Slab-column Connections Research Articles

Correction: Seismic fragility assessment of reinforced concrete and post-tensioned slab-column connections - reliability-based formulations for storey drift limits

Correction: Seismic fragility assessment of reinforced concrete and post-tensioned slab-column connections - reliability-based formulations for storey drift limits

Improving predictive accuracy for punching shear strength in fiber-reinforced polymer concrete slab-column connections via robust deep learning

Amidst the evolving landscape of structural engineering, this study addresses the pressing need for a robust, data-driven model in the context of alternative reinforcement techniques such as Fiber-Reinforced Polymer (FRP) bars and the application of Machine Learning (ML) methodologies for predicting the punching shear strength (PSS). Structural engineering heavily relies on accurate predictions of PSS for ensuring the safety and durability of various constructions. However, existing models often lack the comprehensiveness and precision required to effectively address the diverse and complex factors influencing PSS in FRP-reinforced concrete structures. This research explored the shear strength of FRP-reinforced concrete slabs, with a particular focus on the different types of FRP, namely Carbon Fiber-Reinforced Polymer (CFRP), Basalt Fiber-Reinforced Polymer (BFRP), Glass Fiber-Reinforced Polymer (GFRP), and Hybrid Fiber-Reinforced Polymer (HFRP). Leveraging an innovative deep learning approach, the study utilizes a dataset comprising 285 samples gathered from 56 distinct studies to train models that incorporate 11 dependent variables. This comprehensive approach aims to capture the intricate interplay between geometric, material, and other pertinent factors influencing PSS. The study employs a connection weight method to evaluate the significance of various features and introduces a novel Graphical User Interface (GUI) to enhance user interaction with the Deep Neural Network (DNN) model designed for PSS prediction. Through meticulous experimentation and analysis, the research identifies an optimal DNN architecture that achieves a minimum Mean Absolute Error (MAE) of 0.81, validated through k-fold cross-validation. Key conclusions highlight the critical influence of specific features, such as slab depth, column-to-slab area ratio, and modulus of elasticity, on the predictive accuracy of the model. Conversely, certain factors like slab area, reinforcement ratio, and concrete compressive strength negatively impact predictions. SHAP analysis further elucidates the significance of FRP type and column length-to-width ratio as pivotal factors affecting PSS predictions. These findings underscore the potential of the developed model in enhancing the dependability and practicality of structural engineering applications. Moreover, they point towards future research directions aimed at refining predictive accuracy and exploring broader applications in the field of building engineering.

Punching shear performance of reinforced concrete slab-to-steel column connections incorporating ECC and UHPECC

Unlike the conventional reinforced concrete (RC) slab-column connection, the punching shear generated at the RC slab-to-steel column connection may lead to brittle punching shear failure due to the small area around the steel column. Moreover, the unexpected moments arising from eccentric loading can also lead to the failure of the slab in punching shear mode. This paper proposes employing high-performance concrete (HPC) to fill the critical punching shear zone to improve the punching shear resistance of RC slabs to steel column joints. Experiments on eight RC slabs to steel column connections are reported. The test parameters under investigation are the type of HPC used to fill the critical punching shear zone, the distance (S) of the HPC zone measured from the flanges of the steel column and loading condition (concentric and eccentric). The types of HPC include engineered cementitious composite (ECC) and ultra-high performance ECC (UHPECC). The experimental results show that the proposed techniques can significantly improve the cracking load, elastic stiffness, energy absorption capacity, ductility, failure modes, and ultimate load of the slab-to-column connections. The ultimate load of the tested connections is increased by as much as 33 %, and 28 % for the slabs subjected to concentric and eccentric loading, respectively. However, the ultimate load and energy absorption capacity of the slab with UHPECC having a S value of 1d, where d is the effective depth are lower than those of the control slab. Three-dimensional nonlinear finite element models are developed to simulate the performance of tested slab-to-column connections and validated by experimental results. The parametric study shows that the n (=S/d) value greater than 3.5 has insignificant effects on the ultimate punching shear capacity of the slab. It is demonstrated that the proposed formulas faithfully estimate the ultimate punching shear capacity of slab-to-column connections constructed with different HPCs under concentric and eccentric loadings.

Punching shear behavior of ultra-high-performance fiber-reinforced concrete and normal strength concrete composite flat slabs

This paper presents the results of tests on flat slabs with partial application of ultra-high-performance fiber-reinforced concrete (UHPFRC) mixtures to improve the punching shear capacity of slab-column connections. One normal strength concrete (NSC) slab and two UHPFRC slabs were tested as a reference for tests on 12 UHPFRC-NSC composite slabs with full depth UHPFRC in the center area of the NSC slab. The main test parameters were the steel fiber volume (0.8 % and 1.6 % volume fractions) and the dimensions of UHPFRC mixtures. The load-column displacement curves, crack patterns, slab rotations at failure, and failure loads are presented and discussed. The failure loads are compared with estimates obtained following the yield line analysis, design codes, and other theoretical models. Test results showed that the use of UHPFRC mixtures led to an increase in initial stiffness, punching shear strength, and deformation capacity, along with a change in the slab failure mode. The shear capacity of the slab improved proportionally to the increase in the dimension of the UHPFRC. These tests confirmed the effectiveness of the UHPFRC mixtures as an alternative to enhance the punching shear capacity for slab-column connections.

Simplification of KDS 14 Design Method for Slab–Column Connections Subjected to Unbalanced Moment

The current KDS 14 design method yields reasonable accuracy with acceptable safety in assessing the unbalanced moment-carrying capacity of slab–column connections. However, the model requires considerable computational effort owing to the effects of various design parameters, particularly the gravity-load effect. This study proposes a method to simplify the KDS 14 model to evaluate the unbalanced moment-carrying capacity of slab–column connections. In the proposed method, the gravity-load effect is decoupled from equations used for evaluating unbalanced moment-carrying capacity components. Subsequently, the total unbalanced moment-carrying capacity is determined by establishing an interaction between the gravity shear ratio and unbalanced moment components without considering the gravity-load effect. For practical design purposes, final simplified design equations are proposed. The reliability of the simplified method is validated based on a comparison with the current KDS 14 design code using a comprehensive database encompassing interior, exterior, and corner slab–column connections. Furthermore, a parametric study based on the proposed simplified approach, current design codes, combined with finite-element (FE) analysis is performed to elucidate the effects of constituents on the unbalanced moment-carrying capacity of corner slab–column connections. The results show that the proposed simplified model and KDS design method are strongly correlated with the experimental and FE results for a range of design parameters. Meanwhile, the ACI 318 model consistently provides a lower limit for strength prediction, thus yielding overly conservative and safe results compared with the test and FE results in most cases.

Prediction of punching shear strength in internal slab-column connections without shear reinforcement in reinforced concrete structures through multiple regression models

Prediction of punching shear strength in internal slab-column connections without shear reinforcement in reinforced concrete structures through multiple regression models

Seismic fragility assessment of reinforced concrete and post-tensioned slab-column connections - reliability-based formulations for storey drift limits

Seismic fragility assessment of reinforced concrete and post-tensioned slab-column connections - reliability-based formulations for storey drift limits

Multi-Leg Shear Reinforcement of Gfrp and Steel Lwrc Edge Column-Slab Connections: A Comparison Study

Multi-Leg Shear Reinforcement of Gfrp and Steel Lwrc Edge Column-Slab Connections: A Comparison Study

Punching and lateral cyclic behavior of concrete slab-column connections reinforced with steel sheets

During an earthquake, slab-column structures with high gravity-shear ratios often experience increased local shear stress and deformation in the connection area, leading to reduced unbalanced moment capacity and drift capacity of the connections. This study aims to create a new and more efficient method of enhancing the unbalanced moment capacity and deformation capacity of reinforced concrete slab-column structures through using steel sheets as punching reinforcement. Tests were conducted to evaluate the effects of the thickness, extension length, and layout of this new type of punching reinforcement on the unbalanced moment capacity and deformation capacity of the connections when subjected to vertical and horizontal cyclic loads. The results indicated that as the steel sheet thickness increased, the unbalanced moment capacity of SC-2 and SC-3 rose by 24 % and 48 % respectively, while the drift capacity improved by 20 % and 40 % compared to SC-1. Furthermore, the failure mode shifted from stress-induced punching to drift-induced punching. Compared to SC-1, a cruciform layout with an additional diagonal arrangement of sheets increased the unbalanced moment capacity and drift capacity by approximately 17 % and 20 %, respectively. The extension length of the sheets reduced from 600 to 420 had negligible effect on the unbalanced moment capacity and deformation capacity. Utilizing experimental data, this study compared the relationship between the drift capacity and gravity shear ratio of connections reinforced with different shear reinforcements. The underlying causes for the observed lower drift capacity of the specimens are analyzed, and design recommendations for optimizing the steel sheets are subsequently proffered. After thoroughly analyzing the experimental results, a simplified calculation methodology for assessing the shear strength of steel sheets was developed, taking inspiration from the shear strength calculation approach outlined in ACI 318–19. The efficacy of this simplified approach was subsequently validated by comparing the experimental results with those predicted by current design codes. Furthermore, by comparing the experimental results with the predicted values, the relationship between the punching failure mode of connections and their punching strength was discussed.

Effect of recycled concrete aggregates on the punching strength of slab-column connections without shear reinforcement

This paper presents the results of tests on six reinforced concrete slab-column connections. The slabs were octagonal, centrally supported on square columns, and concentrically loaded at their borders. The tests investigated the effects of replacing natural coarse aggregates with recycled concrete aggregates. The experimental results were also compared to resistance estimates from ACI 318 (2019) and Eurocode 2 (2004) and results from a database with tests on slabs without recycled concrete aggregates. The results show that using RCA reduces the concrete's modulus of elasticity and tensile strength but has little effect on its compressive strength. Furthermore, using RCA has little impact on the flexural response and punching resistance of the slabs. The findings suggest that RCA has potential for use in concrete applications, but further tests are required to draw definitive conclusions.

Shear Strength of Post-Tensioned Slab-Column Connections: Reevaluation of ACI 318-19 Code

Shear Strength of Post-Tensioned Slab-Column Connections: Reevaluation of ACI 318-19 Code

A review of punching behavior of slab–column connections with recycled coarse aggregate concrete

A review of punching behavior of slab–column connections with recycled coarse aggregate concrete

Empirical Punching Shear Capacity Equation for Reinforced Concrete Two-way Slabs with Openings

This study proposes a new equation to estimate the punching shear capacity of Two Way Reinforced Concrete Flat Slab Column (TRFSC) connections with openings. The TRFSC connections with openings in the literature were simulated using the finite element modeling technique. Then, the test results were used to calibrate and verify the finite element model. Next, the number of test data was artificially increased using the finite element model to cover a wide range of critical perimeters. Finally, the effects of several parameters such as the size of the openings in the reinforced concrete slabs, their position, and distance concerning the column on which the punching loading is applied on the variation of punching shear load capacity of TRFSC connections with openings were observed, the results showed that the proposed equation generally gave better results than the several current code equations. For the study used in the verification of the finite element model, it was observed that the ratios of the punching capacity values calculated using the experimental results and the regulations varied between 0.79 and 0.92 on average, and the regulations gave results that were not on the safe side for TRFSC connections with openings. However, with the nonlinear correction coefficient proposed in this study, the ratios of the experimental results and analytically calculated capacity values were calculated as 1.10 on average, and the standard deviation and variant values decreased much more.

ЧИСЛЕННОЕ ИССЛЕДОВАНИЕ РАБОТЫ УЗЛА МОНОЛИТНОГО БЕЗБАЛОЧНОГО ПЕРЕКРЫТИЯ СО СТАЛЕБЕТОННОЙ КОЛОННОЙ, С ПРИМЕНЕНИЕМ СРЕЗНОГО БАЛОЧНОГО УЗЛА, С УЧЕТОМ СОВМЕСТНОЙ РАБОТЫ БЕТОНА И СТАЛИ

The presented study conducts a comprehensive analysis of the performance of a monolithic slab-column connection utilizing a shear key. Utilizing the finite element method in the ANSYS software suite, a detailed geometric model of the structure is developed, facilitating complex numerical simulations. Special attention is paid to the interaction between concrete and steel within the structure, as well as the transfer of forces through the shear key. The obtained results include a detailed assessment of stress and deformation distribution in various components of the structure, enhancing the overall understanding of its mechanical behavior. The aim of the study is not only to analyze the effectiveness of employing a shear key to ensure the strength and stability of the slab-column connection, but also to generate practical recommendations for optimizing the design to improve the interaction between materials and enhance the reliability of construction projects. The presented research is significant for engineers and designers seeking to improve the processes of design and construction in the modern industry, as well as for developers of regulatory documents in the field of construction and infrastructure. The findings of the study can be applied in the development of new construction technologies.

Steel Collar Strengthening of a Slab-Column Connection under Eccentric Load

Steel Collar Strengthening of a Slab-Column Connection under Eccentric Load

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.

Ensemble Learning Models for Prediction of Punching Shear Strength in RC Slab-Column Connections

In reinforced concrete (RC) structures, accurate prediction of the punching shear strength (PSS) of slab-column connections is imperative for ensuring safety. The existing equations in the literature show variability in defining parameters influencing PSS. They neglect potential variable interactions and rely on a limited dataset. This study aims to develop an accurate and reliable model to predict the PSS of slab-column connections. An extensive dataset, including 616 experimental results, was collected from earlier studies. Six robust ensemble machine learning techniques—random forest, gradient boosting, extreme gradient boosting, adaptive boosting, gradient boosting with categorical feature support, and light gradient boosting machines—are employed to predict the PSS. The findings indicate that gradient boosting stands out as the most accurate method compared to other prediction models and existing equations in the literature, achieving a coefficient of determination of 0.986. Moreover, this study utilizes techniques to explain machine learning predictions. A feature importance analysis is conducted, wherein it is observed that the reinforcement ratio and compressive strength of concrete demonstrate the highest influence on the PSS output. SHapley Additive exPlanation is conducted to represent the influence of variables on PSS. A graphical user interface for PSS prediction was developed for users’ convenience. Doi: 10.28991/CEJ-SP2024-010-01 Full Text: PDF

Hybrid Machine Learning Algorithms for Prediction of Failure Modes and Punching Resistance in Slab-Column Connections with Shear Reinforcement

This study presents a data-driven model for identifying failure modes (FMs) and predicting the corresponding punching shear resistance of slab-column connections with shear reinforcement. An experimental database that contains 328 test results is used to determine nine input variables based on the punching shear mechanism. A comparison is conducted between three typical machine learning (ML) approaches: random forest (RF), light gradient boosting machine (LightGBM), extreme gradient boosting (XGBoost) and two hybrid optimized algorithms: grey wolf optimization (GWO) and whale optimization algorithm (WOA). It was found that the XGBoost classifier had the highest accuracy rate, precision, and recall values for FM identification. In testing, WOA-XGBoost has the best accuracy in predicting punching shear resistance, with R2, MAE, and RMSE values of 0.9642, 0.087 MN, and 0.126 MN, respectively. However, a comparison between experimental values and calculated values derived from classical analytical methods clearly demonstrates that existing design codes need to be improved. Additionally, Shapley additive explanations (SHAP) were applied to explain the model’s predictions, with factors categorized according to their impact on failure modes and punching shear resistance. By modifying these parameters, punching resistance can be improved while reducing unpredictable failure. With the proposed hybrid algorithms, it is possible to determine the failure modes and the punching shear resistance of slabs during the preliminary stages of the construction.

Investigation of Key Parameters Influencing Shear Behavior in Glass-Fiber-Reinforced Polymer (GFRP)-Reinforced Concrete (RC) Interior Slab–Column Connections

This article explores the punching shear behavior of GFRP-RC interior slab–column connections. The parameters tested included the column–aspect ratio (1.0, 2.0, 3.0, 4.0, and 5.0), perimeter-to-depth ratio for square column stubs with side lengths of 0.3, 0.4, 0.5, 0.6, and 0.7 m, and span-to-depth ratios of 4, 6, 8, 10, and 12. A review of the literature revealed that no previous study has investigated the effect of these parameters or their interactions on this type of connection. Numerically, twenty-five slabs were created using finite element (FE) software (V3), each with square dimensions of 2.5 m and a constant thickness of 0.2 m. The central column extended 0.3 m from the top and bottom of the slab. All four sides of the slabs were supported, and the specimens underwent pure static shear load testing. The test results demonstrated that all slabs failed due to punching shear. Increasing any parameter value reduced the punching shear stresses. Additionally, the results indicated that Canadian (CSA-S806-12) and Japanese (JSCE-97) standards for FRP-RC materials generally provided the closest predictions of punching shear capacity compared to the American guideline, ACI 440.1R-22. However, all standards exhibited shortcomings and require enhancement and modifications, particularly to consider the impact of the span-to-depth ratio. Therefore, three equations were developed to predict the shear strength of the connections, yielding better results than those prescribed by the North American and Japanese standards.

Punching Shear of FRP-RC Slab–Column Connections: A Comprehensive Database

Several design standards have been developed in the last two decades to estimate the punching capacity of two-way reinforced concrete (RC) slabs reinforced with fiber-reinforced polymer (FRP) reinforcement. FRP-RC design standards include the recently published ACI 440.11-22, CSA/S806-12, and JSCE-2007. These models are either based on empirical data or semi-empirical methods and calibrated using different databases. Additionally, these standards do not have provisions for connections with shear reinforcement. Therefore, a reliable worldwide database for developing and assessing the applicability of such provisions with test results is vital. This study presents a worldwide and up-to-date database for punching shear of FRP-RC slabs. The database includes 197 tested connections, comprising interior and edge connections, with and without shear reinforcement, and a wide range of materials and cross-sectional properties. The database was used to evaluate the accuracy of the mentioned standards in predicting the punching shear capacity. For connections without shear reinforcement, it was determined that the three design standards yielded similar performance with different conservatism levels. ACI 440.11-22 yielded the most conservative results, with average Vexp/Vpred ratios of 2.04 compared to 1.28 and 1.3 for other models. For connection with shear reinforcement, specimens with Evf> 100 GPa resulted in Vexp/Vpred ratios less than 1.0 for ACI and CSA standards.