ARMY TM 5-5420-212-10-1
MARINE CORPS TM 08676A-10/1-1
Section V. OVERBRIDGES - SINGLE STORY
5-12.
GENERAL
This section provides the information needed to construct over bridges in single story configuration. Over bridges
are constructed over existing bridges that have been damaged or have a low class capacity.
The abutments of the existing bridge are used as bearing points for the over bridge. It is important to ensure that
the over bridge does not come into contact with the existing bridge span while traffic is crossing. Over bridges can be built
with or without launching noses.
5-13.
DESIGN
a.
The design for over bridges 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 launching nose cross girder setting.
b.
For all over bridges, the amount of packing under the bankseat beam must be calculated using the following
formula, and steps (1) and (2) below:-
P = P1 + P2
where:
P =
Height of packing
P1 =
Deflection of over bridge
P2 =
Height of existing bridge above baseline through bearing points at ends of existing bridge.
(1)
Measure height of existing bridge (P2) by using as datum, the baseline joining the ground levels at the
proposed locations of the BBS.
(2)
Find maximum deflection (P1) of over bridge to be constructed from the following table 5-7.
(3)
Using information found in b.(1) and (2), determine amount of packing (P) to be used under the ends of
the over bridge.
5-41
