Aluminium Design and Construction John Dwight

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1. Elastic design. The structure is analysed under working load, and stress levels are determined. These must not exceed an allowable stress, which is obtained by dividing the material strength (usually the yield or proof stress) by a factor of safety (FS). For slender members, the allowable stress is reduced to allow for buckling. 2. Limit state design. The structure is assumed to be acted on by factored (up) loading, equal to working loads each multiplied by a loading factor. It is analysed in this condition and a value obtained for the resulting ‘action-effect’ (i.e. axial force, moment, shear force, etc.) arising in its various components. In any component, the actioneffect, thus found, must not exceed the factored (down) resistance for that component, equal to its calculated resistance divided by the material factor. By ‘calculated resistance’ is meant the estimated magnitude of the relevant action-effect necessary to cause failure of that component. What really matters to the user of a structure is its actual safety against collapse. How much overload can it take above the working load before it fails? Safety may be expressed in terms of the quantity LFC. A sensible code is one providing a consistent value of LFC. Too high an LFC is oversafe, and means loss of economy. Too low an LFC is undersafe. By the very way it is formulated limit state design produces a consistent LFC. Elastic Figure 5.1 Static strength: (a) elastic design (S1=material strength, S2=allowable stress, S3=stress arising at nominal working load); (b) limit state design. Copyright 1999 by Taylor & Francis Group. All Rights Reserved.
design does not, because stress at working load is not necessarily an indication of how near a component is to actual failure. 5.1.4 Serviceability limit state The reason for considering this limit state is to ensure that the structure has adequate stiffness, the requisite calculations being usually performed with the structure subjected to unfactored nominal loading. It is usually concerned with the performance of members rather than joints. When a member is first taken up to its nominal working load, its deformation comprises two components: an irrecoverable plastic deflection and a recoverable elastic one (Figure 5.2). The main causes for the plastic deflection are the presence of softened zones next to welds (Chapter 6) and the rounded stress-strain curve. Further factors are local stress concentrations and locked-in stresses, which also lead to premature yielding (as in steel). The serviceability check for a member simply consists of ensuring that its elastic deflection does not exceed an acceptable value: where � E =predicted elastic deflection under nominal loading, and � � E � L (5.5) L =limiting or permitted deflection. A specific design calculation for the plastic deflection (under the initial loading) is never made. This is because it is usually small, and disappears on subsequent applications of the load. However, with materials having a very rounded stress-strain curve, the initial plastic deformation tends to be more pronounced, and there is a danger that it may be unacceptable. We cover this possibility in design by arbitrarily decreasing the limiting Figure 5.2 Elastic (� E ) and plastic (� P ) components of deflection at nominal working load. Copyright 1999 by Taylor & Francis Group. All Rights Reserved.
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Aluminium Design and Construction C
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First published 1999 by E & FN Spon
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2.2.1 Rolling mill practice 2.2.2 P
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5 Limit state design and limiting s
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8.2.6 Use of interpolation for semi
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10.3.2 Inertias for a section with
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Preface Aluminium is easily the sec
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List of symbols The following symbo
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uu, vv principal axes w effective s
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1.1.3 The industrial metal It is on
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where A is the section area (mm 2 )
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1.3.1. The good points about alumin
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Deflection Because of the lower mod
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1.4.4 Establishment of the alloys I
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1.5.2 New technology Most of alumin
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large span, where self-weight is a
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These tend to be in all-aluminium c
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Close-up of the M-dec system, which
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Aluminium glazing system for commer
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Nat West Media Centre, Lords Cricke
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The main requirements for the produ
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in which t and w are in mm. These a
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Figure 2.1 Extrusion process (direc
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Figure 2.2 Typical extrusion die. t
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Figure 2.6 ‘Semi-hollow’ profil
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especially the stronger alloys in t
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Figure 2.9 Conventional profiles. 2
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2.4 TUBES By tubes we mean hollow s
Page 57 and 58: CHAPTER 3 Fabrication 3.1 PREPARATI
Page 59 and 60: Figure 3.1 Alternative designs for
Page 61 and 62: Figure 3.2 Thread insert. a coil-sp
Page 63 and 64: 3.3 ARC WELDING 3.3.1 Use of arc we
Page 65 and 66: adjusted. The technique is claimed
Page 67 and 68: For welds of minimum or fatigue qua
Page 69 and 70: Figure 3.5 Friction-stir welding: s
Page 71 and 72: are, and the designer/fabricator mu
Page 73 and 74: cartridge, and mixing takes place a
Page 75 and 76: 3.7.4 Painting Alloys having durabi
Page 77 and 78: Where a range is given, as for the
Page 79 and 80: will be only slightly above that fo
Page 81 and 82: heating the metal to a temperature
Page 83 and 84: Table 4.4 Characteristics of differ
Page 85 and 86: softening in the heat-affected zone
Page 87 and 88: 60 alloys, are: BSEN.485 plate and
Page 89 and 90: Firure 4.3 Nominal composition and
Page 91 and 92: popular alloys in the series are: 6
Page 93 and 94: Figure 4.6 Variation of tensile str
Page 95 and 96: undercarriages of aircraft. They ar
Page 97 and 98: Figure 4.11 Minimum stress-strain c
Page 99 and 100: AC.51400 This is another non-heat-t
Page 101 and 102: times that of the actual pits) prod
Page 103 and 104: The severity of bimetallic corrosio
Page 105 and 106: Nominal loading. Nominal loads are
Page 107: 2. Material factor (� m ). In the
Page 111 and 112: Table 5.2 Summary of limiting stres
Page 113 and 114: Figure 5.4 Plastic strain at workin
Page 115 and 116: example, a reduced value might be t
Page 117 and 118: The parameter � depends purely on
Page 119 and 120: CHAPTER 6 Heat-affected zone soften
Page 121 and 122: area of softening. With 7xxx-type m
Page 123 and 124: Figure 6.3 Typical hardness plots a
Page 125 and 126: 6.4 SEVERITY OF HAZ SOFTENING 6.4.1
Page 127 and 128: Figure 6.6 Categories of welded joi
Page 129 and 130: Figure 6.10 One-inch rule, extent o
Page 131 and 132: e allowed for in design by replacin
Page 133 and 134: Figure 6.13 Predicted area (A z ) o
Page 135 and 136: Figure 6.15 Overlapping HAZs. nomin
Page 137 and 138: In determining A zp , an appropriat
Page 139 and 140: failure plane in the HAZ, close to
Page 141 and 142: With MIG welding, an electrode-posi
Page 143 and 144: CHAPTER 7 Plate elements in compres
Page 145 and 146: (a) Compression member elements The
Page 147 and 148: Table 7.1 Classification of element
Page 149 and 150: Figure 7.4 Slender internal element
Page 151 and 152: Figure 7.7 shows curves of � ° p
Page 153 and 154: (7.9a) (7.9b) The strain gradient c
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Page 157 and 158: Figure 7.13 Outstands under strain-
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Figure 7.15 Reinforced elements. Th
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Figure 7.18 Stiffener location for
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Figure 7.20 Slender reinforced inte
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CHAPTER 8 Beams 8.1 GENERAL APPROAC
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8.2.2 Section classification The di
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that for the gross section. It woul
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the usual manner. Line 1 in the fig
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1. Fully compact sections. The limi
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Figure 8.8 Transverse and longitudi
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8.3.4 Shear resistance of bars and
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Figure 8.12 Tension-field action. i
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Figure 8.14 Moment/shear interactio
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depending on the estimated degree o
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where a is the stiffener spacing an
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plates (if fitted), p v =limiting m
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ending moment diagram. Two cases ar
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Figure 8.23 Sections covered in Tab
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where: I yy , I vv =inertia about m
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post (Section 8.6.4) or by some oth
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Figure 8.26 Components of deflectio
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9.1.2 Classification of the cross-s
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hole. Alternatively, it might fail
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Figure 9.2 Limiting stress p b for
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The determination of l involves a c
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Figure 9.6 Monosymmetric section. I
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Figure 9.9 Limiting stress p b for
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where s=� s /� t s =slenderness
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Figure 9.11 Type-R sections covered
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Figure 9.14 Four standardized profi
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9.7.2 Secondary bending in trusses
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Table 9.5 Necessary checks for memb
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Figure 9.18 Axial load with biaxial
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1. Tension members. The localized f
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Figure 10.1 Symmetric plastic bendi
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We now turn to monosymmetric sectio
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distance of its centroid from the n
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Figure 10.6 Elements of sections. I
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10.3.3 Product of inertia The produ
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Usually the conditions are such as
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Table 10.2 Torsion constant. Factor
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Figure 10.12 Warping. Conventional
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where b, t=element width and thickn
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10.5.3 Evaluation of warping When t
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For sections where the position of
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(10.31) where: e=distance that S li
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10.5.9 Asymmetric sections Before s
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CHAPTER 11 Joints This chapter cons
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the use of limiting stresses taken
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and the summation is made for all t
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Figure 11.3 Interaction diagram for
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k in order to give a fair compariso
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3. The design is satisfactory if fo
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When the method of surface preparat
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11.3.3 Weld force arising In many c
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Table 11.6 Limiting stress p w (N/m
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where p a =limiting stress for unwe
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Figure 11.11 Interaction diagram fo
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Manufacturers of structural adhesiv
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11.4.6 Creep Shear strength figures
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Figure 11.15 Effect of glue-line th
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Table 11.7 and Figure 11.17 provide
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11.4.11 Resistance calculations for
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high value reflects the various unc
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therefore usually presented in term
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For example: The loading spectrum i
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act on the structure. However, BS.8
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Figure 12.4 Crack propagation: (a)
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12.5 CLASSIFICATION OF DETAILS 12.5
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i.e. a joint extending in the same
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when the design life is low or when
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Methods (2) and (3) are difficult t
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it reverts to line 1. The slope s o
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Aluminium Design and Construction John Dwight

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