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CONTENTS
Volume 28, Number 4, October 2021
 

Abstract
The application of Near Surface Mounted (NSM) method to strengthen reinforced concrete (RC) members in flexure through the use of Fiber Reinforced Polymer (FRP) rods has become a subject of interest to designers and researchers over the past few years. This technique has been extensively applied, and there is still a need for more experiments, analytical, and numerical studies to determine the effects of their parameters on the flexural performance of RC members. Therefore, a detailed 3D nonlinear finite element (FE) numerical model was developed in this study to predict the load-carrying capacity and the response of RC T-beams strengthened in the negative moment region accurately through the use of NSM FRP rods at different depth of embedment which are placed under three-point bending loading. The model was, however, designed with due consideration for the nonlinear constitutive material properties of concrete, yielding of steel reinforcement, NSM rods, and cohesive behaviors to simulate the contact between two neighboring materials. Moreover, the findings of the numerical simulations were compared with those from the experiments by other investigators which involve two specimens strengthened with NSM FRP rods added to one unstrengthened control specimen. The results, however, showed that the mid-span deflection responses of the predicted FE were in line with the corresponding data from the experiment for all the flexural loading stages. This was followed by the use of the validated FE models to analyze the effect of several properties of the FRP materials to provide more information than the limited experimental data available. It was discovered that the FE model developed is appropriate to be applied practically and economically with more focus on the parametric studies based on design to precisely model and analyze flexural negative moment strengthening for the RC members through the use of NSM FRP rods.

Key Words
finite element analysis; flexural strengthening; FRP rods; NSM reinforcement

Address
Yanuar Haryanto: Department of Civil Engineering, College of Engineering, National Cheng Kung University, No. 1 University Road, Tainan, 701, Taiwan, ROC; Department of Civil Engineering, Faculty of Engineering, Jenderal Soedirman University, Jln. Mayjen. Sungkono KM 5, Blater, Purbalingga, 53371, Indonesia
Hsuan-Teh Hu: Department of Civil Engineering, College of Engineering, National Cheng Kung University, No. 1 University Road, Tainan, 701, Taiwan, ROC; Department of Civil and Disaster Prevention Engineering, College of Engineering and Science, National United University, No. 2, Lien Da, Nan Shih Li, Miaoli, 36063, Taiwan, ROC
Ay L. Han: Department of Civil Engineering, Faculty of Engineering, Diponegoro University, Jln. Prof. Soedarto, Tembalang, Semarang, 50375, Indonesia
Fu-Pei Hsiao: Department of Civil Engineering, College of Engineering, National Cheng Kung University, No. 1 University Road, Tainan, 701, Taiwan, ROC; National Center for Research on Earthquake Engineering, 200 Sec. 3, Xinhai Road, Taipei, 10668, Taiwan, ROC
Chrang-Jen Teng: Department of Civil Engineering, College of Engineering, National Cheng Kung University, No. 1 University Road, Tainan, 701, Taiwan, ROC
Banu A. Hidayat: Department of Civil Engineering, College of Engineering, National Cheng Kung University, No. 1 University Road, Tainan, 701, Taiwan, ROC; Department of Civil Engineering, Faculty of Engineering, Diponegoro University, Jln. Prof. Soedarto, Tembalang, Semarang, 50375, Indonesia
Laurencius Nugroho: Department of Civil Engineering, College of Engineering, National Cheng Kung University, No. 1 University Road, Tainan, 701, Taiwan, ROC

Abstract
This paper presents a numerical model to simulate the behavior of the slender RC column strengthened by a steel jacket using angles and strips. The proposed strengthening technique has been verified using experimental results of slender column tests performed by previous research. Both load-deformation relationships and failure modes are investigated. The results of the numerical models are in good agreement with the values from the experimental work used in verification. The results also show that the strengthening technique using steel angles and strips is effective for increasing the ultimate load of the slender column by up to 50% and also increases column stiffness and ductility. It's found that the capacity of the strengthened column increases with steel angles and strips sizes and decreases with increasing slenderness ratio (o).

Key Words
reinforced concrete; slender column; slenderness ratio; steel angles; strengthening; strips

Address
Osman Shallan, Thrwat Sakr, Mahmoud Khater and Ahmed Ismail: Department of Structural Engineering, University of Zagazig, Zagazig, Egypt

Abstract
Recent interest in the development of innovative building materials has brought about the need for a detailed assessment of their mechanical fracture properties. The parameters for these need to be acquired, and one of the possible ways of doing so is to obtain them indirectly - based on a combination of fracture testing and inverse analysis. The paper describes a method for the identification of selected parameters of mortars and other fine-grained brittle matrix composites. The cornerstone of the method is the use of an artificial neural network, which is utilized as a surrogate model of the inverse relation between the measured specimen response parameters and the sought material parameters. Due to the potentially wide range of composite mixtures and hence the wide range of experimental responses likely to be gained from individual specimens, an ensemble of artificial neural networks was created. It allows the entire range of variants to be covered and provides resulting parameter values with sufficient precision. Such a system is also easy to expand if a composite with properties outside the current range is tested. The capabilities of the proposed identification system are demonstrated on two selected types of fine-grained composites with different specimen responses. The first group of specimens was made of composite based on alkali-activated slag with standardized and natural sand investigated within the time interval of 3 to 330 days of aging. The second tested composite contained alkali-activated fly ash matrix, and the effect of the addition of natural fibers on fracture response was investigated.

Key Words
artificial neural network; ensemble; fine-grained composites; mechanical fracture parameters; network inverse analysis; neural

Address
David Lehký, Martin Lipowczan, Hana Šimonová and Zbyněk Keršner: Faculty of Civil Engineering, Brno University of Technology, Veveří 331/95, 602 00 Brno, Czech Republic

Abstract
With the demand in the usage of Self-Compacting Concrete (SCC) there is a need to look into an alternate procedure of mix design to address the present practical issues. The existing standards of SCC mix design either underestimates or overestimates the materials used for the production of concrete which reduces the workability, durability and increases the cost. In the present study a mix design procedure which is based on the plastic viscosity of paste and target compressive strength of the SCC mix is being developed using a micromechanical procedure. Cement Replacement Materials like Slag and Fly ash are used for the present study in binary and ternary mix compositions. To address the issue of scarcity of river sand in India, Crushed Rock Fine is used a fine aggregate for the proposed mix design. To enhance the mechanical characteristics of SCC mixes, influence of varying fiber fraction is also studied for the Ternary SCC mixes. The volume fraction of fibers and aspect ratio of fibers are entered as an input into the programming tool to obtain combinations of SCC mixtures. Hooked end steel fibers with volume ranging from 0.1% to 0.5% are chosen for the experimental investigation. Results indicated that the compressive, split tensile and flexural strengths increased with the increase in fiber volume fraction but the fresh properties slump flow, T500 and J-ring spread, V-funnel and L-box decreased. Further, the study is extended in evaluating the fracture energy of Ternary SCC mixes with and without fibers. Fracture energy increased with the increase in fiber volume and post-peak responses are captured more accurately with the presence of fibers. The evaluated fracture energy will be useful for the analysis of cracked concrete structural components.

Key Words
crushed rock fines; fly ash; GGBS; mix design; plastic viscosity; self-compacting concrete

Address
J.S. Kalyana Rama: Department of Civil Engineering, Ecole Centrale School of Engineering, Mahindra University, Hyderabad, India
Sai Kubair: Department of Civil Engineering, Delft University of Technology, Netherlands
M.V.N. Sivakumar: Department of Civil Engineering, National Institute of Technology, Warangal, India
A. Vasan: Department of Civil Engineering, BITS Pilani-Hyderabad Campus, Hyderabad, India
A. Ramachandra Murthy: CSIR-Structural Engineering Research Centre, Chennai, India

Abstract
In this paper, Shear behavior of soft filling in intact model has been investigated using particle flow code (PFC2D). Firstly, calibration of PF2D was performed to reproduce the concrete sample. Uniaxial strength of concrete was 37.2 MPa. Then, numerical models with dimension of 100 mmx100 mm were prepared. One, two and three rectangular filling were situated at the middle of the model. Dimension of filling were 2.5 mmx5 mm, 2.5 mmx10 mm and 2.5 mmx15 mm were prepared. The fillings were calibrated by parallel bond to reproduce the gypsum samples. Uniaxial strength of gypsum was 7.2 MPa. Totally 9 models were prepared. The shear test condition was added to the models. The normal load was fixed at 3 MPa (oc/3) and shear load was applied to model till failure occurred. The results show that, the filling was failure under normal loading. The tensile crack occurred in filling. Also shear cracks initiates at tip of the model and propagates parallel to shear loading axis till calescence to the filling. The shear strength and maximum shear displacement increase with increasing the dimension and number of fillings.

Key Words
failure pattern; filling; PFC2D; shear strength

Address
Vahab Sarfarazi: Department of Mining Engineering, Hamedan University of Technology, Hamedan, Iran
Kaveh Asgari: Department of Mining Engineering, Shahid Bahonar University of Kerman, Kerman, Iran

Abstract
The preparation of ultra-high performance concrete usually required expensive materials and harsh curing conditions, which limited its application in engineering widely. It may be solved by adding supplementary cementitious materials (fly ash, ground granulated blast slag, silica fume and so on). This paper is dedicated to determining the optimal mix ratio of UHPC under common preparation methods and raw materials and under common maintenance conditions to expand the applications of UHPC. The influence of the ratio of water to binder, the ratio of sand to binder, the content of supplementary cementitious materials on UHPC slump spread, compressive strength of 7 days and 28 days, apparent density and tensile strength of 28 days were researched by orthogonal test. The results revealed that the method of semi-dry mixing could enhance the homogeneity of steel fiber and improve the rate of its utilization. When the replacement of cement achieved 50% by the supplementary cementitious materials, the performances of UHPC were still guaranteed and confirmed. When the ratio of sand to binder reached 1.1, the ratio of water to binder reached 0.17, ground granulated blast slag was 25%, fly ash was 10% and silica fume was 15%, its slump spread reached 580 mm, compressive strength and tensile strength reached 152.9 MPa and 14.2 MPa respectively in 28 days under natural curing conditions. Therefore, the UHPC with supplementary cementitious materials should be considered as one of the sustainable development and environmental protection materials.

Key Words
natural curing condition; orthogonal test; semi-dry mixing; supplementary cementitious materials; ultra-high performance concrete

Address
Zong-cai Deng, Jun-wei Wang and Jian-ming Ding: Key Laboratory of Urban Security and Disaster Engineering, College of Architecture and Civil Engineering, Beijing University of Technology, No.100 pingleyuan, Beijing, China

Abstract
The micromechanical interactions between a crack and a circular hole under uniaxial compression were studied. Concrete samples with a dimension of 150 mmx150 mmx50 mm were prepared. Within the specimen, one joint and one hole were provided. The joint lengths were 1.5 cm and the hole diameter was 2 cm. The hole was situated middle of the sample. The Joint was situated in four different diagonal plane angle related to the hole. Diagonal plane angles were 0, 30, 60, and 90 degrees. In each diagonal plane angle, the joint angle changes from 0o to 90o with increments of 30o. The distance between the joint notch and the hole wall was 2 cm. A total of 16 different models were tested under compressive loading. Concurrent with experimental tests, the models containing the hole and joint were tested numerically by two-dimensional particle flow code (PFC2D). Tensile strength of material was 1 MPa. The axial load rate on the model was 0.05 mm/min. The results show that the failure behaviors of rock samples containing the hole and joint were governed by the configuration of the joint. The uniaxial compressive strengths of the samples were controlled by the scheme of crack propagation and failure process of pre-existing discontinuities. Furthermore, it was shown that the behavior of discontinuities is dictated by the frequency of the tensile fractures which increased as the joint angle was increased in each diagonal plane. Along with the damage failure of the samples, the AE activities are excited. At the beginning of loading, just a small number of AE hits were observed, however, AE hits quickly increase until the applied stress reaches its peak. AE hits rapidly grow before the applied stress reached its peak. Moreover, any stress reduction was followed by many AE hits. Finally, both the laboratory testing and the numerical simulation have identical failure patterns and failure strengths. The current study demonstrates the application and privilege of the application of the bonded-particle model to simulate crack propagation between a hole and a crack.

Key Words
joint; PFC2D; tensile crack; the hole

Address
Vahab Sarfaraz: Department of Mining Engineering, Hamedan University of Technology, Hamedan, Iran
Soheil Abharian: Department of Mining and metallurgical engineering Amirkabir University, Tehran Iran
Nima Babanouri: Department of Mining Engineering, Hamedan University of Technology, Hamedan, Iran
Hossein Salari rad: Department of Mining and metallurgical engineering Amirkabir University, Tehran Iran


Abstract
In recent years, more and more experimental studies have shown that the development of mature active control design in practice requires consideration of robustness criteria in the design process, including robustness and stability in practice considering the uncertainty in the system. This article proposes a robust test method for the control of civil structures. In order to facilitate the calculation of the H performance, a linear matrix inequality (LMI) based on this effective solution is also introduced, which combines H control and LMI fuzzy neural network approach. In order to check the suitability of the proposed method, the earthquake excitation during the active support of digital building models conducted extensive simulations. The model includes a one all steel frame vibration table test. In the simulation, the controller design is based on the uncertainty of the system, and the use of throttle feedback is emphasized for practical reasons. The simulation results show that the performance of the controller proposition is significant, powerful, and the effectiveness. Therefore, this robust control method is suitable for seismic protection of civil structure buildings.

Key Words
fuzzy LMI control; H control

Address
Z.Y. Chen: School of Science, Guangdong University of Petrochem Technol, Maoming 525000, PR China
Rong Jiang: School of Science, Guangdong University of Petrochem Technol, Maoming 525000, PR China
Ruei-Yuan Wang: School of Science, Guangdong University of Petrochem Technol, Maoming 525000, PR China
Timothy Chen: Division of Engineering and Applied Science, California Institute of Technology, Pasadena, CA 91125, USA

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