THE ST. Louis COLISEUM 365 



UNIT STRAINS. 



Tension 16,000 Ibs. per sq. in. 



Compression, for lengths of 90 radii or under 12,000 " " " " 



Compression, for lengths of over 90 radii 17,100 57 I -=- r 



Combined stress due to tension or compression 



and transverse loading 16,000 " " " <; 



Shear on web plates 7,5oo " " " " 



Shear on pins 11,000 " " " " 



Shear on rivets 10,000 " " " " 



Bearing on pins 22,000 " " " " 



Bearing on rivets 20,000 " " " " 



Bending, extreme fibre of pins 25,000 " " " " 



Bending, extreme fibre of beams 16,000- " " " " 



Lateral connections have 25 per cent greater unit strains than the 

 above. 



In Case II of trusses, the above unit strains were increased one- 

 third. The main and radial arch trusses are built a* shown in Fig. 

 170, except that above the haunches the ribs of the radial arches are 

 T-shaped instead of I-shaped, i. e., they have no inside flanges. The 

 purlins are triangular trusses 4^ feet deep, made of angles. The brac- 

 ing between main arch trusses terminates at the bottom with heavy 

 portal struts of triangular box section. The lateral rods are not car- 

 ried to the ground on account of the obstruction they would make. The 

 radial trusses are coupled together in pairs with lateral rods down to 

 the ceiling line. The thrust due to wind is transmitted from them into 

 the line of girders around the structure at this point, and into the ad- 

 joining floor systems. The compression ribs of the main and radial 

 arches are stayed laterally by angle iron ties, connecting to the first 

 panel-point in the bottom chord of the purlins. In the planes of the 

 first diagonal braces of the trusses above the haunches, diagonal rods 

 connect the bottom ribs of the trusses to the upper ribs of the next 

 trusses. No struts were used between the bottom chords, as they would 

 have been directly in the line of vision from the rear gallery seats to the 

 farther end of the arena. The front and rear girders supporting the 

 gallery and main floor beams are tied together with a triangular system 

 of angle iron bracing. 



To provide for expansion, the radial purlins and all the girders be- 

 tween the arches have slotted hole connections in every alternate bay. 

 The diagonal rods between the two lines of ridge purlins were tightly 



