1. Design of Connections by Toby Mottram
School of Engineering, Warwick University
1st CoSACNet Meeting, Southampton
30/01/01

2. “Jointing has a special significance and poses a major challenge
Len Hollaway, 1993
“Jointing has a special significance
and poses a major challenge
to the engineer”

3. CONTENTS 1. Introduction 2. Mechanical Connections 3. Design Guidance
(I) Composites for construction
(II) Connection types
2. Mechanical Connections
3. Design Guidance
(I) ‘Simple’
(II) ‘Rigorous’

4. CONTENTS
4. Research goals
5. Conclusions

5. 1. Introduction (I) Composites for construction
Manufacturing Processes
Contact Moulding (non-structural)
Filament Winding
Resin Transfer Moulding (or RIFT, etc)
PULTRUSION

6. 1. Introduction (I) Composites for construction
Fiberline Footbridge
Standard profiles (I, channel, box)
Cooling Towers
Strongwell specialist market

7. 1. Introduction (I) Composites for construction
Creative Pultrusions Inc.
Bridge decking
Structural frames

8. 1. Introduction (II) Connection types
Mechanical Interlocking (Adhesive Bonding and (sometimes) Mechanical Fastening)
ACCS (Maunsells)
Superdeck (Creative Pultrusions Inc.)

9. 1. Introduction (II) Connection types
Mechanical fastening (bolts, rivets, screws), with Adhesive Bonding
bolting (standard connection method)

10. 2. Mechanical Connections
Web cleated (Strongwell)
‘SIMPLE’
1. Bolted and Bonded capacity controlled by shear in heel of angle
2. Bolted capacity controlled by bearing around fastener or shear of stainless steel fasteners

11. 3. Design Guidance Europe (limit states)
Design Manual, Fiberline Composites, Denmark
1996 -EUROCOMP Design Code and Handbook (GRPs)

12. America (Allowable stress)
3. Design Guidance
America (Allowable stress)
1983 EXTREN Design manual, Strongwell
1993 BRP Design Guide, Bedford Reinforced Pultrusions Inc.
1999 The New and Improved Pultrex Pultrusion Design Manual of Pultrex Standard and Custom Fiber Reinforced Polymer Structural Profiles, Creative Pultrusions Inc. (CD-ROM)

13. Warning - Design Manuals Guidance is different
3. Design Guidance
Warning - Design Manuals
Guidance is different
and is often NOT based on
‘rigorous’ physical testing

14. Why is design of connections difficult?
3. Design Guidance
Why is design of connections difficult?
Many materials, properties and members
Many joint types and connection methods
Lack of material ‘ductility’
Failure can be sudden and ‘brittle’
Need for accurate stress and failure analysis
Lack of knowledge on durability
Need for physical testing to verify new designs
NEED STANDARDISATION AND CO-OPERATION

15. Approved design guidance!!
Can’t have code(s) of practice without practice
Can’t have well-established practice without codes
Industry is fragmented and protective
Academic research perceived to be too scientific
Cost-competitive structures require durable material; decades to establish
Copying practice for steel is not ‘optimum’ solution
Need to understand client’s needs and market

16. 3. Design Guidance (I) ‘Simple’
Assumed three basic modes of failure!!
(a) tensile (b) bearing (c) shear

17. 3. Design Guidance (I) ‘Simple’ and (II) ‘Rigorous’
Tensile test on single bolted connection to determine design properties
Test rig (Turvey 1996) 45o failure

18. 3. Design Guidance (I) ‘Simple’ and ‘Rigorous’
Typical test data for SLS and ULS

19. 3. Design Guidance (I) ‘Simple’ and (II) ‘Rigorous’
World-wide 700 plus individual test results
Development of ‘simple’ and ‘rigorous’ design procedures for connection resistance (ULS)
Less attention paid to any SLS
Variables making generalisation VERY difficult :-
materials (bolts and plates), joint dimensions and bolt lay-out, interface conditions (washer, torque, clearance hole), working loads and working environments

20. 3. Design Guidance (I) ‘Simple’
EUROCOMP Design Code- Six basic load cases
(1 and 2 have bolt, 4 to 6 are notched)

21. 3. Design Guidance (I) ‘Simple’
EUROCOMP Design Code
Problems:
No clearance hole
Not all failure modes
Not validated
Laminates not defined
No damage tolerance

22. 3. Design Guidance (II) ‘Rigorous’
Now to cope with general situation
and involve damage tolerance

23. 3. Design Guidance (II) ‘Rigorous’
STEPS
Finite element (linear elastic) analysis
1 Source: determination of load distributions (bolts and far-field (takes account of real stiffnesses)
2 Target: determination of fastener hole stress distributions
Failure analysis
3 BOLTIC FEA provides specific stress outputs to include ‘damage tolerance’ in the design of bolted connections. The failure criterion is the well-known Point Stress Criterion

24. 3. Design Guidance (II) ‘Rigorous’
Target: Stress analysis includes contact and friction.
Failure check (using Point Stress Criterion (dk is characteristic distance and,k is design tensile strength)) must be at a number of locations.

25. 3. Design Guidance (II) ‘Rigorous’
Progressive failure testing and analysis
Bearing test rig Local stress field
(Mottram 2000) (with clearance hole)

26. 4. Research Goals
Establish worthiness of design guidance for connections (bolted and other methods)
Establish scope and limitations of aerospace design methodologies
Develop understanding and know-how for design of connections to become generalised
Provide information for preparation of approved design guidance
Improve confidence in using pultruded profiles in primary load bearing structures

27. 5. Conclusions
Large number of composite members and types of connections are available; more to appear as emerging technology matures
Important R&D advances have been made in applications of primary structural connections
There is a need for standard connection details giving easy to assemble structures that are safe, reliable and cost-effective

28. 5. Conclusions
Mechanical fastening will be the primary connection method in the coming years because it provides flexibility and is familiar to all construction engineers
Approved design guidance (based on physical testing and advanced numerical modelling) is going to take time to develop; a concerted effort is needed to transfer R&D into better practice