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CONTENTS
Volume 12, Number 3, September 2021
 


Abstract
This article has been devoted to investigate the dynamic response of a graphene oxide powder (GOP) reinforced beam exposed to blast and thermal loads. It is assumed that the blast load has been exerted on the top surface of the beam. The material modeling of GOP-reinforced composite has been performed assuming two types of GOP distribution called uniform and graded in thickness direction. The establishment of the governing equations has been done employing a refined shear deformation beam theory and the consideration of elastic foundation. Finally, the equations have been solved implementing Chebyshev-Ritz method and inverse Laplace transform method. Then, the time history of the beam has been derived and its dependency on GOP percentage, GOP distribution, temperature rise, blast load factor, foundation coefficient band load position.

Key Words
blast load; concrete beam; dynamic response; graphene oxide powder; thermal effect

Address
Wael Najm Abdullah, Basima Salman Khalaf, Ridha A. Ahmed, Raad M. Fenjan and Nadhim M. Faleh: Engineering Collage, Mustansiriah University, P.O. Box 46049, Bab-Muadum, Baghdad 10001, Iraq

Abstract
Several factors need to be considered in modeling of reinforced concrete beams. Bond-slip is one of the most important factors that play a key role in the behavior of reinforced concrete structures, under static and dynamic loads. A comparison between the results of experimental tests and numerical models show that considering a complete bond (perfect with no slip) instead of real bond-slip phenomenon, in numerical finite element models leads to higher estimations for the stiffness. In this study, the effects of the bond-slip phenomenon on the behavior of the reinforced concrete beams are considered. It is shown that the influence of bond-slip behavior between steel and concrete depends on the compressive strength of concrete, the concrete cover, stirrups and rebar diameter. Subsequently, a method is proposed to consider the effects of the interfacial behavior between concrete and rebar while a complete bond assumption remains and the rebar is introduced as embedded element in concrete. The bond-slip effect is considered by adding an equivalent strain of bond to the strain of steel rebar and then modifying the terms of the modulus of elasticity of steel. Validation model and parametric analyses are conducted to consider the effects of bond-slip properties and other parameters affecting the behavior of reinforced concrete beams.

Key Words
bond-slip; embedded element; finite element model; reinforced concrete beam; steel rebar

Address
Seyed Muoud Hosseini, Majid Ghomian, Elham BaniAsad and Mehdi Dehestani: Faculty of Civil Engineering, Babol Noshirvani University of Technology, Babol, Iran

Abstract
This paper investigates the free vibration of bi-dimensional functionally graded simply supported beams by using the continuous element method. The material properties are considered to vary exponentially along the beam thickness and length. The characteristic frequency equations of simply supported beams are derived by transfer matrix method. Validation targets are other analytical methods. The effects of the gradient indexes and the beam slenderness ratio on the natural frequencies of bi-dimensional functionally graded beams are studied.

Key Words
bi-dimensional; continuous elements method; free vibration; functionally graded beam

Address
Abdellatif Selmi: Department of Civil Engineering, College of Engineering, Prince Sattam bin Abdulaziz University, Alkharj, 16273, Saudi Arabia; Civil Engineering Laboratory. B.P. 37, Ecole Nationale d'Ingénieurs de Tunis (ENIT), Le belvédère 1002, Tunis, Tunisia

Abstract
A study has been undertaken to investigate the possibility of using filler as fine aggregate, with different fineness and grading, instead of a conventional fine sand used in producing foam concrete. A conventional sand was replaced by micro silica sand and a comparison has been done to examine the pore structure and properties of investigated foam concrete mixes. Two ways were adopted to incorporate the nano silica sand into the mixture: with part of mixing water and with pre-formed foam bubbles. Compared to conventional foam concrete, it was found that using micro silica sand helped in improving strength (169%), reducing absorbed water (38%) and reducing shrinkage (40%) by enhancing both cement paste microstructure and pore structure. This pore structure enhancement was achieved by reducing pores merging leading to making a narrow pore size distribution and more circular pores with large spaces between them. On the other hand, increasing fineness of normal sand and using nano silica sand resulted in less enhancing in foam concrete properties compared with using the silica sand as its own (at micro level). It was noticed that incorporating the nano particles into mixture with foam bubbles was more effective than the conventional way; with mixing water.

Key Words
drying shrinkage; foam concrete; pore structure; silica sand; sorptivity

Address
Hawaa A. Obaid: Department of Civil Engineering, Al-maaref University College, Iraq
Ameer A. Hilal: Department of Civil Engineering, College of Engineering, University of Anbar, Iraq

Abstract
During past decades fiber-reinforced polymer (FRP) sheets have been externally bonded to structural elements to increase their axial, shear, or bending capacity. FRP bars also have been widely used to replace the steel reinforcements in columns subjected to a harsh environment. In this study, carbon fiber-reinforced polymer (CFRP) strips were used as the transverse reinforcement for concrete columns. Although FRP bars have already been used as the transverse reinforcement in concrete columns, the efficiency and feasibility of CFRP strips have not been investigated. CFRP strips are flexible; therefore, they can be easily shaped as spirals to confine the concrete core of columns. The efficiency of CFRP strips for the confinement of the concrete core was examined through a series of quasi-static cyclic tests on four full-scale columns that had similar size and longitudinal reinforcements. One of the columns was selected as the reference, and steel spirals transversally reinforced it. CFRP strips transversally reinforced the other three columns with different widths and spacing. The obtained results showed that the number of cracks in the CFRP-confined columns was less than the reference column. The length of cracks in the CFRPconfined columns was also relatively shorter. Besides, the CFRP-confined columns had a larger ultimate load, effective yield strength, and displacement ductility ratio compared with the reference column.

Key Words
CFRP; RC column; stirrup; transverse reinforcement; quasi-static cyclic load

Address
Nur Hajarul Falahi Abdul Halim: School of Civil Engineering, Faculty of Engineering, Universiti Teknologi Malaysia, Skudai, Malaysia
Sophia C. Alih: Institute of Noise and Vibration, School of Civil Engineering, Universiti Teknologi Malaysia, Skudai, Malaysia
Mohammadreza Vafaei: School of Civil Engineering, Faculty of Engineering, Universiti Teknologi Malaysia, Skudai, Malaysia

Abstract
Concrete structures are subjected to severe durability issues and freeze-thaw action is one of these detrimental issues. In this paper, the behavior of high-volume Class-F fly ash (FA) and slag (SL) incorporated Engineered Cementitious Composites (ECC) as overlay materials was assessed when they were under cyclic freezing and thawing effect. Silica fume concrete (SFC) was also tested as a control mixture which is generally used for overlaying purposes. Layered ECC/substrate concrete (SC) and SFC/SC beam specimens were produced and subjected to 300 freeze-thaw cycles in accordance with ASTM C666, Procedure A. Laboratory tests performed using the layered specimens were based on the determination changes of (i) residual mechanical properties (flexural strength -mid-span beam deflection curves), (ii) ultrasonic pulse velocity (UPV), (iii) mass loss, (iv) relative dynamic modulus of elasticity (RDME) and (v) durability factor (DF). Test results show that all layered specimens produced with different ECC mixtures safely survived 300 freeze-thaw cycles without any disturbance between the ECC overlay and SC interface. On the other hand, one out of six tested SFC/SC layered specimens survived 300 freeze-thaw cycles and final failure for five failed specimens took place from the interfacial planes. Significantly better frost resistance of overlaid systems produced with ECCs than those with SFC was also verified with all of the tests proposed. Between different ECC mixtures, those produced with slag performed better than that those with Class-F fly ash.

Key Words
engineered cementitious composites (ECC); frost resistance; layered concrete system; mechanical properties

Address
Hasan E. Yücel: Department of Civil Engineering, Nigde Omer Halisdemir University, Nigde, Turkey

Abstract
In this paper, the earthquake component effects on the seismic performance of Bhakra Gravity Dam in India are investigated. For the purpose, Bhakra Dam is modeled two-dimensionally considering dam-reservoir-foundation interaction. In the finite element modeling, dam and foundation are represented by PLANE182 elements in ANSYS with different material properties, and fluid is considered with FLUID29 elements. This type of element provides translation and pressure degrees of freedom. Linear time history analyses on the dam are performed by considering components of the 1991 Uttarkashi and 1999 Chamoli (NW Himalaya) Earthquakes in India. During the analyses firstly the horizontal component of earthquakes are applied to system and results are obtained, and then both of horizontal and vertical components are applied to the systems together. In the analyses, element matrices are computed using the Gauss numerical integration technique. The Newmark method is used in the solution of the equation of motions. Also, Rayleigh damping is considered. The seismic performance of Bhakra Dam is examined and presented by dynamic characteristics, displacements, principal stresses, and demand-capacity ratios. The results showed that the vertical components of the earthquake significantly affect the response of the dam. The results show that the vertical component with the horizontal component cause biggest tensile stresses compared to only the horizontal component for both earthquakes. However, displacement response is changed depending on the ground motion. As a conclusion of this study it can be said that the vertical component changes the structural response of the dam on both of the good and bad behaviors.

Key Words
Bhakra Gravity Dam; demand-capacity curve; finite element modeling; seismic performance; vertical component

Address
Baiş Sevim: Department of Civil Engineering, Yildiz Technical University, Istanbul, Turkey
Ahmet Can Altunişik: Department of Civil Engineering, Karadeniz Technical University, Trabzon, Turkey
Murat Günaydin: Department of Civil Engineering, Karadeniz Technical University, Trabzon, Turkey

Abstract
This paper explores the most feasible technique for producing sustainable structural lightweight concrete (LWC) utilizing high-volume of fly ash cenosphere (FAC), a noble lightweight fine material, as replacement of natural fine aggregate (NFA) with addition of silica fume (SF) as replacement of ordinary Portland cement (OPC). Concrete mixes are designed for different combinations of FAC (60%, 80% and 100%), SF (10%, 15% and 20%) and water-binder (W/B) ratio (0.40, 044 and 0.48) and their mechanical and physical properties are evaluated. Experimental results depict that appropriate dose of SF improves the properties of high-volume FAC based concrete and thus helps in the production of structural LWC satisfying strength and density criteria of ACI 213R-14 (2014). The combinations of 15% SF with 80% FAC at 0.44 and 0.40 W/B ratios result in the properties closer to or even better than the normal concrete. Moreover, the environmental impacts of the concrete mixes comprised of high-volume FAC with addition of SF at different W/B ratio reduce in the range 5.37%-18.86% with respect to the normal concrete. Hence, the structural LWC mixes become sustainable, as they are advantageous from both environmental and social considerations.

Key Words
compressive strength; density; environmental impact; fly ash cenosphere; silica fume; sustainable structural lightweight concrete

Address
Rajib K. Majhi: Department of Civil Engineering, Centurion University of Technology and Management, Paralakhemundi-761211, Odisha, India
Sudeep K. Patel: Department of Civil Engineering, Veer Surendra Sai University of Technology, Burla - 768018, Odisha, India
Amar N. Nayak: Department of Civil Engineering, Veer Surendra Sai University of Technology, Burla - 768018, Odisha, India


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