In some truss structures,such as the roof truss undergoing heavy upward wind load,or the truss on both sides of a footbridge connecting different buildings,the service conditions do not allow us to place lateral support for the compressive chord members.

The calculation for the effective length of the compress ive chord members in the truss can not be considered as hinged joints or fixed i n each member end,because the compressive chord members of the truss are restra ined by the contiguous ones.

The tension chord of trusses has the duty of providing lateral support to the connected compressive web members,so that its slenderness ratio should satisfy necessary requirement and relevant provision in design code has to be amended.

Basing on the comparison of the limitations Of compression member slenderness ratio, flange width- thick-ness ratio, web depth-thickness ratio, the author analyses the differences and similarities Of the Chinese and the American steel structure design codes and regulations.

By comparing local stability limits of I-shaped compression member web for steel truss in both seismic and without seismic areas,main influence factors of local stability of I-shaped compression member web in steel truss are proposed,as well as the solving methods.

A geometrical relation between longitudinal displacement and transverse displacement of a Euler's pole is(obtained) by Lagrange's description method,and a nonlinear dynamic model expressed by partial-differential equations is(established.