Filled Fiber Reinforced Polymer Research Articles

Behavior of square and rectangular ultra high-strength concrete-filled FRP tubes under axial compression

This paper presents results of an experimental program undertaken to investigate the behavior of square and rectangular ultra high-strength concrete (UHSC)-filled fiber reinforced polymer (FRP) tubes (UHSCFFTs) under axial compression. The effects of the amount of confinement, cross-sectional aspect ratio and corner radius were investigated experimentally through the tests of 24 concrete-filled FRP tubes (CFFTs) that were manufactured using unidirectional carbon fiber sheets and UHSC with 108MPa average compressive strength. As the first experimental investigation on the axial compressive behavior of square and rectangular UHSCFFTs, the results of the study reported in this paper allows a number of significant conclusions to be drawn. Of primary importance, test results indicate that sufficiently confined square and rectangular UHSCFFTs can exhibit highly ductile behavior. The results also indicate that confinement effectiveness of FRP tubes increases with an increase in corner radius and as sectional aspect ratio approaches unity. It is found that UHSCFFTs having tubes of low confinement effectiveness may experience significant strength loss along the initial portions of the second branches on their stress–strain curves. Furthermore, it is observed that the behavior of UHSCFFTs at this region differs from their normal-strength concrete counterparts and is more sensitive to the effectiveness of confining tube. The second half of the paper presents the performance assessment of the existing FRP-confined concrete models in predicting the ultimate conditions of the HSC and UHSCFFTs. The results of this assessment demonstrate that the existing models provide unconservative estimates for specimens with higher concrete strengths. To address this, a new model that was developed on the basis of a comprehensive experimental test database and is applicable to both NSC and HSC of strengths up to 120MPa is proposed. The model comparisons demonstrate that the proposed model provides significantly improved predictions of the ultimate conditions of FRP-confined HSC compared to the existing models.

Seismic Behavior of High-Strength Concrete-Filled FRP Tube Columns

This paper reports on an experimental program that investigated the seismic behavior of high-strength concrete (HSC)-filled fiber-reinforced-polymer (FRP) tubes (HSCFFTs), designed to perform as building columns. Five square and one circular concrete-filled FRP tube (CFFT) columns were tested under constant axial compression and reversed-cyclic lateral loading. The main parameters of the experimental study were the axial load level, column cross-sectional shape, concrete strength, amount and type of FRP confinement, and FRP tube corner radius. Examination of the test data resulted in a number of significant conclusions with regard to the influence of the investigated column parameters on the performance of CFFT columns. Of primary importance, the results indicate that square HSCFFT columns are capable of developing very high inelastic deformation capacities under simulated seismic loading. The results also indicate that increasing the FRP tube corner radius up to a certain threshold leads to a significant increase in column lateral drift capacities. By contrast, increasing the corner radius beyond that threshold value provides no additional improvement in the hysteretic behavior of square CFFT columns. The influence of the cross-sectional shape is found to be significant, with the circular CFFT exhibiting a larger lateral drift capacity compared with the companion square CFFTs. A set of comparable columns from previous studies has also been included in the discussion to clarify the influence of each parameter on the column behavior. The results of the experimental program are presented together with a discussion on the influence of the main parameters on the seismic behavior of CFFT columns.

Axial Compressive Behavior of Square and Rectangular High-Strength Concrete-Filled FRP Tubes

AbstractThis paper presents results of an experimental study on the behavior of square and rectangular high-strength concrete (HSC)-filled fiber-reinforced polymer (FRP) tubes (HSCFFT) under concentric compression. The effects of the tube thickness, sectional aspect ratio, and corner radius on the axial compressive behavior of concrete-filled FRP tubes (CFFT) were investigated experimentally through the tests of 24 CFFTs that were manufactured using unidirectional carbon fiber sheets and high-strength concrete with 78 MPa average compressive strength. As the first experimental investigation on the axial compressive behavior of square and rectangular HSCFFTs, the results of the study reported in this paper allow a number of significant conclusions to be drawn. First and foremost, test results indicate that sufficiently confined square and rectangular HSCFFTs can exhibit highly ductile behavior. The results also indicate that confinement effectiveness of FRP tubes increases with an increase in corner radius...

Performance-based seismic design of unbonded precast post-tensioned concrete filled GFRP tube piers

This paper presents a seismic design procedure for self-centering precast post-tensioned bridge piers. The piers presented in this manuscript consisted of concrete filled fiber reinforced polymer (FRP) tubes. A large set of 84 piers with different design parameters were analyzed using finite element models. The backbone curve of each pier was developed and bilinearized. The idealized backbone curves were used to develop a set of empirical equations that were able to reproduce the bilinearized backbone curve of a given pier. Different performance criteria have been proposed for the system according to the intensity and the frequency of occurrence of a seismic event. The developed empirical equations were arranged in a design procedure to achieve a given performance level at a specific seismic zone.

Shake table response and analysis of a concrete-filled FRP tube bridge column

The seismic performance of a concrete filled fiber reinforced polymer (FRP) tube (CFFT) bridge column was studied through shake table testing and nonlinear dynamic analyses of a one-fifth scale two-column bridge pier that also incorporated a conventional RC column. The FRP tube in the CFFT column was a prefabricated composite pipe with glass fibers aligned in ±55° with respect to the tube axis to provide both hoop and longitudinal strengths. The columns had nearly the same flexural capacities. The accumulated dissipated hysteresis energy of the CFFT column normalized by steel ratio was 1.6 times larger than that of the RC column; yet, it remained visibly damage free up to a drift ratio of 7%. The CFFT column failed due to FRP tube rupture under 8.4% drift ratio. The equivalent plastic hinge length of CFFT column was found to be more than twice that of the RC column, which implies larger spread of plasticity and smaller local ductility demands. The nonlinear dynamic modeling of the pier response using OpenSees led to very good agreement with the measured response of the pier under moderate and large-amplitude motions.

Shear Response of Concrete-Filled FRP Composite Cylindrical Shells

This paper presents an analytical procedure for predicting the shear load-deformation response of concrete filled fiber-reinforced polymer (FRP) composite cylindrical shells with full- and noncomposite behavior. The approach is based on a sectional layered analysis with an iterative algorithm to achieve equilibrium and compatibility conditions of the FRP/concrete system, including the cracked behavior of the FRP-confined concrete, until first-ply failure of the FRP composite. The model follows first order mechanics for the shear behavior of structural members in combination with a smeared shear modulus for cracked concrete and inclusion of extension/shear coupling effects of anisotropic FRP laminates. Comparisons of the analytical response with available experimental data from large- and small-scale tests were found to be in reasonable agreement and corroborated the significant influence of the concrete core and the composite interaction details on the shear load-deformation response. Parametric studies on the influence of concrete properties, axial loads, and FRP laminate design are discussed.