Eng-Tips is the largest engineering community on the Internet
Intelligent Work Forums for Engineering Professionals
-
Congratulations waross on being selected by the Tek-Tips community for having the most helpful posts in the forums last week. Way to Go!
slab thickness for anchor bolts
- Thread starter DrejzaVu
- Start date
apetr26542
Structural
Do you have any uplift? The slab depth will depend on a few things
The weight of the machine and the allowable soil bearing pressure will determine the size of the pad, the thickness will have to be determined based on these requirements such that it can distribute the weight of the machine to the soil.
The weight of the machine and the allowable soil bearing pressure will determine the size of the pad, the thickness will have to be determined based on these requirements such that it can distribute the weight of the machine to the soil.
- Thread starter
- #3
DrejzaVu,
apetr26542 is correct in asking the weight of the machine. If it is moving there is work/force being exerted. If the machine is 10K and moving 10 cm that's not so much. If it is 10 T and moving 10 cm, that is a much bigger problem. In other words, the force exerted on the concrete by the anchor bolts is only part of the stress seen by the pad.
Griffy
apetr26542 is correct in asking the weight of the machine. If it is moving there is work/force being exerted. If the machine is 10K and moving 10 cm that's not so much. If it is 10 T and moving 10 cm, that is a much bigger problem. In other words, the force exerted on the concrete by the anchor bolts is only part of the stress seen by the pad.
Griffy
The uplift apetr26542 is refering to is coming from the earthquake induced lateral forces. If you have a greater overturning moment compared to the resisting moment from the equipment weight, you will have uplift forces.
The bolts must be designed to resist both the shear force generated by the lateral forces and uplift (if any). Embedment is recommended to be at least 8 times the bolt diameter. You must have enough concrete cover underside of the bottom of bolt to ensure bolt performance.
Design doesn't end there. If this is a floor mounted equipment, you have to check whether slab alone can resist all forces or whether you need to provide a thickened pad large enough such that you don't get a soil settlement and/or slab failure.
All depends on the size and weight of the equipment as well as applied lateral force.
The bolts must be designed to resist both the shear force generated by the lateral forces and uplift (if any). Embedment is recommended to be at least 8 times the bolt diameter. You must have enough concrete cover underside of the bottom of bolt to ensure bolt performance.
Design doesn't end there. If this is a floor mounted equipment, you have to check whether slab alone can resist all forces or whether you need to provide a thickened pad large enough such that you don't get a soil settlement and/or slab failure.
All depends on the size and weight of the equipment as well as applied lateral force.
- Thread starter
- #6
The unit is a drum end-over-end rotator (we call it a tumbler). It weighs 1050 lbs and can "tumble" 2 drums of up to 800 lbs each at 13 rpm. The bolt hole is 9/16". The manufacturer does not call out any bolt or anchorage. However, an engineer I spoke with said that bolting is intended to keep the unit from "walking" although they haven't seen that happen with the ones they use.
So based on whyun's post, 8 times bolt diameter (i.e., 1.2")would require the anchor to penetrate 4 inches. Would that make sense?
Mark
So based on whyun's post, 8 times bolt diameter (i.e., 1.2")would require the anchor to penetrate 4 inches. Would that make sense?
Mark
apetr26542
Structural
The unit does not sound that heavy, What are its dimensions.?
- Thread starter
- #8
If the loading on the bolts isn't that heavy maybe you can use some sort of post-installed anchors such as epoxy anchors or expansion bolts. The manufacturer will then give you recommendations on minimum slab thickness in their catalogs. Hilti is a commonly used name. Epoxy anchors typically have much better performance while expansion bolts are easier to install. If you choose to go this route make sure you read up on bolts that are intended for use for dynamic loading. I would suggest epoxy anchors and use a higher factor of safety than that used in the catalogs as recommended by the manufacturer.
Either way, for cast in place anchor bolts the code specifies 3" cover on the bottom for exposure to earth without putting a strict minimum on depth as a function of embed thickness. I would suggest you make the embed no more than 2/3 to maybe 3/4 of the depth unless you follow recommendations by a specific manufacturer for a particular bolt you choose such as the post-installed type, or if you have a particularly deep slab(>12"). I should say that usually by the time you size your foundation/slab for all design loads and provide your 3" of clear cover it is usually thick enough to accept your anchors without a big problem.
Either way, for cast in place anchor bolts the code specifies 3" cover on the bottom for exposure to earth without putting a strict minimum on depth as a function of embed thickness. I would suggest you make the embed no more than 2/3 to maybe 3/4 of the depth unless you follow recommendations by a specific manufacturer for a particular bolt you choose such as the post-installed type, or if you have a particularly deep slab(>12"). I should say that usually by the time you size your foundation/slab for all design loads and provide your 3" of clear cover it is usually thick enough to accept your anchors without a big problem.
8 times the diameter is not a strict requirement but minimum length to avoid doubling the design force level per Uniform Building Code (a penalty for having what code defines as "shallow anchors")
I agree with UcfSE about use of post-installed anchors as it is extremely difficult to set the cast-in-place anchors precisely to match the bolt holes of the equipment.
I agree with UcfSE about use of post-installed anchors as it is extremely difficult to set the cast-in-place anchors precisely to match the bolt holes of the equipment.
jheidt2543
Civil/Environmental
The manufacturer should be able to tell you what the loading is on each bolt. From that you can figure out bolt size and embeddment requirements. If they don't want to tell you, push them a little, they know what the loads are and if you are buying (or have already bought) the machine, that is part of the information you are entitled to. You are not asking them to design a foundation, just what the unfactored loads are. From that you can add a factor of saftey and design the anchorage.
In lieu of relying on manufacturer's "claim" on capacities of various bolts, use the anchors that have already been tested.
Visit to search for research reports on various products. For example, if you do the search, you may find ER-4627 which is for Hilti Kwik Bolt II (expansion anchor into concrete). Report provides shear and tensile capacities for various diameters and embedments.
Visit to search for research reports on various products. For example, if you do the search, you may find ER-4627 which is for Hilti Kwik Bolt II (expansion anchor into concrete). Report provides shear and tensile capacities for various diameters and embedments.
jheidt2543
Civil/Environmental
whyun:
I think you misunderstood my comment or I wasn't clear in stating it. What I suggested to DrejzaVu was to talk to the machine manufacturer, they surly know the loads imposed by the manchine and the reactions to the bolts and they have (in my mind) an obligation to provide it to their customers. Once you have that information the sizing of the bolts and anchorage requirements can be determined.
Hilti, Fastenal and other bolt manufacturers know from their own testing and publish in their catalogs their various fastener capacities. Since they are in the business and are reputable, I take them at their word.
I think you misunderstood my comment or I wasn't clear in stating it. What I suggested to DrejzaVu was to talk to the machine manufacturer, they surly know the loads imposed by the manchine and the reactions to the bolts and they have (in my mind) an obligation to provide it to their customers. Once you have that information the sizing of the bolts and anchorage requirements can be determined.
Hilti, Fastenal and other bolt manufacturers know from their own testing and publish in their catalogs their various fastener capacities. Since they are in the business and are reputable, I take them at their word.
- Status
Similar threads
- Question
- Question
- Question