Railroad Loading behind retaining wall

[structbear]

Is the increase of the load required for impact (1.3) for a retaining wall with a railroad surcharge?

 

[RWF7437]

I think the answer may depend on what code you're designing to. If it is AASHTO ( in the US) I believe 1.3 is correct but other codes in other countries may be different.

good luck

 

[PEinc]

Certain, but not all, railroads I've worked around require Cooper E-80 plus 50% impact.

 

[structbear]

AASHTO 3.6.2.1 States that Dynamic Load allowance (Impact) need not be applied to retaining walls not subject to vertical reactions from the superstructure.

I only have a portion of the AREMA code that deals with concrete where it allowa the dissapation if the impact load as determined by the designer.

From your comment it appears that the addition of the impact load shall be specified by Railroad.

If I have a light rail system where a cooper E80 loading will never be achieved in an area where the speed limit will average around 30. Does the AREMA Code require adding a minimum impact load to the surcharge? or is it just generally good practice to do so?

 

[PEinc]

This is long but I copied the following from AREMA's retaining wall section.


© 2002, American Railway Engineering and Maintenance-of-Way Association
AREMA Manual for Railway Engineering 8-5-5
SECTION 5.3 COMPUTATION OF APPLIED FORCES
5.3.1 LOADS EXCLUSIVE OF EARTH PRESSURE (2002)
a. In the analysis of piers, retaining walls and abutments, due account shall be taken of all superimposed
loads carried directly on them, such as building walls, columns, or bridge structures; and of all loads
from surcharges caused by railroad tracks, highways, building foundations, or other loads supported on
the backfill. Piers must also be designed for stream flow pressures as well as ice flow pressures and
collision forces where applicable.
b. In calculating the surcharge due to track loading on an abutment and on wingwalls that are in line with
the abutment backwalls, the entire load shall be taken as distributed uniformly on the surface of the
ballast immediately below the tie, over a width equal to the length of the tie. With increased depth, the
width for distribution can be increased on slopes of 1 horizontal to 2 vertical, with surcharge loads from
the adjacent tracks not being permitted to overlap.
c. To account for variability in backfilling and the dynamic effects of axle loads, abutment backwalls above
bridge seats shall be designed for earth pressures and live load surcharge increased by 100%. This does
not apply to the portion of the abutment below the bridge seat nor the stability of the abutment.
d. In calculating the surcharge due to track loading above a wall and parallel, or roughly parallel, to the
wall, the entire load shall be taken as distributed uniformly over a width equal to the length of the tie.
e. The stability of the abutment or wall as a whole unit, regardless of the distribution of the loads and
surcharges, shall always be checked and shall conform to the requirement of Section 5.4, Stability
Computation.
Concrete Structures and Foundations
f. Live load impact shall not be considered in the design of an abutment or pier unless the bridge bearings
are supported by a structural beam, such as the seat of a spill-through abutment or a pier cap supported
by individual columns, piles, or shafts. In such a case, the impact shall be applied to the beam only, and
not to footings, or piles.
g. For the design of abutments and piers, consideration must be given to all forces transmitted from the
superstructure to the substructure, depending on the bearing fixity conditions.