When multiple box culverts span more than 20 feet, the American Association of State Highway and Transportation Officials (AASHTO) defines them as bridge length and, thus, normally requires the use of a full-strength, rigid bridgerail. Using a rigid bridgerail creates a transition problem between the flexible metal beam guard fence, which is commonly used upstream of the bridgerail. It would be safer and more economical to continue the flexible metal beam guard fence across the culvert even when the culvert is more than 20 feet long and when the soil fill depth over the culvert is less than the standard guardrail post embedment depth (38 inches in texas). It was believed that more post could be used (reduced post spacing) with a shallow embedment to achieve the desired guardrail strength. A metal beamguard fence design of this type was crash tested in this study and proved to be unsatisfactory. Another concept investigated was to rigidly mount steel guard fence posts to the top of the culvert deck when full soil embedment could not be achieved. A design of this type was also crash tested in this study and proved to be satisfactory.
Abstract