Axial Load-carrying Capacity of Steel Tubed Concrete Short Columns Confined with Advanced FRP Composites

Fiber Reinforced Polymers (FRPs) have wide applications in the field of concrete construction due to their superior performance over conventional materials. This research focuses on the structural behavior of steel tube FRP jacket–confined concrete (STFC) columns under axial concentric loading and proposes a new empirical equation for predicting the axial load-carrying capacity of STFC columns having thickness of FRP-fabric ranging from 0.09 mm to 5.9 mm. A large database of 700 FRP-confined concrete specimens is developed with the detailed information of critical parameters, i.e. elastic modulus of FRPs (Ef), compressive strength of unconfined concrete (fc’o), diameter of specimen (D), height of specimen (H), total thickness of FRPs (N.tf), and the ultimate strength of confined concrete (fc’c). After the preliminary evaluation of constructed database, a new empirical model is proposed for the prediction of axial compressive strength of FRP-confined specimens using general regression analysis by minimizing the error functions such as root mean squared error (RMSE) and coefficient of determination (R2). The proposed FRP-confinement strength model presented higher accuracy as compared with previously proposed models. Finally, an equation is proposed for the predictions of axial load carrying capacity of STFC columns. For the validation of proposed equation, an extensive parametric study is performed using the proposed nonlinear finite element model (FEM). The FEM is calibrated using the load-deflection results of STFC columns from literature. A close agreement was observed between the predictions of proposed finite element model and proposed capacity equation

Structural Performance of GFRP Bars based High-Strength RC Columns: An Application of Advanced Decision-Making Mechanism for Experimental Profile Data

Several past studies have shown the use of glass fibre-reinforced polymer (GFRP) bars to alleviate the reinforced steel rusting issue in different concrete structures. However, the practise of GFRP bars in concrete columns has not yet achieved a sufficient confidence level due to the lack of a theoretical model found in the literature. The objective of the current study is to introduce a novel prediction model for the axial capability of concrete columns made with bars of GFRP. For this purpose, two different approaches, such as data envelopment analysis (DEA) and artificial neural networks (ANNs) modelling, are used on a collected dataset of 266 concrete column specimens made with GFRP bars from previous literature works. Eight parameters were used to predict the axial performance of GFRP-based RC columns. The proposed DEA and ANNs predictions demonstrated a good correlation with the testing dataset, having R2 values of 0.811 and 0.836, respectively. A comparative analysis of the DEA and ANNs models is undertaken, and it was found that the suggested models are capable of accurately forecasting the structural response of GFRP-made RC column structures. Then, a comprehensive parametric analysis of 266 GFRP-based columns was performed to study the effect of different materials and their geometrical shape.publishedVersio

The Latest Scientific Problems Related to the Implementation and Diagnostics of Construction Objects

This book contains publications related to the special topic entitled: "The Latest Scientific Problems Related to the Implementation and Diagnostics of Construction Objects". Construction is a sector of the economy that is characterized by a very high variability of execution conditions and a large variety of building structures. In a period of very rapid economic development, this high variability and diversity generates many new scientific problems that must be solved in order to further improve the quality of production, as well as to reduce the cost and time of construction. The purpose of the issue is to present and discuss the results of the latest research in the broad field of construction engineering, particularly concerning: modification of the composition of construction materials using various micro- and nanomaterials, by-products or wastes; modern methods of controlling construction processes; methods of planning and effective management in construction, as well as methods of diagnosing construction objects. The articles published in this issue deal with theoretical, experimental, applied and modeling research conducted worldwide in the above-mentioned scientific areas

Numerical Study of Concrete

Concrete is one of the most widely used construction material in the word today. The research in concrete follows the environment impact, economy, population and advanced technology. This special issue presents the recent numerical study for research in concrete. The research topic includes the finite element analysis, digital concrete, reinforcement technique without rebars and 3D printing

Using data mining algorithms to predict the bond strength of NSM FRP systems in concrete

This paper presents the effectiveness of soft computing algorithms in analyzing the bond behavior of fiber reinforced polymer (FRP) systems inserted in the cover of concrete elements, commonly known as the near-surface mounted (NSM) technique. It focuses on the use of Data Mining (DM) algorithms as an alternative to the existing guidelines’ models to predict the bond strength of NSM FRP systems. To ease and spread the use of DM algorithms, a web-based tool is presented. This tool was developed to allow an easy use of the DM prediction models presented in this work, where the user simply provides the values of the input variables, the same as those used by the guidelines, in order to get the predictions. The results presented herein show that the DM based models are robust and more accurate than the guidelines’ models and can be considered as a relevant alternative to those analytical methods

A Fuzzy Inference System in Constructional Engineering Projects to Evaluate the Design Codes for RC Buildings

Economical design of a building is one of the main aims that should be followed because of its importance in constructional projects. In order to have an economical design, longitudinal reinforcing bars in the reinforced concrete members are among those parts of the structure that can be designed economically. The application of fuzzy inference systems provides an effective tools to handle the uncertainties and subjectivities arising in the designing process of buildings. Therefore, the main purpose of this paper is to propose a fuzzy inference system to evaluate the building design codes from an economical point of view. For this purpose, after designing the mentioned fuzzy inference system, three examples of three-dimensional concrete buildings are analyzed and designed using different codes. For all these codes, the structural properties of concrete buildings, the gravity and the seismic loads are considered to be the same. Finally, it finds that the fuzzy logic theory is an effective and practical tool to compute a value that shows the distance between the designed building and the economically designed building. Also, it concludes that between the studied codes, (EUROCODE 2-1992, Hong Kong CP-04, CSA A23.3-04 and ACI 318-05), the ACI 318-05 and Hong Kong CP04 codes lead to a more economical design for taller buildings. For low-rise buildings, the CSA A23.3-04 and ACI 318-05 codes lead to an economical design. Also, the EUROCODE 2-1992 has a minimum value for the economical design of all the considered buildings

A new mixed model based on the enhanced-Refined Zigzag Theory for the analysis of thick multilayered composite plates

The Refined Zigzag Theory (RZT) has been widely used in the numerical analysis of multilayered and sandwich plates in the last decay. It has been demonstrated its high accuracy in predicting global quantities, such as maximum displacement, frequencies and buckling loads, and local quantities such as through-the-thickness distribution of displacements and in-plane stresses [1,2]. Moreover, the C0 continuity conditions make this theory appealing to finite element formulations [3]. The standard RZT, due to the derivation of the zigzag functions, cannot be used to investigate the structural behaviour of angle-ply laminated plates. This drawback has been recently solved by introducing a new set of generalized zigzag functions that allow the coupling effect between the local contribution of the zigzag displacements [4]. The newly developed theory has been named enhanced Refined Zigzag Theory (en- RZT) and has been demonstrated to be very accurate in the prediction of displacements, frequencies, buckling loads and stresses. The predictive capabilities of standard RZT for transverse shear stress distributions can be improved using the Reissner’s Mixed Variational Theorem (RMVT). In the mixed RZT, named RZT(m) [5], the assumed transverse shear stresses are derived from the integration of local three-dimensional equilibrium equations. Following the variational statement described by Auricchio and Sacco [6], the purpose of this work is to implement a mixed variational formulation for the en-RZT, in order to improve the accuracy of the predicted transverse stress distributions. The assumed kinematic field is cubic for the in-plane displacements and parabolic for the transverse one. Using an appropriate procedure enforcing the transverse shear stresses null on both the top and bottom surface, a new set of enhanced piecewise cubic zigzag functions are obtained. The transverse normal stress is assumed as a smeared cubic function along the laminate thickness. The assumed transverse shear stresses profile is derived from the integration of local three-dimensional equilibrium equations. The variational functional is the sum of three contributions: (1) one related to the membrane-bending deformation with a full displacement formulation, (2) the Hellinger-Reissner functional for the transverse normal and shear terms and (3) a penalty functional adopted to enforce the compatibility between the strains coming from the displacement field and new “strain” independent variables. The entire formulation is developed and the governing equations are derived for cases with existing analytical solutions. Finally, to assess the proposed model’s predictive capabilities, results are compared with an exact three-dimensional solution, when available, or high-fidelity finite elements 3D models. References: [1] Tessler A, Di Sciuva M, Gherlone M. Refined Zigzag Theory for Laminated Composite and Sandwich Plates. NASA/TP- 2009-215561 2009:1–53. [2] Iurlaro L, Gherlone M, Di Sciuva M, Tessler A. Assessment of the Refined Zigzag Theory for bending, vibration, and buckling of sandwich plates: a comparative study of different theories. Composite Structures 2013;106:777–92. https://doi.org/10.1016/j.compstruct.2013.07.019. [3] Di Sciuva M, Gherlone M, Iurlaro L, Tessler A. A class of higher-order C0 composite and sandwich beam elements based on the Refined Zigzag Theory. Composite Structures 2015;132:784–803. https://doi.org/10.1016/j.compstruct.2015.06.071. [4] Sorrenti M, Di Sciuva M. An enhancement of the warping shear functions of Refined Zigzag Theory. Journal of Applied Mechanics 2021;88:7. https://doi.org/10.1115/1.4050908. [5] Iurlaro L, Gherlone M, Di Sciuva M, Tessler A. A Multi-scale Refined Zigzag Theory for Multilayered Composite and Sandwich Plates with Improved Transverse Shear Stresses, Ibiza, Spain: 2013. [6] Auricchio F, Sacco E. Refined First-Order Shear Deformation Theory Models for Composite Laminates. J Appl Mech 2003;70:381–90. https://doi.org/10.1115/1.1572901

Bond strength model for externally bonded FRP-to-timber interface

© 2018 Elsevier Ltd Despite the large number of studies on externally bonded elements using FRP composites, there is a significant knowledge gap to gain a comprehensive understanding of potential parameters such as bond width, bond length, material properties and geometries that influence bond strength. Behaviour of FRP bonded to concrete has been well investigated and there are a number of experimental and theoretical studies in this area; however, limited attempts have been made to investigate the bond behaviour of the FRP to timber interface. This paper reports an investigation on the behaviour of FRP externally bonded to timber. A novel theoretical model has been developed through stepwise regression analysis of 136 single shear FRP-to-timber joints. This has led to establishing a new predictive model for determination of the bond strength for FRP-to-timber joints. Results of this stepwise regression analysis are then assessed with results of experimental tests, and satisfactory comparisons have been achieved between ultimate applied loads and the predicted loads. Finally, a significant improvement in prediction of bond behaviour has been achieved when results of the proposed analytical model compared with the existing models from the literature, signifying the capability of the new models

Étude théorique et analyse non-linière par éléments finis pour la conception de colonnes en béton armé confinées à l’aide de tube en PRF

Les matériaux composites en polymères renforcés de fibres (PRF) ont été utilisés largement dans le domaine de la construction en génie civil, particulièrement pour les structures exposées à un environnement corrosif. L'utilisation des tubes en polymères renforcés de fibres (PRF) est une technique innovante pour les éléments de structures en béton armé tels que les colonnes, les piliers et les poutres, où les tubes en PRF sont utilisés comme coffrage permanent. Des recherches précédentes ont été effectuées pour comprendre le comportement des colonnes (CFFT) sous chargement axial mais il existe très peu de données concernant le comportement des colonnes en béton armé et renforcées de tubes en PRF sous chargement excentrique. Cette thèse présente des données expérimentales, une analyse théorique approfondie et des recommandations de conception pour colonnes cylindriques CFFT armées de barres d'acier ou de barres en polymères renforcés de fibres de carbone (CFRP). Les colonnes CFFT ont été testées sous un chargement monotone avec différents niveaux d'excentricité. Le rapport d'excentricité (e / D), et le type d'armature longitudinale (barre CFRP versus barre en acier) sont considérés comme des variables pour tous les essais effectués. Le diamètre et la hauteur de chaque spécimen sont égaux à 152mm, 912mm respectivement. L'angle d'orientation des fibres du tube a été principalement dans la direction circonférentielle (± 60 degrés par rapport à l'axe longitudinal). Six barres d'armature (acier ou CFRP) ont été utilisées et sont réparties uniformément dans chaque échantillon. Les résultats de cette étude ont révélé que les échantillons armées avec des barres en PRFC se comportent de manière très similaire aux échantillons armés de barres en acier et atteignent, à toute fin pratique, les mêmes résistances axiales. Le mode de rupture des échantillons de CFFT a été dominé par l'instabilité globale des colonnes ainsi que par la combinaison de la rupture en traction du tube en PRF et des barres en PRFC ou en acier. Les résultats expérimentaux de la déformation ont montré que les barres de PRFC développent des déformations élevées sur les côtés de compression (Valeur maximale en compression -5000 lm) et de traction (Valeur maximale en traction 10,400 gE), ainsi les barres PRFC résistent mieux aux contraintes de la traction et de la compression. En outre, la contrainte de traction longitudinale maximale enregistrée dans le tube en PRF est considérée comme étant une contrainte faible par rapport à celle enregistrée dans la direction circonférentielle du tube en PRF. D'après les résultats expérimentaux enregistrés, le confinement induit par le tube en PRF est moins important dans le cas d'une colonne sous charge excentrée. Des diagrammes expérimentaux d'interaction charge axiale-moment ont été présentés pour déterminer l'enveloppe de rupture des échantillons CFFT armées de barres en acier ou de barres en PRFC. De plus, une analyse théorique a été développée pour calculer les résistances des colonnes CFFT soumises à un chargement excentrique. Une comparaison avec les résultats expérimentaux a été effectuée. Aussi, une analyse théorique basée sur l'approche couche par couche a été développée pour prédire la réponse moment versus courbure des colonnes CFFT armées de barres en acier ou de barres en PRFC. Ces résultats ont été comparés aux résultats expérimentaux des courbes de moment-courbure. Il a été conclu que quelques soient le type d'armature (acier versus PRFC) pour les colonnes CFFT et la valeur de l'excentricité, le comportement moment-courbure de tous les échantillons est non linéaire. Par ailleurs, une étude approfondie a été effectuée sur la rigidité en flexion (El) effective des colonnes CFFT. Cette étude est basée sur une étude paramétrique expérimentale et une simulation théorique. Les équations proposées ont été développées et validées par rapport aux résultats expérimentaux afin de représenter la rigidité des colonnes CFFT armées de barres en acier ou de barres en FRPC. Ces équations sont établies pour deux états-limites : les états-limites de service et les états-limites ultimes. Aussi, une formule précise pour la prédiction du taux d'élancement pour contrôler le mode de rupture par flambement pour les colonnes CFFT armées de barres en PRFC a été proposée. Il a été établi qu'un taux d'élancement égal à 14 présente une valeur sécuritaire pour la conception de ces colonnes CFFT en béton armé. Enfin, un modèle non-linéaire par éléments finis utilisant le logiciel ABAQUS a été développé et présenté sur la base d'un modèle de béton confiné « Lam et Teng» prenant en considération la non- linéarité matérielle et géométrique des colonnes CFFT. Ce modèle permet de fournir un aperçu sur le comportement de la structure et du mécanisme de rupture des colonnes CFFT.Abstract: Fibre-reinforced polymer (FRP) composite materials have been extensively used in the field of civil engineering construction, especially in structures subjected to corrosive environments. One of the innovative techniques for using FRP is the FRP tubes which can be used as structurally integrated stay-in-place forms for concrete members as columns, piles, piers and beams. Extensive research was carried out to understand the behavior of concrete-filled FRP tube (CFFT) columns under axial loading, but comparatively limited research was conducted on the reinforced CFFT columns under eccentric loading. This thesis aims to provide experimental work as well as extensive theoretical analysis and design recommendations of circular CFFT columns reinforced with steel bars or carbon fibre reinforced polymer (CFRP) bars. CFFT columns were tested under monotonic loading with different levels of eccentricity. Test variables included the eccentricity to diameter ratio (e/D) and reinforcement type (CFRP bars vs steel). All specimens measured 152 mm in diameter and 912 mm height. The tubes used is basically filament wound glass fibre reinforced polymer tube (GFRP) with a core diameter of 152 mm and a wall thickness of 2.65 mm (6 layers). The fibre orientation of the tube was mainly in the hoop direction (± 60 degree with respect to the longitudinal axis). Six reinforcing bars (steel or CFRP) were used and distributed uniformly in each specimen. Test results indicate that specimens with CFRP reinforcement (CFRP-CFFT) behaved very similar to their steel counterparts with nearly the same nominal axial forces. Failure of CFFT columns was dominant by overall instability of the columns along with the combination of tensile rupture of FRP tube and CFRP bars or steel yielding. Experimental strain results revealed that the CFRP bars developed high strains on the compression and tension sides, thus CFRP bars contribution was considered effective in resisting tensile and compressive stresses. In addition, the maximum tensile strain reached in the GFRP tube was considered low when compared to the GFRP hoop strain, thus, it was concluded that the confinement induced by the GFRP tube become less significant in the case of eccentrically loaded column. Experimental axial-moment interaction diagrams were presented to indicate the failure envelope of steel and CFRP reinforced CFFT columns. Moreover, a theoretical model was developed to indicate the axial-moment capacities of steel and CFRP reinforced CFFT columns using plane sectional analysis and compared to the experimental results counterparts. Theoretical sectional analysis based on layer by layer approach was developed to predict the moment-curvature response for steel and CFRP- reinforced CFFT columns. These results were compared to the experimental moment-curvature curves and it was clear that regardless of the type of reinforcement and value of eccentricity, all specimens exhibit non-linear moment curvature behavior. An extensive study was conducted on the effective flexural stiffness of CFFT columns, on the basis of experimental parametric study and theoretical simulation. Proposed equations were developed and validated against the experimental results to represent the stiffness of steel and CFRP- CFFT circular columns at service and ultimate loads. Moreover, a theoretical investigation was conducted to propose a more precise formula for the critical slenderness limit to control the buckling mode of failure of FRP-reinforced CFFT columns. It was found that the critical slenderness limit of 14 could be used as a safe value for practical design purposes. The theoretical analysis in this research was carried out using excel. Finally, a nonlinear finite element model using ABAQUS software was presented based on Lam and Teng confined concrete model considering material and geometric nonlinearities of CFFT columns. This model aims to provide insight on the structure behavior and failure mechanism of CFFT columns