Thanks Pete. I will do what you suggest.
The center section was welded onto the cross braces. It is 2 inch wide x 3/16 thick aluminum bar stock. There are two pieces, one for each end, and the welding started at the middle and proceeded outward toward each end, one weld after another.
The inner line is the edge of the cross brace before any welding. The outer line is the cross-brace edge just before the last weld is done. The distance between the two is about a millimeter. This shows how aluminum shrinks during welding.
The ramp was made in a similar way except the center bar was welded onto each end first. The middle welds were done second. This produced tension stress in the middle bar due to shrinkage and it contributed to warping the ramp. The ramp middle is bowed upwards.
It is important to pay attention to weld sequence to prevent stresses from shrinkage.
The ramp was held down with blocks under the center and each end was unsupported and tied down. The ramp was bowed under tension in the opposite way it would shrink due to the welding of the center piece.