The Forth Bridge/Inspection and Testing of the Forth Bridge by the Board of Trade

by Wilhelm Westhofen

APPENDIX.

INSPECTION AND TESTING OF THE FORTH BRIDGE BY THE BOARD OF TRADE.

Fig. 157. Diagram showing positions of test loads.

The official inspection and testing by the Board of Trade Inspectors took place on Tuesday, the 18th February, and the two following days. The inspectors were Major-General Hutchinson, R. E. , Major Marindin, K.E., and Major Darwin, R. E., and they were assisted by Mr. W. N. Bakewell and his assistants, of the Forth Bridge Surveying Department.

The conditions, as regards the structure, were the same as on the occasion of the preliminary trials excepting the following:—Ballast, consisting of coarse screened gravel to the extent of about 600 tons, had been distributed over the structure, being laid over the buckle-plates in the 6-ft. way, and between the troughs of the two lines; on the other hand a considerable amount of staging suspended from the cantilevers and central girders had been removed. The dead-weight in the end boxes of the two fixed cantilevers had also been increased to 1000 tons in each case. The trains used on this occasion consisted of:

2 Locomotives and tenders in front	146	tons.
44 Wagons (loaded with pig iron) at 15 tons 10 cwt.	682	,,
1 Locomotive and tender in rear	73	,,
Total for each train	901	,,
Or for both trains	1802	,,

The length of each train was :

3 Engines	44	ft.
44 Wagons	752	ft.	5	in.
Total	896	ft.	5	in.	—close buffered.

The load was thus somewhat more concentrated than on the first occasion.

Along the footpaths on both sides of the internal viaduct stations had been prepared by driving in copper tacks upon which the levelling staffs were placed. There was a station at the centre of each tower, at each of the vertical columns, and at the ends of each bay in the cantilevers, also at each end and at the centre of the central connecting girders. All stations had been levelled several times over, and carefully checked and plotted. On the morning of the inspection, and previous to any train being allowed on the structure, the whole of the stations were gone over again, both by the Forth Bridge surveyors and, subsequently, by the officers of the Board of Trade Major-General Hutchinson taking one side and Major Marindin the other. The stations in the cantilever end piers and at the vertical columns were taken as fixed points, and all other levels were referred to these as benchmarks.

First Position of Trains.—The trains were now moved side by side over the south approach viaduct and along the Queensferry south cantilever until the front engines were close to the south vertical columns. Levels were now taken on both sides at every station, but only maxima are here recorded the intermediate deflections were throughout in proportion.

	Deflection at	ends of	Bays 2 and 3 on	east side =	1¼	in.
,,	,,	,,		west side =	1	in.

Second Position of Trains.—The trains were next moved forward on to the Queensferry north cantilever, the front engines being 6 bays into the south central girder the rear engine being about 40 ft. clear of the Queensferry north vertical columns. The results were as follows :

Deflection at end posts of Queensferry north cantilever, on east side	= 7⅜	in.
Ditto, ditto, on west side	= 7⅜	,,
Deflection at end post of Inchgarvie south cantilever, on east side	2⅛	,,
Ditto, ditto, on west side	2⅛	,,
Upward deflection in Queensferry south cantilever at end of bay 3, on east side	=1¼	,,
Ditto, ditto, on west side	1¼	,,

Third Position of Trains.—The trains were then moved on to the Inchgarvie south cantilever, the front engines being about 40 ft. short of Inchgarvie south; vertical columns, the rear engine 6 bays in south central girder. The results were :

Deflection at end post of Inchgarvie south cantilever, on east side	7⅛	in.
Ditto, ditto, on west side	=7⅛	,,
Deflection at end post of Queensferry north cantilever	colspan=2	not observed
Upward deflection at end post of Inchgarvie north cantilever, on east side	=3⅞	in.
Ditto, ditto, on west side	=3⅞	,,

Fourth Position of Trains.—The trains were next moved into the Inchgarvie north cantilever, the front engines 6 bays into the north central girder the rear engines 40 ft. outside Inchgarvie north vertical columns. The results were :

Deflection at end post of Inchgarvie north cantilever, at east side	=7⅛in.
Ditto, ditto, on west side	=7⅛	,,
Deflection at end post of Fife south cantilever, on east side	=2	,,
Ditto, ditto, on west side	=2	,,
Upward deflection at end post of Inchgarvie south cantilever	=3	,,
Ditto, ditto, on west side	=3¾	,,

This concluded Tuesday's work.

Wednesday, 19th February, 1890.—The position of the locomotive engines were reversed this day—one in front, two in rear. The weights and lengths of trains remained the same.

Fifth Position of Trains.—The trains were first moved into the Fife south cantilever the front engine about 40 ft. short of the Fife south vertical columns—the rear engines 6 bays within north central girder. The results were:

Deflection at end post of Fife south cantilever, on east side	= 7⅛ in.
Ditto, ditto, on west side	=7½	,,
Deflection at end post of Inchgarvie north cantilever, on east side	=2	,,
Ditto, ditto, on west side	=2¼	,,

Upward deflection in Fife north cantilever—

End of Bay 2, on east side	=1½	,,
,, ,, on west side	=1½	,,
End of Bay 3, on east side	=1¾	,,
,, ,, on west side	=1½.	,,

Sixth Position of Trains.—The trains were then moved into the Fife north cantilever—the front engine outside the north cantilever end pier upon the viaduct—the rear engine 40 ft. short of the Fife north vertical columns. The results were as follows:

Deflection at end of bay 3 in Fife north cantilever, on east side	=1	in.
Ditto, ditto, on west side	=1+1⁄8	,,

After this various trials were made with the trains running abreast at moderate speeds, and up to about 20 miles per hour. During these trials observations were taken of the deflections to north or south, as the case might be, of the tops of the vertical columns with the passage of the heavy trains. The observations were taken by means of theodolites placed on the circular granite piers. Referring again to the various positions of the trains as above, the movements noted were as follows:—

First position		:	not observed—see 6th position.				in.
Second	,,	:	Queensferry	vertical columns	moved towards	north	2
,,	,,	:	Inchgarvie	,,	,,	south	1
Third	,,	:	,,	,,	,,	south	2
Fourth	,,	:	,,	,,	,,	north	2
Fifth	,,	:	Fife	,,	,,	south	2
Sixth	,,	:	,,	,,	,,	north	1

From a suitable station near the old castle on Inchgarvie observations were also taken of the deflections of the end posts of the four free cantilevers during the passage at speed of heavy trains, and these agreed exactly with those obtained during the deadweight trials.

For testing the deflections in the central connecting girders two trains were made up, consisting each of three engines and six trucks at each end, these trains weighing 405 tons each, or a total weight of 810 tons upon each girder. Both in the north and south spans the application of this load produced a deflection of slightly over l+¹⁄₂ in. at the centre of the girder. The test loads applied to the 168 ft. spans of the approach viaducts produced deflections ranging from ¹¹⁄₁₆ in. to ¹³⁄₁₆ in., or a mean of ³⁄₄ in.

Various special trials with trains running in opposite directions, and meeting each other at specified points, also took place.

The atmospheric conditions during the three days were not of the most agreeable character—an extremely cold and stiff easterly breeze blowing the whole time, and terminating in the afternoon of the 3rd day in a storm of sleet and rain.

The report by the Board of Trade Inspectors issued on February 24, 1890, is of a highly satisfactory and complimentary character, and enters into every question of interest to the travelling public.

On March 4, 1890, during a violent gale which blew from the south west with a pressure of 20 lb. per square foot, the Prince of Wales closed the last rivet in the north central girder, and from the south port of the south cantilever end pier declared the bridge open. At the banquet which followed the ceremony, and to which nearly 600 guests had been invited, the Prince of Wales annonnced that the Queen had conferred upon the Chairman of the Forth Bridge Company, Mr. Matthew William Thompson, and upon Sir John Fowler, K.C.M.G., the honour of baronetcies; upon Mr. Benjamin Baker the honour of K.C.M.G.; and upon Mr. William Arrol, the honour of a knighthood.

Between five and six o'clock the same night two heavy goods trains passed over the bridge—one from north and one from south, and commencing from the morning of the following day, Wednesday, 5th March—when passenger traffic between Dunfermline and Edinburgh was established between 40 and 50 trains have been run every day and night over the now completed Forth Bridge.