Bob
Thanks for the information. As the subject appears to be rather complex,
I’ll need to do some more digging and post a time line for the changes.
Rupert
From:
CBQ@yahoogroups.com [mailto:CBQ@yahoogroups.com] On Behalf Of Bob Webber
Sent: Tuesday, 4 June 2013 9:49
a.m.
To: CBQ@yahoogroups.com
Subject: Re: [CBQ] RPO structural
requirements
Rupert, the specifications varied by era,
and can be found in the Post Office Publication 19 "A Publication of the
Post Ofice department" "Specification for the Construction of Fulll
and Apartment Railway Post Office Cars".
"Structural requirements" are quite lengthy, and vary from era to
era, and prior to 1912 (? - have to find the exact date) - there was little
standardization. Mail cars often were in the middle of a car with Express
on one side and Baggage on the other, with a passageway between along one side
of the car, and the mail apartment against the other wall, with a door to the
passageway. That changed to be no through door, although there was a
crawl through for emergency purposes. OTW, the car apartment could
not be entered from a non-mail portion of or complete car. Several
cars were "grandfathered" in including the wood cars built for
the D&RG narrow gauge (and the C&S predecessors). Also some
branch line cars. Regardless, after that point, they had to have a
certificate of construction to verify certain points.
Live Loads - by 1956, the loads had to be (at least) 20,000 pounds for a 60'
full mail car, and 10K & 5K for 30 & 15' apartments respectively.
Stresses had a table for tension, compression, shear, rivet sheer and bearing -
for center & side sills and bolsters. The buffing static load ranged
from 50,000 to 400,000 pounds depending upon the total weight of empty train
(pounds). There are pages of formulas and calculations related to the
variety of materials, train size and other concerns. Basically
though, a mail car was expected to be the strongest car in a given train (per
foot). This in an effort to prevent telescoping and other such events
that would impair the mail crew.
Unfortunately (for the purposes of the question), by 1956 truss rods (as
referenced) were a thing of the distant past (although, still in use on the
D&RGW NG cars and odd branchline uses). Even at that, if the cars
were touched beyond normal maintenance (strictly defined), they would have to
be totally reconstructed to meet the latest specifications.
There were a variety of cars that had to have applications to the AAR or ARA
(or MCB - depending on era) for modifications to the specifications in order to
fit in the design. It is interesting to note that companies are always
far more concerned for their employes' (correct alternate spelling, as used by
Pullman amongst others) safety when said employes were in another company's
conveyance. And example is the Pullman company's concern for their
porters and wait staff when ensconced within another builder's
cars. This was trumpeted fairly loudly after the Naperville crash,
as Pullman (quite correctly as it turned out) had been reluctant (?) to allow
their porters to staff Budd sleepers and other cars fearing for their
safety. As it turned out, the largest loss of life in said wreck was in
the Budd diner - including some Pullman employes (not working the diner).
This resulted in the welding of a larger center sill adjunct to existing (Budd
pre-war) cars (which one can see on the Nebraska Zephyr cars at IRM). The
purlines also were an issue as they connected similarly to collision posts in
the body as opposed to the corners of the car. Pullman had not been as
concerned in the past with wood cars, or in composition cars.
Basically, once the Post Office Dept. started publishing specifications, the
requirements were for the best practices and materials then in existence and
certified by the AAR (or ARA, MCB).
Bob Webber