5.1 Steel Connections,Classification of Connections,Type of connecting medium used Bolted connections Welded connections Bolted-welded connections Riveted connections Type of internal forces the connections transmit Shear (semi-rigid, simple) connection Moment (rigid) connection 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,Type of members the connections are joining Beam-to-beam connections Column-to-column connections Beam-to-column connections Hanger connections,Effect of connections on structures,Mechanical property of connections Strength Stiffness Stability Number and complexity of connections Time for statical analysis Production of drawings Production of connection In the fabrication shop consume much of work content Site production ease for erection,Components of Connections,Welding Is a process of joining metal parts by fusing them and filling in with molten metal from the electrode. Used extensively to join parts and members, attach cleats, stiffeners, end plates, etc. and to fabricate complete elements. Is one of the oldest and reliable methods of joining.,Advantages of Welding Connection Enables direct transfer of stress between members eliminating gusset and splice plates necessary for bolted structures. Hence, joint weight is minimum. Absence of holes improves the efficiency of the section. Less fabrication cost. Offer air tight and water tight joining, and hence is ideal for oil storage tanks, ships etc. Neat appearance and enables the connections of complicated shapes. Rigidity. Welded joints are as strong or stronger than base metal. Less stress concentration. Disadvantages of Welding Connection Requires skilled manpower for welding as well as inspection. Non-destructive evaluation may have to be carried out to detect defects. Welding in field may be difficult due to location or enviroment. Welded joints are highly prone to cracking under fatigue loading. Large residual stresses and distortion developed.,Electric arc welding Manual arc welding: Using a hand-held electrode coated with a flux which melts and protects the molten metal Weld quality depends very much on the skill of the welder Automatic arc welding: A continuous wire electrode is fed to the weld pool. An inert gas is blown over the weld to give protection.,Weld Types,Butt welds Named after the edge preparation, i.e. single and double U and V. Butt welds Fillet weld size is specified by the leg. Partial butt and fillet welds Deep penetration fillet welds,Crack & defects caused by welding Contraction on cooling causes cracking in the weld. Hydrogen absorption is the main cause of hydrogen-induced cracking in heat-affected zone. Lamellar tearing along a slag inclusion is the main problem in plates.,Following defects caused byfaulty welding procedure Over-reinforcement and undercutting Incomplete penetration and lack of side-wall fusion Slag inclusions and porosity,Welding inspection Visual inspection for uniformity of weld; Surface tests for cracks using dyes or magnetic particles; X-ray and ultrasonic tests to check for defects inside the weld; Only visual and surface tests can be used on fillet welds; Butt welds can be checked internally, and such tests should be applied to important butt welds in tension.,Bolts Non-preloaded bolts Hexagon head ordinary bolt with nut and washer is the most commonly used structural fastener in the industry. Common strength grades: 4.6, 4.8. Preloaded or friction-grip bolts Made from high-strength steel. Be tightened to give a high shank tension. Shear in the connected plates is transmitted by friction. Used where strong joints are required, and a major use is in the joints of rigid continuous frames. Must be used with hardened steel washers to prevent damage to the connected parts. Surface in contact must be free of mill scale, rust, paint, grease, etc. Care must be taken to ensure that bolts are tightened up to the required tension.,Methods to achieve shank tension Part-turning Torque control Load-indicating washers and bolts,Connection Design,Weld design Strength calculation of a fillet weld is using throat thickness, which is taken as 0.7 times the size of leg length.,Design of butt welds depends on the welding quality. Design strength is generally taken as equal to that of the parent metal provided matching electrode are used. Full penetration depth is ensured if the weld is made from both sides or if backings run is made on a butt weld made from one side.,Bolts design Depending on the connection shape and the bolts location, bolts are loaded in tension, shear or in combined tension and shear.,For non-preloaded bolts, a shear joint can fail in the following four ways By shear on the bolt shank; By bearing on the member or bolt; By shear at the end of the member; By tension in the member,Shear Failures can be prevented from following measures For modes