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Although research has shown a considerable influence of the pre-cracking phenomenon on steel-congested concrete members, only normal concrete (NC) has been considered in the literature. The intention in this paper is thus to study the effect of the pre-cracking phenomenon on the bond response of pre-cracked NC with different slump flow values and self-consolidating concrete (SCC). Initial crack widths ranging from 0.0 to 0.5 mm are studied. Results show that initial crack widths larger than 0.10 mm have a significant influence on bond properties, such that reduction factors greater than 30% and 50% are obtained for the maximum bond strength of concrete specimens exposed to initial crack widths of 0.2 mm and 0.4 mm, respectively. Results show that concrete mixtures with higher workability are less sensitive to the pre-cracking phenomenon as compared to NC mixtures. The average bond stress of steel rebar in the pre-cracked SCC is found to be similar to that of the NC with a slump flow of 200 mm, which is considerably better than for NC with a slump flow of 97 mm. Moreover, results show that 65.8, 80.6, 88.5 and 93.1% fracture energy reductions are obtained for crack widths of 0.20, 0.30, 0.40 and 0.50 mm, respectively, as compared to the small crack width of 0.15 mm.

Carbon steel rebar (ASTM A615) has been widely used in reinforced concrete (RC), but its susceptibility to chloride ions remains a critical issue. Low alloy chromium steel has been used to increase corrosion resistance and extend service life, such as in 9% Cr rebar (ASTM A1035-CS). In this work, we characterized two electrochemical systems over time: ASTM A615 and A1035-CS corrugated rebar immersed in SCPS in the presence of NaCl for 12 months. The interfacial processes evolution for the ASTM A1035-CS rebar for both general and local corrosion showed different active-passive responses from those of carbon steel. Because the 3.5% wt. NaCl exceeded the chloride threshold for passive breakdown of both materials, the ASTM A1035-CS showed a five-fold higher impedance and lower general corrosion rate. In localized conditions, the low alloy chrome content rebar showed less density localized attack than the ASTM A615 rebar. These results were attributed to the overall damage evolution involving the formation and stability of corrosion products over time. The local attack appeared to be a random spatial process due to changes in the local environment.

Due to the assumption of uniform bond stress, the development length of fibre reinforced polymer (FRP) bars by design standards can be unnecessarily long and difficult to provide in practice. Hence, the bond stress distribution and required development length of a glass fibre reinforced polymer (GFRP) rebar is investigated. Four beam-bond specimens, two following RILEM specifications and two based on a procedure by ACI are tested to evaluate the effect of test method on bond strength. Ten pullout tests are also performed using the same bar. The two test methods yield similar results, but the ACI test is easier to perform. The bond stress distribution in the beams is highly nonlinear but in the pullout tests approaches uniformity. The actual development length is found to be 50% to 250% less than that required by the aforementioned standards. Consequently, a new equation is proposed based on the logistic growth function to model the non-uniform bond stress distribution and estimate the required development length.

This study experimentally explores the effects of applying various types of fibres to concrete mixes on the flexural behaviour of longitudinal structural members with basalt fibre reinforced polymer (BFRP) bars. The main objective is to research the viability of using new advanced fibres of basalt to enhance the concrete response. Basalt fibre and basalt fibre reinforced polymer rebar and compared with the conventional concrete and with a 40 MPa compressive strength target, eighteen beams were fabricated and tested; twelve with basalt fibre reinforced polymer rebar concrete and six with conventional concrete Basalt fibre lengths 30 mm with 15 µm and BFRP bar length of 800 mm with 8 mm diameter were taken into account. Flexural tests were done using a four-point test setup on both of the BFRP- conventional concrete (CC) beams. The test matrix would include BFRP bar reinforcing beams and conventional steel rebar for comparative purposes. Results showed that the application of basalt fibres to concrete enhanced the ductility of these beams' curvature. Due to the delay in the concrete failure in the compression zone, a significant improvement in bending ability was also reported, which supported the BFRP bars achieved a higher ultimate strength. The opening and deep formation of a crack have been effectively limited by the aggregate interlock of basalt fibres, which maintained the crack widths lower than in the 0.7 mm permissible maximum in service. Basalt fibres of 4%, 6%, and 8% were done. Compared to conventional concrete 6% basalt fibre at 28 days of the curing period, the maximum compressive strength was attained 52.38 N/mm2, tensile strength was attained 5.55 N/mm2, Flexural strength increases to 7.45 N/mm2. However, basalt fibre reinforced polymer rebar concrete was larger than conventional concrete beams.

One of the major durability issues of Reinforced Concrete (RC) structures is the steel reinforcement corrosion. Its effect needs to be evaluated on the lateral load capacity of the structures for understanding their seismic performance. In the present paper, the precise FE modelling and simulation of corroded RC frames subjected to lateral loads and its validation with full scale shake table tests on corroded RC frames is demonstrated. The rebar corrosion is induced in RC frames by accelerated impressed current technique and shake table tests are performed by simulating real time earthquakes with increasing excitation till failure of the frames is achieved. The tests showed that there was higher degradation of the frequency of the corroded structure with respect to pristine structure with increase in earthquake excitation levels. Numerical simulation of the tests is carried out using 2D micro-modelling, incorporating the effect of bond strength reduction, reduction in rebar diameter and decrease in mechanical properties of corroded steel in the model. Nonlinear static pushover analysis is performed to evaluate load displacement characteristics of the corroded and uncorroded frames and the results are compared with dynamic pushover obtained from shake table tests. It was observed that compared to un-corroded frame there is 13% reduction in the failure load due to earthquake excitation for the 7.5% corroded frame and numerical results for 10% corroded frame showed 22% reduction in the lateral load carrying capacity.

In this article, the outcomes from an experiential program aimed at investigating the effect of high- performance fiber reinforced cementitious composite (HPFRCC) layers and stirrups distance on flexural performance, ductility, moment redistribution, and plastic hinge length of two-span continuous concrete beams. The unique characteristics of reinforced HPFRCC continuous beams. Under flexural loading, such as high resistance to splitting cracks, less rebar slippage, damage localization in a single or few flexural cracks, inelastic strain concentration within a small region of rebar, and failure by the fracture of tensile longitudinal reinforcement in the plastic hinge region motivated this research study. The specimens have rectangular cross section of 250 mm (height) × 200 mm (width) and are continuous over two spans of 1800 mm each and two concentrated equal statically monotonic loads are applied at the mid-span of each beam. Eight beams specimens divided into three groups A, B and C were designed and cast due to the type of concrete and the stirrup spacing. Group A, consisted of two normal concrete beams with conventional stirrup spacing (d/2) (reference specimen) and compact stirrup spacing (d/4), and Group B consisted of four continuous beams made of high- performance fiber reinforced cementitious composite (HPFRCC) were layered with conventional stirrup spacing stirrups (d/2), and Group C, consisted of two continuous beams made of completely high- performance fiber reinforced cementitious composite(HPFRCC) with conventional (d/2) and compact stirrups spacing (d/4). The test results indicated that application of HPFRCC instead of conventional concrete in different section of beams with compact stirrups in critical length induced to increasing the ductility of Continuous beams. It can also be seen that increasing the transverse reinforcement, had a positive effect on the achieved moment redistribution compared with the reference beam with conventional spacing transverse reinforcement. In flexure, a highly nonlinear plastic strain distribution of the primary tensile reinforcement is observed at dominant crack locations, leading to significant differences in plastic hinge length and behavior as compared to ordinary reinforced concrete flexural members.

This paper presents the experimental results of bond and anchorage behaviours under Steel Strap Tensioning Technique (SSTT) confined high-strength concrete (HSC). The experimental tests consisted of pull-out test with short bond length and pull-out test with long bond length were performed to determine the bonding and anchorage capacity of SSTT-confined HSC. A total 36 specimens with short bond length and 16 specimens with long bond length were tested in this study. Three batches of concrete with compressive strength of 30 MPa, 60 MPa and 90 MPa were tested. Other parameter in this study was rebar diameter of 12 mm and 16 mm and different SSTT confinement ratios ranging from 0 to 0.2. To determine the effects of confinement on development bond and anchorage, an analytical expression was developed based on the parameters tested in this study. The equation is then verified with the bond strength proposed by the existing bond equations. The results from conducted tests indicated that the application of SSTT as an external confinement can increase the bond strength of confined concrete by up to 50%.

Ultra-high performance concrete (UHPC) with high bond characteristics with reinforcing bars could significantly shorten the lap splice length of rebars. UHPC-based rebar lap splice connections offer larger tolerance and simpler operation than traditional rebar connection approaches, which could ease and accelerate the on-site construction process of precast concrete structures. This paper characterizes the seismic behavior of precast beam-column joints where the longitudinal rebars of columns are connected using UHPC with a lap length of 15 times rebar diameter (15db). Full-scaled cyclic tests on two precast joints and two corresponding monolithic joints to compare were carried out keeping a high axial compression ratio (n) at 0.5. It was demonstrated that the beam-column subassemblies failed characterized by flexural failure of beam end instead of the column or joint core. The arch-like load–displacement curves and stable hysteretic behavior were still captured considering the p-delta effect. The proposed precast beam-column joints with UHPC-based connections could achieve similar bearing capacity, ductility and stiffness degradation rule to the monolithic counterparts. The degenerated four-linear restoring force model was presented and verified. Moreover, the numerical simulation was also performed, and the predicted structural behavior was in agreement with the experimental results.

The central pull-out tests were performed on C60 steel-fiber high-strength recycled concrete (SFHSRC) under the monotonic load. The failure mode characteristic of the specimens and the direction of the cracks were observed and described. The bond strength and slip displacement were measured. The effects of two parameters, replacement ratio of recycled coarse aggregate (RCA) and addition ratio of steel fiber, on failure mode and bond-slip mechanicals behaviors of SFHSRC were also analyzed. The experimental results showed that when the replacement ratio of RCA was kept unchanged, the slip displacement of rebar increased with the increase of addition ratio of steel fiber, but the bond strength increased first and then decreased; with the addition ratio of steel fiber was remained unchanged, the bond strength and slip displacement of rebar decreased with the increased of the replacement ratio of RCA. The bond strength and slip displacement mentioned above reached the maximum when the steel fiber addition ratio was 0.8%; that is, when the replacement ratio of RCA was 0 and the addition ratio of steel fiber was 0.8%, the bond strength reached the maximum. Based on the theoretical analysis of experimental data, a reasonable bond-slip constitutive model was established in this paper, which can help promote more extensive application of RAC and realize persistent development strategy of building, resources and environment to a certain extent.

The normal grouting material which has been widely used in traditional grouted sleeve connections has high brittleness and it often burst when broken. Moreover, these grouted sleeve connections required larger anchorage length and exhibited a worse cyclic load capacity than the steel bar. In this research, three kinds of fibers, including polypropylene fiber, polyvinyl alcohol fiber and basalt fiber, were selected as mixing materials in the grouting material. Their performance was tested in three areas: basic mechanical properties, toughness, and the optimal content and length of each fiber. Then, a total of 120 grouted sleeve connections with three selected optimal fiber grouting materials and five different anchorage lengths were manufactured. The mechanical performance of the grouted sleeves connections was tested under two loading schemes: cyclic loading at high stress (CH) and cyclic loading at large strain (CL). The compression test results of grouting materials demonstrated that fiber was an ideal material for improving the toughness of the grouting material. The optimal content of each fiber in grouting material was 0.5% (PP), 0.3% (BF) and 0.1% (PVA) and the optimal length was 9 mm (PP), 3 mm (BF) and 3 mm (PVA), respectively. Meanwhile, the minimum anchorage length of rebar in the grouted sleeves could be reduced by at least 1 d (d: diameter of rebar) when the fiber reinforced grouting material was adopted. According to the load–deflection curves under cyclic loading, the fiber reinforced grouted sleeve connections exhibited better residual deformation and stiffness degradation. Test results demonstrated that the fiber could clearly enhance the residual bond strength and ductility of the reinforced section, and the residual bond strength of the connections with the fiber grouting material could be increased by 3.8% ~ 22.8% when the steel bar was pulled out.

The mechanical properties of reinforced concrete (RC) structures are closely related to the bond stress-slip relationship of rebar-concrete interface. In this paper, a novel bond stress-slip model under monotonic and cyclic loading is proposed. For interfacial behaviour under monotonic loading, an innovative micro-element model, consisting of a spring element, a friction element and a switch element, is proposed to effectively characterize the interfacial micro-damage mechanical behaviours in a physical sense. By adopting a parallel system of micro-elements and setting the fracture threshold of individual spring element as a random variable, the expressions of the bond stress-slip relationship and interfacial damage variable are derived. Subsequently, succinct practical expressions for the bond strength, peak slip under monotonic loading are formulated. The bond stress-slip model for rebar-concrete interface under monotonic loading are further established. For cyclic constitutive model of rebar-concrete interface, a new method of cyclic correction factor for the degradation law of bond strength is developed. The bond strength degradation under cyclic loading affected by the number of cycles, maximum slip value and opposite loading can be reflected with reasonable accuracy. Furthermore, the predictions calculated by the proposed model under monotonic and cyclic loading are in favorable agreement with experimental results. All parameters in the model have clear physical meaning.

Partially encased composite (PEC) columns are efficient structural elements that offer ease and agility for prefabrication, requiring no molds for casting concrete. The manufacture of these elements involves anchoring the reinforcement to the metallic profile, which is a laborious process. Thus, alternative solutions capable of maintaining the column performance can propel PEC columns, providing more practical construction technics. One of these alternatives is substituting steel rebar with Fiber Reinforced Concrete (FRC), saving time. The benefits of such solutions were already proven with laboratory experiments. Therefore, this study aims to numerically analyze the structural behavior of PEC columns under different load conditions from available experiments based on a calibrated numerical model. The performance of the models was compared using two reinforcement configurations: conventional reinforcement and steel fiber reinforced concrete. Several cases of eccentric axial loads were evaluated, presenting the influence of the eccentricity and the skew angle relative to the major axis of inertia. Finally, simulations were carried out on columns subjected to non-uniform moments along with their height. The models showed a more abrupt rupture when bending around the minor axis of inertia when subjected to a constant moment on the length. Regarding non-uniform moments, the critical situation in all cases investigated occurs when the moment is constant along with the height. Results were favorable to FRC use because the two reinforcement configurations evaluated showed similar behavior in all the conducted analyses; the model of FRC showed higher ductility than the model with conventional reinforcement, mainly due to the confinement provided by fibers. Nevertheless, columns with FRC presented more significant lateral displacements, resulting in slightly lower maximum loads than those shown by columns with conventional reinforcement.

The effects and causes of different factors on the secondary tensile mechanical properties of corroded rebars (reinforcing bar) after yielding were investigated through experimental and simulation analyses to evaluate the secondary resistance performance of corroded rebar concrete members after stress and yielding. Different specimens were designed, and the rust depth, unloading level, and aging time of the rebars were used as influence variables in loading and unloading tests. The influence of each variable on the secondary tensile mechanical properties of corroded rebars after tensile yielding was studied, and reliability was verified by simulation analysis. The results showed that (a) when corroded rebars were in monotonic or secondary tension, the plastic deformation performance gradually decreased with the increase in corrosion depth, the engineering tensile strength decreased, and the pit section tensile strength increased; (b) the cold-draw hardening and aging properties of corroded rebars had no remarkable correlation with corrosion depth. (c) corrosion does not change the stress–strain constitutive relationship of the rebars during monotonic or secondary tension but affects the similarity of the stress–strain curve to the load–displacement (or average engineering stress–strain) curve of intact rebar.

Stainless steel (SS) is gaining popularity as a reinforcement of structural elements in many countries, primarily due to its enhanced corrosion resistance, improved performance against fire, and resilient behavior. This paper investigates the flexural response of concrete beams reinforced with plain stainless steel rebars. Considering variations in two concrete strength and three reinforcement ratios, this experimental program included a total of eight SS and four conventional mild steel (MS) reinforced concrete beams under four points bending test. The experimental results of SS reinforced beams of each category are presented in terms of force–displacement relation, failure pattern, beam deformation, and force-strain response. The experimental results suggest that the moment capacity of concrete beams can be improved by applying SS rebars when a low reinforcement ratio is used. Apart from common flexural and shear failure, rebar debonding failure at the beam ends was observed in SS reinforced beams. The ratios of experimental cracking moment capacity to the code recommended value are found in a range of 1 ± 0.3 for SS reinforced beams. The ultimate moment capacity of SS reinforced beams is observed 12–36% smaller than the code recommended capacity. The overall outcome of this study allows the engineers to think and apply SS as an alternative to MS as reinforcement of concrete beams.

Authors proposed to use low-bond high-strength reinforcement (LBHSR) as the longitudinal reinforcement of reinforced concrete (RC) columns to develop the self-centering RC engineering structures based on the experimental conclusions that the LBHSR minimized residual deformation of test columns because of the low-bond high-strength property. Because the structural form of the proposed RC column was simple and the technology was low-cost, author proposed to use this type of RC column to fabricate the bridge column system. Two bridge archetypes with single and double columns reinforced by LBHSRs and high-bond normal-strength reinforcements (HBNSRs) were designed for numerical analysis using OpenSees program. A modified Young’s modulus of steel rebar was used to simulate the steel-bond slip behavior of the proposed RC column with LBHSRs, and the comparison results proved the applicability of this method. Based on the proposed OpenSees element model, seismic fragility and post-earthquake reparability of the designed bridge archetypes with LBHSRs and HBNSRs were compared based on the incremental dynamic analysis results. It was found that the use of LBHSR could greatly improve the post-earthquake reparability and reduce the collapse probability of bridge archetypes. The equations of the FEMA and JRA codes (FEMA, 2009; Tarfan et al., 2019) were used to predict the residual lateral drifts of bridge archetypes, and the comparison results indicated that both codes much overestimated the residual lateral drifts.

Low back disorder continues to be prevalent amongst construction workers, especially the rebar workers who are often engaged in repetitive stooping postures. Wearable robots, exoskeletons, are recent ergonomic interventions currently explored in the construction industry that have potentials of reducing the risks of low back pain by augmenting users’ body parts and reducing demands on the back. This paper presents the assessment of a commercially available passive wearable robot, BackX, designed for reducing low back disorder amongst rebar workers. The study evaluated the exoskeleton in terms of task performance and physiological conditions. Outcome measures such as completion time were employed to evaluate the effect of the exoskeleton on task performance, while activations of Erector Spinae and Latissimus Dorsi muscles, and perceived discomfort across body parts were employed to assess the physiological effects of the exoskeleton. The results indicated mixed effects of the exoskeleton on muscle activations. Although the results revealed that the exoskeleton can reduce muscle activations across the Latissimus Dorsi, mixed effects were observed for the Erector Spinae especially during the forward bending tasks. The exoskeleton reduced completion time by 50% during the rebar tasks. There was also a 100% reduction in perceived discomfort on the back, but discomfort was tripled at the chest region when the exoskeleton was worn. This study reveals the potentials of the exoskeleton for reducing low back disorder and improving productivity amongst the rebar workers. However, the unintended consequences such as increased discomfort at the chest region and activations of the muscles highlight the need for improving existing exoskeleton designs for construction work.

Steel rebars for reinforced concrete usually stated in a form of bar bending schedule. In a project, an inefficient activity of cutting steel rebar can result a waste in the form of trim loss. This can lead to profit loss and cause an impact to environment. The optimization needs to be done in order to minimize the trim loss from the steel rebar cutting. Previously, there has been many studies on steel bar trim loss optimization using metaheuristic methods as well as studies on cutting pattern generator. However, if the steel rebar variation is too many, the cutting pattern generator will produce a large number of cutting patterns. Therefore, this study aims to solve the optimization problem by producing more efficient cutting pattern while still obtaining minimum trim loss at any conditions. The data used in this research is obtained from a real-life office project. In the process, the study will be comparing the performance of both PSO and SOS from each cutting patterns generator and conditions. The performance of the two methods is assessed from its minimum, maximum, average, standard deviation and the convergence graph of each iteration. The result shows that SOS performed better in finding the minimum trim loss on undersupply condition.

Diaphragm wall was adopted for the subsurface excavation for LG06 underground station, one of the Wanda line stations in Taipei MRT, and it encountered many geological challenges during construction. The geological conditions in this zone are mostly clay and hard rock layer. The unconfined compression strengths of the extremely hard rock samples were tested during construction. The results were far beyond that obtained during site investigation, and hence is a big challenge for constructing the diaphragm wall. Furthermore, the Tai-power 161 kV high-voltage power cable box is longitudinally crossing the entire station zone. It leads to great difficulty during the construction of diaphragm walls. The neighbored houses are very close to the job site and cause a high risk of diaphragm wall construction. Engineers must find the solution to protect the Tai-power cable box and the adjacent houses to prevent any disasters. This paper presents how the borehole drilling method was adopted to conquer the complicated rock problem for diaphragm wall excavation. Engineers proposed a unique method by moving the rebar cage horizontally to avoid damaging the 161 kV power concrete box. Besides, a series of grouting piles with reinforcing bars were installed before excavating guide ditches for the diaphragm wall. With the innovative mitigations, the challenges, as mentioned earlier, have been mitigated. Sustainable construction technologies were successfully executed for the diaphragm wall of the LG06 station project, Wanda line of Taipei MRT.

The reinforcing bar (rebar) produced by Tempcore process had tempered martensite structure on its surface, owing to quenching and tempering, and ferrite–pearlite structure at the core owing to slow cooling rate. Bainite, a low-temperature transformation phase, was observed in the transition area. Mechanical properties of the rebar are significantly influenced by area ratio and hardness of the tempered martensite. In this study, microstructure and area ratio of the tempered martensite of the rebar produced by the Tempcore process were predicted using finite volume method and a continuous cooling transformation diagram. The area ratio of the tempered martensite was predicted with error range of ± 6%. Furthermore, association between the microstructure and hardness was determined by a non-isothermal tempering experiment. The hardness of the tempered martensite was successfully predicted using the tempering temperature with R-squared 98%. The proposed methodology can be effectively used to control the mechanical properties of the rebars.

Super ductile thermo-mechanically treated (SD TMT) reinforcing steel bars are commonly used these days for RC constructions given their excellent thermal and seismic resistant properties. The superior performance of SD TMT rebars is due to their distinct cross-sectional phase distribution (CSPD) of martensite, bainite, and pearlite, which impart better combinations of strength and ductility than conventional classes of steel. This paper presents an investigation carried out to study the influence of corrosion-induced damage to cross-sectional phase distribution (CSPD) on mechanical properties of SD TMT bars in comparison with the performance of conventional mild steel and ordinary TMT steel bars exposed to an aggressive environment. The influence of corrosion-induced damage to cross-sectional phase distribution (CSPD) on the stress–strain response of SD TMT bars has been investigated through tensile tests in a displacement controlled UTM. The study involved tensile tests carried out on SD TMT bars corroded to 25 different levels ranging from (0–45%) on five different rebar diameters (8mmO, 10mmO, 12mmO, 16mmO and 20mmO). The results suggest better characteristic performance of SD TMT steel bars over conventional hot-rolled rebars in mechanical behaviour's critical aspects. A correlation predicting the reduction of mechanical properties of corroded TMT bars' residual capacity concerning corrosion percentage has been suggested.

Substitution of only steel rebar with fiber-reinforced polymer (FRP) or in combination with steel rebar has been recommended to reduce corrosion effects in steel rebar. This paper has pursued the impact of hybrid concrete beams reinforced with High Strength Steel Bars (HSS) and Glass Fiber-Reinforced Polymer Bars (GFRP) manufactured employing High-Performance Fiber-Reinforced Cementitious Composites (HPFRCC) instead of conventional concrete through experimental tests. Seven concrete beams including conventional concrete and HPFRCC in three separate groups, having identical compressive strengths and longitudinal steel reinforcement ratios, have been tested following respected codes and regulations to supply sufficient development lengths using GFRP headed bars, under four-point loading tests. The first and second groups, each represented one conventional concrete beam and an HPFRCC model with GRFP or HSS; the third group included three HPFRCC beams using GRFP and Steel rebar to assess flexural behavior of beams under different reinforcement ratios. Experimental results indicated that HPFRCC beams demonstrated improvements in their load capacity, flexural strength, bending stiffness, ductility, and energy absorption compared to similar conventional concrete beams. Also, in hybrid beams compared to steel reinforced concrete beams both cast with HPFRCC, the more the effective reinforcement ratio of both single and hybrid bars increased, the more ductility was improved between 37 and 88 percent. Displacement ductility of hybrid beams having effective reinforcement ratios up to 1.35 and 1.25 times more than the balance ratio was increased 23 and 37.5 percent, respectively. Energy absorption for HPFRCC beams reinforced only with GFRP or steel rebar was increased 31 and 250 percent compared to identical conventional concrete beams, respectively. In hybrid compared to GFRP reinforced beams both cast with HPFRCC, the more effective reinforcement ratio increased, the more energy absorption was increased in a range of 51 up to 174 percent. Therefore, it can be concluded that using the hybrid of GFRP and HSS bars result in up to 30 percent improvement in flexural strength because of the effective performance of GFRP after steel rebar yielding and ductility increase due to HSSs yielding.

The external wall insulation and fire prevention problems are hard to solve due to the lack of economical insulating and flame-retardant materials. By taking the wallboard structure as the cut-in point, a novel ceramsite concrete composite wallboard is proposed in this study, which inputs the insulation materials inbetween two wallboards to not only solve the fire prevention problem of the insulation materials thoroughly, but also prevent peeling-off of insulation wall during the construction and using processes. In order to apply this type of wallboard in shear wall structure, a T-shaped joint component of the new ceramsite concrete composite wallboard that adopts U-shaped rebar connection way is proposed in this paper as well. Three same specimens and one contrast specimen are designed in total. Meanwhile the seismic performance of the joint is also studied through the low-cyclic reversed loading experiment. And both the experimental phenomenon and the failure mechanism show that, shearing failure is the failure form of the specimen. The core area of the joint plays a dominating role during the stress process. By analyzing the seismic parameters of the specimen, such as hysteresis, skeleton, ductility and energy consumption, conclusions are made that the specimen is featured in good overall seismic performance, meeting the design requirement of “strong joint, weak component” in the specifications. The study on the T-shaped joint of the novel ceramsite concrete wallboard complements the connection methods of this new type of insulation wallboard, and provides a reliable basis for applying this type of wallboard in practical construction.

To reduce the amount of reinforcement and control crack width, ultra-high strength rebar reinforced Engineered Cementitious Composites (UHSRRE) beams are considered a promising choice. A model is developed for predicting the flexure deflection of UHSRRE beams in service stage based on internal force equilibrium and the compatibility of deformation. In this model, the bilinear stress–strain model for Engineered Cementitious Composites (ECC) and ultra-high strength rebar is adopted, and the tensile zone of UHSRRE beams is considered. The flexure tests of seven beams with different reinforcing ratios and matrix materials are carried out for verifying the proposed model. It is observed that the experimental results are basically consistent with the predicted results. This model can provide a useful tool for the calculation of deflection. Additionally, parametric analysis is conducted to analyze the influence of reinforcement bars and matrix materials on the bending deformation of UHSRRE beams. Through comparison of the results, it is found that using higher strength grade bars not only reduces the amount of reinforcement but also maintains excellent bending performance.

Polymer coatings can be used to mitigate the corrosion of steel in high-chloride environments. Obtaining speciation information from thin corrosion layers can be important for understanding corrosion mechanisms, including polymer coating failure. This study outlines the effectiveness of collecting glancing angle x-ray absorption near edge spectroscopy (GA-XANES) spectra at the Fe K-edge to obtain chemical speciation information at the polymer/steel interface without removal of the polymer film. The depth of penetration of the incident x rays can be altered by changing the incidence angle, allowing for more fluorescence signal from corrosion products to be detected relative to the Fe metal fluorescence signal in GA-XANES spectra. This study demonstrates the use of GA-XANES to study thin layers of steel corrosion and obtain depth profile information of steel corrosion products beneath a polymethyl methacrylate polymer coating.

Based on magnetic medium theory, a newly invited magnetic corrosion detector (MCD) showed great potential in quantitative monitoring the corrosion process of steel rebar in concrete. To furtherly explore the application performance of MCD, a numerical model was established to simulate the magnetic induction intensity variation caused by corrosion of steel rebar. And the influence of the length and the positioning variance of steel rebar on the measurement were discussed based on experimental and numerical investigation. The research results indicate that the numerical simulation is a valid approach to reveal the essential performance of MCD in measuring the corrosion ratio of steel rebar in concrete. Based on the geometric and physical properties of MCD, the corrosion ratio of the steel rebar can be effectively measured. And the positioning variance of steel rebar has significant influence on the precision and sensitivity of MCD. It is suggested that the steel rebar should be placed right at the center of the test area during the measurement to achieve a high accuracy.

This article presents the materials of deformability studies of pre-stressed steel-concrete beams reinforced with a package of reinforcement with different ratio of tape and rebar in the pure bending moment zone. The aim of the research was determination of the reinforcement percentage influence, for pre-stressed reinforced concrete beams reinforced with a package of reinforcement on their deformability. Also, the aim was to evaluate the effectiveness of using pre-stressed rebar in combined reinforcement. The practical significance of the experimental research is to study the deformability in pre-stressed bending elements with external tape and rebar reinforcement, taking into account the influence of different ratios of reinforcement areas within the combined reinforcement and development of proposals for such structures` calculation and design. The scientific novelty of the research is in obtaining the deformability characteristics of reinforced concrete beams reinforced with a package of reinforcement (tape and steel bars with periodic profile) with different ratios in the case of static loads` action.

The present study has been focused on the environment-friendly corrosion inhibitor. Conifer cone (Pinus resinosa) has been used as a novel corrosion inhibitor to mitigate the corrosion of steel rebars in simulated concrete pore solutions (SCPS) in the presence and absence of chloride ions. The corrosion inhibitor is extracted by simple chemical methods. The functional groups present in the extracted conifer cone (ECC) powder are characterized as well as the surface morphology of ECC has been examined. The corrosion inhibition performance has been evaluated by the electrochemical and weight loss methods. The experimental results indicate that ECC possesses a corrosion inhibition efficiency of 81.2% at a dosage of 1000 mg·L-1, after 720 h of immersion in chloride-contaminated SCPS. Adsorption isotherm and their standard Gibbs free energy (ΔGads0) values are calculated by Langmuir, Freundlich, and Temkin isotherm methods, and the results indicate that the ECC is initially adsorbed on the steel rebar surface by physisorption and then it turns to chemisorption. The steel rebar surfaces have been characterized after exposure to the ECC containing SCPS, and the results indicate that the ECC containing cationic adsorbate molecules, which interact with steel rebar, leads to retardation of metal dissolution in corrosive chloride medium.

Roadways in thick coal seams are widely distributed in China. However, due to the relatively developed cracks and brittleness of coal, the support failure of thick-coal-seam roadways frequently occurs. Therefore, the study of bolt failure characteristics and new anchoring technology is very important for the safety control of thick-coal-seam roadways. Based on field observations, the failure mechanism of selected roadway failures under distinct conditions at three representative coal mines in eastern and western China was analyzed. Recommendations are provided for roadway safety control. The results show that the strength and dimension of the anchoring structure in the coal roof of thick-coal-seam roadways are the decisive factors for the resistance of the roadway convergence and stress disturbance. The thick anchoring structure in the roof constructed by flexible long bolts can effectively solve the problem of support failure caused by insufficient support length of traditional rebar bolts under the condition of extra-thick coal roof and thick coal roof with weak interlayers. The concepts and techniques presented in the paper provide a reference for the design of roadway support under similar geological conditions and dynamic load.

A simplified reinforcement model is proposed to consider the effects of both corrosion and reinforcement slip-on seismic performance of reinforced concrete columns. The mechanical properties deterioration of corroded reinforcement are obtained by regression analysis of the available experimental data. Since corrosion may also have a significant influence on bond-slip, a local bond-slip curve with corrosion effect is constructed, by shifting the curve for uncorroded rebar in the slip direction. To fully consider the non-uniformity of bond stress distribution along the development length, a stepped equivalent bond stress is used to simplify the integral calculation of theoretical slip. Subsequently, the cumulative slip and the equivalent strain with slip effect are formulated to modify the parameters of monotonic and hysteretic models of perfectly bonded corroded reinforcement. The response of corroded reinforced concrete columns under cyclic loading is simulated by the fiber section beam element model. Finally, the numerical simulation results and the experimental data are compared. The results show that the ignorance of slip will overestimate the stiffness and bearing capacity of the column by 28.3 and 13.5% respectively, and the yield load, peak load and peak lateral displacement of column decrease with corrosion in longitudinal reinforcement gradually, by 33.8, 16.3 and 56.6% for mass loss percentage 8.0%, respectively. This confirms the ability of the proposed model to simulate the nonlinear seismic response of structures in a corrosive environment.

In a comprehensive investigation, the simultaneous effectiveness of the factors of temperature (five temperatures), volume ratio of steel fibers (three volume ratios), and concrete cover thickness over the rebar (three covers) on the compressive strength, tensile strength, and concrete-steel rebar bond behavior was evaluated. 180 specimens comprised of 45 cubic specimens for the compression test, 45 cylindrical specimens for the splitting tensile strength test, and 90 prismatic specimens for the pull-out test were made. The results demonstrated raising the temperature reduced the compressive strength such that the strength of the plain specimens after exposure to 800 ℃ declined by 71.6%, compared to that of the corresponding non-heated specimens. Moreover, at a given temperature, the presence of steel fibers improved the tensile strength. After exposure to 800 ℃, the tensile strength of specimens with 1% steel fibers in volume was 127.9% higher than that of similar specimens without fibers. At a given temperature, the use and content of steel fibers had an effective role in compensating for losses in the tensile strength and bond strength induced by applying heat. Furthermore, as the concrete cover over the rebar increased, the failure mode became more ductile. The effect of steel fibers on increasing the bond strength of the specimens with a thinner concrete cover heated at elevated temperature was greater and more noticeable. Also, the concrete cover over the rebar had an effective role in compensating for the heat-induced bond strength loss, such that increasing the concrete cover from 25 to 65 mm easily compensated for the concrete-rebar bond strength reduction for every 200 ℃ increment in the exposure temperature.

Spliced region is a place where the concrete-rebar bond plays a significant role, and reduced bond strength in this region negatively affects the structure safety and integrity due to corrosion. This research has studied the combined corrosion effects of the main reinforcements and stirrups in the spliced region on the concrete-rebar bond strength in lap-spliced beams. A total of 15 lap-spliced RC beams with different stirrup spacing in the spliced region failed under 4-point bending; tensile bar and stirrup corrosions were the variables in this study. Finally, Response Surface Methodology (RSM) was used for estimating the relative bond strength of this beams. According to the results, adding corroded stirrups in the spliced region will cause negative effects on the bond strength in beam specimens via combined tensile bar-stirrup corrosion in the spliced region. Gradients in the descending part of the curve for relative bond strength versus corrosion were calculated at −0.0154, −0.016 and −0.017 when stirrups are 1, 2 and 3, respectively. Also, beams with 25% corrosion have the largest increase in the stirrup-induced bond strength. The results show that the model presented by RSM is in good agreement with the experimental results.

The effect of additives on the performance, durability and multi-functional service sustainability of a novel self-compacting concrete (SCC) was investigated in this research. Constant partial replacement of cement with 40% fly ash and admixture of M25 grade conplast SP 430 were used to form the SCC. This was followed with the addition of varying amount (0–4%) of diethanolamine as an organic corrosion inhibitor, while one set of concrete was made without the additive, to act as a control. The effect of the additives on the compressive strength, split tensile strength, the corrosion rate of the reinforcement steel rebar and the ability of electrical energy being harnessed from the concrete were analyzed. It was observed that the amount of diethanolamine to be added for maximum enhancement of mechanical properties and corrosion resistance of SCC was 3.2%. The mechanical properties of the SCC and its corrosion resistance were found to be better. Also, the energy that could power some DC components and devices was harvested or generated from the concrete beam. Hence, the study concluded that diethanolamine is a good corrosion inhibitor for reinforced concrete steel rebar and that the presence of fly ash and admixture of M25 grade conplast SP 430, strengthened the concrete.

Objective: To design, fabricate and evaluate the new features of a portable manual rebar bender, a Hand Tool that is used for bending rebar and other malleable materials. Methods: The researcher improves on the previously available portable manual rebar bender. Experts assessed the acceptability of this bender in terms of design and portability. Furthermore, as previously stated, the study significantly improves the usefulness of the inexpensively produced bending machine for reinforcing concrete with negligible human force. Findings: The device created has a valuable impact on the construction industry’s human force due to its affordability and marketability. Also,the present tools guaranteed strength, durability, and lightness in weight. Furthermore, the portable manual rebar is made of different elements such as a center axle, stationary backup roller, and sleeve. The results after ten trials showed that the portable manual rebar bender could finish 9 mm, 20mm, and 12 mm stirrup at an average of 24.3 seconds, 26.3 seconds, and 27.7 seconds, respectively. Additional results from seven to ten trials showed the bending time for 24 seconds stirrup for 9mm, 26 seconds stirrups for 10 mm, and 28 seconds stirrup for 12 mm. Furthermore, after a series of ten trials, the instrument achieved an accurate angle bent of 90 degrees. The M= 4.77 and 4.82 are very acceptable in terms of design and portability tools based on the evaluators’ rating. Novelty: The design is novel in terms of cost, portability, and efficiency. The device can be a great help in the structures and buildings. Furthermore, the construction industry will use the portable manual rebar bender to build houses and other local infrastructure to test its effectiveness. Then, the researcher is encouraged to engage in another research to try the innovation. Keywords: Improvised; Innovative; Locally made; Device; Bender

Reinforcement corrosion is a major culprit that undermines the service life of reinforced concrete (RC) structures. It costs billions of dollars each year in the US alone and negatively impacts safety, reliability, resilience, and environmental performance of RC infrastructure. Corrosion monitoring of steel rebar is critical to provide early warning of deficiency, enable timely and effective maintenance strategies, and prevent catastrophes associated with premature failure of RC structures. To improve corrosion monitoring in the engineering practice, this work comprehensively reviews the state of the art of five major types of techniques, that is, electrochemical sensors, optical fiber sensors, sensors based on elastic wave methods, sensing based on electromagnetic methods, and untouched sensors. Each type of technique is systematically divided into sub-categories based on the sensing principle and key characteristics. For each sensor type, its maturity, application range, and the problems that hinder its application are discussed, aimed to provide guidance in selecting the appropriate sensors for specific engineering applications. This work concludes with an overview of opportunities and challenges, including the following six aspects for future research: spatial resolution, sensitivity, and measurement range; reliability and interpretation of the measurement; sensor selection based on three corrosion stages of steel rebar; long-term stability and service life; cost-efficiency of the sensing system; and monitoring of existing structure.

The paper shows the results of an experimental campaign aimed at investigating the cyclic behavior of a column-to-foundation joint for precast concrete elements. The tested connection is realized adopting corrugated steel ducts embedded into the foundation, in which column protruding rebars are anchored by grouting high performance mortar. The experimental program consists in testing six full-scale reinforced concrete square-section columns subject to quasi-static cyclic lateral load with a constant axial compression. A preliminary series of bond tests was carried out to define some experimental variables, i.e., longitudinal rebar diameter and anchorage length. Results of the precast joints are compared with those of two reference cast-in-place specimens with the same geometric characteristics, showing similar hysteretic behavior, energy dissipation and ductility values. Lastly, the plastic hinge height is computed for all the specimens based on experimental concrete strains, and compared to current codes formulations.

This article presents the results of experimental studies of reinforcement with prestressed basalt-composite rebar in the tensile zone of the structure. The studies were performed on beam type models, taking into account the characteristic aspects of the reinforced concrete structures of the hydraulic engineering construction (HEC). Reinforcement is made by the method of tension “on concrete.” The models were tested for bending moment and transverse force.

Combining fiber reinforced polymer (FRP) with seawater sea-sand concrete (SSC) can solve the shortage of river sand that will be used for marine engineering construction. The bond performance of BFRP bars and SSC specimens is researched by pull-out test in this paper. The effects of the parameters, such as bar type, bar diameter, concrete type and stirrup restraint, are considered. It is beneficial to the bonding performance by the reduction of bar diameter. The utilization of seawater sea-sand has a low influence on the bond properties of concrete. The bond strength of BFRP is slightly lower than the steel rebar, but the difference is relatively small. The failure mode of the specimen can be changed and the interfacial bond stress can be improved by stirrups restraint. The bond-slip curves of BFRP ribbed rebar include micro slip stage, slip stage, descent stage and residual stage. The bond stress shows the cycle attenuation pattern of sine in the residual stage. In addition, the bond-slip model of BFRP and SSC is obtained according to the experimental results and related literature, while the predicted curve is also consistent well with the measured curve.

A model is developed for moisture absorption by rebar made of basalt fiber-reinforced polymer composite (BFRP), taking account of Fick diffusion, structural relaxation, and the design features of the rebar in the initial stages of climatic aging. The model is experimentally confirmed. The analytical solution may be used for kinematic approximation of moisture absorption by other reinforced polymer composites.

The formation of open porosity in rebar made of basalt fiber-reinforced polymer composite (BFRP) is investigated during exposure tests in northern climates. A statistical model is proposed for pore formation in BFRP rebar.

Ground-penetrating radar (GPR) has been widely applied to the nondestructive inspection of concrete structures such as tunnel lining, bridge deck, and retaining wall, which are usually reinforced by steel bars. The scattering of electromagnetic (EM) waves caused by the dense steel rebar embedded in the concrete structures has a severe influence on the penetration capacity of GPR waves. In this letter, the scattering and penetration characteristics of EM waves propagating through rebar net are investigated via both numerical and laboratory experiments, with an aim to select the antenna nominal frequency for a different reinforcement density. The results show that the rebar, which is perpendicular to the polarization direction of GPR waves and has a very small diameter compared with the wavelength, is almost transparent to the impinged GPR waves. The scattering and interaction of GPR waves caused by the rebar that is parallel to the polarization direction result in a shielding effect, which is manifested as a blind band in the low-frequency range in the transmitted spectrum. This result violates the rule of thumb commonly used in the GPR community, i.e., the lower frequency has a deeper GPR penetration depth. In the end, a low cutoff frequency is recommended for selecting a GPR antenna with an appropriate nominal frequency when it is used in the detection of an anomaly inside and behind a reinforced concrete structure, in which the spacing of the rebar net is known.

A technique to enhance the mechanical and thermal properties of flat radomes integrated with high-power horns is presented. Specifically, metallic strips, referred to as rebars (from reinforcing bars), are deployed as structural reinforcement across the radome-enclosed antenna aperture. This enables the use of thinner, more fragile materials, with lower loss and permittivity, as protective covers without detrimentally affecting the RF performance. A maximum gain greater than 15.4 dBi and voltage standing wave ratio (VSWR) < 1.5 are maintained with the rebar across the 18–45 GHz band for a given horn and radome. Moreover, the pressurization handling for the baseline radome is improved from 5 to 14 psig while theoretically maintaining the ability to support 750 W of continuous wave power. The studies are carried out in the electrical, thermal, and mechanical domains.

The shape memory alloys (SMAs) are special materials able to withstand large non-elastic deformations regaining their original form by removing stress. High fatigue strength and proper resistance to corrosive agents are the specific characteristics of these alloys. This article explores the SMA and carbon fiber reinforced polymer (CFRP) at designated points of reinforced concrete (RC) structures to evaluate the behavior against selected earthquakes. Three RC frames with 5, 10 and 15 stories were modeled and various cases were considered for SMA location in different story levels and for each structure, there are 8 different cases. In the first part, the incremental dynamic analysis (IDA) was employed to assess the entire range of structural dynamic behavior using 13 ground-motion far-field records set. In the second part, by using the produced data from IDA method, fragility evaluation was conducted on multiple limit states to provide a comprehensive performance assessment for each case. The extracted graphs show that the strengthening of the frames studied by the SMA rebar and the CFRP layers, causes an increase in the maximum drift rates and spectral acceleration (Sa) and thus increases the ductility. Consequently, the rate of probability of seismic damage decreased and the frame is more resistant to collapse.

A substantial amount of work was carried out on the use of fiber-reinforced polymer (FRP) in reinforced concrete structural elements, which demonstrated considerable inelasticity or deformity through monotonic and cyclic loads. Even so, the action of FRP bars in reinforced concrete columns and frame structures has not yet been studied during reversed cyclic loading. In this research, reversed cyclic loading was applied on three beam-column joint models using the finite element method with ANSYS software. The first model was for a joint designed with steel rebar for both the longitudinal and transversal reinforcement. Glass fiber reinforced polymer (GFRP) rebar was used in the second joint model for the longitudinal reinforcement with steel transversal reinforcement. The third joint model was designed with hybrid steel/GFRP reinforcement for the longitudinal reinforcement and steel transversal reinforcement. The performance of the three models under reversed cyclic loading, such as load vs. story drift and energy dissipation capacity, were compared. The GFRP-reinforced model displayed a predominantly elastic behavior up to failure. Although its energy dissipation was lower, its performance in terms of total story drift demand was satisfactory

The present work deals with the investigation of core compressive strength in reinforced concrete column with the slip angle orientation and bond stress relationship using Magneto rheological fluid...

As part of ongoing research to validate the efficacy of a potentiodynamic polarization technique of determining the critical chloride threshold (CCRIT) value of steel reinforcing bars exposed to ch...