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CONTENTS
Volume 29, Number 4, April 2022
 


Abstract
In order to analyze the static and dynamic structural characteristics of the Obermeyer gate under overflow conditions, the force characteristics and vibration characteristics of the shield plate structure are studied based on the fluid-solid coupling theory. In this paper, the effects of the flow rate, airbag pressure and overflow water level on the structural performance of shield plate of air shield dam are explored through the method of controlling variables. The results show that the maximum equivalent stress and total deformation of the shield plate decrease first and then increase with the flow velocity. In addition, they are positively correlated with the airbag pressure. What's more, we find that the maximum equivalent stress of the shield plate decreases first and then increases with the overflow water level, and the total deformation of the shield plate decreases with the overflow water level. What's more importantly, the natural frequency of the shield structure of the Obermeyer gate is concentrated at 50 Hz and 100 Hz, so there is still the possibility of resonance. Once the resonance occurs, the free edge of the shield vibrates back and forth. This work may provide a theoretical reference for the safe and stable operation of the shield of the Obermeyer gate.

Key Words
fluid-solid coupling; Obermeyer gate; stable operation; static and dynamic analysis

Address
Jinhai Feng: Institute of Water Resources and Hydropower Research, Northwest A&F University, Shaanxi Yangling 712100, P.R. China
Shiyue Zhou: Institute of Water Resources and Hydropower Research, Northwest A&F University, Shaanxi Yangling 712100, P.R. China
Boxiang Xue: Institute of Water Resources and Hydropower Research, Northwest A&F University, Shaanxi Yangling 712100, P.R. China
Diyi Chen: Institute of Water Resources and Hydropower Research, Northwest A&F University, Shaanxi Yangling 712100, P.R. China; Key Laboratory of Agricultural Soil and Water Engineering in Arid and Semiarid Areas,
Ministry of Education, Northwest A&F University, Shaanxi Yangling 712100, P.R. China
Guoyong Sun: Institute of Water Resources and Hydropower Research, Northwest A&F University, Shaanxi Yangling 712100, P.R. China
Huanhuan Li: Institute of Water Resources and Hydropower Research, Northwest A&F University, Shaanxi Yangling 712100, P.R. China

Abstract
Strengthening slender reinforced concrete (RC) columns is a challenge. They are susceptible to overall buckling that induces bending moment and axial compression. This study presents the precise three-dimensional finite element modeling of slender RC columns strengthened with fiber-reinforced polymer (FRP) composites sheets with various patterns under concentric or eccentric compression. The slenderness ratio r (height/width ratio) of the studied columns ranged from 15 to 35. First, to determine the optimal modeling procedure, nine alternative nonlinear finite element models were presented to simulate the experimental behavior of seven FRP-strengthened slender RC columns under eccentric compression. The models simulated concrete behavior under compression and tension, FRP laminate sheets with different fiber orientations, crack propagation, FRP–concrete interface, and eccentric compression. Then, the validated modeling procedure was applied to simulate 58 FRP-strengthened slender RC columns under compression with minor eccentricity to represent the inevitable geometric imperfections. The simulated columns showed two cross sections (square and rectangular), variable r values (15, 22, and 35), and four strengthening patterns for FRP sheet layers (hoop H, longitudinal L, partial longitudinal Lw, and longitudinal coupled with hoop LH). For r=15-22, pattern L showed the highest strengthening effectiveness, pattern Lw showed brittle failure, steel reinforcement bars exhibited compressive yielding, ties exhibited tensile yielding, and concrete failed under compression. For r>22, pattern Lw outperformed pattern L in terms of the strengthening effectiveness relative to equivalent weight of FRP layers, steel reinforcement bars exhibited crossover tensile strain, and concrete failed under tension. Patterns H and LH (compared with pattern L) showed minor strengthening effectiveness.

Key Words
concrete modeling; contact analysis; FRP modeling; FRP strengthening; nonlinear finite element analysis; slender RC columns behavior and modeling

Address
Ahmed M. El-Kholy, Ahmed O. Osman and Alaa A. EL-Sayed: Department of Civil Engineering, Faculty of Engineering, Fayoum University, Kiman Fares, El-Fayoum, 63541, Egypt

Abstract
The concrete quality relies on general factors like preparation technique, uniformity of the compaction, amount and appropriateness of the additives. The current article investigates the impact of a well knows amino acid, L-arginine as an additive on water requirements, setting durations and characterization of various cement samples. Compressive strength tests of reference and L-arginine added cements at age of 2, 7 and 28 days were carried out according to TS-EN 196-1. Samples were blended by incorporating various amounts of L-arginine (25 ppm, 50 ppm and 75 ppm) in the cement water mixture which were tested with Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), thermo-gravimetric analysis (TG), scanning electron microscopy (SEM) and the energy-dispersive X-ray spectroscopy (EDS) on the 28th day. Results revealed that L-arginine does not affect the setting time, volume expansion of cement and water demands negatively; rather it imparts enhanced sustainability to the samples. It was determined that the highest value belonged to the 75L mortar with an increase of 2.6% compared to the reference sample when the compressive strengths of all mortars were compared on the 28th day. Besides, it has been observed that the development of calcium silicate hydrate or C–S–H gel, calcium hydroxide or CH and other hydrated products are associated with each other. L-arginine definitely has a contribution in the consumption of CH formed in the hydration process.

Key Words
cement; compressive strength; hydration; L-arginine; microstructure; thermal properties

Address
Mine Kurtay Yildiz: Department of Mechanical Engineering, Corrosion Research Laboratory, Faculty of Engineering, Duzce University, 81620, Duzce, Turkey
Husnu Gerengi: Department of Mechanical Engineering, Corrosion Research Laboratory, Faculty of Engineering, Duzce University, 81620, Duzce, Turkey
Yilmaz Kocak: Department of Civil Engineering, Technology Faculty, Duzce University, 81620, Duzce, Turkey

Abstract
In this study, the problem of discontinuous contact in two functionally graded (FG) layers resting on a rigid plane and loaded by two rigid blocks is solved by the finite element method (FEM). Separate analyzes are made for the cases where the top surfaces of the problem layers are metal, the bottom surfaces are ceramic and the top surfaces are ceramic and the bottom surfaces are metal. For the problem, it is accepted that all surfaces are frictionless. A two-dimensional FEM analysis of the problem is made by using a special macro added to the ANSYS package program The solution of this study, which has no analytical solution in the literature, is given with FEM. Analyzes are made by loading different Q and P loads on the blocks. The normal stress (oy) distributions at the interfaces of FG layers and between the substrate and the rigid plane interface are obtained. In addition, the starting and ending points of the separations between these surfaces are determined. The normal stresses (ox, oy) and shear stresses (txy) at the point of separation are obtained along the depth. The results obtained are shown in graphics and tables. With this method, effective results are obtained in a very short time. In addition, analytically complex and long problems can be solved with this method.

Key Words
discontinuous contact; finite element method; functionally graded material; separate; stress

Address
Alper Polat: Department of Civil Engineering, Munzur University, 62000, Tunceli, Turkey
Yusuf Kaya: Department of Civil Engineering, Gümüşhane University, 29000, Gümüşhane, Turkey

Abstract
The present study investigates the effects of Cattaneo-Christov thermal effects of stagnation point in Walters-B nanofluid flow through lubrication of power-law fluid by taking the slip at the interfacial condition. The impacts of thermophoresis and Brownian motions are further accounted. The fluid impinging orthogonally on the surface is due to power-law slim coating liquid. The generalized newtonian fluid equation is used that obeys the power law constitutive equation to model our problem. The effect of velocity profiles, temperature for different values of n are investigated. The prandtl on the temperature distribution for partial slip and no slip cases is also observed. It is found that for larger values of prandtl number thermal diffusivity of fluid reduces and it enhance the decrease in temperature and boundary layer thickness.

Key Words
Newtonian fluid; power-law; stagnation point; temperature distribution; thermophoresis

Address
Manzoor Ahmad: Department of Mathematics, University of Azad Jammu and Kashmir, Muzaffarabad, 1300, Azad Kashmir, Pakistan
Muzamal Hussain: Department of Mathematics, University of Malakand at Chakdara, Dir (Lower), Khyber Pakhtoonkhwa, Pakistan
Mohamed A. Khadimallah: Civil Engineering Department, College of Engineering, Prince Sattam Bin Abdulaziz University, BP 655, Al-Kharj, 16273, Saudi Arabia; Laboratory of Systems and Applied Mechanics, Polytechnic School of Tunisia, University of Carthage, Tunis, Tunisia
Hamdi Ayed: Department of Civil Engineering, College of Engineering, King Khalid University, Abha, Kingdom of Saudi Arabia; Higher Institute of Transport and Logistics of Sousse, University Sousse, Tunisia
Muhammad Taj: Department of Mathematics, University of Azad Jammu and Kashmir, Muzaffarabad, 1300, Azad Kashmir, Pakistan
Adil Alshoaibi: Department of Physics, College of Science, King Faisal University, Al-Hassa, P.O Box, Hofuf, 31982, Saudi Arabia

Abstract
Limestone calcined clay cement (LC3) is a low carbon alternative to conventional cement. Literature shows that using limestone and calcined clay in LC3 increases the thermal degradation of LC3 pastes and can increase the magnitude of fire risk in LC3 concrete structures. Higher thermal degradation of LC3 paste prompts this study toward understanding the fire performance of LC3 concrete and the associated magnitude of fire risk. For fire performance, concrete prepared using ordinary Portland cement (OPC), pozzolanic Portland cement (PPC) and LC3 were exposed to 16 scenarios of different elevated temperatures (400oC, 600oC, 800oC, and 1000oC) for different durations (0.5 h, 1 h, 2 h, and 4 h). After exposure to elevated temperatures, mass loss, residual ultrasonic pulse velocity (rUPV) and residual compressive strength (rCS) were measured as the residual properties of concrete. XRD (X-ray diffraction), TGA (thermogravimetric analysis) and three-factor ANOVA (analysis of variance) are also used to compare the fire performance of LC3 with OPC and PPC. Monte Carlo simulation has been used to assess the magnitude of fire risk in LC3 structures and devise recommendations for the robust application of LC3. Results show that LC3 concrete has weaker fire performance, with average rCS being 11.06% and 1.73% lower than OPC and PPC concrete. Analysis of 106 fire scenarios, in Indian context, shows lower rCS and higher failure probability for LC3 (95.05%, 2.22%) than OPC (98.16%, 0.22%) and PPC (96.48%, 1.14%). For robust application, either LC3 can be restricted to residential and educational structures (failure probability <0.5%), or LC3 can have reserve strength (factor of safety >1.08).

Key Words
exposure duration; exposure temperature; fire risk; fire scenario; LC3 concrete; Monte Carlo simulation; residual strength; three-factor ANOVA

Address
Sanchit Gupta: Department of Civil Engineering, Indian Institute of Technology Indore, Simrol, Indore 453552, India
Dheerendra Singh: Department of Civil Engineering, Indian Institute of Technology Indore, Simrol, Indore 453552, India
Trilok Gupta: Department of Civil Engineering, College of Technology and Engineering, MPUAT, Udaipur, India
Sandeep Chaudhary: Department of Civil Engineering, Indian Institute of Technology Indore, Simrol, Indore 453552, India


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