54n 



STEEL ROOF TRUSSES AND MILL BUILDINGS. 



inertia of the truss to the moment of inertia of the column equal to infinity. The formula is 

 sufficiently accurate with a ratio of four and is on the safe side. 



Case IV. Columns Fixed at Base and Fixed at Top. Formulas for Case II and Case III 

 may be used, the value of h being taken as the distance from the point of contraflexure to a point 

 midway between the foot of the kneebrace and the top of the column. The point of contraflexure 

 may be calculated by formula (4), page 556. 



Stresses in Rigid Frames. Formulas for stresses in rigid frames with pin-connected 

 columns, for different loadings are given in Fig. 63. Formulas for the general case are given 

 in the second column, while formulas for special- cases are given in the third column. The 

 formulas are very much simplified where the columns and the top girder have the same moment 

 of inertia. 



CASE I. COLUMNS HINGED AT BASE AND TOP: CONSTANT OR VARIABLE CROSS-SECTION. 



A 

 d 



.H' 



Hd 

 r/fe 



H'd- 

 Pe-'M 



CASE 2. COLUMIiSHlHGEDATBASE AfiD FlXED ATTop:C/?05S-5ECTWrt CONSTANT. 



CASE 3. COLUMNS HINGED AT BASE AND FIXED ATTOP: CROSS-SECTION VARIABLE. 



H 



FIG. 62. STRESSES IN MILL BUILDING COLUMNS CARRYING CRANE LOADS. 



