pony truss stability

huangyhg

pony truss stability
using the holt procedure (t.v. galambos, "guide to stability design criteria for metal structures,"5th ed., wiley).
table 15.1 has various values for 1/k values for cl/p and n, however it only goes to 16 panels.  how would you extrapolate values for a 18, 20 and 22 panel truss?
would you use both the value interpolated from colum 16 panels only, and then from the lutz fisher column only? the one that gives the biggest buckling factor k you should be able to use for one conservative result.
aastho recommends the timoshenko method for highway pony trusses and the holt method for pedestrian bridges, why differnt recommended methods?
thanks, rich