huangyhg

1 ton hoist calculation
i am putting a 1 ton hoist up. it is a 16 ft length and 15 ft high. we have a base of 32 in square 3/4 inch thick steel. the base is anchored to a poured concrete slab that is at least 8 inches thick. the 8 anchors are rated at 9000 lb in tension. the moment at the top of the beam is m=fd= 32000 ftlbs. so how do i figure the amount of resisting moment is needed and if the 8 anchors will be enough?
the simple approach.....the moment at the base can be replaced by a couple...use the upward side of the couple to check your tension as if it were for a single bolt at the innermost edge of your bolt group (statically determinate). then divide by the number of bolts on that side only and you should be close!
is this a free standing jib crane with a circular base?
is it supported on a structural slab above grade or slab-on-grade?
if it is at grade, you need to provide a square footing with enough weight to exceed (counterbalance) the overturning moment by a factor of safety of two. you would also need to check the soil bearing pressure under the footing. jib crane manufacturers will sometimes have a suggested footing size that you can use as a starting place or you can do it by trial and error.
you should calculate the actual tension in the anchor bolts and then make sure that it cannot pull out of the concrete or yield with an appropriate factor of safety. aci 318-02 appendix d can give you some guidance.
this is not a free-standing jib, it will be ties into a overhead crane rail structure. it is just a slab on grade. i will liiik into the aci code
thank you
if i understand your last post, the member that is supporting the rail wil have supoorts at the top and bottom (that is at the floor level and the rail system above). if this is the case, the the moment can be resolved into a couple of horizontal forces at the top and bottom. you will the have a horizontal force to take care of at the top connection of the supporting member, and the bottom force will have a horizontal force and a vertical force, which is equal to the hoist load + the weight of the hoist, rail and support
is this a jib crane on a column which spans from the floor to the rail structure above? if that is the case, then why do you have such a large base plate with so many anchor bolts?
does the rail structure provide bracing in both directions, or just one? i would hope that you would want bracing in two directions.
the crane rail structure is only attached at the top of the column. it is attached with two welded 3 in square beams. the column sits off from the crain rail by 12 inches.
will you have lateral (horizontal) support at the top of the column from the connection to the crane rail? also, will you have a moment connection at the hoist rail (supporting the one ton hoist) to the column? if the answers are both yes, then see my previous post.
from your first description i gathered this to be a free-standing crane attached at through a baseplate into a concrete slab. since you have top and bottom attachment, i agree with jec67's answer; considering that your are not actually transferring moment to the slab, but the bolts will be in horizontal shear. have you considered the effect of this crane's loading and moment on the crane rail to which it is attached?
the reason for you asking the question and the good advice given above.
a little caveat based on an incident that i observed a few years ago. a similar mounted jib (3 ton) crane along with a newly installed overhead crane 15 tons vs original 10 ton with supposedly completely rerated support steel came crashing down. fortunately only feelings were hurt. in short the overhead crane was at its capacity? along with the jib? at capacity. as the overhead passed the jib something moved and overhead came down. the support columns were free standing with only x bracing. 3 columns had to replaced. i didn’t get to see how they were bent
the report on the incident wasn’t made public. there were all kinds of tales about the incident such as the new beam crane was 2" short and the had 1" spacers ready to install on the crane rail support offset brackets, there were already had 1" spacers under the brackets. another was that the base plate bolt holes had been slotted, they were, i saw them in the scrap pile. another was that both cranes were overloaded at the time, probably based on what was on the shop floor at the time.
to top it all off the company that done the design and supervised the redesign and installation of the new crane conducted the failure investigation.
here is some information on jib cranes. these people always seemed quite helpful when we used them.

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