D’APPRENTISSAGE AUTOMATIQUE - XGBOOST 77
Montage expérimentalFigure 3.14 Montage expérimentalPhotographie du montage expérimental
3.4
Collecte des données pour le modèle prédictif d’ap-
prentissage automatique - XGBoost
Une base de données complète contenant 283 résultats d’essais effectués sur des poteaux en béton armé de PRF a été assemblée pour le modèle prédictif d’apprentissage automatique. Les données expérimentales ont été collectées à partir de divers travaux publiés par Ab- delazim et al. [2020a,b,c]; Afifi et al. [2014a,b]; Barua and El-Salakawy [2020]; El-Gamal and AlShareedah [2020]; Elchalakani et al. [2019, 2020]; Elchalakani and Ma [2017]; Fan and Zhang [2016]; Guérin et al. [2018a,b]; Hadhood et al. [2017a,b,c,d, 2018a,b, 2017e]; Hadi et al. [2017, 2016]; Hadi and Youssef [2016]; Hales et al. [2016]; Khorramian and Sa- deghian [2020]; Luca et al. [2010]; Maranan et al. [2016]; Mohamed et al. [2014]; Othman and Mohammad [2019]; Salah-Eldin et al. [2019a,b]; Tobbi et al. [2012, 2014]; Tu et al. [2019]; Xue et al. [2018] et ElMessalami et al. [2021]. En plus de ces données, vingt-quatre spécimens de la phase expérimentale du présent projet ont servi également à construire la base de données des poteaux.
La base de données est constituée de variables quantitatives et qualitatives. Les variables quantitatives sont composées de la largeur (b) et la hauteur (h) de la section rectangulaire du poteau, le diamètre de la section circulaire du poteau (D), la hauteur du poteau (H), l’élancement du poteau (λ), la section totale de béton (Ag), la résistance à la compression
78 CHAPITRE 3. PROGRAMME DE RECHERCHE du béton (f′
c), le taux d’armature longitudinale (ρF RP), le module d’élasticité (EF RP) et
la résistance ultime (fF RP u) à la traction des barres de PRF, l’espacement ou le pas des
armatures transversales (tspacing), le facteur d’excentricité (er) et la charge axiale maximale
du poteau (Pmax). Les variables qualitatives comprennent le type d’armature transversale
et longitudinale, le type de section du poteau, le type de béton ainsi que la configuration du confinement du poteau. La figure 3.15 présente la corrélation entre chaque variable numérique de la base de données.
20 40 60 0 20 Ag (1 0 4m m 2) 25 50 75 f 0(Mc Pa ) 2 4 FR P (% ) 50 100 150 EFRP (G Pa ) 1000 2000 fFRPu (M Pa ) 100 200 300 tspac ing (m m ) 0 50 100 er (% ) 0 50 0 10000 Pmax (k N) 0 25 Ag(104mm2) 50 100
fc0(MPa) 0 FRP(%)5 0EFRP100(GPa) fFRPu1000 2000(MPa) t0spacing(mm)250 0er(%)100 0 10000Pmax(kN)
CHAPITRE 4
BEHAVIOR OF LWSCC COLUMNS REINFOR-
CED WITH GFRP BARS AND SPIRALS UN-
DER AXIAL AND ECCENTRIC LOADS
Avant-propos
Auteurs et affiliation :
Abdoulaye Sanni Bakouregui :Étudiant au doctorat, Département de génie civil et de
génie du bâtiment, Faculté de génie, Université de Sherbrooke, 2500, boul. de l’Université, Sherbrooke (Québec) J1K 2R1, Canada.
Hamdy M. Mohamed : Enseignant et chercheur associé, Département de génie civil et
de génie du bâtiment, Faculté de génie, Université de Sherbrooke, 2500, boul. de l’Univer- sité, Sherbrooke (Québec) J1K 2R1, Canada.
Ammar Yahia :Professeur agrégé, Département de génie civil et de génie du bâtiment,
Faculté de génie, Université de Sherbrooke, 2500, boul. de l’Université, Sherbrooke (Qué- bec) J1K 2R1, Canada.
Brahim Benmokrane : Professeur titulaire, Département de génie civil et de génie du
bâtiment, Faculté de génie, Université de Sherbrooke, 2500, boul. de l’Université, Sher- brooke (Québec) J1K 2R1, Canada.
Accepté pour publication :27 octobre 2020 Titre du journal : ACI Structural Journal
Titre en français :Étude du comportement de poteaux en BAP léger armé de barres et
de spirales en PRFV sous charges axiales et excentrées.
Résumé en français :
Cet article présente les résultats d’une étude expérimentale menée sur 14 poteaux cir- culaires de grandeur réelle en béton autoplaçant (BAP) léger, renforcés avec des barres et des spirales en polymère renforcé de fibres de verre (PRFV). Les poteaux de 300 mm (12 pouces) de diamètre ont été dimensionnés conformément aux exigences de la norme CAN/CSA S806-12. Un BAP léger optimisé a été utilisé pour la fabrication des poteaux et ces derniers ont été soumis à des charges axiales et excentriques. Les paramètres d’étude
80 CHAPITRE 4. BEHAVIOR OF LWSCC COLUMNS REINFORCED WITH GFRPBARS AND SPIRALS UNDER AXIAL AND ECCENTRIC LOADS étaient le rapport excentricité/diamètre, le taux d’armature longitudinal et le type de renforcement (acier, PRFV). Quatre rapports d’excentricité/diamètre ont été estimés et appliqués (8,2%, 16,4%, 32,8% et 65,6%) pour développer l’enveloppe de rupture nominale. Les résultats des essais indiquent que l’augmentation du taux d’armature longitudinale de PRFV a amélioré les performances post-pic des poteaux en BAP léger. D’autre part, le mécanisme de rupture des poteaux en BAP léger testés était similaire à celui des poteaux conventionnels en béton de densité normale armé. Sur la base des principes fondamentaux d’équilibre des forces internes et de la compatibilité des déformations, les paramètres équi- valents de bloc de contrainte et les dispositions de dimensionnement dans la littérature ont été utilisés pour prédire la résistance en flexion composée des poteaux en BAP léger avec armatures de PRFV testés. Les diagrammes d’interaction P-M ont été présentés et discutés.
Mots-clés :Béton de granulats léger, béton autoplaçant (BAP) léger, poteaux circulaires
en béton armé, charge axiale et excentrique, barres et spirales en PRFV, taux d’arma- ture, résistance en flexion composée, diagramme d’interaction P-M analytique, codes de conception.
Abstract
This paper presents the test results of an experimental investigation conducted on 14 full- scale circular lightweight self-consolidating concrete (LWSCC) columns reinforced with glass fiber-reinforced polymer (GFRP) bars and spirals. The 300-mm (12 in) diameter columns were designed according to CAN/CSA S806-12 code requirements. The columns were constructed using new designed and developed LWSCC and tested under axial and eccentric loading. The test variables were the eccentricity-to-diameter ratio, longitudinal- reinforcement ratio, and type of reinforcement (steel versus GFRP). Four eccentricity-to- diameter ratios were estimated and applied (8.2, 16.4, 32.8, and 65.6%) to develop the nominal failure envelope. Test results indicate that increasing the GFRP longitudinal- reinforcement ratio enhanced the post-peak performance of LWSCC columns. On the other hand, the failure mechanism of the tested LWSCC columns was similar to that reported previously for conventional reinforced normal-weight concrete columns. Based on the fundamentals of equilibrium of forces and compatibility of strains, the available equivalent stress-block parameters and design provisions in the literature were used to predict the axial–flexural capacity of the tested GFRP-reinforced LWSCC columns. The predicted P–M interaction diagrams are presented and discussed.
Keywords :Lightweight-aggregate concrete (LWAC) ; Lightweight self-consolidating concrete
4.1. INTRODUCTION 81 and spirals ; Reinforcement ratio ; Axial-flexural capacity ; Analytical P-M interaction dia- gram ; Design codes.
4.1
Introduction
Lightweight-aggregate self-consolidating concrete (LWSCC) is a high-performance concrete that combines the advantages of structural lightweight-aggregate concrete (LWAC) to re- duce the dead loads of structures and self-consolidating concrete (SCC). Several resear- chers have shown that the average weight reduction of lightweight concrete ranges from 20% to 35%, and its structural capacity is comparable to normal-weight concrete (NWC) [Chen et al., 2018]. SCC is able to flow and spread under its own weight to properly fill the formwork and encapsulate the reinforcement without any mechanical consolidation [ACI 237R-07; Yahia and Khayat 2012]. The elimination of vibrating equipment faci- litates the casting of complex geometries and congested reinforced members. SCC has become an attractive solution in precast concrete and construction to reduce construction duration and cost [Yahia et al., 2011]. LWAC offers many advantages, including lower permeability, higher fire-resistance, reduced section dimensions, and lower transportation cost of concrete elements. Furthermore, using pre-wetted lightweight aggregates (LWAs) in concrete provide internal curing, lead to an increased resistance to early-age cracking, and enhance durability [Meng et al., 2018]. The air-dry density of LWAC is less than 1850 kg/m3 (115.5 lb/ft3) with a 28-day compressive strength not less than 20 MPa (2.9
ksi) [CAN/CSA A23.3 :19]. LWAC has been used in many applications, including multi- story building frames and floors, shell roofs, folded plates, bridges, precast elements, and prestressed structures [Chandra and Berntsson, 2002].
In the last decade, the use of fiber-reinforced polymer (FRP) bars as an alternative reinfor- cing material in reinforced-concrete (RC) structures has emerged as an innovative solution to the steel corrosion problem [ACI 440.1R-15]. In particular, valuable research work has been conducted to study the concentric and eccentric behavior of normal-weight concrete (NWC) columns reinforced with FRP bars [Afifi et al., 2014a; Fillmore and Sadeghian, 2018; Hadhood et al., 2019; Maranan et al., 2016; Tobbi et al., 2012]. The behavior of square and circular NWC columns reinforced with glass-FRP (GFRP) and carbon-FRP (CFRP) has been evaluated under concentric loading [Afifi et al., 2014b; Tobbi et al., 2012]. It was found that the longitudinal GFRP bars contributed up to 10% of the column axial nominal capacity. On the other hand, using GFRP ties, spirals, and hoops was found to be efficient in confining the NWC core, delaying initiation and propagation of unstable cracks, as well as preventing the buckling of GFRP longitudinal bars at peak load [Moha- med et al., 2014]. Hadi et al. [2016] investigated the behavior of circular NWC columns
82 CHAPITRE 4. BEHAVIOR OF LWSCC COLUMNS REINFORCED WITH GFRPBARS AND SPIRALS UNDER AXIAL AND ECCENTRIC LOADS reinforced with GFRP bars and spirals under different loading conditions. Their experi- mental results show that the axial load and bending-moment capacity of the GFRP RC columns were comparable to those of conventional steel RC columns with similar reinfor- cement ratios, concrete strength, and cross-sectional area. Maranan et al. [2016] reported that the geopolymer-concrete columns reinforced with GFRP bars under concentric loa- ding performed better than cement-based concrete columns. Hadhood et al. [2017d] tested full-scale circular high-strength concrete (HSC) columns under concentric and eccentric loading. They reported that GFRP bars could be effectively integrated into normal-weight HSC column to resist tensile stresses. Guérin et al. [2018a] tested square NWC columns reinforced with GFRP bars and ties under eccentric loading. The test results indicated that the specimens reinforced with two comparable types of GFRP bars (deformed and/or sand-coated) under different levels of eccentricity behaved similarly to their steel-reinforced concrete counterparts. Salah-Eldin et al. [2019a,b] tested full-scale normal-weight HSC co- lumns under low and large eccentricity. The test results showed that using GFRP and basalt-FRP reinforcement allowed the columns to reach higher peak loads and develop hi- gher tensile strain in the FRP bars compared to columns made with NSC. In conclusion, the latest valuable experimental work on GFRP-reinforced NWC columns led to North American codes and standards (CAN/CSA S806-12 ; CAN/CSA S6 :19 ; forthcoming ACI 440-H code) recommending the use of GFRP bars in compression members.
Despite of the potential advantages of LWC, limited studies have been conducted on the performance of LWAC columns [AL-Eliwi et al., 2018; Wu et al., 2018]. The moduli of LWAC are generally lower than that of normal-weight concrete. Furthermore, concrete brittleness might not only affect the failure mode, but also the strength capacity of com- pression members [Cui et al., 2012]. An early study conducted on square and circular LWAC columns reinforced with steel reinforcement [Allington et al., 1998] indicated that the LWAC columns behaved in a ductile manner when an adequate amount of transverse reinforcement was provided to confine the core concrete and prevent the buckling of the longitudinal reinforcement. Recently, Wu et al. [2018] investigated the behavior of LWAC columns reinforced and confined with steel reinforcement. The test results indicated that the crack pattern of LWAC columns exhibited significant differences with the NWC spe- cimens, showing that the failure planes passed through the coarse aggregates or occurred at the interface between the coarse aggregate and cement paste. In addition, Wu et al. [2018] concluded that the brittle behavior of LWAC could be significantly improved by reasonably selecting the tie configuration and adding the amount of lateral steel needed for excellent ductile behavior.
4.2. RESEARCH SIGNIFICANCE 83