•Experimental lateral impact tests of bare and FRP strengthened CFST members are conducted.•The failure modes and dynamic structural responses are investigated to evaluate the effectiveness of FRP ...wrapping.•Externally bonded FRP sheets improved impact resistance by minimising lateral displacement and core concrete cracks’ width.
Due to the increasing popularity of concrete-filled steel tubular (CFST) members, there will be more chances of vehicles/vessels or terrorist attacks on these structures in near future. Fibre-reinforced polymer (FRP) strengthening can be an effective option to reduce impact damage or failure of CFST members. However, existing knowledge is very limited in understanding the behaviour of FRP strengthened CFST structures under lateral impact loading. This paper outlines drop hammer impact test results of a series of experimental programs of bare and FRP strengthened CFST specimens. A total of sixteen CFST specimens were prepared and tested under lateral impact at their mid-span. The results indicate that permanent lateral displacement of CFST members can be reduced up to 18.2% by externally bonded FRP sheets. The effects of FRP type, FRP wrapping direction, carbon fibre-reinforced polymer (CFRP) wrapping layers, wrapping length, and impact velocity were investigated to understand the influences of these parameters on the behaviour of strengthened CFST specimens. CFRP laminates were found to be weak under impact loading when wrapped in only longitudinal direction. However, a combination of longitudinal and hoop layers of CFRP laminates, or only GFRP wrapping, can remarkably minimise the severity of damage and failure of FRP in CFST specimens under lateral impact. A comparison of current test results with recent works has been presented to understand the effect of impact energy on the lateral displacement control ability of FRP strengthened CFST members.
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•The first study to investigate bonding behavior between FRP and SFRC.•The effect of short fibers on interfacial bond strength is studied.•The effect of short fibers on interfacial ...bond-slip relationship is examined.•Semi-empirical models of bond strength and interfacial bond-slip are given.
Bonding behavior between FRP and Steel fibre reinforced concrete is not well studied. This study experimentally investigates the interfacial bond behavior between basalt fibre reinforced polymer sheet (BFRP) and steel fibre reinforced concrete (SFRC). Short steel fibres with four volume fractions were used to investigate the interfacial bond behavior of BFRP-SFRC as the mechanical properties of the concrete substrate (i.e. compressive strength and tensile strength) can be improved by adding steel fibres. The effects of volume fraction on the bond strength, effective bond length, local slip at the peak shear stress, and interfacial bond-slip relationship are evaluated and discussed. The experimental results showed that the debonding process becomes more ductile as the debonding plateau in the load and displacement curves has been significantly extended. Findings from the present tests show that the specimens with steel fibres of 0.25%, 0.50% and 1.0% experienced significant increase in the peak interfacial shear stress up to 31%, 53%, and 76% over the control specimen without steel fibres, respectively. In addition, the analytical bond strength models and interfacial bond-slip models, incorporating the effect of short steel fibres, are proposed.
•CFRP and GFRP strengthenings are very effective to mitigate the seismic vulnerability of CHSs.•CFRP strengthening is more effective to enhance the moment capacity and stiffness.•GFRP strengthening ...is performed better to improve the rotational capacity.•GFRP strengthened beams exhibited higher ductility and energy dissipation capacity.•Appropriate cyclic design factors have been recommended.
Steel structures are becoming more common in engineering construction as steel possesses excellent ductility, but steel members are often vulnerable to buckling, especially under seismic or cyclic loading. Hollow structural sections (HSS) often buckle locally under loading due to their thin steel walls and the need for rehabilitation and strengthening is increasing. In the present study, circular hollow section (CHS) steel members have been strengthened with both carbon fibre reinforced polymer (CFRP) and glass fibre reinforced polymer (GFRP). Their structural performance, along with that of their bare counterparts, is investigated subjected to monotonic and quasi-static large-displacement cyclic loading experimentally. The types of FRP reinforcement (CFRP and GFRP) and the loading condition (monotonic and cyclic) are chosen as two main parameters in the test program. Results reveal the significant structural improvements of the strengthened CHS members under monotonic and cyclic loading. The ultimate moment capacities of the beams under monotonic and cyclic loading are enhanced by 51.0% and 35.4% respectively with CRFP strengthening and 43.3% and 31.5% respectively with GFRP strengthening compared to the bare beam. In addition, all the FRP strengthened specimens achieved higher moment capacities, rotational capacities, stiffness, energy dissipation capacities and ductility in comparison to their bare counterparts. Moreover, there is a good agreement found between the experimental and theoretically predicted ultimate moment capacities of the bare and strengthened CHSs with a mean ratio of 1.04 and a COV of 0.05.
•Geometrical interpretation of analysis-oriented models for FRP-confined concrete.•Methodology for calibrating analysis-oriented models.•Justification of design-oriented models.
An important ...application of fibre-reinforced polymer (FRP) composites in structural engineering is to confine concrete. In contrast to actively confined concrete, the stress-strain curve of FRP-confined concrete can have a second ascending branch when sufficient confinement is applied. Numerous analytical models have been proposed to predict the axial stress–strain behaviour of FRP-confined concrete. These models can be classified into two categories: (a) analysis-oriented models and (b) design-oriented models. In this paper, a 3-dimensional geometrical approach is proposed to interpret the general theory of analysis-oriented models based on three general equations. This approach provides an intuitive perspective to understand the analysis-oriented models and the mechanism of FRP-confined concrete. With this approach, a systematic methodology for calibrating analysis-oriented models is demonstrated, and the parameters in design-oriented models are justified. This methodology can also be applied to build analysis-oriented models for other concrete-type materials.
•Cyclic axial compression tests of 12 seawater and sea sand concrete-filled FRP- carbon steel composite tube (SFSCT) columns were conducted.•The thickness and type of FRPs were used as variables to ...test the failure mode, envelope and plastic strain.•The strain recoverable performance of FRPs is beneficial to the concrete shrinkage and the suppression of plastic strains.•A new stress–strain model was developed for predicting the full cyclic stress–strain response.
This paper presents an experimental investigation of a novel seawater and sea sand concrete (SSC)-filled fibre-reinforced polymer (FRP)-carbon steel composite tube column (SFSCT) subjected to cyclic axial compression loadings. The proposed structure is covered with FRP on both the inner and outer walls of a traditional carbon steel tube to solve the corrosion problem of seawater and sea sand concrete and to improve considerably the mechanical properties of the structure at the same time. Cyclic axial compression tests for 12 SFSCTs and 2 concrete-filled steel tubes were carried out. The thickness and type of FRP were used as variables to assess the mode of failure, envelope, plastic strain and stiffness at unloading. The results show that FRP can confine effectively the lateral expansion of concrete. Carbon fibre-reinforced polymer (CFRP) has a better confinement performance than basalt fibre-reinforced polymer (BFRP). According to the different confinement mechanisms of the internal and external layers of FRP on concrete, a more reasonable cyclic stress–strain model was proposed, and the superiority of the proposed model was verified by comparison with the experimental results.
•The seismic behaviour of an innovative precast sandwich wall panel is accessed.•Results of in-plane cyclic tests on real scale precast sandwich wall panels are presented.•The seismic behaviour of ...precast sandwich wall panels with and without openings is compared.
In recent past, the authors developed an innovative modular system for low rise building made by structural sandwich panels. This system was conceived with the focus on the rationalization of the construction process and on the thermal efficiency of the building. Thus, the precast panels comprise two outer Steel Fibre Reinforced Self-Compacting Concrete (SFRSCC) layers, a thermal insulation material and Glass Fibre Reinforced Polymer (GFRP) connectors. Studies previously made by the authors have proved the viability of the proposed solution when subjected to flexural loads (out-of-plane loads). However, the in-plane biaxial cyclic behaviour of these type of panels has not yet been assessed. Therefore, to investigate the response of these panels to loading conditions that can occur in a seismic event, an experimental program was carried out. This program was composed of almost real-scale panels (2.0 m by 2.0 m), with and without openings, which were subjected to a constant vertical load representative of the load transferred by the slab to the panel, while horizontal reversed cyclic loading was imposed to the top of the panel. The in-plane cyclic behaviour of the panels was evaluated in terms of strength, stiffness, ductility and energy dissipation. The results have shown that the tested prototypes were able to withstand high values of lateral loads, namely 212kN and 155kN in the prototypes without and with opening, respectively.
Self-compacting polyolefin fibre reinforced concrete has shown high performance in both fresh and hardened state. Post-cracking behaviour provides significant residual strengths especially for large ...deformations. For small deformations, flexural residual strength could be enhanced with a small amount of steel-hooked fibres, obtaining a hybrid fibre-reinforced concrete well suited for structural use. Four types of conventional fibre-reinforced concrete with steel and polyolefin fibres were produced on the basis of the same self-compacting concrete also manufactured as reference. These concrete mixtures were manufactured separately with the same fibre contents being subsequently used for two more hybrid mixtures. Flexural and uniaxial fracture tests were performed in addition to the assessment of fresh and mechanical properties. The research showed both synergies (with the two types of fibres working together in the fracture processes) and an improvement of the orientation and distribution of the fibres on the fracture surface.
The building industry, and especially the concrete industry, consumes a considerable proportion of the natural resources extracted from the lithosphere and is responsible for a large part of the ...solid waste generated worldwide. Unfortunately, this fact has not yet generated a movement to counter the trend; rather, a huge increase in the use of concrete in new structures can be observed. It is imperative to counteract this development by optimally exploiting the material properties of concrete in order to improve its efficiency. One strategy being pursued at the University of Natural Resources and Life Sciences, Vienna and TU Wien is to reduce the amount of concrete and reinforcement in structures by using high‐performance materials such as carbon‐fibre‐reinforced polymers (CFRP) in ultra‐high‐performance concrete (UHPC) members. This permits a crucial reduction in the self‐weight and allows for the design of very lightweight precast concrete elements. The authors' goal is to use CFRP rods as bending reinforcement and a combination of flat and preformed CFRP textiles as shear and structural reinforcement. In the first part of this paper, the research approach is introduced and a comprehensive overview of the state of the art of UHPC and CFRP reinforcement is given. The second part contains a description of the conceptual design of some structural members (one floor element and two T‐beams), starting with the development of a suitable UHPC mixture. Furthermore, preliminary uniaxial tensile tests of textile‐reinforced UHPC strips are described and evaluated. In the final part of this paper, the authors present parameter studies for different reinforcement types, values, additional prestressing of the rod reinforcement and the first prototypes. They are used to give an estimation of the feasibility, the load‐bearing and deflection behavior of the proposed building components.
This manuscript proposes a strength and ductility of reinforced concrete (RC) using basalt fibre-reinforced polymers (BFRP). The lightweight materials like fibre-reinforced polymers (FRPs) are ...providing superior structural performance and durability in reinforced concrete members over traditional materials. Due to its light weight property, they are proposed for building repair and strengthening works compared to conventional methods. Although, they exhibit excellent allowing them to be easily tailored and molded into any desired size and shape. The current study focuses on the strength and ductility improvement of reinforced concrete circular members externally reinforced by basalt fibre-reinforced polymers (BFRPs). M25 grade concrete mix was used for casting the RC circular samples. Twelve RC circular members were casted; among them 3 were bare samples and the remaining samples wrapped with one, two and three layers of BFRP sheets. An axial compressive force is applied to all RC circular samples both unwrapped and wrapped with BFRP. RC samples wrapped with BFRP sheets showed an extensive strength and ductility enhancement compared to bare sample. Finally, an optimum wrapping scheme is suggested for RC circular samples under compression.
Recently, several filler materials, such as carbon black (CB), have been added to glass fibre reinforced polymers (GFRP) to enhance their mechanical and electrical performance. So far, we have ...insufficient information on the effect of these additives on the recyclability of GFRP and the resulting products. Within this context, this is the first research developed to study the effect of these additives on pyrolysis behaviour of GFRP. The experiments were started with dispersion of CB in epoxy resin solution, then CB/GFRP panels were prepared using vacuum-assisted resin transfer technique, followed by grinding to prepare the feedstock. The ultimate, proximate, and morphological properties of the CB/GFRP samples were analysed. Afterwards, TG-FTIR-GC measurements were conducted on the milled samples at several heating rates. Depending on the TG analysis, the pyrolysis kinetics of CB/GFRP were studied using both linear and nonlinear isoconversional methods (i.e., Kissinger, KAS, FWO Friedman, Vyazovkin, and Cai). Also, TGA-DTG data was simulated using the distributed activation energy model and the independent parallel reactions kinetic model. The results show that the fibre is rich in volatile content (45%), while aromatic benzene and C–H bond were the major groups in the TG-FTIR analysis. In addition, phenol and p-Isopropenylphenol were the major compounds in the GC-Ms measurements with abundance of 67% (with improvement of 146% compared with neat GFRP) and 33%. Meanwhile, the pyrolysis kinetic showed that KAS, Vyazovkin, and Cai models are the most appropriate isoconversional methods that can be used to study of the pyrolysis kinetic of CB/GFRP with estimated activation energies in the ranges of 198–209 kJ/mol (with improvement of 64% compared with neat GFRP). Based on that, the filler materials added to GFRP composites, including CB filler, act as self-catalysts during the pyrolysis treatment leading to increased yield and better quality of the formulated volatile compounds.
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•Pyrolysis behaviour of CB/GFRP was studied using TG-FTIR-GC–MS.•The elemental, proximate, and compositional analyses of CB/GFRP was measured.•Pyrolysis kinetics were studied using linear and nonlinear isoconversional methods.•TGA and DTG curves were simulated using DAEM and IPR models.•Phenol and p-Isopropenylphenol were the major compounds in GC-MS.
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