Constant Spacing Method

Using this method, the user specifies the Minimum Distance from Curb between the left curb and the left wheel of the truck or the right curb and the right wheel of the truck. The Constant Center to Center Spacing between two consecutive live load positions is also specified. Once the user inputs these two values, the program will generate the first position by placing the truckload at the minimum distance from the left curb. The next position is obtained by moving the live load (truck) to the right of the first position by the constant center-to-center spacing. This process is continued transversely across the bridge width as long as the distance between the right wheel of the truck and the right curb is greater than or equal to the minimum spacing allowed.

Note: For lane loads, the first position is adjacent to the left curb (without any minimum spacing from the curb). The next position is obtained by moving the lane load to the right by the constant center-to-center spacing. The process is continued as long as there is enough space to accommodate another lane load between the rightmost end of the previous position and the right curb. The same process is repeated by placing the lane load adjacent to the right curb and moving it transversely from right to left across the bridge until no more space for the lane load to be placed.

Once all the live load positions are determined, Substructure creates the different live load combinations depending upon the number of loaded lanes selected.

Setting

Description

Minimum Distance from Curb (For Constant Spacing)

Setting	Description
This is the minimum user-specified distance from either the left curb of the bridge to the left wheel of the live load or the right curb to the right wheel of the live load. This input value is only used for truck or tandem loads and not for lane loads.	Default values: 2 ft or 0.6 m.	Range of values that can be input: 0 to 10 ft (or 0 to 3 m).	Note: For the constant spacing method, the lane load is always placed adjacent to the left or right curb.

Center to Center Spacing (For Constant Spacing)

This is the user-specified, center-to-center spacing for placement of various live loads (lane, truck or tandem) for the generation of different live load positions. For example, if center-to-center spacing = 5 ft, Substructure will first, determine the initial position of the live load from the left end of the bridge (first live load position). Assume that the first position is 6.5 ft from the left end; the program will then add the center-to-center spacing to the first position to obtain the second live load position, which is 11.5 ft away from the left end of the bridge. Substructure will repeat the same process by starting from the right side of the bridge.

Default values: 10 ft or 3 m.

Range of values that can be input: 1 to 20 ft (or 0.3 to 6.0 m).