Practical Guide to Diagnosing Structural Movement in Buildings

Introduction ix

List of Figures xii

Acknowledgements xix

Part 1 First Principles 1

1.1 First Principles 3

1.2 Crack Patterns and Cracks 8

1.3 Rotational Movement 9

1.4 Contra Rotational Movement 11

1.5 Weak Routes 14

1.6 Load Distribution 22

1.7 Movement and Orientation 26

1.8 Summary of First Principles and Process 28

Part 2 Cracks in Buildings Not Related to Foundations 31

2.1 Expansion Cracking 33

2.2 Cavity Wall Tie Corrosion 44

2.3 Corrosion of Metal Built into Walls 53

2.4 Vibration of Built-in Fixings 57

2.5 Roof Spread 60

2.6 Springing from Deflected Beams 67

2.7 Lack of Lateral Stability 70

2.8 Lack of Lateral Stability in Modern Gable Walls 76

2.9 False Chimneys, Lateral Instability and Movement in Gable Walls 79

2.10 Overloaded Beams 86

2.11 Absence of Lintels (Beams) Over Openings in Cavity Walls 91

2.12 Overloaded Floors 98

2.13 Overloaded Walls 102

2.14 Differential Movement 106

2.15 Arch Thrust and Arch Flattening 108

2.16 Arch Spread in Chimneys Built over Alleys in Terrace Housing 113

2.17 Buckling of Jambs to Sash Windows and Arch Flattening 118

2.18 Wall Shortening and Sequential Movement in Walls and Roofs (Holland’s Multiple Factor Diagnosis) 123

2.19 Load Path Cracking 135

2.20 Bulging of Walls Due to Decay of Bonding Timbers 138

2.21 Bulging and Separation in Solid Brick Walls 141

2.22 Separation of Rubble-Filled Stone Walls 144

2.23 Floor Slab Settlement (Compaction) 146

2.24 Load Concentrations 153

2.25 Sulphate Attack 155

2.26 Concrete Block Shrinkage 161

2.27 Shrinkage of Calcium Silicate Bricks 165

2.28 Heat Expansion of Flue Blocks 168

2.29 Floor Cracking in Suspended Concrete Beam and Block Floors 172

2.30 Vehicular Impact Damage (Usually Garages) 177

Part 3 Cracks in Buildings Related to the Foundations and Ground Movement 183

3.1 Introduction 185

3.1.1 Design for Load 187

3.1.2 Design for Stability 189

3.1.3 Identifying Below Ground Defects 190

3.2 Foundation Movement Caused by Clay Shrinkage 193

3.3 Clay Heave 201

3.4 Seasonal Expansion of Clay Subsoil 204

3.5 Eccentric Loading on Foundations 206

3.6 Uneven Loading 209

3.7 Load Concentrations on Foundations 211

3.8 Differential Foundation Movement 213

3.9 Initial Settlement after Construction or Alterations 218

3.10 Differential Foundation Settlement Cracking between Chimneys and Party Walls, in Alleys Running through Terraces 221

3.11 Leaking Drains and Water Discharge near to Buildings 225

3.12 Drains and Drain Trenches 228

3.13 Cracking Associated with Raft Foundations 231

Part 4 Repair Methods 241

4.1 Introduction 243

4.2 Re-pointing 245

4.3 Re-pointing with Epoxy Mortar 247

4.4 Stitching in Brickwork 248

4.5 Reinforcing Brick Mortar Joints 249

4.6 Tie Bars 251

4.7 Restraint Straps 254

4.8 Buttresses/Piers 256

4.9 Preventing Roof Spread 257

4.10 Underpinning 259

4.11 Expanding Foam Underpinning 263

4.12 Grouting 265

4.13 Root Barriers 267

Index 269