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CONTENTS
Volume 66, Number 4, May25 2018
 

Abstract
This pioneer study focuses on finite element modeling and numerical modeling of three types of Reinforced Concrete Haunched Beams (RCHBs). Firstly, twenty RCHBs, consisting of three types, and four prismatic beams which had been tested experimentally were modeled via a nonlinear finite element method (NFEM) based software named as, ATENA. The modeling results were compared with experimental results including load capacity, deflection, crack pattern and mode of failure. The comparison showed a good agreement between the results and thus the model used can be effectively used for further studies of RCHB with high accuracy. Afterwards, new mechanism modes and design code equations were proposed to improve the shear design equation of ACI-318 and to predict the critical effective depth. These equations are the first comprehensive formulas in the literature involving all types of RCHBs. The statistical analysis showed the superiority of the proposed equation to their predecessors where the correlation coefficient, R2 was found to be 0.89 for the proposed equation. Moreover, the new equation was validated using parametric and reliability analyses. The parametric analysis of both experimental and predicted results shows that the inclination angle and the compressive strength were the most influential parameters on the shear strength. The reliability analysis indicates that the accuracy of the new formulation is significantly higher as compared to available design equations and its reliability index is within acceptable limits.

Key Words
haunched beam; reinforced concrete; finite element; shear capacity; design code

Address
Mehmet Eren Gulsan and Abdulkadir Cevik: Civil Engineering Department, Gaziantep University, University Avenue-Central Campus, Gaziantep, Turkey
Hasan M. Albegmprli: Department of Building & Construction Engineering, Northern Technical University, Engineering Technical College of Mosul, Iraq

Abstract
This paper presents a numerical study on the behavior of continuous hollow steel beam strengthened using carbon fiber reinforced polymers (CFRP). Most previous studies on the CFRP strengthening of steel beams have been carried out on the steel beams with simple boundary conditions. No independent study, to the researcher\'s knowledge, has studied on the CFRP strengthening of square hollow section (SHS) continuous steel beam. However, this study explored the effect of the use of adhesively bonded CFRP flexible sheets on the behavior of the continuous SHS steel beams. Finite Element Method (FEM) has been employed for modeling. Eleven specimens, ten of which were strengthened using CFRP sheets, were analyzed under different coverage length, the number of layers, and the location of CFRP composite. ANSYS software was used to analyze the SHS steel beams. The results showed that the coverage length, the number of layers, and the location of CFRP composite are effective in increasing the ultimate load capacity of the continuous SHS steel beams. Application of CFRP composite also caused the ductility increase some strengthened specimens.

Key Words
hollow continuous steel beam; CFRP strengthening; ultimate capacity; numerical investigation

Address
Amir Hamzeh Keykha: Department of Civil Engineering, Zahedan Branch, Islamic Azad University, Zahedan, Iran

Abstract
In this paper the effects of particle size and model scale of concrete have been investigated on point load index, tensile strength, and the failure processes using a PFC2D numerical modeling study. Circular and semi-circular specimens of concrete were numerically modeled using the same particle size, 0.27 mm, but with different model diameters of 75 mm, 54 mm, 25 mm, and 12.5 mm. In addition, circular and semi-circular models with the diameter of 27 mm and particle sizes of 0.27 mm, 0.47 mm, 0.67 mm, 0.87 mm, 1.07 mm, and 1.27 mm were simulated to determine whether they can match the experimental observations from point load and Brazilian tests. The numerical modeling results show that the failure patterns are influenced by the model scale and particle size, as expected. Both Is(50) and Brazilian tensile strength values increased as the model diameter and particle sizes increased. The ratio of Brazilian tensile strength to Is(50) showed a reduction as the particle size increased but did not change with the increase in the model scale.

Key Words
model scale; particle size; point load test; Brazilian test; PFC2D

Address
Hadi Haeri and Zheming Zhu: College of Architecture and Environment, Sichuan University, Chengdu 610065, China
Vahab Sarfarazi: Department of Mining Engineering, Hamedan University of Technology, Hamedan, Iran
Ahmadreza Hedayat: Department of Civil and Environmental Engineering, Colorado School of Mines, Golden, CO 80401, United States
Mohammad Fatehi Marji: Associate Professor, Department of Mining Engineering, Yazd University, Yazd, Iran

Abstract
Three points bending flexural test was modelled numerically to study the crack propagation in the pre-cracked beams. The pre-existing double internal cracks inside the beam models were considered to investigate the crack propagation and coalescence paths within the modelled samples. Notch configuration effects on the failure stress were considered too. This numerical analysis shown that the propagation of wing cracks emanating from the tips of the pre-existing internal cracks caused the final breaking of beams specimens. It was also shown that when two notches were overlapped, they both mobilized in the failure process and the failure stress was decreased when the notches were located in centre line. However, the failure stress was increased by increasing the bridge area angle. Finally, it was shown that in all cases, there were good agreements between the discrete element method results and, the other numerical and experimental results. In this research, it is tried to improve the understanding of the crack propagation and crack coalescence phenomena in brittle materials which is of paramount importance in the stability analyses of rock and concrete structures, such as the underground openings, rock slopes and tunnel construction.

Key Words
three point bending test; beam; pre-existing double internal cracks

Address
Hadi Haeri and Zheming Zhu: College of Architecture and Environment, Sichuan University, Chengdu 610065, China
Vahab Sarfarazi: Department of Mining Engineering, Hamedan University of Technology, Hamedan, Iran
Ahmadreza Hedayat: Department of Civil and Environmental Engineering, Colorado School of Mines, Golden, CO 80401, United States
Maryam Firoozi Nezamabadi: Department of Civil Engineering, South Tehran Branch, Islamic Azad University, Tehran, Iran
Mohammadamin Karbala: Department of Mining Engineering, Amirkabir University of Technology (Tehran Polytechnic), Tehran, Iran

Abstract
In this paper, a new meta-heuristic optimization method is presented. This new method is named \"Numbers Cup Optimization\" (NCO). The NCO algorithm is inspired by the sport competitions. In this method, the objective function and the design variables are defined as the team and the team members, respectively. Similar to all cups, teams are arranged in groups and the competitions are performed in each group, separately. The best team in each group is determined by the minimum or maximum value of the objective function. The best teams would be allowed to the next round of the cup, by accomplishing minor changes. These teams get grouped again. This process continues until two teams arrive the final and the champion of the Numbers Cup would be identified. In this algorithm, the next cups (same iterations) will be repeated by the improvement of players\' performance. To illustrate the capabilities of the proposed method, some standard functions were selected to optimize. Also, size optimization of three benchmark trusses is performed to test the efficiency of the NCO approach. The results obtained from this study, well illustrate the ability of the NCO in solving the optimization problems.

Key Words
optimization; meta-heuristic; standard function; truss structure; size optimization

Address
Mojtaba Riyahi Vezvari, Ali Ghoddosian and Amin Nikoobin: Faculty of Mechanical Engineering, Semnan University, Semnan, Iran

Abstract
This study aims to investigate the influence of individual and hybrid fiber on the local bond–slip behavior of medium and high strength concrete after exposure to different high temperatures. Tests were conducted on local pullout specimens (150 mm cubes) with a reinforcing bar embedded in the center section. The embedment lengths in the pullout specimens were three times the bar diameter. The parameters investigated include concrete type (control group: ordinary concrete; experimental group: fiber concrete), concrete strength, fiber type and targeted temperature. The test results showed that the ultimate bond stress in the local bond stress versus slip curve of the high strength fiber reinforced concrete was higher than that of the medium strength fiber reinforced concrete. In addition, the use of hybrid combinations of steel fiber and polypropylene fiber can enhance the residual bond strength ratio of high strength concrete.

Key Words
hybrid fiber reinforced concrete; residual bond strength; pullout test

Address
Chao-Wei Tang: Department of Civil Engineering & Geomatics, Cheng Shiu University, No. 840, Chengcing Rd., Niaosong District, Kaohsiung City, Taiwan R.O.C.


Abstract
The purpose of the present paper is to study the bending and free vibration of Functionally Graded Material (FGM) plate using user-defined material subroutine on the finite element software ABAQUS. The FGM plate is simply supported and subjected to sinusoidal and uniform load. The Poisson\'s ratio is kept constant. The results obtained compared to those available in the literature show the convergence, the exactitude and the efficiency of the method used with various power index of the materials.

Key Words
FGM plate; power law; UMAT; finite element method; stress; displacement

Address
Khalid Messaoudi and Abdelkrim Boukhalfa: Computational Mechanics Laboratory, University of Tlemcen, Faculty of Technology, Mechanical Engineering Department, Algeria
Youcef Beldjelili:
1) Material and Hydrology Laboratory, University of Sidi Bel-Abbes, Faculty of Technology, Civil Engineering Department, Algeria
2) Structures et Materiaux Avances dans le Genie Civil et Travaux Publics, Faculte des Technologie, Departement de Genie Civil, Universite de Sidi Bel-Abbes, Algeria
3) Laboratoire de Modelisation et Simulation Multi-echelle, Faculte des Sciences Exactes, Departement de Physique,
Universite de Sidi Bel-Abbes, Algeria

Abstract
The current study is dedicated to study the thermal effects of wave propagation in beams, reinforced by carbon nanotubes (CNT). Beams, made up of carbon nanotube reinforced composite (CNTRC) are the future materials in various high tech industries. Herein a Winkler elastic foundation is assumed in order to make the model more realistic. Mostly, CNTs are pervaded in cross section of beam, in various models. So, it is tried to use four of the most profitable reconstructions. The homogenization of elastic and thermal properties such as density, Yong\'s module, Poisson\'s ratio and shear module of CNTRC beam, had been done by the demotic rule of mixture to homogenize, which gives appropriate traits in such settlements. To make this investigation, a perfect one, various shear deformation theories had been utilized to show the applicability of this theories, in contrast to their theoretical face. The reigning equation had been derived by extended Hamilton principle and the culminant equation solved analytically by scattering relations for propagation of wave in solid bodies. Results had been verified by preceding studies. It is anticipated that current results can be applicable in future studies.

Key Words
wave propagation; graphene; thermal effects; CNTRC; Winkler elastic foundation; rule of mixture; beam; CNT

Address
Farzad Ebrahimi and Pooya Rostami: Department of Mechanical Engineering, Faculty of Engineering, Imam Khomeini International University, Qazvin, Iran

Abstract
Steam flooding is widely used in heavy oil reservoir with coupling effects among the formation temperature change, fluid flow and solid deformation. The effective stress, porosity and permeability in this process can be affected by the multi-physical coupling of thermal, hydraulic and mechanical processes (THM), resulting in a complex interaction of geomechanical effects and multiphase flow in the porous media. Quantification of the state of deformation and stress in the reservoir is therefore essential for the correct prediction of reservoir efficiency and productivity. This paper presents a coupled fluid flow, thermal and geomechanical model employing a program (MATLAB interface code), which was developed to couple conventional reservoir (ECLIPSE) and geomechanical (ABAQUS) simulators for coupled THM processes in multiphase reservoir modeling. In each simulation cycle, time dependent reservoir pressure and temperature fields obtained from three dimensional compositional reservoir models were transferred into finite element reservoir geomechanical models in ABAQUS as multi-phase flow in deforming reservoirs cannot be performed within ABAQUS and new porosity and permeability are obtained using volumetric strains for the next analysis step. Finally, the proposed approach is illustrated on a complex coupled problem related to steam flooding in an oil reservoir. The reservoir coupled study showed that permeability and porosity increase during the injection scenario and increasing rate around injection wells exceed those of other similar comparable cases. Also, during injection, the uplift occurred very fast just above the injection wells resulting in plastic deformation.

Key Words
effective stress; multi-physical coupling; porous media; volumetric strain; permeability

Address
Roohollah Taghizadeh and Kaveh Ahangari: Department of Mining Engineering, Science and Research Branch, Islamic Azad University, Tehran, Iran
Kamran Goshtasbi: Department of Mining Engineering, Faculty of Engineering, Tarbiat Modares University, Tehran, Iran
Abbas Khaksar Manshad: Department of Petroleum Engineering, Faculty of Petroleum Engineering, Petroleum University of Technology, Abadan, Iran

Abstract
Multiple hazards (multihazard) conditions may cause significant risk to structures that are originally designed for individual hazard scenarios. Such a multihazard condition arises when an earthquake strikes to a bridge pre-exposed to scour at foundations due to flood events. This study estimates the impact spectrum of flood-induced scour on seismic vulnerability of bridges. Characteristic river-crossing highway bridges are formed based on the information obtained from bridge inventories. These bridges are analyzed under earthquake-only and the abovementioned multihazard conditions, and bridge fragility curves are developed at component and system levels. Research outcome shows that bridges having pile shafts as foundation elements are protected from any additional seismic vulnerability due to the presence of scour. However, occurrence of floods can increase seismic fragility of bridges at lower damage states due to the adverse impact of scour on bridge components at superstructure level. These findings facilitate bridge design under the stated multihazard condition.

Key Words
bridges; earthquake; flood; multihazard; fragility

Address
Taner Yilmaz: Department of Civil Engineering, Ozyegin University, Istanbul, Turkey
Swagata Banerjee: Department of Civil Engineering, Indian Institute of Technology Bombay, Powai, Mumbai 400076, India

Abstract
In this paper an analytical model in a closed form able to reproduce the monotonic flexural response of external RC beam-column joints with smooth rebars is presented. The column is subjected to a constant vertical load and the beam to a monotonically increasing lateral force applied at the tip. The model is based on the flexural behavior of the beam and the column determined adopting a concentrated plasticity hinge model including slippage of the main reinforcing bars of the beam. A simplified bilinear moment-axial force domain is assumed to derive the ultimate moment associated with the design axial force. For the joint, a simple truss model is adopted to predict shear strength and panel distortion. Experimental data recently given in the literature referring to the load-deflection response of external RC joints with smooth rebars are utilized to validate the model, showing good agreement. Finally, the proposed model can be considered a useful instrument for preliminary static verification of existing external RC beam-column joints with smooth rebars for both strength and ductility verification.

Key Words
joint; beam; column; shear; flexure; smooth rebars

Address
Giuseppe Campione, Francesco Cannella, Liborio Cavaleri and Alessia Monaco: Department of Civil, Environmental, Aerospace and Material Engineering (DICAM) - University of Palermo,
Viale delle Scienze, 90128 Palermo, Italy


Abstract
Fiber Reinforced Polymer (FRP), which has a high strength to weight ratio, are now regularly used for strengthening of deficient reinforced concrete (RC) structures. While various researches have been conducted on FRP strengthening, an area that still requires attention is predicting the debonding failure load of prestressed FRP strengthened RC beams. Application of prestressing increases the capacity and reduces the premature failure of the beams largely, though not entirely. Few analytical methods are available to predict the failure loads under flexure failure. With this paucity, this research proposes a method for predicting debonding failure induced by intermediate crack (IC) for prestressed FRP-strengthened beams. The method consists of a numerical study on beams retrofitted with prestressed FRP in the tension side of the beam. The method applies modified Branson moment-curvature analysis together with the global energy balance approach in combination with fracture mechanics criteria to predict failure load for complicated IC-induced failure. The numerically simulated results were compared with published experimental data and the average of theoretical to experimental debonding failure load is found to be 0.93 with a standard deviation of 0.09.

Key Words
debonding; fracture energy; FRP strengthening; global energy balance; prestressing

Address
Nusrat Hoque: Department of Civil Engineering, University Malaya, Jalan University, 50603, Kuala Lumpur, Malaysia
Mohd Z. Jumaat: Department of Civil Engineering, University Malaya, 50603, Kuala Lumpur, Malaysia

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