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  1. DEVELOPMENT IN CONCRETE-FILLED STEEL TUBULAR STRUCTURES A SEMINAR REPORT SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF Master of Technology in…
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  • 1. DEVELOPMENT IN CONCRETE-FILLED STEEL TUBULAR STRUCTURES A SEMINAR REPORT SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF Master of Technology in Structural Engineering BY ALOK B. RATHOD Bhartiya Vidya Bhavan’s SARDAR PATEL COLLEGE OF ENGINEERING, MUMBAI DEPARTMENT OF STRUCTURAL ENGINEERING 2015
  • 2. Bhartiya Vidya Bhavan’s SARDAR PATEL COLLEGE OF ENGINEERING, MUMBAI DEPARTMENT OF STRUCTURAL ENGINEERING CERTIFICATE This is to certify that Mr. ALOK BHAKTIRAM RATHOD Roll no. MCSI016 has successfully completed the seminar work entitled “DEVELOPMENT IN CONCRETE FILLED STEEL TUBULAR STRUCTURES” in the partial fulfillment of M.Tech. (Structural Engineering) Date : Place : Mumbai
  • 3. ACKNOWLEDGEMENT I wish to express my thanks to Prof. Dr. M.M. Murudi (Head of the Structural Engineering Department), Prof. Dr. A. A. Bage, Prof. Dr. Tanuja Bandivadekar for their support in the completion of this Report. I also express my deep sense of gratitude to all my Professors, Department of Structural Engineering, Sardar Patel College of Engineering, Mumbai for valuable guidance, constant encouragement and creative suggestions offered during the course of this seminar and also in preparing this report. Date: Alok B. Rathod Place: Mumbai Roll No. MCSI-016 SPCE, Mumbai
  • 4. I CONTENTS CHAPTER NO. TITLE PAGE NO. ABSTRACT lll LIST OF FIGURES lV LIST OF TABLES VI CHAPTER 1 INTRODUCTION 1 CHAPTER 2 REVIEW OF LITERATURE 2 CHAPTER 3 COMPONENT BEHAVIOUR 4 CHAPTER 4 DEVELOPMENT OF CFST FAMILY 6 CHAPTER 5 MATERIALS FOR CONCRETE-FILLED STEEL TUBES 10 5.1 Steel 10 5.2 Concrete 11 CHAPTER 6 RESEARCH ON CONCRETE-FILLED STEEL TUBULAR MEMBERS 13 6.1 Research framework 13 6.2 Static performance 13 6.3 Dynamic performance 15 6.4 Fire performance 16 6.5 Construction and durability issues 17 CHAPTER 7 DESIGN CRITERIA 20
  • 5. II CHAPTER 8 CONSTRUCTION CONSIDERATIONS 23 8.1 Placement of concrete 23 8.2 Fabrication issues 24 CHAPTER 9 SOME CONSTRUCTION EXAMPLES 25 9.1 Buildings 25 9.2 Bridges 28 9.3 Other structures 29 CHAPTER 10 CONCLUSIONS 32 REFERENCES 33
  • 6. III ABSTRACT CFST is the member with concrete filled into steel tubes. It is a new structure that evolved and developed based on SRC Structures, spiral stirrup structures and steel tube structures. Concrete-filled steel tubular (CFST) structure offers numerous structural benefits, and has been widely used in civil engineering structures. This report reviews the development of the family of concrete-filled steel tubular structures up to date and effectively presents a detail study on CFST members. The research development on CFST structural members in most recent years, particularly in China, is summarized and discussed. The current design approaches from various countries are examined briefly. Some projects in China utilizing CFST members are also introduced.
  • 7. IV LIST OF FIGURES FIGURE NO. TITLE PAGE NO. Fig no. 1 Typical concrete-filled steel tubular cross sections. 4 Fig no. 2 Schematic failure modes of hollow steel tube, concrete and CFST stub columns. 5 Fig no. 3 Axial compressive behavior of CFST stub column. 5 Fig no. 4 General CFST cross sections. 6 Fig no. 5 Combinations of CFST sections. 8 Fig no. 6 Inclined, tapered and curved CFST columns. 9 Fig no. 7 Framework of research on CFST structures. 13 Fig no. 8 Schematic failure modes of steel tube, concrete and CFST under tension, bending and torsion. 14 Fig no. 9 Time (t) - load (N) - temperature (T) path. 17 Fig no. 10 Full scale test of core concrete placement (Z2). 18 Fig no. 11 Compressive strength for CFST short column. 21 Fig no. 12 φ-λ relationship for CFST column 21 Fig no. 13 Flexural strength for CFST column. 22 Fig no. 14 Axial load versus moment interaction curve for CFST column 22 Fig no. 15 Schematic view of concrete placement. 23 Fig no. 16 CFST hybrid structural systems for high-rise buildings 25 Fig no. 17 SEG plaza in Shenzhen 26 Fig no. 18 Ruifeng building in Hangzhou. 26 Fig no. 19 Canton Tower. 27 Fig no. 20 Cross section for mega CFST column (units: mm). 28 Fig no. 21 CFST used in bridges. 28
  • 8. V LIST OF FIGURE FIGURE NO. TITLE PAGE NO. Fig no. 22 Wangcang East River Bridge. 29 Fig no. 23 Zhaohua Jialing River Bridge. 29 Fig no. 24 Subway stations using CFST columns. 30 Fig no. 25 A power plant workshop using CFST columns. 30 Fig no. 26 Zhoushan electricity pylon 31 Fig no. 27 A CFDST pole. 31
  • 9. VI LIST OF TABLES TABLE NO. TITLE PAGE NO. Table No. 1 Structural steel mechanical properties according to GB/T 700 and GB/T 1591. 11 Table No. 2 Design value of steel strength (N/mm2) in GB50017. 11 Table No. 3 Material properties of concrete in GB50010. 11 Table No. 4 Scope of application for various building codes relevant to CFST columns. 20
  • 10. 1 CHAPTER 1 INTRODUCTION 1. INTRODUCTION The concrete-filled steel tubular (CFST) structure offers numerous structural benefits, including high strength and fire resistances, favorable ductility and large energy absorption capacities. There is also no need for the use of shuttering during concrete construction; hence, the construction cost and time are reduced. These advantages have been widely exploited and have led to the extensive use of concrete-filled tubular structures in civil engineering structures. China has seen a great deal of research and use of concrete-filled steel tubular structures in practice. There are numbers of books published in public domain in recent years. Some codes of practice and local specifications were developed to provide design guidance as well. This report reviews the state-of-the-art for concrete-filled steel tubular structures, especially some the most recent developments in China. Current design approaches from various countries are examined briefly. Some practical projects using CFST members are presented, and the development trends are discussed.
  • 11. 2 CHAPTER 2 LITERATURE REVIEW Shankar Jagadesh in May 2014, Concrete-filled steel tubes are gaining increasing prominence in a variety of engineering structures, with the principal cross-section shapes being square, rectangular and circular hollow sections. The study about the behavior and the characteristics of CFST columns is the prime need of the hour. This review paper outlines the important contributions on CFST columns contributed in the recent years. This paper presents the innovative experimental investigations conducted on CFST columns and the load deflection response characteristics of columns are also addressed. A comprehensive summary of various analytical and numerical studies on modeling of CFST members is portrayed in this paper. The design specifications and standards by AIJ, Eurocode-4, ANSI/AISC and AIK are addressed. Lin-Hai Han, Wei Li, Reidar Bjorhovde in June 2013, Concrete-filled steel tubular (CFST) structure offers numerous structural benefits, and has been widely used in civil engineering structures. This paper reviews the development of the family of concrete-filled steel tubular structures to date and draws a research framework on CFST members. The research development on CFST structural members in most recent years, particularly in China, is summarized and discussed. The current design approaches from various countries are examined briefly. Some projects in China utilizing CFST members are also introduced. Finally, some concluding remarks are made for CFST members. Baochun CHEN in July 2008, The Concrete Filled Steel Tubular (CFST) structure has been applied prevalently and rapidly to arch bridges since 1990 and this trend is continued with more and more long span CFST arch bridges been built since 2000. This paper briefly introduces the present situation of CFST arch bridges, their five main structure types and the construction methods. Many selected CFST arch bridges built since 2000 and some still under construction are presented. BaoChun Chen in 2009, this paper briefly introduces the present situation of concrete filled steel tube (CFST) arch bridges in China. More than 200 CFST arch bridges were investigated and analyzed based on the factors of type, span, erection method, geometric parameters, and material. Some key issues in design calculation were presented, such as check of strength, calculation of section stiffness, and joint fatigue strength. It will provide a comprehensive reference of CFST arch bridges for the bridge designers and builders.
  • 12. 3 LinHai Han, ShanHu He, LianQiong Zheng, Zhong Tao in March 2012, A series of tests on curved concrete filled steel tubular (CCFST) built-up members subjected to axial compression is described in this paper. Twenty specimens, including 18 CCFST built-up members and 2 curved hollow tubular built-up columns, were tested to investigate the influence of variations in the tube shape (circular and square), initial curvature ratio (β, from 0 to 7.4%), nominal slenderness ratio (λ, from 9.9 to 18.9), section pattern (two main components, three main components and four main components), as well as brace pattern (battened and laced) on the performance of such composite built-up members. The experimental results showed that the ultimate strength and stiffness of CCFST built-up specimens decreased with increasing βr or. Different load- bearing capacities and failure modes were obtained for the battened and laced built-up members. A simplified method using an equivalent slenderness ratio was suggested to calculate the strength of CCFST built-up members under axial compression.
  • 13. 4 CHAPTER 3 COMPONENT BEHAVIOUR 3. COMPONENT BEHAVIOUR Fig. 1(a) depicts three typical column cross-sections, where the concrete is filled in a circular hollow section (CHS), a square hollow section (SHS) or a rectangular hollow section (RHS), where D and B are the outer dimensions of the steel tube and t is the wall thickness of the tube. It is noted that the circular cross section provides the strongest confinement to the core concrete, and the local buckling is more likely to occur in square or rectangular cross-sections. However, the concrete-filled steel tubes with SHS and RHS are still increasingly used in construction, for the reasons of being easier in beam-to-column connection design, high cross- sectional bending stiffness and for aesthetic reasons. Other cross-sectional shapes have also been used for aesthetical purposes, such as polygon, round-ended rectangular and elliptical shapes, as shown in Fig. 1(b). Fig. 1. Typical concrete-filled steel tubular cross sections. It is well known that the compressive strength of concrete is much higher than its tensile strength. Furthermore, the compressive strength is enhanced under bi-axial or tri-axial restraint. For the structural steel, the tensile strength is high while the shape may buckle locally under compression. In concrete-filled steel tubular members, steel and concrete are used such that their natural and most prominent characteristics are taken advantage of. The confinement of concrete is provided by the steel tube, and the local buckling of the steel tube is improved due to the support of the concrete core. Fig. 2 shows schematic failure modes for the stub concrete-filled steel tubular column and the corresponding steel tube and concrete. It can be seen that both inward and outward buckling is found in the steel tube, and shear failure is exhibited for the plain concrete stub column. For the CFST, only outward buckling is found in the tube, and the inner concrete fails in a more ductile fashion.
  • 14. 5 Fig. 2. Schematic failure modes of hollow steel tube, concrete and CFST stub columns Fig. 3(a) shows a comparison of the measured results between a steel stub column, a reinforced concrete stub column and a concrete-filled steel tubular stub column without steel reinforcement, where D and t are the outer diameter and the wall thickness of the circular steel tube, respectively; fY is the yield strength of the steel; fcu is the compressive strength of the concrete cube. The geometric dimension of the circular hollow steel section is the same as in both steel column and composite column, and also the same for the concrete parts in both the reinforced concrete column and the composite column. The term "steel tube + RC" in Fig. 3 indicates the summation of the ultimate strength of the steel tube and the reinforced concrete (RC) specimens. It clearly shows that the ultimate strength for a concrete-filled steel tube is even larger than the summation of the strength of the steel tube and the RC column, which is described as “1(steel tube) + 1 (concrete core) greater than 2 (simple summation of the two materials)”. Fig. 3(b) shows a schematic view of the load versus deformation relationship of the hollow steel tube, the concrete stub column by itself and the concrete-filled steel tube. It can be seen that the ductility of the concrete-filled steel tube is significantly enhanced, when compared to those of the steel tube and the concrete alone. Fig. 3. Axial compressive behavior of CFST stub column.
  • 15. 6 CHAPTER 4 DEVELOPMENT OF CFST FAMILY 4. DEVELOPMENT OF CONCRETE-FILLED STEEL TUBE FAMILY Apart from the common concrete-filled steel tubes shown in Fig. 1, there are other types of “general” member designation in the CFST family. Some of them are shown in Fig. 4, i.e. concrete-filled double skin steel tubes (CFDST), concrete-encased concrete-filled steel tubes as well as reinforced and stiffened concrete-filled steel tubes. The characteristics of these “general” CFST members are as follows: 1) they consist of the steel tube(s) and the filled concrete; 2) the concrete and the steel tube(s) sustain the axial load together. Fig. 4. General CFST cross sections. The CFDST consists of inner and outer tubes, and the sandwiched concrete between two tubes, as shown in Fig. 4(a). The concrete-steel- concrete sandwich cross-section has high bending stiffness that avoids instability under external pressure. Research results have shown that the inner tube provides effective support to the sandwich concrete, and the behavior of the composite member is similar to that of the concrete-filled steel tube. The outward buckling of the outer tube and the inward buckling of the inner tube was observed after beam
  • 16. 7 and column ultimate strength tests. The steel tubes and the concrete can work together well and the integrity of the steel-concrete interface is maintained. This composite column could also have higher fire resistance than the regular CFST columns, due to the inner tubes being protected by the sandwiched concrete during fire. The CFDST could be a good option when designing members with large cross-sections. The thickness of the steel tube wall can be reduced significantly when compared to the steel tube member by itself, and the self-weight is less when compared to the concrete-filled steel tube. Another advantage of the CFDST is that both the outer and the inner steel tubes can act as primary reinforcement and permanent formwork, which is convenient for construction. At the same time, different materials can be utilized for the inner and outer tubes in order to have the additional advantages of esthetics as well as corrosion resistance. Thus, an outer stainless steel tube and an inner carbon steel tube has been described as one option. Fig. 4(b) displays the concrete-encased CFSTs which consist of an inner CFST and an outer encased reinforced concrete (RC). This steel-concrete composite member is somewhat similar to the traditional steel reinforced concrete member. The basic concept of this member is to use the concrete-filled steel tube to replace the I-section steel in the steel reinforced concrete. The embedded inner tube can provide extra confinement to the in-filled core concrete, such that the ultimate strength of the column is improved. The outer encased reinforced concrete can also provide fire protection to the inner tube, therefore the fire resistance of the concrete- encased CFST is enhanced when compared to a conventional CFST column. In addition, the local buckling and the corrosion of the steel tube can be avoided. This kind of column is fairly easily connected to either reinforced concrete or steel beams in a structural system, and has been utilized in some high-rise buildings and bridges in China. The inner steel tube can be erected first, followed by the binding of reinforced bars, and the inner and outer concrete is then placed. When it is connected to a reinforced concrete beam, the beam-column joint can be designed according to the criteria of traditional reinforced concrete structure. Structural steel and steel reinforcements are usually used to enhance the resistances of the concrete-filled steel tubes, as shown in Fig. 4(c). The structural steel sections contribute a lot to column capacities with- out changes of column profiles. The contribution to the column capacities can be considered as the combined capacities of the structural steel and the concrete-filled steel tubular parts. For the reinforcing bars, since they are well anchored in the concrete, they may be taken into account for the resistance of the column. However, if the longitudinal reinforcements and the stirrups are considered as construction measures, the capacities of these bars could be conservatively neglected in design. In the usual concrete-filled steel tubular columns, the local buckling of the steel tube normally occurs after the ultimate strength of the composite member is reached. This could be a critical issue for the development and application of thin-walled tubes with high strength steel. Longitudinal or transverse stiffeners can be welded on the steel tube to improve the strength and the ductility of the composite column. For the column with large cross section, the stiffeners can be welded on the inner surface of the tube. Binding bars can also be welded to the stiffeners to strengthen the tying force, as shown in Fig. 4(d). The effectiveness of the longitudinal stiffeners in delaying the local buckling of the steel tube were demonstrated by
  • 17. 8 experimental studies. On top of being used as single elements in construction, various combinations of concrete- filled steel tubular members are also used. A schematic view of some examples is shown in Fig. 5. These combinations aim at utilizing the advantage of various composite components to meet the construction requirements. For example, single concrete-filled steel tubular members can be connected using double steel plates, and the cavity between steel plates could be filled with concrete as well (Fig. 5(a)). Hollow steel tubes can be used to form a latticed member (Fig. 5(b)), and concrete-filled steel tubes can also be connected by welding together to form a cluster section (Fig. 5(c)) and had been used in arch bridges in China. The concrete-filled steel tubes may also be combined with reinforced concrete to form a composite section, which can serve as piers or arches in a bridge, as shown in Fig. 5(d). Such cross sections have also been used in some recent bridges in China. Fig. 5. Combinations of CFST sections Most concrete-filled steel tubular members used in constructions are prismatic. However, due to architectural or structural requirements, inclined or non-prismatic members were used. The inclined column could serve as a load transfer member in the structure with irregular architectural style, as illustrated in Fig. 6(a). The tapered members could be used for aesthetic or economic purposes, as shown in Fig. 6(b). In some large-span structures or bridges, curved members could be used, as shown in Fig. 6(c). The research results from short column tests have shown that the steel tube and the concrete can work together well despite the inclined or tapered angle. The failure mode of the non- prismatic inclined and tapered members under compression is similar to that of the prismatic member, which is th
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