Chicago,
August 16th, 1900.
A.F. Robinson, Bridge Engr.,
Topeka, Kans.
Dear Sir:-
I enclose you letter received from Resident Engr. Phillips on strength of Howe Truss Rods in bridges built on Eastern Oklahoma and Guthrie & Western Railways. I will be obliged if you will explain how the discrepancy occurred and if rods of sufficient size were not on hand, why an order was not placed for new rods. Assuming that you used 10,000 # per square inch, in determining the size, shown as your dimensions in the table given by Mr. Phillips and where yours are not given, taking the size provided for on standard plans, I make the strain as follows:-
Bridge No 54, Span No. 1 --- 150â
1st Panel 10,500 2nd ã 10 500 3rd ã 10 400 4TH ã 10 600 5TH ã 10 000 6TH ã 10 000 Span No 2 - - - 126ä 1st Panel 10,200 2nd ã 11 800 3rd ã 10 400 4th ã 9 700 5th ã 7 200In this span Mr. Phillips gives for third panel, one 2-1/8 rod and two 1-7/8 rods with a total of 9.854 inches. There is either an error in the size of the rods or in the calculation as the area of the rods as given is only 9.069 sq. in. I have assumed this corrected area in calculating strains.
Span No. 3 - - -126â 1st Panel 12,300 2nd ã 12,800 3rd ã 12,900 4th ã 10,200 5th ã 10,000 Span No 4 - - - 126â 1st Panel 12,900 2nd ã 11,800 3rd ã 14,400Page 99 Volume 23 Splinters transcribed in altered form for the Web by Russell Crump
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4th Panel 11,900 5th ã 10,000The area of the five 2-3/8 rods required on standard plan in first panel is given by Mr. Phillips as 21,150 sq in. whereas it should be 22,150 sq. in.
Span No. 5 Iron not yet provided. Span No 6 - - - - - - 150â 1st Panel 10,500 2nd ã 10 400 3rd ã 10 500 4th ã 10 600 5th ã 10 000 6th ã 10 000 Bridge No 5, Guthrie & Western, 126â span 1st Panel 12,900 2nd ã 11 900 3rd ã 11 900 4th ã 13 300 5th ã 10 000 Bridge No 55, 106â span ö Eastern Oklahoma. 1st Panel 14 500 2nd ã 12 600 3rd ã 13 800 4th ã 10 000 Bridge No. 56, 106â span. 1st Panel 14,500 2nd ã 12 600 3rd ã 11 100 4th ã 10 000I do not think that any of these strains are high enough to warrant changing the rods unless you have used higher strains per square inch than I assume, namely 10,000#. The only points where strains are at all high, being in Span No. 4, Cimarron bridge, where rods in third panel have 14,400# per sq. in. Bridge 55 and 56, Eastern Oklahoma, where strains in first panel are 14,500# per sq. in. and in bridge No. 5, Guthrie & Western, where strains in fourth panel are 13,300# per sq. in.
Please go over the matter carefully with the plans and advise me what loads these bridges are designed for and what will be the maximum strains per sq. in. due to the specified load.
Page 100 Volume 23 Splinters transcribed in altered form for the Web by Russell Crump
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I have written to Mr. Phillips to ascertain what rods, if any, he has left over and wish you would find out whether we have any larger sized rods on hand, that we could substitute for some of the smaller ones at the week spots in these bridges and replace them.
Yours truly,
(James Dun)
Page 101 Volume 23 Splinters transcribed in altered form for the Web by Russell Crump
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