How Structures Work

Preface x

1 Brackets and Bridges 1

Cooper’s tragedy 2

The Forth Bridge 4

Members in compression 6

The Quebec Bridge 8

Forces in a bracket 9

The design process 13

Stresses 14

2 Stiffening a Beam – Girder Bridges 16

The simple truss 22

Tension trusses 27

Girder bridges: The Forth Bridge 31

3 Arches and Suspension Bridges 33

Building an arch 35

Blackfriars Bridge 37

Pontypridd Bridge 39

The forces in an arch 39

Practical issues 41

Forces within the arch ring 43

Edwards’s failure 48

An unexpected failure 49

Arch with point load 50

Iron and concrete arches 51

The suspension bridge 54

Arches in buildings: Flying buttresses 57

Arches in walls 60

4 Bringing the Loads to the Ground – The Structural Scheme 63

Introduction 63

The alternatives 64

Nature of the loads 66

Choices 68

‘Flow of forces’ or action and reaction 71

Describing the structure 73

Structures are three?dimensional 75

Statically indeterminate structures 76

5 Safe as Houses? – Walls 79

Bricks and mortar 81

Point loads and openings 85

Cavity walls 88

Thick walls 90

Foundation loads 93

Horizontal loads 94

Rafter thrusts 98

Foundation stresses 101

6 Frames – A Problem of Stability 103

Timber framing 104

Construction of a barn 108

Bracing forces 111

Bending in the post 112

Light frame construction 113

The coming of iron 115

The frame today 122

The multistorey frame 126

Columns 130

7 Floors and Beams – Deflections and Bending Moments 134

The need for science 140

Floors and deflections 140

The forces in the beam 142

Strain 143

Galileo’s cantilever 145

Finding the stresses 147

From cantilever to beam 148

Iron and steel beams 150

Cast iron 150

Reinforced concrete beams 153

Continuous beams 155

Shear 159

Two?way floors 160

Other structures in bending 163

Prestressing 168

8 Providing Shelter – Roofs 173

Common rafter roofs 174

Purlin roofs 179

Longitudinal stability 185

The roof truss 188

The coming of iron 190

Three?dimensional roofs 192

9 Structures in a Three?Dimensional World 198

Vaults 198

The pointed vault 202

Elaborations on the basic vault form 203

Building vaults 206

Domes 207

Some historical examples 212

The modern three?dimensional structure 216

Anticlastic forms 220

Structures in tension 222

Structures for their time and place 224

10 Materials and Workmanship 226

Walling materials 227

Timber 228

Iron and steel 229

Compatibility of materials 233

Material development and design 234

Appendix: Some Elements of Grammar 235

Glossary 241

Index 250