CFRP Steel Research Articles

Research on concrete-filled square CFRP steel tube under compressive-torsional hysteresis loading

Concrete-filled CFRP steel tube structures are presently employed on extensively in various engineering practices. This study examines the mechanical performance of concrete-filled square CFRP steel tubes under compressive-torsional hysteresis loads. Through the analysis of nine specimens, the research focuses on failure modes, torque–angle (T–θ) behavior, triaxial strain, and the synergistic effects of the steel tube and CFRP during cyclic loading. A numerical simulation method is initially introduced based on the test data to predict the actions of concrete-filled CFRP steel tube compressive-torsional specimens under hysteresis loading. This method is subsequently verified by contrasting it with the outcomes from representative experiments. In addition, the stress distribution of each material during the entire loading process of the sample is examined. Finally, using data from experiments and finite elements, combined with the trilinear model, a hysteretic model under compressive-torsional hysteresis stresses has been established for square CFRP steel tube filled with concrete. The calculated outcomes of the developed finite element model closely align with those of the hysteretic model.

Comparison of Material Performance through Experiments between CFRP and CFRP Hybrid and Steel

Comparison of Material Performance through Experiments between CFRP and CFRP Hybrid and Steel

Study on the Bending-Shear Properties of Concrete-Filled Circular Carbon Fibre Reinforced Plastic Steel Tubes.

In order to study the bending-shear performance of CFRP concrete-filled steel tubes, static tests were conducted on 15 circular concrete-filled CFRP steel tube bending-shear specimens. For all specimens, Ds was 120 mm, ts was 2 mm, and ml was 1. The shear displacement (V-Δ) curve of the specimen and the collaborative work between the steel tube and CFRP are discussed. ABAQUS was applied to simulate the V-Δ curve and failure mode of the specimen. We explored the effects of CFRP layers, material strength, the steel ratio, and the shear span ratio on the bending-shear performance of components. The experimental results show that a steel tube and CFRP can work together. As the shear span ratio increased, the bearing capacity and stiffness of the specimen decreased. An increase in the number of transverse CFRP layers could improve the bearing capacity of the specimen, but it had no significant effect on the stiffness. Calculating the elastic stage stiffness and bearing capacity of 15 short columns of test and FE curves revealed an average error of 6.71% and a mean square error of 0.83 for the elastic stage stiffness. The simulation results of the established finite element model are in good agreement with the experimental results. The average error of the bearing capacity was 3.88%, with a mean square error of 0.94. Based on experimental and finite element results, the moment shear correlation equation for concrete-filled CFRP steel tube bending-shear members is presented.

Research on Seismic Performance of Eccentric Beam–Column Joint Retrofitted with CFRP–Steel Plate

Research on Seismic Performance of Eccentric Beam–Column Joint Retrofitted with CFRP–Steel Plate

Axial compressive behaviour of SWSSC-filled stainless steel tube columns with in-built CFRP or stainless steel tubes

Axial compressive behaviour of SWSSC-filled stainless steel tube columns with in-built CFRP or stainless steel tubes

Safety assessment of underground steel pipelines with CFRP protection against subsurface blast loading

Underground steel pipelines are one of the most important mediums for transport of water, oil, natural gas and other hazardous or highly toxic gases. Its assessment against blast has become very crucial due to intentional and accidental explosions in the route of buried pipelines. In present study, evaluation of X70 grade steel pipelines against subsurface blasts is carried out numerically. A computational model with finite element technique is developed by implementing Coupled Eulerian-Lagrangian method in ABAQUS. A protective covering of Carbon Fiber Reinforced Polymer has been introduced to alleviate the impact of blast waves. The Jones-Wilkins-Lee, ideal gas Equation of State (EoS), Mohr-Coulomb plasticity criteria, are used to model the behaviour of explosive substances, air, and soil respectively. Hashin damage criteria and Johnson-Cook model are employed to assess the response of CFRP blanket and steel pipe, respectively. The Finite Element (FE) results were validated with available experiments and empirical formulae. The influence of different factors namely thicknesses of pipe, internal pressure, explosive charges, type of soil, and thickness of CFRP on performance of pipes against blast load are analysed and mitigation provided by protective covering is determined. The maximum decrease in strain was found to be 69.2% and 67.4% in the 14.6 mm and 26.2 mm thick steel pipe covered with 10 mm thick CFRP sheet, respectively. The maximum reduction in peak displacement values was found to be 36% and 55% for 14.6- and 26.2-mm thick pipes respectively. Also, safety criteria/zone for underground pipeline against subsurface blast loading is proposed. The present work could be helpful for blast resistant design of underground steel pipelines.

Comparison of Punching Shear Behaviour of Two-Way Concrete Slab Reinforced with CFRP Grid and Steel Bars

Two punching shear failure tests of two-way concrete slab reinforced by CFRP grid and HRB 400 steel were studied in this paper. The reinforcement ratio of slab reinforced with CFRP grid and HRB400 is 0.33% and 0.37 respectively. The upper and lower surfaces of the concrete slab’s tensile and compressive strains, the reinforcement strains, the load deflection of the slabs, and the applied load value were analyzed. The results show that under approximately the same reinforcement ratio, the concrete slab reinforced with CFRP grid has higher bearing capacity. Both slab failure formed with punching cones, the punching cone angle of CFRP grid slab is 24.1°, which is far less than 38° for reinforced concrete slabs. The tests results indicated that there is a cooperative between longitudinal and transverse limb of CFRP grid.

Externally bonded CFRP composites versus steel stirrups for the confinement of substandard lap spliced GFRP bars in RC beams

Externally bonded CFRP composites versus steel stirrups for the confinement of substandard lap spliced GFRP bars in RC beams

Experimental study on mixed mode-I & II bond behavior of CFRP-to-steel joints with a ductile adhesive

Utilizing ductile adhesive on CFRP-reinforced steel structures makes the bonded interface with good resistance to dynamic and fatigue loading, which is suitable for the rehabilitation of steel bridges. Currently, considerable studies on the aspect of the CFRP–steel interface are focused only on mode-II loading, ignoring the effects of mode-I loading which could lead to a catastrophic collapse of the retrofitted structures. In the present paper, modified CFRP-to-steel bonded double overlapped joints with various initial peeling angles (θ) were manufactured in order to consider mode-I loading and study the bond behavior of CFRP-to-steel joints under mixed mode-I&II loading. The results showed that the bonded side with weaker adhesion between CFRP and adhesive debonded first and presented a CFRP-adhesive interfacial debonding mode, while the debonding of the other side was delayed and showed a cohesive failure mode in the adhesive. The bond shear stress vs. slip relationship of the debonded side showed to have a bi-linear trend in which the bond strength and interfacial fracture energy were low whilst the other side showed a trapezoidal relationship with a constant plastic plateau and with higher interfacial fracture energy. It was found that sudden debonding caused a quick propagation in the CFRP strain as well as on the global interfacial slip of the joints. It was also found that the peeling angle had significantly deteriorated the local bond response in mode-II, i.e. the trapezoidal bond shear stress vs. slip relationship in the joints with θ=0° shifted to a bi-linear relationship in the joints with θ=1°, θ=2° and with θ=3° in which the bond strength, slip and fracture energy, all decreased very much. Moreover, with θ=4° was experimentally determined as the threshold angle from which the associated mode-I loading can, per se, separate the CFRP from steel.

Experimental Research on Seismic Behavior of Seismic-Damaged Double-Deck Viaduct Frame Pier Strengthened with CFRP and Enveloped Steel

This paper investigates the seismic behavior of a seismic-damaged double-deck viaduct frame pier (DVFP) strengthened with CFRP and enveloped steel, four strengthened DVFP specimens with different degrees of initial damage were tested under quasi-static cyclic loading. Based on the test results, the hysteretic behavior, the stiffness and strength degradation, crack propagation, and failure mechanism were firstly analyzed. Then, the damage indexes of the tested specimens were calculated with different models to evaluate the seismic strengthening performance. Results of this study show that CFRP and enveloped steel strengthening could effectively improve the strength and ductility of pre-damaged DVFPs. The ultimate load, the failure displacement and the displacement ductility of the moderately damaged specimen after being strengthened were found to increase by 120.74%, 35% and 32.33%, respectively. For the severely damaged specimens with CFRP and enveloped steel strengthening, the figures were 105.36%, 25.98% and 31.41%, respectively. The research results can provide reference for the hybrid strengthening application of seismic-damaged DVFP.

Experimental and theoretical study on mechanical behaviors of CFRP–steel interface

The performance of the CFRP–steel interface is crucial to the reinforcement efficiency of the steel structures strengthened by using externally pasted CFRP sheet method; while it is influenced significantly by adhesive properties and geometrical characteristics of joints. The present study aims to optimize the adhesive layer of the CFRP–steel interface and establish a theoretical model of predicting the interfacial behaviors of the optimized CFRP–steel joints. A commercially available adhesive was modified by addition of Nano-SiO2 ranged from 0 to 7wt% to ascertain the optimal content of Nano-SiO2. A series of tensile tests were carried out on dog-bone adhesive specimens, single-lap shear specimens and CFRP–steel double-lap joints to obtain the mechanical properties of the adhesive at different content of nanofiller and the corresponding bond–slip laws in the unmodified and modified CFRP–steel interfaces. Accordingly, theoretical models were derived to predict the load capacity of the joints and the bond stress distribution along the CFRP–steel interface during different loading phases. The results show that the mechanical properties of the adhesive are improved with the addition of nano-SiO2 up to 1.4 wt%. When the content of nano-SiO2 rises from 1.4 to 7 wt%, the tensile and shear strengths as well as the tensile modulus decline gradually whereas the ductility keeps growing with a lower growth rate. These indicate the nano-SiO2 content of 1.4 wt% is favorable. Both the peak stress and the load capacity of the CFRP–steel joint increase with the adhesive thickness varying from 0.5 to 1 mm. The bond–slip law of the unmodified CFRP–steel interface can be simplified to be bilinear, regardless of the adhesive thickness and curing duration. In contrast, the modified interface presents a trilinear curve due to the special plastic plateau caused by the filling of nano-SiO2. Consequently, a larger fracture toughness and a higher load capacity can be reached by the optimized joints. The theoretical results are in agreement with the experimental phenomena and results. The modified adhesive is beneficial to utilize the CFRP material better and improve the reinforcement efficiency.

Behavior of CFRP-reinforced concrete columns at elevated temperatures

Current design codes preclude FRP bars being used as main reinforcement in compression members because of the general recognition that the compressive strength of FRP bars is lower than their tensile strength and the lack of reliable data related to their performance at elevated temperatures. The present study evaluates the properties of CFRP bars as compression reinforcement in RC columns and investigates experimentally the structural performance after cooling of the columns reinforced with CFRP bars that were subjected to elevated temperatures. Twenty-four short columns specimens were fabricated considering the use of CFRP bars or steel bars as main reinforcement, the spacing of tie bar confinement and the exposure temperature (0, 150, 300 and 450 °C). The test members were subjected to concentric axial loading and the test results measured after cooling down to room temperature were compared with analytic results based on current standard for concrete columns. The investigation showed that, compared to the CFRP-reinforced columns let at room temperature, those exposed to elevated temperatures experienced compressive resistance that first improved by 3 % to 15.9 % at 150 °C, but degraded at higher temperatures by 7 % to 13.6 % at 300 °C, and by more than 50 % at 450 °C.

Study on Shearing Behavior of Circular Concrete-Filled CFRP (Carbon Fiber-Reinforced Plastics)-Steel Tube.

Concrete-filled CFRP steel tube (CF-CFRP-ST) structures often suffer from shear loading in practical engineering, such as joints with diagonal braces. To study the shear properties of CF-CFRP-ST, we take the concrete strength and the longitudinal CFRP layers as the main parameters, and static shear tests of overall 9 circular concrete-filled CFRP-steel tube (C-CF-CFRP-ST) and 3 circular concrete-filled steel tube (C-CFST) are carried out. The research is carried out from two aspects: experiment and finite element. The experimental results show that the shear loading-displacement curves of the specimens can be divided into elastic stage, strengthening stage, and softening stage. The increases of the strength of the concrete and the layers of the transverse CFRP can both enhance the shearing load carrying capacity of the specimen. With the increase of concrete strength, there is no obvious change in the shape of the shear stress-shear strain curves of the specimens, and the shear stress and the stiffness of the curve in the elastic stage of the specimen are slightly increased. The shear loading-displacement curves of the specimens are simulated by using finite element software ABAQUS and it is found that the predicted results agree reasonably well with the test results. Then, the whole process of loading and the parameters of the main influencing factors are analyzed. Finally, the calculation equation of CFRP concrete-filled steel tubular shear capacity is established.

Static Behavior of Circular Section CFRP Concrete-Filled Steel Tubes Under Compressive–Torsional Load

In order to study the compressive torsional behavior of concrete-filled CFRP steel tubes (CF-CFRP-STs), the static test of eight circular section CF-CFRP-ST compression torsional specimens was carried out. The characteristics of the torque–angle (T–θ) curve and shear stress shear–strain (τ–γ) curve, failure mode, cooperative work between steel tubes and CFRP, and cross-section assumption were studied. The T–θ curve, τ–γ curve, and failure mode of the specimen are simulated by ABAQUS. Based on the above research, the stress distribution of each component material is analyzed. The effects of transverse CFRP layers, material strength, steel ratio, and axial compression ratio on the static performance of members are discussed. Based on the performance analysis, the bearing capacity equation of CF-CFRP-ST compression-torsional members is proposed.

A Study on the Bond-Slip Relationship of the CFRP-Steel Interface of CFRP Strengthened Steel.

The bonding interface between the CFRP and the steel plate is the weak link of CFRP-strengthened steel structures. This paper studies the bond–slip relationship of the CFRP–steel interface by experiments and numerical tests. First, a series of double-strap experiments on a CFRP-strengthened steel plate are carried out. The results show that the maximum shear stress of the bonding interface of the Q345B specimen is larger than that of the X100 specimen. The initial slip and maximum slip become larger as the thickness of the bonding interface becomes larger. Finite element analysis of the above tests is carried out; we introduce the maximum stress criterion to simulate the bonding interface, which assumes that when the nominal stress of the material reaches the maximum nominal stress of damage, the material begins to damage. The FE model established has proved very effective for analyzing the bond characteristics of CFRP-strengthened steel plates. Finally, a verification test was carried out, using an FE analysis to verify the accuracy of the modified equations; the results prove that the results of the modified equations are in good agreement with the numerical results and experiment results, which verifies the effectiveness of the equations.

Theoretical and experimental study of the bending collapse of partially reinforced CFRP–Steel square tubes

Bending collapse of thin-walled steel tubes is a major energy absorption mechanism in lightweight structures, especially for crashworthiness. External composite reinforcements can increase the energy absorption and strength of steel tubes. However, to this date there are still difficulties to determine the maximum load and the collapse behavior of reinforced, multi-material shapes, e.g., steel shapes covered by CFRP. In this work, a theoretical analysis of the collapse of a partially reinforced CFRP–Steel tube is performed, which encompasses the calculation of both the peak bending moment and the bending collapse curve of tubes with either the flanges or webs with reinforcements. The theoretical approach is validated with three-point bending experimental tests and an adequate agreement with experiments is found. The results also show an important increase of up to 57% in the peak load and 45% in the specific energy absorbed for partially reinforced tubes, with a maximum 14% increase in weight, when compared with unreinforced tubes. The developed theoretical model enhances even further the existing bending collapse theories, as it incorporates reinforcements in the model and provides a powerful tool for engineering analyses, and can be implemented in concept models, and optimization algorithms with ease. These findings can be used for enhancing existing and new lightweight structures and improving the crashworthiness of several automotive structures.

Seismic behavior assessment of historical Alaeddin Bey Mosque and strengthening suggestions by CFRP fabric and steel plate

In this study, the effects of different strengthening methods that can be applied for earthquake-damaged historical masonry structures on structural performance were investigated. For this purpose, the Historical Alaeddin Bey Mosque in the central district of Muş was modeled in three dimensions according to the macromodeling technique using the finite element method in the SAP2000 program. The earthquake performance of the structure was determined by considering the earthquake-acceleration records of Erzincan, Kocaeli, and Van, respectively. The maximum tensile and compressive stresses in all three directions on the structural elements were taken into account as the earthquake behavior parameters of the structure. According to the earthquake analysis made in the time domain, it was determined that the polygonal pulpit of the minaret was at risk of being damaged under the effect of the Erzincan earthquake, and it has been concluded that this region should be strengthened. The damaged area of the minaret was strengthened by the application of CFRP fabric and steel plate materials (together or separately) in five different ways, from inside and outside and at different distance intervals. The conclusions obtained as a result of the earthquake analyses on the reinforced models were examined, and it was explained in detail with the help of tables and graphics that method would be more effective in strengthening such damages.

Analysis on Experimental Performance of Hysteretic Behavior of Concrete-Filled Circular CFRP Steel Tubular Beam-Column

In order to study the test performance of the concrete-filled CFRP steel tubular (CF-CFRP-ST) beam-column under hysteretic load, 12 specimens were designed. During the test loading, the effects of axial compression ratio and longitudinal CFRP reinforcement coefficient on hysteric load were studied. Based on experimental research, a finite element method for establishing CF-CFRP-ST beam-column is proposed by FE simulation, and the influence of main parameters on performance is studied by this method. The test results show that CFRP and the steel tube can work together well, and the local buckling of specimens is delayed. In addition, the simulation results are in good agreement with the experimental results. Based on the experiment and finite element method, the influence of main parameters on the hysteretic behavior of specimens is studied.

Shear response of RC beams encompassing hybrid CFRP strips and steel stirrups: Beam depth effect

In this study, nonlinear finite element analysis (FEA) was conducted to investigate the shear behavior of reinforced concrete (RC) beams encompassing hybrid CFRP strips and steel stirrups. Primal FEA models were calibrated and verified by comparing the load–deflection response, cracking, and failure modes with the experimentally tested RC beams. A parametric case study was then implemented to evaluate the influence of critical parameters including: configurations of CFRP strips (strip width, orientation angle), size effect, and concrete compressive strength. The results showed that changing the individual CFRP strip width while maintaining a constant total width has no significant effect on the behavior of the RC beams. Increasing the concrete compressive strength improves the bond strength between the CFRP strips and concrete leading to higher load capacity. Changing the orientation angle of the CFRP strips up to 45° has minor effect on the RC beam shear capacity. The contribution of the CFRP strips was more pronounced as the beam depth increased. A comparison showed that internally-integrated CFRP strips leads to better enhancement in the shear strength of RC beams than externally strengthening with CFRP composites.

Effect of transverse circular and helical reinforcements on the performance of circular RC column under high explosive loading

Columns are primary load-carrying members of the framed structure which transfer external lateral loads and gravity load of the structure to the foundation. Columns under extreme loadings such as blast may become a local hazard, failure of which can lead to the disproportionate or progressive collapse of the building. Not only the subversive reasons but accidental explosions may also cause the failure of the column(s) or building, resulting in a huge loss of economy and human lives. Blast resistance of the columns in the building is of serious concern under explosive loadings. Following the validation of experimentally tested square RC column with seismic lateral reinforcement carrying axial load subjected to an explosive charge of 100 kg ANFO (82 kg-TNT equivalent) at a scaled distance of 1.00 m/kg1/3 with 10 mm mesh size using ABAQUS/CAE software equipped with concrete damage plasticity model, equivalent circular columns to the experimentally tested one having seismic circular transverse reinforcement, and column with helical transverse reinforcement carrying the same axial load under the blast are considered. Additional transverse reinforcement of CFRP is also considered over confining regions. Additional wrappings of CFRP and mild steel sheets are also used to study their effect on the blast performance of the columns. Blast performance in terms of maximum displacement, stresses, and damage to the columns are compared and discussed. The present research provides insight into the blast performance of the circular RC columns and provisions to reduce the explosive-induced failure risk.