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

“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”

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’

CONTENTS 4. Research goals 5. Conclusions

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

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

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

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

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

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

3. Design Guidance Europe (limit states) 1995 - Design Manual, Fiberline Composites, Denmark 1996 -EUROCOMP Design Code and Handbook (GRPs)

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)

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

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

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

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

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

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

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

3. Design Guidance (I) ‘Simple’ EUROCOMP Design Code- Six basic load cases (1 and 2 have bolt, 4 to 6 are notched) 4 5 6

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

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

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

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.

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

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

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

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