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CONTENTS
Volume 30, Number 4, February25 2019
 

Abstract
Creating different cutout shapes in order to make doors and windows, reduce the structural weight or implement various mechanisms increases the likelihood of buckling in thin-walled structures. In this study, the effect of cutout shape and geometric imperfection (GI) is simultaneously investigated on the critical buckling load and knock-down factor (KDF) of composite cylindrical shells. The GI is modeled using single perturbation load approach (SPLA). First, in order to assess the finite element model, the critical buckling load of a composite shell without cutout obtained by SPLA is compared with the experimental results available in the literature. Then, the effect of different shapes of cutout such as circular, elliptic and square, and perturbation load imperfection (PLI) is investigated on the buckling behavior of cylindrical shells. Results show that the critical buckling load of a shell without cutout decreases by increasing the PLI, whereas increasing the PLI does not have a great impact on the critical buckling load in the presence of cutout imperfection. Increasing the cutout area reduces the effect of the PLI, which results in an increase in the KDF.

Key Words
composite shell; buckling; cutout; single perturbation load approach; geometry imperfection; knock-down factor

Address
Department of Mechanical Engineering, Faculty of Engineering, University of Isfahan, 81746-73441, Isfahan, Iran.


Abstract
Double skin composite walls offer structural and economic merits over conventional reinforced concrete counterparts in terms of higher capacity, greater stiffness, and better ductility. This paper investigated the axial behavior of double skin composite walls with steel truss connectors. Full-scaled tests were conducted on three specimens with different height-to-thickness ratios. Test results were evaluated in terms of failure mode, load-axial displacement response, buckling loading, axial stiffness, ductility, strength index, load-lateral deflection, and strain distribution. The test data were compared with AISC 360 and Eurocode 4 and it was found that both codes provided conservative predictions on the safe side.

Key Words
axial behavior; composite wall; truss connector; height-to-thickness ratio; structural performance

Address
(1) Ying Qin, Gan-Ping Shu, Jian-Hong Han:
Key Laboratory of Concrete and Prestressed Concrete Structures of Ministry of Education, and National Prestress Engineering Research Center, School of Civil Engineering, Southeast University, Nanjing, China;
(2) Xiong-Liang Zhou, Yun-Fei He:
Zhejiang Southeast Space Frame Group Company Limited, Hangzhou, China.

Abstract
This paper presents geometrically nonlinear behavior of cracked fiber reinforced composite beams by using finite element method with and the first shear beam theory. Total Lagrangian approach is used in the nonlinear kinematic relations. The crack model is considered as the rotational spring which separate into two parts of beams. In the nonlinear solution, the Newton-Raphson is used with incremental displacement. The effects of fibre orientation angles, the volume fraction, the crack depth and locations of the cracks on the geometrically nonlinear deflections of fiber reinforced composite are examined and discussed in numerical results. Also, the difference between geometrically linear and nonlinear solutions for the cracked fiber reinforced composite beams.

Key Words
fiber reinforced composite; geometrically nonlinear analysis; beams; crack; finite element method; total Lagrangian

Address
Department of Civil Engineering, Bursa Technical University, Yıldırım Campus, Yıldırım, Bursa 16330, Turkey.


Abstract
The objective of this paper is to investigate the confinement coefficient of concrete-filled square stainless steel tubular (CFSSST) stub columns under axial loading. A fine finite 3D solid element model was established, which utilized a constitutive model of stainless steel considering the strain-hardening characteristics and a triaxial plastic-damage constitutive model of concrete with features of the parameter certainty under axial compression. The finite element analysis results revealed that the increased ultimate bearing capacity of CFSSST stub columns compared with their carbon steel counterparts was mainly due to that the composite action of CFSSST stub columns is stronger than that of carbon steel counterparts. A further parametric study was carried out based on the verified model, and it was found that the stress contribution of the stainless steel tube is higher than the carbon steel tube. The stress nephogram was simplified reasonably in accordance with the limit state of core concrete and a theoretical formula was proposed to estimate the ultimate bearing capacity of square CFSSST stub columns using superposition method. The predicted results showed satisfactory agreement with both the experimental and FE results. Finally, the comparisons of the experimental and predicted results using the proposed formula and the existing codes were illustrated.

Key Words
square stainless steel tube; finite element analysis; composite action; ultimate bearing capacity; confinement coefficient

Address
(1) Fa-xing Ding, Yi-xiang Yin, Liping Wang, Yujie Yu, Liang Luo, Zhi-wu Yu:
School of Civil Engineering, Central South University, Changsha, Hunan Province, 410075, PR China;
(2) Fa-xing Ding, Liping Wang, Zhi-wu Yu:
Engineering Technology Research Center for Prefabricated Construction Industrialization of Hunan Province, 410075, PR China.


Abstract
Earthquake and fire are both severe disasters for building structures. Since earthquake-induced damage will weaken the structure and reduce its fire endurance, it is important to investigate the behavior of structure subjected to post-earthquake fire. In this paper, steel-concrete composite beam-to-column joints were tested under fire with pre-damage caused by cyclic loads. Beforehand, three control specimens with no pre-damage were tested to capture the static, cyclic and fire-resistant performance of intact joints. Experimental data including strain, deflection and temperature recorded at several points are presented and analyzed to quantify the influence of cyclic damage on fire resistance. It is indicated that the fire endurance of damaged joints decreased with the increase of damage level, mainly due to faster heating-up rate after cyclic damage. However, cracks induced by cyclic loading in concrete are found to mitigate the concrete spalling at elevated temperatures. Moreover, the relationship between fire resistance and damage degree is revealed from experimental results, which can be applied in fire safety design and is worthwhile for further research.

Key Words
post-earthquake fire; composite joint; cyclic loading; fire-resistant performance; fire endurance

Address
(1) Zhongnan Ye, Shouchao Jiang, Yingchao Li and Guoqiang Li:
College of Civil Engineering, Tongji University, Shanghai, 200092, China;
(2) Amin Heidarpour:
Department of Civil Engineering, Monash University, VIC 3800, Melbourne, Australia.

Abstract
In steel frame-tube structures (SFTSs) the application of flexural beam is not suitable for the beam with span-to-depth ratio lower than five because the plastic hinges at beam-ends can not be developed properly. This can lead to lower ductility and energy dissipation capacity of the SFTS. To address this problem, a replaceable shear link, acting as a ductile fuse at the mid length of deep beams, is proposed. SFTS with replaceable shear links (SFTS-RSLs) dissipate seismic energy through shear deformation of the link. In order to evaluate this proposal, buildings were designed to compare the seismic performance of SFTS-RSLs and SFTSs. Several sub-structures were selected from the design buildings and finite element models (FEMs) were established to study their hysteretic behavior. Static pushover and dynamic analyses were undertaken in comparing seismic performance of the FEMs for each building. The results indicated that the SFTS-RSL and SFTS had similar initial lateral stiffness. Compared with SFTS, SFTS-RSL had lower yield strength and maximum strength, but higher ductility and energy dissipation capacity. During earthquakes, SFTS-RSL had lower interstory drift, maximum base shear force and story shear force compared with the SFTS. Placing a shear link at the beam mid-span did not increase shear lag effects for the structure. The SFTS-RSL concentrates plasticity on the shear link. Other structural components remain elastic during seismic loading. It is expected that the SFTS-RSL will be a reliable dual resistant system. It offers the benefit of being able to repair the structure by replacing damaged shear links after earthquakes.

Key Words
steel frame-tube structure (SFTS); replaceable shear link; hysteretic behaviors; dynamic behaviors; finite element analyses

Address
School of Civil Engineering, Xi'an University of Architecture and Technology, Xi'an, China.


Abstract
Passive steel dampers have shown favorable performance in last earthquakes, numerical and experimental studies. Although steel dampers are more affordable than other types of damper, they are not economically justified for ordinary buildings. Therefore, in this paper, an innovative steel damper with shear yielding mechanism is introduced, which is easy to fabricate also can be easily replaced after sever earthquakes. The main goal of implementing such a mechanism is to control the possible damage in the damper and to ensure the elastic behavior of other structural components. The numerical results indicate an enhancement of the hysteretic behavior of the concentrically braced frames utilizing the proposed damper. The proposed damper change brittle behavior of brace due to buckling to ductile behavior due to shear yielding in proposed damper. The necessary relations for the design of this damper have been presented. In addition, a model has been presented to estimate load-displacement of the damper without needing to finite element modeling.

Key Words
passive steel dampers; stiffness; ductility; seismic behavior

Address
(1) Ali Ghamari, Alireza Khaloo:
Department of Civil Engineering, Sharif University of Technology, Tehran, Iran;
(2) Hadi Haeri, Zheming Zhu:
MOE Key Laboratory of Deep Underground Science and Engineering, School of Architecture and Environment, Sichuan University, Chengdu 610065, China.


Abstract
Cold-formed steel (CFS) has a great potential to meet the global challenge of fast-track and durable construction. CFS members undergo large buckling instabilities due to their small wall thickness. CFS beams with corrugated webs have shown great resistance towards web buckling under flexure, when compared to the conventional I-sections. However, the magnitude of global imperfections significantly affects the performance of CFS members. This paper presents the first attempt made to experimentally study the effect of global imperfections on the structural efficiency of various strengthening schemes implemented in CFS beams with corrugated webs. Different strengthening schemes were adopted for two types of beams, one with large global imperfections and the other with small imperfections. Strength and stiffness characteristics of the beams were used to evaluate the structural efficiency of the various strengthening schemes adopted. Six tests were performed with simply supported end conditions, under four-point loading conditions. The load vs. mid-span displacement response, failure loads and modes of failure of the test specimens were investigated. The test results would compensate the lack of experimental data in this area of research and would help in developing numerical models for extensive studies for the development of necessary guidelines on the same. Strengthening schemes assisted in enhancing the member performance significantly, both in terms of strength and stiffness. Hence, providing an economic and time saving solution to such practical structural engineering problems.

Key Words
cold-formed steel; experiment; strengthening; beams; imperfections; buckling; capacity

Address
(1) M. Adil Dar:
Department of Civil Engineering, Indian Institute Technology Delhi, New Delhi, India;
(2) N. Subramanian:
Consulting Engineer, Maryland, USA;
(3) A.R. Dar, Muheeb Majid, Mohd Haseeb, Mugees Tahoor:
Department of Civil Engineering, National Institute Technology Srinagar, J&K, India.


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