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CONTENTS
Volume 82, Number 3, May10 2022
 


Abstract
The active learning surrogate model based on adaptive sampling strategy is increasingly popular in reliability analysis. However, most of the existing sampling strategies adopt the trial and error method to determine the size of the Monte Carlo (MC) candidate sample pool which satisfies the requirement of variation coefficient of failure probability. It will lead to a reduction in the calculation efficiency of reliability analysis. To avoid this defect, a new method for determining the optimal size of the MC candidate sample pool is proposed, and a new structural reliability analysis method combining polynomial chaosbased Kriging model (PC-Kriging) with adaptive sampling region is also proposed (PCK-ASR). Firstly, based on the lower limit of the confidence interval, a new method for estimating the optimal size of the MC candidate sample pool is proposed. Secondly, based on the upper limit of the confidence interval, an adaptive sampling region strategy similar to the radial centralized sampling method is developed. Then, the k-means++ clustering technique and the learning function LIF are used to complete the adaptive design of experiments (DoE). Finally, the effectiveness and accuracy of the PCK-ASR method are verified by three numerical examples and one practical engineering example.

Key Words
adaptive sampling region; optimal number of Monte Carlo samples; PC-Kriging; real failure probability interval estimation; reliability analysis

Address
Zhenliang Yu: School of Mechanical and Power Engineering, Yingkou Institute of Technology, 46 Powen Road, West City District, Yingkou 115014, Liaoning, PR China; School of Mechanical Engineering and Automation, Northeastern University, Wenhua Road, Heping District, Shenyang 110819, Liaoning, PR China
Zhili Sun, Fanyi Guo, Runan Cao and Jian Wang: School of Mechanical Engineering and Automation, Northeastern University, Wenhua Road, Heping District, Shenyang 110819, Liaoning, PR China

Abstract
An inerter is a passive mechanical element whose inertance can be thousands of times its own physical mass. This paper discusses the application of an inerter-based passive control system, termed rotational inertial double-tuned mass damper (RIDTMD), to mitigate human-induced floor vibrations. First, the acceleration frequency response function of the floor with an RIDTMD is first derived. It is then employed to determine the optimal design parameters of the RIDTMD using the extended fixed-points technique. Based on a theoretical analysis, design-oriented empirical functions are proposed for the RIDTMD optimal parameters, whose performance for floor vibration control is evaluated by numerical examples, in which three typical human-induced load types are considered: walking, jumping, and bouncing. The results indicate that the applicability and effectiveness of the RIDTMD for human-induced floor vibration control are robust for various load types, load frequencies, and floor natural frequencies. For the same mass ratio, the RIDTMD is better than the TMD in reducing the floor vibration amplitude and improving the effective frequency suppression bandwidth, and for the same vibration suppression effect, the mass of the RIDTMD is much lighter than that of the TMD.

Key Words
extended fixed-points technique; floor vibrations; human-induced loads; inerter; vibration control

Address
Pengcheng Wang: Department of Structural Engineering, Tongji University, 1239 Siping Road, Shanghai, PR China
Jun Chen: Department of Structural Engineering, Tongji University, 1239 Siping Road, Shanghai, PR China; State Key Laboratory of Disaster Reduction in Civil Engineering, Tongji University, 1239 Siping Road, Shanghai, PR China
Ziping Han: National Maglev Transportation Engineering R&D Center, Tongji University, 4800 Cao'an Road, Shanghai, PR China

Abstract
This study investigates the effects of nano silica (NS) and micro steel fiber on the properties of ultra-highperformance concrete (UHPC). The experimental consists of three groups, each one with five percentages of NS content (0%, 2%, 4%, 6% and 8%) in addition to the 20% silica fume and 20% quartz powder proportioned according to the weight of cement added to the mixtures. In addition, three percentages of micro steel fibers (0%, 1% and 2%) were considered. Different mixtures with varying percentages of NS and micro steel fibers were prepared to set the water-to-binder ratio, such as 0.16% and 1.8% superplasticizer proportioned according the weight of the binder materials. The fresh properties, mechanical properties and elevated temperatures of the mixtures were calculated. Then, the results from the microstructure analyses were compared with that of the reference mixtureand it was found that 6% replacement of cement with NS was optimum replacement level. When the NS content was increased from 0% to 6%, the air content and permeability of the mixture decreased by 35% and 39%, the compressive and tensile strength improved by 21% and 18% and the flexural strength and modulus of elasticity increased by 20% and 11.5%, respectively. However, the effect of micro steel fibres on the compressive strength was inconclusive. The overall results indicate that micro steel fibres have the potential to improve the tensile strength, flexure strength and modulus of elasticity of the UHPC. The use of 6% NS together with 1% micro-steel fiber increased the concrete strength and reduce the cost of concrete mix.

Key Words
air content; elevated temperature; mechanical property; micro steel fibres; microstructure; nanosilica; permeability; ultra-high-performance concrete

Address
Ibrahim Y. Hakeem: Department of Civil Engineering, Najran University, Najran, Saudi Arabia
Mohamed Amin: Civil and Architectural Constructions Department, Faculty of Technology and Education, Suez University, Egypt
Bassam Abdelsalam Abdelsalam: Civil and Architectural Constructions Department, Faculty of Technology and Education, Suez University, Egypt
Bassam A. Tayeh: Civil Engineering Department, Faculty of Engineering, Islamic University of Gaza, P.O. Box 108, Gaza Strip, Palestine, Pakistan
Fadi Althoey: Department of Civil Engineering, Najran University, Najran, Saudi Arabia
Ibrahim Saad Agwa: Civil and Architectural Constructions Department, Faculty of Technology and Education, Suez University, Egypt

Abstract
Steel laminated elastomeric bearings are commonly used in bridge structures to control displacements and rotations and transfer forces from the superstructure to the substructure. Proper knowledge of design, fabrication and erection procedures is important to ensure stability and adequate structural performance during the lifetime of the bridge. Difference in elevations sometimes leads to large size gaps between the bearing and the girder which makes the grout thickness that is commonly used for leveling deviate beyond standards. This paper investigates the structural response of High Strength Fiber Reinforced Cementitious (HSFRC) thin plinths that are used to close gaps between bearing pads and precast girders. An experimental program was developed for this purpose where HSFRC plinths of different size were cast and tested under vertical loads that simulate bridge loading in service. The structural performance of the plinths was closely monitored during testing, mainly crack propagation, vertical reaction and displacement. Analytically, the HSFRC plinth was analyzed using the beam on elastic foundation theory as the supporting elastomeric bearing pads are highly compressible. Closed form solutions were derived for induced displacement and forces and comparisons were made between analytical and experimental results. Finally, recommendations were made to facilitate the practical use of HSFRC plinths in bridge construction based on its enhanced load carrying capacity in shear and flexure.

Key Words
beam theory; closed-form solution; concrete plinth; crack; displacement; elastic foundation; steel fiber

Address
Antoine N Gergess and Julie Challita: Department of Civil Engineering, University of Balamand, Deir Al Balamand, Lebanon

Abstract
Previous major earthquakes indicated that the earthquake induced ground motions are typical non-stationary processes, which are non-stationary in both amplification and frequency. For the convenience of aseismic design and analysis, it usually assumes that the ground motions at structural supports are stationary processes. The development of time-frequency analysis technique makes it possible to evaluate the non-stationary responses of engineering structures subjected to nonstationary inputs, which is more general and realistic than the analysis method commonly used in engineering. In this paper, the wavelet-based stochastic vibration analysis methodology is adopted to calculate the non-stationary responses of multi-support structures. For comparison, the stationary response based on the standard random vibration method is also investigated. A frame structure and a two-span bridge are analyzed. The effects of non-stationary spatial ground motion and local site conditions are considered, and the influence of structural property on the structural responses are also considered. The analytical results demonstrate that the non-stationary spatial ground motions have significant influence on the response of multi-support structures.

Key Words
non-stationary process; seismic analysis; spatially varying ground motions; stationary process

Address
Zhaoheng Xu, Tian-Li Huang: School of Civil Engineering, Central South University, Changsha, Hunan 410075, China
Kaiming Bi: Centre for Infrastructure Monitoring and Protection, School of Civil and Mechanical Engineering, Curtin University, Kent St., Bentley, WA 6102, Australia

Abstract
An understanding of the mechanism of concrete girders repaired with CFRP plates and its influence on the dynamic parameters is presented in this paper. Dynamic parameters are governed by the relationship with the physical properties of concrete girders and CFRP plates as well as the adhesive layer between them. A brief explanation of the mechanism of the composite action of concrete girders repaired with CFRP is also given in this paper. Experimental work was carried out to validate the theory of the composite action. The results show a decrease in the modal parameters of CFRP repaired girders that were turned over during the repair procedure, which contrasts with the proven static-based results that CFRP plates increase the stiffness of repaired girders. The composite action theory has explained the results based on the tension and compression forces' growth at the adhesive layer between the CFRP plates and girder surface during the repair procedure. Other girders were prepared and repaired without turning over in order to avoid tension and compression forces at the adhesive layer. The experimental results show an increase in the dynamic parameters of CFRP repaired girders that were not turned over during the repair procedure, which aligns with the static-based results. The study concludes that the dynamic parameters are excellent indicators for the assessment of CFRP repaired concrete girders. The study also suggests that researchers should not turn over damaged concrete girders to repair them with CFRP plates if they intend to study the dynamic parameters, in order to avoid the proposed composite action effect on modal parameters.

Key Words
bond mechanism; dynamic and modal parameters; fibre reinforced polymer; interface adhesive layer

Address
Moatasem M. Fayyadh: Asset Lifecycle, Sydney Water, 2150 NSW, Australia
Hashim A. Razak: Department of Civil Engineering, University of Malaya, 50603 Kuala Lumpur, Malaysia

Abstract
The effect of hydrodynamic damping on intake tower is twofold: one is fluid damping and another is structural damping. Fluid damping can be derived analytically from the governing equation of the fluid-structure-interaction (FSI) problem which yields a very complicated solution. To avoid the complexity of the FSI problem water-tower system can be simplified by considering water as added mass. However, in such a system a reconsideration of structural damping is required. This study investigates the effects of this damping on the dynamic response of the intake tower, where, apart from the "no water (NW)" condition, six other cases have been adopted depending on water height. Two different cross-sections of the tower are considered and also two different damping properties have been used for each case as well. Dynamic analysis has been carried out using horizontal ground motion as input. Finally, the result shows how hydrodynamic damping affects the dynamic behavior of an intake tower with the change of water height and cross-section. This research will help a designer to consider more conservative damping properties of intake tower which might vary depending on the shape of the tower and height of water.

Key Words
dynamic response; fluid-structure interaction; hydrodynamic damping; intake-tower; reduced damping ratio

Address
Md Ikram Uddin: Department of Civil and Environmental Engineering, Kongju National University, Cheonan-si, Republic of Korea
Tahmina Tasnim Nahar: Department of Civil Engineering, Pabna University of Science and Technology, Pabna-6600, Bangladesh
Dookie Kim and Kee-Dong Kim: Department of Civil and Environmental Engineering, Kongju National University, Cheonan-si, Republic of Korea

Abstract
In this study, an equivalent boundary conditions (BCs) determination method is developed numerically for a panel reinforced concrete (RC) slab to realistically analyze the deformation and fatigue behaviors of a bridge RC slab. For this purpose, a finite element analysis of a bridge RC slab is carried out beforehand to calculate the stiffness of the bridge RC slab, and then the equivalent BCs for the panel RC slab are determined to achieve the same stiffness at the BCs to the obtained stiffness of the bridge RC slab at the corresponding locations of the bridge RC slab. Moreover, for the simulation of fatigue behaviors, fatigue analysis of the panel RC slab is carried out employing a finite element method based on a numerical model that considers the bridging stress degradation. Both the determined equivalent BCs and the BCs that have been typically applied in past studies are employed. The analysis results confirm that, in contrast to the panel RC slab with typically used BCs, the panel RC slab with equivalent BCs simulate the same bending moment distribution and deformation behaviors of the bridge RC slab. Furthermore, the equivalent BCs reproduce the extensive grid crack pattern in the panel RC slab, which is alike the pattern normally witnessed in a bridge RC slab. Conclusively, the panel RC slab with equivalent BCs behaves identical to the bridge RC slab, and, as a result, it shows more realistic fatigue behaviors observed in the bridge RC slab.

Key Words
boundary conditions; bridge RC slab; bridging stress degradation; fatigue; grid crack pattern

Address
Arslan Q. Khan: Department of Civil Engineering, The University of Lahore, Lahore, Pakistan; Graduate School of Engineering, Hokkaido University, Sapporo, 060-8628, Japan
Pengru Deng, Takashi Matsumoto: Faculty of Engineering, Hokkaido University, Sapporo, 060-8628, Japan

Abstract
Sky-bridges between adjacent buildings can enhance lateral stiffness and limit the impact of lateral forces. This study analysed the structural capabilities and dynamic performances of sky-bridge-coupled buildings under various sets of ground motions. Finite Element (FE) analyses were carried out with the link being iteratively repositioned along the full height of the structures. Incremental dynamic analysis (IDA) and probabilistic damage distribution were also applied. The results indicated that the establishment of sky-bridges caused a slight change in the natural frequency and mode shapes. The sky-bridge system was shown to be efficient in controlling displacement and Inter-Storey Drift Ratio (%ISDR) and reducing the probability of damage in the higher floors. The most efficient location of the sky-bridge, for improving its rigidity, was found to be at 88% of the building height. Finally, the effects of two types of materials (steel and concrete) and end conditions (hinged and fixed) were studied. The outcomes showed that coupled buildings with a sky-bridge made of steel with hinged connection could withstand ground motions longer than those made of concrete with fixed connection.

Key Words
beta distribution function; coupled high-rise buildings; fragility curves; optimization; sky-bridge; vulnerability functions

Address
Ahmad Housam Arada: School of Civil Engineering, Universiti Sains Malaysia, Engineering Campus, 14300 Nibong Tebal, Penang, Malaysia
Baki Ozturk: Department of Civil Engineering, Hacettepe University, Faculty of Engineering, Beytepe Campus, 06800, Ankara, Turkey
Moustafa Moufid Kassem: School of Civil Engineering, Universiti Sains Malaysia, Engineering Campus, 14300 Nibong Tebal, Penang, Malaysia
Fadzli Mohamed Nazri: School of Civil Engineering, Universiti Sains Malaysia, Engineering Campus, 14300 Nibong Tebal, Penang, Malaysia
Chee Ghuan Tan: Department of Civil Engineering, Faculty of Engineering, Universiti Malaya, 50603 Kuala Lumpur, Malaysia

Abstract
The aim of this study is to examine the frictionless double receding contact problem for two functionally graded (FG) layers pressed with a uniformly distributed load and resting on a homogeneous half plane (HP) using analytical and numerical methods. The FG layers are made of a non-homogeneous material with an isotropic stress-strain law with exponentially varying properties. It is assumed that the contact at the FG layers and FG layer-HP interface is frictionless. The body force of the FG layers and homogeneous HP are ignored in the study. Firstly, an analytical solution for the contact problem has been realized using the theory of elasticity and the Fourier integral transform techniques. Then, the problem modeled and two-dimensional analysis was carried out by using the ANSYS package program based on FEM. Numerical results for contact lengths and contact pressures between FG layers and FG layer-HP were provided for various dimensionless quantities including material inhomogeneity, distributed load width, the shear module ratio, and the heights of the FG layers for both methods. The results obtained using FEM were compared with the results found using the analytical formulation. It was found that the results obtained from analytical formulation were in perfect agreement with the FEM study.

Key Words
contact mechanics; finite element method; functionally graded layer; theory of elasticity

Address
Murat Yaylaci: Department of Civil Engineering, Recep Tayyip Erdogan University, 53100, Rize, Turkey
Bahar Şengül Şabano: Department of Civil Engineering, Karadeniz Technical University, 61080, Trabzon, Turkey
Mehmet Emin Özdemir: Department of Civil Engineering, Cankiri Karatekin University, 18100, Çankiri, Turkey
Ahmet Birinci: Department of Civil Engineering, Karadeniz Technical University, 61080, Trabzon, Turkey

Abstract
In this paper, we propose a new concept for error estimation in finite element solutions, which we call mode-based error estimation. The proposed error estimation predicts a posteriori error calculated by the difference between the direct finite element (FE) approximation and the recovered FE approximation. The mode-based FE formulation for the recently developed self-updated finite element is employed to calculate the recovered solution. The formulation is constructed by searching for optimal bending directions for each element, and deep learning is adopted to help find the optimal bending directions. Through various numerical examples using four-node quadrilateral finite elements, we demonstrate the improved predictive capability of the proposed error estimator compared with other competitive methods.

Key Words
deep learning; error estimation; finite element analysis; four-node quadrilateral finite element; mode-based formulation; self-updated finite element

Address
Jaeho Jung: Korea Atomic Energy Research Institute, 989 Daedeok-daero, Yuseong-gu, Daejeon 34057, Republic of Korea
Seunghwan Park, Chaemin Lee: Department of Mechanical Engineering, Korea Advanced Institute of Science and Technology, 291 Daehak-ro, Yuseong-gu, Daejeon 34141, Republic of Korea


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