Reinforced Concrete Research Articles

Evaluating the Performance of Ensemble Machine Learning Algorithms Over Traditional Machine Learning Algorithms for Predicting Fire Resistance in FRP Strengthened Concrete Beams

In recent years, fiber-reinforced polymers (FRP) have emerged as a highly effective solution for strengthening reinforced concrete (RC) structures. However, accurately assessing the fire resistance of FRP-strengthened members remains a significant challenge due to the limited guidance available in current building codes, often leading to conservative and cost-intensive evaluations. Experimental testing and numerical analysis required for such assessments are resource-demanding, highlighting the need for more efficient methods. This study investigates the application of machine learning (ML) techniques to predict the fire resistance of FRP-strengthened RC beams. Twelve ML models, including eight ensemble methods and four traditional approaches, were employed. The models were trained using a comprehensive dataset comprising over 21,000 data points obtained from numerical simulations and experimental tests. The dataset captured variations in geometric configurations, insulation strategies, loading conditions, and material properties. To enhance predictive accuracy, Bayesian optimization and k-fold cross-validation were applied for model tuning, while the Shapley Additive Explanations (SHAP) method was utilized to assess the relative importance of features influencing fire resistance. Among the models tested, Extreme Gradient Boosting (XGBoost), Categorical Boosting (CatBoost), Light Gradient Boosting (LGBoost), and Gradient Boosting (GRB) demonstrated superior performance, achieving accuracy rates exceeding 92%. Key factors identified as significantly affecting fire resistance included loading ratio, area of tensile reinforcement, insulation depth, concrete cover thickness, and FRP area. The findings underscore the potential of ensemble ML techniques over traditional methods for accurately predicting the fire resistance of FRP-strengthened RC beams, offering critical insights for optimizing design practices and enhancing structural fire safety.

Experimental and numerical investigation on RC beams with web openings subjected to pure torsion strengthened by ferrocement technique or GFRP sheets

The main objective of the current experimental and numerical study is to investigate the effect of strengthening by ferrocement layers on the behavior of reinforced concrete (RC) beams with openings subjected to pure torsion and compare it with the beams that were strengthened by Glass Fiber Reinforced Polymer (GFRP). The experimental investigation consists of twelve reinforced concrete (RC) beams that have been divided into four groups. The parameters under investigation included the strengthening technique (ferrocement or External Bonded Glass Fiber Reinforced Polymer EB-GFRP), type of steel mesh (welded wire mesh and expanded metal mesh), number of layers of mesh (1, 2, 3), extension length outside opening (50, 100 or 200) mm, strengthening configuration (full or U-shape) wrapping, and the anchoring system effect. The experimental work consists of one solid beam and eleven beams with openings. The tested beams yielded results such as cracking and ultimate torques, angle of rotation, and mechanism of failure. Creating an opening in the control solid beam resulted in a 38.46 % decrease in ultimate torque, while using different techniques during this research proved efficiency in the strengthening process. Using GFRP U-wrapping and fully wrapping to strengthen the area around the beam's opening increased the ultimate torque by 50 % and 81.25 %, respectively, compared to the un-strengthened beam with an opening. Adding fully wrapped ferrocement layers to the beam with an opening greatly improved its torsional strength. The ultimate torque increased by 40.63 % to 81.25 % compared to the beam with an unreinforced opening. Increasing the number of welded steel mesh layers from 1 to 3 in the ferrocement strengthening technique led to an increase in ultimate torque from 40.63 % to 75 % compared with the un-strengthened beam with the opening. The tests showed that using expanded metal mesh instead of welded wire mesh in strengthened beams with holes led to a 9.43 % higher ultimate torsional capacity, indicating that the expanded metal mesh worked better than the welded wire mesh. Using the U-shape ferrocement wrapping with anchors was better than without anchors, resulting in a 9.1 % increase in the ultimate torsional capacity. Applying a fully wrapped GFRP sheet or expanded metal mesh ferrocement strengthening achieved the highest ultimate torque, 81.25 % more than the un-strengthened beam with an opening. Moreover, a 3D non-linear finite element analysis is conducted using ABAQUS software to forecast the torsional properties of beams strengthened by either ferrocement or EB-GFRP. The numerical model captured the failure patterns, twisting angle, and ultimate load of tested beams. The experimental and analytical results were in good agreement. The research concluded the effectiveness of using the ferrocement reinforced with different steel mesh types in strengthening reinforced concrete beams with openings under pure torsion, the cost-efficiency and simplicity of ferrocement as a solution compared to its results with EB-GFRP techniques.

Metaheuristic optimization of extreme gradient boosting machine for enhanced prediction of lateral strength of reinforced concrete columns under cyclic loadings

The estimation of lateral strength in reinforced concrete (RC) columns subjected to cyclic loads is crucial in structural design. The failure of RC columns under lateral forces can lead to catastrophic structural collapses. This fact emphasizes the need for accurate assessments of their dynamic behavior. This paper proposes a data-driven model for estimating the lateral strength of RC columns. A historical dataset comprising 12 predictor variables and 247 samples has been compiled to train and validate of the proposed approach. The extreme gradient boosting machine (XGBoost) is employed to establish a predictive relationship between the lateral strength of RC columns and their influencing factors. Since model selection is critical for constructing a reliable prediction mode, this study relies on utilizing metaheuristic approaches, including Genetic Algorithm, Particle Swarm Optimization, Artificial Bee Colony, and Ant Colony Optimization, to optimize the performance of the XGBoost model. Experimental results show that the integration of Ant Colony Optimization and XGBoost can help attain outstanding prediction accuracy with a correlation of determination (R2) of 0.95. Additionally, an asymmetric squared error loss function is utilized to reduce overestimations by 12 %. The newly developed method can be utilized in practical applications where reliable predictions of the lateral strength of RC columns under cyclic loads are required.

Numerical analysis of load-bearing capacity of shear-strengthened reinforced concrete beams without shear reinforcement using side-bonded CFRP sheets

As CFRP (carbon fiber-reinforced polymer) offers high retrofit efficiency for structural members in bending and shear due to its superior mechanical properties compared to steel, sheets made from this material have become ubiquitous in strengthening existing reinforced concrete (RC) structures. However, there needs to be more research on RC beams with no stirrups that have been shear-strengthened with side-bonded CFRP sheets. As such, this study aims to investigate this specific topic and assess design-related parameters that impact the load-bearing capacity of these shear-strengthened beams. To achieve this, nonlinear finite element models of four RC beams, including one control beam and three beams strengthened with side-bonded CFRP sheets, were built and verified regarding shear capacity, crack patterns, and failure mechanisms. The simulated beams demonstrated a high level of accuracy in all mentioned aspects. Numerical models were then developed to evaluate the design-oriented parameters that affect the response of shear-strengthened beams, including the concrete compressive strength, the amount of steel reinforcement, the number of CFRP layers, the CFRP bonding configuration, and the shear span-to-effective depth ratio. The results showed that not only the compressive strength of the concrete but also the amount of steel longitudinal reinforcement had a significant relationship with the load-bearing capacity of shear-strengthened beams. Meanwhile, the bonding configuration and the layer number of side-bonded CFRP sheets considerably influenced the ductility, the crack pattern, and the failure mode of shear-strengthened beams.

Cost-oriented fire safety design of urban structures

Providing adequate fire safety for urban buildings is a life-saving goal, and can be addressed in different ways. Reported studies integrating fire safety and life cycle cost (LCC) of conventional urban structures are rare. To address this gap, a cost–performance framework was developed. Four- and seven-storey steel (with and without fireproofing coatings) and reinforced concrete (RC) structures were designed, first for conventional loads and then fireproofed to meet their required fire-resistance rating. A range of sprinkler spacings, from 3200 mm (based on NFPA 13) to 12 000 mm, was configured. Fire was simulated using a fire dynamic simulation tool and the results were used to monitor evacuation plans and structural responses. The steel structures were additionally analysed under the assumption that they were not fireproofed. Human and financial damage costs were then estimated and the LCC for every case/scenario was determined. Interestingly, the results showed that the optimum LCC was not achieved for cases designed based on NFPA 13; instead, a sprinkler spacing of 6000 mm led to the optimum LCC. It was also found that steel structures without fireproofing do not have a higher LCC if the sprinklers are placed over a shorter distance. This result could be particularly beneficial for existing structures that are not fireproofed.

Corrosion level estimation in reinforced concrete beams by acoustic emission sensing and selective crack measurements

AbstractAccurate corrosion assessment plays an important role in ensuring structural safety of reinforced concrete (RC) structures. However, on‐site assessment of existing concrete structures presents many challenges, including high costs, limited inspection timeframes, and difficult accessibility. To facilitate inspection‐based corrosion assessment, this paper presents a novel approach by combining short‐term acoustic emission (AE) monitoring with selective crack width measurements for corrosion level (CL) assessment. AE sensing is a monitoring technique which can detect ongoing internal degradation mechanisms by analyzing ultrasonic waves emitted by the damage process. Yet, two major challenges arise on site: (1) practical limitations prevent continuous AE monitoring over the structure's entire lifetime and (2) AE can only generate relative results in the absence of reference measurements. This paper addresses both challenges to bridge the gap between laboratory experiments and on‐site monitoring of corroding RC structures. First, short periods of AE monitoring data are analyzed to investigate the potential of AE sensing over limited timeframes. Second, AE data of corroding RC beams are combined with sparse crack width measurements in order to obtain absolute CLs. The proposed methodology is experimentally validated by corroding eight beams with varying dimensions, corrosion zones, and reinforcement layouts. The experimental results prove that the estimated CLs closely match the rebar mass losses, with a mean absolute error of 1.53% CL for beams reaching up to 14% CL, confirming the potential of the combined AE and crack width measurement technique as an efficient and accurate condition assessment approach. Moreover, AE sensing provides detailed spatial variability of the rebar corrosion in the monitored zone, which is challenging to obtain with conventional techniques. By using this dual‐technique approach, shorter monitoring periods prove nearly as effective as continuous AE monitoring in accurately estimating CLs.

State-of-the-art of mechanical properties of 3D printed concrete

The utilization of 3D printing in civil engineering has expedited the progression of intelligent construction and building industrialization. A plethora of studies in recent years have contributed to the advancement of 3D printed concrete technology. In contrast to traditional concrete construction techniques, 3D printed concrete technology offers additional benefits such as cost-effectiveness, reduced environmental impact, and a simpler process. The mechanical properties of 3D printed concrete are crucial for its application in building structures. This article provides a comprehensive review of the latest research endeavors in 3D printed concrete, covering both research and application. Firstly, this manuscript examines the size parameters and fabrication methods of the specimens utilized for mechanical performance tests. Subsequently, the mechanical properties of 3D printed concrete are described, and the effect of time-gap as a significant parameter on the performance of 3D printed concrete is discussed. Finally, the existing 3D printed concrete reinforcement technologies and their applications are summarized and categorized based on fibers and steel bars. Moreover, the key technical obstacles in the application of 3D printed concrete in building structures are identified. The ultimate objective of this article is to chart a course for the development and implementation of 3D printed concrete in building structures.

Economical design strategies for reinforced concrete one-way slabs: a parametric approach considering material strength and rebar size

Despite the rapid advancements in optimization algorithms for economical reinforced concrete (RC) structures, their application to RC slabs has been significantly limited. The primary constraint is slab depth, governed only by deflection control criteria, which impedes further depth reduction—a key factor in cost optimization. The deflection check relies solely on one design parameter—span length, which is often fixed. This constraint limits the effectiveness of even advanced algorithms, which have consistently failed to deliver substantial cost savings in slab design. To address this issue, this study presents a detailed parametric investigation of three key cost-reducing factors in RC one-way slabs: steel strength, concrete strength, and reinforcing bar sizes, in accordance with the ACI 318–19 code. By bypassing algorithmic constraints, the study formulates optimal design strategies through extensive manual design iterations, providing novel trend-based solutions for cost-effective slab design. The findings indicate that for lower live loads, grade 280 steel offers a 20–30% cost reduction compared to higher-grade steel, despite the latter's strength advantage. However, for higher loads, grade 420 or 500 is recommended. Additionally, optimal bar sizes and concrete strengths are recommended for varying load conditions, offering practical design strategies. This approach provides designers with actionable insights to achieve cost-efficient designs without relying on traditional optimization algorithms.

Comparison between Design Methods for Seismic Retrofit of Reinforced Concrete Frames Using Dissipative Bracing Systems

Braces equipped with dissipative devices are among the most widespread methods for the seismic strengthening of seismically prone reinforced concrete (RC) frames. It allows for high reductions in seismic vulnerability with inexpensive, quickly executed interventions. They can often be carried out mainly at the exterior, resulting in interruptions of use that are limited both in time and to only small portions of the building. The design methods of dissipative devices are based on the extensive use of pushover analyses (POA). POA is capable of highlighting the structural deficiencies of the building and comparing the performances of design performed according to different methods and sizing criteria. In the present work, with reference to a case study represented by a four-story spatial frame having characteristics representative of design and construction common practice of the 1970s in Southern European countries, the performances of three different design methods were evaluated and compared. The examined procedures differ, including the following: (i) methods for estimating the peak displacement response of the nonlinear systems, namely (i1) the well-known equal displacement rule and (i2) the equivalent (secant) stiffness and damping rule, and (ii) criteria for distributing stiffness and strength of the braces along the height, namely (ii1) the distribution of stiffness and strength proportionally to those of the frame and (ii2) methods that vary the stiffness and strength along the height in order to minimize the eventual irregularity in elevation of the bare frame. The effectiveness of the procedures was checked by both POA and nonlinear response history analysis, the latter performed assuming both unidirectional and bidirectional input. The stiffness was found to increase by about 10 times and the strength between 7.5 to 3.7 times depending on the design method, and reduction in the displacements ranged between 31% and 42% compared to the values of the original frame. The pros and cons of each procedure are summarized, as all procedures are able to provide brace designs that meet the performance requirements set during the design phase.

Experimental Study on the Behavior of Reinforced Concrete Derailment Containment Provisions under Quasi-Static Loads

Derailments pose a significant threat to high-speed rail safety. The development of effective derailment containment provisions (DCPs) that can be installed within a track gauge and withstand impact loads of derailed wheels while controlling the lateral movement of derailed trains is essential. This paper presents an experimental study on the behavior of reinforced concrete (RC) DCP systems under quasi-static loading. Three steel anchors were assessed for their performance and load-bearing capacity in a single-anchor test. Four full-scale DCP system tests were carried out to examine the effects of scenarios of impact load positions at the anchor and mid-span of the DCPs. The crack pattern, failure mechanism, load–displacement relationship, initial stiffness, and absorber energy capacity of the DCP specimens were acquired. The findings reveal that the failure mode of the DCP specimens was predominantly affected by the tension failure of the steel anchors. The load-carrying capacity and performance equivalent of the DCP system under the applied load scenarios significantly exceeded the design load, ranging from 125% to 168%. Also, the initial stiffness of the DCP system remains largely unaffected by the applied load positions, whereas the absorption energy capacity exhibits a contrasting trend.

Post-fire performance of hybrid GFRP-steel reinforced concrete columns

The fire safety requirements and knowledge on the use of Glass Fiber Reinforced Polymer (GFRP) bars as an alternative to conventional steel in reinforced concrete structures have been progressively evolving. This study investigates the post-fire axial performance of square GFRP reinforced concrete (RC) columns, addressing a significant gap in current knowledge. Five column specimens of the same cross-section and length were tested, where the main parameters considered are the clear cover depths (40, 50, and 65 mm) and the use of a 40-mm insulation on one column. The columns were subjected to a long 3-hour fire exposure per ASTM E119 standard without sustained loading. The columns were tested upon cooling under concentric axial loading. Despite the notable temperature differences between columns with 40 and 65 mm concrete cover (300 and 500 °C after 3 hours), the post-fire residual axial capacity appeared unaffected. This is primarily attributed to the minimal differences in the retained mechanical properties of GFRP bars at temperatures exceeding 200 °C. The study's findings indicate that GFRP longitudinal bars do not significantly influence the performance of columns in fires. Consequently, future research should focus on columns reinforced with GFRP ties as well. The predicted values of post-fire axial capacity closely match the experimental data for non-insulated columns, indicating a high degree of accuracy. The study provides design recommendations to enhance the fire performance of such elements. The use of insulation results in a substantial reduction of temperature at various depths of the column. Post-fire residual capacities for non-insulated columns were approximately 30 %, whereas insulated columns demonstrated a 60 % residual capacity.

An Experimental Study and Result Analysis on the Dynamic Effective Bond Length of a Carbon Fiber-Reinforced Polymer Sheet Attached to a Concrete Surface

A carbon fiber-reinforced polymer (CFRP) is a common material utilized for the enhancement in reinforced concrete (RC) constructions. Previous research indicates that the bonding performance between a CFRP sheet and concrete determines whether the bonding of CFRP material is effective. However, the majority of existing research on the bonding performance of the CFRP–concrete interface is concentrated on static loading conditions. In order to clarify the effect of dynamic load on the bonding performance of the CFRP sheet–concrete interface, this study adopts the double-sided shear test method to carry out dynamic experimental research. The test findings reveal that the damage pattern of the CFRP sheet–concrete interface remains consistent across different loading rates. The ultimate bearing capacity increases as the strain rate increases. As the strain rate increases from 10−5 s−1 to 10−2 s−1, the effect of bond length on ultimate bearing capacity increases by about 7%. As the strain rate increases, both the maximum strain of CFRP and the maximum interfacial shear stress demonstrate a corresponding increase, with respective increase rates of 60% and 20%. The effective bond length decreases by about 20% when the strain rate rises from 10−5 s−1 to 10−2 s−1. Finally, a formula for calculating the dynamic effective bond length of a CFRP sheet, grounded in the Chen and Teng formula, has been proposed and verified.

Degradation law of bond strength of reinforced concrete with corrosion-induced cracks and machine learning prediction model

During long term operation service, reinforced concrete (RC) structures are subjected to corrosive media such as chloride salts, which results in the degradation of interface bond performance, subsequently reducing the load bearing capacity and service life of the structures. To accurately assess the durability of RC structures in environments such as oceans and salt lakes, this study combines experimental methods with machine learning (ML) techniques to explore the degradation patterns and predictive models of bond performance under chloride salt corrosion. Accordingly, a series of central pull-out tests were conducted based on an electrochemical accelerated-dry-wet cycle corrosion regime to investigate the degradation patterns of bond performance between corroded steel bars and concrete under different corrosion degree and corrosion-induced crack widths. By comparatively analyzing the evolution patterns of cracks and the morphology of the steel bars in reinforced concrete specimens and their failure modes, and integrating the mechanical degradation mechanism with chemical and microscopic corrosion mechanisms, an in-depth analysis of the corrosion-induced degradation patterns at the bond interface was performed. The internal relationships between corrosion degree, corrosion-induced crack width and bond strength were discussed, and the variation patterns of bond strength with corrosion-induced crack width and corrosion degree were explored. Moreover, the bond strength patterns were analyzed from an energy perspective. The results indicate that bond strength and bond energy decrease with an increase in the corrosion-induced crack width of the concrete. Additionally, based on the experimental data from this study, ML predictive models for bond strength were established using corrosion-induced crack width as the control variable. The results show that the ML-based bond strength predictive models fit well with the experimental data, offering higher accuracy and reliability compared to traditional bond strength models. The research findings provide significant theoretical basis and practical guidance for safety assessment, maintenance, reinforcement, and full-life design of corroded RC structures.

On the ductility of RC beam section: A revision and up to date of conclusions

In the context of reinforced concrete (RC) structures, standards aim to relate the ductility of these structures to the ductility of the steels used in their construction. Among other requirements, EC8 requires the use of special ductility steels to achieve high ductility in structures. After reviewing the relevant literature, this study aims to evaluate the impact of various parameters on the ductility at the cross-section level of RC elements subjected to bending. The study concludes that there is no consensus on the assessment of ductility, nor a standardized framework for the various alternatives. Additionally: i) Some contradictions exist regarding the impact of fundamental parameters on the assessment of ductility; ii) A one-size-fits-all methodology is impractical given the diverse factors influencing ductility in RC elements. It is proposed to consider the ductility of RC element sections as a function of the mechanical ratio of tensioned reinforcement. A proposal is also made to enhance the ductility of cross-sections without significantly increasing their strength: by increasing the width of the section while keeping other parameters unchanged.

Numerical Investigation on Torsional Reinforced Concrete Stepped Beams with Various Reinforcement Patterns

Numerical Investigation on Torsional Reinforced Concrete Stepped Beams with Various Reinforcement Patterns

Experimental and Theoretical Study on Local Damage of Reinforced Concrete Column under Rectangular Charge

During an explosion, a building’s stability is directly impacted by reinforced concrete (RC) columns. However, there is currently no theoretical analysis model that can precisely predict damage to RC columns after close-in/contact explosions. In the present study, the local damage response of RC columns under a rectangular charge was experimentally and numerically investigated, and a theoretical analysis model for predicting local damage after a contact explosion was developed. The experimental results verify the effects of concrete strength, standoff distance, transverse reinforcement spacing, and axial load on damage to RC columns. When the standoff is 100 mm, increasing the axial load can effectively reduce the damage to the center of the column surface. Numerical simulations were carried out to study the effect of different parameters on concrete damage, showing that the damage span of reinforced concrete increases with increased stirrup distance; however, when the stirrup distance decreases to 70 mm, the distance between the stirrups and the explosives is too close to limit the damage. The prediction model innovatively considers the attenuation of steel cross-section transmission and the characteristics of rectangular charges. Compared with traditional semi-empirical calculation models, it can accurately calculate local damage caused by contact explosions on reinforced concrete columns.

Behavior of Reinforced Concrete Circular Columns Subjected to Double Curvature Buckling Moment

This paper investigates experimentally and numerically structural performance of reinforced concrete (RC) circular column under double curvature buckling moment. RC circular columns are popularity embraced in RC structures not only owing to its esthetic, attractive appearance and easy for construction, but also for its better contribution for stress resistance. However, the corner or edge columns may be exposed to edge moment (EM) transferred from beam–column joint with double curvature effect. The current investigation proposes to understand the structural exhibition of such columns subjected to double curvature buckling edge moment generated at beam–column joint considering some parameters. A total number of 11 full-scale RC circular columns were constructed, installed, and then tested up to failure studying four parameters. These parameters were: clear height-to-diameter ratio (λ), longitudinal and lateral steel ratios (μ and ρ, respectively) and concrete type. The λ ratio has been introduced with: 4.89, 4.51 and 4.14. The μ ratio has been presented by: 2.2%, 2.3%, 2.6%, and 3.1%, while the ρ ratio was employed with: 0.84%, 0.93%, 1.00% and 1.18%. Three concrete types were studied; one of them was normal concrete (NC), while the other ones were high-performance concretes (HPCs) which were engineered cementitious composite (ECC) and high-strength fiber reinforced concrete (HSFRC). Experimental outcomes revealed that all studied parameters could affect and upgrade the structural performance; however, both longitudinal reinforcement and height-to-diameter ratio provided significant enhancement (about 51%–64%). Parallel to those exploited experimentally, nonlinear three-dimensional finite element models (FEMs) were installed, executed and established considering experimental outcomes producing an acceptable model with an under/over-estimation of about 4%.

Bayesian updating of relationships between crack width and corrosion level in reinforced concrete based on a large set of experimental data

AbstractThe evaluation of rebar corrosion in reinforced concrete (RC) structures presents a significant challenge for structural engineers, with on‐site visual inspections and crack width measurements playing a key role in the preliminary assessment. A general approach is to use corrosion models to predict the corrosion level of existing structures, and subsequently update these predictions by means of on‐site data. In this process, empirical models are often applied that relate the observed damage, such as corrosion‐induced cracks, to the corrosion level. However, these models have large uncertainties and are often not applicable to conditions that deviate from the test setups used to derive the empirical relations. This research aims to expand the applicability of these practical, existing empirical models for on‐site corrosion assessment through Bayesian updating techniques. To this aim, a Bayesian framework is developed to update crack width–corrosion models. The Bayesian updating methodology is illustrated for a simple regression model, and for a more complex relation that accounts for additional variables. A novel online database (KUL‐edCCRC) is used that is published accompanying this paper. The obtained results illustrate that the updated models have better agreement with the experimental results, and it is found that the confidence intervals of the regression parameters decrease for an increasing number of observations, even for a small number of additional datapoints. The results hence prove the efficiency of the approach to integrate information from new observations with prior information to adjust the crack width–corrosion model for specific conditions or cases, resulting in a more relevant model as more information becomes available.

Local and global integrative retrofitting of reinforced concrete frames using in‐plane buckling steel braces

AbstractTwo large‐scale, single‐storey, single‐bay reinforced concrete (RC) moment frames, designed as per an outdated seismic code to represent a typical framing detail of a four‐storey building, have been tested under displacement‐controlled quasi‐static loading protocol as per ACI 374.1‐05. The RC frames include a plinth beam with brick infill underneath, a slab monolithically cast with the top beam and provision for applying axial load to the column to simulate real construction scenario. One of the frames has been tested as a bare frame, and the second one has been retrofitted with conventional steel braces designed to undergo in‐plane buckling. The size of the brace has been selected based on the result of a nonlinear time history analysis of representative low‐ to mid‐rise open‐ground storey RC buildings. Post‐installed chemical anchors have been utilized to connect the steel braces to the narrow RC frame members following the outcomes of an experimental investigation by the same authors. Local‐level retrofitting by steel jacketing using adhesives has been designed and utilized on columns and beams to achieve the desired seismic response. The seismic performance of the retrofitted frame has been compared with the bare frame in terms of strength, stiffness, ductility, energy dissipation and hysteretic damping. The tests provide insight into the role of the plinth beam, effect of RC slab on the strong‐column weak‐beam aspect and the achievement of the desirable hinge mechanism through a precise design and detailing of global and local level retrofitting technique.

Numerical investigation on plastic hinge behavior of hybrid steel-FRP reinforced concrete columns

This paper presents a numerical study on the plastic hinge behavior and rotation capacity of concrete columns reinforced with a combination of steel bars and fiber-reinforced polymer (FRP) bars. A meso-scale numerical model, which considers the internal heterogeneity of concrete and bond behavior between concrete and longitudinal reinforcements, was developed and validated. The failure modes, lateral load-displacement responses, and the physical plastic hinge lengths of hybrid steel-FRP reinforced concrete (SFRC) columns were investigated and compared with those of conventional steel-reinforced concrete columns. The results indicated that the steel yielding zone and curvature localization zone of SFRC columns with FRP longitudinal bars were enlarged, due to the relatively low modulus of FRP bars. After that, a parametric analysis was performed to study the plastic hinge length of SFRC columns with respect to the nominal area ratio of FRP longitudinal bars, shear span-to-depth ratio, axial load ratio, and longitudinal reinforcement ratio. A new empirical model was proposed to predict the equivalent plastic hinge length, which was subsequently integrated into an analytical method for predicting the ultimate rotation. The comparison of predictions with simulation and test results demonstrated the accuracy of both the proposed empirical model and analytical method.