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CONTENTS
Volume 42, Number 4, February25 2022
 

Abstract
Cutouts in the beams or plates are often unavoidable due to inspection, maintenance, ventilation, structural aesthetics purpose, and sometimes to lighten the structures. Therefore, there will be a substantial reduction in the strength of the structure due to the introduction of the cutouts. However, these cutouts can be reinforced with the different patterns of ribs (stiffener) to enhance the strength of the structure. The present study highlights the influence of the elliptical cutout reinforced with a different pattern of ribs on the stability performance of such stiffened composite panels subjected to non-uniform edge loads by employing the Finite element (FE) technique. In the present formulation, a 9-noded heterosis element is used to model the skin, and a 3-noded isoparametric beam element is used to simulate the rib that is attached around a cutout in different patterns. The displacement compatibility condition is employed between the plate and stiffener, and arbitrary orientations are taken care by introducing respective transformation matrices. The effect of shear deformation and rotary inertia are incorporated in the formulation. A new mesh configuration is developed to house the attached ribs around an elliptical cutout with different patterns. Initially, a study is performed on the panels with different stiffener schemes for various ply orientations and for different stiffener depth to width ratios (ds/bs) to determine an optimal stiffener configuration. Further, various parametric studies are conducted on an obtained optimal stiffened panel to understand the effect of cutout size, cutout orientation, panel aspect ratio, and boundary conditions. Finally, from the analysis, it can be observed that the arrangement of the stiffener attached to a panel has a major impact on the buckling capacity of the stiffened panel. The stiffener

Key Words
9-noded heterosis element; buckling; composite laminates; elliptical cutout; finite element method; nonuniform edge loads; reinforced cuto

Address
Akshay Prakash Kalgutkar:Indian Institute of Technology Bombay

Sauvik Banerjee:Indian Institute of Technology Bombay

T. Rajanna:BMS College of Engineering,

Abstract
Cold-formed steel (CFS) sections are thin-walled, therefore, more susceptible to different types of geometric imperfections. Global type of geometric imperfections has a significant impact on the load-carrying capacity of flexural members. This paper reports an experimental study that discusses the influence of global imperfections on the flexural response of CFS built-up I-beams composed of two lipped channels, with simply supported ends, under four-point loading. Global imperfections of magnitude over eight times the maximum permissible ones were induced in the specimens, leading to their distress. Using various simple stiffening schemes, the capacity and stiffness of the distressed specimens were improvised. The performance comparisons were made based on the maximum loads resisted, flexural stiffnesses offered, and failure modes experienced by the specimens. As experimental data on such distressed specimens are currently lacking in the literature, the test results of the present study will provide the necessary data needed by future researchers to numerically extend this study further, which will help in the development of necessary design guidelines for the same. The stiffening schemes significantly improved the structural efficiency of distressed specimens in terms of strength and stiffness, by over 60%. As a result, an effective and time-saving solution to such realistic structural engineering problems is given.

Key Words
beam; built-up; cold-formed steel; experiment; global imperfection; strength

Address
M. Adil Dar:Department of Civil and Environmental Engineering, National University of Singapore, Singapore

M. Anbarasu:Department of Civil Engineering, Government College of Engineering Salem, Tamil Nadu, India

A.R. Dar:Department of Civil and Environmental Engineering, National University of Singapore, Singapore

Naqeeb Ul Islam:Department of Civil Engineering, National Institute of Technology Srinagar, J&K, India

Ahmad Fayeq Ghowsi:Department of Civil Engineering, Indian Institute of Technology Delhi, New Delhi, India

Hermes Carvalho:Department of Structural Engineering, Federal University of Minas Gerais, Brazil

Abstract
In this paper a model for the prediction of the ultimate axial compressive capacity of square and rectangular Concrete Filled Steel Tubes, based on an Artificial Neural Network modeling procedure is presented. The model is trained and tested using an experimental database, compiled for this reason from the literature that amounts to 1193 specimens, including long, thin-walled and high-strength ones. The proposed model was selected as the optimum from a plethora of alternatives, employing different activation functions in the context of Artificial Neural Network technique. The performance of the developed model was compared against existing methodologies from design codes and from proposals in the literature, employing several performance indices. It was found that the proposed model achieves remarkably improved predictions of the ultimate axial load.

Key Words
artificial neural network; CFST column; soft computing; ultimate axial load

Address
Minas E. Lemonis:Computational Mechanics Laboratory, School of Pedagogical and Technological Education, 14121 Athens, Greece

Angeliki G. Daramara:Computational Mechanics Laboratory, School of Pedagogical and Technological Education, 14121 Athens, Greece

Alexandra G. Georgiadou:Computational Mechanics Laboratory, School of Pedagogical and Technological Education, 14121 Athens, Greece

Vassilis G. Siorikis:Computational Mechanics Laboratory, School of Pedagogical and Technological Education, 14121 Athens, Greece

Konstantinos Daniel Tsavdaridis:School of Civil Engineering, Faculty of Engineering and Physical Sciences, University of Leeds, Woodhouse Lane, West Yorkshire, Leeds LS2 9JT, U.K.

Panagiotis G. Asteris:Computational Mechanics Laboratory, School of Pedagogical and Technological Education, 14121 Athens, Greece


Abstract
The shear stiffness of headed-stud shear connectors has no unified definition due to the nonlinear characteristics of its load-slip relationship. A unified framework was firstly adopted to develop a general expression of shear load-slip equation for headed-stud shear connectors varying in a large parameter range based on both force and energy balance. The pre- and postyield shear stiffness were then determined through bilinear idealization of proposed shear load-slip equation. An updated and carefully selected push-out test database of 157 stud shear connectors, conducting on studs 13~30mm in diameter and on concretes 30~180 MPa in cubic compressive strength, was used for model regression and sensitivity analysis of shear stiffness. An empirical calculation model was also established for the stud shear stiffness. Compared with the previous models through statistical analysis, the proposed model demonstrates a better performance to predict the shear load-slip response and stiffness of the stud shear connectors.

Key Words
energy balance approach; push-out test; shear load-slip relationship; shear stiffness; stud shear connector

Address
Huawen Ye:School of Civil Engineering, Southwest Jiaotong University, Chengdu 610031, China

Ruosen Huang:School of Civil Engineering, Southwest Jiaotong University, Chengdu 610031, China

Shiqing Tang:School of Civil Engineering, Southwest Jiaotong University, Chengdu 610031, China

Yu Zhou:School of Civil Engineering, Southwest Jiaotong University, Chengdu 610031, China

Jilin Liud:School of Civil Engineering, Southwest Jiaotong University, Chengdu 610031, China

Abstract
This paper proposes a numerical optimization method to design the mesoscale architecture of textile composite for simultaneously enhancing mechanical and thermal properties, which compete with each other making it difficult to design intuitively. The base cell of the periodic warp and fill yarn system is served as the design space, and optimal fibre yarn geometries are found by solving the optimization problem through the proposed method. With the help of homogenization method, analytical formulae for the effective material properties as functions of the geometry parameters of plain-woven textile composites were derived, and they are used to form the inverse homogenization method to establish the design problem. These modules are then put together to form a multiobjective optimization problem, which is formulated in such a way that the optimal design depends on the weight factors predetermined by the user based on the stiffness and thermal terms in the objective function. Numerical examples illustrate that the developed method can achieve reasonable designs in terms of fibre yarn paths and geometries.

Key Words
design optimization; effective elastic properties; effective thermal conductivity; fibre tow geometry parameters; homogenization; plain-woven textile composite

Address
Xiao-Yi Zhou:Department of Bridge Engineering, Southeast University, 2 Southeast University Road, Nanjing, Jiangsu, China

Neng-Wei Wang:Department of Bridge Engineering, Southeast University, 2 Southeast University Road, Nanjing, Jiangsu, China

Wen Xiong:Department of Bridge Engineering, Southeast University, 2 Southeast University Road, Nanjing, Jiangsu, China

Xin Ruan:Department of Bridge Engineering, Tongji University, 1239 Siping Road, Shanghai, China

Shao-Jin Zhang:Guangzhou Pearl River Huangpu Bridge Construction Co. Ltd., Guangzhou, China

Abstract
This work studies the effect of a three-variable viscoelastic foundation on wave propagation in functionally graded (FG) sandwich plates using a simple quasi-3D plate theory. The presented solution is based on a four-unknown plate theory that simplifies the calculations and considers the stretching effect. The theory employs a simple sinusoidal function for the shear deformation shape. The studied plates are composite sandwiches in which the layers are ceramic, metal, or FG ceramic-metal. The governing differential equations are obtained for the proposed quasi-3D plate theory using Hamilton's principle. The eigenvalue problem is formulated for the wave propagation and solved for the studied desperation relations. Finally, new results that examine the influences of the foundation parameters, the FGM exponent and the core-to-thickness ratio on the various dispersion relations of wave propagation are presented.

Key Words
FGM; Quasi-3D plate theory; viscoelastic foundation; wave propagation

Address
Saeed I. Tahir:Department of Civil and Environmental Engineering, King Fahd University of Petroleum & Minerals,
31261 Dhahran, Eastern Province, Saudi Arabia

Abdelouahed Tounsi:YFL (Yonsei Frontier Lab), Yonsei University, Seoul, Korea

Abdelbaki Chikh:Material and Hydrology Laboratory, University of Sidi Bel Abbes, Faculty of Technology, Civil Engineering Department, Algeria

Mohammed A. Al-Osta:Department of Civil and Environmental Engineering, King Fahd University of Petroleum & Minerals,
31261 Dhahran, Eastern Province, Saudi Arabia

Salah U. Al-Dulaijan:Department of Civil and Environmental Engineering, King Fahd University of Petroleum & Minerals,
31261 Dhahran, Eastern Province, Saudi Arabia

Mesfer M. Al-Zahrani:Department of Civil and Environmental Engineering, King Fahd University of Petroleum & Minerals,
31261 Dhahran, Eastern Province, Saudi Arabia

Abstract
This paper reports on experiments addressing the buckling and collapse behavior of an innovative built-up coldformed steel (CFS) columns. The built-up column consists of four individual CFS lipped channels, two of them placed back-toback at the web using two self-drilling screw fasteners at specified spacing along the column length, while the other two channels were connected flange-to-flange using one self-drilling screw fastener at specified spacing along the column length. In total, 12 experimental tests are reported, covering a wide range of column lengths from stub to slender columns. The initial geometric imperfections and material properties were determined for all test specimens. The effect of screw spacing, load-versus axial shortening behaviour and buckling modes for different lengths and screw spacing were investigated. Nonlinear finite element (FE) models were also developed, which included material nonlinearities and initial geometric imperfections. The FE models were validated against the experimental results, both in terms of axial capacity and failure modes of built-up CFS columns. Furthermore, using the validated FE models, a parametric study was conducted which comprises 324 models to investigate the effect of screw fastener spacing, thicknesses and wide range of lengths on axial capacity of back-to-back and flange-to-flange built-up CFS channel sections. Using both the experimental and FE results, it is shown that design in accordance with the American Iron and Steel Institute (AISI) and Australia/New Zealand (AS/NZS) standards is slightly conservative by 6% on average, while determining the axial capacity of back-to-back and flange-to-flange built-up CFS channel sections.

Key Words
axial strength; back-to-back and flange-to-flange channels; buckling; cold-formed steel; direct strength method; finite element modeling; tests

Address
Beulah Gnana Ananthi G:Division of Structural Engineering, College of Engineering Guindy Campus, Anna University, Chennai, India

Krishanu Roy:School of Engineering, The University of Waikato, Hamilton 3216, New Zealand

James B.P. Lim:Department of Civil and Environmental Engineering, The University of Auckland, Auckland, New Zealand


Abstract
Concentrically braced frames (CBFs) possess high stiffness and strength against lateral loads; however, they suffer from low energy absorption capacity against seismic loads due to the susceptibility of CBF diagonal elements to bucking under compression loading. To address this problem, in this study, an innovative damper was proposed and investigated experimentally and numerically. The proposed damper comprises main plates and includes a flange plate angled at θ and a trapezius-shaped web plate surrounded by the plate at the top and bottom sections. To investigate the damper behaviour, dampers with θ= 0°, 30°, 45°, 60°, and 90° were evaluated with different flange plate thicknesses of 10, 15, 20, 25 and 30 mm. Dampers with θ= 0° and 90° create rectangular-shaped and I-shaped shear links, respectively. The results indicate that the damper with θ= 30° exhibits better performance in terms of ultimate strength, stiffness, overstrength, and distribution stress over the damper as compared to dampers with other angles. The hysteresis curves of the dampers confirm that the proposed damper acts as a ductile fuse. Furthermore, the web and flange plates contribute to the shear resistance, with the flange carrying approximately 80% and 10% of the shear force for dampers with θ= 30° and 90°, respectively. Moreover, dampers that have a larger flange-plate shear strength than the shear strength of the web exhibit behaviours in linear and nonlinear zones. In addition, the over-strength obtained for the damper was greater than 1.5 (proposed by AISC for shear links). Relevant relationships are determined to predict and design the damper and the elements outside it.

Key Words
concentrically braced frames; shaped; shear; over-strength; ultimate strength; yielding

Address
Ali Ghamari:Department of Civil Engineering, Ilam Branch, Islamic Azad University, Ilam, Iran

Young-Ju Kim:Korea Institute of Structural Engineering & Consulting., Busan, Republic of Korea

Jaehoon Bae:Department of Architecture Design, College of Engineering Science, Chonnam National University,
50 Daehak-ro Yeosu-si, Jeonnam, 59626, Republic of Korea

Abstract
This paper explored the viability of utilising titanium alloy bolts in the construction industry through an experimental programme, where a total of sixty-six titanium alloy (Ti/6Al/4V) bolts were tested under axial tension, pure shear and combined tension and shear. In addition, a series of Charpy V-notch specimens machined from titanium alloy bolts, conventional high-strength steel bolts, austenitic and duplex stainless steel bolts were tested for impact toughness comparisons. The obtained experimental results demonstrated that the axial tensile and pure shear capacities of titanium alloy bolts can be reasonably estimated by the current design standards for steel structures (Eurocode 3, AS 4100 and AISC 360). However, under the combined tension and shear loading conditions, significant underestimation by Eurocode 3 and unsafe predictions through AS 4100 and AISC 360 indicate that proper modifications are necessary to facilitate the safe and economic use of titanium alloy bolts. In addition, numerical models were developed to calibrate the fracture parameters of the tested titanium alloy bolts. Furthermore, a design-based selection process of titanium alloy bolts in the structural applications was proposed, in which the ultimate strength, ductility performance and corrosion resistance (including galvanic corrosion) of titanium alloy bolts was mainly considered.

Key Words
design method; galvanic corrosion; impact toughness; numerical model; titanium alloy bolt; ultimate strength

Address
Dongxu Li:School of Civil Engineering, The University of Sydney, Sydney, NSW 2006, Australia

Brian Uy:School of Civil Engineering, The University of Sydney, Sydney, NSW 2006, Australia

Jia Wang:School of Civil Engineering, The University of Sydney, Sydney, NSW 2006, Australia

Yuchen Song:School of Civil Engineering, The University of Sydney, Sydney, NSW 2006, Australia

Abstract
This paper presents a combined experimental and numerical study on stainless steel end-plate connections, with an emphasis placed on their ultimate behaviour and rotation capacity. In the experimental phase, six connection specimens made of austenitic and lean duplex stainless steels are tested under monotonic loads. The tests are specifically designed to examine the close-to-failure behaviour of the connections at large deformations. It is observed that the rotation capacity is closely related to fractures of the stainless steel bolts and end-plates. In the numerical phase, an advanced finite element model suitable for fracture simulation is developed. The incorporated constitutive and fracture models are calibrated based on the material tests of stainless steel bolts and plates. The developed finite element model exhibits a satisfactory accuracy in predicting the close-to-failure behaviour of the tested connections. Finally, the moment resistance and rotation capacity of stainless steel end-plate connections are assessed based on the experimental tests and numerical analyses.

Key Words
end-plate connection; fracture simulation; rotation capacity; stainless steel bolt; stainless steel; ultimate behaviour

Address
Yuchen Son:School of Civil Engineering, The University of Sydney, Sydney, NSW 2006, Australia

Brian Uy:School of Civil Engineering, The University of Sydney, Sydney, NSW 2006, Australia

Dongxu Li:School of Civil Engineering, The University of Sydney, Sydney, NSW 2006, Australia

Jia Wang:School of Civil Engineering, The University of Sydney, Sydney, NSW 2006, Australia

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