Chapter XVIII: Conclusion

In bringing these chapters, dealing largely with questions affecting maintenance, to a close, it may be well to draw attention to the fact that economy in design (apart from improper reduction of sections) goes hand-in-hand with economy of upkeep. Given good material, that which favours low first cost, simplicity of detail, fewness of parts, absence of smithing, the use of rolled sections, and good depth to girders, favours also small expenditure in maintenance. The less complex the design, the easier will it be to keep the structure in order; the less the number of parts, the fewer will be the connections. Freedom from smithing eliminates liability to failure at cranks, or other work which has been subject to fire. It is apparent also that the free use of rolled instead of built-up sections, reduces the liability to trouble from bad riveting, or from good riveting overstressed. A liberal depth to all girders, by reducing deflections, limits the inclination of the ends and gives the connections a better chance of remaining intact. Lastly, with work of this character, the labour of scraping and painting is simplified and cheapened.

The author wishes to reiterate the statement made in the opening paragraphs of this book, that all instances of decrepitude, failure, or peculiar behaviour cited, have been under his direct observation. The fact is insisted upon simply that the reader may appreciate that the information is at first hand.

It has not been thought necessary, nor was it considered desirable, to indicate the locality of each case referred to; but it may be said that the matter of these chapters has been accumulating during many years, and relates to structures under the control of many different bodies.

The study of old bridges is strongly recommended, particularly with respect to stress and strain, which in structures new or old, occur possibly as may be expected--certainly as they must. Consideration of existing work may thus be a useful check upon the fanciful requirements of some methods of design. There is a recent tendency, for instance, in English practice to over-stiffen the webs of plate-girders, such that if the theory upon which the results are based were true, many old bridges carrying their loads with no sign of distress, should have failed long ago. Excess in riveting is a common extravagance, to which the same criticism may in a less degree apply. Considerable impact allowances for girders of large span may also be referred to as an application of empiric theory not justified by experience, which, as in all cases where such considerations fight with facts, should be modified or rejected.

INDEX

Abutments, leaning, 82, 173
-- movements of, 158
-- settlement of, 78
Adjustment of centre girders, 128
-- of distributing girders, 120
Angular distortions, 88
Arches, equilibrium of, 162
-- repair of, 163
Arrangement of cross girders, 21, 175
Asphalt, 26

Ballast, 29
Bearing pressure on rivets, 47, 51, 57
Bearings, skew, 4
Bottom booms, end bays, 18
Bracing, additional, 117
-- effects of, 34
-- flat bars, 37
-- incomplete, 41
-- sea piers, 42
Bridge floors, 20
-- repairs, 107
-- surveys, 107
Bridges, life of, 165
Breaks in [T] bars, 16
Buckling of webs, 16

Camber, 24, 80
Cast-iron arches, 80, 145
-- -- bridges, 141
-- -- columns, 7,144
-- -- girders, 141
-- -- in sea water, 101
Centre girders, 122
Cinder ballast, 29
Cold-blast iron, 141
Cooling stresses in cast iron, 145
Construction depth, 173
Corrugated sheeting, 29
Cost of centre girders, 135
-- of maintenance, 168
Counterbracing, 19
Cracked bedstones, 3
-- columns, 7
-- web plates, 13, 14, 15, 50
Cross girder arrangement, 21
-- girders, fixed ends, 22, 118
-- -- rusted, 29, 97
-- -- weak, 30, 66

Decay and painting, 96
-- of floor plates, 109
-- of timber, 28, 150
Deflection, 85
-- due to booms and web, 86
-- exceptional cases, 88
-- in new and old work, 85
-- working formulæ, 87
Deformations, 73
Depth of girders, 23, 89, 184
Diagonal ties, 19, 42
Distortion due to temperature changes, 79, 84
Distributing girders, 120
Drainage holes, 25
“Drop” loads, 89
Dwarf walls under floors, 26

Early steel girders, 68
Economy, 184
Effect of earth slips, 157
-- of floor on deflection, 88
-- -- -- on stresses, 23, 30
-- of high stress, 86
-- of permanent way on stresses, 18
--of skew on bridge floors, 25
-- -- -- on centre girders, 131
-- of transverse bracings, 34
-- of vibration on masonry, 162
-- of wave action on sea piers, 42
End bays, bottom booms, 18
Equilibrium of masonry arches, 162
Examination of bridges, 107
Examples of cast-iron bridges overstressed, 141
-- of high stress, 70
-- of life of bridges, 167
-- of rivet stress, 56
-- of strengthening, 114
-- -- -- by centre girders, 131, 134
Excessive bearing pressure, 51

Faulty workmanship, 80
Fixed ends to cross girders, 22, 118
Flange stresses, 63, 66, 67
Flanges, side loaded, 9, 73
Flat bar bracing, 37
Flexing of girders, 9, 74, 76
Flexure curves, 138
Fractured bedstones, 3
-- rails, 30
-- webs, 13, 14, 15, 50
Fractures in cast iron, 7, 145

Girder bearings, 2
Girders on columns, 7
-- on masonry, 8
Girderwork in masonry, 101

Headway, 173
High stress, 61
-- in cast iron, 141
-- in rivets, 47, 52
Holes for drainage, 25

Impact, 20, 62
Inclination of girder ends, 23, 53
Incomplete bracing, 41
Initial set, 88
Interference with traffic, 177

Jack arches, 29, 101
Joints in rails, 29, 109
-- in trough floors, 28, 180
Junction between metallic and masonry bridges, 183
-- -- new and old masonry bridges, 182
-- -- new and old metallic bridges, 180

Lattice girder stresses, 47-66
Liberal depth to girders, 23, 89, 184
Life of bridges, 165
Limit of elasticity, 61
Linen tapes, 172
Longitudinal floor girders, 23
Loose rivets, 21, 25, 51, 53, 56, 109

Main girders, 9-17
Masonry bridges, 157
-- enduring character of, 161
Memel timber, 150
Methods of calculation, 46, 61
-- of observing deflection, 90
-- of setting out deflection curves, 138
Movements of abutments, 158
-- of cast-iron bridge, 82
-- of piers, 42, 83, 159
-- of rollers, 7
-- of wrought-iron bridges, 4, 21, 38, 73

New members to old work, 116

Oiling steelwork, 99
Old drawings unreliable, 108
-- rivets, 21, 51, 54, 55
Open webs, 17
Overhead bracing, 39
-- girders, 118

Painting, 98
Parapets, 79
Permissible stress in old work, 110
Piers, movements of, 42, 83, 159
-- out of plumb, 159
Piles, decay of, 102, 150
Pitch pine, 28
Plasticity, 61
Plate webs, 9
Plated floors, 23, 25, 30
Pointing masonry, 164
Proposed rivet stresses, 58

Quickly applied loads, 89

Rail joints, 29, 109
Rails, breaks in, 30
Reaction of cross girder with centre support, 127
Red-lead, 98, 100
Relative merits of bridges, 169
Relief by centre girders, 122
Repainting, 100
Repair of bridges, 107, 147, 155, 163
-- of timber piles, 156
Replacing flange plates, 110
-- rivets, 111
Resistance of cast iron to rust, 101
Riveted connections, 45, 86
Rivets in cramped positions, 20
-- in cross girder ends, 21, 49, 53, 54
-- in road bridges, 60
-- in webs of main girders, 46
-- spacing of, 60, 80
-- stresses in, 56
Rocking of piers, 8, 83, 159
Roller bearings, 7
Rubble masonry, 161-164
Running load and deflection, 95
Rusting, instances of, 29, 96
-- of steelwork, 99
-- over sea-water, 98

Sag in timber bridges, 150
-- of tapes, 172
Scour under piers, 161
Sea piers, 42, 102
Setting bedstones, 3, 129, 176
Settlements, 76, 157
Skew bearings, 4
-- bridges, right and left, 173
-- -- floors, 25
Skirting plate, 26
Slope of girder ends, 92
Softening of cast-iron in sea-water, 101
Spacing of rivets, 60, 79
Spread of abutments, 157
Spring joints, 23
Steel trough girders, 68
-- troughing, 70
Stiffening girders from floor, 12, 40
-- to webs, 16, 38, 185
Stop piers, 158
Strength of light top booms, 40
Strengthening of bridges, 107, 122
-- bridge floors, 118
-- cross girders, 123
Stress in plated floors, 31
Study of old bridges, 185

Tall piers, 42, 159
Timber bridges, 149
-- floors, 27
-- staging, 177
Top booms, 18
Traffic during reconstruction, 177
Transverse bracing, 34, 117
Trough floors, 27, 180
-- girders, 50, 74
[T] stiffeners, breaks in, 16
Twin girders, 15, 75
Twisting of girders, 11, 68, 73
-- -- -- corrected, 12
Types of reconstruction, 174

[U]-shaped booms, 18
Uncomplicated stress, 62
Uniform pressure on bearings, 6

Value of E in deflection formulæ, 87
Vibration, 162

Wasted webs, 14, 29, 96
Water, scour of, 161
Web buckling, 16
-- plates, cracked, 13, 14, 15, 50
-- rivets, 46, 50
-- stiffening, 16, 38, 185
Widening masonry bridges, 182
-- metallic bridges, 179
Wide spaced rivets, 79
Wind pressure, 41, 43

Yielding of piers, 8, 83, 159

LONDON: PRINTED BY WILLIAM CLOWES AND SONS, LIMITED,
GREAT WINDMILL STREET, W., AND DUKE STREET, STAMFORD STREET, S.E.

Transcriber's Notes:

The text of the original work (including inconsistent spelling, hyphenation, formatting etc.) has been retained, except as mentioned below.

The slight differences between the Table of Contents and the text have not been changed.

Changes made to the text:

Some punctuation errors and obvious typographical errors have been corrected silently.

Several illustrations have been moved to where they are described in the text.

Page 123, formula (2): the original shows an unclear superscript after the first L. As described in the following line of the text, this has been changed to L{_l_}.

End of Project Gutenberg's The Anatomy of Bridgework, by William Henry Thorpe