The Artizan . alterations which have been made in themachinery of the Great Ship since our last notice. PEACTICAL PAPERS FOR PRACTICAL MEN—No. Lattice Gikdees. As girders constructed with a lattice weh are now becoming numerous,it is very desirable that some ready means of calculating the strength ordimensions of any lattice combination should be generally known; wetherefore purpose to enter fully into an investigation of the principles ofsuch structures. Many theories of lattice girders have been published, allon the same principle, that we shall adopt in the present paper, and theyare
The Artizan . alterations which have been made in themachinery of the Great Ship since our last notice. PEACTICAL PAPERS FOR PRACTICAL MEN—No. Lattice Gikdees. As girders constructed with a lattice weh are now becoming numerous,it is very desirable that some ready means of calculating the strength ordimensions of any lattice combination should be generally known; wetherefore purpose to enter fully into an investigation of the principles ofsuch structures. Many theories of lattice girders have been published, allon the same principle, that we shall adopt in the present paper, and theyare all tolerably simple, hut with the one disadvantage of being expressedby trigonometrical qualities, and this we shall especially avoid, so thatour calculations may be readily comprehended by those who have notstudied the elements of trigonometry. We-will commence with some preliminary remarks upon the resolutionof forces, confining ourselves to the problems which have reference to ourpresent subject. Let b o (Fig. 1) represent a beam fixed into a wall obliquely, as shownand let its upper end be prevented from deflecting by a flexible tie a b •from the pomfc b let a weight w be suspended, then will this weight betransmitted to the wall a o through the bar b c, solely for the tie a bbeing flexible, cannot bear any part of the load when in a horizontalposition, although it will be subject to a certain amount of tension,produced by the tendency of b c to revolve round the point c. We maynow state axiom No. 1; deduced from the foregoing remarks it is asfollows:— If a triangular framie of bars be fixed at two of its angles, and a forcebe caused to act at the remaining angle, its direction lying in the plane ofthe triangle, then mill two bars be strained by forces acting in the directionof their length, viz., the bars containing the angle on which the force bending moment can act upon the bar b c, because its extremity b ccannot deflect. It now remains for us to
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