Improvement of Freeboard Conditions on Pontons in High-Velocity Flow: Model Investigation
Abstract
Model studies of pontons used in the construction of floating military bridges were conducted at the Waterways Experiment Station during 1945-1946 for the Engineer Board, Fort Belvoir, Virginia. The general purpose of the studies was to develop a ponton bow shape to increase freeboard on the bow and sides when used with (a) individual pontons, (b) pontons normally spaced in a bridge (15-ft centers), and (c) pontons closely_ spaced in a fully reinforced bridge (7.5-ft centers). Of particular concern was the improvement of side freeboard conditions on the H4 pont on when used in a raft or bridge. All tests were conducted on pontons constructed to a scale of 1:15 and located in a flume 4ft wide with the flow maintained at a depth equivalent to 20 ft in the prototype. To investigate the expected performance of adjacent pontons in a floating bridge, rafts of four- and seven-ponton units were constructed and tested in the model. It was determined from the model study that, while the present M4 ponton performed satisfactorily as a single ponton unit, its performance in high-velocity flow when used as a support for rafts or bridges was inadequate. The wave formed by the bow of the pontons, being restricted to the narrow space between pontons, resulted in a rapid loss of freeboard in this area. In order to improve conditions when the pontons are used in a raft or bridge, it was found necessary to flatten the rake of the bow and to increase the frontal area so as to direct a larger percentage of the flow under the pontons rather than along the sides. The flat rake and increased frontal area resulted in full use of the dynamic force of t~e stream as a lifting factor. The design providing best freeboard conditions at the bow and on the sides of pontons in a raft incorporated a scow bow shape and has been designated in this report as the type "B" scow bow ponton.
Document Details
- Document Type
- Technical Report
- Publication Date
- Jun 01, 1948
- Accession Number
- ADA637728