NOTES ON THE EXACT COMPUTATION OF 

 THE QUEEN POST TRUSS. 



The Queen Post Truss is extensivel}^ used in the con- 

 struction of ordinary hig-hway bridges, as on account of 

 its simple details it is easily constructed by the averag-e 

 carpenter. As usually built by him, there are no coun- 

 ter braces in the middle panel, so that for an eccentric 

 load, the stiffness of the chord has to be depended upon 

 to transfer part of the load to either abutment. Plate 1 

 represents a bridge composed of two Queen Post trusses 

 placed parallel to the line of road and sixteen feet apart 

 in the clear. The ends of these trusses rest upon wood- 

 en timbers (wall plates) at either abutment and the long- 

 vertical rods hold up the suspended beams which extend 

 under the bridge from truss to truss. The joists which 

 hold up the planking of the roadway are placed parallel 

 to the trusses and rest at their ends upon the suspended 

 beams and the wall plates. Any load which comes upon 

 the planking is transferred by these joists, acting as 

 beams, to the suspended beams and wall plates. The 

 load thus transferred to a suspended beam is carried to 

 its ends and thence by the vertical rods to the upper 

 joints of the truss, whence it travels down the rafters or 

 main braces to the abutments. For a uniform load over 

 the bridge both suspended beams carry the same loading 

 and .the computation of the stresses in the truss members 

 is made in the usual manner. If, however, a heavy con- 

 centrated load, as that due to a road roller or a crowd of 

 people, is supposed to act on only one suspended beam, 

 the investigation is of a different character. The part of 

 this concentrated load which is held up by the vertical 

 rods, meeting at an upper joint of a single truss, will be 



