a structure is only as strong as its

A structure is only as strong as its weakest link.

CONNECTIONS IN STEEL STRUCTURES

Bolts

Welds

Connecting Plates

Connecting Angles


1. On the Basis of Connecting Medium

Riveted Connections

Bolted Connections

Welded Connections

Bolted-Welded Connections

Pinned Connections


2. According to the type of internal forces the connections are expected to transmit

Shear (semi rigid, simple) connections

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 &

Ductility characteristics –

Fully welded.


Welded

End Plate Connection

Bolted

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 Connection)

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 shear-

unless 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


a structure is only as strong as its

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