This paper presents a groundbreaking contribution to the field of slender fiber-reinforced polymer (FRP) reinforced concrete (RC) column design, addressing a critical aspect in the context of ACI 318-19 methodology—the prediction of effective flexural stiffness. Acknowledging the inherent differences in the properties of FRP bars compared to steel bars, this study introduces a novel analytical equation derived from an extensive simulation of 11,520 FRP RC columns. The proposed model meticulously accounts for key parameters influencing column behavior, including the concrete strength, longitudinal reinforcement ratio, modulus of elasticity of FRP bars, eccentricity ratio, and column slenderness ratio. To validate the efficacy of the new formula, a comprehensive verification was conducted on 71 FRP RC columns, combining data from existing literature (63 columns) and experimental results obtained by the authors (eight columns, detailed in a separate publication). Notably, the newly proposed equation demonstrates a conservative approach, predicting lower flexural stiffness while exhibiting no specimens in the failure zone. This conservative yet accurate prediction underscores the proposed model’s potential superiority over existing models, emphasizing the necessity for different equations tailored to the distinct properties of FRP bars. The results of this study contribute significantly to advancing the understanding and design methodologies for slender FRP RC columns, providing engineers with a reliable tool for predicting flexural stiffness in a manner that aligns with the unique characteristics of FRP materials and the latest advancements in structural engineering.

Experimental and parametric investigation on flexural performance of post-tensioned reinforced concrete beams with large-diameter strands

Effect of uncertainty in calibrated chloride diffusion coefficients on maintenance and life-cycle decisions of reinforced concrete structures

The investigation of oblique projectile impacts on concrete structures has become increasingly significant, particularly in the contexts of defense and critical infrastructure. Although extensive research previously has been conducted on the normal impact response of concrete panels, studies focusing on oblique impacts remain limited, despite their relevance in practical scenarios. This study examined the effects of angular/oblique impacts of hard projectiles on plain concrete (PC) and reinforced concrete (RC) panels. An innovative experimental setup was established to examine the oblique impacts on these concrete panels. Twelve specimens, comprising six PC and six RC specimens, were exposed to projectile impacts at three varying incidence angles: 0°, 30°, and 60° relative to the normal of the panel face. Two specimens were tested at each angle, and crucial parameters such as depth of penetration (DOP), crater damage, reaction force, acceleration, and strain were measured to evaluate the panels’ performance under different angular impacts. The findings indicated a decrease in penetration and reaction force with increasing incidence angle, although a slight increase in crater damage was noted. Furthermore, a numerical model using Abaqus was employed to ascertain the true critical incidence angle of 40°, which resulted in the maximum crater damage for this scenario. Ultimately, the experimental data concerning crater damage and DOP were compared with existing probabilistic formulae accounting for the influence of incidence angle on damage parameters. Importantly, the design and protection of concrete structures against oblique impacts should consider not only penetration but also crater damage.

This study advances sustainable reinforced concrete (RC) design by performing structural optimization, and embodied CO₂, while maintaining code-compliant strength, serviceability, and ductile failure behavior under bending stress. Full-scale experimental tests are combined with finite element analyses to investigate RC beams incorporating inclined stirrups and arranged voids forming truss-like configurations, including Vierendeel, Warren (30°, 45°, and 60° inclination angles), Warren with verticals, Pratt, and Howe layouts. Beams with spans between 3 m and 7 m are designed according to Eurocode 2, showing comparable yielding force, failure, and deflection to a solid benchmark RC beam. Performance indicators such as first-crack load, yielding and ultimate load, and corresponding displacements are evaluated. Embodied CO₂ is quantified through life-cycle assessment (LCA) (modules A1-A5 and C1-C4), and the structural efficiency under is expressed via a strength-to-carbon efficiency (SCE). The results show that the first-crack force decreases by 8.6%, with the reductions observed mostly for the Vierendeel and Warren 30° layouts. Warren configurations with 45°–60°, with or without verticals, improve crack distribution and limit stiffness loss, while solid beams with alternative stirrup layouts exhibit comparable crack initiation. Vierendeel layouts concentrate stresses and may fail in shear-compression, whereas Warren 45°, Warren 60°, Warren with verticals, Pratt and Howe reach 90–105% of the benchmark capacity with ductile response. Void alignment with principal stress trajectories is critical; diagonals and/or verticals support strut-and-tie flow and become increasingly beneficial for longer spans. CO₂ savings are driven by reduced concrete in A1-A3; Warren 45° achieves 10.8% to 22.9% savings (A1-A5 +C1-C4) and SCE gains up to 27.7%, increasing with span. Warren 60°, Warren with verticals, Pratt, or Howe layouts are recommended for spans exceeding 4 m, while Warren 45° or Warren 60° without verticals are suitable for shorter spans. A hybrid layout, transitioning from Warren 45° near midspan to Warren 60° and subsequently to Warren with verticals, Pratt, or Howe towards the supports, emerges as a design strategy. The conclusions are limited to flexure-dominated response under four-point bending; future work should evaluate shear-dominated and combined bending-shear-torsion actions, uniformly distributed loading, long-term deformation and durability, and joint behavior including load placement relative to joints.

Structures that are located in seismic zones are vulnerable to severe seismic activities. Subsequently, the structures are subjected to enhanced base shear, acceleration, and displacements, which diminish the structure’s seismic performance. Several dampers have been implemented to control the seismic responses of buildings, but they have their own limitations. Therefore, a negative stiffness device, (NSD), which is a truly passive device, has been introduced, producing a true negative stiffness, thereby introducing reduced stiffness in the building. In the current study, a 9-story open-ground reinforced concrete frame building is considered to assess its seismic performance with the implementation of NSD at different locations in the ground story by considering 24 models. The optimum properties of the NSD suited for the building are evaluated by performing the nonlinear static analysis and performed various iterations to get optimum design parameters. The variables considered for the current investigation are the base shear, individual story acceleration, displacement, and drift of the structure. Moreover, the optimal location and number of NSDs are also evaluated. When the structure is susceptible to seven distinct seismic events, a nonlinear time history analysis (NLTHA) is performed. The deployment of NSD is found to be efficient in improving the seismic behavior of the structure. The seismic parameters, such as base shear and acceleration of the structure, are attenuated by 30% and 25%, respectively, and the optimum models are considered keeping in view of best attenuation of base shear, acceleration, and the number of NSDs deployed.

Abstract Concrete is widely used due to its high compressive strength; however, its brittleness and low tensile strength make it highly susceptible to cracking and fracture. Therefore, accurate modeling of its damage evolution is critical for ensuring structural safety. This paper proposes a novel micropolar peridynamic damage model integrated with Timoshenko beam theory. More importantly, the model introduces independent/coupled nonlinear damage criteria for tensile, compressive, shear, and torsional deformations by embedding the damage evolution criteria directly into the micropolar beam‐based formulation. The model is specifically designed to investigate the influence of microstructural interactions in concrete, with a particular focus on capturing complex damage mechanisms stemming from the Poisson effect, crack development, and shear failure. This model is integrated within the open‐source analysis platform OpenSees to leverage its extensive libraries of nonlinear solution algorithms and parallel computing capabilities. The proposed Timoshenko micropolar peridynamic (TMP) damage model is verified through two application examples: a uniaxial compression test of specimens with different Poisson's ratios and a pushover analysis of a reinforced concrete (RC) column. The results demonstrate that the TMP damage model, integrated into the OpenSees framework, can effectively capture the complex damage behaviors of RC components, including strength deterioration, stiffness degradation, and the Poisson effect at the macroscopic scale, as well as concrete crack development and rebar reinforcement behavior at the microscopic scale. This study provides a robust tool for better predicting and analyzing the multiscale damage behavior of RC components under complex loading conditions.

Spirulina based DFNS/Cellulose nano hybrid as a bioactive reinforcement for durable foamed concrete.

This research focuses on the need to clearly define the lateral design force distribution shape for the seismic design of reinforced concrete (RC) buildings. It specifically looks at the effects of soil-structure interaction (SSI) and inelastic structural behavior. Traditional seismic design methods usually assume fixed-base conditions and overlook SSI. This can result in inaccurate predictions of how much the structure will deform. To create a more reliable, data-driven seismic design framework, the study conducted extensive nonlinear time-history analyses on various regular RC buildings using OpenSeesPy both for generating a building database based on current code provisions and for assessing their dynamic response. These models vary across important factors, including fundamental periods, slenderness ratios, , and soil conditions. The spectral acceleration at the first mode period served as the measure of ground motion intensity (IM). The collected data were used to derive classical regression equations and to train machine learning models, including Neural Network Regression and Gradient-Boosting Regression Trees, to predict the optimal lateral force profile shape. These methods are essential for understanding the complex, nonlinear relationships between seismic input factors and the dynamic characteristics of a building, as well as engineering demand parameters (EDPs) such as storey drift. The study found that the key factors affecting nonlinear lateral displacement and force-shape profile include the structure's slenderness ratio , the fixed-base and flexible-base fundamental periods, and , and the IM, . By providing a probabilistic assessment, this methodology seeks to improve the outcomes of seismic design codes and enhance performance-based design for RC buildings.

Experimental investigation of bond behavior of steel, GFRP, and CFRP reinforcement in self-compacting and fiber-reinforced concrete using RILEM beam tests.

This study describes a dataset from an experimental campaign investigating the quasi‐static cyclic lateral response of two full‐scale, two‐storey, two‐bay reinforced concrete (RC) frames with masonry infills representative of mid‐20th century European construction practice. The nominally identical specimens were tested in both as‐built and retrofitted configurations. The dataset aims to provide new experimental evidence on the investigation of the effectiveness of a cross‐laminated timber (CLT)‐based retrofit system, in which the external masonry wythe is replaced by a CLT panel connected to the RC frame through a glulam subframe and dissipative fasteners, while the internal wythe is retained to ensure compatibility with finishing layers. The campaign comprises snap‐back tests to characterize initial dynamic properties and quasi‐static cyclic tests conducted up to near‐collapse conditions. The dataset includes actuator forces and displacements, local deformations of masonry infills and CLT panels, relative slip at connections and material characterization tests. The work presented aims at contributing to the calibration and validation of numerical/analytical models and, possibly, to the development of guidelines for integrated seismic and energy renovation of existing infilled RC framed buildings.

Among the most critical structural deficiencies observed in existing reinforced concrete (RC) buildings worldwide are inadequately detailed beam–column joint regions, often constructed without reinforcement. Despite extensive research, the numerical modeling of these critical components still remains a major challenge, as a robust and universally accepted modeling framework has yet to be established, especially when extensive nonlinear analyses have to be performed. This study specifically addresses how joint reinforcement detailing governs the transition between flexure-dominated and shear-dominated joint behavior in non-ductile exterior sub-assemblages, and evaluates whether and how a simplified macro-model can reliably reproduce these mechanisms at full scale. The seismic behavior of exterior RC beam–column joints without adequate transverse reinforcement was first investigated herein through a full-scale experimental program. Five sub-assemblages were tested under quasi-static cyclic loading with increasing displacement history. They mainly differ for beam and column longitudinal reinforcement amount and joint panel (light or null) reinforcement layout, with equal geometric and material properties. The experimental results are first investigated in terms of global response, damage evolution, and energy dissipation capacity, comparing their seismic performance with varying beam or joint reinforcement. Then, nonlinear analyses were carried out by using a computationally efficient macro-modeling strategy in the OpenSees platform to numerically reproduce the observed response. The joint panel behavior was idealized through an empirical quadrilinear rotational spring, whereas flexural and fixed-end-rotation contributions are mechanically defined. The simulations reproduced the global load–drift envelopes, stiffness deterioration, and post-peak softening branch with satisfactory accuracy, although some discrepancies can be observed in the pinching effect. Nevertheless, the comparison between experimental and full-scale numerical results confirms that the adopted model provides reliable predictions of the cyclic response of non-ductile RC joints, also resulting in suitable solutions for extensive analyses as required, for example, for large-scale studies.

Many existing reinforced concrete (RC) structures have undergone increases in service loads due to changes in use, functional upgrades, and evolving design codes. This highlights the need for reliable requalification methods that account for long-term degradation mechanisms, particularly those related to sustained loading and creep. This study investigates the residual flexural behavior of RC beams after long-term loading and evaluates its effects on stiffness and ultimate strength. Three RC beams were loaded to 43% of their short-term yielding moment and kept under sustained load for 210 days, while three identical specimens were maintained as unloaded references. Afterward, all beams were subjected to repeated four-point loading–unloading cycles to detect changes in stiffness, strength, and cyclic response. The results indicate that long-term loading did not significantly affect the beams’ ultimate load-carrying capacity compared with the reference specimens. However, the long-term-loaded beams exhibited a clear reduction in initial stiffness. This difference was most evident during the first loading cycle and gradually decreased in subsequent cycles. To interpret these findings, a layered fiber model was developed to simulate cyclic behavior while incorporating time-dependent concrete effects. The model successfully reproduced the main experimental trends, reinforcing the reliability of both the testing program and the analytical approach. The study enhances understanding of stiffness degradation in RC elements subjected to increased service loads.

ABSTRACT Reinforced concrete (RC) structures in marine environments are vulnerable to reinforcement corrosion, which degrades the bond between reinforcement and concrete and threatens structural durability. This study investigated the bond performance of steel bars, basalt fiber reinforced polymer (BFRP) bars, and steel‐fiber composite bars (SFCBs) embedded in concrete under seawater immersion, wet‐dry cycling, and wet‐dry cycling with pre‐cracking for corrosion ages of 30, 60, and 90 days. The results show that the bond‐slip behavior of BFRP bars and SFCBs exhibits four stages, whereas steel bars do not display a residual stage. The bond strength of the steel bar and concrete increased from 12.87 to 19.36 MPa during the first 60 days due to rust expansion but subsequently decreased by approximately 25%. After 90 days, the bond strength decreased from 16.74 to 12.44 MPa for BFRP bars and from 12.77 to 11.58 MPa for SFCBs, corresponding to reductions of 25.69% and 9.32%, respectively, demonstrating superior long‐term corrosion resistance compared with steel reinforcement. The MBPE model accurately fitted the experimental bond‐slip curves, with R 2 > 0.90 for all groups except B‐I‐30. These results support the application of FRP reinforced concrete structures in marine environments.

ABSTRACT To elucidate the punching–shear failure mechanism and effect pattern of reinforced concrete (RC) slab–column joints with stirrups and/or openings, punching–shear failure tests were systematically conducted on 11 RC slab–column joint specimens to study the effects of the reinforcement configurations and joint openings on failure modes, punching–shear bearing capacity, and strain evolution, and the applicability of the methods in the existing codes was verified. The results showed that different reinforcement combinations can significantly affect the failure modes; punching–shear-resisting stirrups can effectively and synergistically increase the punching–shear capacity and deformation capacity; the stirrup ratio and horizontal longitudinal reinforcement ratio have interactive effects; and the stirrup ratio and spacing of the bidirectional stirrups have significant effects. Increasing the horizontal longitudinal reinforcement ratio can increase the punching–shear capacity, and the longitudinal reinforcement ratio has a threshold effect. With respect to hidden beams, reasonable openings in the joint area have a limited effect on the punching–shear performance of the slab–column joint. Through the use of existing punching–shear capacity calculation methods, the proposed calculation method considers the beneficial effects of horizontal longitudinal reinforcements and can accurately predict the punching–shear capacity.

This study examines the use of 15 different intensity measures (IMs) for estimating structural collapse using results from incremental dynamic analysis (IDA). IDA results from 54 numerical models were considered, including (i) 12 reinforced concrete (RC) frame structures, (ii) 16 RC wall–frame structures and (iii) 26 steel buckling‐restrained braced frame structures. The height of the structures ranged from 2 to 20 storeys, with the initial fundamental period varying from 0.25 to 2.3 s. IMs were evaluated using two existing criteria: efficiency and sufficiency, along with their predictability and practicality. Among the 11 period‐independent IMs examined, peak ground velocity (PGV) and velocity spectrum intensity (VSI) were the best correlated with the intensity at collapse. For structures with an initial period shorter than 1 s, VSI was the most efficient of all IMs considered. For structures with periods longer than 1 s, the period‐dependent IMs—average spectral acceleration and filtered incremental velocity—were found to be the most efficient IMs. The efficiency of the IMs was observed to be relatively insensitive to the lateral load‐resisting system. In general, the period‐independent and period‐dependent IMs identified above exhibited comparable levels of sufficiency. Results indicate that velocity‐based IMs, such as PGV and VSI, performed well in terms of efficiency and sufficiency, particularly for short period structures. From a practical perspective, PGV and VSI offer advantages due to their efficiency, simplicity and period independence, making them suitable IMs for region‐wide or portfolio‐level assessments.

An experimental investigation was conducted to evaluate the flexural-shear behavior of deteriorated reinforced concrete (RC) beams strengthened with carbon fiber fabric-reinforced cementitious matrix (C-FRCM) composites, focusing on their failure modes, ultimate bearing capacity, ductility, and stiffness. The strengthening efficiencies of a carbon fiber woven mesh and a carbon fiber cloth were comparatively analyzed. The results indicated that the C-FRCM effectively restrained the crack propagation process: the RC beams strengthened with the C-FRCM (carbon fiber woven mesh) exhibited relatively uniform crack development trends, whereas those strengthened with carbon fiber-reinforced polymer (CFRP) exhibited delayed crack growth prior to steel bar yielding. Future studies will add strengthening tests with different numbers of layers to further verify the generality of this law. Under two-layer strengthening conditions, smaller mesh sizes produced more significant performance improvements. Conversely, for mesh sheets with constant distribution ratios, increasing the number of layers further improved the effectiveness of strengthening. The C-FRCM also enhanced the ductility and flexural stiffness of deteriorated RC beams to a certain extent, providing improvement trends that were consistent with those observed in the ultimate bearing capacity. However, the ductility enhancement varied among the samples, with differentiation arising from the stiffness improvement characteristics and plastic deformation capacities associated with different strengthening configurations. A calculation method for determining the flexural bearing capacities of C-FRCM-strengthened degraded RC beams was proposed, accounting for concrete strength degradations, cross-sectional damage characteristics, the steel corrosion rate, reinforcement configuration parameters, the effective utilization rates of composite materials, and fiber strength exploitation efficiency. The validity of the proposed methodology was established through an experimental validation by incorporating statistical performance metrics such as the mean error and coefficient of variation, while a comparative analysis against the existing code-based formulations demonstrated its technical advantages.

ABSTRACT The growing demand for sustainable construction materials has encouraged the adoption of natural fibers as alternatives to synthetic reinforcements in concrete. Cactus fiber (CF) has emerged as a promising reinforcement due to its renewable nature, favorable mechanical properties, and low environmental impact. However, predicting the nonlinear compressive strength behavior of cactus fiber-reinforced concrete (CFRC) remains challenging using conventional empirical approaches. This study applied four advanced machine learning algorithms – Support Vector Regression – Multilayer Perceptron (SVR-MLP) ensemble, Light Gradient Boosting Machine (LightGBM), Extreme Gradient Boosting (XGBoost), and Extreme Learning Machine (ELM) – to predict CFRC compressive strength. A comprehensive dataset was compiled from published literature incorporating key variables such as cement content, aggregate proportions, fiber dosage, water – binder ratio, and curing age. Model evaluation results showed that XGBoost achieved superior predictive performance with the highest accuracy (R2 = 0.9720) and lowest prediction errors compared to other models. The developed machine learning framework enables reliable strength prediction and optimization of fiber dosage under controlled mix conditions. Findings confirm cactus fiber as a viable low-carbon reinforcement material and demonstrate the effectiveness of artificial intelligence in supporting sustainable, data-driven concrete mix design and enhanced performance reliability.

The behavior of Reinforced Concrete (RC) rectangular, slender columns is examined in this study upon exposure to heat-damage effects and fully confined by Carbon Fiber Reinforced Polymer (CFRP) wraps, where a new interaction diagram is proposed. The Nonlinear Finite Element Analysis (NLFEA) method is adopted to comprehensively understand the behavior of the RC columns, where a validation process takes place, followed by a wide parametric study. The studied parameters include the effect of different temperatures (23 °C (room temperature), 200 °C, 400 °C, 600 °C, and 800 °C) and nine eccentricity-to-height ratios where biaxial moments exist (0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, and 0.8). It has been found that the deformation, toughness, and the axial column’s strength are significantly improved by providing one layer of CFRP sheets for heat-damaged RC columns, while the stiffness behavior is only marginally affected. In addition, increasing the temperature reduces the energy absorption capacity and the ultimate strength of the columns while these are reduced by increasing the loading eccentricity value. However, columns experience a sudden and brittle failure when subjected to combined bending and axial loadings that might be accompanied by steel yielding or buckling of the column’s cross-section. Finally, the interaction diagram between the load and bending actions was constructed by addressing the results of the simulated columns.

This study aims to comparatively evaluate the seismic performance of steel and reinforced concrete (RC) structural systems. Based on the data of existing 4-story and 12-story RC buildings located in the Taşburun neighborhood of Elbistan district in Kahramanmaraş province, the same buildings were re-modeled using both RC and steel structural systems. Performance analyses were conducted using linear and nonlinear analysis methods in accordance with the Turkish Building Earthquake Code (TBDY-2018) and the Design, Calculation and Construction Principles for Steel Structures. The analysis results indicate that steel structures exhibit lower relative story drifts, fewer plastic hinge formations, lower structural weight, and higher energy dissipation capacity compared to RC structures. Particularly in high-rise buildings, steel systems were found to reach the “Immediate Occupancy” or “Limited Damage” performance level, while RC systems could only achieve “Collapse Prevention” under the same conditions and, in some cases, “Life Safety” levels after strengthening. This difference is attributed to the ductility, lightweight nature, and controlled energy absorption capacity of steel material. The findings of this study suggest that promoting steel structural systems in earthquake-prone countries like Turkey is a strategic necessity in terms of engineering design, public safety, and post-disaster recovery processes.