Handbook of Civil Engineering Calculations

FIGURE 7

The excess area = hole area - allowable area = 4.00-3.13 = 0.87in^2 (5.613 cm^2 ). Con-
sider that this excess area is removed from the outstanding legs of the angles, at both the
top and the bottom.

4. Compute the moment of inertia of the net section

in^4 dm^4

One web plate,/o 3,456 14.384

Four flange angles,/o 35 0.1456

yfy^2 = 4(6.94)(23.17)^2 14,900 62.0184

Two cover plates:

Ay^2 = 2(7.0)(24.50)^2 8,400 34.9634

/of gross section 26,791 111.5123

Deduct 2(0.87)(23.88)^2 for excess area 991 4.12485

/of net section 25,800 107.387

5. Establish the allowable bending stress
   Use the Specification. Thus h/tw = (48.5 - 8)70.375 < 24,000/(22,00O)
   0
   
   
   • 5
     ; /. 22,000 lb/in
     2
     (151,690.0 kPa). Also, M= flic = 22(25,800)/[24.75(12)] = 1911 ft-kips (2591.3 kN-m).
   
   
   
   


6. Calculate the horizontal shear flow to be resisted
   Here Q of flange = 13.88(23.17) + 7.0(24.50) - 0.87(23.88) = 472 in
   3
   (7736.1 cm
   3
   ); q =
   VQII= 180,000(472)725,800 = 3290 Ib/lin in (576,167.2 N/m).
   From a previous calculation procedure, Rds. = 18,040 Ib (80,241.9 N); Rb =
   42,440(0.375) - 15,900 Ib (70,723.2 N); s = 15,900/3290 - 4.8 in (121.92 mm), where s =
   allowable rivet spacing, in (mm). Therefore, use a 4%-in (120.65-mm) rivet pitch. This
   satisfies the requirements of the Specification.
   Note: To determine the allowable rivet spacing, divide the horizontal shear flow into
   the rivet capacity.

DESIGN OF A WELDED PLATE GIRDER

A plate girder of welded construction is to support the loads shown in Fig. Sa. The dis-
tributed load will be applied to the top flange, thereby offering continuous lateral support.

Plate

Web plate

angle

CA. of angles