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CONTENTS
Volume 27, Number 6, June 2021
 

Abstract
Brick infill walls (BIW) have significant effects on reinforced concrete (RC) structures' seismic performances. However, mechanical effects on the structural performance of BIWs, which are regarded as only weight at the design stage, are not considered in many seismic codes. Therefore, seismic performances of new and existing RC structures could not be realistically obtained. This study aims to investigate the effects on the structural behavior of BIWs, stucco types, and soft story. RC structures with and without BIWs are modeled by using the SAP2000 program. BIW is modeled with the equivalent diagonal compression strut method, and mechanical properties of BIWs plastered with conventional and polypropylene fibrous stuccos are taken from literature. Seismic performances of all structures are investigated using the pushover analysis method, according to Turkish Seismic Code-2007 (TSC-2007) principles. Besides, natural periods, rigidities, ductilities and energy dissipation capacities of all structures are obtained. As a result of analyses, it is determined that BIWs have significant effects on structural performances in terms of rigidity and ductility, and fibrous stucco considerably increases RC structures' rigidity and ductility. These walls can even lead to the collapse of structures in severe earthquakes if design engineers don't regard BIWs or BIWs are placed as asymmetric or deficient on the structure.

Key Words
brick infill wall; RC structure; stucco; polypropylene fiber; structural safety; nonlinear analysis

Address
Ali Demir: Department of Civil Engineering, Manisa Celal Bayar University, Manisa, Turkey
Mehmet Mete Cengiz: General Directorate for Highways, İzmir, Turkey

Abstract
In the present study, fresh and mechanical properties of self-compacting concrete (SCC) mixes made up of quartz sand, micro silica, Ground Granulated Blast-furnace Slag (GGBS) and fibers have been evaluated for three grades of concrete (M40, M50 and M60). Plastic viscosity based mix proportioning is adopted in the present study. Further, steel fibers have been added to the respective mixes in various proportions (0.5%, 1.0% and 1.5% by volume of concrete) to examine the effect of fibers on fresh and mechanical properties. The fresh properties include slump flow, V-funnel, T50 cm slump, and L-box. It is found that the fresh properties for all the mixes are within the limits mentioned by EFNARC. Compressive strength, split tensile strength and flexural strength were evaluated for 3, 7, 28, 56, 90 and 180 days for M40, M50 and M60 grades with and without fibers. It is observed that the workability of all the mixes corresponding to M40, M50 and M60 is decreased with the increase of steel fibre volume fraction. The mechanical properties, split tensile strength, flexural strength increased with the increase of percentage of fibers. The compressive strength is increased up to 1.0% fibre volume and marginally decreases for 1.5% fibre volume and however, it is higher than the mix with 0.5% fiber volume. The increase in mechanical properties may be due to additional formation of CSH. Multiple linear regression analysis has been performed by considering about 75% of the mixed experimental mechanical data and three equations are proposed and validated with the remaining dataset. It is found that the predicted mechanical properties are closely matching with the related experimental observations. Further, Artificial neural network based model has been developed to predict the compressive strength of various SCC mixes. The back propagation training technique and Levenberg-Marquardt algorithm was employed to develop ANN model. It was found that the model could predict the compressive strength of various SCC mixes +-12% compared to experimental observations.

Key Words
self-compacting concrete; steel fibres; fresh properties; mechanical properties; multiple regression analysis; artificial neural network

Address
B. Seshaiah: Department of Civil Engineering, JNTUK Kakinada, Andhra Pradesh, India
P. Srinivasa Rao: Department of Civil Engineering, JNTUH Hyderabad, Telangana, India
P. Subba Rao: Department of Civil Engineering, JNTUK Kakinada, Andhra Pradesh, India

Abstract
A hysteretic moment-curvature relation for analyzing reinforced concrete (RC) members subjected to blast loading is introduced in this paper. After constructing a monotonic envelope curve for the moment-curvature relation, the hysteretic behaviors of unloading and reloading are defined based on the hysteretic curve of steel. The use of the moment-curvature relation in the blast analysis becomes possible by introducing a dynamic increase factor (DIF), which is defined in terms of the curvature rate. This makes it possible to analyze RC structures composed of many bending structural members. In addition to defining a basic hysteretic moment-curvature relation, additional influencing factors such as the bond-slip effect and direct shear behavior, which are expected to affect the structural responses, are taken into consideration for an exact simulation of the nonlinear dynamic response of RC flexural members. The validity of the introduced hysteretic moment-curvature relation is established by correlation studies between the analytical results and experimental data experiencing repeated unloading and reloading phases. The obtained numerical results also show the importance of the bond-slip effect and the hysteretic behavior on the structural response of RC flexural members subjected to blast loading.

Key Words
blast loading; dynamic increase factor; bond-slip; cyclic moment-curvature relationship; direct shear behavior

Address
Gang-Kyu Park, Hyo-Gyoung Kwak: Department of Civil and Environmental Engineering, Korean Advanced Institute for Science and Technology, 291 Daehak-ro, Yuseong-gu, Daejeon 34141, Republic of Kiorea
Filip C. Filippou: Department of Civil and Environmental Engineering, University of California, Berkeley, USA

Abstract
Concrete is globally the most used building material. This fact shows the need to make advances in the prediction of its mechanical behavior. Despite being considered homogenous in many cases for simplification purposes, this material naturally has a high degree of heterogeneity, which presents challenges in terms of fracture process modeling, due to phenomena such as scale effect and softening behavior. In this context, the objective of this work is to present a 3D probabilistic cracking model based on the finite element method, in which material discontinuities are explicitly represented by interface elements. The threedimensional modeling of cracks makes it possible to analyze the fracture process in a more realistic way. In order to estimate statistical parameters that define the material heterogeneity, an inverse analysis procedure was performed using general laws defined by experimental investigations. The model and the inverse analysis strategy were validated mainly by the verification of scale effect at a level similar to that experimentally observed, taking into account the tensile failure of plain concretes. Results also indicate that different softening levels can be obtained.

Key Words
concrete; probabilistic cracking model; size effect; tensile failure; FEM

Address
Magno T. Mota, Eduardo M.R. Fairbairn, Fernando L.B. Ribeiro: Department of Civil Engineering, COPPE, Federal University of Rio de Janeiro, Centro de Tecnologia - Ilha do Fundão, CEP 21941-909, Rio de Janeiro-RJ, Brazil
Pierre Rossi: Department of Materials and Structures, Gustave Eiffel University, Cite Descartes, Champs-sur-Marne, 77454 Marne-la-Vallee Cedex 2, France
Jean-Louis Tailhan: Department of Materials and Structures, Gustave Eiffel University, Laboratoire de Biomecanique Appliquee, Bd P. Dramard - 13916 Marseille Cedex 20, France
Henrique C.C. Andrade, Mariane R. Rita: Department of Civil Engineering, COPPE, Federal University of Rio de Janeiro, Centro de Tecnologia - Ilha do Fundão, CEP 21941-909, Rio de Janeiro-RJ, Brazil

Abstract
In this study, the effect of SiO2 nanoparticles on the bonding behavior of steel and glass fiber reinforced polymer (GFRP) bar embedded in contained Light-weight Self-Consolidating Concrete (LWSCC) has been studied experimentally and numerically. The measurement of the mechanical properties of LWSCC modified with SiO2 nanoparticles, including compressive and tensile strength, elastic modulus and density were also carried out. Studies are conducted on 7, and 28-day aged LWSCC samples containing 0, 2 and 5% SiO2 nanoparticles with 12 mm and 16 mm diameter GFRP and steel bars. The results show that LWSCC modified with SiO2 nanoparticles increases the bonding strength between concrete and bar. In LWSCC with 2 and 5 wt.% SiO2, the maximum pull-out force of 16 mm diameter steel bar is increased by 48.5% and 54.7%, respectively, compared to the LWSCC without nanoparticle addition. Also, bonding improvement between GFRP bars with a diameter of 16mm and LWSCC having 2 and 5 wt.% SiO2 is 32.3% and 40%, respectively.

Key Words
light-weight self-consolidating concrete; SiO2 Nanoparticles; pull-out behavior; GFRP bar

Address
Hamed Arjomandi and Ali Foroghi Asl: Department of Civil Engineering, University of Tabriz, Tabriz, Iran

Abstract
The present study investigates the static behavior of concrete beams impregnated with silicon dioxide (SiO2) nanoparticles. Nanosilica, by virtue of its small particle size, can affect the microstructure of concretes and enhance their properties. Voigt's model is used to take account of the agglomeration effect and obtain the equivalent nano-composite properties. Furthermore, the reinforced concrete beam is simulated mathematically with higher-order shear deformation theory because of its simplicity and accuracy. The soil medium is simulated with Pasternak elastic foundation, including a shear layer, and Winkler spring. The equilibrium equations are derived using the principle of virtual work, and using Hamilton's principle, the energy equations are obtained. Also, analytical methods are employed to obtain the closed-form solutions of simply supported beams. Numerical results are presented, considering the effect of different parameters such as the volume percent of SiO2 nanoparticles, mechanical loads, geometrical parameters, and soil medium, on the static behavior of the beam. The majority of findings from this work indicate that the use of SiO2 nanoparticles in concretes increases their mechanical resistance, and that the deflections and stresses decrease. In addition, the elastic foundation has a significant impact on the bending of concrete beams.

Key Words
static behavior; reinforced-concrete beam; silica nanoparticles; elastic foundation

Address
Zouaoui R. Harrat: Laboratoire des Structures et Materiaux Avances dans le Genie Civil et Travaux Publics, University of Djillali Liabes, Sidi Bel Abbes, Algeria; Clermont Auvergne University, CNRS, Clermont INP, Institut Pascal, UMR 6602, Clermont-Ferrand, France
Sofiane Amziane: Clermont Auvergne University, CNRS, Clermont INP, Institut Pascal, UMR 6602, Clermont-Ferrand, France
Baghdad Krour: Laboratoire des Structures et Materiaux Avances dans le Genie Civil et Travaux Publics, University of Djillali Liabes, Sidi Bel Abbes, Algeria
Mohamed Bachir Bouiadjra: Laboratoire des Structures et Materiaux Avances dans le Genie Civil et Travaux Publics, University of Djillali Liabes, Sidi Bel Abbes, Algeria; Thematic Agency for Research in Science and Technology (ATRST), Algiers, Algeria

Abstract
This study presents a nonlinear finite element (FE) model development of reinforced concrete (RC) beams externally strengthened with aluminum alloy (AA) plates. The aim of this numerical study was to elucidate the effects of different anchorage schemes on the capacity, ductility, and failure mode of AA plate strengthened beams reported in a published test. Three FE models were developed; namely, a reference RC beam, a beam externally bonded (EB) with an AA plate, and a beam EB with an AA plate with carbon fiber reinforced polymers (CFRP) U-wraps at the plate's end. Validation of the developed FE models was carried out by comparing their load-deflection plots, maximum attained loads, deflections at failure, and failure modes with those reported during the test. The results of each FE model yielded an absolute percentage error less than 5%. Moreover, premature failure modes like end-plate and intermediate crack debonding were simulated and closely agreed with those observed during the test. Finally, the validated models were used to employ a parametric study comprising of twelve beams varying in size of steel reinforcement, presence of AA plates, and end-anchorage. It was concluded that the developed FE models could serve as a design platform for assisting structural engineers during flexural retrofit applications using AA plates.

Key Words
strengthening; aluminum alloy plate; finite element; anchorage; capacity; ductility; failure modes

Address
Omar R. Abuodeh: Glenn Department of Civil Engineering, Clemson University, Clemson, SC, 29634, USA
Rami A. Hawileh, Jamal A. Abdalla: Department of Civil Engineering, American University of Sharjah, Sharjah, United Arab Emirates

Abstract
Three different materials GP, RM and GGBFS in addition to MK were used to produce geopolymer mortars which were activated by using NaOH and Na2SiO3. In addition to these materials, GF was also introduced into the mixtures. The performance of the produced geopolymers was investigated by means of compressive strength, flexural strength, split tensile strength, chemical analysis and abrasion resistance measurements and microstructure investigation by means of SEM. In geopolymer mortar production MK is found more compatible with RM than GP in terms of strength development and abrasion resistance. Moreover, positive effect of GF (6 mm and 12 mm) addition was found to increase with the presence of GP and also with increased length of the fiber length.

Key Words
geopolymer; glass fiber; strength development; abrasion resistance; glass powder; red mud; metakaolin

Address
Ashraf Awad, Tülin Akçaoğlu: Department of Civil Engineering, Faculty of Engineering, Eastern Mediterranean University, Famagusta, North Cyprus, Mersin 10, Turkey
Beste Cubukcuoglu: Department of Civil Engineering, Faculty of Civil and Environmental Engineering, Near East University, Nicosia, North Cyprus, Mersin 10, Turkey
Orhan Canpolat: Civil Engineering Department, Yildiz Technical University, Davutpasa Campus, Istanbul, Turkey

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