Transcript Design of Composites

Design of Connections
by
Toby Mottram
School of Engineering, Warwick
University
1st CoSACNet Meeting, Southampton
30/01/01
Len Hollaway, 1993
“Jointing has a special significance
and poses a major challenge
to the engineer”
CONTENTS
1. Introduction
(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
(I)
1. Introduction
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)
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)
3. Design Guidance
Warning - Design Manuals
Guidance is different
and is often NOT based on
‘rigorous’ physical testing
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
3. Design Guidance
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
(Mottram 2000)
Local stress field
(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