Lightweight Sandwich Construction

J.M. Davies DSc, PhD, FREng, FICE, FIStructE is Professor of Structural Engineering at the University of Manchester.He has spent a lifetime carrying out research and consultancy into many aspects of steel construction and has written more than 150 technical papers. In recent years, he has concentrated on aspects of lightweight construction, including cladding and its supporting members. Sandwich construction has been an important part of his work. At the University of Manchester, he has a large fire engineering laboratory and has developed an increasing interest in the performance of lightweight construction in fire. He is a joint author of Plastic Design to BS 5950, written for the Steel Construction Institute and published by Blackwell Science, and also The Manual of Stressed Skin Diaphragm Design.

"The publication is based on 30 years of the author's research...It is therefore an excellent "state of the art" that will be useful to both practitioners and manufacturers" R M Lawson, The Steel Construction Institute, August 2001

• List of Contributors xiiPreface xiii1 Introduction 11.1 The origins of sandwich technology 11.2 Principles of sandwich construction 21.3 Requirements for sandwich cladding panels 41.4 Wall panels 51.5 Panels for cold stores 61.6 Roof panels 71.7 Methods of manufacture 81.7.1 Manufacture of facings 81.7.2 Panels with bonded cores 81.7.3 Foamed cores 91.8 Design requirements for structural sandwich panels 101.9 Structural design of sandwich panels 111.10 Layout of this book 122 Materials 142.1 Introduction 142.2 Facing materials 142.2.1 Steel facings 152.2.2 Aluminium sheeting 202.2.3 Other metal face materials 222.2.4 Other facing materials 242.3 Core materials 262.3.1 Rigid plastic foam materials 282.3.2 Characteristic properties of rigid foams 332.3.3 Inorganic core material 362.3.4 Characteristic properties of mineral wools 382.4 Honeycomb cores 392.5 Adhesives and other components 402.5.1 Mechanical properties 412.6 Fasteners and other components 412.7 References 413 Thermal Performance and Water-Tightness 433.1 Introduction 433.2 Insulation theory 433.2.1 Factors influencing the thermal conductivity of a material 443.3 Thermal resistance 463.3.1 Total thermal resistance of a building element 473.4 Thermal transmittance coefficient (U-value) 473.4.1 Calculation method for profiled panels 483.5 Thermal capacity 493.6 Thermal bridges 503.7 Air-tightness 513.7.1 Test methods for air-tightness 533.8 Water-tightness 533.8.1 Test methods for water-tightness 543.9 Moisture 553.9.1 Surface condensation 573.9.2 Moisture transfer 573.10 Thermographic surveys 583.11 The advantage of sandwich construction in the context of thermal insulation 593.12 Energy saving 593.13 Reference 614 Acoustics 624.1 Introduction 624.2 What is sound? 624.2.1 Decibel arithmetic 644.3 Fundamental acoustic parameters 654.4 Sound insulation 664.4.1 Example 1 674.5 Weighted sound reduction index 674.6 Overall sound reduction index 684.6.1 Example 2 694.7 Flanking transmission 694.8 Sound reduction index for holes and slits 704.9 Sound reduction index for a sandwich panel 714.10 Sound in rooms 734.10.1 Sound absorption 734.10.2 Sound absorption for sandwich panels 744.11 Noise reduction in small industrial premises 754.11.1 Example 3 764.12 Noise reduction in large industrial premises 764.12.1 Reverberation time 764.12.2 Room classification 774.12.3 Sound propagation 784.12.4 General sound level reduction 784.12.5 Example 4 794.13 References 805 Fire 815.1 General aspects of fire behaviour 815.1.1 Introduction 815.1.2 Objectives of fire safety design 825.1.3 Phases of a fire 835.1.4 Assessment of the threat to life 865.1.5 Fire severity 885.1.6 Introduction to reaction to fire 925.1.7 Introduction to fire resistance 945.1.8 Fire safety legislation 975.1.9 Large-scale fire tests and experience of actual fires 985.2 Fire tests 995.2.1 Use of standard fire tests 995.2.2 Reaction-to-fire tests 995.2.3 Fire resistance tests 1025.3 Material properties at elevated temperature 1035.3.1 Face materials 1035.3.2 Core materials 1075.3.3 Adhesives 1115.3.4 Mechanical fasteners 1115.4 Design considerations 1125.4.1 General 1125.4.2 Design for fire safety 1125.4.3 Fire regulations 1135.4.4 Insurance requirements 1145.4.5 Structural support for panel assemblies 1145.4.6 Loading and restraint of the panel assembly 1155.4.7 Spread of fire within the core 1185.4.8 Fire stopping 1185.4.9 Joints in the panel assembly 1195.4.10 Sealants 1205.4.11 Fire protection 1215.4.12 Retention of panel facings 1225.4.13 Fire load of panels 1285.4.14 Choice of panel facings 1295.4.15 Choice of core material 1295.4.16 Choice of adhesives 1305.4.17 Required behaviour for horizontal panels (both ceiling and roof panels) 1305.4.18 Required behaviour for vertical panels (internal and external walls) 1315.5 Engineering solutions 1315.5.1 External walls 1325.5.2 Internal walls 1375.5.3 Roofs 1385.5.4 Ceilings 1395.6 Reparability after fire 1415.7 Check list for designers 1415.8 References 1445.8.1 Additional references for wider reading 1466 Durability 1486.1 General aspects of durability 1486.2 Prediction of the lifetime of a structure 1506.3 Actions on sandwich panels which may cause degradation 1516.3.1 Actions causing mechanical degradation 1526.3.2 Actions causing physical degradation 1526.4 Accelerated test methods 1536.4.1 Durability of the panel 1536.4.2 Effect of temperature variations and moisture on strength properties 1576.4.3 Tests for durability 1586.4.4 Durability of the adhesive 1616.4.5 Durability of facing materials 1646.5 Guidelines for the choice of materials and fasteners 1666.5.1 Core material 1666.5.2 Adhesives 1666.5.3 Face material 1666.5.4 Fasteners 1676.6 References 1677 Refrigerated Warehouses, Cold Stores and Chill Rooms 1687.1 Introduction 1687.1.1 Cold stores and chill rooms inside the building 1707.2 Thermal insulation 1717.3 Air-tightness 1717.4 Moisture barriers 1727.5 Fire 1737.6 Details 1737.7 Special considerations applying to sandwich panel outer walls 1757.7.1 Allowing for reactions to mechanical and thermal loads 1757.7.2 Thermal expansion/contraction and panel deformation 1777.8 The engineering design of sandwich panels 1777.8.1 Using panel supports having lateral degrees of freedom 1787.8.2 Pre-flexed panel outer faces 1807.9 Structural features requiring special attention 1828 Special Architectural Applications 1848.1 Introduction 1848.2 Cladding details 1848.3 Industrial and commercial buildings 1848.3.1 Esso UK plc corporate headquarters, Leatherhead, UK 1858.3.2 Manufacturing facility for Compaq Computer Corporation, Erskine, Scotland 1858.4 High-technology architectural wall panels 1858.4.1 Case Study: Aspect Mark II 1878.5 References 1919 Principles of Structural Behaviour 1939.1 Introduction 1939.1.1 Types of panels 1949.2 Analysis of panels with flat or lightly profiled faces 1959.2.1 Case 1: Simply supported panel with a uniformly distributed load 1979.2.2 Case 2: Simply supported panel with a point load 1999.2.3 Case 3: Simply supported panel with a temperature difference 2009.2.4 Solutions for two- and three-span panels 2019.2.5 More general cases of loading and support conditions 2029.3 Analysis of panels with profiled faces 2049.3.1 Simply supported panel with a uniformly distributed load of q per unit length 2069.3.2 Simply supported panel with a point load anywhere in the span 2089.3.3 Simply supported panel with a temperature difference between the faces 2099.3.4 Solutions for two- and three-span panels 2109.4 Approximate solutions for some simple cases 2109.5 Finite-element and other numerical methods 2179.5.1 Force-deformation relationships2199.6 Axially loaded sandwich panels 2239.7 Sandwich panels spanning in two directions (sandwich plates) 2239.7.1 Simply supported panel with flat or quasi-flat faces 2249.8 References 22510 Load-bearing Capacity 22710.1 Principles of the evaluation of resistance 22710.2 Failure modes 22910.2.1 Tensile and compressive failure of the faces 23010.2.2 Failure of the core and face at the support with positive support reaction 23710.2.3 Failure of the core and face at a support subject to negative support reaction 24810.2.4 Shear failure of the core 25210.2.5 Shear failure of a profiled face 25410.2.6 Connections 25410.2.7 Deflections 25610.3 Derivation of the theoretical expressions for buckling stress 25810.4 Derivation of expressions for the interaction at intermediate supports 26210.5 Conclusions 26610.6 References 26711 Loads, Load and Material Factors and Design Procedure 26911.1 Design equation 26911.2 Loads on sandwich panels 27111.3 Choice of the method of analysis 27311.4 Safety factors 27411.5 Load combinations 27611.6 Permissible short-term and long-term deflections 28011.7 Conclusions 28111.8 References 28212 Additional Structural Considerations 28412.1 Introduction 28412.2 Details of sandwich structures 28412.2.1 Details for external walls 28512.2.2 Details for external roofs 28512.2.3 Details for internal walls 28612.2.4 Details for ceilings 28812.3 Connections between a sandwich panel and the supporting structure 28812.4 Effect of openings 29312.5 Flexibility of fasteners and supports 29812.6 Lateral and rotational stiffness of fastenings 30412.7 Capacity under axial load 30712.8 Diaphragm action 31112.9 Conclusions 31312.10 References 31313 Mechanical Testing 31513.1 Introduction 31513.2 Tests on core materials 31613.3 Tests to determine the wrinkling stress 32313.4 Tests to determine the interactions between bending moment and support force 32413.5 Creep and long-term strength tests 32513.6 Tests on fasteners 32513.7 Tests used in quality control 32513.8 Statistical interpretation of test data 32713.9 Detailed test procedures 32713.9.1 General 32713.9.2 Test environment and conditioning of test specimens 32813.9.3 Test procedures for material properties 32813.9.4 Tests on complete panels 33413.9.5 Tests on fasteners and connections 34213.10 References 34514 Examples of Calculation Procedures 34614.1 General 34614.2 Two-span wall panel 34614.2.1 Actions (loads) 34714.2.2 Cross-section of the panel 34714.2.3 Design values for the panel 34814.2.4 Load, material and combination factors 34814.2.5 Ultimate limit state 34814.2.6 Serviceability limit state 35014.2.7 Comments on the calculations 35614.3 Two-span roof panel 35714.3.1 Actions (loads) 35714.3.2 Cross-section of the panel 35814.3.3 Design values for the panel 35814.3.4 Load, material and combination factors 35914.3.5 Calculation of the initial design parameters 35914.3.6 Ultimate limit state 35914.3.7 Serviceability limit state 36314.3.8 Design of fasteners 36714.3.9 Comments on the calculations 36714.4 Reference 367Index 369