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Chapter 8 Connection of flange plate with web 1 7.1 Introduction The web is machined and is in close contact with flange; therefore, the vertical loads are directly transmitted to the web direct bearing. The bearing stress on the web should not exceed 0.75 Fy (Clause 2.6.6, p. 22). The connection of flange plate to web is done by intermittent welding. If we have a very short piece of a girder length (a) having two moments M1&M2 and nearly the same shearing force Q, taking the moment about point m; 2 M1- M2 + Qa = 0 M2- M1 = Qa M1= F1 h M2= F2 h F2 h - F1 h = Qa F2 - F1 Q a h F1 s M1 F2 Q Q F2 a a a M2 F1 a = 50 cm 3 Since F2 is higher than F1, there is tendency for flange plate to slide along the web and this tendency must be resisted by weld between web and flange plate. F2 h - F1 h = change in flange stress F2 - F1 Q rate of change in flange stress a h If the thickness of the weld = S, the weld is continuous and the allowable weld stress Fw, Q 2 S Fw h 4 Fw = 0.2 Fu (Clause 5.6.3.2, p. 84) s s For one side weld, Q S Fw h (a) s (b) 5 For one side intermediate weld L2 L L2 L Q S Fw h L L2 L L2 L L2 L L2 Lo (c) For two sides intermediate weld, L2 L L2 L L2 Lo L Q 2 S Fw h L L2 (d) 6 5.6.3.3 Maximum effective length of fillet weld (Not for plate girder) l eff = 70 Size For l > l eff use reduction factor = 1.2 – (0.2 L) / (70 S) 5.6.3.3 One side fillet weld for any plate thickness is allowed 7 L2 L L2 L L2 b Lo b L2 t1 b1 L L2 L L2 t t/2 Lo b t s 8 -Intermittent fillet weld L 0.75 b or 0.75 b1 Tension L1 or L2 16 t or 16 t1 or 200 mm or 12 t1 or 200 mm Compression L1 or L2 12 t 9 The minimum size of fillet welds is 4 mm for building and 6 mm for bridges. The maximum size of fillet weld should not exceed the thickness of the thinner plate to be welded. The minimum size of fillet weld depend on the thickness of the thicker plate:thickness t 10 mm 10-20 (mm) Size of weld S 4 mm 5 mm (mm) 20-30 30-50 50-100 6 mm 8 mm 10 mm 10 - - There are no limitations for the length of fillet weld for flange to web in weld built up plate girder. - Single side fillet welds may be utilized only for static loads 11