FAQQuestion: Due to the position of the load points the loading plane and associated bracing, etc may be asymmetrical. But what about other elements of the bridge? For example, if I need to double a truss member to adequately support the 3cm position, would I need to double the corresponding truss member on the 6cm side as well, or could I leave it as a single or possibly eliminate it altogether? Would this be allowed, or would my bridge be disqualified?
Answer: There is no requirement for any kind of symmetry in the contest rules.
Question: Does the bridge need to be symmetric about centerline longitudinally and/or transversely?
Answer: There is no requirement for symmetry in the contest specifications. Given that the loading locations are not symmetric it is not practical to require that the bridge be symmetric.
Question: In the specifications, 2c states that the bridge must provide a horizontal
support for the loading plate. My design is 40 mm wide, so the loading plate is in full contact with the bridge width wise at both loading points. When the loading rod is at 6 cm from the center of the bridge, the loading plate overhangs the end unsupported for 12 mm. Does the entire loading plate have to be in contact with my bridge, or can it overhang on the end?
Answer: It is not required that the entire lower surface of the loading plate be in contact with the bridge. It is very common to see bridges that only support the loading plate with two thin strips in the lateral direction at each loading location. One of these strips being on each side of each loading location to provide stability. It is also common for bridges to only provide support with thin strips in the longitudinal direction. These often being main structural elements of the bridge.
Question: If I build my bridge such that the loading plane is located on the top surface of the bridge, then is contest rule 2d which requires passing a PVC pipe horizontally across the bridge irrelevant with respect to the minimum width needed for the bridge?
Answer: There is no minimum width requirement in the specifications. All bridges whether they have portions above the loading plane or not must allow the 1.5 inch schedule 40 PVC pipe to pass horizontally across it. The passing of the pipe across the bridge has two purposes: (1) to simulate the passage of traffic across a real world bridge and (2) to check that the supports at the loading locations are in the same horizontal plane. If a bridge is entirely below the loading plane then passing the pipe across it should not pose a challenge. The second check of all supports at the loading locations be in the same horizontal plane is still required.
Question: In the construction portion of the rules, part d states that a PVC pipe has to be passed horizontally across the bridge with the pipes lower surface on the loading plane and the pipe must be touching both loading locations simultaneously. Since I am designing my loading plane to be located at the top of my bridge (90 mm above the base of the bridge), is it required to have some sort of support beams located at the side of my bridge in order to prevent the pipe from rolling off to the sides? Or will the judges move the PVC pipe by hand in a way that the pipe won't be allowed to roll off?
Answer: There is no need for a railing above the support surface to make sure the PVC pipe does not roll off the bridge. It is the responsibility of the check-in judges to control the PVC pipe while they are using it to check a bridge.
Last update: November 19, 2016
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