Cast-in-bolt Development Lengths to AS3600 1

[ljk80oze]

Hi

I am curious as to what embedment depth and end fixing arrangement is being specified for cast-in-bolts. AS3600 defines the development length of plain bars to rely on standard hooks, except that the straight extension shall be the greater of 8db or 140mm. Doesn’t this imply that a plain bar can only ever develop 50% of its capacity (limited to 1 hook).

When dealing with cast-in-bolts I have always specified a reasonable cast-in-depth of at least 20db (more in blockwork) and a bolt head & washer at the end of the bolt. The basis for this being that the end ‘head’ would develop the bar (>10 area of the bar – Cl. 13.1.2.6) and that anything shorter than 20db ‘doesn’t look right’. Cl 13.1.2.7 however, limits the development to hooks only and my approach would not comply.

What is the approach being adopted by other engineers? Is the 8db and 140mm straight extension for the cogs being used – this must be painful in blockwork?!?!

Also as follow on question: Is the approach being adopted for both grade 4.6 & grade 8.8 bolts? It seems flawed if the development lengths would remain the same – it seems intuitive that the development length in the embedment material should be proportional to the load……?

Cheers

Liam

 

[csd72]

Liam,

Look at the Australian AISC steel connections manual or the design of portal frame buildings book these have a page on required embedment for hooked and headed studs.

csd

 

[dbuzz]

The Australian Steel Institute's Design of Structural Connections is a great reference for the design of anchor bolts and anchor bolt groups. Don't rush out and by a copy, a new edition one is due late-2007. I typically specify Grade 250 round bar for anchor bolts.

 

[csd72]

dbuzz,

yeah thats the one I meant, the green book.

csd

 

[ljk80oze]

Hmmm probably should have looked there first!

Thanks guys.

 

[sdz]

The anchorage methods in the green book are out of date.
You are best to use ACI 318M, Appendix D.
Hooks on plain bars can straighten and pull out so use of headed anchors is preferred.

 

[apsix]

I would guess that not many of us would have access to ACI 318M.
I agree that the short hook example shown in the green book is suspect.

 

[sdz]

ACI 318M D.5.3.5
The pullout strength of a single hooked bolt ... shall not exceed
Np=0.9 f'c eh do

where 3do <= eh <= 4.5do

cap reduction factor=0.7, N*<= 0.7Np