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CONTENTS
Volume 27, Number 1, January 2021
 

Abstract
This work presents a safety assessment of an underground tunnel subjected to a ballistic missile attack employing the numerical approach. For the impact simulation, a box shaped reinforced concrete (RC) structure with a cross section dimension of 8.0x10.0 m under a soil layer that was attacked by a SCUD missile was modeled using finite element (FE) software LS-DYNA. SCUD missile is one of a series of tactical ballistic missiles developed by Soviet Union during the Cold War, which is adopted for a short-range ballistic missile. The developed FE simulation for the penetration depth of the missile impacting into the soil structure was verified from the well-known formula of the penetration prediction. The soil-structure interaction, the soil type, and the impact missile velocity effects on the penetration depth of the missile into the different soil types were investigated. The safety assessment of the underground tunnel was performed with regard to the different depths of the underground tunnel. For each missile velocity and soil type, a specific depth called the unsafe depth was obtained from the analysis results. The structure beneath the soil beyond this depth remains safe. The unsafe depth was found to be increased with the increasing missile velocity.

Key Words
underground tunnel; missile impact; safety assessment; numerical simulation; and dynamic analysis

Address
Duc-Kien Thai: Department of Civil and Environmental Engineering, Sejong University, 98 Gunja-dong, Gwangjin-gu, Seoul, 143-747, Korea
Duy-Liem Nguyen: Department of Civil Engineering and Applied Mechanics, Ho Chi Minh City University of Technology and Education, 1 Vo Van Ngan St., Thu Duc District, Ho Chi Minh City, Vietnam
Thanh-Tung Pham: Department of Concrete Structures, National University of Civil Engineering, 55 Giai Phong, Hanoi, Vietnam
Thai-Hoan Pham: Department of Concrete Structures, National University of Civil Engineering, 55 Giai Phong, Hanoi, Vietnam

Abstract
In this paper, the elevated temperature on a concrete-galvalume composite beam's flexural strength based on the numerical and experimental methods is investigated. The strategy is to perform modeling and simulation of the flexural test based on finite element method (FEM) at room temperature and validate its results by using experiments at the same temperature. With material constants and boundary conditions set-up provided from the validation, we model and simulate the same flexural tests for the composite at higher temperatures. The study concludes that the flexural strength of the beam decreases at higher temperature. Additionally, it was shown that cracking moments is very sensitive to the temperature fluctuation and the failure modes are sensitive with respect to the elevated temperature.

Key Words
concrete-galvalume composite; elevated temperature; flexure strength; FEM; failure

Address
Agus Maryoto: Department of Civil Engineering, Universitas Jenderal Soedirman, Jl. Mayjend Sungkono KM 5, Purbalingga, Central Java, Indonesia
Han Ay Lie: Department of Civil Engineering, Diponegoro University, Semarang, Indonesia
Hendrik Marius Jonkers: Department of Civil Engineering and Geoscience, Delf Technical University, Delf, Netherland

Abstract
The Artificial Neural Network (ANN) is a system, which is utilized for solving complicated problems by using nonlinear equations. This study aims to investigate compressive strength, rebound hammer number (RN), and ultrasonic pulse velocity (UPV) of sustainable concrete containing various amounts of fly ash, silica fume, and blast furnace slag (BFS). In this study, the artificial neural network technique connects a nonlinear phenomenon and the intrinsic properties of sustainable concrete, which establishes relationships between them in a model. To this end, a total of 645 data sets were collected for the concrete mixtures from previously published papers at different curing times and test ages at 3, 7, 28, 90, 180 days to propose a model of nine inputs and three outputs. The ANN model's statistical parameter R2 is 0.99 of the training, validation, and test steps, which showed that the proposed model provided good prediction of compressive strength, RN, and UPV of sustainable concrete with the addition of cement.

Key Words
artificial neural network; nondestructive tests; Ultrasonic Pulse Velocity (UPV); compressive strength; sustainable concrete; pozzolanic materials

Address
Ahmed M. Tahwia: Civil Engineering Department, Faculty of Engineering, Mansoura University, Egypt
Ashraf Heniegal: Civil Engineering Department, Faculty of Engineering, Suez University, Egypt
Mohamed S. Elgamal: Civil Engineering Department, Faculty of Engineering, Mansoura University, Egypt
Bassam A. Tayeh: Civil Engineering Department, Faculty of Engineering, Islamic University of Gaza, Gaza, Palestine

Abstract
This study aimed to develop a method for the determination of the damaged story in reinforced concrete (RC) structure with ambient vibrations, based on modified jerk energy methodology. The damage was taken as a localized reduction in the stiffness of the structural member. For loading, random white noise excitation was used, and dynamic responses from the finite element model (FEM) of 4 story RC shear frame were extracted at nodal points. The data thus obtained from the structure was used in the damage detection and localization algorithm. In the structure, two damage configurations have been introduced. In the first configuration, damage to the structure was artificially caused by a local reduction in the modulus of elasticity. In the second configuration, the damage was caused, using the Elcentro1940 and Kashmir2005 earthquakes in real-time history. The damage was successfully detected if the frequency drop was greater than 5% and the mode shape correlation remained less than 0.8. The results of the damage were also compared to the performance criteria developed in the Seismostruct software. It is demonstrated that the proposed algorithm has effectively detected the existence of the damage and can locate the damaged story for multiple damage scenarios in the RC structure.

Key Words
concrete structures; dynamics; ambient vibrations; seismic damage; damage detection

Address
Saqib Mehboob and Qaiser U. Zaman: Department of Civil Engineering, University of Engineering and Technology Taxila, 47080, Pakistan

Abstract
This paper introduced three new strengthening systems for isolated footings: BFRP wrapping system, CFRP wrapping system, and steel jacketing system. The proposed systems are more practical than the current traditional methods, which involves installing many dowel bars and splicing reinforcing steels to join new and old concrete segments. In the proposed three new systems, BFRP wraps, CFRP wraps, or steel jackets are installed on the exterior surface of the enlarged footing, with construction adhesive or a few steel dowels being applied to the contact surfaces. To investigate the effectiveness of three systems, forty-four models were constructed in ABAQUS, with different parameters being considered. All footings investigated failed in punching shear, including original and retrofitted footings. According to FEA results and parametric studies, the three strengthening systems were capable of improving the punching shear resistance of footings. By introducing a new factor n, the punching shear equation in Eurocode 2 was modified to predict the punching shear resistances of the strengthened footings. A linear formula was developed to present the relationship between the new factor n and the investigated parameters.

Key Words
isolated footing; strengthening; FRP wrapping; steel jacketing; punching shear; finite element analysis; modified equation

Address
Xingji Lu: Department of Bridge Engineering, Tongji University, Shanghai, China
Riyad S. Aboutaha: Department of Civil and Environmental Engineering, College of Engineering and Computer Science, Syracuse University, Syracuse, USA

Abstract
The concrete fatigue analysis can be performed with the use of fracture mechanics. The fracture mechanics defines the fatigue crack propagation as the relationship of crack growth rate and stress intensity factor. In contrast to metal, the application of fracture mechanics to concrete is more complicated and therefore many authors have introduced empirical expressions using Paris law. The topic of this paper is development of a new prediction of fatigue crack propagation for concrete using rheological-dynamical analogy (RDA) and finite element method (FEM) in the frame of linear elastic fracture mechanics (LEFM). The static and cyclic fatigue three-point bending tests on notched beams are considered. Verification of the proposed approach was performed on the test results taken from the literature. The comparison between the theoretical model and experimental results indicates that the model proposed in this paper is valid to predict the crack propagation in flexural fatigue of concrete.

Key Words
fatigue of concrete; RDA crack propagation; three-point bending tests; fatigue failure

Address
Aleksandar Pancic, Dragan D. Milasinovica and Danica Golesb: Faculty of Civil Engineering Subotica, University of Novi Sad, Kozaracka 2a, Subotica 24000, Serbia

Abstract
In this study, a new stopping criterion, called "backward controlled stopping criterion" (BCSC), was proposed to be used in Genetic Algorithms. In the study, the available stopping citeria; adaptive stopping citerion, evolution time, fitness threshold, fitness convergence, population convergence, gene convergence, and developed stopping criterion were applied to the following four comparison problems; high strength concrete mix design, pre-stressed precast concrete beam, travelling salesman and reinforced concrete deep beam problems. When completed the analysis, the developed stopping criterion was found to be more accomplished than available criteria, and was able to research a much larger area in the space design supplying higher fitness values.

Key Words
genetic algorithm; genetic algorithm operators; stopping criteria

Address
Mustafa Kaya: Faculty of Engineering, Aksaray University, Aksaray, Turkey
Asim Genc: TUSAS-Kazan Vocational School, Gazi University, Ankara, Turkey

Abstract
In this article, the mechanical buckling analysis of simply-supported functionally graded plates is carried out using a higher shear deformation theory (HSDT) in conjunction with the stress function method. The proposed formulation is variationally consistent, does not use a shear correction factor and gives rise to a variation of transverse shear stress such that the transverse shear stresses vary parabolically through the thickness satisfying the surface conditions without stress of shear. The properties of the plate are supposed to vary across the thickness according to a simple power law variation in terms of volume fraction of the constituents of the material. Numerical results are obtained to study the influences of the power law index and the geometric ratio on the critical buckling load.

Key Words
functionally graded materials; HSDT; stress function method; buckling analysis

Address
Ahmed Bakoura: Material and Hydrology Laboratory, Faculty of Technology, Civil Engineering Department, University of Sidi Bel Abbes, Algeria; Departement de Genie Civil, Faculte d'Architecture et de Genie Civil, Universite des Sciences et de la Technologie d'Oran, BP 1505 El M'naouer, USTO, Oran, Algeria
Fouad Bourada: Material and Hydrology Laboratory, Faculty of Technology, Civil Engineering Department, University of Sidi Bel Abbes, Algeria; Departement des Sciences et de la Technologie, Universite de Tissemsilt, BP 38004 Ben Hamouda, Algerie
Abdelmoumen Anis Bousahla: Laboratoire de Modelisation et Simulation Multi-echelle, Universite de Sidi Bel Abbes, Algeria
Abdeldjebbar Tounsi: Material and Hydrology Laboratory, Faculty of Technology, Civil Engineering Department, University of Sidi Bel Abbes, Algeria; Laboratoire de Modelisation et Simulation Multi-echelle, Universite de Sidi Bel Abbes, Algeria
Kouider Halim Benrahou: Material and Hydrology Laboratory, Faculty of Technology, Civil Engineering Department, University of Sidi Bel Abbes, Algeria
Abdelouahed Tounsi: Material and Hydrology Laboratory, Faculty of Technology, Civil Engineering Department, University of Sidi Bel Abbes, Algeria; YFL (Yonsei Frontier Lab), Yonsei University, Seoul, Korea; Department of Civil and Environmental Engineering, King Fahd University of Petroleum & Minerals, 31261 Dhahran, Eastern Province, Saudi Arabia
Mesfer Mohammad Al-Zahrani: Department of Civil and Environmental Engineering, King Fahd University of Petroleum & Minerals, 31261 Dhahran, Eastern Province, Saudi Arabia
S.R. Mahmoud: GRC Department, Jeddah Community College, King Abdulaziz University, Jeddah, Saudi Arabia

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