Pretensioning anchor bolts

[s_saranya]

Hi,
To model anchor bolts in ABAQUS, pretensioning force should be specified? The anchor bolts are embedded in the concrete

 

[JLNJ]

Is it part of your design intent to pretension the anchor rods?

 

[s_saranya]

No, intent is simulating a anchor bolts in ABAQUS. The anchor bolts are attached to the foundation of a machine. The nut is present on one side only. The other side is inside the foundation. In that case, is it necessary to consider the pretension? . Pretension will be generally considered for a bolt having tightened nuts on bolt side. Also, I am not clear about the concept. I need a proper clarification.


Thank you,

 

[HTURKAK]

SARANYA,

I read your last post 3-4 times and still not sure for your understanding of preloaded anchor bolts..
Is this vibrating machine ? Can you post more info to get more specific responds ?

-I will suggest you search this forum for (with machine anchor preload ) some of the outcomes ;

thread507-192501
thread507-473362
thread507-474830


- Grouting Handbook - A Step-by-Step Guide for Foundation Design and Machinery Installation ( by Donald M. Harrison)
- FOUNDATIONS FOR INDUSTRIAL MACHINES,( by BHATIA )










I cannot give you the formula for success, but I can give you the formula for failure..It is: Try to please everybody.

 

[SWComposites]

Saranya, why are you modelling anchor bolts? What real problem are you trying to solve? Please post a picture or figure of the attachment you are analyzing.

 

[s_saranya]

Hi,
This is a cooling tower model which will be located on roof top of a building. Sub assemblage modelling of connections I am doing in ABAQUS. Spring elements are attached between two base plates to reduce the vibration effects to buildings. Post installed expansion anchor bolts (HSL 3G, M16 grade)are used as shown in the attached picture. The bolts will be arranged in the base plate holes. The base plate is attached to a concrete foundation of M45 concrete of thickness 200 mm (simulating the thickness of roof slab). The connection behaviour will be studied from nonlinear time history analysis later. For this,

i) Pretension load is needed for the bolt(0.8Fy) ?
ii) If pretension load is needed, at what length it should be applied (The anchorage length of bolt is 130mm?
iii) The interaction between concrete and steel bolt should be given as surface to surface contact or embedded constraint?
iv) I am getting error when applying pretension load and surface to surface contact between shank and surrounding area simultaneously.
v) How to classify bolts as high strength bolts? Need some references.

 

[centondollar]

Just do a hand calculation. Check if the roof is axially much stiffer compared to the bolt (this depends on e.g., how well the base plate transmits prestressing from the bolt nut to), choose a thick base plate, and remember to calculate losses (anchorage slip). Also, M16 is a size, not a grade. Make sure the bolt is strong enough (it should be high-strength prestressing wire or a rod with fy >1100,...,1800 MPa) to allow reasonable amount of pretension after losses.

With a 130mm anchorage length, you will find that the losses due to slip - which increase inversely with bolt stressing length - will be very large, and the concept may be infeasible.

i) you decide this, and it is a function of e.g., number of bolts and material of bolts, length of bolts, and of course external tension force.
ii) prestress affects the entire bolt
iii) a hand calculation avoids this problem
iv) a hand calculation avoids this problem
v) it depends on the application, but prestressing strand has yield strength up to 1800 MPa and prestressing rods have up to around 1100 MPa. with a short bolt, the losses may be too large no matter the bolt yield strength.

 

[s_saranya]

Thank you,

I am validating ABAQUS model with experimental results. So the dimensions are already fixed.

for i) , iii) and iv)
Can you suggest any standard reference books?

 

[dold]

s_saranya, you should read the HILTI literature. I think they do specify an installation torque but not a preload. That can be calculated though, I suppose. I'd be shocked if you were able to develop 0.8Fy out of a post installed anchor into the top of a concrete pad.
But, like centondollar said, just do a hand calc for overturning and shear on the anchors and that's it. Doing a nonlinear time history analysis on a piece of rooftop equipment is...ridiculous. I don't mean any offense, but that is a colossal waste of time. Unless you're designing the actual cooling tower and not just the anchorage? Even then, that is way overkill.

 

[s_saranya]

Hi dold,

0.8Fy as suggested from literatures. I am simulating a shake table testing experiment in ABAQUS model and validating it. So it is necessary .