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CONTENTS
Volume 75, Number 3, August10 2020
 

Abstract
In general, the study of a high-rise building's behaviour when subjected to a horizontal load (wind or earthquake) is carried out through numerical modelling with finite elements method. This paper proposes a new, original approach based on the use of a multi-beams model. By redistributing bending and axial stiffness of horizontal elements (beams and slabs) along vertical elements, it becomes possible to produce a system of differential equations able to represent the structural behaviour of the whole building. In this paper this approach is applied to the study of bending behaviour in a 37-storey building (Torre Pontina, Latina, Italy) with a regular reinforced concrete structure. The load considered is the wind, estimated in accordance with Italian national technical rules and regulations. To simplify the explanation of the approach, the wind load was considered uniform on the height of building with a value equal to the average value of the wind load distribution. The system of differential equations' is assessed numerically, using Matlab, and compared with the obtainable solution from a finite elements model along with the obtainable solutions via classical Euler-Bernoulli beam theory. The comparison carried out demonstrates, in the case study examined, an excellent approximation of structural behaviour.

Key Words
multi-beams system; high-rise building; structural modelling; structural mechanics

Address
Faculty of Architecture, Architectural Engineering and Urban Planning, Université catholique de Louvain, Louvain-la-Neuve, Belgium

Abstract
The construction of Reinforced Concrete (R/C) buildings with unreinforced masonry infills is part of the traditional building practice in many countries with regions of high seismicity throughout the world. When these buildings are subjected to seismic motions the presence of masonry infills and especially their configuration can highly influence the seismic damage state. The capability to avoid configurations of masonry infills prone to seismic damage at the stage of initial architectural concept would be significantly definitive in the context of Performance-Based Earthquake Engineering. Along these lines, the present paper investigates the potential of instant prediction of the damage response of R/C buildings with various configurations of masonry infills utilizing Artificial Neural Networks (ANNs). To this end, Multilayer Feedforward Perceptron networks are utilized and the problem is formulated as pattern recognition problem. The ANNs' training data-set is created by means of Nonlinear Time History Analyses of 5 R/C buildings with a large number of different masonry infills' distributions, which are subjected to 65 earthquakes. The structural damage is expressed in terms of the Maximum Interstorey Drift Ratio. The most significant conclusion which is extracted is that the ANNs can reliably estimate the influence of masonry infills' configurations on the seismic damage level of R/C buildings incorporating their optimum design.

Key Words
reinforced concrete buildings; masonry infills; seismic damage; artificial neural networks; pattern recognition

Address
Konstantinos G. Kostinakis: Department of Civil Engineering, Aristotle University of Thessaloniki, 54124, Thessaloniki, Greece
Konstantinos E. Morfidis: Institute of Engineering Seismology and Earthquake Engineering (ITSAK-EPPO), 55535, Thessaloniki, Greece

Abstract
In applying the spectral stochastic finite element methods to the frequency response analysis, the conventional methods are known to give unstable and inaccurate results near the natural frequencies. To address this issue, a new sensitivity based stabilized formulation for stochastic frequency response analysis is proposed in this paper. The main difference over the conventional spectral methods is that the polynomials of random variables are applied to both numerator and denominator in approximating the harmonic response solution. In order to reflect the resonance behavior of the structure, the denominator polynomials is constructed by utilizing the natural frequency sensitivity and the random mode superposition. The numerator is approximated by applying a polynomial chaos expansion, and its coefficients are obtained through the Galerkin or the spectral projection method. Through various numerical studies, it is seen that the proposed method improves accuracy, especially in the vicinities of structural natural frequencies compared to conventional spectral methods.

Key Words
uncertainty quantification; spectral stochastic finite element method; frequency response; natural frequency sensitivity

Address
Gil-Yong Lee and Yong-Hwa Park: Department of Mechanical Engineering, KAIST, 291 Daehak-ro Yuseong-gu Daejeon 34141, Republic of Korea
Seung-Seop Jin: Sustainable Infrastructure Research Center, Korea Institute of Civil Engineering and Building Technology (KICT), Goyang-Si 10223, Republic of Korea

Abstract
The stability and dynamic performance of a flapper-nozzle servo valve depend on several factors, such as the motion of the armature component and the deformation of the spring tube. As the only connection between the armature component and the fixed end, the spring tube plays a decisive role in the dynamic response of the entire system. Aiming at predicting the vibration characteristics of the servo valves to combine them with the control algorithm, an innovative dynamic stiffness based on a distributed parameter model (DPM) is proposed that can reflect the dynamic deformation of the spring tube and a suitable discrete method is applied according to the working condition of the spring tube. With the motion equation derived by DPM, which includes the impact of inertia, damping, and stiffness force, the mathematical model of the spring tube dynamic stiffness is established. Subsequently, a suitable program for this model is confirmed that guarantees the simulation accuracy while controlling the time consumption. Ultimately, the transient response of the spring tube is also evaluated by a finite element method (FEM). The agreement between the simulation results of the two methods shows that dynamic stiffness based on DPM is suitable for predicting the transient response of the spring tube.

Key Words
servo-valve; distributed parameters; spring tube; transient response; mathematical model

Address
Department of Fluid Control and Automation, Harbin Institute of Technology,
Box 3040, Science Park, No. 2, Yikuang Street Nangang District, Harbin 150001, PR China

Abstract
In this article, a developed bond-based peridynamic model for functionally graded materials (FGMs) is proposed to simulate the dynamic fracture behaviors in FGMs. In the developed bond-based peridynamic model for FGMs, bonds are categorized into three different types, including transverse directionally peridynamic bond, gradient directionally peridynamic bond and arbitrary directionally peridynamic bond, according to the geometrical relationship between directions of peridynamic bonds and gradient bonds in FGMs. The peridynamic micromodulus in the gradient directionally and arbitrary directionally peridynamic bonds can be determined using the weighted projection method. Firstly, the standard bond-based peridynamic simulations of crack propagation and branching in the homogeneous PMMA plate are performed for validations, and the results are in good agreement with the previous experimental observations and the previous phase-field numerical results. Then, the numerical study of crack initiation, propagation and branching in FGMs are conducted using the developed bond-based peridynamic model, and the influence of gradient direction on the dynamic fracture behaviors, such as crack patterns and crack tip propagation speed, in FGMs is systematically studied. Finally, numerical results reveal that crack branching in FGMs under dynamic loading conditions is easier to occur as the gradient angle decreases, which is measured by the gradient direction and direction of the initial crack.

Key Words
crack propagation; crack branching; FGMs; gradient direction; bond-based peridynamics

Address
Miaomiao Kou: 1. School of Civil Engineering, Qingdao University of Technology, Qingdao, 266033, China
2. Cooperative Innovation Center of Engineering Construction and Safety in Shandong Blue Economic Zone, Qingdao, 266033, China
Jing Bi: School of Civil Engineering, Guizhou University, Guiyang, 550000, China
Binhang Yuan :Computer Science Department, Rice University, 6100 Main Street, Houston, Texas, USA
Yunteng Wang: Chongqing University, Chongqing, 400045, China

Abstract
The objective of this article is investigation of dynamic response of thick multilayer functionally graded (FG) beam under generalized dynamic forces. The plane stress problem is exploited to describe the constitutive equation of thick FG beam to get realistic and accurate response. Applied dynamic forces are assumed to be sinusoidal harmonic, sinusoidal pulse or triangle in time domain and point load. Equations of motion of deep FG beam are derived based on the Hamilton principle from kinematic relations and constitutive equations of plane stress problem. The numerical finite element procedure is adopted to discretize the space domain of structure and transform partial differential equations of motion to ordinary differential equations in time domain. Numerical time integration method is used to solve the system of equations in time domain and find the time responses. Numerical parametric studies are performed to illustrate effects of force type, graduation parameter, geometrical and stacking sequence of layers on the time response of deep multilayer FG beams.

Key Words
forced vibration; transient response; 2D deep beam; multilayered functionally graded; finite element; implicit time integration

Address
Mohamed A. Eltaher: Mechanical Engineering Department, Faculty of Engineering, King Abdulaziz University, P.O. Box 80204, Jeddah, Saudi Arabia
Mohamed A. Eltaher: Department of Mechanical Design & Production, Faculty of Engineering, Zagazig University,P.O. Box 44519, Zagazig, Egypt
Şeref D. Akbaş: Deparment of Civil Engineering, Bursa Technical University, Bursa, Turkey

Abstract
The life of conventional steel plastic injection molds is long but manufacturing cost and time are prohibitive for using these molds for producing prototypes of products in limited numbers. Commonly used 3D printers and rapid prototyping methods are capable of directly converting the digital models of three-dimensional solid objects into solid physical parts. Depending on the 3D printer, the final product can be made from different material, such as polymer or metal. Rapid prototyping of parts with the polymeric material is typically cheaper, faster and convenient. However, the life of a polymer mold can be less than a hundred parts. Failure of a polymeric mold during the injection molding process can result in serious safety issues considering very large forces and temperatures are involved. In this study, the feasibility of the inspection of 3D printed molds with the surface response to excitation (SuRE) method was investigated. The SuRE method was originally developed for structural health monitoring and load monitoring in thin-walled plate-like structures. In this study, first, the SuRE method was used to evaluate if the variation of the strain could be monitored when loads were applied to the center of the 3D printed molds. After the successful results were obtained, the SuRE method was used to monitor the artifact (artificial damage) created at the 3D printed mold. The results showed that the SuRE method is a cost effective and robust approach for monitoring the condition of the 3D printed molds.

Key Words
3D printed mold; structural health monitoring; damage detection; composites; inspection, SuRE

Address
Shervin Tashakori, Amin Baghalian, Ibrahim N. Tansel; Department of Mechanical & Materials Engineering, Florida International University, Miami, FL, USA
Saman Farhangdoust and Armin Mehrabi: Department of Civil and Environmental Engineering, Florida International University, Miami, FL, USA
Dwayne McDaniel: Applied Research Center, Florida International University, Miami, FL, USA

Abstract
Modern long-span floor system typically possesses low damping and low natural frequency, presenting a potential vibration sensitivity problem induced by human activities. Field test and numerical analysis methods are available to study this kind of problems, but would be inconvenient for design engineers. This paper proposes a simplified method to determine the acceleration amplitudes of long-span floor system subjected to walking or running load, which can be carried out manually. To theoretically analyze the acceleration response, the floor system is simplified as an anisotropic rectangular plate and the mode decomposition method is used. To facilitate the calculation of acceleration amplitude aP, a coefficient ɑwmn or ɑRmn is introduced, with the former depending on the geometry and support condition of floor system and the latter on the contact duration tR and natural frequency. The proposed simplified method is easy for practical use and gives safe structural designs.

Key Words
human activities, vibration serviceability, long-span floor, mode decomposition method, simplified analytical method

Address
Liang Cao: 1. School of Civil Engineering, Chongqing University, Chongqing, China; 2. Key Laboratory of New Technology for Construction of Cities in Mountain Area (Chongqing University),
Ministry of Education, Chongqing 400045, China
Y. Frank Chen: 1. School of Civil Engineering, Chongqing University, Chongqing, China; 2. Department of Civil Engineering, The Pennsylvania State University, Middletown, PA, USA

Abstract
An infill wall made of high-performance fiber-reinforced cementitious composites (HPFRCC) was utilized in this study to strengthen the reinforced concrete (RC) frame structures that had not been designed for seismic loads. The seismic performance of the RC frame structures strengthened by the HPFRCC infill walls was investigated through the experimental tests, and the test results showed that they have improved strength and deformation capabilities compared to that strengthened by the RC infill wall. A simple numerical modeling method, called the modified longitudinal and diagonal line element model (LDLEM), was introduced to consider the seismic strengthening effect of the infill walls, in which a section aggregator approach was also utilized to reflect the effect of shear in the column members of the RC frames. The proposed model showed accurate estimations on the strength, stiffness, and failure modes of the test specimens strengthened by the infill walls with and without fibers.

Key Words
seismic performance, infill wall, shear wall, HPFRCC, LDLEM

Address
Hyun-Do Yun: Department of Architectural Engineering, Chungnam National University, 99 Daehak-ro, Yuseong-gu, Daejeon 34134, Republic of Korea
Jin-Ha Hwang, Seung-Ho Choi and Kang Su Kim: Department of Architectural Engineering, University of Seoul, 163 Seoulsiripdae-ro, Dongdaemun-gu, Seoul 02504, Republic of Korea
Mee-Yeon Kim: Architectural 2 Part, Design Development Team, MIDAS IT, 17 Pangyo-ro 228 beon-gil, Bundang-gu,
Seongnam-si, Gyeonggi-do 13487, Republic of Korea
Wan-Shin Park: Department of Construction Engineering Education, Chungnam National University, 99 Daehak-ro, Yuseong-gu, Daejeon 34134, Republic of Korea

Abstract
Unlike the existing truss models for shear and torsion analysis, in this study, the torsional capacities of reinforced concrete (RC) members were estimated by introducing multi-potential capacity criteria that considered the aggregate interlock, concrete crushing, and spalling of concrete cover. The smeared truss model based on the fixed-angle theory was utilized to obtain the torsional behavior of reinforced concrete member, and the multi-potential capacity criteria were then applied to draw the capacity of the member. In addition, to avoid any iterative calculation in the existing torsional behavior model, a simple strength model was suggested that considers key variables, such as the effective thickness of torsional member, principal stress angle, and strain effect that reduces the resistance of concrete due to large longitudinal tensile strain. The proposed multi-potential capacity concept and the simple strength model were verified by comparing with test results collected from the literature. The study found that the multi-potential capacity could estimate in a rational manner not only the torsional strength but also the failure mode of RC members subjected to torsional moment, by reflecting the reinforcing index in both transverse and longitudinal directions, as well as the sectional and material properties of RC members.

Key Words
multi-potential capacity; failure criteria; reinforced concrete; torsion; strength model

Address
Hyunjin Ju, Alfred Strauss and Wei Wu: Department of Civil Engineering and Natural Hazards, University of Natural Resources and Life Sciences
Feistmantelstraße 4, 1180 Vienna, Austria
Sun-Jin Han, Kang Su Kim: Department of Architectural Engineering, University of Seoul,
163 Seoulsiripdae-ro, Dongdaemun-gu, Seoul 02504, Republic of Korea


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