Computer study—Truss Stiffening Strategy. For the truss in Example 8.7, use the RISA-2D computer program to 

(a) Recompute the vertical deflection of F if the areas of members BC, CD, DE, EF, FA, FC, and CE are doubled. What is the percent increase in total volume of material used? What is the percent reduction in deflection? 

(b) Recompute the vertical deflection of F if only members AB and BF have double the area. What is the percent increase in total volume of material used? What is the percent reduction in deflection? 

(c) Using only Table 8.2, explain your result.

Example 8.7

(a) Determine the relative movement between joints B and E, along the diagonal line between them, produced by the 60-kip load at joint F (Figure 8.12a). Area of bars AF, FE, and ED = 1.5 in.² , area of all other bars = 2 in.² , and E = 30,000 kips/in.².

 (b) Determine the vertical deflection of joint F produced by the 60-kip load.

 (c) If the initial elevation of joint F in the unstressed truss is to be 1.2 in. above a horizontal line connecting supports A and D, determine the amount each bar of the bottom chord should be shortened.

Figure 8.12a

Table 8.2