Reinforced Concrete Structures Research Articles

Experimental Evaluation on Blast Resistance of Reinforced Concrete Structures under Partially Confined Explosion

As the risk of accidental explosions at ammunition storage or hydrogen charging station increases in populated area, it is needed to design the facilities against blast loading, particularly subjected to partially confined explosion. However, the partially confined explosion lacks experimental test data to efficiently design the facilities subjected to the potential threat, when compared to unconfined or confined explosion cases. As a fundamental study on partially confined explosion, two partially buried tunnel-type structures with normal- and high-strength concretes were tested under a weight charge of 5.9 kg TNT explosion. The major parameters were concrete compressive strength and reinforcement ratio. The test result showed that the damage of the concrete structure with normal-strength concrete was extremely severe, whereas that of the specimen with high-strength was relatively mild. Further, finite element (FE) analyses were performed to investigate the confinement effect of blast load. The FE analysis result showed that under partially confined explosion, the reduction of the maximum displacement by using higher concrete strength was significant, while preventing the failure of the structure. This study provides fundamental data for designing the facilities with explosives subjected to the partially confined explosion.

Feasibility of Repairing Concrete with Ultra-High Molecular Weight Polyethylene Fiber Cloth: A Comprehensive Literature Review

This review explores the use of Ultra-High Molecular Weight Polyethylene (UHMWPE) fiber cloth as an innovative solution for the repair and reinforcement of concrete structures. UHMWPE is a polymer formed from a very large number of repeated ethylene (C2H4) units with higher molecular weight and long-chain crystallization than normal high-density polyethylene. With its superior tensile strength, elongation, and energy absorption capabilities, UHMWPE emerges as a promising alternative to traditional reinforcement materials like glass and carbon fibers. The paper reviews existing literature on fiber-reinforced polymer (FRP) applications in concrete repair in general, highlighting the unique benefits and potential of UHMWPE fiber cloth compared to other commonly used methods of strengthening concrete structures, such as enlarging concrete sections, near-surface embedded reinforcement, and externally bonded steel plate or other FRPs. Despite the scarcity of experimental data on UHMWPE for concrete repair, this review underscores its feasibility and calls for further research to fully harness its capabilities in civil engineering applications.

Non-Destructive Inspection Method Using Elastic Waves for Quality Management in the Bending Process Region of BFRTP

In order to establish a sustainable infrastructure, structures must maintain their minimum required performance for an extended period. Typically, existing concrete structures are reinforced with steel, but the susceptibility of steel reinforcements to corrosion, attributed to factors such as carbonation and chlorides, can lead to performance degradation, rendering the specified requirements unmet. As a remedy, there has been a growing interest in using lightweight and corrosion-resistant fiber-reinforced polymer (FRP) bars as an alternative to traditional steel reinforcement in concrete structures. Particularly noteworthy is the use of FRP bars manufactured with thermoplastic resins (FRTP) due to their ease of processing and convenient applicability on construction sites. This study delves into the mechanical behavior evaluation by examining the propagation characteristics of elastic waves in the curved section of basalt FRTP (BFRTP). Multiple BFRTP bars underwent a 180-degree bending process, subject to various conditions, including heat and twist variations. Subsequent measurements focused on the propagation characteristics of elastic waves in the curved sections, emphasizing wave attenuation, frequency features, and propagation velocity. Additionally, bending tensile tests were conducted on the curved bars, and a comparative analysis was performed between the tensile strength and the aforementioned elastic wave propagation characteristics. The results affirm a consistent correlation between the propagation characteristics of elastic waves (amplitude ratio, centroid frequency, velocity) during the traversal of the curved BFRTP section and its tensile strength. Notably, both centroid frequency and velocity exhibited correlation coefficients exceeding 0.7, suggesting their potential efficacy as reliable indicators for estimating tensile strength.

Behavioural Study of Beam-Column Joint for Seismic Loading

Abstract: The seismic performance of Reinforced Concrete (RC) structures is a critical aspect of structural engineering, particularly in regions prone to seismic activity. This project presents a detailed study focusing on the behaviour of joints in RC structures following seismic events, utilizing the powerful computational tool ETABS. The primary objectives include understanding the response of joints under seismic loading, assessing their vulnerability, and proposing strategies for enhancing their seismic resilience. The study employs ETABS, a widely used software package for structural analysis and design, to simulate seismic actions on RC structures. Various types of joints, including beam-column joints and slab-column connections, are meticulously analysed under different seismic intensities and structural configurations. Through comprehensive analysis, the project aims to identify critical failure modes, such as shear failure, flexural failure, and joint sliding, and evaluate their impact on overall structural performance. Findings from this study contribute to the advancement of seismic design and retrofitting practices, offering insights into effective strategies for enhancing the seismic resistance of RC structures. The outcomes are valuable for engineers, researchers, and practitioners involved in earthquake engineering, providing essential knowledge for designing resilient structures capable of withstanding seismic hazards. This project underscores the importance of understanding joint behaviours in RC structures subjected to seismic loading, offering practical implications for improving structural safety and mitigating the impact of earthquakes on the built environment.

Automatic Detection Method for Concrete Spalling and Exposed Steel Bars in Reinforced Concrete Structures Based on Machine Vision

Automatic Detection Method for Concrete Spalling and Exposed Steel Bars in Reinforced Concrete Structures Based on Machine Vision

Post Fire Assessment of RCC Buildings Through Rapid Visual Screening

The effectiveness of rapid visual screening (RVS) in determining the fire risk of reinforced concrete (RCC) buildings is examined in this review. RVS provides a quick and practical approach to evaluate fire risks, addressing the shortcomings of traditional methods. Through a comprehensive examination of methodology, advantages, limitations, and future directions, this study aims to enhance understanding and application of RVS in fire assessment. The study employs a systematic approach to evaluate the effectiveness of RVS, analyzing its application in assessing fire vulnerability in RCC structures. Key aspects of RVS methodology, including visual inspection, identification of structural vulnerabilities, and categorization of damage, scrutinized. A case study of the Chopasani Housing Boards building in Jodhpur provides empirical evidence of RVS's utility in identifying fire-related structural vulnerabilities. The concluded, the analysis reveals that RVS effectively categorizes fire-induced damage in RCC buildings, facilitating prioritization of mitigation efforts. Damage classifications, ranging from mild to extreme, are discerned through RVS, underscoring its ability to swiftly assess structural vulnerabilities. Additionally, RVS analysis elucidates the residual strength of RCC components post-incident, providing valuable insights for retrofitting and maintenance efforts. Overall, this study highlights the pivotal role of RVS in bolstering structural fire safety measures, emphasizing its practicality, cost-effectiveness, and accessibility. However, limitations such as subjectivity and inadequate assessment of complex structures necessitate ongoing refinement and integration with advanced technologies. The findings underscore the importance of RVS in enhancing fire safety assessment practices and mitigating fire risks in urban buildings, particularly in the context of reinforced concrete structures.

Approaches to estimate global safety factors for reliability assessment of RC structures using non-linear numerical analyses

The study is focused on the comparison and discussion of different approaches within the use of the global resistance method (GRM) for safety assessment of reinforced concrete (RC) systems using non-linear numerical analyses (NLNAs). With this purpose, a benchmark dataset, comprising 56 experimental results obtained from tests on 40 RC columns with variable slenderness and 16 non-slender RC elements including walls, deep beams and shear walls, is considered. The NLN models for all the 56 members adopt solution strategies able to optimize the agreement between numerical predictions and experimental outcomes. Then, probabilistic hypotheses have been defined regarding both aleatory (i.e., materials and geometry) and epistemic uncertainties (i.e., model) associated with all the 56 RC members. These assumptions form the basis for developing a comprehensive set of probabilistic analyses of the global structural resistance for each RC member. The results of these probabilistic analyses offer valuable insights into the impact of the different sources of uncertainties on the global structural response. In detail, three distinct approaches for estimating the global safety factors within the GRM are outlined and compared. The purpose is to address the effectiveness of the different approaches for the reliability evaluation of RC members within the GRM together with the relevance of both aleatory and epistemic uncertainties. Ultimately, recommendations are provided regarding the adoption of the GRM in the upcoming generation of design codes.

Comparative Study of RCC Structure of different types by using Shear Wall, Damper & Bracing System

In seismically active places, earthquake restrictions would provide a difficulty to the majority of multistory buildings. The fundamental issue in the design of the multi-story building is lateral stability, which is required to control lateral drift and displacement, withstand lateral pressures, and avoid buckling. Reinforced concrete (RCC) structures usually utilise a damper, bracing, and shear wall system to mitigate the impacts of seismic activity. Both systems have significant structural performance. Despite the fact that both technologies are used for the same purposes, their effects and behaviour in response to seismic load differ. The G+12 storey building, shear wall and bracings will all be considered in this project's analysis. The following criteria will be used to evaluate the building's performance: base shear, storey displacement, and storey drift. This research includes dampers, shear walls, and bracings at various places, and the Etabs 2018 programme will be utilised for the entire analysis.

Prediction of residual performance of corroded RC beams from observed surface cracks by 3D RBSM with MPC

Corrosion of reinforcing steel in concrete structures can significantly compromise their performance. Accurately estimating this deterioration for in-service structures is challenging due to uncertainties surrounding the distribution of internal corrosion and cracking patterns, compounded by the limitations of destructive testing. This research proposes a novel approach to predict the remaining load-bearing capacity of corroded reinforced concrete (RC) structures based on the pattern of surface cracks caused by corrosion. The method integrates a model predictive control (MPC) algorithm with a three-dimensional Rigid Body Spring Model (3D RBSM) to estimate internal corrosion levels from observed cracks and a normal 3D RBSM simulation to predict the residual performance. The proposed system is validated through analysis of four corroded beam specimens based on experimental work reported in the literature. In use, the MPC algorithm first estimates a corrosion distribution in a RC beam and generates simultaneous corrosion-induced crack and stress predictions. This information is then used to predict residual load-bearing capacity. The system accurately forecasts the non-uniform corrosion distribution, flexural capacity, and load-displacement curves of a specimen, offering insight into the performance differences among the specimens and demonstrating its potential to assess the serviceability of existing RC structures with corrosion issues.

Numerical evaluation of impact resistance of reinforced concrete walls

Reinforced concrete(RC) structures are occasionally subjected to accidental impact during service, which can cause economic losses and casualties. Most previous research on the impact resistance of RC structures has focused on beams, columns, and slabs except walls. Thus, it is necessary to study the impact response and resistance performance of essential RC walls with high resistance requirements, such as critical shear walls, important structures, and vital protective structures of high-rise buildings in earthquake and mountainous areas under low-speed impact. This research verified the finite element model (FEM) through pendulum impact experiments on RC walls (with an impact mass of 2 tons) firstly, then proposed the damage assessment parameters of the RC wall, and analysed the impact response mechanism and resistance performance of RC walls with several reinforcement ratios under different impact loads. The research results indicate that the impact effect on the wall must consider the different value (D-value) between local and global deformation. The impact load significantly influences the peak impact force and the displacement of the RC wall. The mass affects the RC wall’s global residual deflection. At the same time, the velocity significantly influences local displacement, and correspondingly, the RC wall is more prone to local damage with high velocity. Thickness, the concrete fc, and the reinforcement ratio affect the impact resistance of the RC wall. The thicker wall can cause a shorter impact duration, and milder concrete damage, but the smaller rebar stress. The larger fc will bring greater rebar stress and milder concrete damage. A high reinforcement ratio will increase the impact force platform value and the RC wall’s concrete damaged ratio but will reduce the plastic strain of the rebars.

Vierendeel action in progressive collapse of three-storey RC structures under corner column removal scenario

Previous studies have found that the Vierendeel action (VA) is one of the main mechanisms against progressive collapse of multi-storey reinforcement concrete (RC) frame structures in the event of corner column failure. However, the knowledge remains inadequate in terms of the behavior, mechanism, and quantitative contribution of the VA to the collapse resistance. To fill this gap, quasi-static tests were performed on a 1/3 scale single-storey RC substructure and a three-storey RC substructure with identical geometry, material, reinforcements and boundary conditions under corner column removal scenario. Test results found that, compared with the single-storey substructure experiencing no VA, the three-storey substructure developed additional plastic hinges at the beam ends near the corner column and at the lower end of the corner column as a result of the VA. The ultimate resistance of the three-storey substructure was 10.6% more than the triple ultimate resistance of the single-storey substructure. Then, numerical analysis was conducted to cognize the formation sequence of the plastic hinges and the effect of slabs. Furthermore, two coefficients were defined to reveal the mechanism of the VA in the three-storey substructure, i.e., the displacement-related coefficient ed and the coefficient associated with ultimate resistance eu. Finally, a simplified analytical model was proposed to predict the ultimate resistance of the three-storey structures with consideration of the VA.

Experimental study on improving the fire performance of the concrete beams with Fe-SMA

The conventional approach to satisfying the fire resistance requirements in designing reinforced concrete (RC) structures is to ensure enough concrete cover depth for the steel reinforcements. The objective is to prevent the temperature of steel reinforcements from rising too quickly. However, excessive concrete cover depth may increase the risk of concrete spalling during a fire and lead to a larger crack width. Fire is a natural heat source that can activate the shape memory effect of iron-based shape memory alloys (Fe-SMA) to generate recovery stress. This study proposes a new active approach for improving the fire performance of RC structures based on the Fe-SMA. The main objective is to investigate the feasibility of improving the fire performance of RC structures through the recovery stress generated by Fe-SMA under fire. The fire test of nine Fe-SMA RC beams was conducted. The temperature profile in the furnace was similar to ISO834, and the maximum temperature exceeded 800 °C. The flexural behavior of the concrete beams reinforced with Fe-SMA during and after the fire was tested. The experimental results demonstrate that the Fe-SMA has great potential in improving the fire performance of RC structures. The mid-span deflection of the Fe-SMA RC beams under fire is significantly lower than the conventional RC beams. The fire resistance of Fe-SMA RC beams increases from 97 min to 133 min at load level 0.3 and from 69 min to 103 min at load level 0.5. The residual deformation of Fe-SMA RC beams reduces from 46.3 mm to 27.6 mm at load level 0.3 and from 34.7 mm to 19.8 mm at load level 0.5. In addition, after 1 h of fire exposure, the Fe-SMA can develop permanent prestress after the beam cools to room temperature, improving the mechanical properties after fire. The residual bearing capacity and residual stiffness of the Fe-SMA RC beams are 21% and 86%–121% higher than the conventional RC beams, respectively. The prestress generated by Fe-SMA after 1 h of fire exposure was estimated using the equivalent section method.

Comparison of mass timber structure and RC structure with regard to sustainability by life cycle assessment

Since the 18th-century Industrial Revolution, high-rise have played a crucial role in addressing urbanization challenges, remaining a primary solution for urban living. However, this architectural advancement has also contributed to environmental decline. Presently, steel and concrete stand out as the predominant materials for high-rise construction, with well-documented significant carbon emissions. This paper delves into the potential of timber as an environmentally friendly alternative in high-rise construction to address such environmental concerns. Furthermore, it examines the impact of these structures on land load. The paper conducts a comprehensive review of life cycle assessment (LCA) studies and offers a comparative analysis of the climate change impacts associated with timber versus conventional materials like reinforced concrete (RC), underscoring the urgent need for sustainable development in the vertical expansion of our cities. The findings demonstrate that both the mass and carbon emissions of high-rise timber structures, in comparison to RC structures, can be reduced by approximately half. The paper aims to underscore the benefits of timber in comparison to conventional reinforced concrete methods, thereby informing material selection in favor of sustainable urban development.

Bearing Characteristics with Effect of Bond–Slip Behavior in Massive Ring-Type Reinforced Concrete Structures

The bond–slip behavior of the steel–concrete interface is critical in reinforced concrete (RC) structures since the bond action is the mechanism that ensures the two materials work in co-operation. However, there is little research considering the bond–slip behavior in massive ring-type reinforced concrete (MRRC) structure bearing analyses due to the complexity of modeling the interfacial behavior. Hence, the influence of the bond–slip behavior on the bearing characteristics of MRRC structures remains unclear. Steel-lined reinforced concrete penstock is such an MRRC structure, composed of steel liner and reinforced concrete and commonly used in diversion pipelines. This paper aims to explore the bearing characteristics considering the bond–slip behavior in the composite penstock by using a promising numerical method, the cohesive zone model. Three interface models were proposed to represent the different interaction conditions at the steel–concrete interface. Moreover, a sensitivity analysis was performed to study the impact of the bond strength on the bond performance and structural behavior. The simulation results showed that the prediction results (steel stress and crack process) considering the bond–slip behavior were in good agreement with the experimental results. The steel stresses near the cracks were smaller and more uniform after considering the bond–slip behavior, since the stresses were no longer concentrated on the crack but distributed in an area near the crack. However, the steel stress differences in these models were within 10%, which means that the bond performance had a limited effect on the structural safety design. The crack widths were greatly influenced by the bond conditions, and the maximum crack width (0.461 mm) in poor conditions was beyond the limiting value (0.3 mm). Consequently, bond–slip behavior must be paid more attention in durability design.

Crack Resistance of Lightly Reinforced Concrete Structures.

The crack resistance of concrete structures with low reinforcement ratios requires a broader examination. It is particularly important in the case of foundations working in changing subsoil conditions. Unfavorable phenomena occurring in the subsoil (e.g., ground subsidence, landslips, non-uniform settlement) can lead to unexpected cracking. Therefore, it is necessary to check the effectiveness of the low reinforcement provided. As there are limited studies on lightly reinforced concrete structures, we performed our own experimental investigation and numerical calculations. In the beams analyzed, the reinforcement ratio varied from 0.05% to 0.20%. It was found that crack resistance in concrete members depends on the reinforcement ratio and steel bar distribution. A comprehensive method was proposed for estimating the crack resistance of lightly reinforced concrete members in which both the reinforcement ratio and the reinforcement dispersion ratio were taken into account. Furthermore, the method considered the size effect and the fracture properties of concrete. The proposed method provides the basis for extrapolation of the test results obtained for small elements and conclusions for members with large cross-sections, such as foundations, which frequently use lightly reinforced concrete.

Mesoscale discrete simulation of flexural behavior of FRP-strengthened RC beams using 3D RBSM

A widely adopted method of strengthening existing reinforced concrete (RC) structures, especially for marine concrete structures, is to use external bonded fiber-reinforced polymer (FRP). However, although numerous studies in this field have been reported, accurate simulation of localized material behaviors such as crack opening and interfacial sliding remains challenging. Compared to other simulation methods, mesoscale models offer the promise of capturing these complexities. Nevertheless, there has been very little application of mesoscale simulations in analysis of FRP-strengthened RC structures due to a lack of relevant constitutive models. To fill this gap, the authors have recently developed local bond models for the FRP-concrete interface in the three-dimensional rigid body spring model (3D RBSM). The model’s parameters are defined with easily interpretable physical implications and straightforward computational methods. In this work, this mesoscale model is extended and applied to simulate the flexural behavior of FRP-strengthened RC beams. The simulation results closely align with experiments in both global and local behaviors. The parametric study conducted in this work highlights the critical role of interfacial normal bond strength between FRP and concrete in dictating flexural behavior. The capability of 3D RBSM in simulating the strain distribution along the FRP and capturing intricate localized behaviors aligned with flexural and shear forces is demonstrated. Overall, this paper reinforces the potential of 3D RBSM as a robust tool for analyzing the complex behaviors of FRP-strengthened concrete structures.

Effects of long-term exposure of NSM CFRP-to-concrete bond to natural and accelerated aging environments

Carbon fiber reinforced polymer (CFRP) composites can be used to strengthen existing reinforced concrete (RC) structures. The CFRP laminate can be bonded to RC structure using epoxy adhesive via near-surface mounted (NSM) strengthening technique. However, existing literature generally lacks data about durability of NSM CFRP-to-concrete bond. In this study, strengthened concrete elements were exposed to laboratory-controlled environments (at approximately 20 °C/55 % RH, and water immersion at 20 °C) and natural field environments (to promote natural aging induced mainly by carbonation, high temperatures, freeze–thaw attack, and airborne chlorides) for up to four years. Durability tests were conducted yearly for the bond and its constituent materials. The highest bond strength degradations were nearly 12 % and 9 % for the specimens immersed in water and those exposed to freeze–thaw attack, respectively. Besides, environmental conversion factors of 0.88 and 0.93 were derived from a database of existing accelerated, and natural aging data from the present work, respectively.

Effect of BFRP ties on the axial performance of RC columns reinforced with BFRP and GFRP rebars

The adoption of fiber-reinforced polymer (FRP) bars in lieu of traditional steel reinforcement for concrete structures has gained prominence. Nevertheless, prevailing international standards have not incorporated provisions to assess the significant contribution of FRP materials to the axial capacity and deformability of compression members. This study investigates the impact of Basalt (BFRP) ties on the axial performance of full-scale concrete columns reinforced with BFRP and Glass (GFRP) rebars, alongside traditional steel longitudinal rebars. Ten columns were subjected to concentric loading, with parameters including the type of longitudinal rebars (BFRP, GFRP, and steel), spacing of BFRP ties (180 mm, 120 mm, and 60 mm), and diameter of steel rebars (16 mm and 20 mm). Varied steel rebar diameters aimed to discern the influence of axial stiffness on column behavior. Results indicate an 18 % to 26 % higher axial load capacity in steel-reinforced concrete (RC) columns compared to FRP-RC columns. Both types of FRP rebars contributed approximately 12 % to the axial capacity. Reducing BFRP tie spacing from 180 mm to 60 mm significantly increased deformability by up to 250 % in FRP-RC columns and ductility by up to 14 % in steel-RC columns. The study highlights conservative predictions in existing design equations (ACI 440.11–22 and CSA S806-12) for the axial load capacity of BFRP and GFRP RC columns, underestimating by 14 % to 20 %, as they neglect the contribution of FRP rebars. Utilizing a concrete crushing strain of 3,000 µε and 3,500 µε as the ultimate FRP compressive strain produced predictions closest to the experimental axial load capacity.

Calculation of Characteristic Point Parameters for Restoring Model of Corroded Short-Pier RC Shear Walls

Based on the quasi-static tests of 12 corroded RC (reinforced concrete) shear walls, it was found that reinforcement corrosion has a great influence on the skeleton curve of RC shear walls. With an increase in the degree of corrosion, the bearing capacity of specimens decreases, and the deformation capacity worsens. Increasing the diameter of longitudinal reinforcements can significantly improve the bearing capacity of corroded RC shear walls, while the deformation capacity of corroded specimens can be improved by increasing the lateral distributed reinforcement or the transverse reinforcement in the embedded column. In order to accurately evaluate the seismic performance of corroded RC shear walls, we considered descent segments of four broken-line models to estimate the skeleton curve. After considering the influence of corrosion on the parameters of the characteristic point for the skeleton curve, the calculation formulas of the characteristic point parameters of the skeleton curve for the corroded RC shear wall were determined based on the test data fitting. It was proven that the formula for the characteristic point parameters for the skeleton curve of corroded RC shear walls has good applicability. This study lays a theoretical foundation for the seismic performance evaluation of an RC shear wall structure in a salt fog environment. It provides a theoretical basis for further improving the life-cycle seismic capacity evaluation system for RC structures.

Experimental study on the flexural performance of prestressed RC beams with post-tensioned CFRP strands

Carbon fiber reinforced polymer (CFRP) exhibits multiple advantages over conventional steel, such as high strength and corrosion resistance. By replacing prestressing steel with prestressing CFRP in new prestressed reinforced concrete (RC) structures, the corrosion issue of prestressing steel can be resolved. At present, there remains scarce research on the application of CFRP strands in the prestressed RC structures. An experimental study was conducted on prestressed RC beams with internal post-tensioned CFRP strands under flexure. The study aimed to analyze the effects of the prestress level, number of CFRP strands, layout shape of CFRP strands, bonding layer, and reinforcement ratio of steel bars on the flexural behavior. The test results indicated that all specimens experienced concrete crushing failure. After applying prestressing CFRP strands to ordinary RC beams, the cracking load increased by 50.0% to 102.2%, the yielding load increased by 20.2% to 38.6%, and the ultimate load increased by 20.3% to 41.4%. Reducing the reinforcement ratio of steel bars had a minor effect on the cracking load but resulted in a noticeable decrease in the yielding and ultimate loads of the prestressed CFRP strand-reinforced concrete beams. Moreover, the bonded specimen showed a slight increment in the cracking, yielding, and ultimate loads as well as stiffness compared to the unbonded specimen, while the deformation capacity of the unbonded specimen remained superior. The specimens with curved and straight prestressing CFRP strands exhibited very similar mechanical properties.