Art. 154. STRESSES IN TRUSSES WITH SUB-PANELS. 



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154. Maximum Stresses in Trusses with Sub-panels. 



In Fig. 208 let us consider the members in the double panel 5-7. 

 When the top chord 5' 7' is a maximum and when the diagonal 

 6'-7 is a maximum there is no stress in the counter G'-7'. When 

 the counter 6'-7' is a maximum, .there is no stress in the dia^o- 



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nal 6'-7. Hence the position of the loads for maximum stresses 

 in these members, cut by the section lm, can be determined by 

 the previous methods. The counter 6'-7' is determined c.s 

 9'-10'. 



The maximum stresses in 6-6' and G'-o result from a maxi- 

 mum load at 6, but G'-5 may also take tension when acting with 

 the counter 6'-7'.' When 5-7' is -stressed, 6'-7 is not in action. If 

 6'-7 is not in action, the only stress in 6'-5' comes from 6'-6, but a 

 stress in 6'-6 tends to produce compression in 6'-5, hence for max- 



Fig. 208. 



imum tension in 6'-5, 5'-7 and 6'-6 may be considered removed, 

 and the stress in 5-7' is found as for a single diagonal in a panel 

 (5-7) equal to 2p. It must be remembered, however, that the 

 maximum in 6 r -7' comes when the panel 6-7 is considered, as 

 given above. (136.) 



When 5'-6' is a maximum, 6'-7' is not in action. Now we 

 may consider any load at 6 as carried to 5 and 7, and that that 

 part of it carried to 7 is taken through 7-5 ' as though it had been 

 brought to 7 by the stringer. Hence for a maximum in 5'-6', we 

 may disregard 6-6' and 5-6' if we call the panel length 5-7=2p. 

 Then we have the ordinary case of a single diagonal in a panel. 



For 5-5' we may do as for 5'-6', since they get their maxi- 

 mum stresses from the same loading. 



For 5-7 the center of moments is at 5'. This case is evidently 



