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CONTENTS
Volume 74, Number 4, May25 2020
 

Abstract
The force resisting ability of a connection has direct implications on the overall response of a timber framed structure to various actions, thereby governing the integrity and safety of such constructions. The behavior of timber framed structures has been studied by many researchers by testing full-scale-connections in timber frames so as to establish consistent design provisions on the same. However, much emphasis in this approach has been unidirectional, that has focused on a particular connection configuration, with no research output stressing on the refinement of the existing connection details in order to optimize their performance. In this regard, addition of adhesive to dowelled timber connections is an economically effective technique that has a potential to improve their performance. Therefore, a comparative study to evaluate the performance of various full-scale timber frame Nailed connections (Bridled Tenon, Cross Halved, Dovetail Halved and Mortise Tenon) supplemented by adhesive with respect to Nailed-Only counterparts under tensile loading has been investigated in this paper. The load-deformation values measured have been used to calculate stiffness, load capacity and ductility in both the connection forms (with and without adhesion) which in turn have been compared to other configurations along with the observed failure modes. The observed load capacity of the tested models has also been compared to the design strengths predicted by National Design Specifications (NDS-2018) for timber construction. Additionally, the experimental behavior was validated by developing non-linear finite element models in ABAQUS. All the results showed incorporation of adhesive to be an efficient and an economical technique in significantly enhancing the performance of various timber nailed connections under tensile action. Thus, this research is novel in a sense that it not only explores the tensile behavior of different nailed joint configurations common in timber construction but also stresses on improvising the same in a logical manner hence making it distinctive in its approach.

Key Words
timber frame; joint configuration; tensile capacity; failure modes; bearing strength

Address
Department of Civil Engineering, National Institute of Technology Srinagar, Hazratbal-190006 Jammu and Kashmir, India

Abstract
This paper aims to study the effect of the elastic nonlocality on the transient waves in a two-dimensional thermoelastic medium influenced by thermal loading due to the laser pulse. The bounding plane surface is heated by a non-Gaussian laser beam. The problem is discussed under the Eringen\'s nonlocal elasticity model and the Green-Naghdi (G-N) theory with and without energy dissipation. The normal mode analysis method is used to get the exact expressions for the physical quantities which illustrated graphically by comparison and discussion. The effects of nonlocality and different values of time on the displacement, the stresses, and the temperature were made numerically. All the computed results obtained have been depicted graphically and explained.

Key Words
nonlocal; laser pulse; Green-Naghdi theory; normal mode; ramp parameter

Address
Nantu Sarkar: Department of Applied Mathematics, University of Calcutta, Kolkata-700 009, India
Sudip Mondal: Department of Mathematics, Basirhat College, North 24 Parganas-743412, India
Mohamed I.A. Othman anomalous: Department of Mathematics, Faculty of Science, P.O. Box 44519, Zagazig University, Zagazig, Egypt

Abstract
In this paper, a probability-based procedure to evaluate the performance of existing RC structures exposed to seismic and fire actions is presented. The procedure is demonstrated with reference to an existing old school building, located in Italy. The vulnerability assessment of the building highlights deficiencies under both static and seismic loads. Retrofit operations are designed to achieve the seismic safety. The idea of the work consists in assessing the performance of the existing and retrofitted building in terms of both the seismic and fire resistance. The seismic retrofit and fire resistance upgrading follow different paths, depending on the specific configuration of the building. A good seismic retrofit does not entail an improving of the fire resistance and vice versa. The goal of the current work is to study the variation of response due to the uncertainties considered in records/fire curves selection and to carry out the assessment of the studied RC structure by obtaining fragility curves under the effect of different records/temperature. The results show the fragility curves before and after retrofit operations and both in terms of seismic performance and fire resistance performance, measuring the percent improving for the different limit states.

Key Words
fragility curves; cloud analysis; multiple stripe analysis; fire resistance; seismic retrofit

Address
Department of Structures for Engineering and Architecture, University of Naples Federico II, Via Claudio, 21, Napoli, 80125, Italy

Abstract
This study investigated the effects of prestressing force on the natural frequency of concrete beams considering changes in the self-weight of the beam. For this, a finite element formulation was derived to account for the increase in the stiffness of a beam-tendon system due to the axial force and deformation induced by prestressing of the tendon. The developed finite element formulation was validated with the data obtained in laboratory experiments. The experimental natural frequencies of the small prestressed concrete (PSC) beam specimens were consistent with those obtained using the proposed method. The first natural frequency increased almost linearly as the prestressing force increased. The proposed method was then applied to four actual PSC bridges typically employed in the field. Different from the laboratory specimens, the first natural frequencies of the actual PSC bridges barely changed or increased with increasing prestressing force. The results of an analytical parametric study showed that the increase in the natural frequency strongly depended on the magnitude of the prestressing force relative to the total weight of the structure. Thus, the variation in the natural frequencies of the actual PSC bridges with high total weight relative to the prestressing force was negligible due to the application of the prestressing force.

Key Words
prestressed concrete bridge; prestressing force; self-weight; natural frequency; geometric stiffness

Address
Soobong Shin,and Jong-Han Lee: Department of Civil Engineering, Inha University, 100 Inha-ro, Michuhol-gu, Incheon 22212, Korea
Hokyoung Lee: Korea Bridge Institute Co., 252 Gilju-ro, Wonmi-gu, Bucheon, Gyeonggido 14548, Korea

Abstract
This study proposes prediction models for the shear strength of steel fiber reinforced concrete (SFRC) and ultra-highperformance fiber reinforced concrete (UHPC) beams using a Bayesian parameter estimation approach and a collected experimental database. Previous researchers had already proposed shear strength prediction models for SFRC and UHPC beams, but their performances were limited in terms of their prediction accuracies and the applicability to UHPC beams. Therefore, this study adopted a statistical approach based on a collected database to develop prediction models. In the database, 89 and 37 experimental data for SFRC and UHPC beams without stirrups were collected, respectively, and the proposed equations were developed using the Bayesian parameter estimation approach. The proposed models have a simplified form with important parameters, and in comparison to the existing prediction models, provide unbiased high prediction accuracy.

Key Words
SFRC; UHPC; shear strength; steel fiber; bayesian parameter estimation

Address
Hae-Chang Cho, Won-Hee Kang: Centre for Infrastructure Engineering, Western Sydney University, Penrith, NSW 2751, Australia
Min-Kook Park: Department of Civil and Environmental Engineering, Nazarbayev University, 53 Qabanbay Batyr Ave., Nul-sultan, 010000, Kazakhstan
Jin-Ha Hwang, and Kang Su Kim: Department of Architectural Engineering, University of Seoul, 163 Siripdaero, Dongdaemun-gu, Seoul 02504, Republic of Korea


Abstract
In the modern era, the world is facing unprecedented challenges in form of environmental pollution and international agencies are forcing scientists and materialists to look for green materials and structures to counter this problem. Composites based on renewable sources like plant based fibres, vegetable fibres are finding increasing use in interior components of automobile vehicles, aircraft, and building construction. In the present study, jute and flax fibre based composites were developed and tested for assessing their suitability for possible applications in interior cabin and parts of automobile and aerospace vehicles. Matrix system involves epoxy as resin and fibre weight fractions used were 45% and 55% respectively. Composites samples were prepared as per American society for testing and materials (ASTM) standard and were tested for individual fiber tensile strength, composite tensile strength, and flexural strength to analyse its behavior under various loading conditions. The results revealed that the Jute fibre composites possess enhanced mechanical properties over Flax fibre composites.

Key Words
composites; natural fibres; mechanical testing; Jute; flax; ASTM

Address
School of Mechanical Engineering, SASTRA Deemed University, Thanjavur, Tamilnadu 613402, India

Abstract
A floating dry dock is an advanced structure that can provide a solution for dry dock space shortages. The critical point in floating dock operation is compensating the deflection caused by a heavy payload by adjusting the water level in the ballast system. An appropriate ballasting plan warrants safe and precise construction on a floating dock. Particularly, in the case of a 2D floating dock, ballasting plan evaluation is crucial due to complex deformation modes. In this paper, we developed a method to calculate the optimal ballasting plan for accurate and precise construction on a 2D floating dock. The finite element method was used for considering the flexibility of the floating dock as well as the construction blocks. Through a gradient-based optimization algorithm, the optimal ballasting plan for the given load condition was calculated in semi-real time (5 min). The present method was successfully used for the actual construction of an offshore structure on the 2D floating dock.

Key Words
floating dock; offshore structure; finite element model; optimization; ballasting plan

Address
Kyungho Yoon, Hyo-Jin Kim, Seungkyun Yeo: Department of Mechanical Engineering, Korea Advanced Institute of Science and Technology,
291, Daehak-ro, Yuseong-gu, Daejeon 34141, Republic of Korea
Younghwa Hong, Jihye Cha: Institute of Industrial Technology, Samsung Heavy Industries,
217, Munji-ro, Yuseong-gu, Daejeon 34051, Republic of Korea
Hyun Chung: Department of Naval Architecture & Ocean Engineering,
Chungnam National University, 99, Daehak-ro, Yuseong-gu, Daejeon 34134, Republic of Korea

Abstract
An optimal design method for a spoke double-layer cable-net structure (SDLC) is proposed in this study. Simplified calculation models of the SDLC are put forward to reveal the static responses under vertical loads and wind loads. Next, based on an energy principle, the relationship among the initial prestress level, cross-sectional areas of the components, rise height, sag height, overall displacement, and relative deformation is proposed. Moreover, a calculation model of the Foshan Center SDLC is built and optimized. Given the limited loading cases, material properties of the components, and variation ranges of the rise height and sag height, the self-weight and initial prestress level of the entire structure can be obtained. Because the self-weight of the cables decreases with increasing of the rise height and sag height, while the self-weight of the inner strut increases, the total weight of the entire structure successively exhibits a sharp reduction, a gradual decrease, a slow increase, and a sharp increase during the optimization process. For the simplified model, the optimal design corresponds to the combination of rise height and sag height that results in an appropriate prestress level of the entire structure with the minimum total weight.

Key Words
spoke double-layer cable-net; simplified calculation model; energy principle; structural optimal design; comparative analysis

Address
Mingmin Ding: College of Civil Engineering, Nanjing Forestry University, Nanjing 210037, Jiangsu, China
Bin Luo and Zhengxing Guo: Department of Civil Engineering, Southeast University, Nanjing 210096, Jiangsu, China
Lifeng Han: Cob Development (Suzhou) Co. Ltd., Wuxi 214001, Jiangsu, China
Qianhao Shi: Wuxi Civil Architecture Design Institute Co. Ltd., Wuxi 214072, Jiangsu, China


Abstract
In this paper, an automatic adaptive mesh refinement procedure is presented for two-dimensional problems on the basis of a new probabilistic error estimator. First-order perturbation theory is employed to determine the lower and upper bounds of the structural displacements and stresses considering uncertainties in geometric sizes, material properties and loading conditions. A new probabilistic error estimator is proposed to reduce the mesh dependency of the responses dispersion. The suggested error estimator neglects the refinement at the critical points with stress concentration. Therefore, the proposed strategy is combined with the classic adaptive mesh refinement to achieve an optimal mesh refined properly in regions with either high gradients or high dispersion of the responses. Several numerical examples are illustrated to demonstrate the efficiency, accuracy and robustness of the proposed computational algorithm and the results are compared with the classic adaptive mesh refinement strategy described in the literature.

Key Words
adaptive mesh refinement; error estimation; stochastic finite element; mesh dependency; first-order perturbation theory

Address
Department of Civil Engineering, Shahed University, Persian Gulf Highway, Tehran, Iran

Abstract
This paper intends to progress models to accurately estimate the behavior of fresh concrete under vibration using artificial neural networks (ANNs). To this end, behavior of a full scale precast concrete mold was investigated numerically. Experimental study was carried out under vibration with the use of a computer-based data acquisition system. In this study measurements were taken at three points using two vibrators. Transducers were used to measure time-dependent lateral displacements at these points on mold while both mold is empty and full of fresh concrete. Modeling of empty and full mold was made using ANNs. Benefiting ANNs used in this study for modeling fresh concrete, mold design can be performed. For the modeling of ANNs: Experimental data were divided randomly into two parts such as training set and testing set. Training set was used for ANN\'s learning stage. And the remaining part was used for testing the ANNs. Finally, ANN modeling was compared with measured data. The comparisons show that the experimental data and ANN results are compatible.

Key Words
modeling; artificial neural networks (ANNs); precast concrete mold; compaction of fresh concrete; vibration

Address
Gultekin Aktas: Department of Civil Engineering, Dicle University, 21280 Diyarbakir, Turkey
Mehmet Sirac Ozerdem: Department of Electrical and Electronics Engineering, Dicle University, 21280 Diyarbakir, Turkey

Abstract
Considerable controversy surrounds the choice of the best abutment type for implant prosthetics. The two most common structures are hex and non-hex abutments. The non-hex abutment typically furnishes a larger contact area between itself and the implant than that provided by a hex structure. However, when a hex abutment is loaded, the position of its contact area may be deeper than that of a non-hex abutment. Hence, the purpose of this study is to determine the different biomechanical behaviors of an internal bone-level implant based on the abutment type—hex or non-hex—and clinical crown length under static and cyclic loadings using finite element analysis (FEA). The hex structure was found to increase the implant and abutment stability more than the non-hex structure among several criteria. The use of the hex structure resulted in a smaller volume of bone tissues being at risk of hypertrophy and fatigue failure. It also reduced micromovement (separation) between the implant components, which is significantly related to the pumping effect and possible inflammation. Both static and fatigue analyses, used to examine short- and long-term stability, demonstrated the advantages of the hex abutment over the non-hex type for the stability of the implant components. Moreover, although its impact was not as significant as that of the abutment type, a large crown-implant ratio (CIR) increased bone strain and stress in the implant components, particularly under oblique loading.

Key Words
finite element analysis; dental implant; abutment type; fatigue; micromovement

Address
Hyeonjong Lee: Department of Prosthodontics, School of Dentistry, PU.S.A.n National University, 49, BU.S.A.ndaehak-ro,
Mulgeum-eup, Yangsan-si, Gyeongsangnam-do, 50612, Republick of Korea
Si-Myung Park: Center for Medical Robotics, Korea Institute of Science and Technology, 5, Hwarang-ro 14-gil,
Seongbuk-gu, Seoul, 02792, Republic of Korea
Kwantae Noh: Department of Prosthodontics, School of Dentistry, Kyung Hee University, 26,
Kyungheedae-ro, Dongdaemun-gu, Seoul, 02447, Republic of Korea
Su-Jin Ahn: Department of Biomaterials & Prosthodontics, Kyung Hee University Hospital at Gangdong,
School of Dentistry, Kyung Hee University, 892, Dongnam-ro, Gangdong-gu, Seoul, 05278, Republic of Korea
Sangkyun Shin and Gunwoo Noh: School of Mechanical Engineering, Kyungpook National University, 80, Daehak-ro, Buk-gu, Daegu, 41566, Republic of Korea


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