CONNECTIONS IN STEEL STRUCTURES SEMINAR ON CONNECTIONS IN STEEL STRUCTURES

Introduction Connections are structural elements used for joining different members of a structural steel frame work. Steel Structure is an assemblage of different member such as “BEAMS,COLUMNS” which are connected to one other, usually at member ends fastners,so that it shows a single composite unit.

Components Of A Connections Bolts Weld

Connecting Plates Connecting Angles

Classification of Connections On the Basis of Connecting Medium. According to the type of internal forces. According to the type of structural Elements According to the type of members joining

On the Basis of Connecting Medium Riveted Connections Bolted Connections

Welded Connections Bolted-Welded Connections

Riveted Connections Used for very long time. Made up of: Round Ductile steel bar called shank. A head at one end The length of the rivet should sufficient to form the second head. Design - very similar to bearing type of bolted connection.

Installation 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

Riveting is no longer used… The introduction of high strength structural bolts. The labour costs associated with large riveting crews The cost involved in careful inspection and removal of poorly installed rivets. The high level of noise associated with driving rivets.

Bolted Connections Included - Decreased stregth. Fastened Together primarily by Bolts. Bolts may be loaded in: Tension Shear Both Tension & Shear Threads of bolts under shear force: Excluded - Increased strength Included - Decreased stregth.

Types Of Bolts Bearing type bolts High strength friction grip bolts (HSFG)

The most common type is bearing bolts in clearance holes, often referred to as 1. Black Bolts Ordinary, unfinished, rough, or common bolts. Least Expensive Primarily - Light structures under static load such as small trusses, purlins etc

2. 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

3. 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

High Strength Friction Grip (HSFG) Uses when bearing type bolts slips under shear High strength bolts (8G or 10K grade) Pre-tensioned against the plates to be bolted together so that contact pressure developed between the plates being joined Prevents relative slip when extra shear is applied Higher Shear Resistance.

Advantages Disadvantages 1. The bolting operation is very silent 2. Bolting is a cold process hence there is no risk of fire 3. Bolting operation is more quicker than riveting. Less man power is required in making the connections. Disadvantages 1. If subjected to vibratory loads, results in reduction in strength get loosened. 2. Unfinished bolts have lesser strength because of non uniform diameter

Welded Connections whose components are joined together primarily by welds. Welding Notations were developed by American Welding Society (AWS).

Types Of Weld • 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.

Positions of the welds Horizontal Vertical Overhead Flat

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.

Disadvantage No provision for expansion or contraction therefore greater chances of cracking. Uneven heating and cooling - member may distort - may result in additional stresses. Inspection is difficult and more costlier than rivets

Bolted- Welded Connections Most connections are Shop Welded and Field Bolted types. More Cost Effective Better Strength & Ductility characteristics –Fully welded.

According to the type of internal Shear (semi rigid, simple) connections Moment (rigid) connections

Shear (semi rigid, simple) connections Allows the beam end to rotate without a significant restraint. Transfers shear out of beam Most Common Types: Double clip Shear End Plate Fin Plate

Moment (rigid) connections 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.

Field Bolted Moment Connection Bolted splice Moment Connection Field Bolted Moment Connection

According to the type of structural Elements Single plate angle Connections Double web angle connections Top and seated angle connections Seated beam connections

Single plate angle Connections Two Step Process A plate is welded to secondary section (beam) An Angle is welded to Primary Section (column or Beam) single shear plate welded to secondary beam and bolted to Primary beam or column.

Double web angle connections 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).

Top and seated angle connections 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

Seated beam connections 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.

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

Beam to beam connections Two Types Primary Beam to Secondary Beam Connection Beam Splice

Column to column connections (column splices) 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.

Beam to Column Connections 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 single plate welded to the end of the beams Bolted to the column flange or web - two or bolts pair. Fin plate connections Single Plate welded to the Column. Beams are normally attached using two or more bolts through the web.

Column Base Plate 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.

R Usually cost of fabrication and erection constitute as high as 50% of the total cost of steel structures, per tones of material used