## Load Distribution Among Fasteners

## Load Distribution Among Fasteners

(OP)

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.

## RE: Load Distribution Among Fasteners

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.

## RE: Load Distribution Among Fasteners

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?

## RE: Load Distribution Among Fasteners

http://naca.larc.nasa.gov/reports/1947/naca-tn-1458/naca-tn-1458.pdf

There are many other interesting reports at the same web site.

## RE: Load Distribution Among Fasteners

Nigel Waterhouse

nigelw@flightcraf t.ca

Kelowna Flightcraft

A licensed aircraft mechanic and a proffessional engineer, who attended university in England and graduated in 1996. Currenty living in British Columbia,Canada and working for Kelowna Flightcraft as a design engineer responsible for aircraft mods and STC

## RE: Load Distribution Among Fasteners

## RE: Load Distribution Among Fasteners

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

## RE: Load Distribution Among Fasteners

In order to determine the load distribution, a finite element based analysis can be used. The joint is broken down into a series of spring elements. The plates are divided into a number of springs lying between each fastener, which is its self, portrayed as a spring. The spring constant of the plate is a function of cross sectional area and E (Youngs modulous), the spring constant of the fastener (C) is calculated using the NACA document. Once the equations describing deformations of these springs has been derived they can be solved simply in Excel using simple martix inversion methods (which Excel does very well). You don’t need to spend vast sums of dollars and time with expensive FEA software to do this.

The whole point of this exercise is to determine what variation in the plate thickness (spring stiffness) will give an even load distribution. The results of this detailed design and analysis can be seen in joints that are tapered or stepped

The next stage in the joint analysis is the assessment of the severity factor. This accounts for the effects of the fastener type, method of installation, interference, hole preparation and so on.

Once the severity factor has been determined the fatigue life of the joint can be predicted. This is very important in new designs and also in repair and modification. Fatigue life of repairs and mods can be compared to the original structure, which forms a sound basis for assessing its suitability.

Fastener load distribution is important and can be calculated with relative ease.

Nigel Waterhouse

nigelw@flightcraf t.ca

Kelowna Flightcraft

A licensed aircraft mechanic and a proffessional engineer, who attended university in England and graduated in 1996. Currenty living in British Columbia,Canada and working for Kelowna Flightcraft as a design engineer responsible for aircraft mods and STC

## RE: Load Distribution Among Fasteners

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.