AASHTO Design Criteria Applied to Hydraulic Bascule Bridges

is opened and closed, the designer must calculate these factorsbased on small increments of opening. We have foundthe use of a computer to be very beneficial in making thecalculation since the computer can perform such calculationsfor eacli degree of opening in a very short time. This wouldallow tne designer to make the most optimum selection ofcylinder size arid horsepower required. With the proper programthe designer could input leaf dimensions, geometriclocat ions of trunriion, connection points of the cylinders,number of cylinders, size of cylinders, size of the pistonrod, angle of opening under various loading conditions, hisestimate of horsepower required, the efficiency of the systell1and time for acceleration. Because of the rotation ofthe leaf the moment arm between the center of rotation andtne piston rod vary with each degree of opening and sincethe 10 pound wind load is applied to the vertical projectionof the leaf, the forces applied to the cylinder vary witheach moment of opening. With the computer program the designerwould analyze in one degree increments, all conditionsof loading, calculate the length of stroke, momentarm, forces required to push tne leaf up and pull the leafdown, pressures encountered, and time required to move theleaf through each degree of opening.Once the hydraulic cylinders, motor, pumps have beenestablished, various other components must be selected. Inorder to utilize the hydraulic cylinders as an effectivebrake in which the leaf can be held in any position, checkvalves are necessary and should be located as close tocylinder ports as is practical. In our case, pilot actuatedcheck valves are necessary so that when pressure isapplied to the cylinder at one port, the check valve at theother end is automatically opened. Thus whenever the poweror pumps are shut-off the crleck valves automatically closelocking fluid in cylinders and therefore results in holdingtile bridge in its current position. Relief valves are sonecessary that operating pressures do not exceed designliioitations. As we discussed, the maximum operating pressurefor load condition C would be in the range of 1500 toLUUU psi and we should therefore have at an appropriatelocation, a relief valve which is set to the maximum operatingpressure expected, and since the cylinders are to beutilized as brakes with the capability of withstanding theZu pound holding force, a second set of relief valves wouldbe necessary which would have a pressure setting ofsomewhere between 25UO and 3000 psi. The selection ofother components such as counter balance valves andfour-way directional valves, would be selected based on the