Anchor bolt configuration on a base plate
Anchor bolt configuration on a base plate
(OP)
Hi,
The connection of a silo leg to a foundation has been designed. There are 4 anchor bolts on a rectangular the base plate. The shear and tension capacity of 2 bolts is sufficient. If I replace the 4 bolts by 2 bolts would the configuration matter. What is the minimum number of bolts required?
Thanks
The connection of a silo leg to a foundation has been designed. There are 4 anchor bolts on a rectangular the base plate. The shear and tension capacity of 2 bolts is sufficient. If I replace the 4 bolts by 2 bolts would the configuration matter. What is the minimum number of bolts required?
Thanks






RE: Anchor bolt configuration on a base plate
While 4 bolts can be assumed as a FR base, 2 bolts would mean a low PR base (depending on how you arrange the bolt configuration). the K factor for the column leg would be double (at least in one axis) which would result to unusually large leg for a silo. The pedestal/footing size would be substantially reduced due to the absence of FR moments.
my opinion was based on my previous designs of silos. hope to hear comments from anyone.
RE: Anchor bolt configuration on a base plate
For your silo, if its part of a complete component that would stand on its own, you probably don't have to worry about it - but if the silo leg is initially placed by itself, there would be a concern.
As far as structural design goes, two bolt columns have been used in the past. However, if one bolt gets damaged (which does happen quite often) then you'd be in trouble with only one bolt left.
RE: Anchor bolt configuration on a base plate
i was referring to silo legs with no braces, case where bulk carriers are loading underneath and other equipment installations that prohibits braces. one of my previous design (1990) was a 450 MT fly ash silo on 15m legs, no braces, 2-75mm dia. x 1.4m anchor bolts (2 bolts - specifically requested by client engineer, my objections then).
if your silo legs are fully braced, then 2 bolts would not be a problem, it only boils down if there are codes that prohibit it, on the design point of view, i cant remember any.
RE: Anchor bolt configuration on a base plate
The silo is seismic rated and the legs are braced. There are 6 legs placed in a circular fashion. Meaning 24 bolts to be placed in precast. Due to the constrution issues if even one bolt is off by an inch, can the precast anchors be replaced by drilled in anchors?
Silo's are usually pre engineered. So, is it the suppliers responsibility to determine whether the silo needed is seismic rated or non seismic?
RE: Anchor bolt configuration on a base plate
I've worked in the silo and agg bin industry in the US for about 12 years. Concerning your question about "the suppliers responsibility to determine whether the silo needed is seismic rated or non seismic" I'd have to say based on my experience that sometimes they do design per the appropriate requirements, but many times they don't. If you are concerned (and you probably should be) ask someone in a position of responsibility to get the design specs and if necessary the calcs. Is there a PE involved? Who is the engineer of record?
Regards,
-Mike
RE: Anchor bolt configuration on a base plate
"OSHA Safety and Health Standards for the Construction Industry, 29 CFR 1926 Part R Safety Standards for Steel Erection" (can be found at www.osha.gov)
RE: Anchor bolt configuration on a base plate
DaveAtkins
RE: Anchor bolt configuration on a base plate
RE: Anchor bolt configuration on a base plate
i am not in the US, so i am not concerned with OSHA. but as a thought, ive been working on many projects (all outside US) and 2-bolt configuration is very common, which in design can be modelled as PR base or even conservatively as pin base (at least in one plane). one obvious advantage with 2-bolt configuration is the simplicity in construction for cast-in-place anchor bolts. during construction, i have not observed damage in erections of 2-bolt config. either, as long as the column is properly erected with temporary braces/guy wires.
RE: Anchor bolt configuration on a base plate
DaveAtkins
RE: Anchor bolt configuration on a base plate
"Post means a structural member with a longitudinal axis that is essentially vertical, that (1) weighs 300 pounds or less and is axially loaded (a load presses down on the top end), or (2) is not axially loaded, but is laterally restained by the above member. Posts typically support stair landings, wall framing, mezzanines and other structures."
RE: Anchor bolt configuration on a base plate
DaveAtkins