A footbridge on a hiking trail is constructed using two timber logs each having a diameter d = 0.5 m (see figure a). The bridge is simply supported and has a length of L = 4 m. The top of each log is trimmed to form the walking surface (see Fig. b). A simplified model of the bridge is shown in Fig. c. Each log must carry its own weight w 51.2 kN/m= and the weight (P 5 850 N) of a person at mid-span. (see Fig. b).

(a) Determine the maximum tensile and compressive stresses in the beam (Fig. b) due to bending.

(b) If load w is unchanged, find the maximum permissible value of load P_max if the allowable normal stress in tension and compression is 2.5 MPa.

Transcribed Image Text:

Ascent Xmedia/Getty Images