load distribution among fasteners

huangyhg

load distribution among fasteners
does anyone know of a formula for how the load is divided among a line of fasteners (bolts or rivets) when two strips are overlapped and joined by numerous (>2) fastenters in a row, then subjected to tension? i've found qualitative information that the end fasteners carry the bulk of the load, but no quantitative formulas. this same situation would apply to riveted joints in plates where more than 2 rows of rivets are used.
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hi butelja!
i guess there is no formula available for the loads taken by each bolts, because the complete set up has many unknowns and we have 3 basic plane static equations. yes u are right in saying that end fastners carry more load than the intermediate bolts. in general civil engineering practice these rivets/fasteners are designed assuming that all the fasteners share the loads equally. infact we consider the critical path of the failure and then compute the tensile capacity of the connection(the objective of the civil engineer ends here). i guess as a mechanical engineers u must be well aware of this fact.
yeah one thing can be done - analyse the connection on ansys or cosmos by fea. i will try to check the answer and see if anything turns up.
bye and thank you for a good querry.
interesting question. as a structural engineer, we assume the load is always equally distributed. however, it seems to make sense that the end connection could potentially see the most load.
i have found no provision in the 1997 ubc to support this and wonder if a cyclical loading intensifies this effect.
do you suppose that welds also have stress concentrations near the ends?
butelja (visitor)7 dec 99 13:48
i have found the answer to my earlier post. the problem was analyzed and experimentally verified by naca (precursor to nasa) in the 1947 technical paper "analytical and experimental investigation of bolted joints, technical note no. 1458", by samuel j. rosenfeld. it is available (free) in its entirety at:
there are many other interesting reports at the same web site.
i have devised a method based on the naca document you found. it is an excel spread sheet that determines the load distribution through joints, if you are interested in it let me know.
nigel waterhouse
the comments about ductility of structural steel (and some other metals that have not been hardened) are quite correct when we consider the ultimate strength of a statically loaded typical civil engineering structure.
however, structures that have connection with mechanical equipment that produces cyclic loading (particularly higher frequencies with stress reversals) may not quickly reach the point where the whole joint becomes ductile in normal service. the unequal stress situation may remain 'locked-in'. in instances like this the unequal load distribution may be critical and produce premature failure of the more highly stresses fasteners if they are not equally stressed
the importance of fastener load distribution depends on the application of the joint. if the joint is to be statically loaded, then an 鈥榓verage鈥?load distribution is satisfactory. the maximum running load of a riveted or bolted lap joint being equal to the number of fasteners multiplied by the joint strength of the fastener multiplied by the number of rows, divided by the pitch. if, on the other hand, the joint is subjected to regular cyclic stress, load distribution becomes very important from a fatigue point of view. this is particularly important under loading conditions in which the fasteners behave as linear elastic   
cfpeng the detail of joint dynamics is very interesting. as a civil structural the assumptions of joint failure mode are as previously mentioned.
the performance of bolted timber connections however are probably more critical in that ultimate yield does not really have a true plastic state . ( or does it ? )
the other question that pops up is related to joint performance under seismic conditions. i am not sure if this is a serious concern.