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Volume 33, Number 4, November25 2019

A shear-deformable finite element model (FEM) with five nodes and thirteen degrees of freedom (DOFs) for free vibrations of laminated composite beams with arbitrary lay-up is presented. This model can be capable of considering the elastic couplings among the extensional, bending and torsional deformations, and the Poisson's effect. Lagrange's principle is employed in derivation of the equations of motion, and thus the element matrices are obtained. Comparisons of the present element's results with those in experiment, available literature and the 3D finite element analysis software (ANSYS®) are made to show its accuracy. Some further results are given as referencing for the future studies in vibrations of laminated composite beamst.

Key Words
laminated composite beam; free vibration; finite element method; anisotropy

(1) Volkan Kahya, Sebahat Karaca:
Karadeniz Technical University, Faculty of Engineering, Department of Civil Engineering, 61080 Trabzon, Turkey;
(2) Thuc P. Vo:
School of Engineering and Mathematical Sciences, La Trobe University, Bundoora, VIC 3086, Australia.

In order to obtain high bearing capacity and good ductility simultaneously, a structural column with hybrid normal and high strength steel (HNHSS) welded box section has been developed. Residual stress is an important factor that can influence the behaviour of a structural member in steel structures. Accordingly, the magnitudes and distributions of residual stresses in HNHSS welded box sections were investigated experimentally using the sectioning method. In this study, the following four box sections were tested: one normal strength steel (NSS) section, one high strength steel (HSS) section, and two HNHSS sections. Based on the experimental data from previous studies and the test results of this study, the effects of the width-to-thickness ratio of plate, yield strength of plate, and the plate thickness of the residual stresses of welded box sections were investigated in detail. A unified residual stress model for NSS, HSS and HNHSS welded box sections was proposed, and the corresponding simplified prediction equations for the maximum tensile residual stress ratio (σrt/fy) and average compressive residual stress ratio (σrc/fy) in the model were quantitatively established. The predicted magnitudes and distributions of residual stresses for four tested sections in this study by using the proposed residual stress model were compared with the experimental results, and the feasibility of this proposed model was shown to be in good agreement.

Key Words
residual stress; hybrid box section; sectioning method; high strength steel

(1) Lan Kang, Yuqi Wang:
School of Civil Engineering and Transportation, South China University of Technology, Guangzhou, Guangdong Province, 510641, People\'s Republic of China;
(2) Lan Kang, Yuqi Wang:
State Key Laboratory of Subtropical Building Science, South China University of Technology, Guangzhou, Guangdong Province, 510641, People\'s Republic of China;
(3) Xinpei Liu, Brian Uy:
School of Civil Engineering, Faculty of Engineering & Information Technologies, The University of Sydney, NSW2006, Australia.

In the present work, the buckling analysis of micro sandwich plate with an isotropic/orthotropic cores and piezoelectric/polymeric nanocomposite face sheets is studied. In this research, two cases for core of micro sandwich plate is considered that involve five isotropic Devineycell materials (H30, H45, H60, H100 and H200) and an orthotropic material also two cases for facesheets of micro sandwich plate is illustrated that include piezoelectric layers reinforced by carbon and boron-nitride nanotubes and polymeric matrix reinforced by carbon nanotubes under temperature-dependent and hydro material properties on the elastic foundations. The first order shear deformation theory (FSDT) is adopted to model micro sandwich plate and to apply size dependent effects from modified strain gradient theory. The governing equations are derived using the minimum total potential energy principle and then solved by analytical method. Also, the effects of different parameters such as size dependent, side ratio, volume fraction, various material properties for cores and facesheets and temperature and humidity changes on the dimensionless critical buckling load are investigated. It is shown from the results that the dimensionless critical buckling load for boron nitride nanotube is lower than that of for carbon nanotube. It is illustrated that the dimensionless critical buckling load for Devineycell H200 is highest and lowest for H30. Also, the obtained results for micro sandwich plate with piezoelectric facesheets reinforced by carbon nanotubes (case b) is higher than other states (cases a and c).The results of this research can be used in aircraft, automotive, shipbuilding industries and biomedicine.

Key Words
biaxial buckling analysis; micro sandwich plate; isotropic and orthotropic cores; piezoelectric layers reinforced by carbon and boron nitride nanotubes facesheets; polymeric matrix reinforced by carbon nanotubes; temperature-dependent and hydro material properties; micro-mechanical and the extended rule of mixture approaches

Department of Solid Mechanics, Faculty of Mechanical Engineering, University of Kashan, P.O. Box: 87317-53153, Kashan, Iran.

The seismic performance of steel frames equipped with a particular type of bending dissipative braces (BDBs) having U elements, which has recently been introduced and tested by the authors, is investigated. For this purpose, two structural systems, i.e., simple and dual steel building frames, both with diagonal BDBs and different number of stories, are considered. After providing a design method of this new BDB, the detailed structural models are developed in the OpenSees platform to perform nonlinear dynamic analyses. Seismic performance factors like ductility, overstrength, response modification and deflection amplification factors are calculated using incremental dynamic analysis (IDA). In addition, to assess the damage probability of the structural models, their seismic fragilities are developed. The results show high energy dissipation capacity of both structural systems while the number of U elements needed for the bracing system of each story in the moment frames are less than those in the corresponding non-moment (simple) frames. The average response modification and deflection amplification factors for both structural schemes are obtained about 8.6 and 5.4, respectively, which are slightly larger than the corresponding recommended values of ASCE for the typical buckling-restrained braces (BRBs).

Key Words
bending dissipative brace; U-shaped element; seismic factors; nonlinear dynamic analysis; seismic fragility

(1) Farshad Taiyari, Saman Bagheri:
Faculty of Civil Engineering, University of Tabriz, 51666-16471 Tabriz, Iran;
(2) Federico M. Mazzolani:
Department of Structures for Engineering and Architecture, University of Naples "Federico II", P.le Tecchio 80, 80125 Naples, Italy.

Korea and Japan have done a lot of research on composite girders with corrugated steel webs and built many bridges with corrugated steel webs due to the significant advantages of this type of bridges. Considering the demanding on the calculation method of such types of bridges and lack of relevant reinforcement design method, this paper proposes the spatial grid analysis theory and tensile stress region method. First, the accuracy and applicability of spatial grid model in analyzing composite girders with corrugated steel webs was validated by the comparison with models using shell and solid elements. Then, in a real engineering practice, the reinforcement designs from tensile stress region method based on spatial grid model, design empirical method and specification method are compared. The results show that the tensile stress region reinforcement design method can realize the inplane and out-of-plane reinforcement design in the top and bottom slabs in bridges with corrugated steel webs. The economy and precision of reinforcement design using the tensile stress region method is emphasized. Therefore, the tensile stress region reinforcement design method based on the spatial grid model can provide a new direction for the refined design of composite box girder with corrugated steel webs.

Key Words
corrugated steel webs; composite girder bridge; grid reinforcement; tensile stress region; spatial grid analysis theory

(1) Hu Zhao:
China Railway Siyuan Survey and Design Group CO., LTD, Wuhan, Hubei province, 430063, P.R. China;
(2) Hongye Gou:
Department of Bridge Engineering, School of Civil Engineering, Southwest Jiaotong University, Chengdu, Sichuan province,611756, P.R. China;
(3) Ying-Sheng Ni:
Research Institute of Highway Ministry of Transport, M.O.T, Beijing, 100088, P.R. China;
(4) Dong Xu:
Department of Bridge Engineering, Tongji University, Shanghai, 200092, P.R. China.

This proposed project presents the bi-axial and uni-axial stability behavior of laminated composite plates based on an original three variable "refined" plate theory. The important "novelty" of this theory is that besides the inclusion of a cubic distribution of transverse shear deformations across the thickness of the structure, it treats only three variables such as conventional plate theory (CPT) instead five as in the well-known theory of "first shear deformation" (FSDT) and theory of "higher order shear deformation" (HSDT). A "shear correction coefficient" is therefore not employed in the current formulation. The computed results are compared with those of the CPT, FSDT and exact 3D elasticity theory. Good agreement is demonstrated and proved for the present results with those of "HSDT" and elasticity theory.

Key Words
stability analysis; isotropic; laminated composite plate

(1) S.R. Mahmoud:
GRC Department, Jeddah Community College, King Abdulaziz University, Jeddah 21589, Saudi Arabia;
(2) Abdelouahed Tounsi:
Civil and Environmental Engineering Department, King Fahd University of Petroleum & Minerals, Dhahran, Saudi Arabia;
(3) Abdelouahed Tounsi:
Material and Hydrology Laboratory, University of Sidi Bel Abbes, Faculty of Technology, Civil Engineering Department, Algeria.

Corrugated steel plate shear wall (CSPSW) as an innovative lateral load resisting system provides various advantages in comparison with the flat steel plate shear wall, including remarkable in-plane and out-of-plane stiffnesses and stability, greater elastic shear buckling stress, increasing the amount of cumulative dissipated energy and maintaining efficiency even in large story drifts. Employment of low yield point (LYP) steel web plate in steel shear walls can dramatically improve their structural performance and prevent early stage instability of the panels. This paper presents a comprehensive structural performance assessment of corrugated low yield point steel plate shear walls having circular openings located in different positions. Accordingly, following experimental verification of CSPSW finite element models, several trapezoidally horizontal CSPSW (H-CSPSW) models having LYP steel web plates as well as circular openings (for ducts) perforated in various locations have been developed to explore their hysteresis behavior, cumulative dissipated energy, lateral stiffness, and ultimate strength under cyclic loading. Obtained results reveal that the rehabilitation of damaged steel shear walls using corrugated LYP steel web plate can enhance their structural performance. Furthermore, choosing a suitable location for the circular opening regarding the design purpose paves the way for the achievement of the shear wall's optimal performance.

Key Words
steel plate shear wall; corrugated web plate; low yield point steel; circular opening; cyclic loading

(1) Mahdi Shariati, Nguyen-Thoi Trung:
Division of Computational Mathematics and Engineering, Institute for Computational Science, Ton Duc Thang University, Ho Chi Minh City, Vietnam;
(2) Mahdi Shariati, Nguyen-Thoi Trung:
Faculty of Civil Engineering, Ton Duc Thang University, Ho Chi Minh City, Vietnam;
(3) Shervin Safaei Faegh, Peyman Mehrabi:
Department of Civil Engineering, K.N. Toosi University of Technology, Tehran, Iran;
(4) Seyedmasoud Bahavarnia:
Department of Civil Engineering, Qeshm International Branch, Islamic Azad University, Qeshm, Iran;
(5) Yousef Zandi:
Department of Civil Engineering, Tabriz Branch, Islamic Azad University, Tabriz, Iran;
(6) Davood Rezaee Masoom:
Department of Civil Engineering, Islamic Azad University, Central Tehran Branch, Tehran, Iran;
(7) Ali Toghroli:
Institute of Research and Development, Duy Tan University, Da Nang 550000, Vietnam;
(8) Musab N A Salih:
School of Civil Engineering, Faculty of Engineering, Universiti Teknologi Malaysia, 81310 Johor Bahru, Malaysia.

In the areas highly exposed to earthquakes, concrete-filled steel tube columns (CFSTCs) are known to provide superior structural aspects such as (i) high strength for good seismic performance (ii) high ductility (iii) enhanced energy absorption (iv) confining pressure to concrete, (v) high section modulus, etc. Numerous studies were reported on behavior of CFSTCs under axial compression loadings. This paper presents an analytical model to predict ultimate load capacity of CFSTCs with circular sections under axial load by using multivariate adaptive regression splines (MARS). MARS is a nonlinear and non-parametric regression methodology. After careful study of literature, 150 comprehensive experimental data presented in the previous studies were examined to prepare a data set and the dependent variables such as geometrical and mechanical properties of circular CFST system have been identified. Basically, MARS model establishes a relation between predictors and dependent variables. Separate regression lines can be formed through the concept of divide and conquers strategy. About 70% of the consolidated data has been used for development of model and the rest of the data has been used for validation of the model. Proper care has been taken such that the input data consists of all ranges of variables. From the studies, it is noted that the predicted ultimate axial load capacity of CFSTCs is found to match with the corresponding experimental observations of literature.

Key Words
concrete-filled steel tube column (CFSTC); concrete; steel; modeling; ultimate axial load capacity; multivariate adaptive regression splines (MARS); composite structures; statistical modeling technique; nonlinear regression model

Department of Transportation Engineering, Faculty of Engineering, Yalova University, Yalova, 77200, Turkey.

In cold-formed steel (CFS) structures, such as trusses, transmission towers and portal frames, the use of back-to-back built-up CFS unequal angle sections are becoming increasingly popular. In such an arrangement, intermediate welds or screw fasteners are required at discrete points along the length, preventing the angle sections from buckling independently. Limited research is available in the literature on axial strength of back-to-back built-up CFS unequal angle sections. The issue is addressed herein. This paper presents an experimental investigation on both the welded and screw fastened back-to-back built-up CFS unequal angle sections under axial compression. The load-axial shortening and the load verses lateral displacement behaviour along with the deformed shapes at failure are reported. A nonlinear finite element (FE) model was then developed, which includes material nonlinearity, geometric imperfections and modelling of intermediate fasteners. The FE model was validated against the experimental test results, which showed good agreement, both in terms of failure loads and deformed shapes at failure. The validated FE model was then used for the purpose of a parametric study to investigate the effect of different thicknesses, lengths and, yield stresses of steel on axial strength of back-to-back built-up CFS unequal angle sections. Five different thicknesses and seven different lengths (stub to slender columns) with two different yield stresses were investigated in the parametric study. Axial strengths obtained from the experimental tests and FE analyses were used to assess the performance of the current design guidelines as per the Direct Strength Method (DSM); obtained comparisons show that the current DSM is conservative by only 7% on average, while predicting the axial strengths of back-to-back built-up CFS unequal angle sections.

Key Words
axial strength; back-to-back built-up sections; buckling; cold-formed steel; finite element modelling; unequal angle sections

(1) G. Beulah Gnana Ananthi:
Division of Structural Engineering, College of Engineering Guindy Campus, Anna University, Chennai, India;
(2) Krishanu Roy, Boshan Chen, James B.P. Lim:
Department of Civil and Environmental Engineering, The University of Auckland, Auckland, New Zealand.

This paper aims to study the compressive behavior of circular hollow and concrete-filled steel tubular stub columns under simulated marine atmospheric corrosion. The specimens after salt spray corrosion were tested under axial compressive load. Steel grade and corrosion level were mainly considered in the study. The mechanical behavior of circular CFST specimens is compared with that of the corresponding hollow ones. Design methods for circular hollow and concrete-filled steel tubular stub columns are modified to consider the effect of marine atmospheric corrosion. The results show that linear fitting curves could be used to present the relationship between corrosion rate and the mechanical properties of steel after simulated marine atmospheric corrosion. The ultimate strength of hollow steel tubular and CFST columns decrease with the increase of corrosion rate while the ultimate displacement of those are hardly affected by corrosion rate. Increasing corrosion rate would change the failure of CFST stub column from ductile failure to brittle failure. Corrosion rate would decrease the ductility indexes of CFST columns, rather than those of hollow steel tubular columns. The confinement factor

Key Words
CFST; hollow steel tube; compressive behavior; stub column; simulated marine atmosphere; salt spray corrosion

(1) Shan Gao, Zhen Peng:
Shaanxi Key Laboratory of safety and durability of concrete structures, Xijing University, Xi\'an, China;
(2) Shan Gao, Xuanding Wang:
Postdoctoral Station of Civil Engineering, Chongqing University, Chongqing, China;
(3) Jiepeng Liu:
School of Civil Engineering, Chongqing University, Chongqing, China.

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