method (FEM) is utilized in the development of products to realistically analyze and predict the mechanical behavior of materials in various fields. However, the approach based on the numerical analysis of glass fiber reinforced plastic (GFRP) composites, for which the fiber orientation and strain rate affect the mechanical properties, has proven to be challenging. The purpose of this study is to define and evaluate the mechanical properties of glass fiber reinforced plastic composites using the numerical analysis models of Digimat, a linear, nonlinear multi-scale modeling program for various composite materials such as polymers, rubber, metal, etc. In addition, the aim is to predict the behavior of realistic polymeric composites. In this regard, the tensile properties according to the fiber orientation and strain rate of polybutylene terephthalate (PBT) with short fiber weight fractions of 30wt% among various polymers were investigated using references. Information on the fiber orientation was calculated based on injection analysis using Moldflow software, and was utilized in the finite element model for tensile specimens via a mapping process. LS-Dyna, an explicit commercial finite element code, was used for coupled analysis using Digimat to study the tensile properties of composites according to the fiber orientation and strain rate of glass fibers. In addition, the drawbacks and advantages of LS-DYNA's various anisotropic material models were compared and evaluated for the analysis of glass fiber reinforced plastic composites.

• Structural Engineering and Mechanics
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• v.87 no.6
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• pp.585-599
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• 2023

Geopolymer concrete (GC) can be competently utilized as a practical replacement for cement to prevent a high carbon footprint and to give a direction toward sustainable concrete construction. Moreover, previous studies mostly focused on the axial response of glass fiber reinforced polymer (glass-FRP) concrete compressive elements without determining the effectiveness of repairing them after their partial damage. The goal of this study is to assess the structural effectiveness of partially damaged GC columns that have been restored using carbon fiber reinforced polymer (carbon-FRP). Bars made of glass-FRP and helix made of glass-FRP are used to reinforce these columns. For comparative study, six of the twelve circular specimens-each measuring 300 mm×1200 mm-are reinforced with steel bars, while the other four are axially strengthened using glass-FRP bars (referred to as GSG columns). The broken columns are repaired and strengthened using carbon-FRP sheets after the specimens have been subjected to concentric and eccentric compression until a 30% loss in axial strength is attained in the post-peak phase. The study investigates the effects of various variables on important response metrics like axial strength, axial deflection, load-deflection response, stiffness index, strength index, ductility index, and damage response. These variables include concentric and eccentric compression, helix pitch, steel bars, carbon-FRP wrapping, and glass-FRP bars. Both before and after the quick repair process, these metrics are evaluated. The results of the investigation show that the axial strengths of the reconstructed SSG and GSG columns are, respectively, 15.3% and 20.9% higher than those of their original counterparts. In addition, compared to their SSG counterparts, the repaired GSG samples exhibit an improvement in average ductility indices of 2.92% and a drop in average stiffness indices of 3.2%.

• Steel and Composite Structures
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• v.11 no.2
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• pp.93-114
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• 2011

Flange and web local buckling in beam plastic hinge regions of steel moment frames can prevent beam-column connections from achieving adequate plastic rotations under earthquake-induced forces. This threat is especially valid for existing steel moment frame buildings with beams that lack adequate flange/web slenderness ratios. As the use of fiber reinforced polymers (FRP) have increased in strengthening and repair of steel members in recent years, using FRPs in stabilizing local instabilities have also attracted attention. Previous computational studies have shown that longitudinally oriented glass FRP (GFRP) strips may serve to moderately brace beam flanges against the occurrence of local buckling during plastic hinging. An experimental study was conducted at Izmir Institute of Technology investigating the effects of GFRP reinforcement on local buckling behavior of existing steel I-beams with flange slenderness ratios (FSR) exceeding the slenderness limits set forth in current seismic design specifications and modified by a bottom flange triangular welded haunch. Four European HE400AA steel beams with a depth/width ratio of 1.26 and FSR of 11.4 were cyclically loaded up to 4% rotation in a cantilever beam test set-up. Both bare beams and beams with GFRP sheets were tested in order to investigate the contribution of GFRP sheets in mitigating local flange buckling. Different configurations of GFRP sheets were considered. The tests have shown that GFRP reinforcement can moderately mitigate inelastic flange local buckling.

• Steel and Composite Structures
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• v.22 no.1
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• pp.13-24
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• 2016

In the present paper, glass fibers are substituted partially with monofilament fishnet and polyester matrix for making the composites. The composite specimens were prepared in accordance with ASTM for analyzing the flexural strength and dynamic mechanical properties. Furthermore, machinability revealed the interaction of glass fiber and partial substituted monofilament fishnet fiber with the matrix. Fiber pullouts on the fractured specimen during the physical testing of the composites are also investigated by COSLAB microscope. The results reveal that the fishnet based composites have appreciably higher flexural properties. Furthermore, the glass fiber, woven roving and fishnet composite has more storage modulus and significant mechanical damping. The composite specimens were fabricated by hand lay-up method. Hence, these composites are the possible applications to develop the value added products. The results of this study are presented.

• Proceedings of the Korea Concrete Institute Conference
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• 2001.11a
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• pp.515-520
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• 2001

This study discusses the flexural performance of rehabilitated composite sections, consisting originally of R/C beams and subsequently strengthened by, Hybrid Fiber Reinforced Polymers(FRPs) and adhesives. Experimentations were peformed with 8 specimens to compare the rehabilitated effect of the length of FRPs, 2plies of FRPs, and 3plies of FRPs. The results show that the increase of the FRP strengthening length is effective on the flexural capacity and strength. Also, R.C beams retrofitted with hybrid FRPs are more effective on the increase of flexural capacity, strength, stiffness, and ductility than with a single kind of FRPs.

• Journal of the Korea Concrete Institute
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• v.19 no.6
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• pp.727-734
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• 2007

The influence of the differences in the physical and mechanical properties between fiber-reinforced polymer (FRP) and conventional steel, concentrated reinforcement in the immediate column region, as well as using steel fiber-reinforced concrete (SFRC) in the slab near the column faces, on the punching behavior of two-way slabs were investigated. The punching shear capacity, stiffness, ductility, strain distribution, and crack control were investigated. Concentrating of the slab reinforcement and the use of SFRC in the slab enhanced the punching behavior of the slabs reinforced with glass fiber-reinforced polymer (GFRP) bars. In addition the test results of the slabs with concentrated reinforcement were compared with various code equations and the predictions proposed in the literature specifically for FRP-reinforced slabs. An appropriate method for determining the reinforcement ratio of slabs with a banded distribution was also investigated to allow predictions to properly reflect the benefit of the slab reinforcement concentration.

• Advanced Composite Materials
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• v.18 no.3
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• pp.209-219
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• 2009

Carbon nanotubes (CNTs) have shown great potential for the reinforcement of polymers or fiber-reinforced composites. In this study, mechanical properties of multi-walled carbon nanotube (MWNT)-filled plain-weave glass/epoxy composites intended for use in radar absorbing structures were evaluated with regard to filler loading, microstructure, and fiber volume fraction. The plain-weave composites containing MWNTs exhibited improved matrix-dominant and interlaminar fracture-related properties, that is, compressive and interlaminar shear strength. This is attributed to strengthening of the matrix rich region and the interface between glass yarns by the MWNTs. However, tensile properties were only slightly affected by the addition of MWNTs, as they are fiber-dominant properties.

• Advances in concrete construction
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• v.2 no.4
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• pp.281-300
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• 2014

This study presents the experimental results of twenty three reinforced concrete beams with rectangular web openings externally strengthened with Fiber Reinforced Polymers (FRP) composites bonded around openings. All tested beams had the same geometry and reinforcement details. At openings locations, the stirrups intercepted the openings were cut during fabrication of reinforcement cage to simulate the condition of inclusion of an opening in an existing beam. Several design parameters are considered including the opening dimensions and location in the shear zone, the wrapping configurations, and the amount and the type of the FRP composites in the vicinity of the openings. The wrapping configurations of FRP included: sheets, strips, U-shape strips, and U-shape strips with bundles of FRP strands placed at the top and sides of the beam forming a fan under the strips to achieve closed wrapping. The effect of these parameters on the failure modes, the ultimate load, and the beam stiffness were investigated. The shear contribution of FRP on the shear capacity of tested beams with web openings was estimated according to ACI Committee 440-08, Canadian Standards S6-06, and Khalifa et al. model and examined against the test results. A modification factor to account for the dimensions of opening chords was applied to the predicted gain in the shear capacity according to ACI 440-08 and CSA S6-06 for bonded Glass Fiber Reinforced Polymers (GFRP) around openings. The analytical results after incorporating the modification factor into the codes guidelines showed good agreement with the test results.