ct26-design guide for shs cfc 11-04-05.pdf
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Design guide for SHS concrete filled columns
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Design Guide for Concrete Filled Columns
Original text by :-
S J Hicks BEng, PhD (Cantab.)
G M Newman BSc(Eng), CEng, MIStructE, MIFireE
Additional text by :-
M Edwards BSc (Lond)
A Orton BA (Cantab), CEng, MICE, MIStructE
Publication 2002 Corus Tubes Care has been taken to ensure that the contents of this publication are accurate, but Corus UK Limited and its subsidiary companies do not accept responsibility for errors or for information which is found to be misleading. Suggestions for or descriptions of the end use or application of products or methods of working are for information only and Corus UK Limited and its subsidiaries accept no liability in respect thereof. Before using products supplied or manufactured by Corus UK Limited customers should satisfy themselves of their suitability.
Main text 2002 The Steel Construction Institute
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This publication was collated and edited at Corus Tubes, Corby from original contributions by Dr Stephen Hicks and Mr Gerald Newman of SCI and supplementary text from Mr Mike Edwards and Mr Andrew Orton of Corus. It brings together the latest available information on the design and construction of buildings using concrete filled structural hollow sections and supersedes other publications by Corus and SCI.
The Steel Construction Institute develops and promotes the effective use of steel in construction. It is an independent, membership based organisation.
SCI's research and development activities cover many aspects of steel construction including multi-storey construction, industrial buildings, light steel framing systems and modular construction, development of design guidance on the use of stainless steel, fire engineering, bridge and civil engineering, offshore engineering, environmental studies, value engineering, and development of structural analysis systems and information technology.
Membership is open to all organisations and individuals that are concerned with the use of steel in construction. Members include designers, contractors, suppliers, fabricators, academics and government departments in the United Kingdom, elsewhere in Europe and in countries around the world. The SCI is financed by subscriptions from its members, revenue from research contracts and consultancy services, publication sales and course fees.
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Contents Page No.
1 INTRODUCTION 1 1.2 Applications of concrete filled columns 4
2 NORMAL DESIGN 9 2.1 General 9 2.2 Material properties 9 2.3 Partial safety factors 11 2.4 Basis of design method 11 2.5 Restrictions on the simplified design method 13 2.6 Properties of cross-section 13 2.7 Column buckling resistance 17 2.8 Analysis of bending moments due to second-order effects 20 2.9 Combined compression and bending 21 2.10 Longitudinal and transverse shear 31 2.11 Load introduction 32
3 FIRE DESIGN 36 3.1 General 36 3.2 Protected columns 38 3.3 Unprotected columns 39 3.4 Partial safety factors 40 3.5 Properties of the cross-section 41 3.6 Column buckling resistance 42 3.7 Combined compression and bending 43 3.8 Material properties 45
4 FABRICATION AND CONNECTIONS 47 4.1 General 47 4.2 Column Splices and Flange plate connections 47 4.3 Beam-to-column connections 49 4.4 Shearhead connections to slabs 52 4.5 Base plate connections 53
5 PRACTICAL CONSIDERATIONS 54 5.1 Concrete Filling 54
6 SOFTWARE 58
7 REFERENCES 60
A concrete filled structural hollow section provides architects and engineers with a robust and inherently fire resistance column. This publication contains design information for these columns for both the normal and fire conditions. The information is based on Eurocode 4. Also included are case studies illustrating the use of concrete filled columns and practical guidance on concrete filling and connection design.
Design software, ConcFill 2, is described which will analyse sections for the normal and fire conditions.
Structural Hollow Sections (SHS) are the most efficient of all structural steel sections in resisting compression. Their availability in the high yield material Celsius 355 gives them a high strength to weight ratio and produces slender attractive lines that make them a natural choice for building structures. In addition, SHS can achieve a constant external dimension for all weights of a given size, which enables them to achieve standardisation of architectural and structural details throughout the full height of the building.
Celsius is the brand name for Corus Tubes hot-finished structural hollow sections, Celsius 355 being produced to the European Standard, EN 10210 S355J2H. Celsius sections are produced by the electric weld process and the J2 denotation signifies that they have a Charpy impact minimum average energy value of 27J at 20oC, making them suitable both for internal and external applications. Celsius sections are produced to the technical delivery requirements of EN 10210-1:1994 with dimensions and tolerances to EN 10210-2:1997. However, for Celsius sections, there is an improved corner profile of 2T maximum.
By filling hollow sections with concrete a composite section is produced (see Figure 1.1), which will increase the sections room temperature load carrying capacity, whilst retaining all the advantageous features of the basic unfilled section. Alternatively, for the same original load capacity, it permits smaller composite sections to be used. The reduction in section size also gives advantages in subsequent construction processes, including a reduced surface area for painting or fire protection. In the fire condition the presence of the concrete filling acts as a heat sink.
Concrete or grout filled hollow sections can be divided into those that are externally protected against fire by fire-rated boards, lightweight sprayed protection or intumescent coatings, and those that have no such protection. A further division can be made, by differentiating between those that are filled with plain concrete mixes and those that contain steel reinforcement within the mix.
Figure 1.1 Concrete filled square hollow section
Externally protected composite sections are designed compositely at room temperature and external fire protection is applied to achieve the required fire rating of the column. The composite action is maintained in the fire limit state, the external protection serving to limit the rise in steel temperature such that the column capacity is always in excess of the fire limit state design load over the required fire resistance period. In general, externally protected sections will not need to contain reinforcement in the mix in order to achieve the desired fire rating - reinforcement is usually added to such columns so to enhance axial capacity while minimising or maintaining column SHS size. Reductions in the thickness of the external protection are possible because of the heat sink effect, which effectively reduces the section factor of the column; these reductions have been shown to be substantial in the case of filled hollow sections with intumescent coatings. In cases where smaller columns are used, particularly if speed of construction is an issue, consideration should be given to sizing the SHS such as to use a plain fill with external protection, so that reinforcement can be dispensed with. Note that because of the tensile capacity of the steel in the composite column, in almost all cases, grout may be used interchangeably with concrete as the