check fittings

hi -

check fittings have always been classed as being able to double slippage on load bearing fittings i.e 12.2 kN when used with class A DOUBLES.

in the bs1139 and EN74 it sets out the testing limits but I have not seen info in there on check fittings ...

if this is the case the should this information come from the manufacturer of the double?

cheers OW

outward bound said:

hi -

check fittings have always been classed as being able to double slippage on load bearing fittings i.e 12.2 kN when used with class A DOUBLES.

in the bs1139 and EN74 it sets out the testing limits but I have not seen info in there on check fittings ...

if this is the case the should this information come from the manufacturer of the double?

cheers OW

Click to expand...

Do you mean Check Couplers or Supplementary Couplers??
Checks are what you place top & Bottom of a hanger as a failsafe coupler. (added security not capacity)
Supplementary couplers are the additional ones used when you have exceeded the allowable load on a coupler. (added capacity)

Many years ago SGB did a test on banked, Band & Plates but I don’t know of any tests for doubles in the supplementary formation.
That said if a coupler had a slip value and you use two instead of one then it was always safe to multiply the load capacity by two. Etc etc.

This seemed to change in TG20, when they fell into the “I don’t know the answer” category and used the old fall back of “obtain the information from the manufacturer” get out clause.

However they go further by stating EN12811-1 Annex C table C! IMPLIES that a combined slip resistance of two class AA right angle couplers should be assumed as 1.5 x the slip resistance of a single coupler. And 1.67 for Class BB couplers.

This also indicates to me that they go no further than the addition of a single supplementary coupler!!
Christ know what they would do with my designs from the 80’s with banks of 4, 5 and 6 additional couplers????????

See section 5.9 TG20:13 for more information.

Regards
Alan

Alan,

Agree with all of your comments above. NASC are currently updating the their TG guidance document TG14:?? to take account of testing performed on supplementary couplers by a well known coupler manufacturer. I believe the new document will state that a coupler with supplementary coupler below is good for 1.5 x the load of a single coupler. The testing indicated that the orientation of the supplementary coupler is significant: a forged supplementary coupler works better if installed at 90° to the main coupler whereas a pressed coupler works best if installed in-line. In the meantime we are still using 2 x SWL as is common practice in the industry. A lot of the boiler scaffolds will need re-design as there are usually at least 3 couplers supporting the load.