Search

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.

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.

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.

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.

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.

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.

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.

Relevance. In recent years, composite materials have become widespread in the construction of reinforced concrete structures for industrial, civil and transport structures. It is proposed to strengthen the reinforced concrete structures of hydraulic structures with prestressed basalt composite rebar. It took an experimental and theoretical substantiation of technical solutions to strengthen the reinforced concrete structures of hydraulic structures with prestressed basalt composite reinforcement. The aim of the work was to carry out a set of experimental and theoretical studies of the stress-strain state and internal forces in low-reinforced concrete structures of hydraulic structures reinforced with prestressed basalt composite rebar. Methods. Experimental studies of the stress-strain state and internal forces were carried out on the basis of low-reinforced concrete beam-type models with interblock construction joints, harden with prestressed basalt composite reinforcement in the stretched (compressed) zones of the models. Theoretical studies of the stress-strain state and internal forces were carried out on the basis of the theory of reinforced concrete and structural mechanics. Results. As a result of the research carried out on typical low-reinforced concrete structures of hydraulic structures with interblock construction joints, the main stages of the stress-strain state of hydraulic reinforced concrete structures were formulated. Based on the data of experimental and theoretical studies, taking into account the reinforcement with prestressed basalt composite rebar, as well as with prestressed clamps in the shear zone, a method was developed for calculating the strength of low-reinforced hydrotechnical reinforced concrete structures with interblock construction joints.

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.

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.

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.

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.

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

Experimental testing of deformed rebar anchors (DRAs) has not been performed extensively, so there is limited test data to understand their failure behavior. This study aims to expand upon these limited tests and understand the behavior of these anchors, when loaded in tension. Analytical benchmark models were created using available test data and a parametric study of deformed rebar anchors was performed. Anchor diameter, spacing, embedment, and number of anchors were varied for a total of 49 concrete breakout simulations. The different failure modes of anchors were predicted analytically, which showed that concrete breakout failure is prominent in the DRA groups. The predicted concrete breakout values were consistent with mean and 5% fractile concrete capacities determined from the ACI concrete capacity design (CCD) method. The 5% fractile factor determined empirically from the simulation results was kc = 26. This value corresponds closely with kc = 24 specified in ACI 318-19 and ACI 349-13 for cast-in place anchors. The analysis results show that the ACI CCD formula can be conservatively used to design DRAs loaded in tension by applying a kc factor no greater than 26.

When utilizing ultra-high performance concrete (UHPC) and normal strength concrete (NSC) together, the interface between the UHPC and NSC in this composite structural member is essential and needs to be clearly understood. In this paper, push-off tests are carried out on 10 UHPC-NSC joint specimens with considerations of the castellated key size and the use of dowel rebar. The effect of the cohesion between the UHPC and NSC on the interfacial shear resistance is found to be very limited and can be ignored. The UHPC-NSC joints with castellated keys of 10 mm have the best mechanical performance if no dowel rebar is applied. When there is dowel rebar in the joint specimens, the specimens have shear resistance with post-peak residual loads. The dowel rebar configured specimens with larger castellated keys have higher residual shear resistances because of the improved post-peak residual interlocking effect.

Regular construction practices focus makes use ofreinforcing bars for transferring forces. Method of lap Splice isgenerally used for ensuring continuity of reinforcement steel.However, this method results in minor defects such as jointfailure, inadequate length for lapping, improper welding ofbars, increased cost of labor etc.A comparative study of column reinforcement with couplersand without couplers as lap splices was carried out through acase study of an under construction building. Initially thequantity of reinforcing bars required for conventional lapsplicing of columns was estimated. The value of steel forproviding lap splices within the columns was also determined.Finite element analysis of coupled rebar is carried out to checkfor the yielding and ultimate stresses developed. These valuesare verified with that specified in the code. The use of couplerssignificantly decreases construction time and quantity of steelrequired in lapping.The use of couplers as lap splices provides an economic wayof connecting reinforcement without adversely affecting thestrength of the joint.

Due to the rapidly increasing urbanisation in China, the energy consumption of buildings and infrastructures has increased; this has resulted in environmental problems such as excessive carbon emissions. Increasing the strength of steel rebars enables manufacturers to use less steel and save more energy. The micro-alloyed 635 MPa hot-rolled ribbed high strength rebars (HRHSR) offer the advantages of high strength, good ductility, and low costs, compared to ordinary rebars. Bond anchorage is one of the key problems that limits the promotion and application of 635 MPa HRHSRs in practice. In this study, the bond properties of 635 MPa HRHSRs embedded in concrete subjected to monotonic loads were investigated. A total of 120 specimens, which consisted of 60 simple-anchored and 60 hooked-anchored specimens, were subjected to direct pull-out tests to evaluate the effects of anchorage length, hoop ratio, concrete cover, rebar diameter, concrete strength, and anchorage types on the anchorage feature. Meanwhile, the mechanical properties and failure modes of 635 MPa HRHSRs were also analysed. The results demonstrated that the concrete compressive strength, cover size, anchorage length, and stirrups ratio had a positive influence on the ultimate bond strength, whereas the bar size had a negative influence on the ultimate bond strength. Furthermore, four typical failure modes were analysed, including rebar yielding, concrete splitting, concrete crushing, and rebar rupturing, which occurred during the pull-out tests. Thereafter, a modified equation for calculating the ultimate bond strength of 635 MPa HRHSRs in concrete was derived based on the mechanical model and further verified using the test data. This study is expected to be beneficial in promoting the widespread application of 635 MPa HRHSRs and enabling resource savings in the future.

Additional hysteretic experiments for corroded rectangular reinforced concrete (RC) columns with an axial load ratio of 0.27 were implemented. A quasi-static cyclic lateral loading with constant axial force was subjected to tests. Herein, a modified ductility factor model for corroded RC column is developed on the basis of the previous work and additional experiments. The model involves the influence of both the corrosion ratio of longitudinal rebar and the axial load ratio. A four-linear envelope curve model concerning lateral load and displacement is proposed in a combination of determination rules of the peak point and the failure strength point. The hysteretic model of corroded RC columns is developed by considering both degraded unloading stiffness and reloading stiffness on the history peak point. The hysteretic model can predict the residual life of corroded RC columns under seismic loading.

A new 3D finite element model is presented to analyze creep in reinforced concrete (RC) and prestressed concrete (PC) bridges. The proposed hybrid model uses a 12-node solid element to simulate concrete and a 2-node truss element to simulate rebars, the volume occupied by rebars in concrete and ducts. Structures are meshed with a special meshing technique and truss element connects with solid element through non-nodal connection. In this study, an additional two-node spatial truss element with a negative area is introduced to consider the non-negligible influence of rebar ducts in concrete and obtain a more precise and efficient simulation of RC and PC bridges. Different uses of the truss element with a negative area in both RC and PC structures are also explained, and two drop-frame cases and associated construction stages are investigated to validate the applicability of this model. The construction process analysis of a simplified PC continuous rigid frame bridge is also conducted in this study to further demonstrate the ability of the newly developed program to capture shear lag effect. The results show that the proposed model with negative-area truss elements enables the long-term behavior of RC and PC structures to be effectively predicted.

This paper examines the performance of reinforced concrete girders under cyclic loading. Seven T-girders were casted and tested. All girders were loaded under different constant cyclic loading in the midspan with the load ratio of 0.14∼0.23 and frequency of 3∼4 Hz. The study shows that the longitudinal reinforcement fracture is the main cause of girder rupture. And during cyclic loading, the concrete cracks, strains, and deflections generally indicate a “three-stage” law. The measured data were small but developed quickly in the initial stage. Thereafter, the degradation gradually stabilized and continued for a long time. In the final stage, the cracks, strains, and stiffness degradation developed sharply and the girders failed quickly. The duration of the stage is very short and may be difficult to be caught. For the life estimation, the longitudinal rebar S-N curve is fitted using different collected data. The results show that the curve is in good agreement with the corresponding data, which may be an excellent candidate for the evaluation of fatigue life.

This paper presents a laboratory investigation on the performance of grouted rebar couplers with the connection details similar to those utilized on the precast concrete elements of the Keg Creek Bridge on US 6 in Iowa. The testing program consisted of a series of static load tests, a fatigue test, and evaluation of the chloride penetration resistance of laboratory specimens. The goal of this testing was to evaluate the ability of the grouted rebar couplers to develop flexural capacity at the joint between the precast elements as well as the durability of the connection. For structural load testing, seven full-scale specimens, each with #14 epoxy-coated rebars spliced by epoxy-coated grouted couplers, were fabricated and tested in three different loading cases: four-point bending, axial tension plus bending, and a cyclic test of the system in bending. The static load testing demonstrated that the applied axial load had a minimal effect on the formation of cracks and overall performance of the connection. When ultra-high performance concrete was used as a bedding grout, the initiation of crack was slightly delayed but no considerable improvement was observed in the magnitude of the crack width during loading or the crack closure on unloading. The results of the seventh specimen, tested in fatigue to 1 million cycles, showed little global displacement and crack width throughout the test, neither of which expanded measurably. No evidence of moisture or chloride penetration was detected at the grouted joint during the 6-month monitoring.

In recent years, the deterioration of harbor structures has become a matter for concern, and the establishment of effective repair methods has become urgent. In this study, a repair method for installing permanent formwork panels and filling them with underwater inseparable mortar is proposed as an effective section-restoring method for deteriorated concrete caisson sidewalls. To investigate the integrity between existing concrete and repaired parts as well as the effect of thickness increase due to panel installation, static bending tests of a flat-reinforced concrete (RC)-beam-modeled side wall used in caisson structures are conducted. The results obtained from this study are as follows: (1) by attaching the permanent formwork panels to the flat RC beam, the bending crack occurring load was improved by a factor of three, and the rebar yielding load and maximum load were doubled. This tendency was the same even when the RC beam had a cross-sectional defect. (2) The RC beam with the permanent formwork panels finally failed with diagonal cracks opening after the maximum load was reached. The ductility ratio at this time was approximately 6. To improve the deformation performance, it is necessary to apply shear reinforcement. (3) The analysis results by the fiber model assuming the complete adhesion of the permanent formwork panels, underwater inseparable mortar, and RC beam were performed, and the results were compared with the experimental results. As a result, it was clarified that the adhesion of each constituent material was retained until the yield of the main reinforcing bar. After that, pulling out of the main reinforcing bar from the concrete and damage to the permanent formwork panel became apparent. (4) The curvature of the cross-section at the yield of the main reinforcing bar was φyc = 0.007 m−1, and it was confirmed that the assumption of plane conservation was valid in the cross-section with a curvature less than that. This research is expected to promote the efficient maintenance of existing concrete caisson structures. As the amount of cement used and the construction period can be reduced, it is assumed that the environmental load can be reduced as well.

Gas protective walls are safety elements that can withstand the pressure of fires or explosions caused by gas leaks, thus preventing the spread of explosion damage to other facilities or operators. However, in the new construction or expansion of gas facility rooms in existing buildings, the barrier must often be built even if it does not satisfy the legal standards regarding the accepted construction methods. In these cases, the gas barrier for the existing building should be constructed by the new construction method using chemical anchor bolts. However, no performance evaluation data or reliable engineering verification results are available for the entire gas facility room based on actual experiments. In this study, based on a review of regulations on gas barriers, the protective performances of the new barriers were compared in terms of displacement, rotation angle, rebar strain, and yield value of the concrete surface through actual strength demonstration experiments. Based on these results, the protection performance of an entire gas facility room that could not be constructed and tested in real time was evaluated by a fluid structure interaction (FSI) analysis using the TNT(Trinitrotoluene) equivalency method and three-dimensional AUTODYN.

This paper presents a novel configuration of high strength U-shaped steel-encased concrete composite beam (HUCB) in which shear studs connect concrete and U-shaped steel at top flanges and bottom plate. The junction surface of upper slab and lower portion is strengthened by evenly distributed inserted circular rebar. Two steel reinforcements are arranged in the composite beam along the longitudinal direction to reduce the deformation of encased concrete and provide adequate bending capacity under fire condition. Based on the flexural experiments of five specimens, the test failure pattern, load-deflection relation curves, sectional strain distribution at different height and ultimate flexural performance of the HUCB were obtained and are reported in this research. The experimental results show that the HUCB has high ductility and excellent flexural performance. According to test results of five specimens, new calculation formulae were presented to theoretically analyze the flexural capacity of the HUCB. The theoretical analysis values of flexural capacity according to the proposed calculation formulae are consistent with the test results of all specimens. A three-dimensional finite element model is also established to investigate structural performance of the proposed novel composite beam. Test results of five specimens verify the accuracy and validity of finite element analysis results. Parametric studies of the HUCB under positive bending moment are carried out to further analyse the influence of concrete compressive strength, yield strength of U-shaped steel plate and flange width of concrete slab on the flexural performance of the proposed new composite beam.

This paper describes the role of epoxy resin in the development of advanced building materials. It reviews in brief the growth of epoxy resin-based high-performance concrete and masonry mortar technology, and epoxy resin as protective coating on mild-steel bar (rebar) for concrete reinforcement. Literature survey reveals that the properties of concrete could be improved significantly with the variation of concentration of the epoxy resin in the composition of polymer-modified concrete (PMC), and that makes the PMC very versatile in applications. Challenges on the use of epoxy resin in the concrete and masonry mortar composition and contribution of the resin on the mechanical and physical properties of building materials have been described. Some ambiguous results on epoxy resin-based concrete available in the literature have been verified in the laboratory, and the confusions have been diffused. Performance of the epoxy resin as a protective coating on rebar has also been discussed. Experimental results show that epoxy resin-based concrete exhibits high compressive strength, less chloride-ion permeation and high chemical resistance to the corrosive environment. Finally, the perspectives of epoxy resin for overall use in building materials and also in specific applications such as repairing of building, the protection of constructions from flood, saline water, and prevention of liquid from penetration into interior of materials have been discussed.

This study investigates the behavior and the load-bearing mechanism of a typical flat slab with rectangular panels in several scenarios including the removal of a corner, penultimate, and internal columns. The scenarios are rather similar to those used in the conventional evaluation of the progressive collapse potential; however, application of the uniformly distributed loading over panels adjacent to the removed columns was not limited to twice the value of the initial load. Thus, load-deflection curves were drawn up to the point in which a great number of longitudinal slab bars ruptured. Introducing 5 stages on each curve, finite element outputs on concrete cracking pattern and rebar stress state were presented. A significant increase in the stresses along the diagonals of the slab panels accompanied by bar ruptures around columns adjacent to the removed column proved contribution of an important load-bearing mechanism in addition to the behavior called “quasiframe action.” Consecutive rupture of bars showed formation of a zipper-type collapse mode as well as a great tendency to transfer load share of missing column mainly along shorter direction of slab panels. Moreover, the findings indicated that the slab damaged zone could exceed the panels under uniform overloading.

Reinforcing steel bars (rebars) in the concrete need to be inspected to prevent the structure from collapsing. Magnetic nondestructive testing methods can inspect the rebar without the influence of concrete. However, since the inspection is performed at a high lift-off on concrete, a strong applied magnetic field is required in order to measure a sufficient magnetic signal generated from the rebar. In addition, if a single sensor is used to measure the rebar, this requires the scanning of extensive area along the invisible rebar covered with the concrete. To overcome these problems, we have developed a method to detect and image the defect signal using unsaturated ac magnetic flux leakage (USAC-MFL) testing combining a magnetic sensor array probe. The USAC-MFL is a method that uses an alternating magnetic field in the initial magnetization characteristics of steel, which does not require a strong applied magnetic field compared to the conventional MFL method. By measuring the magnetic flux from the rebar in a wide area using the magnetic sensor array probe, the defect signal was able to be detected and imaged. The defect signal was able to be confirmed up to the lift-off of 100 mm even when the defect was half length of the rebar or located on the back side.

Background In revision total knee arthroplasty, osteolysis, mechanical abrasion, and infection may leave patellar bone stock severely attenuated with cavitary and/or segmental rim deficiencies that compromise fixation of patellar implant pegs. The purpose of this study was to retrospectively review the use of cortical “rebar” screws to augment cement fixation in revision patelloplasty. Methods From 2006 to 2018, dorsal patellar rebar technique was used for patellar reconstruction in 128 of 1037 revision total knee arthroplasty cases (12.3%). Follow-up was achieved with serial radiographs and prospective comparison of Knee Society Scores (KSSs) for clinical outcome. Complications and implant failures requiring reoperation or modified rehabilitation were also assessed. Results Of the 128 patellar revisions performed using the rebar technique, 69 patients were women and 59 patients were men. The average age of the group was 69.5 years (range, 32-83 years). The mean follow-up of the cohort was 37 months (range, 13-109 months). The most common causes for revision were kinematic conflict, periprosthetic joint infection, and aseptic loosening. The median number of rebar screws used was 5 (range, 1-13). Preoperative KSSs for the study cohort averaged 50 (range, 0-90) At latest follow-up, mean KSS was 85 (range, 54-100). There were 4 patellar-related complications (3.1%) with no implant failures at study conclusion. Retrieval analysis revealed rigid fixation of the reconstructed patellar component in all cases. Conclusions Patellar rebar screw augmentation is a useful technique when there are significant cavitary deficiencies and limited segmental rim deficiencies. This technique allows the surgeon to extend indications for patellar revision arthroplasty.

In actual production, deep coal mine roadways are often under typical static-dynamic coupling stress (SDCS) conditions with high ground stress and strong dynamic disturbances. With the increasing number of disasters and accidents induced by SDCS conditions, the safe and efficient production of coal mines is seriously threatened. Therefore, it is of great practical significance to study the deformation and failure characteristics of the roadway surrounding rock under SDCS. In this paper, the effects of different in-situ stress fields and dynamic load conditions on the surrounding rock are studied by numerical simulations, and the deformation and failure characteristics are obtained. According to the simulation results, the horizontal stress, vertical stress and dynamic disturbance have a positive correlation with the plastic failure of the surrounding rock. Among these factors, the influence of the dynamic disturbance is the most substantial. Under the same stress conditions, the extents of deformation and plastic failure of the roof and ribs are always greater than those of the floor. The effect of horizontal stresses on the roadway deformation is more notable than that of vertical stresses. The results indicate that for the roadway under high-stress conditions, the in-situ stress test must be strengthened first. After determining the magnitude of the in-situ stress, the location of the roadway should be reasonably arranged in the design to optimize the mining sequence. For roadways that are strongly disturbed by dynamic loads, rock supports (rebar/cable bolts, steel set etc.) that are capable of maintaining their effectiveness without failure after certain dynamic loads are required. The results of this study contribute to understanding the characteristics of the roadway deformation and failure under SDCS, and can be used to provide a basis for the support design and optimization under similar geological and geotechnical circumstances.

This paper introduces the structure and principle of a new isolation device—rebar isolation pier—which is mainly composed of vertical steel bar and asphalt ointment. It is used to reduce the earthquake action of the building structure. Compared with other isolation devices, the rebar isolation pier has the following advantages: simple structure, convenient construction, low cost, simple maintenance, and easy to fetch material. In the experiment, the test model is a two-layer frame, and the Taft wave and the Wolong wave were selected to simulate the actual earthquake. In order to study the damping effect of asphalt ointment, two different isolation piers (filled and unfilled with asphalt ointment) were included. The dynamic characteristics and isolation effect of the rebar isolation pier are studied by analysis of acceleration, displacement, and hysteresis loops. At the same time, according to the principle of energy method, the energy balance equation of the rebar isolation pier was proposed, and the total input energy and damping energy are used to analyze the energy of the isolation pier. The results demonstrate that the rebar isolation pier can effectively reduce the natural frequency, acceleration response, and absorbed seismic energy of the structure when the peak ground acceleration reaches 0.3 g, and it still has the potential to withstand greater seismic action.

In this research, prestressed concrete-encased CFST beams that incorporate CFST in the compression zone to improve the concrete strength, and prestressed strands in the tension zone to control cracks in reinforced concrete beams are numerically investigated. On account of the insufficient research and the unknown behavior of these beams, the study objective is the finite element analysis of parameters which are not feasible to be examined through experimental specimens such as the stress of steel and concrete, shear span-to-depth ratio, loading pattern, load transfer mechanism, in addition to longitudinal rebar ratio, prestressed strand ratio, core concrete ratio, and the steel tube ratio indices. Hence, the experimental study has been done to validate the nonlinear finite element modeling and a full-scale model is constructed to explore the flexural behavior of beams. The numerical results indicate the increasing effect of prestressed strand, longitudinal rebar, steel tube, and core concrete ratios, on the ultimate moment. The gain in the prestressed strand and longitudinal rebar ratios further escalate the flexural stiffness. Among investigated indices, the prestressed strand ratio has the greatest influence on elevating the flexural strength, the displacement ductility, and the entire absorbed energy. This is associated with the effect of the prestressed strand in improving the core concrete confinement, the tension zone crack control, and the cross section strengthening at the tension zone. Subsequently, a strut-and-tie model is proposed for the load transfer mechanism of beams. In addition, as the failure mode changes from flexural–shear to flexural, the ultimate moment capacity increases.

Reinforced concrete (RC) structures are applied widely in low-voltage transmission towers. However, the structural damage caused by the corrosion or fracture of rebar in cement towers seriously affects the safety of transmission lines. Thus, the accurate detection of rebar can effectively maintain cement towers. There are many methods for detecting rebar corrosion, but most of them cannot accurately locate the corrosion, and they do not consider the factors such as the depth of the rebar and the different types of rebar. Therefore, this article proposes a rebar corrosion detection method based on the change of peak slope of magnetic flux density. First, this article analyzes the common pitting corrosion in engineering, then theoretically analyzes the principle of magnetic induction detection of rebar. Then the magnetic flux density peak and the measured position on the 2-D coordinate are plotted, and the rebar corrosion is detected according to the slope. The peak function of flux density without corrosion is fit by the least squares method and the corrosion criterion is defined. Finally, the proposed method is verified through simulation and experiment.

One of the major issue faced by the construction industry is the degradation of structures due to different loads acting on the structure. So retrofitting and rehabilitation has become quite inevitable and it can help in regaining the original strength of the structure. Use of ferrocement is an effective method and it is used in developed countries as it is considerably cheap and materials of construction are easily available. Ferrocement is a system of construction using reinforced mortar or plaster applied over an armature of metal mesh, woven expanded-metal or metal-fibers and closely spaced thin steel rods such as rebar. The skill required is of low level and it has superior strength properties as compared to conventional reinforced concrete. The main drawback of ferrocement is corrosion. Thus to avoid corrosion stainless steel jacketing is employed for rehabilitation within the study that opens the scope for a new jacketing methodology.

A core test is practiced to determine in-situ cube strength, but most codes give different results depending on the factors used. The general problems of core testing are well known. The factors including core diameter, length-to-diameter ratio (L/d), concrete age, aggregate characteristics, the direction of coring, and the moisture condition at the time of testing are known, which affect the relationship between core strength and the corresponding standard cube or cylinder strength. Another potential factor influencing the testing of cores is the presence of reinforcing bars within the core. Only a few researchers have investigated the effects of steel bars on the strength of cores. Along with these existing factors, the inclination of rebar is believed to influence the core strength, but which has not been taken into consideration so far. In this paper, the finite element simulation studies carried out on concrete cores embedded with reinforcing bars at various inclination is described in detail. The wave propagation through the concrete core is studied, and regression analysis is carried out considering the multiple factors.

By considering the application requirements of automatic welding of labels on the heads of bundled rebars in the iron and steel industry, an automatic label welding robot system is developed based on machine vision and image processing. The system consists of six modules: pickup unit, image unit, control unit, welding stud unit, label unit, and rebar unit. It can automatically pick up welding studs, pick up labels, perform welding, detect dropped labels, and detect dropped welding studs. The development process of label welding mainly includes the following steps. First, the Cascade RCNN object detection algorithm is used to detect the rebar head, so that the number of rebars and the pixel coordinates of the rebar head centers can be obtained. The detection accuracy of the number of rebars can reach 100%, and the Cascade RCNN average score is 0.9801. Then, an algorithm to identify the center of bundled rebar heads based on the variable-scale method (Davidon–Fletcher–Powell formula (DFP)) is proposed. In addition, limiting conditions, and a process for selection of weldable points for double-label welding are provided. And the coordinate conversion equations of weldable points in different coordinate systems are derived. Finally, a serious of functional verification tests of the robot system were carried out on an actual rebar production line, which verified the accuracy of the weldable point image recognition process, and the usability of the robot system. The results indicate that the accuracy of weldable point recognition can reach 98.99%.

In order to achieve greater ductility and strength, as well as to produce a more economical design, a novel composite beam and floor system have been developed to achieve higher strength and ductility, as well as to yield a more economical design purpose. This paper has put focus on this newly developed composite beam system which consists of a profiled metal decking slab made with self-compacting concrete (SCC). It has been joined cold-formed steel (CFS) built-up beams. These beams have been infilled with SCC by means of U-shaped rebar used as shear connectors. The researcher, in order to construct an open section, put together two CFS C-lipped channel sections in a back-to-back formation, and to construct a closed section, the formation was made to be toe-to-toe. The flexural behaviour of the partly encased composite beam was evaluated through experimentation by the researchers. So that the researchers could observe the failure modes and flexural capacity of the construction, a four-point bending test procedure was performed on two samples taking into consideration both closed and open built-up beam sections. The results of the test demonstrated that the open sections were able to exhibit a 24 percent higher ultimate moment capacity as well as greater stiffness and higher vertical deflection. As can be seen from the results of the experimental bending test, the built-up design had a great impact on the capacity and deflection of the section, and the section that was encased was able to reach the ultimate strength when the proposed shear connector was placed in the composite action. In order to validate the present test results, the design and analysis of the new composite beams have been evaluated.

Structure health monitoring is a necessary step for regular monitoring of a structure. This helps to prevent any casualty in the structure and adopt necessary preventive methods before the collapse. Non-destructive Testing (NDT) has been used to evaluate the characteristics of the structure and plays a good role in the inspection and monitoring of the existing buildings. This paper describes the NDT testing on the residential reinforced cement concrete (RCC) structure located at Vikaspuri, New Delhi. The RCC structure having G + 3 Floor and building was constructed at 1995. Ultrasonic pulse velocity, rebound hammer, and rebar locator test was used on this building to identify the quality and strength of the concrete structure. The structural drawing was not found of this structure so conducted the Rebar locator test to examine the diameter of reinforcement and cover between reinforcement and the concrete surface. Test results showed that the quality of the concrete was poor and the strength of the concrete in between 12 and 15 MPa was observed in the column. This study revealed that retrofitting should be providing for the column and beam structure to enhance the strength of the structure.

Compressive strength test is the most common test carried out on concrete and is considered good enough for design and decision making for concrete and reinforced concrete works. Meanwhile the quality of steel used for reinforcement works is determined by its tensile strength, yield strength, weight and elongation. In addition, the chemical composition content which affects the quality is also determined. However, it is difficult to know all these things for a common man and so a simple test called bend test conducted on site is usually carried out to assess the quality of steel. When bent to make an angle of 90 to 135 degrees and then bent back straight, there should be no cracks on the rebar and its original shape retained once it is straightened, one can be assured that it is of best quality. Even at this the strength of the rebar which informs its Grade cannot be known. Since the compression strength test is universally acceptable for concrete grading, it should be equally universally acceptable for rebars. This informed the authors decision to work and recommend appropriate ratio of height to diameter as 2 for yield stress for circular rebars. Fourteen and twenty four Samples of supposed mild steel rebars and high yield steel rebars where tested in compression. Half of this was tested for height to diameter ratio of 1 and the other half tested for a ratio of 2. The result revealed for a ratio of 2 that the high yield steel where of grade 60 or grade 420 since the average of the stresses for this ratio was 460.01N/mm2 meanwhile the supposed mild steel was actually medium tensile steel and not mild steel as was reported in the purchase certificate. The result of this study support the grading in ASTM A 615, BS4449, Euro Standard(DIN 488) and Indian Standard (IS: 1786) and compares favorably with recent works. Key Words: Rebar, Steel, Grade, yield, Strength, Concrete