Connections in steel structures

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1. Connections In Steel Structures By Hariyali Pujara

2. Introduction Connections are the devices which are used to join elements of a structure together at a point such that forces can be transferred between them safely. Historically, most major structural failures have been due to some form of connection failure. Steel connections have a direct influence on the cost of the framing system. While a connection may be efficient in the use of material, it may still be very expensive to erect. Repetitive connection design may save costs.

3. Continue…. Components of connection Bolts ( Image is from Google)

4. Rivets Continue…. ( Image is from Google)

5. Weld Continue…. ( Image is from Google)

6. Connecting Plates Connecting Angles Continue…. seat angle and clip plate, end plate, cleats ( Image is from Google)

7. Types Of Connections Connections depend on: Type of loading, Strength and stiffness, Economy, Difficulty or ease of erection Based on means of connections Bolted Connections Welded Connections Riveted Connections Based on forces to be transferred Shear Connections Moment Connections Beam and column Splices connections Bracket connections etc….

8. 1.Bolted Connections Bolting is the preferred method of connecting members on the site. S everal types  of bolts are used in bolted connection. Unfinished bolts or black bolts or C grade bolts (IS 1363 : 2002) Turned bolts Precision bolts or A grade bolts (IS 1364 : 2002) Semi-precision bolts or B grade bolts (IS 1364 : 2002) Ribbed bolts High strength friction grip bolts (IS 3757 : 1985 and IS 4000 : 1992)

9. Continue.. Black Bolts: It is the most common type of bearing bolts in clearance holes, often referred to as ordinary bolts. They are popular since they are economical, both in terms of material and installation costs. The force transfer mechanism under shear is as shown in Fig.

10. Bolt Shear Transfer Mechanism In Bearing Connections The force is transferred by bearing between the plate and bolts at the bolt holes. The bolts experience single or double shear depending upon the plate configuration. The failure may be either by shearing of the bolts or bearing of the plate and the bolt. Disadvantage: B earing type of bolted connections is that the elements undergo some slip even under a small shear, before being able to transfer force by bearing ( Image is from Google)

11. 2. H igh strength friction grip (HSFG) bolts. In HSFG bolted joints, high strength bolts are pre-tensioned against the plates to be bolted together, so that contact pressure is developed between the plates being joined. When external shear force is applied, the frictional resistance to slip between the plates prevents their relative slip. These bolted joints achieve higher stiffness in shear because of frictional resistance between the contact surfaces. Continue..

12. Bolt Shear Transfer Mechanism In HSFB Connections Only when the externally applied force exceeds the frictional resistance between the plates, the plates slip and the bolts bear against the bolt holes. Thus even after slip, there is a reserve strength due to bearing. Disadvantage: The HSFG bolts are expensive both from material and installation points of view. They require skilled labour and effective supervision. ( Image is from Google)

13. Continue… Bolted connection further can be classified in two: Lap joint Butt Joint Lap Joint : When the two members to be connected together by overlapping then the joint is called lap joint . A single bolted lap joint and a double bolted lap joint are shown in figure respectively. ( Image is from Google)

14. Continue… Butt Joint : When the two members are to be connected by placing the members end to end and additional plate/plates provided on either one or both sides to attach them properly , then this joint is called butt joint and the additional plate is called cover plate. ( Image is from Google)

15. Which joint is better and which joint is more desirable? It is more desirable to provide a butt joint rather than a lap joint for main two reasons: In the case of a double cover butt joint , the total shear force to be transmitted by the members is split into two parts and the force acts on each half. But in the case of lap joints , there is only one plate one which the forces acts and therefore, the shear-carrying capacity of a bolt in a double cover butt joint is double that of a bolt in a lap joint.   In the case of a double cover butt joint , eccentricity of forces does not exist and hence bending is eliminated , whereas it exists in the case of a lap joint.

16. Continue.. ( Image is from Google)

17. 2.Riveted Connections Riveted joints are very rare in modern steel construction practice, were predominantly used in railway bridges (vibration) in India and it is very similar to bearing type of bolted connections. S tructural rivets are driven hot, the rivet shank expands to fill the hole while being driven. ( Image is from Google)

18. Types of riveted joints A riveted joint may be classified according to arrangement of rivets and plates Lap joint Single riveted lap point Double riveted lap point Butt joint Single riveted single cover butt joint Single riveted double cover butt joint Double rivet double cover butt joint

19. 3.Welded Connections Welded connections are direct and efficient means of transferring forces from one member to the adjacent member. Welded connections are generally made by melting base metal from parts to be joined with weld metal, which upon cooling form the connection. The welded connections in a majority of the cases may be categorised as fillet weld and butt (or groove) welds .

20. Continue.. Fillet welds , are made against two surfaces of adjacent plates to join them together. Butt welds , are made by butting plate surfaces against one another and filling the gap between contact surfaces with weld metal, in the process fusing the base metal also together. ( Image is from Google)

21. Fillet Weld Butt Weld simple, fast and economical to make more expensive than fillet welds because of the edge preparation required no prior edge preparation is necessary, easily designed and fabricated to be as strong as the member does not require very skilled labour. require more skilled manpower, than that required for filled welds. less attractive in appearance. better appearance, compared to fillet welds, and poorer performance under fatigue loading, and better fatigue characteristics, compared to fillet welds, Throat thickness=0.707 x weld size Thickness=(5/8) x thickness of thinner plate not appropriate to transfer forces large in magnitude easy to detail and the length of the connection is considerably reduced. Difference Between Fillet Weld And Butt Weld

22. B ased on forces to be transferred 1. Shear Connection A shear connection (also called a simple connection) transfers shear forces and little or no moment to the connecting member, thus allowing end rotation of the member . Shear connections may be made to the web of the supported member while the flanges remain unconnected. ( Image is from Google)

23. Continue.. Colum web in shear ( Image is from Google)

24. 2. Moment Connections Moment connections are also called rigid connections. Moment connections carry a portion or the full moment capacity of the supported member thus preventing any end-rotation of the member and also carry the shear component of the load. Relative rotation between the supporting and supported members is negligible. In this type of connection both the webs and flanges are connected. ( Image is from Google)

25. Continue.. Column flange in bending ( Image is from Google)

26. 3. Beam and column splices It is often required to join structural members (Beam, column) along their length due to the available length of sections being limited and also due to transportation and erection constraints. Such joints are called splices. Typical bolted column splices used for  rolled I section and hollow section  members are shown in the figure on the right. ( Image is from Google)

27. Thank You….!!!!