Structural behaviour of tubular skeletal framework

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Structural behaviour of tubular skeletal framework

 

Author: Yu, Wai-kin Dominic
Title: Structural behaviour of tubular skeletal framework
Degree: Ph.D.
Year: 2004
Subject: Hong Kong Polytechnic University -- Dissertations
Tubular steel structures
Structural stability
Steel, Structural
Department: Dept. of Civil and Structural Engineering
Pages: xxiv, 299 leaves : ill. ; 30 cm
Language: English
InnoPac Record: http://library.polyu.edu.hk/record=b1756575
URI: http://theses.lib.polyu.edu.hk/handle/200/1591
Abstract: This thesis reports the findings of a four year research project in which the structural behaviour of tubular skeletal framework is studied through both experimental and numerical investigations. This research project aims to examine the structural behaviour of tubular skeletal framework, in particular, bamboo scaffolds and steel scaffolds which are widely employed in building construction in the South East Asia. It should be noted that column buckling is always critical in these structures due to the use of very slender compression members. Structural engineers often find it difficult to determine the effective lengths of these compression members due to complicated member configurations and bracing members. Consequently, the load carrying capacities of these tubular skeletal framework are traditionally assessed through testing. It will be highly desirable to provide simple but effective design methods to allow for column buckling in both bamboo and steel scaffolds, and hence, to evaluate the load carrying capacities of these scaffolds through rational design methods. Detailed understanding on the structural instability of these structures will also be provided to promote safe and effective use in practice. The major activities and findings of the project are summarized as follows: Advanced non-linear analysis of tubular skeletal framework In order to investigate the structural stability of tubular skeletal framework, finite element technique was employed to study the interactive column buckling of beam-column sub-frames. A literature review on finite element formulation using one-element-per-member was carried out to acquire the basic knowledge of advanced non-linear finite element modeling, and the advanced non-linear finite element software developed at the Department of Civil and Structural Engineering of the Hong Kong Polytechnic University, NIDA, was employed in this project. A number of finite element models for various beam-column sub-frames with different member configurations were established to study their structural behaviour against local, overall and interactive column buckling. Moreover, the effects of bracing members and support conditions were studied in order to examine the structural performance of these structures in practice. The effects of initial imperfections in terms of both magnitude and mode shape were also examined. Furthermore, the effectiveness of restraints from both attached members and external supports were studied. After acquiring experiences on advanced non-linear analysis on beam-column sub-frames, two types of practical tubular skeletal framework, namely, bamboo scaffolds and modular steel scaffolds, were studied extensively, and rational design methods were developed for practical design. Bamboo scaffolds Bamboo scaffolds had been used in building construction in China for many hundreds years. In Hong Kong and other parts of the Southern China, bamboo scaffolds were ones of the few traditional building systems, which survived by self-improvement trough practical experiences of scaffolding practitioners over generations. There were two bamboo species, namely Bambusa Pervariabilis (or Kao Jue) and Phyllostachys Pubescens (or Mao Jue), commonly used in bamboo scaffolds. Nowadays, in spite of open competition with many steel scaffolds imported all over the world, bamboo scaffolds remained to be one of the most preferred access scaffolds in building construction in Hong Kong and the neighbouring areas. In order to promote the use of structural bamboo members as effective and green construction materials, the mechanical properties of structural bamboo were established through systematic test series with a large number of compression and bending tests. The characteristic values of both the strengths and the Young's moduli of bamboo species for limit state structural design were also established. Moreover, a total of 72 column buckling tests with bamboo culms of typical dimensions and properties were executed to study the column buckling behaviour of structural bamboo. A limit state design method against column buckling of structural bamboo based on modified slenderness was also established and carefully calibrated against test data. Four full-scale bamboo scaffolds were built and tested to failure in order to examine the overall structural stability of bamboo scaffolds. The measured load carrying capacities of these bamboo scaffolds with different member configurations and lateral restraint arrangements were compared with practical load requirements. Furthermore, an advanced non-linear finite element model with one-element-per-member formulation was employed to investigate the structural behaviour of these bamboo scaffolds. A newly formulated design method for both bamboo column buckling and bamboo scaffolds was proposed for practical design after careful calibration against test data. Steel scaffolds Modular steel scaffolds were commonly employed as supporting scaffolds in building construction. The modular units were typically fabricated from slender members made from high strength cold-formed steel tubes. The advantages of modular steel scaffolds were easy fabrication, installation and dismantling. However, structural collapses in these scaffolds occurred from time to time due to inadequate design against column buckling, poor construction with insufficient bracing, and over-loads on sites. In order to minimize work hazards, the structural behaviour of these steel scaffolds should be clearly understood, and a rational design method of these steel scaffolds would be highly desirable to ensure structural adequacy in practice. In order to study the stability behaviour of these modular steel scaffolds, experimental investigation was carried out on typical modular steel scaffolds. Moreover, the advanced non-linear analysis method was adopted to evaluate the load carrying capacities of these scaffolds under different support conditions. Comparisons between the experimental and the numerical results on the structural stability of these modular steel scaffolds were also presented. Due to complicated member configurations, the restraining effects of external supports were studied through advanced non-linear finite element models. The predicted load carrying capacities and deformations at failure of these models under partially restrained conditions were found to be close to the experimental results. A design method for column buckling with equivalent effective length coefficients for practical applications was also suggested. Project significance This research project provides detailed understanding on the structural behaviour of tubular skeletal framework commonly used in building construction. A new unified design method against column buckling applicable to both bamboo scaffolds and modular steel scaffolds is established after careful calibration against test data. In order to promote effective use of structural bamboo and bamboo scaffolds, the scientifically developed design method enables re-engineering of bamboo scaffolds with proven structural safety. Moreover, based on this design method, the load carrying capacities of modular steel scaffolds with practical initial imperfections and supporting conditions may be readily evaluated. Structural engineers are thus encouraged to design tubular skeletal framework using both the advanced non-linear finite element methods and the unified design method to achieve enhanced structural economy and safety.

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