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CIVL473 Fundamentals of Steel Design
Prepared By
Assoc.Prof.Dr. Murude Celikag
CHAPTER 7
Connections
7.
7. Connection Design
Why do we need connections?Connections are essential to join discontinuous
elements, e.g. beams and columns, to create
structures.
a) Welded Connections• Fillet Welds: Weld metal is outside the
profile of connected element• Butt Welds: Weld metal is deposited within
the profile of the connected elements
DOUBLE LEFT WELD (any type of loading)
SINGLE LEFT WELD (shear only)
LAP SPLICE(any type of loading)
DOUBLE V BUTT WELD SINGLE V BUTT WELD
SINGLE BEVEL BUTT WELD
Fig. 7.1 Fillet Welds
Fig. 7.2 Butt Welds
b) Bolted Connections: Generally used for site connections
• Bearing (ordinary) Bolts in Clearance HolesAdvantages – low cost for buying and installingDisadvantages – slips into bearing at a low load shear
• High Strength Friction Grip Bolts (HSFG)Advantages – high stiffness in shearDisadvantages – expensive
• Other Components of ConnectionsFlats, plates, angles, tees, gusset plates, etc.
Fig. 7.3 Bearing (ordinary) BoltsFig. 7.4 Examples of other components in connections
Why connection design is important?Strong connections are essential to transfer the loads
among structural members. Weak connections could
cause failure of any structure.
a) Economy of StructureDesigners of connections should bear in mind the
following regarding economical fabrication and erection
process.
Maintaining ease of access for welding
Optimizing the use of automatic equipment
Minimizing precise fitting
Achieving repetition of standard details, etc.
Ease of access for site bolting
Provision for supporting the element self-weight
quickly so that the crane can be released
Ease of adjustment for alignment
Simplicity and repetition, etc.
b) Economy of DesignConnection design is a significant part of the total
design cost for the structure. Most connection design
should be a simple, routine matter. A simple calculation
to determine the minimum number of bolts (based on
shear and bearing capacity) would be sufficient.
Design approach for connections?Connection behaviour is both complex and more
variable than the connected elements.
Geometric imperfections due to welding distortion,
cutting and machining imperfections, and permitted
misalignment of clearance holes for bolts between
plies
Residual stresses and strains due to lack of fit and
welding shrinkage
Geometric complexity within the connection
Fig. 7.5 Simple web cleat beam-column connections: contrast between design assumptions and detailed behaviour
Fig. 7.6 Bolt force distribution in beam-column connections with end-plates
Local elements in connectionsUltimate strength design methods are appropriate for
the design of bolts and welds. Deformation may be
limited at times to prevent corrosion. The following are
the effects relevant to connection design.
a) Web yielding at points of concentrated load orreactionConcentrated load at bearings and intermediate points
on girder flanges may produce compressive yielding in
the adjacent web. The extent of the concentration
depends on the effective stiff length of the bearing
surface and the depth of material between the seating
and the girder web (Fig. 7.9).
7.7 7.8
b) Web buckling at points of concentrated load or reaction
c) Local bending of plates or flanges d) Eccentric connection to tie memberse) Shear in panels at member junctions
Fig. 7.9 Web crushing or bearing
Fig. 7.10 Length of bearing
Fig. 7.11 Effective bearing zone in beam web
7.12
7.13
Fig. 7.14 Beam-to-beam connections: erection-stiff
Fig. 7.15 Beam-to-beam connections: fully rigid