ARMY TM 5-5420-212-10-1MARINE CORPS TM 08676A-10/1-1Section V. OVERBRIDGES - DOUBLE STORY6-12.GENERALThis section provides the information needed to construct overbridges in double story configuration. Over bridgesare constructed over existing bridges that have been damaged or have a low class capacity. The abutments of theexisting bridge are used as bearing points for the overbridge. It is important to ensure that the overbridge does not comeinto contact with the existing bridge span while traffic is crossing. Overbridges can be built with or without launchingnoses.6-13.DESIGNa.The design for overbridges constructed with launching noses is the same as a bridge being built over a gap.Particular attention must be paid to deflection of the far bank end of bridge and the launching nose cross girder setting.b.For all overbridges, the amount of packing under the bankseat beam must be calculated using the followingformula and steps (1) and (2) below:P = P1 +P2where:P = Height of packingP1 = Deflection of overbridgeP2 = Height of existing bridge above baseline through bearing points atends of existing bridge.(1)Measure height of existing bridge (P2) by using, the baseline joining the ground levels at the proposedlocations of the BSBs as a datum.(2)Find maximum deflection (P1) of overbridge to be constructed from the following table 6-30.(3)Using information found in (1) and (2), determine amount of packing (P) to be used under the ends ofthe overbridge.6-67
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