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CONTENTS
Volume 42, Number 1, January10 2022
 

Abstract
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 reported by the authors on back-to-back built-up CFS unequal angle sections with intermediate stiffeners under axial compression. The load-axial shortening behaviour along with the deformed shapes at failure are reported. A nonlinear finite element (FE) model was then developed, which includes material non-linearity, 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 finite element model was then used for the purpose of a parametric study comprising 96 models to investigate the effect of longer to shorter leg ratios, stiffener provided in the longer leg, thicknesses and lengths on axial strength of back-to back built-up CFS unequal angle sections. Four different thicknesses and seven different lengths (stub to slender columns) with three overall widths to the overall depth (B/D) ratios 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% and 5% on average, while predicting the axial strengths of back-to-back built-up CFS unequal angle sections with and without the stiffener, respectively.

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

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

Krishanu Roy:1)Division of Structural Engineering, College of Engineering Guindy Campus, Anna University, Chennai, India 2)Department of Civil and Environmental Engineering, The University of Auckland, Auckland, New Zealand

James B.P. Lim: 1)Division of Structural Engineering, College of Engineering Guindy Campus, Anna University, Chennai, India 2)Department of Civil and Environmental Engineering, The University of Auckland, Auckland, New Zealand

Abstract
In this paper, a nonlinear numerical method to solve the large deflection problem is introduced. And the nondimensional load-deflection behavior of functionally graded carbon nanotube-reinforced composite (FG-CNTRC) plates is parametrically investigated. The large deflection problem is formulated according to the von Kármán nonlinear theory and the (1,1,0)* hierarchical model, and it is approximated by 2-D natural element method (NEM). The shear locking phenomenon is suppressed by the selectively reduced integration method. The nonlinear matrix equations are solved by combining the incremental loading scheme and the Newton-Raphson iteration method. The proposed method is validated from the benchmark experiments, where the propose method shows an excellent agreement with the reference methods. The nonlinear behavior of FG-CNTRC plates is evaluated in terms of the non-dimensional load-deflection curve, and it is parametrically investigated with respect to the existence/non-existence and gradient pattern of CNTs, the width-to-thickness and aspect ratios of plates and the type of boundary conditions. The non-dimensional central deflection is significantly reduced when CNTs and added, and it decreases with the volume fraction of CNTs. But, it shows a uniform increase in proportion to the width-to-thickness and aspect ratios. Both the gradient pattern of CNTs and the type of boundary conditions do also show the remarkable effects.

Key Words
CNT-reinforced; composite plates; functionally graded; Natural element method (NEM); non-dimensional load-deflection curve; nonlinear bending deflection

Address
Jin-Rae Cho:Department of Naval Architecture and Ocean Engineering, Hongik University, Sejong 30016, Korea

Abstract
This paper researches a lightweight composite structure referred to as the Profiled Steel Sheeting Dry Board (PSSDB). It is fundamentally produced by connecting a Profiled Steel Sheeting to Dry Board using mechanical screws. It is mainly employed as floor panels. However, almost all studies have focused on researching the one-way structural performance. Therefore, this study focuses on the bending behaviour of the two-way PSSDB floor system using both of Finite Element (FE) and Experimental analysis. Four panels were used in the experimental tests, and a mild steel plate has been applied at the bottom for two panels. For the FE process, models were created using ABAQUS software. 4 parametric studies have been utilized to understand the system's influential elements. From the experimental tests, it was found that using Steel Plate shall optimize the two-way action of the system and depending on the type of dry board the improvement in stiffness may reach up to 38%. It was shown from the FE analysis that the dry board, profiled steel sheeting and steel plat can affect the system by up to 10 %, 17% and 3% respectively, while applying a uniform load demonstrate a better two-way action.

Key Words
dry board; floor; profiled steel sheeting; two-way

Address
Marwan S. Al-Shaikhli:Building and Construction Technology Engineering Department, Madenat Alelem University College, Baghdad, Iraq

Wan Hamidon Wan Badaruzzaman:Director of PRASARANA, Universiti Kebangsaan Malaysia, Bangi, Selangor, Malaysia

Ahmed W. Al Zand:Department of Civil Engineering, Universiti Kebangsaan Malaysia, Bangi, Selangor, Malaysia

Abstract
This paper presents a study on the behavior of a bolted T-stub to square tube connection using Thread-fixed One side Bolts (TOBs) through tests and numerical simulations. It outlines a research work of four connections with focus on the failure modes and strengths of the connection under tensile load. It was observed that the thread anchor failure caused by shear failure of hole threads controlled the final failure of the connection in the tests. Meanwhile, the out-of-plane deformation of tube wall resulted in the contact separation between hole threads and bolt threads, which in turn reduced the shear strength of hole threads. Finite element models (FEMs) allowing for the configuration details of the TOBs fixed connection are then developed and compared with the test results. Subsequently, the failure mechanism of hole threads and stress distribution of each component are analyzed based on FEM results. It was concluded that the ultimate strength of connection was not only concerned with the shear strength of hole threads, but also was influenced by the plastic out-of-plane deformation of tube wall. These studies lay a foundation for the establishment of suitable design methods of this type of connection.

Key Words
effective shear area; hole wall thread failure; plastic out-of-plane deformation; thread-fixed one-side bolts

Address
Tuoya Wulan:1)Civil Engineering College of Shandong University, Jinan, Shandong Province, 250061, China 2)Transportaion Institute of Inner Mongolia University, Hohhot, Inner Mongolia, 010000, China

Peijun Wang:Civil Engineering College of Shandong University, Jinan, Shandong Province, 250061, China

Chengxin Xia:Civil Engineering College of Shandong University, Jinan, Shandong Province, 250061, China

Xinyu Liu:Civil Engineering College of Shandong University, Jinan, Shandong Province, 250061, China

Mei Liu:Civil Engineering College of Shandong University, Jinan, Shandong Province, 250061, China

Fangzhou Liu:Civil Engineering College of Shandong University, Jinan, Shandong Province, 250061, China

Ou Zhao:School of Civil and Environmental Engineering, Nanyang Technological University, Singapore

Lulu Zhang:School of Civil and Environmental Engineering, Nanyang Technological University, Singapore

Abstract
This study introduces a general reliability-based, performance-based design framework to design frames regarding their uncertainties and user-defined design goals. The Iterative-R method extracted from the main framework can designate a proper R (i.e., response modification factor) satisfying the design goal regarding target reliability index and pre-defined probability of collapse. The proposed methodology is based on FEMA P-695 and can be used for all systems that FEMA P-695 applies. To exemplify the method, multiple three-dimensional, four-story steel special moment-resisting frames are considered. Closed-form relationships are fitted between frames' responses and the modeling parameters. Those fits are used to construct limit state functions to apply reliability analysis methods for design safety assessment and the selection of proper R. The frameworks' unique feature is to consider arbitrarily defined probability density functions of frames' modeling parameters with an insignificant analysis burden. This characteristic enables the alteration in those parameters' distributions to meet the design goal. Furthermore, with sensitivity analysis, the most impactful parameters are identifiable for possible improvements to meet the design goal. In the studied examples, it is revealed that a proper R for frames with different levels of uncertainties could be significantly different from suggested values in design codes, alarming the importance of considering the stochastic behavior of elements' nonlinear behavior.

Key Words
first-order reliability method; response modification coefficient; response surface method; seismic performance-based design; special moment-resisting frame; steel frames

Address
Mohammad Hesam Soleimani-Babakamali:Department of Civil and Environmental Engineering, Virginia Polytechnic Institute and State Univ., Blacksburg, VA, U.S.A.

Kourosh Nasrollahzadeh:Department of Civil Engineering, K. N. Toosi University of Technology, Tehran, Iran

Amin Moghadam:Department of Civil and Environmental Engineering, Virginia Polytechnic Institute and State Univ., Blacksburg, VA, U.S.A.

Abstract
The pointwise equilibrium polynomial (PEP) element considering local second-order effect has been widely used in direct analysis of many practical engineering structures. However, it was derived according to Euler-Bernoulli beam theory and therefore it cannot consider shear deformation, which may lead to inaccurate prediction for deep beams. In this paper, a novel beam-column element based on Timoshenko beam theory is proposed to overcome the drawback of PEP element. A fifth-order polynomial is adopted for the lateral deflection of the proposed element, while a quadric shear strain field based on equilibrium equation is assumed for transverse shear deformation. Further, an additional quadric function is adopted in this new element to account for member initial geometrical imperfection. In conjunction with a reliable and effective three-dimensional (3D) co-rotational technique, the proposed element can consider both member initial imperfection and transverse shear deformation for second-order direct analysis of frame structures. Some benchmark problems are provided to demonstrate the accuracy and high performance of the proposed element. The significant adverse influence on structural behaviors due to shear deformation and initial imperfection is also discussed.

Key Words
beam-column element; bowing effect; direct analysis; member imperfection; Timoshenko beam theory

Address
Yi-Qun Tang:Department of Engineering Mechanics, Jiangsu Key Laboratory of Engineering Mechanics, Southeast University, Nanjing, China

Yue-Yang Ding:Department of Civil and Environmental Engineering, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong, China

Yao-Peng Liu:2)Department of Civil and Environmental Engineering, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong, China 3) NIDA Technology Company Limited, Hong Kong Science Park, Shatin, N.T., Hong Kong, China

Siu-Lai Chan:Department of Civil and Environmental Engineering, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong, China

Er-Feng Du:Department of Engineering Mechanics, Jiangsu Key Laboratory of Engineering Mechanics, Southeast University, Nanjing, China

Abstract
Concrete-filled square stainless steel tubes (CFSSST), which possess relatively large flexural stiffness, high corrosion resistance and require simple joint configurations and low maintenance cost, have a great potential in constructional applications. Despite that the use of stainless steel may result in high initial cost compared to their conventional carbon steel counterparts, the whole-life cost of CFSSST is however considered to be lower, which offers a competitive choice in engineering practice. In this paper, a comprehensive experimental and numerical program on 24 CFSSST stub column specimens, including 3 austenitic and 3 duplex stainless steel square hollow section (SHS) stub columns and 9 austenitic and 9 duplex CFSSST stub columns, has been carried out. Finite element (FE) models were developed to be used in parametric analysis to investigate the influence of the tube thickness and concrete strength on the ultimate capacities more accurately. Comparisons of the experimental and numerical results with the predictions made by design guides ACI 318, ANSI/AISC 360, Eurocode 4 and GB 50936 have been performed. It was found that these design methods generally give conservative predictions to the ultimate capacities of CFSSST stub columns. Improved calculation methods, developed based on the Continuous Strength Method, have been proposed to provide more accurate estimations of the ultimate resistances of CFSSST stub columns. The suitability of these proposals has been validated by comparison with the test results, where a good agreement between the predictions and the test results have been achieved.

Key Words
compressive behavior; concrete-filled square stainless steel tubes; Continuous Strength Method; parametric study; stub column tests

Address
Peng Dai:1)The Key Laboratory of Urban Security and Disaster Engineering of Ministry of Education,
Beijing University of Technology, Beijing 100124, China
2)Beijing Engineering Research Centre of High-rise and Large-span Prestressed Steel Structures,
Beijing University of Technology, Beijing 100124, China

Lu Yang:1)The Key Laboratory of Urban Security and Disaster Engineering of Ministry of Education,
Beijing University of Technology, Beijing 100124, China
2)Beijing Engineering Research Centre of High-rise and Large-span Prestressed Steel Structures,
Beijing University of Technology, Beijing 100124, China

Jie Wang:Department of Architecture and Civil Engineering, University of Bath, Bath BA2 7AY, U.K.

Keyang Ning:1)The Key Laboratory of Urban Security and Disaster Engineering of Ministry of Education,
Beijing University of Technology, Beijing 100124, China
2)Beijing Engineering Research Centre of High-rise and Large-span Prestressed Steel Structures,
Beijing University of Technology, Beijing 100124, China

Yi Gang:1)The Key Laboratory of Urban Security and Disaster Engineering of Ministry of Education,
Beijing University of Technology, Beijing 100124, China
2)Beijing Engineering Research Centre of High-rise and Large-span Prestressed Steel Structures,
Beijing University of Technology, Beijing 100124, China

Abstract
Past studies have shown that the aspect ratio (width-to-height) of a steel plate shear wall (SPSW) can significantly affect its seismic response. SPSWs with lower aspect ratio (narrow SPSW) may experience low lateral stiffness and flexure dominated drift response. As the height of the frame increases, the narrow SPSWs prove to be uneconomical and demonstrate inferior seismic response than their wider counterparts. Moreover, the thicker web plates required for narrow SPSWs exerts high inward pull on the VBEs. The present study suggests the limiting values of the aspect ratio for an SPSW system by evaluating the seismic collapse performance of 3-, 6- and 9-story SPSW systems using FEMA P695 methodology. For this purpose, nonlinear models are developed. These models are validated with the past quasi-static experimental results. Non-linear static analyses and Incremental dynamic analyses are then carried. The results are then utilized to conservatively suggest the limiting values of aspect ratios for SPSW system. In addition to the conventional-SPSW (Conv-SPSW), the collapse performance of staggered-SPSW (S-SPSW) is also explored. Its performance is compared with the Conv-SPSW and the use of S-SPSW is suggested in the cases where SPSW with lower than recommended aspect ratio is desired.

Key Words
collapse margin ratio; fragility analysis; incremental dynamic analysis; seismic analysis; steel plate shear wall

Address
Abhishek Verma and Dipti R. Sahoo:Department of Civil Engineering, Indian Institute of Technology Delhi, Hauz Khas, New Delhi 110016, India

Abstract
The fundamental period (FP) is one of the most critical parameters for the seismic design of structures. In the reinforced concrete (RC) infilled frame, the infill walls significantly affect the FP because they change the stiffness and mass of the structure. Although several formulas have been proposed for estimating the FP of the RC infilled frame, they are often associated with high bias and variance. In this study, an efficient soft computing model, namely the group method of data handling (GMDH), is proposed to predict the FP of regular RC infilled frames. For this purpose, 4026 data sets are obtained from the open literature, and the quality of the database is examined and evaluated in detail. Based on the cleaning database, several GMDH models are constructed and the best prediction model, which considers the height of the building, the span length, the opening percentage, and the infill wall stiffness as the input variables for predicting the FP of regular RC infilled frames, is chosen. The performance of the proposed GMDH model is further underscored through comparison of its FP predictions with those of existing design codes and empirical models. The accuracy of the proposed GMDH model is proven to be superior to others. Finally, explicit formulas and a graphical user-friendly interface (GUI) tool are developed to apply the GMDH model for practical use. They can provide a rapid prediction and design for the FP of regular RC infilled frames.

Key Words
fundamental period; group method of data handling; reinforced concrete infilled frame structure; soft computing

Address
Viet-Linh Tran:1)Department of Civil and Environmental Engineering, Sejong University, 98 Gunja-Dong, Gwangjin-Gu, Seoul 05006, South Korea 2)Department of Civil Engineering, Vinh University, Vinh 461010, Vietnam

Seung-Eock Kim:Department of Civil and Environmental Engineering, Sejong University, 98 Gunja-Dong, Gwangjin-Gu, Seoul 05006, South Korea

Abstract
To simplify the design and reduce the construction cost of traditional multi-girder structural systems, twin I-girder structures are widely used in many countries in recent years. Due to the concern on post-fracture redundancy, however, twin girder bridges are currently classified as fracture critical structures in AASHTO specifications for highway bridges. To investigate the after-fracture behavior of such structures, a composite steel and concrete twin girder specimen was built and an artificial fracture through the web and the bottom flange was created on one main girder. The static loading test was performed to investigate its mechanical performance after a severe fracture occurred on the main girder. Applied load and vertical displacement curves, and the applied load versus strain relationships at key sections were measured. To investigate the load distribution and transfer capacities between two steel girders, the normal strain development on crossbeams was also measured during the loading test. In addition, both shear and normal strains of studs were also measured in the loading test to explore the behavior of shear connectors in such bridges. The functions and structural performance of structural members and possible load transfer paths after main girder fractures in such bridges were also discussed. The test results indicate in this study that a typical twin I-girder can resist a general fracture on one of its two main girders. The presented results can provide references for post-fracture performance and optimization for the design of twin I-girder bridges and similar structures.

Key Words
collapse; fracture; loading test; redundancy; two girder

Address
Weiwei Lin: Department of Civil Engineering, Aalto University, 02150 Espoo, Finland

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