material ch29
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1Connection Design Requirements Teaching Resource in Design of Steel Structures
IIT Madras, SERC Madras, Anna Univ., INSDAG
CONNECTION DESIGN REQUIREMENTS
PROF. V. KALYANARAMANDepartment of Civil Engineering
Indian Institute of Technology Madras
Chennai 600036email: k alyan@civ i l .i i tm .ernet.in
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2Connection Design Requirements Teaching Resource in Design of Steel Structures
IIT Madras, SERC Madras, Anna Univ., INSDAG
CONNECTION DESIGN
REQUIREMENTS
OUTLINE
INTRODUCTION
COMPLEXITIES OF CONNECTIONS
TYPES OF CONNECTIONS
CONNECTION DESIGN PHILOSOPHY
COST OF CONNECTIONS
SUMMARY
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3Connection Design Requirements Teaching Resource in Design of Steel Structures
IIT Madras, SERC Madras, Anna Univ., INSDAG
INTRODUCTION
Necessity for ConnectionsLimited Length of Members
Rolling & Transportation Constraints
Larger Size of Structures
Importance of Connection
Structure is only as strong as the weakest link
Connection failure to be avoided before member
failureThe full strength of members is to be utilised
Connection failure is usually not ductile
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IIT Madras, SERC Madras, Anna Univ., INSDAG
INTRODUCTION
Requirements of Connection Designs
Strength, Stiffness, and Ductility
Deflection control & stability under service load
Large Defection & Ductility at Ultimate load (over load)
Connections are Complex BecauseThe are more complex to design than members
They have greater potential for variability in
behaviour & strength
Most vulnerable component of a structure
Failure of a connection often leads to failure of the
structure
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5Connection Design Requirements Teaching Resource in Design of Steel Structures
IIT Madras, SERC Madras, Anna Univ., INSDAG
COMPLEXITY OF CONNECTIONS
Relaibility or Safety of a design depends on
Variability of loads
Variability of the member strength
Variability of Connection Strength
Larger Uncertainty of Connections is Due toComplexity of Connection Geometry
Highly Indeterminate
Stress concentration
Non-Linearity due to slip, & local yielding
Geometric Imperfections
Residual Stresses & Strains
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6Connection Design Requirements Teaching Resource in Design of Steel StructuresIIT Madras, SERC Madras, Anna Univ., INSDAG
COMPLEXITY OF GEOMETRY
Angle
Stiffener
Flange Plate
Beam
Tee
Bolted Connection Welded Connection
BoltsColumn Bracket
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COMPLEXITY OF CONNECTIONS
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8Connection Design Requirements Teaching Resource in Design of Steel StructuresIIT Madras, SERC Madras, Anna Univ., INSDAG
COMPLEXITY OF CONNECTIONS
GEOMETRIC IMPERFECTIONS
Bow in members as rolledLack of fit in Black Bolts in clearance holes
Fabrication Errors
Member deflections
Welding distortions
Gaps & tolerances in fabrication & erection
RESIDUAL STRESSES & STRAINS
Differential cooling after hot rolling, gas cutting & welding
Premature yielding under loading
Lack of fit in bolted fabrication (Distortions)
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9Connection Design Requirements Teaching Resource in Design of Steel StructuresIIT Madras, SERC Madras, Anna Univ., INSDAG
TYPES OF CONNECTIONS
WELDED CONNECTIONSFillet welding
Butt welding
BOLTED CONNECTIONSBearing type Carbon steel / High strength
Friction type HSFG
RIVETED CONNECTIONSMild steel
High strength steel
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10Connection Design Requirements Teaching Resource in Design of Steel StructuresIIT Madras, SERC Madras, Anna Univ., INSDAG
WELDED CONNECTIONS
Fil let Welds Bu t t welds
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12Connection Design Requirements Teaching Resource in Design of Steel StructuresIIT Madras, SERC Madras, Anna Univ., INSDAG
BOLTED CONNECTIONS
Bearing Type:
Clamping
Force, P0
T
T
X
Bearing
Stress
ContactPressure, P0
T
T
Frictional
Force T
Notice no slip is observed in-
between plates in HSFG
Connection
Friction Type:
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Merits& Demerits
Welded Connections
Transfer of forces between elements more directRequires little additional elements like gussets
Shorter length of joints
No reduction in member strength due to bolt holes etc.
Rigid connections easy to achieve
Requires skilled manpower
Requires special equipment
not easy to achieve at difficult locationsless ductile
prone to defects& fatigue cracks under cyclic loading
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Merits& DemeritsBolted Connections
Bearing Type
Easy to install even at difficult locations
EconomicalDoes not require highly skilled manpower
Slip causes flexible joint
Joint size larger
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15Connection Design Requirements Teaching Resource in Design of Steel StructuresIIT Madras, SERC Madras, Anna Univ., INSDAG
Merits& DemeritsBolted Connections
Friction Type
Rigidity of connectionBetter fatigue performance
Expensive due to material & installation labour
Requires skilled manpower
Requires better inspection
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RIGIDITY OF MOMENT CONNECTIONS
Type of connections
Rigid Hinged Semi-Rigid
>90
hMr
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RIGIDITY OF MOMENT CONNECTIONS
h
Moment
Mr
Rotation
Rigid joint
H inged joint
Semi-r igid joint
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18Connection Design Requirements Teaching Resource in Design of Steel StructuresIIT Madras, SERC Madras, Anna Univ., INSDAG
CONNECTION DESIGN PHILOSOPHYConnections are complex
The strength is variableLarge numbers have to be designed
Exact analysis:
Complex but possible
Accuracy depends on assumptions
Not practically feasible
Practical, simplified Methods are Appropriate
Should satisfy equilibriumDuctility requirements (static loading)
Fatigue strength requirements (cyclic loading)
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19Connection Design Requirements Teaching Resource in Design of Steel Structures
IIT Madras, SERC Madras, Anna Univ., INSDAG
TRANSFER OF MEMBER FORCES
Factors:
Understand the expected connection behaviour.Model this appropriately in analysis.
Determine the forces and moments transferred to the
connection.
Consider the joint size to reduce forces transferred
Replace the forces/moments transferred by member
Equivalent system of forces on interface elements in the joint
Consider the mechanism of force transfer in the member
Transfer to elements in consistency with their relative stiffness
The system of forces be in equilibrium with the force to be
transferred
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IIT Madras, SERC Madras, Anna Univ., INSDAG
TRANSFER OF MEMBER FORCES
V V
(a) Connection (b) F reebody Diagram
Critical section
for block shear
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IIT Madras, SERC Madras, Anna Univ., INSDAG
FORCE FLOW IN A JOINT
Force flow is complex
High degree of indeterminacy
Local stress concentration and yielding
Effect of Residual stress, which is unknown
Connection force flow AnalysisMaking simplifying Assumptionssharing of forces
Satisfying Equilibrium
Ensuring adequacy of strengthEnsuring adequacy of stiffness
Ensuring adequacy of ductility
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IIT Madras, SERC Madras, Anna Univ., INSDAG
SIMPLIFIED ANALYSIS OF JOINTS
Assume sharing of forces among alternate elements
Stiffer elements attract larger proportion of the imposed force
Plate elements are stiff in resisting forces imposed in their plane
Plate elements are flexible in resisting forces imposed out-of-plane
The assumed forces may be at variance from the elastic results
Equilibrium & Compatibility are to be satisfied in elastic analysisOnly equilibrium is assumed in the simplified analysis
Ensure adequacy of ductility to redistribute forces as
assumed
Redistribution is necessary since assumed sharing may at variance
Ensure adequacy of strength of elements in the load path
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IIT Madras, SERC Madras, Anna Univ., INSDAG
SIMPLIFIED ANALYSIS OF JOINTS
C
T
T
C
S1
S2
COST OF CONNECTIONS
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IIT Madras, SERC Madras, Anna Univ., INSDAG
COST OF CONNECTIONSDesign cost
Consumes a major portion of efforts
Simplified design methods reduce the costStandardised designs and details are desirable
Design handbook, aids and software
Fabrication / Erection cost
Repetitive use of standard details
Good access, easy support, ease of joining at location
Mix of automatic and manual fabrication
Choice of connection methodOther factors
Simple detail, simple techniques appropriate to requirement
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25Connection Design Requirements Teaching Resource in Design of Steel Structures
IIT Madras, SERC Madras, Anna Univ., INSDAG
SUMMARY
Sound Connection Design Requires Understanding of
the requirement
force flow
relative stiffness of elements, and
ductility of elements
Good design can considerably reduce cost of steel
structure
Thank you for your attention