Inter-rivet buckling 1

[midsidenode]

I'm performing some crippling analysis using Needham and need to compute some allowable inter-rivet buckling stress of some aluminum skin. The fasteners are countersunk tension head rivets and i planned on using L'/p = (2(2^.5)s)/t with the applicable column instability curve to get by allowable value. This would be fine with one row of rivets -but there are 2 rows of rivets (staggered) on this compression member. Does anyone know how to compute L'/p for 2 staggered rows of rivets?

 

[graemew]

A complicated subject with an empirical base, connected to effective sheet widths. See Bruhn Section C7.12 to C7-20 for discourse. Fir is elastic, wrinkling is plastic.
With staggered rows, use the lengthwise spacing of each row to calculate Fir for each row unless the 1/2W calculated from the effective sheet width puts each row within the influence of the other (this will normally be the case). If so then use p=diagonal spacing between rivets to compute Fir.
Bear in mind that the whole deal is empirical.

 

[40818]

I have seen the use of the short fastener span length as the unsupported distance when the diagonal length gave the "wrong" answer. This in certification files of a major OEM for a very popular commercial aircraft.

 

[737eng]

40818,
Was the answer too conservative or did testing show that the panel buckled between fasteners prior to what was calculated?