Hybrid Bars Research Articles

Experimental and numerical behaviour of hybrid R.C. columns under the effect of fire furnace

PurposeThe purpose of this research is to study the effect of high temperature on concrete columns which are considered the most important part of the concrete structure. Glass fibres were used to study the effect of heat on them as well as on the properties of reinforcing steel and concrete.Design/methodology/approachHigh tensile stress may develop at the tension zone of the column section when the column is exposed to an axial compressive load with a relatively high eccentricity. Since fibre bars have a higher tensile strength than steel bars, they can be used in the tension zone of hybrid reinforced concrete columns to resist tensile stress, while steel bars can be used in the compression zone to resist compressive stress. However, as documented in prior research studies and advised by standards and codes, the mechanical qualities of concrete, steel and fibre bars are considerably damaged when hybrid columns are exposed to high temperatures.FindingsWhen the fire temperature rises, the ultimate load value of the reinforced concrete column decreases. Also, steel bar reinforcing is more efficient than glass fibre bars in resisting high temperatures. The rate decrease in the strength of reinforced concrete columns to applied load on it decreases with the rise of the temperature to which the specimen was exposed during the burning period.Originality/valueThe experimental and numerical work includes a study of the effect of a fire furnace on the behaviour of hybrid R.C. columns. Three types of reinforcement were used steel bars only, G.F.R.P bars only and hybrid (steel and G.F.R.P) bars. These columns specimens were cast and divided into three groups according to the details of reinforcement, the effect of fire temperature and according to the eccentricity ratio. Two types of hybrid are used in this work. Fourteen R.C. columns were casted and divided into, 4 specimens not burn and 10 specimens burn at temperatures 300, 500 and 700.

Behavior of Hybrid Natural Fiber Reinforced Polymers Bars Under Uniaxial Tensile Strength and Pull-Out Loads with UHPC

This study evaluated the uniaxial tensile strength and bond performance of natural hybrid reinforcement bars. Hybrid FRP combines multiple fibers and matrixes, resulting in a desirable performance. Two types of hybrid bars were tested: one with natural fibers surrounded by glass fiber, and the other with a steel core surrounded by natural fiber and then glass fiber. Thirteen samples were used to assess tensile behavior, with four groups including glass fiber, flax, sisal, and jute fibers. Pull-out behavior testing was conducted on twelve samples, divided into four groups of fiberglass, flax, sisal, and jute. Each group used three types of concrete: normal, high strength, and ultra-high-performance concrete (UHPC). The results refer to flax samples that had a higher tensile strength and elastic modulus of 143MPa and 38GPa, respectively, than samples made of sisal and jute fibres. The hybrid bars with a steel core exhibited a significant improvement in elastic modulus of 206% in compared to samples made solely from glass, sisal, and jute fibers. On the other hand, the samples with UHPC showed the highest bond strength. The sample U-GFRP with ultra-high-performance concrete showed the highest bond strength 9.32MPa, while the sample N-GFRP with normal concrete showed the lowest bond strength 5.87MPa, respectively. However, this study suggests that hybridizing natural fibers can be a cost-effective and eco-friendly alternative to synthetic fibers.

Structural performance of hybrid reinforced concrete beams containing polyvinyl alcohol fibers under thermal loads

This study focused on the efficiency of concrete beams containing polyvinyl alcohol fibers (PVA) under thermal loads. The eighteen concrete beams were reinforced with hybrid bars or a combination of GFRP bars and steel reinforcement bars (hybrid scheme). The main experimental variables were the level of temperature (25o, 300o, and 600o C), PVA fiber volume (0 %, 0.50 %, and 1.0 %), and the flexural reinforcement bars. The experimental test results are discussed in terms of the first crack load, flexural capacity, and load-deflection curves. Moreover, the initial and post-crack stiffness, ductility factor, and failure modes are discussed. The test results demonstrated a significant increase in the capacity of PVA concrete beams reinforced with hybrid reinforcement bars. At a temperature of 300o C, the inclusion of 0.50 % and 1.0 % PVA ratios improved the flexural capacities by 11 % and 24 %, respectively. Furthermore, the addition of PVA fibers enhanced the toughness by 34 % and 67 %, respectively, when compared to normal concrete beams. The results also demonstrate that using PVA fibers prevents the spalling of concrete beams after exposure to elevated temperatures. At 600 °C, beams containing 0.50 % and 1.0 % PVA fibers exhibited flexural capacities that were 9 % and 6 % higher, respectively, compared to normal concrete beams. Additionally, the inclusion of PVA fibers increased the toughness by 27 % and 21 % for the respective fiber ratios. Finally, a nonlinear finite element analysis (NLFEA) simulation was performed to verify the experimental test results and supplement experiments by predicting the results that are difficult to accomplish through experiments. With an average ratio of 1.02 between experimental and NLFEA ultimate capacity, the numerical results were an exact match of the patterns observed in the experimental results.

Experimental and numerical study on the shear behavior of hybrid BFRP/steel RC beams without shear reinforcement

Hybrid reinforcement of steel and fiber-reinforced polymer (FRP) bars can provide a balanced performance between strength, ductility, and durability for the concrete structures. Thus, this study evaluates the shear performance of hybrid Basalt-FRP/steel-RC beams without shear reinforcement. A total of twelve RC beams were cast and tested under four-point loading to study the influence of reinforcement type, reinforcement ratio of longitudinal bars and axial stiffness between FRP and steel ratio, [Formula: see text] on the shear performance of the concrete beams. The test results were analyzed in terms of crack patterns, load-midspan deflection, load-crack width relationships, and shear strength of the tested beams. In addition, the experimental results were compared with the theoretical results obtained from various design codes and guidelines. Moreover, a finite element (FE) model was created, and the experimental results were used for validation of the FE model. The test results revealed that the beam specimens designed with similar effective reinforcement ratio exhibits comparable shear strength nevertheless the tensile reinforcement used. Experimental test results demonstrated that using hybrid bars increased the shear capacity of the beams by 11% compared to steel bars. Furthermore, the energy absorption of the hybrid-RC beams was enhanced by 16% compared to FRP-RC beams. By elevating the [Formula: see text] ratio from 1.25 to 2.44, both the shear strength and energy absorption improved by approximately 10%. Notably, there was a significant decrease in the deflection and crack width of the hybrid-RC beams in comparison to the FRP-RC beams. The design codes ACI440.11-22 and CSA S806-12 displayed accurate enough estimates of the shear strength, while JSCE-1997 showed a conservative result.

Static and fatigue behavior of concrete bridge deck slabs reinforced with BFRP and steel bars

Using Fiber-reinforced polymer (FRP) has proved great promise as an alternative to conventional steel in bridge constructions owing to its high tensile strength and corrosion resistance. However, using Hybrid reinforced concrete (RC) slabs displayed enhanced stiffness, narrower crack width and larger bending capacity compared with FRP-RC slabs. This paper studies the static and fatigue performance of concrete bridge deck slabs reinforced with hybrid basalt-FRP (BFRP) and steel bars. The main parameters were the effective reinforcement ratio, the FRP-to-steel bars ratio Af/As, and the fatigue limit. The test results exhibited that superior fatigue behavior was achieved in the hybrid-RC slabs because the hybrid bars can better distribute the load and reduce stress concentration. In addition, the fatigue life growths with increasing the effective reinforcement ratio while reverse trend was observed when increasing Af/As ratio. In addition, increasing the upper fatigue load limit deteriorates the slab stiffness and significantly reduces the fatigue life. A regression analysis has been performed and revealed that the concrete deck slab can withstand 2 million cycles after fatigue loading of an upper fatigue load limit of 34 % of its ultimate static capacity.

Structural efficiency of concrete beams reinforced with hybrid reinforcement bars under thermal loads

Nine reinforced concrete (RC) beams were experimentally tested to assess the effect of temperatures on the flexural performance of concrete beams with hybrid bars and GFRP-steel reinforcement. The study focused on the temperature levels (25 °C, 300 °C, and 600 °C), the reinforcement ratios, and the type of reinforcement bar. The test findings revealed a significant decline in the stiffness of beams with GFRP-steel reinforcement compared to hybrid reinforcement bar (HRB) beams. The stiffness decreased by 17 % and 31 % for 300 °C and 600 °C, respectively. Moreover, all beam specimens exhibited a flexural failure mode. Non-linear finite element analysis (NLFEA) results accurately reflected the trends observed in the experimental results, and the average ratio of the experimental and NLFEA ultimate capacity was 1.02. Finally, experimental results were used to evaluate nominal flexural strength. The comparison showed that nominal flexural strength predicts flexural stress. The average experimental-nominal flexural strength ratio was 1.14.

Application of Composite Bars in Wooden, Full-Scale, Innovative Engineering Products-Experimental and Numerical Study.

The commercialization of modular timber products as cost-effective and lightweight components has resulted in innovative engineering products, e.g., glued laminated timber, laminated veneer lumber, I-beams, cross-laminated timber and solid timber joined with wedge joints. With the passage of time, timber structures can deteriorate, or new structural elements are required to increase the stiffness or load-bearing capacity in newly built structures, e.g., lintels over large-scale glazing or garages, or to reduce cross-sectional dimensions or save costly timber material while still achieving low weight. It is in such cases that repair or correct reinforcement is required. In this experimental and numerical study, the static performance of flexural timber beams reinforced with prestressed basalt BFRP, glass GFRP and hybrid glass-basalt fiber bars is shown. The experimental tests resulted in an increase in the load-carrying capacity of BFRP (44%), GFRP (33%) and hybrid bars (43%) and an increase in the stiffness of BFRP (28%), GFRP (24%) and hybrid bars (25%). In addition to this, glued laminated timber beams reinforced with prestressed basalt rods subjected to biological degradation, 7 years of weathering and prolonged exposure to various environmental conditions were examined, and an increase in the load-bearing capacity of 27% and an increase in stiffness of 28% were obtained. In addition, full-size laminated timber beams reinforced with prestressed basalt bars were investigated in the field as an exploratory test under fire conditions at elevated temperatures, and the effect of the physical-mechanical properties during the fire was examined via an analysis of these properties after the fire. In addition, a satisfactory correlation of the numerical simulations with the experimental studies was obtained. The differences were between 1.1% and 5.5%. The concordance was due to the fact that, in this study, the Young, Poisson and shear moduli were determined for all quality classes of sawn timber. Only a significant difference resulted in the numerical analysis for the beams exposed to fire under fire conditions. The experimental, theoretical and numerical analyses in this research were exploratory and will be expanded as directions for future research.

Durability of carbon/basalt hybrid fiber reinforced polymer bars immersed in alkaline solution

AbstractUsing basalt fiber‐reinforced polymer (BFRP) bars to substitute for steel rebar in seawater sea‐sand concrete (SSC) members is one of effective solutions to steel corrosion. However, there is a concern about the durability of BFRP due to the alkaline of SSC. In this study, a layer of carbon fibers coating (volume fraction was set at 10% and 20%) was used to improve the alkaline resistance of BFRP, which named as carbon/basalt fiber‐reinforced polymer (C/BFRP) hybrid bars. The tensile properties, interlaminar shear strength, and water absorption and diffusion behavior of the C/BFRP were examined by laboratory acceleration methods. The immersion solution temperatures were set at room temperature, 40 and 60°C, immersion mediums were tap‐water and two kinds of alkaline solutions (pH = 10 or 13). Carbon fiber coating is beneficial for improving the mechanical properties of the composite. The higher the fiber volume fraction, the better the long‐term resistance of C/BFRP can be found. However, carbon‐basalt fiber interface is still a weak part in the durability of C/BFRP. The higher the volume fraction of the coating carbon fibers, the greater the quasi‐equilibrium water uptake, which can be attributed that the smaller diameter of carbon fibers embedded the voids between basalt fibers. Reducing environment alkalinity is also beneficial for increasing the service life of C/BFRP, and the tensile strength retention increased by 12% when pH decreased from 13 to 10 after 50‐year.Highlights Carbon fiber coating is beneficial for improving the properties of BFRP. Carbon‐basalt fiber interface is a weak part for the durability of C/BFRP. Reducing alkalinity can improve the durability of BFRP.

Impact of developed hybrid polypropylene fiber inclusion on the flexural performance of concrete beams reinforced with innovative hybrid bars

This paper investigates the impact of incorporating a hybrid combination of structural polypropylene fibers on the flexural behavior of concrete beams reinforced with steel, GFRP, and innovative hybrid bars. A new ductile hybrid bar with equivalent bilinear stress-strain characteristics has been developed to address steel corrosion and FRP ductility issues. Fourteen half-scale RC beams were fabricated and tested under four-point loading configuration to study the flexural response. The tensile reinforcement types (steel, GFRP, and hybrid), hybrid reinforcement ratios (0.85 %, 1.26 %, and 1.70 %), reinforcement hybridization schemes (hybrid-hybrid, hybrid-GFRP, and GFRP-steel), and hybrid fiber ratio (0.0 %, 1.0 %, and 2.0 %) are the major parameters studied. The test results were recorded and analyzed in terms of mid-span deflection, cracking load, flexural capacity, and failure mechanism. The results demonstrated that the addition of hybrid fibers and using hybrid bars significantly improved the peak strength, ductility index, and bending stiffness. Moreover, the hybrid-reinforced concrete beams exhibit large inelastic deformations similar to steel-reinforced concrete beams. The inclusion of hybrid fibers improves the post-peak response of the tested beam due to fiber bridging capabilities. For design purposes, a simplified formula proposed by ACI 544 for predicting the nominal flexural capacity of hybrid fiber concrete beams reinforced with hybrid bars was presented, compared with experimental results and validated with 44 specimens from other studies. The predicted and test results were in good agreement with a standard deviation of 0.12. Additionally, 3D nonlinear finite element analysis was developed to validate the test results, demonstrating reasonable accuracy in predicting the flexural behavior of the beams.

Investigation on the Impact Response of Concrete Beams Reinforced with Hybrid Steel–BFRP Bars

An appropriate hybrid form of steel and fiber-reinforced polymer (FRP) bars in reinforced concrete members can prevent steel corrosion and ensure capacity and ductility. To investigate the impact resistance of concrete beams reinforced with hybrid steel and basalt FRP (BFRP) bars, a three-dimensional numerical model was developed that takes into account the strain-rate strengthening effect. The validity of the numerical model was first verified. Subsequently, drop hammer impacts were simulated on 10 concrete beams reinforced with hybrid steel–BFRP bars to determine the influence of the BFRP bar proportion and position on their impact resistance. The results indicated that the level of concrete damage in the hybrid bar–RC beams is between those of the concrete beams with steel bars and concrete beams with BFRP bars. As the proportion of BFRP bars increased from 0 to 1, the peak impact force and internal force of the beams linearly decreased by 20%, the reaction force linearly declined by 50%, while the peak midspan displacement linearly increased by 20%. Except for the midspan deflection, the comparable degree of damage among beams with four different bar configurations indicates the equivalent impact resistance of the beams. The change in the frequency of the hybrid bar–RC beams before and after impact loading can reflect their impact resistance.

Numerical study on the structural performance of the continuous concrete slabs reinforced with hybrid BFRP/steel bars

AbstractThis study is mainly focused on the behavior of continuous concrete slabs reinforced with hybrid bars. Moment redistribution is a specific phenomenon in statically indeterminate structures due to the existence of redundant constraints and non‐uniform flexural stiffness of the reinforced concrete (RC) members. In this paper, a numerical one‐factor‐at‐a‐time parametric study was conducted using ABAQUS software to intensely understand the impact of several parameters on the performance of the hybrid RC continuous slabs. The investigated parameters were reinforcement type and ratio, FRP‐to‐steel ratio, and arrangement of reinforcement. The analysis results showed that the difference between sagging and hogging axial stiffness is the most influential parameter on the moment redistribution of hybrid‐RC continuous slabs. In addition, increasing the amount of reinforcement ratio at the mid‐span section is more effective in enhancing the load capacity of the slabs than over middle support section. Based on the obtained numerical results, some modifications to the Tarek et al. equations were proposed to be valid for hybrid‐RC continuous slabs. The presented modifications yielded good agreement with the numerical results predicting the moment redistribution of continuous concrete slabs with hybrid reinforcement.

Flexural Behaviour of Hybrid Bar Reinforced Concrete Beams (GFRP Bars with Steel Wires): An Experimental Study

Flexural Behaviour of Hybrid Bar Reinforced Concrete Beams (GFRP Bars with Steel Wires): An Experimental Study

Structural Behavior of Hollow Beam Reinforced with Different types of GFRP stirrups

The structure could be impacted by concrete's steel reinforcement corroding. When exceptional corrosion resistance capabilities are required, fiber-reinforced polymer (FRP) reinforcements offer a practical choice for constructions exposed to hostile environments. However, only a small number of the building's most important structural components are currently permitted to use FRP bars as interior concrete reinforcement, leaving the rest of the building unprotected. This is due to the lack of available curved or shaped reinforcing FRP pieces, which have subpar structural performance.
 Eighteen concrete beams with dimensions (1200×225×150) mm were divided into three groups and each group had five beams with three References and five different types of stirrups in each group and tested them up to failure. The first group included longitudinal reinforcing steel bars 6Ø10mm, the second group longitudinal reinforcing GFRP bars 6Ø10mm, and the third group longitudinal reinforced with hybrid (3steel+ 3GFRP) bars 6Ø10mm. All beams are self-compacting concrete with a longitudinal hollow with dimensions (50×100) mm.
 The results showed that the ultimate load of a hollow beam reinforced with steel reinforcement is less than a solid beam reinforced with steel (reference 1) by (15%) and a hollow beam reinforcing with GFRP reinforcement is less than a solid beam reinforced with GFRP (reference 2) by (5%), and a hollow beam hybrid reinforced with (Steel+ GFRP) reinforcement is less than a solid beam reinforced with GFRP (reference 3) by (4%).

Performance of RC beams with novelty GFRP under the bending load: An experimental and FE study

A total of eight reinforced concrete (RC) beams were examined in the experiment to investigate the flexural performance of concrete beams reinforced with locally fabricated hybrid bars. The variables include the type of reinforcement bar (hybrid, GFRP, and steel). Two types of hybrid bars, the first was hybrid reinforcement bars (HRB), which have a steel core encased by GFRP. Steel core had the volume fraction 0.25 %, 0.44 %, and 0.70 % from the total volume of HRB. Second, advanced hybrid reinforcement bars (AHRB) were produced by adding metal powders to the matrix of GFRP with weight percentages of 5 %, 10 %, and 15 %. The load-deflection and crack patterns, failure modes, toughness, and ductility were studied of RC beams. An analytical framework has been developed and verified for RC beams based on the non-linear deformation model. The experimental results show that using hybrid bars instead of GFRP bars improves stiffness significantly. Failure loads for RC beam with volume fractions 0.25 %, 0.44 %, and 0.70 of HRB were 51 kN, 55 kN, and 71 kN, respectively, while failure loads with metal powder 5 %, 10 %, and 15 % of AHRB were 62 kN, 64 kN, and 70 kN, respectively. The failure load of the HRB beams increased to 94.16 %, while the AHRB beams increased to 92.25 % of the total failure loads of the beam with steel bars. The failure mode in the beams reinforced with HRB was a ductile flexural failure, while the beams with AHRB failed under compression failure at the range of the loading points. The HRB and AHRB demonstrated significantly improved ductility index up to 91.10 % and 75.60 %, respectively, compared to sample with GFRP bars. ANSYS Software was used to conduct a finite element model (FEM) analysis. It could be seen good agreement compared to the experimental results and those obtained of the predicted values.

Review on flexural performance of reinforced concrete beams designed with hybrid bars

Reinforced steel bars, commonly used in concrete construction, are prone to corrosion due to their insufficient corrosion resistance, which ultimately leads to reduced durability and long-term performance. Moisture interaction is the leading cause of corrosion, which results in rust, cracks, and spalling, leading to durability and long-term performance issues. To address this problem, FRP bars are now being introduced to the market, which offer numerous benefits over steel bars, such as strong corrosion resistance, higher tensile strength, and reduced weight, leading to lower shipping and labor costs. Concrete gains mechanical stability, stiffness, durability when polypropylene fibres are used, improving the material's effectiveness. The purpose of this study is to examine the flexural behavior, load-deflection characteristics, and ductility of hybrid reinforced concrete beams. that use both GFRP bars and steel bars, as well as compare them with reinforced concrete beams that use only GFRP bars or steel bars with and without using polypropylene fibres as a supplement. In order to enhance the beams flexural strength as well as ductility, it has been identified that 0.25% of their volume should be made up of polypropylene fibres. After the experimental investigation is finished, analytical studies using ANSYS simulation will be carried out to determine the load-deflection behaviours.

Structural performance and corrosion resistance of fiber reinforced polymer wrapped steel reinforcing bars

Structural behavior and corrosion resistance of hybrid fiber reinforced polymer (FRP) wrapped steel bars is investigated for use in reinforced concrete structures. Experiments were conducted in the laboratory to assess the axial tensile capacity and corrosion resistance of the composite bars, and flexural behavior of beams reinforced with these hybrid bars. Data from short term and long-term corrosion experiments were used to evaluate the resistance to degradation provided by the FRP, including applied defects to determine any gain in corrosion resistance over standard epoxy-coated bars. Corrosion experiments are performed by placing bars with and without applied defects in an aggressive solution that mimics a concrete pore environment. Corrosion rates of standard epoxy-coated bars and hybrid carbon and glass FRP wrapped steel bars were compared considering the crevice corrosion at applied defects. In addition to their contributions to the strength capacity of steel bars confirmed by the tensile tests, FRP-wrapped steel reinforcing bars have high corrosion resistance. The overall behavior of beams reinforced with hybrid FRP-steel bars was similar to those reinforced with epoxy coated bars. During the experiments, no debonding was observed between the hybrid bars and concrete inside the beams before failure.

Behavior of R.C. beams with lap-spliced hybrid bars under flexure

ABSTRACT The steel fiber-reinforced polymer composite bars Known as (SFCB) are new kind of reinforcement, for concrete structures. A layer of glass fibers and reinforced polymer surrounding the steel bars resulting in the (GFRP), when used as concrete reinforcement contributes for enough, serviceability strength, and durability. Increasing the elastic modulus of GFRP bar, which have function of protecting corrosion in addition to reduce the initial cost of the FRP bar, is the purpose of hybridization. SFCB has the advantages of being noncorrosive, nonmagnetic nonconductive, and light in weight, along with high strength. This study presents the behavioral characteristics of RC beams, with tensile lap-spliced steel fibers—coated bars under flexure. Ten beam specimens were tested, with concrete cross-section of (25*40*420) cm and compressive strength of 30 MPa. One beam specimen, (R) was taken as reference as it was reinforced with no lap splice. Nine beam specimens were divided into three groups. Group (A) contained three beam specimens reinforced with SFCB of diameter 16 mm and lap splice of 50φ, one with stirrups, without stirrups and with staggered lap splice. Group(B) contains three beams reinforced with SFCB of 16 mm diameter and lap splice of 55 φ one with stirrups, without stirrups and with staggered lap splice. Group(C) contains three beam specimens reinforced with SFCB of 16 mm diameter and lap splice of 60 φ one with stirrups, without stirrups and with staggered lap splice. Beams were exposed to pure flexure. Crack patterns and results are presented along with stress-strain curves. Finally, conclusions are summarized and presented.

Flexural Behavior of Insulated Concrete Sandwich Panels using FRP-Jacketed Steel-Composite Connectors

This study presented the experimental and theoretical results of insulated concrete Sandwich panels with innovative dumbbell-shaped steel fiber-reinforced polymer (FRP) composite bar (SFCB) connectors under flexural load. The influences of FRP thickness and raised thickness of dumbbell ends of connectors, axial compression ratio, the content of vitrified microspheres in the wythes, and loading direction were discussed. The increase in thickness of a glass FRP (GFRP) jacket on the hybrid bar from 2 to 3 mm led to increased initial cracking load, ultimate load, and flexural stiffness of the Sandwich panels by 75, 49, and 16%, respectively. The increase in the thickness of dumbbell ends from 4 to 6 mm led to increased initial cracking load, ultimate load, and flexural stiffness of the Sandwich panels of 18, 46, and 9%, respectively. The incorporation of vitrified microspheres in concrete wythes resulted in a significant increase in the load-carrying capacity of Sandwich panels but decreased ductility. Increased axial compression ratio from 0/1 to 0.2/1 contributed in improving the crack resistance and ultimate loads of Sandwich panels. Further increase of the axial compression ratio to 0.4/1 led to crushing failure of concrete wythe ends. Specimens under negative loads had higher ultimate loads than the counterparts under positive loads. Three-dimensional finite-element (FE) models were developed to simulate Sandwich panel flexural behavior and numerical results compared with the test data. Then, the verified FE model was used to analyze the influence of the arrangement of dumbbell-shaped SFCB connectors. Increased connector spacing from 550 to 650 mm was found to have an insignificant influence on load-deflection responses. Moreover, analytical solutions for deflection of Sandwich panels under combined axial-flexural load were obtained, in which the effect of slipping between the facade and structural wythes and shear deflection were considered. The predicted deflection at the ultimate load agreed well with the test results. This study provided a theoretical basis and design reference for FRP-jacketed steel-composite connectors in applications of Sandwich wall panels with large insulation layer thickness.

Damage Monitoring of Engineered Cementitious Composite Beams Reinforced with Hybrid Bars Using Piezoceramic-Based Smart Aggregates.

In order to explore the crack development mechanism and damage self-repairing capacity of ECC beams reinforced with hybrid bars, the smart aggregate-based active sensing approach were herein adopted to conduct damage monitoring of ECC beams under cyclic loading. A total of six beams, including five engineered cementitious composite (ECC) beams reinforced with different bars and one reinforcement concrete counterpart, were fabricated and tested under cyclic loading. The ultimate failure modes and hysteresis curves were obtained and discussed herein, demonstrating the multiple crack behavior and excellent ductility of ECC material. The damage of the tested beams was monitored by smart aggregate-based (SA) active sensing method, in which two SAs pasted on both beam ends were used as actuator and sensor, respectively. The time domain analysis, wavelet packet-based energy analysis and wavelet packet-based damage index analysis were performed to quantitatively evaluate the crack development. To evaluate the self-repairing capacity of the beams, a self-repairing index defined by the difference of damage index at loading and unloading peak points was proposed. The results in time domain and wavelet packed analysis were in close agreement with the observed crack development, revealing the feasibility of smart aggregate-based active sensing approach in damage detection for ECC beams. Especially, the proposed damage self-repairing index can describe the same structural re-centering phenomena with the test results, showing the proposed index can be used to evaluate the damage self-repairing capacity.

Comparison of flexural behaviors between plain and steel-fiber-reinforced concrete beams with hybrid GFRP and steel bars

This study investigates the flexural behavior of steel-fiber-reinforced concrete (SC) beams with hybrid glass fiber reinforced polymer (GFRP) and steel bars. The experimental results of current SC beams are compared with those of the plain concrete (PC) beams conducted in our previous research. Taking account of the differences in nominal reinforcement ratio and reinforcement layout of seven tested SC beams, the test results including cracking load, ultimate load, failure mode, crack spacing and width, and mid-span deflection were firstly discussed. Then, a comprehensive comparison of flexural behaviors between SC beams and PC beams with same reinforcements was conducted in this paper. Especially, the crucial effects of type and strength of concrete on flexural capacity and failure mode of test beams were analyzed in detail. Finally, for concrete beams reinforced with hybrid (GFRP and steel) bars, the optimization of two balanced nominal reinforcement ratios was proposed to ensure the beam’s flexural failure in an appropriate-reinforced mode without rupture of GFRP bars.