B-36 Some material savings can be achieved when adopting a limited capacity beam, strengthened by two cover plates to flanges in zones of higher bending requirements. w Length of cover plate Strength due to cover plate Capacity of W-shape M-diag. x x tptp ApAp tptp d

B-37 After plate thickness and width are determined, the plate length is determined from the B.M. diagram. x x tptp ApAp tptp d

B-38 For the simple beam shown, design the beam utilizing W 18x46 which is available in stack, Fy = 36 ksi Assume full lateral bracing (L b = 0). Solution Factored load W u = 1.2 D.L L.L. = 1.2 x x 2.8 = 5.92 k/ft. Example B – ft DL = 1.2 k/ft LL = 2.8 k/ft

B-39 = = in 3 > in 3 O.K. Shear strength of w 18  46  v V n = 176 kips  v V n > V u = 59.2 k OK Length of Cover Plates: Moment capacity of beam =  b M p = 0.9  90.7  36/12 = 245 k·ft.

B-40 The beam moment capacity is good up to (x) location. The middle region requires coved-plates. 20 ' need plate x 5.92 k/ft x

B-41 Development, length. Need extra length to develop the strength of the plate, This extra length at each end is called “development length”. This should be added to the theatrical length to get the actual length..  Minimum extra length at each end = 2  width of plate In this example, need total length (twice width) Use 9'- 4" length 5'- 4" 9'- 4" 5'- 4" 20' W18  46 plate