According According to the type of internal forces the connections are expected to transmit
2.
Shear (semi rigid, simple) connections
Moment Moment (rigid) connections
3.
According to the type of structural Elements that made up the connections
Single plate angle Connections
Double web angle connections
Top and seated angle connections
Seated beam connections
4.
According to the type of members joining
Beam to beam connections
Column to column connections (column splices)
Beam to Column Connections
Column Base Plate Connections
Riveted Connections
Used for very long time.
Made up of:
Round Ductile steel bar called shank.
A head at one end
Design - very similar to bearing type of
bolted connection.
The installation of the rivet requires:
Heating of the rivet
Inserting it to an oversize hole
- pressure to the head.
Squeezing the plain end by Pneumatic driver - Round head.
On Cooling Reduces in Length–Clamping Force.
Rivets are no longer used due to:
Intro of high strength bolts
Pre-Heating of rivets prior to driving.
Labor Costs
High Level of Noise
Replacing of poorly installed rivets.
Fastened Together primarily by Bolts.
Bolts may be loaded in:
Tension
Shear
Both Tension & Shear
Threads of bolts:
Excluded
Included
While under action of Shear forces, threads of bolts may be:
Excluded – Increased strength
Included - Relatively Decreased stregth.
Two types of bolts are used in bolted connection:
Bearing type bolts
High strength friction grip bolts (HSFG)
The most common type is bearing bolts in clearance holes, often referred to as Black Bolts.
Black Bolts
Ordinary, unfinished, rough, or common bolts.
Least Expensive
Primarily - Light structures under static load such as small trusses, purlins etc
Turned Bolts
Similar to unfinished bolts.
Shanks - Hexagonal Rods
Primarily - Light structures under static load such as small trusses, purlins etc
Expensive – Limited use – Structures with no Slippage Connections
Ribbed Bolts
Round head similar to Rivets.
Raised ribs parallel to the shank.
Actual Diameter - slightly Larger than the hole – Tightly fit into the hole.
Popular – Economical in Material & Installation
Bolts used in Slip Critical Connections
High Strength Friction Grip (HSFG) bolts Pretensioned – contact pressure between the surfaces. Friction between plates – Prevents relative slip – Higher Shear Resistance. External Force increases than friction between plates – Slip Occurs – reserve strength due to bolt.
Advantages
Bolting operation is Silent.
Cold Process - No Risk of fire
Quicker process than riveting
Less Man power needed.
Disadvantages
When Subjected to vibratory loads – loosened – reduction of strength
Thread area at root is less – less strength
Unfinished bolts – lesser strength – less diameter.
Most important feature - Quality of the weld Types of Welds are:
Groove ( More reliable than others) Fillet (Mostly used, Weaker than groove and others) Plug (expensive – poor transmission of tensile forces) Slot (expensive - poor transmission of tensile forces)
Plug and Slot welds – stitch different parts of members together.
Type of Joints
Butt
Lap
Corner Tee
Typical Welded Corner Joint
Positions of the welds:
Horizontal
Vertical
Overhead Flat
Welding Notations were developed by American Welding Society (AWS). Requires Highly Skilled Labors
Advantages
Economical – Cost of materials and labors.
Efficiency is 100% as compared to rivets (75-90%)
Fabrication of Complex Structures – Easy – like Circular Steel pipes.
Provides Rigid Joints – Modern Practice is of Rigid Joints.
Disadvantages
No provision for expansion or contraction – greater chances of cracking.
Uneven heating and cooling – member may distort – may result in additional stresses.
Inspection is difficult and more costlier than rivets
Most connections are Shop Welded and Field Bolted types.
More Cost Effective Better Strength &
Welded Bolted
Ductility characteristics – Fully welded. End Plate Connection
Purpose - used to connect the members which are required to rotate relative to each other. Pins are cylindrical in shape, made of structural carbon steel, forged and machined to accurate dimensions
Two Types of Pinned Connections
Allows the connecting members - turn through large angles, such as in machine parts, crane booms etc.
Allows rotation through
small angles, primarily due to elastic deformation of the members.
Advantages
Easy Analysis – Moment is Zero at pin.
Free to rotate – to allow for elastic deformations.
Allow for Thermal Contraction and Expansion
Secondary Stresses – Eliminated to some extent.
Disadvantages
Lacks rigidity - noisy joints. E,g bridge under heavy traffic. (so used for very large spans)
Cannot resist longitudinal tension – produces friction that prevents free turning of pins.
Allows the beam end to rotate without a significant restraint.
Transfers shear out of beam
Most Common Types:
Double clip
Shear End Plate
The Tee
Shear Connection
Part of the connection remains stiff in shear - little restraint to motion perpendicular to its plane.
Double Clip (Double Angle Shear
End Plate Shear Connection
Fin Plate Connection
Designed to resist both Moment and Shear. Often referred - rigid or fully restrained connections - provide full continuity between the connected members - designed to carry the full factored moments. Principal Reason - buildings has to resist the effect of lateral forces such as wind and earthquake.
Uses
Between main beams and columns, creating a rigid frame.
Principally to resist lateral loads, however, vertical gravity load - negative bending moments at the ends of the beams.
Bolted splice Moment Connection
Field Bolted Moment Connection
Extended End Plate Moment Connection
Eaves Haunch Moment Connection
Two Step Process
A plate is welded to secondary section (beam) An Angle is welded to Primary Section (column or Beam)
OR single shear plate welded to secondary beam and bolted to Primary beam or column.
The angle or plate will be bolted or welded after erection of the beam.
Skew Plate Connection
Single Angle Connection
Two angles welded or shop bolted to the web of a secondary beam.
After erection the angles are bolted or site welded to the primary member (beam or column).
Double Angle Bolted Connection
Double Angle Weld Bolted Connection
Generally used in case of moment connections.
Two angles are provided at top and bottom of the beam to resist moment.
Generally used for lesser moments where heavy loads are not acting
Top and Seated Angle Connection
Generally used in case of shear connections.
A seating angle - at bottom of secondary beam - shop welded to the primary member.
Seating angle resists vertical shear coming from the beam.
Seated beam connection
Connects beam to beam.
Two Types
Primary Beam to Secondary Beam Connection and
Beam Splice.
Beam to Beam Connection
Beam Splice
Connects column to column.
Column splice comes under this category.
Used to connect column sections of different sizes.
Splices - designed for both moment and shearunless intended to utilize the splices as internal hinges.
Column to Column Connection
Welded Column Splice
Connects Beam to column.
Very Common
A wide range of different types are used
Fin Plates
End Plates
Web or Flange Cleats
Hunched Connections
Beams are normally attached using two or more bolts through the web.
End plate connections
a single plate welded to the end of the beams
Bolted to the column flange or web - two or more bolts pair.
Fin plate connections
Single Plate welded to the Column.
Beams are normally attached using two or more bolts through the web.
Beam to column connections
Steel plates placed at the bottom of Columns.
Function - to transmit column loads to the concrete pedestal.
The design of a column base plate:
determining the size of the plate.
determining the thickness of the plate
A layer of grout should be placed between the base plate and its support for the purpose of leveling. Anchor bolts should be provided to stabilize the column during erection or to prevent uplift.
Column-Base Plate Connections (Also a Moment-connection)
Usually cost of fabrication and erection constitute as high as 50% of the total cost of steel structures, per tones of material used
