12 Report of a Plan for luilding 



ford's plan for building a hanging iron bridge across the Menai 

 Strait, and the evidence taken last year by the Holyhead Road 

 Comnnssioners. 



With the view of being able to lay before the House all that could 

 be advanced to prove the prncticability of this plan, your Com- 

 mittee examined Mr. Telford concerning each specific part of it, 

 and they then examined Mr. Rennie, to ascertain how far he 

 concurred in the calculations and opinions of Mr. Telford : they 

 also examined Mr. Donkin, whose attention has been for a con- 

 siderable time applied t() this principle of bridge-building, and 

 who ranks very high as a civil and practical engineer, and is 

 Chairman of the Committee of Mechanics of the Society of Arts 

 and Manufactures. 



In order to bring the whole subject before the House in the 

 most distinct manner, it appears to be adviseable to treat of it 

 under the following heads : — 1. The Abutments. — 2. The Iron 

 Work. — 3. The Strength of the Bridge. — 4. What probable Un- 

 dulation or Side Vibration. — 5. What Contraction or Expansion. 

 — G. The Means of Repairing the Bridge. 



I. 77ie j4hittments. — The abutments will consist of the whole 

 of the masonry work which is expressed on the plan ; each of 

 the two principal piers will be 60 by 42^ feet at high-water mark, 

 having a foundation of rock. These piers when connected with 

 the whole of the remainder of the masonry will form a mass con- 

 structed with blocks of hard limestone, of much greater power 

 than is ictiuisite foi supporting a bridge of this kind. Mr. Rennie 

 being asked this question, " Can there be any difficulty in making 

 the piers capable of bearing the bridge ?" answered, " None in 

 the world ;" and explained to your Committee, that it was equally 

 practicable to make a pier to sustain a weight drawing inward, 

 as this bridge will draw, as to sustain a weight pressing outward, 

 in the way an arched bridge presses: from thence he argued, that 

 the lateral tension of the proposed bridge would not occasion any 

 difficulty. He mentioned that the lateral pressure of the side 

 arches of the Southwark bridge was about 3,700 tons, and that 

 this was infinitely greater than the strain of Mr. Telford's bridge. 



IJ])on the summit of each of the two main piers will be erected 

 a frame of cast metal, of a pyramidical form, for the purpose of 

 raising the cables, from which the bridge is to be suspended. 

 As the cables will l)e carried from the tops of the pyramids, so 

 as to form nearly similar angles on each side of them, the pres- 

 sure vyill be almost perpendicular; and Mr. Telford says, " It is 

 quite impossible the weight of the bridge can crush them, in con- 

 sc<iuencc of the well ascertained fact, that it requires a weight 

 of from four to five tons to crush a cube of a quarter of an inch 

 of good cast metal." 



2. The 



