47 JOURNAI^ OF THE 



In the elevation of one truss of the structures shown 

 by fig-. 2, the centre line of chord is 45 ft. long- and is di- 

 vided into three equal panels. From centre line of chord 

 to bottom of posts is 4 feet, thus g-iving- the leng-th of 

 inclined rods AC (from washer to foot of post) 15.52 feet 

 and the leng-th of horizontal rods CC 15 feet. 



We shall suppose that the two suspended beams on 

 either side of the left post, transfer to the chord throug"h 

 the hang-ers, a load of 14 thousand pounds and the sus- 

 pended beams at the rig-ht post similarly transfer a load 

 of 4.5 thousand pounds. [All loads, reactions and stresses 

 will be expressed in thousand pounds.] 



Call/ the part of the load 14 that is supported by the 

 chord acting- as a beam and therefore 14 — p will be the 

 part held up by the left post. The downward thrust of 

 the post on the ties g-ives a stress in the left inclined tie 

 = 15.52(14— /))-^4 and in the horizontal tie, 15(14— /)-^4. 

 This last tension, when resolved at foot of rig"ht post into 

 components, g"ives a tension in inclinced tie there and 

 compression in post, the same cis found at the left apex 

 C, the triang-les of forces being* equal at the two apices 

 as the stress in the horizontal tie is the same in both. 



The rig-ht post thus pushes upwards with a force 

 14 — /, which is assumed, as we shall find it to be, g-reat- 

 er than the load 4.5 applied to chord at rig-ht post. The 

 difference (14 — f) — 4.5 —^.z^^p represents then, the up- 

 ward thrust ag-ainst the chord there which must be sus- 

 tained by the chord acting- as a beam. 



The chord acting- as a beam, therefore sustains a 

 downward force over left post of/ and an upward force 

 at rig-ht post of (9.5 — f). By the law of the lever, these 

 forces cause a downward pressure at the left abutment 

 of {-p — 3.166) and an upward effort at rigfht abutment 

 equal to (6.333 — p). 



As the vertical components in both inclined rods are 

 each ( 14 — p) we have, as the total pressure of truss on 

 left abutment, (;^— 3.166) + (14—/) = 10.833 and at rig-ht 



