Hi,
Can someone explain why an achor has reduced strength compared to a bolt of the same diameter and grade?
For a bolt the reduction factor is 0.8, but for an anchor is around 0.71 the maximum. Not entirely sure if the smaller reduction factor is only for post installed anchors or should be applied to cast in anchors as well.
Thank you.
Hi Steluta,
Thank you for your reply.
Yes, you are right, the new standard as 5216 uses same design formula as SA TS 101. For the steel strength calculation, it remains unchanged. The link below provides more information on AS 5216:
https://ask.hilti.com.au/questions/what-is-as5216-it-seems-to-be-related-to-anchoring/dxuk9t
Also, I would like to confirm that the design of the tensile steel capacity for post install anchors.
AS 5216/SA TS101 requires the charactersitc tensile steel strength to be calculated to AS 4100
In AS 4100:1998, Clause 9.3.2.2, it provides the nominal tensile capacity (Ntf) of a bolt in tension as below
Once the characterstic tensile steel strength is calculated, then apply the capacity reduction factor from AS 5216, Table 3.2.4 as below.
The capacity reduction factor of G5.8, G8.8 is 0.667.
Hence, the design steel strength in tension shall be 0.667 * tensile stress area * the ultimate tensile strength of the steel.
Profis anchor design software was programmed under this logic.
The lower reduction factor utilsed in the standard for post installed anchors is due to influences of the variations found in this fastening connection.
Cheers,
Dom
Hi Steluta,
Thank you for your question.
Is your question pertaining to the steel strength only? As per AS 5216 clause 6.2.2 as shown below, the steel strength shall be calculated as per AS 4100.
May I know how you got the 0.71 reduction factor in steel strength?
Cheers,
Dom
Hi Dom,
Thank you for your response. Yes, my question is pertaining to the steel strength only.
At the moment I only have SA TS 101:2015 available, so table 3-1 shows the following formula for Steel failure - fasteners/Tension ØMs=5fyf/(6fuf)<=1/1.4 which results in 0.667 for G8.8; 1/1.4=0.714
I should have AS 5216 available today, but I assume ØMs formula has not changed since Hilti PROFIS software comes up with the same value for G8.8.
As per AS 4100 the capacity factor for bolts is 0.8.