Full Page Ad, 3mm Bleed Steel Designers' Manual - 6th Edition (2003) Contents Introduction to the sixth edition Contributors Notation xi xv xxv This material is copyright - all rights reserved Reproduced under licence from The Steel Construction Institute on 12/2/2007 To buy a hardcopy version of this document call 01344 872775 or go to http://shop.steelbiz.org/ SECTION 1: DESIGN SYNTHESIS Single-storey buildings Range of building types; Anatomy of structure; Loading; Design of common structural forms Multi-storey buildings Introduction; Factors influencing choice of form; Anatomy of structure; Worked example 42 Industrial steelwork Range of structures and scale of construction; Anatomy of structure; Loading; Structure in its wider context 94 Bridges Introduction; Selection of span; Selection of type; Codes of practice; Traffic loading; Other actions; Steel grades; Overall stability and articulation; Initial design; Worked example 124 Other structural applications of steel Towers and masts; Space frames; Cable structures; Steel in residential construction; Atria 169 SECTION 2: STEEL TECHNOLOGY Applied metallurgy of steel Introduction; Chemical composition; Heat treatment; Manufacture and effect on properties; Engineering properties and mechanical tests; Fabrication effects and service performance; Summary 222 Fracture and fatigue Fracture; Linear elastic fracture mechanics; Elastic–plastic fracture mechanics; Materials testing for fracture properties; Fracture-safe design; Fatigue 248 Sustainability and steel construction 275 Introduction; Economic impacts; Social impacts; Environmental impacts; Embodied energy; Operational energy; Summary iii Steel Designers' Manual - 6th Edition (2003) iv Contents SECTION 3: DESIGN THEORY Introduction to manual and computer analysis Introduction; Element analysis; Line elements; Plates; Analysis of skeletal structures; Finite element method 286 10 Beam analysis Simply-supported beams; Propped cantilevers; Fixed, built-in or encastré beams; Continuous beams; Plastic failure of single members; Plastic failure of propped cantilevers 325 11 This material is copyright - all rights reserved Reproduced under licence from The Steel Construction Institute on 12/2/2007 To buy a hardcopy version of this document call 01344 872775 or go to http://shop.steelbiz.org/ Plane frame analysis Formulae for rigid frames; Portal frame analysis 342 12 Applicable dynamics Introduction; Fundamentals of dynamic behaviour; Distributed parameter systems; Damping; Finite element analysis; Dynamic testing 354 SECTION 4: ELEMENT DESIGN 13 Local buckling and cross-section classification Introduction; Cross-sectional dimensions and moment–rotation behaviour; Effect of moment–rotation behaviour on approach to design and analysis; Classification table; Economic factors 373 14 Tension members Introduction; Types of tension member; Design for axial tension; Combined bending and tension; Eccentricity of end connections; Other considerations; Cables; Worked examples 383 15 Columns and struts Introduction; Common types of member; Design considerations; Cross-sectional considerations; Compressive resistance; Torsional and flexural-torsional buckling; Effective lengths; Special types of strut; Economic points; Worked examples 402 16 Beams Common types of beam; Cross-section classification and moment capacity, Mc; Basic design; Lateral bracing; Bracing action in bridges – U-frame design; Design for restricted depth; Cold-formed sections as beams; Beams with web openings; Worked examples 431 17 Plate girders Introduction; Advantages and disadvantages; Initial choice of crosssection for plate girders in buildings; Design of plate girders used in buildings to BS 5950: Part 1: 2000; Initial choice of cross-section for plate girders used in bridges; Design of steel bridges to BS 5400: Part 3; Worked examples 470 Steel Designers' Manual - 6th Edition (2003) Contents v Members with compression and moments Occurrence of combined loading; Types of response – interaction; Effect of moment gradient loading; Selection of type of cross-section; Basic design procedure; Cross-section classification under compression and bending; Special design methods for members in portal frames; Worked examples 511 19 This material is copyright - all rights reserved Reproduced under licence from The Steel Construction Institute on 12/2/2007 To buy a hardcopy version of this document call 01344 872775 or go to http://shop.steelbiz.org/ 18 Trusses Common types of trusses; Guidance on overall concept; Effects of load reversal: Selection of elements and connections; Guidance on methods of analysis; Detailed design considerations for elements; Factors dictating the economy of trusses; Other applications of trusses; Rigid-jointed Vierendeel girders; Worked examples 541 20 Composite deck slabs Introduction; Deck types; Normal and lightweight concretes; Selection of floor system; Basic design; Fire resistance; Diaphragm action; Other constructional features; Worked example 577 21 Composite beams Application of composite beams; Economy; Guidance on span-todepth ratios; Types of shear connection; Span conditions; Analysis of composite section; Basic design; Worked examples 601 22 Composite columns 651 Introduction; Design of encased composite columns; Design of concretefilled tubes; Worked example SECTION 5: CONNECTION DESIGN 23 Bolts Types of bolt; Methods of tightening and their application; Geometric considerations; Methods of analysis of bolt groups; Design strengths; Tables of strengths 671 24 Welds and design for welding 685 Advantages of welding; Ensuring weld quality and properties by the use of standards; Recommendations for cost reduction; Welding processes; Geometric considerations; Methods of analysis of weld groups; Design strengths 25 Plate and stiffener elements in connections Dispersion of load through plates and flanges; Stiffeners; Prying forces; Plates loaded in-plane 711 26 Design of connections Introduction; Simple connections; Moment connections; Summary; Worked examples 721 Steel Designers' Manual - 6th Edition (2003) vi 27 Contents Foundations and holding-down systems Foundations; Connection of the steelwork; Analysis; Holding-down systems; Worked examples 816 SECTION 6: OTHER ELEMENTS Bearings and joints Introduction; Bearings; Joints; Bearings and joints – other considerations 842 29 Steel piles Bearing piles; Sheet piles; Pile driving and installation; Durability 867 30 This material is copyright - all rights reserved Reproduced under licence from The Steel Construction Institute on 12/2/2007 To buy a hardcopy version of this document call 01344 872775 or go to http://shop.steelbiz.org/ 28 Floors and orthotropic decks Steel plate floors; Open-grid flooring; Orthotropic decks 906 SECTION 7: CONSTRUCTION 31 Tolerances Introduction; Standards; Implications of tolerances; Fabrication tolerances; Erection tolerances 917 32 Fabrication Introduction; Economy of fabrication; Welding; Bolting; Cutting; Handling and routeing of steel; Quality management 948 33 Erection Introduction; The method statement; Planning; Site practices; Site fabrication and modifications; Steel decking and shear connectors; Quality control; Cranes and craneage; Safety; Special structures 971 34 Fire protection and fire engineering Introduction; Standards and building regulations; Structural performance in fire; Developments in fire-safe design; Methods of protection; Fire testing; Fire engineering 1013 35 Corrosion and corrosion prevention The corrosion process; Effect of the environment; Design and corrosion; Surface preparation; Metallic coatings; Paint coatings; Application of paints; Weather-resistant steels; The protective treatment specification 1030 36 The Eurocodes The Eurocodes – background and timescales; Conformity with EN 1990 – basis of design; EC3 Design of steel structures; EC4 Design of composite steel and concrete structures; Implications of the Eurocodes for practice in the UK; Conclusions 1053 Steel Designers' Manual - 6th Edition (2003) Contents This material is copyright - all rights reserved Reproduced under licence from The Steel Construction Institute on 12/2/2007 To buy a hardcopy version of this document call 01344 872775 or go to http://shop.steelbiz.org/ Appendix Steel technology Elastic properties of steel European standards for structural steels Design theory Bending moment, shear and deflection tables for cantilevers simply-supported beams built-in beams propped cantilevers Bending moment and reaction tables for continuous beams Influence lines for continuous beams Second moments of area of two flanges rectangular plates a pair of unit areas Geometrical properties of plane sections Plastic modulus of two flanges rectangles Formulae for rigid frames Element design Explanatory notes on section dimensions and properties, bolts and welds General Dimensions of sections Section properties Bolts and welds Tables of dimensions and gross section properties Universal beams Universal columns Joists Universal bearing piles Hot-finished: circular hollow sections square hollow sections rectangular hollow sections Cold-formed: circular hollow sections square hollow sections rectangular hollow sections Asymmetric beams Parallel flange channels vii 1071 1072 1077 1079 1087 1094 1102 1105 1116 1118 1122 1124 1127 1128 1130 1148 1149 1151 1160 1166 1172 1175 1178 1181 1183 1185 1187 1190 1192 1195 1197 Steel Designers' Manual - 6th Edition (2003) This material is copyright - all rights reserved Reproduced under licence from The Steel Construction Institute on 12/2/2007 To buy a hardcopy version of this document call 01344 872775 or go to http://shop.steelbiz.org/ viii Contents Two parallel flange channels: laced back to back Equal angles Unequal angles Equal angles: back to back Unequal angles: long legs back to back Castellated universal beams Structural tees cut from universal beams Structural tees cut from universal columns Extracts from BS 5950: Part 1: 2000 Deflection limits (Section two: Table 8) Design strengths for steel (Section three: Table 9) Limiting width-to-thickness ratios for sections other than CHS and RHS (Section three: Table 11) Limiting width-to-thickness ratios for CHS and RHS (Section three: Table 12) Bending strengths (Section four: Tables 16 and 17) Strut table selection (Section four: Table 23) Compressive strength (Section four: Table 24) Connection design Bolt data Hole sizes Bolt strengths Spacing, end and edge distances Maximum centres of fasteners Maximum edge distances Back marks in channel flanges Back marks in angles Cross centres through flanges Bolt capacities Non-preloaded ordinary bolts in S275 Non-preloaded countersunk bolts in S275 Non-preloaded HSFG bolts in S275 Preloaded HSFG bolts in S275: non-slip in service Preloaded HSFG bolts in S275: non-slip under factored loads Preloaded countersunk HSFG bolts in S275: non-slip in service Preloaded countersunk HSFG bolts in S275: non-slip under factored loads Non-preloaded ordinary bolts in S355 Non-preloaded countersunk bolts in S355 Non-preloaded HSFG bolts in S355 Preloaded HSFG bolts in S355: non-slip in service Preloaded HSFG bolts in S355: non-slip under factored loads 1201 1202 1203 1204 1206 1207 1208 1214 1218 1220 1221 1222 1223 1224 1227 1228 1236 1236 1237 1237 1238 1240 1240 1241 1242 1244 1246 1247 1248 1249 1250 1251 1253 1255 1256 1257 Steel Designers' Manual - 6th Edition (2003) Contents ix This material is copyright - all rights reserved Reproduced under licence from The Steel Construction Institute on 12/2/2007 To buy a hardcopy version of this document call 01344 872775 or go to http://shop.steelbiz.org/ Preloaded countersunk HSFG bolts in S355: non-slip in service Preloaded countersunk HSFG bolts in S355: non-slip under factored loads Bolt and weld groups Bolt group moduli – fasteners in the plane of the force Bolt group moduli – fasteners not in the plane of the force Weld group moduli – welds in the plane of the force Capacities of fillet welds Weld group moduli – welds not in the plane of the force 1258 1260 1264 1266 1270 1271 Other elements Sheet pile sections Larssen sections Frodingham sections Box sheet piles High modulus piles H-piles Floor plate design tables 1274 1275 1276 1277 1279 1280 1259 Construction Fire information sheets Section factors for universal beams universal columns circular hollow sections rectangular hollow sections rectangular hollow sections (square) Minimum thickness of spray protection Basic data on corrosion 1302 1303 1304 1305 1306 1307 1308 Codes and standards British and European standards covering the design and construction of steelwork 1311 Index 1323 1282 Full Page Ad, 3mm Bleed Steel Designers' Manual - 6th Edition (2003) 36 Single-storey buildings Roof systems Current Part L 2007 U Value 0.45 W/m2K 0.35 W/m2K 0.16 W/m2K Current Part L 2007 0.45 W/m2K 0.35 W/m2K 0.25 W/m2K This material is copyright - all rights reserved Reproduced under licence from The Steel Construction Institute on 12/2/2007 To buy a hardcopy version of this document call 01344 872775 or go to http://shop.steelbiz.org/ Wall systems As a consequence of the above, the insulation thickness in either composite, glass fibre or rock fibre cladding systems will significantly increase This will have an effect on the dead load that is applied to the supporting structure, and could result in some nominal increases in section sizes of the primary and secondary steelwork of the building 1.4.8.2 Air leakage index It will be mandatory for buildings to be designed and constructed so that an air leakage index will not be exceeded This index will be set at a specific value of volume of air leakage per hour per square metre of external surface at a pressure difference of 50 pascals Present proposals for this air leakage index are as follows: Maximum leakage rate: Maximum leakage rate: December 2002 2007 10.0 m3/hr/m2 @ 50 Pa 5.0 m3/hr/m2 @ 50 Pa To achieve the above, care must be taken to specify and effectively construct sealed junctions between elements, thereby minimizing air leakage The air leakage index will be quantified by in situ air pressurization tests, using fans, which must always be used on buildings with a floor area that exceeds 1000 m2 Should the building fail the test, remedial measures must be undertaken, and further tests carried out until the building is deemed to comply to the satisfaction of building control 1.4.8.3 ‘As-built’ inspections In order that the revised insulation standards are adhered to, it will be necessary to ensure that the provision of insulation within the fabric itself does not exhibit zones that could compromise the specification For example, there should be no signifi- Steel Designers' Manual - 6th Edition (2003) Design of common structural forms 37 cant leakage paths between panels; thermal bridges should be minimized; insulation should be continuous, dry and as ‘uncompressed’ as possible One method of ascertaining compliance would be by use of infra-red thermography, where the external fabric of the building is ‘photographed’ using specialist equipment By this method, areas of the external fabric that are ‘hot’ – implying poor insulation and heat loss from the building – will be shown as colours at the red end of the spectrum Conversely, areas that are ‘cold’ will be shown at the blue end of the spectrum This material is copyright - all rights reserved Reproduced under licence from The Steel Construction Institute on 12/2/2007 To buy a hardcopy version of this document call 01344 872775 or go to http://shop.steelbiz.org/ 1.4.8.4 Whole building design As the title of this subsection suggests, the building should be designed taking due account of how the constituent parts interact with each other To this end, insulation, air tightness, windows, doors and rooflights, heating systems and the like should not be viewed as individual elements, but rather as elements that, in some way, have influence on the in-service performance of each other 1.4.8.5 Material alterations Material alteration is intended to cover substantial works to existing buildings that were designed and constructed prior to the changes in Approved Document Part L For example, should major works be required to roof or wall cladding, it will be necessary to provide insulation to achieve the U value of a new building Following on from the latter eventuality will be the need to make provision for improving the building’s air-tightness The replacement of doors and windows will also entail the use of products that meet the requirements of new buildings, as too will the installation of new heating systems, for example 1.4.8.6 Building log books and energy meters The building owner will initially be provided with details of all the products that constitute the building, including a forecast of annual energy consumption based on the building design specification The owner in turn will be required to keep detailed maintenance records and the like to ensure that the products within the building are properly maintained, and, when replaced, fully comply with the new requirements Steel Designers' Manual - 6th Edition (2003) 38 Single-storey buildings Energy meters should be provided to ensure that comparisons of energy consumption can be made with those forecast at design stage These meters in turn will provide any new owner/tenant with detailed information on which to base future energy forecasts The cladding has also to withstand the applied loads of snow, wind, and foot traffic during fixing and maintenance It must also provide the necessary lateral stability to the supporting purlin and siderail systems Occasionally it will form part of the lateral stability of the structure in the form of a stressed-skin diaphragm, mentioned above This material is copyright - all rights reserved Reproduced under licence from The Steel Construction Institute on 12/2/2007 To buy a hardcopy version of this document call 01344 872775 or go to http://shop.steelbiz.org/ 1.4.8.7 Cladding systems A variety of systems is available to suit environmental and financial constraints The most common are listed below Single-skin trapezoidal roofing This was widely used in the past with plasterboard or similar material as the lining material, and fibreglass insulation in the sandwich The construction is susceptible to the plasterboard becoming damp due to condensation An alternative is the use of rigid insulation boards, which are impervious to damp, supported on tee bars between the purlins Unless the joints are sealed, which is difficult to achieve, condensation is likely to form Although inexpensive, this type is therefore limited in its applicability The minimum slope is governed by the need to provide watertight joints and fasteners If manufacturers’ instructions on the use of sealants and stitching to laps are rigorously followed, this type can be used down to slopes of approximately 4° Double-shell roof construction In this form of construction the plasterboard has been replaced by a steel liner sheet of 0.4 mm thickness with some stiffening corrugations The lining is first installed and fastened to the purlins, followed by the spacing Zeds, insulation and outer sheet The liner tray is not designed to take full wind and erection loads, and therefore large areas should not be erected in advance of the outer skin The liner tray is normally supplied in white polyester finish, providing a pleasing internal finish The weatherproofing criteria are the same as for single-skin systems and generally the minimum slope is 4° Differing thicknesses of insulation are accommodated by varying spacer depths The norm is 80 mm of fibreglass giving a nominal U value of 0.44 W/m2 °C Steel Designers' Manual - 6th Edition (2003) Design of common structural forms 39 This material is copyright - all rights reserved Reproduced under licence from The Steel Construction Institute on 12/2/2007 To buy a hardcopy version of this document call 01344 872775 or go to http://shop.steelbiz.org/ Standing seam systems The traditional forms of construction described above suffer from the inherent disadvantage of having to be fixed by screw-type fasteners penetrating the sheet Traditional fixing methods also limit the length of sheet that can be handled even if, in theory, long lengths can be rolled; thus laps are required The need for weathertightness at the lap constrains the minimum slope A 5000 m2 traditional roof has 20 000 through fasteners and has to resist around million gallons of water a year The difficulty in ensuring that this large number of fasteners is watertight demonstrates the desirability of minimizing the number of penetrations This has led to the development of systems having concealed fastenings and the ability to roll and fix long lengths In order to cater for the thermal expansion in sheets, which may be 30 m long, the fastenings are in the form of clips which, while holding down the sheeting, allow it to move longitudinally.As discussed elsewhere, this may reduce the restraint available to the purlins and affect their design When used in double-skin configuration the liner panel is normally conventionally fastened and provides sufficient restraint The available permutations are too numerous to give general rules but purlin manufacturers will give advice It is necessary to fasten the sheets to the structure at one point to resist downslope forces and progressive movement during expansion and contraction With the through fasteners reduced to the minimum and laps eliminated or specially detailed, roof slopes as low as 1° (after deflection) can be utilized The roofs must be properly maintained since accumulation of debris is more likely and ponding leads to a reduced coating life Standing seam systems are used to replace the traditional trapezoidal outer sheets in single- and double-skin arrangements as described earlier Composite panels This most recent development in cladding systems provides solutions for many of the potential problems with metal roofing The insulating foam is integral with the sheets and so totally fills the cavity, and with good detailing at the joints condensation can be eliminated in most environments The strength of the panel is dependent on the composite action of the two metal skins in conjunction with the foam Theoretical calculations are possible although there are no codified design procedures Since both steel and foam properties can vary, and these are predetermined by the manufacturer, it is a question of selecting the panels from load tables provided rather than individual design In addition to having to resist external loads, the effects of temperature differential must be taken into account The critical combinations are wind suction with summer temperatures and snow acting with winter temperatures The range of temperature considered is dependent on the colour and hence heat absorption of the outer skin; darker colours for roofs should only be considered in conjunction with the manufacturer, if at all Steel Designers' Manual - 6th Edition (2003) 40 Single-storey buildings This material is copyright - all rights reserved Reproduced under licence from The Steel Construction Institute on 12/2/2007 To buy a hardcopy version of this document call 01344 872775 or go to http://shop.steelbiz.org/ Both standing seam and traditional trapezoidal forms are available with the same slope restrictions as non-composite forms A particular advantage is the erectability of the panels, which is a one-pass operation and, therefore, a rapid process This is combined with inherent robustness and walkability Since the integrity of the panel is important, and it is difficult to inspect the foam and its adhesion once manufactured, quality control of the materials and manufacturing environment in terms of temperature and dust control is vital Reputable manufacturers should, therefore, be specified and their manufacturing methods ascertained External firewall Where buildings are close to the site boundary the Building Regulations require that the construction is such that reasonable steps are taken to prevent fire spreading to adjacent property It has been demonstrated by tests that walls of double-skin steel construction with fibreglass or mineral wool insulation can achieve a four hour fire rating The siderails and fixings require special details which were included in the test arrangements of the particular manufacturer and it is important that these are followed closely They include such things as providing slotted holes to allow expansion of the rails rather than induce buckling, which may allow gaps to open in the sheeting at joints References to Chapter 1 Horridge, J.F (1985) Design of Industrial Buildings Civil Engineering Steel Supplement, November British Standards Institution (1998) Part 3: Code of practice for imposed roof loads BS 6399 BSI, London British Standards Institution (1997) Part 2: Code of practice for wind loads BS 6399 BSI, London British Standards Institution (2000) Part 1: Code of practice for design – Rolled and welded sections BS 5950 BSI, London King C.M (2001) In-plane Stability of Portal Frames to BS 5950-1 : 2000 (SCI-P292) The Steel Construction Institute, Ascot British Standards Institution (1998) Part 5: Code of practice for design of cold formed thin gauge sections BS 5950 BSI, London Steel Designers' Manual - 6th Edition (2003) References 41 This material is copyright - all rights reserved Reproduced under licence from The Steel Construction Institute on 12/2/2007 To buy a hardcopy version of this document call 01344 872775 or go to http://shop.steelbiz.org/ Davies J.M & Raven G.K (1986) Design of cold formed purlins Thin Walled Metal Structures in Buildings, pp 151–60 IABSE Colloquium, Zurich, Switzerland The Building Regulations (2002) Part L: Conservation of Fuel and Power HMSO, London Steel Designers' Manual - 6th Edition (2003) Chapter Multi-storey buildings by ALAN HART and PHILIP PEACOCK This material is copyright - all rights reserved Reproduced under licence from The Steel Construction Institute on 12/2/2007 To buy a hardcopy version of this document call 01344 872775 or go to http://shop.steelbiz.org/ 2.1 Introduction The term multi-storey building encompasses a wide range of building forms This chapter reviews some of the factors that should be considered when designing the type of multi-storey buildings commonly found in Europe, namely those less than 15 storeys in height Advice on designing taller buildings may be found in the references to this chapter.1–5 2.1.1 The advantages of steel In recent years the development of steel-framed buildings with composite metal deck floors has transformed the construction of multi-storey buildings in the UK During this time, with the growth of increasingly sophisticated requirements for building services, the very efficiency of the design has led to the steady decline of the cost of the structure as a proportion of the overall cost of the building, yet the choice of the structural system remains a key factor in the design of successful buildings The principal reasons for the appeal of steel for multi-storey buildings are noted below • • • • • • • Steel frames are fast to erect The construction is lightweight, particularly in comparison with traditional concrete construction The elements of the framework are prefabricated and manufactured under controlled, factory conditions to established quality procedures The accuracy implicit in the manufacturing process by which the elements are produced enables the designer to take a confident view of the geometric properties of the erected framework The dryness of the form of construction results in less on-site activities, plant, materials and labour The framework is not susceptible to drying-out movement or delays due to slow strength gain Steel frames have potential for adaptability inherent in their construction Later 42 Steel Designers' Manual - 6th Edition (2003) Introduction • 43 modification to a building can be achieved relatively easily by unbolting a connection; with traditional concrete construction such modifications would be expensive, and more extensive and disruptive The use of steel makes possible the creation of large, column-free internal spaces which can be divided by partitions and, by eliminating the external wall as a loadbearing element, allows the development of large window areas incorporated in prefabricated cladding systems This material is copyright - all rights reserved Reproduced under licence from The Steel Construction Institute on 12/2/2007 To buy a hardcopy version of this document call 01344 872775 or go to http://shop.steelbiz.org/ 2.1.2 Design aims For the full potential of the advantages of steel-frame construction to be realized, the design of multi-storey buildings requires a considered and disciplined approach by the architects, engineers and contractors involved in the project They must be aware of the constraints imposed on the design programme by the lead time between placing a contract for the supply of the steel frame and the erection of the first pieces on site The programme should include such critical dates on information release as are necessary to ensure that material order and fabrication can progress smoothly The designer must recognize that the framework is the skeleton around which every other element of the building will be constructed The design encompasses not only the structure but also the building envelope, services and internal finishes All these elements must be co-ordinated by a firm dimensional discipline, which recognizes the modular nature of the components, to ensure maximum repetition and standardization Consequently it is impossible to consider the design of the framework in isolation It is vital to see the frame as part of an integrated building design from the outset: the most efficient solution for the structure may not be effective in achieving a satisfactory solution for the total building In principle, the design aims can be considered under three headings: • • • Technical Architectural Financial Technical aims The designer must ensure that the framework, its elements and connections are strong enough to withstand the applied loads to which the framework will be subjected throughout its design life The system chosen on this basis must be sufficiently robust to prevent the progressive collapse of the building or a significant part of it under accidental loading This is the primary technical aim However, as issues related to strength have become better understood and techniques for the strength design of frameworks have been formalized, designers have progressively used Steel Designers' Manual - 6th Edition (2003) 44 Multi-storey buildings lighter and stronger materials This has generated a greater need to consider serviceability, including dynamic floor response, as part of the development of the structural concept Other important considerations are to ensure adequate resistance to fire and corrosion The design should aim to minimize the cost, requirements and intrusion of the protection systems on the efficiency of the overall building This material is copyright - all rights reserved Reproduced under licence from The Steel Construction Institute on 12/2/2007 To buy a hardcopy version of this document call 01344 872775 or go to http://shop.steelbiz.org/ Architectural aims For the vast majority of buildings the most effective structural steel frame is the one which is least obtrusive In this way it imposes least constraint on internal planning, and produces maximum usable floor area, particularly for open-plan offices It also provides minimal obstruction to the routeing of building services This is an important consideration, particularly since building services are becoming more extensive and demanding on space and hence on the building framework Occasionally the structure is an essential feature of the architectural expression of the building Under these circumstances the frame must achieve, among other aims, a balance between internal planning efficiency and an expressed structural form However, these buildings are special, not appropriate to this manual, and will not be considered in more detail, except to give a number of references Financial aims The design of a steel frame should aim to achieve minimum overall cost This is a balance between the capital cost of the frame and the improved revenue from early occupation of the building through fast erection of the steel frame: a more expensive framework may be quicker to build and for certain uses would be more economic to a client in overall terms Commercial office developments are a good example of this balance Figure 2.1 shows a breakdown of construction costs for a typical development 2.1.3 Influences on overall design concept Client brief Clients specify their requirements through a brief It is essential for effective design to understand exactly the intentions of the client: the brief is the way in which the client expresses and communicates these intentions As far as the frame designer is concerned, the factors which are most important are intended use, budget cost limits, time to completion and quality Once these are understood a realistic basis for producing the design will be established The designer should recognize however that in practice the brief is likely to evolve as the design develops Steel Designers' Manual - 6th Edition (2003) This material is copyright - all rights reserved Reproduced under licence from The Steel Construction Institute on 12/2/2007 To buy a hardcopy version of this document call 01344 872775 or go to http://shop.steelbiz.org/ Introduction 45 Fabric A Demolition Piling foundations and concrete work 11% B Steel Frame Deck and Fire Protection 10% C Brickwork and Drywalling 4% D External and internal Cladding and Sunscreens 22% E Roofing and Rooflights 5% 52% Finishes F Ceiling and Floors 7% G Stone 5% H Others 8% 20% Fig 2.1 Services I Plumbing and Sprinklers 4% J H.V.A.C .12% K Electrics 8% L Lifts 4% 28% Typical cost breakdown Statutory constraints The design of all buildings is subject to some form of statutory constraint Multistorey buildings, particularly those in an urban environment, are subject to a high level of constraint, which will generally be included in the conditions attached to the granting of outline planning permission The form and degree that this may take could have significant impact on the frame design For example, street patterns and lighting restrictions may result in a non-rectilinear plan with a ‘stepped-back’ structure If an appropriate layout is to be provided it is vital to understand these constraints from the outset Certain government buildings, financial headquarters and other strategically sensitive buildings may need to be designed to resist terrorist threats Provision may be in the form of blast-resistant flows, walls and facades to vulnerable areas Physical factors The building must be designed to suit the parameters determined by its intended use and its local environment Steel Designers' Manual - 6th Edition (2003) 46 Multi-storey buildings Its intended use will dictate the intensity of imposed loadings, the fire protection and corrosion resistance requirements and the scope of building services Certain government buildings, financial headquarters and other strategically sensitive buildings may need to be designed to resist terrorist threats Provision may be in the form of blast-resistant oors, walls and faỗades to vulnerable areas The local environment will dictate the lateral load requirements but more importantly it will determine the nature of the existing ground conditions To achieve overall structural efficiency it is essential that the structural layout of the frame is responsive to the constraints imposed by these ground conditions These factors are considered in more detail in the next section This material is copyright - all rights reserved Reproduced under licence from The Steel Construction Institute on 12/2/2007 To buy a hardcopy version of this document call 01344 872775 or go to http://shop.steelbiz.org/ 2.2 Factors influencing choice of form Environmental There are a number of factors which influence the choice of structural form that are particular to the site location These can have a dominant effect on the framing arrangement for the structure The most obvious site-dependent factors are related to the ground conditions A steel-framed building is likely to be about 60% of the weight of a comparable reinforced concrete building This difference will result in smaller foundations with a consequent reduction on costs In some cases this difference in weight enables simple pad foundations to be used for the steel frame where the equivalent reinforced concrete building would require a more complex and expensive solution For non-uniformly loaded structures it will also reduce the magnitude of differential settlements and for heavily loaded structures may make possible the use of a simple raft foundation in preference to a large capacity piled solution (Fig 2.2) Difficult ground conditions may dictate the column grid Long spans may be required to bridge obstructions in the ground Such obstructions could include, for example, buried services, underground railways or archaeological remains Generally, a widely spaced column grid is desirable since it reduces the number of foundations and increases the simplicity of construction in the ground Other site-dependent constraints are more subtle In urban areas they relate to the physical constraints offered by the surrounding street plan, and the rights of light of adjoining owners They also relate to the planning and architectural objectives for specific sites The rights of light issues or planning considerations may dictate that upper floors are set back from the perimeter resulting in stepped construction of the upper levels Invariably the resulting framing plan is not rectilinear and may have skew grids, cantilevers and re-entrant corners These constraints need to be identified early in the design in order that they are accommodated efficiently into the framing For example, wherever possible, stepped-back faỗades should be arranged so that steps take place on the column grid and hence avoid the need for heavy bridging structures In other situations the designer should always investigate ways in which the impact of lack of uniformity in building form can be contained within a simple structural framing system which generates a minimum of element variations and produces simple detailing Steel Designers' Manual - 6th Edition (2003) Factors influencing choice of form 47 This material is copyright - all rights reserved Reproduced under licence from The Steel Construction Institute on 12/2/2007 To buy a hardcopy version of this document call 01344 872775 or go to http://shop.steelbiz.org/ 20% reduction approximate rot t foundation Fig 2.2 piled foundation Foundation savings Building use The building use will dictate the planning module of the building, which will in turn determine the span and column grids Typical grids may be based on a planning module of 600/1200 mm or 500/1500 mm However, the use has much wider impact, particularly on floor loadings and building services The structural arrangement, and depth selected, must satisfy and accommodate these requirements For example, financial-dealing floors require clear open spaces located on the lower floors, which would dictate a different structural solution to the rest of the building.This may necessitate the use of a transfer structure to carry the upper floors on an economical column grid (Fig 2.3) Floor loadings Because steel-framed buildings are relatively light in weight, excessive imposed loadings will have a greater effect on the sizing of structural components, particularly floor beams, than with reinforced concrete structures The floor loadings to be supported by the structure have two components: • The permanent or dead loading comprising the self-weight of the flooring and the supporting structure together with the weight of finishes, raised flooring, ceiling, air-conditioning ducts and equipment Steel Designers' Manual - 6th Edition (2003) Multi-storey buildings Fig 2.3 This material is copyright - all rights reserved Reproduced under licence from The Steel Construction Institute on 12/2/2007 To buy a hardcopy version of this document call 01344 872775 or go to http://shop.steelbiz.org/ 48 Typical load transfer systems • The imposed loading, which is the load that the floor is likely to sustain during its life and which will depend on the building use Imposed floor loads for various types of building are governed by BS 6399 but the standard loading for office buildings is usually kN/m2 with an additional allowance of kN/m2 for movable partitioning For normal office loadings, dead and imposed loadings are roughly equal in proportion but higher imposed load allowances will be necessary in plantrooms or to accommodate special requirements such as storage or heavy equipment Floor beams will be designed to limit deflection under the imposed loadings British Standard BS 5950 governing the design of structural steelwork sets a limit for deflection under imposed loading of (span/200) generally and (span/360) where there are brittle finishes Edge beams supporting cladding will be subject to restriction on deflection of 10–15 mm Deflections may be noticeable in the ceiling layout and should be taken into account when determining the available clearance for service routes The designer should therefore check the cumulative effect of deflections in the individual members of a floor system although the actual maximum displacement is in practice almost always less than that predicted In some instances, vibrations of floor components may cause discomfort or affect sensitive equipment, and the designer should check the fundamental response of the floor system The threshold of perceptible vibrations in building is difficult to define, and present limits are rather arbitrary There is some evidence that modern lightweight floors can be sensitive to dynamic loads, which may have an effect on delicate equipment However, in most situations a simple check on the natural frequency of the floor system is all that is required Building services and finishes In buildings requiring anything other than minimal electrical services distribution, the inter-relationship of the structure, the mechanical and electrical services and the building finishes will need to be considered together from the outset Steel Designers' Manual - 6th Edition (2003) This material is copyright - all rights reserved Reproduced under licence from The Steel Construction Institute on 12/2/2007 To buy a hardcopy version of this document call 01344 872775 or go to http://shop.steelbiz.org/ Factors influencing choice of form 49 It is essential to co-ordinate the details of the building services, cladding and structure at an early stage of the project in order to produce a building which is simple to fabricate and quick to erect Apparently minor variations to the steelwork, brought about by services and finishes requirements defined after a steel fabrication contract has been let, can have a disproportionate effect on the progress of fabrication and erection Steel buildings impose a strict discipline on the designer in terms of the early production of final design information If the designer fails to recognize this, the advantages of steel-framed building cannot be realized The integration of the building services with the structure is an important factor in the choice of an economic structural floor system The overall depth of the floor construction will depend on the type and distribution of services in the ceiling void The designer may choose to separate the structural and services zones or accommodate the services by integrating them with the structure, allowing for the structural system to occupy the full depth of the floor construction (See Fig 2.4.) Separation of zones usually requires confining the ducts, pipes and cables to a horizontal plane below the structure, resulting in either a relatively deep overall floor construction or close column spacings Integration of services with structure requires either deep perforated structural components or vertical zoning of the services and structure For the range of structural grids used in conventional building, traditional steel floor construction is generally deeper than the equivalent reinforced concrete flat slab: the difference is generally 100–200 mm for floor structures which utilize composite action and greater for non-composite floors (Fig 2.5) The increased depth is only at the beam position; elsewhere, between beams, the depth is much less and the space between them may accommodate services, particularly if the beams may be penetrated (Fig 2.6) The greater depth of steel construction does not therefore necessarily result in an increase in building height if the services are integrated within the zone occupied by the structure A number of possible solutions exist for raised floor raised floor slob slab structure +I services zone I+ (b) structure and services ceiling ceiling Fig 2.4 Building services and floor structure: (a) separation of services and structure; (b) integration of services and structure ... channels vii 10 71 1072 10 77 10 79 10 87 10 94 11 02 11 05 11 16 11 18 11 22 11 24 11 27 11 28 11 30 11 48 11 49 11 51 116 0 11 66 11 72 11 75 11 78 11 81 118 3 11 85 11 87 11 90 11 92 11 95 11 97 Steel Designers'' Manual - 6th... loads 12 01 1202 12 03 12 04 12 06 12 07 12 08 12 14 12 18 12 20 12 21 1222 12 23 12 24 12 27 12 28 12 36 12 36 12 37 12 37 12 38 12 40 12 40 12 41 1242 12 44 12 46 12 47 12 48 12 49 12 50 12 51 1253 12 55 12 56 12 57 Steel. .. corrosion 13 02 13 03 13 04 13 05 13 06 13 07 13 08 Codes and standards British and European standards covering the design and construction of steelwork 13 11 Index 13 23 12 82 Full Page Ad, 3mm Bleed Steel