Reading CFAST result in Patran

[mavechin81]

I have fittings connected with 3 CFASTs. If I would like to check the tension load and shear load in the fastener, should I sum all the loads in tension or just take the maximun will do? same goes for the shear?

Any idea?

Thanks.
Mave

 

[rb1957]

each CFAST models an individual fastener ?

so each fastener sees the individual CFAST results, yes?

(ie, why would you sum ? ... possibly you might average over the 3)

shear would be the vector sum of the two in-plane results, yes?

Quando Omni Flunkus Moritati

 

[mavechin81]

The 3 CFASTs are represent the fasterner joint through the fittings. Consider only one bolt.

 

[rb1957]

ok, so they're the 3 orthogonal directions (x,y,z).

if one is aligned to be tension then vector sum the other two for the shear.

if not, vector sum the three components, figure out the tension direction, dot product for the tension, and vector sum for the shear component.

i don't think you can vector summ the three components and compare to tension allowable.

if it generates a +ve MS, you can numerically add the three components and compare to the smaller (tension or shear) allowable. this is a short cut (some might say sloppy) but i'd defend it (as being extremely conservative) if it shows a large MS.

the point about the large MS is why do a "fussy" calc and get MS >> 2 when a simple calc gives you MS > 2

Quando Omni Flunkus Moritati

 

[mavechin81]

Thanks for your reply rb1957 .
However, I had once consulted the MSC guy and they suggested me to use the Max load among those CFASTs. Just I not sure what is the logic/assumption behind so I would like to know more details about this.

BTW, the 3 CFASTs are in-line (out-of-plane), see below:

____|o|o|o|____
________________| |_________________

 

[mavechin81]

********** ____|o|o|o|____
________________| |_________________

2 L-fittings on the top connected horizontally at the vertical flange to Back-to-back angle at the bottom

 

[rb1957]

ok, you have a tension clip with three tension fasteners ...

1) it'd be reasonable to apply the average of the three elements to all three fasteners;
2) remember "heel and toe"
3) account for the preload
4) draw better sketches next time ... sketch something (in Word, with pencil and paper, ...) and attach a file

Quando Omni Flunkus Moritati