Hybrid GFRP-concrete Research Articles

Shear behavior of multi-row perforated GFRP rib shear connectors in GFRP-concrete hybrid beams/desks

Perforated GFRP ribs (PFRs) and epoxy bonding are commonly used shear connections ensuring a full composite action in FRP-concrete hybrid beam/deck. This study demonstrates test results of 27 push-out specimens to compare the failure modes, shear load-slip (P-S) curves, and shear performance of PFRs and epoxy bonding. The variables included the sanding depth on GFRP profiles (0.5 mm/1.0 mm) and the rows of PFRs (1/2/3/5). The push-out tests highlighted that the PFR specimens with 0.5 mm or 1.0 mm sanding depth experienced interface debonding failure and shearing failure of PFR, respectively. The epoxy bonding specimens with 0.5 mm or 1.0 mm sanding depth suffered adhesive failure and cohesive failure, respectively. Increasing the sanding depth from 0.5 mm to 1.0 mm is an effective approach to prevent the debonding failure. The typical shear load-slip (P-S) curves for PFRs exhibit the micro-slipping stage (slip≤0.2 mm) and the slipping stage (slip>0.2 mm). The P-S curves of epoxy bonding showed only the elastic stage. The shear capacity of the double-row PFR connector was close to epoxy bonding. The shear capacity and stiffness of the PFRs increased 37.2∼47.3 % and 99.7∼119.7 % with the sanding depth improved from 0.5 mm to 1.0 mm, respectively. Increasing the sanding depth would improve the shear stiffness of epoxy bonding. The shear capacity and stiffness of PFRs decreased with the rows of PFRs increased. Calculation equations for the shear capacity of epoxy bonding and PFRs were evaluated by comparing the test results collected from the literature and calculated results. Based on the elastic foundation beam theory, a calculation equation for the shear stiffness of PFRs was proposed and a theoretical bi-linear model was suggested to predict the load-slip curves.

Experimental and numerical study on behavior of channel-shaped GFRP perforated rib shear connectors

Effective shear connections at the interface of Pultruded Fiber Reinforced Polymer (FRP) - concrete hybrid system play a pivotal role in maintaining the structural integrity of composite structures. In this vein, this study presents a comprehensive investigation-encompassing experimental, analytical, and numerical approaches-into the shear behavior of a novel, channel-shaped Glass Fiber Reinforced Polymer (GFRP) perforated rib shear connector (GPRSC), designed for hybrid GFRP-concrete systems. Ten full-scale push-out specimens were tested to investigate the effect of the inclusion and diameter of the perforating rebar, the diameter and the spacing of the perforated hole, and concrete strength on the shear behavior of the channel-shaped GPRSC. The push-out tests highlighted two distinct failure modes: (i) shear failure of concrete dowel, and (ii) debonding failure of interface. To supplement these findings, numerical models were established that incorporate 2D Hashin's theory to account for laminate damage of GFRP. This allowed for an in-depth examination of the load transfer and failure mechanisms of the channel-shaped GPRSC. Finally, calculation formulae for shear resistance and load-slip relationship were proposed. A comparative evaluation between experimental results and values predicted by these formulae yielded a reasonably strong correlation. This research constitutes a significant advancement in the field of hybrid GFRP-concrete systems.

Thermal Insulation of Hybrid GFRP-Lightweight Concrete Structures

This paper presents a numerical study on the thermal effect of the insulation of lightweight concrete in hybrid GFRP-concrete structures. In these hybrid structures, the GFRP profiles are totally covered by normal and lightweight concrete and subjected to thermal loads. The problem with GFRP structures is their weak thermal resistance, even at moderately high temperatures. To promote some thermal insulation, it is recommended to cover the GFRP profile with concrete, but this increases its weight. Therefore, lightweight concrete may be a good solution due to its insulation capabilities. For this study, the thermal loads used in the numerical campaign are based on a nominal fire-curved ISO-834, and the temperature is measured at several points. Using these temperatures, it is possible to conclude that the effect of lightweight concrete may provide structural benefits when compared with classical standard structural concrete for covering GFRP profiles using different cover values (from 5.0 cm to 2.5 cm). For this work, commercial finite element software was used for the thermal nonlinear analysis. It was possible to conclude that with lightweight concrete, it is likely to have half of the cover and still maintain the same level of insulation as regular concrete.

Flexural Performance of Encased Pultruded GFRP I-Beam with High Strength Concrete under Static Loading.

There is an interesting potential for the use of GFRP-pultruded profiles in hybrid GFRP-concrete structural elements, either for new constructions or for the rehabilitation of existing structures. This paper provides experimental and numerical investigations on the flexural performance of reinforced concrete (RC) specimens composite with encased pultruded GFRP I-sections. Five simply supported composite beams were tested in this experimental program to investigate the static flexural behavior of encased GFRP beams with high-strength concrete. Besides, the effect of using shear studs to improve the composite interaction between the GFRP beam and concrete as well as the effect of web stiffeners of GFRP were explored. Encasing the GFRP beam with concrete enhanced the peak load by 58.3%. Using shear connectors, web stiffeners, and both improved the peak loads by 100.6%, 97.3%, and 130.8%, respectively. The GFRP beams improved ductility by 21.6% relative to the reference one without the GFRP beam. Moreover, the shear connectors, web stiffeners, and both improved ductility by 185.5%, 119.8%, and 128.4%, respectively, relative to the encased reference beam. Furthermore, a non-linear Finite Element (FE) model was developed and validated by the experimental results to conduct a parametric study to investigate the effect of the concrete compressive strength and tensile strength of the GFRP beam. The developed FE model provided good agreement with the experimental results regarding deformations and damaged patterns.

Flexural Behavior of Composite GFRP Pultruded I-Section Beams under Static and Impact Loading

In this study, the effect of glass fiber reinforced polymer (GFRP) section and compressive strength of concrete in composite beams under static and low velocity impact loads was examined. Modeling was performed and the obtained results were compared with the test results and their compatibility was evaluated.‎ Experimental tests of four composite beams were carried out, where two of them are control specimen with 20 MPa compressive strength of concrete deck slab and 50 MPa for other. Bending characteristics were affected by the strength of concrete under impact loading case, as it increased maximum impact force and damping time at a ratio of 59% and reduced the damping ratio by 47% compared to the reference hybrid beam. Under static loading, there was an increase in all the parameters, including the maximum load, ductility, and stiffness. Mid-span deflection was reduced by 25% under static and impact loads. A finite element analysis was performed by using the ABAQUS software. The midspan deflection value was greater than the experimental values by 6% and 3% for impact and static loads, respectively, and all other results showed a high rate of agreement with the obtained test results. The agreement between the numerical and experimental results indicates that the developed numerical model is capable of analyzing the impact and static behavior of such hybrid GFRP-concrete system. Doi: 10.28991/cej-2020-03091608 Full Text: PDF

Flexural behavior of novel hybrid multicell GFRP-concrete beam

A novel hybrid beam consisting of pultruded GFRP three-cell box-section and concrete slab was proposed for pedestrian bridges. The flexural behavior of the proposed beam was investigated through experimental and analytical studies. First, material characterization tests were conducted to evaluate the mechanical properties of the GFRP material. Second, four- and three-point bending tests were carried out on four beams with varying span lengths. The flexural and shear stiffness of the beams were calculated and evaluated based on the experimental results. Design equations were proposed to predict the ultimate flexural strength of the hybrid beam. Finite element (FE) models were constructed to validate the effectiveness of the proposed hybrid beam. A good correlation was found between the experimental results, the analytical predictions from the proposed design equation, and the numerical results from FE modeling. The combined bolted and bonded connection provided effective shear transfer between GFRP and concrete, ensuring a good composite action of the hybrid beam. Additionally, the proposed three-cell box-beam increased the web local buckling strength of GFRP beams subjected to a concentrated load, avoiding the premature buckling failure of the entire beam. The proposed hybrid GFRP-concrete beam provides an effective approach to increase the span length of GFRP structures.

Static behaviour up to failure of a full-scale GFRP-concrete hybrid footbridge

This paper presents an experimental investigation on the short-term behaviour up to failure of a full-scale GFRP-concrete hybrid footbridge. The connection between the slab and the GFRP profiles is a mixed bonding/bolting connection. The footbridge was first tested in the elastic domain under different configurations to mobilize the flexural and torsional stiffness. The numerous measurements show that the behaviour is in accordance with the regulatory requirements at SLS. The footbridge was finally loaded up to failure. The shear failure obtained in the GFRP section showed that the mixed connection used played its role perfectly and made it possible to fully exploit the bending capacity of the structure. In addition, the comparison with the results of the beam tests shows that the two-beam bridge can be analysed with sufficient precision as the juxtaposition of the two single-sided beams. This study confirms the important capacity of these hybrid GFRP-concrete structures in the construction of bridges or footbridges with classical engineer design tools.

Theoretical analysis on long-term deflection of GFRP-concrete hybrid structures with partial interaction

The creep and shrinkage of concrete and the creep of glass-fiber reinforced polymer (GFRP) may lead to the increase of long-term deflection of GFRP-concrete hybrid structures under service loading, due to the change of internal forces and stresses. This paper presents a calculation model to consider the influence of the aforementioned changes in analyzing the long-term deflection of GFRP-concrete hybrid structures with partial interaction under service loading, based on the age-adjusted effective modulus method (AEMM). The calculated results from the proposed calculation model agree well with the available experimental results. A further discussion is also made about the effects of the concrete creep and shrinkage and the GFRP creep, as well as the shear stiffness of shear connectors on long-term behavior of GFRP-concrete hybrid structures. Especially, the significant influence of concrete shrinkage on long-term interface slip, interface shear and long-term deflection is found. What’s more, the long-term deflection may increase with the augment of horizontal shear stiffness of shear connectors.

Experimental and finite element analysis of the long-term behaviour of GFRP-concrete hybrid beams fabricated using adhesive bonding

This paper presents experimental and numerical investigations about the short- and long-term behaviour of a hybrid beam consisting of a GFRP pultruded profile bonded by an epoxy adhesive joint to a reinforced concrete slab. The experimental program included flexural creep tests on GFRP I-profiles and on hybrid beams subjected to constant loads. The deflections and the longitudinal strains were measured in natural environmental conditions and recorded for time durations up to 3500 h. Also, three-dimensional models, based on the incremental form of the linear viscoelastic theory, were proposed to study the evolution of strains and stresses over time for the structures. The results of the sustained-load test show that creep deflections on the order of 27–37% of the initial static deflections were observed for the hybrid beams after about 5 months of loading. It is also found that, for the hybrid beam, the rapid degradation of bond strength, resulted from the combined effect of environmental conditions and applied loading, leads to debonding and subsequently a brutal failure. Furthermore, the finite-element analysis is found to be able to simulate the long-term behaviour of the hybrid beam and help understand the complex changes in the stress state that occur over time.

Performance of a hybrid GFRP-concrete beam subject to low-velocity impacts

In the present study, the impact behaviour of a hybrid beam consisting of a rectangular hollow GFRP pultruded profile filled with concrete is studied. The hollow pultruded GFRP box profile not only provides tensile strength but also protects the concrete block inside from suffering chemical attacks. The concrete on the other hand provides the system with bulk size and structural stability. A series of beams were subjected to low-velocity impacts by using a high capacity drop weight machine. A nonlinear finite element model was developed and calibrated to analyse the failure of the beams. In particular, it was used to reveal the failure modes, the cracking pattern, and damage sequences within the concrete hidden inside the pultruded profile. The calibrated finite element model was subsequently used to analyse hybrid beams of similar size to prestressed concrete railway sleepers. The numerical simulations revealed that in terms of the maximum load, the hybrid beam outperforms the prestressed concrete sleeper. Indeed, if the proposed beam is to be used as a railway sleeper, it needs to display better or equal dynamic properties to existing railway sleepers.

Durability of GFRP-concrete adhesively bonded connections: Experimental and numerical studies

In order to overcome the main mechanical drawbacks of GFRP profiles, namely their high deformability and proneness to instability phenomena, several GFRP-concrete hybrid solutions comprising bonded connections with epoxy adhesive have been proposed. Although being able to provide almost full interaction at the GFRP-concrete interface(s) (at least in the short-term), there is very little information about the durability of such connection systems, which raises concerns about the long-term performance of hybrid structural solutions. This paper presents experimental and numerical investigations on the durability of adhesively bonded connections between pultruded GFRP profiles and steel fibre reinforced self-compacting concrete (SFRSCC). GFRP-SFRSCC specimens were first subjected to accelerated ageing, involving thermal and wet-dry cycles, and then subjected to push-out tests. The accelerated ageing did not have significant influence on the strength of the GFRP-SFRSCC connection; however, it had a very deleterious effect on its stiffness. The numerical study included the development of finite element models of the specimens tested. Using bi-linear bond-slip laws, it was possible to simulate the test results with good accuracy. In the final part of the paper, the influence of the interface stiffness reduction on the deformability of a real hybrid structure (the São Silvestre footbridge) is analysed. Although the stiffness of the GFRP-SFRSCC interface is considerably reduced by the ageing processes, this results in a very small increase of the overall mid-span deflections of the footbridge.

Flexural performance of a hybrid GFRP-concrete bridge deck with composite T-shaped perforated rib connectors

In this study, the flexural performance of an innovative hybrid GFRP-concrete deck is evaluated. The proposed hybrid composite deck consists of a pultruded GFRP plate with T-shaped perforated ribs for resisting tensile stresses, while concrete with reinforcements is placed at the compressive side of the deck. In order to better understand the flexural performance of proposed hybrid decks under sagging moment, a total of six full-scale hybrid deck models were experimentally investigated. Five test parameters were considered, namely: (i) hole spacing, (ii) presence of bent-up rebars, (iii) quality of GFRP composites surface treatment, (iv) deck depth, and (v) type of reinforcements. Experimental results identified three different typical failure modes, namely: diagonal and longitudinal shear, as well as flexure. Furthermore, it was found that the inclusion of bent-up rebars, sand bonded to GFRP plates surfaces, and increasing deck thickness enhance the ultimate strength of the proposed hybrid deck. It was also concluded that the hole spacing and the reinforcement type have negligible influence on ultimate capacity of the proposed deck. Moreover, finite element models considering the laminate damage based on Hashin’s theory were built and load transfer and failure mechanisms of GFRP perforated ribs were discussed. The validity of the proposed analytical method, with respect to failure mode and ultimate strength for the hybrid deck, was confirmed through the close correlation between analytical and experimental results.

Experimental investigation on hybrid GFRP-concrete decks with T-shaped perforated ribs subjected to negative moment

This paper proposes a hybrid glass fiber reinforced polymer (GFRP)-concrete deck consisting of pultruded GFRP plate with T-shaped perforated ribs in tension part and reinforced concrete in compression part. To better understand the structural behavior of the proposed hybrid deck over main girders in the transverse direction (perpendicular to the traffic direction), static tests on five full-scale deck models were conducted under negative bending moment. The main parameters of these experimental deck models were reinforcement ratio and the presence/absence of bent-up bars. The load-displacement relationship, ultimate capacity, strain distribution of GFRP plates and steel bars, and crack development were measured during the test. Experimental results indicated that flexural and shear failure modes occurred depending on the reinforcement ratio and the presence/absence of bent-up bars. The arrangement of the bent-up bars near the negative moment region can increase the ultimate loading capacity especially with respect to shear strength, but has little influence on the stiffness of the hybrid deck. GFRP T-shaped ribs are effective in controlling cracking. Simplified calculation methods were proposed to evaluate the flexural and shear strength and to predict the average crack spacing, which were calibrated by experimental results. The agreement of theoretical results with experimental ones demonstrates the accuracy and effectiveness of proposed equations for estimating the ultimate capacity and cracking behavior of such hybrid GFRP-concrete decks.

Compressive Behavior of Concrete Filled Glass Fiber Reinforced Polymer (GFRP) Box Profiles

The use of concrete filled fiber reinforced polymer (FRP) profiles for beams and columns has been studied extensively in recent years. Glass Fiber Reinforced polymers (GFRP) profiles are one of these materials. GFRP box profiles serve as formwork, and provide shear and flexural reinforcement in novel hybrid GFRP–concrete structural system. GFRP box profiles also protect the concrete and increase the strength of hybrid materials. This study presents results of an experimental study using concrete filled pultruded GFRP profiles. A series of compression tests were carried out to study the compression behavior of the proposed hybrid GFRP-concrete materials. Hybrid compression samples were fabricated and tested in three different strength classes. The results showed that compressive strength of hybrid material significantly increased when compared to reference samples.

Thermal analysis on composite girder with hybrid GFRP-concrete deck

Since the coefficients of thermal expansion (CTE) between concrete and GFRP, steel and GFRP are quite different, GFRP laminates with different laminas stacking-sequence present different thermal behavior and currently there is no specification on mechanical properties of GFRP laminates, it is necessary to investigate the thermal influence on composite girder with stay-in-place (SIP) bridge deck at different levels and on different scales. This paper experimentally and theoretically investigated the CTE of GFRP at lamina's and laminate's level on micro-mechanics scales. The theoretical CTE values of laminas and laminates agreed well with test results, indicating that designers could obtain thermal properties of GFRP laminates with different lamina stacking-sequence through micro-mechanics methods. On the basis of the CTE tests and theoretical analysis, the thermal behaviors of composite girder with hybrid GFRP-concrete deck were studied numerically and theoretically on macro-mechanics scales. The theoretical results of concrete and steel components of composite girder agreed well with FE results, but the theoretical results of GFRP profiles were slightly larger than FE and tended to be conservative at a safety level.

Experimental study of GFRP-concrete hybrid beams with low degree of shear connection

Recent developments in the design of advanced composite materials for construction have led researchers to create novel high-performance structural elements that combine fiber-reinforced polymer (FRP) shapes with traditional materials. The current study analyzes the experimental structural response of eight hybrid beams made of pultruded glass FRP (GFRP) profiles mechanically connected to reinforced concrete (RC) slabs, suitable for building floors as well as footbridge and marine pier superstructures. The influence of partial interaction is studied by considering a low degree of shear connection and an analytical assessment of the whole response is carried out using previous formulations, highlighting a good accuracy. The behavior of the hybrid beams is further evaluated against that of equivalent reinforced concrete beams and single GFRP profiles, thus proving the feasibility of the solution.

Fatigue behavior of hybrid GFRP-concrete bridge decks under sagging moment

This paper presents a new cost-effective hybrid GFRP-Concrete deck system that the GFRP panel serves as both tensile reinforcement and stay-in-place form. In order to understand the fatigue behavior of such hybrid deck, fatigue test on a full-scale specimen under sagging moment was conducted, and a series of static tests were also carried out after certain repeated loading cycles. The fatigue test results indicated that such hybrid deck has a good fatigue performance even after 3.1 million repeated loading cycles. A three-dimensional finite element model of the hybrid deck was established based on experimental work. The results from finite element analyses are in good agreement with those from the tests. In addition, flexural fatigue analysis considering the reduction in flexural stiffness and modulus under cyclic loading was carried out. The predicted flexural strength agreed well with the analytical strength from finite element simulation, and the calculated fatigue failure cycle was consistent with the result based on related S-N curve and finite element analyses. However, the flexural fatigue analytical results tended to be conservative compared to the tested results in safety side. The presented overall investigation may provide reference for the design and construction of such hybrid deck system.

현장타설 고강도콘크리트와 유리섬유 FRP 판 사이의 부착슬립관계에 관한 연구

Recently it has been actively studied that the use of hybrid GFRP-concrete structure with dual purpose of both a permanent forwork and main tensile reinforcement of GFRP plank. In applying general analysis and design technique to evaluate the performance of hybrid structures with cast-in-place high strength concrete and GFRP plank, it is essential that the characteristics of the bond slip model is identified. In this study a simplified bilinear bond slip model for hybrid structure with GFRP plank and cast-in-place high strength concrete is proposed. Maximum average bond stress of simple bond slip relationship that has been proposed in this study is 3.29MPa, initial slope is 35.66MPa/mm, the total slip is 0.23mm and interfacial fracture energy is 0.37kN/m.

Structural behaviour of a GFRP-concrete hybrid footbridge prototype: Experimental tests and numerical and analytical simulations

Glass fibre reinforced polymer (GFRP) pultruded profiles are being increasingly used in the construction industry since the last few decades. The high potential of GFRP profiles for structural applications stems from their high strength, low self-weight and corrosion resistance. In opposition, the high deformability, the susceptibility to instability phenomena and the lack of specific design codes have been hindering a wider use of these advanced composite materials. Several hybrid systems in which GFRP materials are combined with traditional materials, namely concrete, have been proposed in order to overcome the aforementioned limitations of the GFRP material. This paper presents experimental, analytical and numerical investigations about the flexural behaviour of a GFRP-concrete hybrid footbridge prototype comprising two I-shaped GFRP main girders and a thin steel fibre reinforced self-compacting concrete (SFRSCC) deck. With the aim of limiting the structure’s deformability, the footbridge features an external prestress system consisting of two ordinary steel rebars screwed tighten to the structure at the support sections. A small-scale footbridge prototype, 6.0m long and 2.0m wide, was built and tested in a 5.5m simply supported span. The experimental programme included (i) serviceability tests, with and without the application of the external prestress system, and (ii) failure tests. Results of flexural tests proved the feasibility and advantages of the structural concept proposed: the judicious combination of GFRP and SFRSCC enabled the development of a lightweight, high performance and relatively inexpensive structural system for footbridges; furthermore, the external prestress system was very effective in limiting deflections. The analytical and numerical models developed in this study were able to predict with good accuracy (i) the linear elastic behaviour of the structure up to failure, (ii) the effects of the external prestress, and (iii) the failure mode and strength, proving to be accurate tools for the design of GFRP-concrete structural solutions.

Modal identification of a GFRP-concrete hybrid footbridge prototype: Experimental tests and analytical and numerical simulations

The use of fibre reinforced polymer (FRP) structural elements, including glass fibre reinforced polymer (GFRP) pultruded profiles, has increased in the last few decades. The high potential of these materials for civil engineering structural applications, particularly for footbridges, stems from their high strength, low self-weight and good durability. However, when designing GFRP structures, the high deformability and the susceptibility to instability phenomena seldom allow the full exploitation of the GFRP material. In order to overcome these limitations, several hybrid structural systems have been proposed, namely GFRP-concrete hybrid systems. In this context, the evaluation of the dynamic characteristics of GFRP-concrete hybrid structural systems is very important, especially for footbridge applications, whose design is generally governed by pedestrian comfort criteria. This paper first presents modal identification experimental tests on a 6.0m long and 2.0m wide GFRP-concrete hybrid footbridge prototype, made of two I-shaped GFRP main girders and a thin steel fibre reinforced self-compacting concrete (SFRSCC) deck. The tests consisted of applying an excitation to the deck with an impact hammer and measuring both the applied excitation and the structure’s response. The natural modes of vibration, frequencies and damping were determined using (i) a conventional input–output modal identification technique, based on the Rational Fraction Polynomial method, and (ii) a simple output-only method directly based on the Fast Fourier Transform (FFT) of the response (mode frequencies only). In the second part of the paper, experimental data are compared with analytical and numerical simulations in order to assess the accuracy of such design tools in predicting the dynamic behaviour of GFRP-SFRSCC hybrid structures, in terms of mode shapes and frequencies.