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8/12/2019 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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CONNECTION DESIGN

REQUIREMENTS

OUTLINE

INTRODUCTION

COMPLEXITIES OF CONNECTIONS

TYPES OF CONNECTIONS

CONNECTION DESIGN PHILOSOPHY

COST OF CONNECTIONS

SUMMARY


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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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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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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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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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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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WELDED CONNECTIONS

Fil let Welds Bu t t welds


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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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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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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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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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TRANSFER OF MEMBER FORCES

V V

(a) Connection (b) F reebody Diagram

Critical section

for block shear


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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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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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SIMPLIFIED ANALYSIS OF JOINTS

C

T

T

C

S1

S2

COST OF CONNECTIONS


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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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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

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