Through the iterative design process, the layout of the proposed Sea Bright pedestrian bridge superstructure and substructure has been designed. The proposed bridge has a design width of 30 feet and consists of either 56-foot spans, totaling a 448-foot total span. Using Microsoft Excel, a trial girder was selected and tested for shear, flexure, and deflection. A W21x68 girder was selected to adequately support the pedestrian live load of 90 psf. Following the girder selection, shear studs were designed to properly transfer the forces from the 6" concrete deck onto the girders. The calculations yielded a requirement of 122 shear studs, spaced 6 inches center to center.
The bridge is supported by a concrete pier cap and three concrete columns at 10-foot spacing. A design height of 24 inches, a width of 30 inches, and a total length of 30 feet were selected. The pier cap is subjected to a max shear of 152 kips and a max moment of 375 kip*feet. The pier cap holds the required reinforcement of 6 #8 rebars in the bottom and 6 #8 rebars spanning 23 feet in the top half of the pier cap. The top reinforcement was designed using the moment diagram and developmental length to determine the location and length. Tied reinforcement of #4 stirrups at 11" spacing was calculated to provide additional reinforcement to the pier cap. Using RISA2D, the deflection of the pier cap was tested with two supports at each end and three supports spaced evenly from each end. The two supports produced a deflection of 1.62 inches, while the three supports produced 0.041 inches of deflection. Three columns were selected due to the maximum allowed deflection of 0.36 inches, per NJDOT and AASHTO. A cross section of the substructure and superstructure of the bridge can be seen in Figure 1.
The geotechnical analysis of the bridge loads was performed and it was determined that due to drivability issues with piles, the bridge will be supported by drilled shafts. The drilled shafts will be 36 inches in diameter with a total length of 117 feet. The longitudinal reinforcement was determined to be 12 #18 rebar and the transverse was determined to be #3 rebar at 12-inch spacing. Topping the drilled shafts is a concrete pile cap that is 35'x15'x3'. A detail of the deep foundation design can be seen below in Figure 2.
The intersections on either side of the existing bridge were redesigned featuring a small, single-lane, roundabout on the Rumson side of the bridge. The area previously occupied by the vehicular bridge will be used to create a recreational area and a parking area for those using the pedestrian-only bridge. In Sea Bright, the existing traffic layout was converted to have 2 11-foot lanes in each direction to handle traffic and reduce congestion. Additionally, a 7-foot bike lane was added along with more sidewalks and crosswalks to promote a more walkable environment. Figure 3 and Figure 4 show the proposed redesign located in Rumson and in Sea Bright, respectively.
