# Should P-Δ effect be considered for struts of a braced excavation?

Building codes such as BS5950 provide clear guidelines on how to consider P-Δ effect due to sway of a vertically loaded portal frame or single storey building, causing additional moment in the columns.

Should this sway frame effect be extended to the horizontal members of the braced frame structure in an excavation if the walls are not so stiff (such as an interlocking pipe pile wall system in water) and can move longitudinally (in-plane)? If so, how would the effects of P-delta (I am only interested in the big delta) be applied to the waling-strut combination.

I would appreciate if answerers can point to relevant literature to support the answer.

Generally, in geotechnical engineering you won't allow much movement, especially for excavation support. Nevertheless, you will always have small movements but this is usually too small to consider P-Δ effect and safety factors account for it. Most software automatically do this. If you really want to be conservative allow $0.02H$, where $H$ is your height of excavation as movement and calculate P-Δ.