The old footbridge over Montlake Boulevard to the IMA has been hit by (yet another) truck and needs to be replaced. The UW is looking for a new design that will be lightweight, green, and at a slightly higher elevation to avoid future truck hits. The initial proposals are to use a bridge consisting of two parallel glue-lam arches with steel ties to resist the outwards thrust. The span is 80 ft, the proposed rise is 10 ft, and the deck width is 12 ft. It is estimated that the total self-weight will be 40 psf of deck area. It must be designed for a pedestrian LL of 100 psf uniformly distributed, or a maintenance vehicle (with no other LL present) that can be represented by a point load of 5 kips. The timber can be stressed to a maximum of 600 psi in tension or compression. a. What cross-sectional area of timber is needed in each arch rib to satisfy the self- weight plus pedestrian LL? b. The vehicle load will cause a moment, which must be resisted in addition to the compression caused by the self-weight. If the ratio h/b for the cross-section of each rib is to be no more than 2.5, select the smallest rib size possible, to the nearest inch. c.Will this size be sufficient to resist the moments arising from the worst case of partial pedestrian loading? If not, find new dimensions that will satisfy both conditions.