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Dear Engineers, Without going into any in-depth design I have just checked roughly the steel column size required for the stability concern, i-e, the size required to keep the slenderness ratio (k l/r) within 200, it comes out to be around 36 X 36 inches X 1/2 inch thickness, which gives the slenderness ratio of 187. I am not sure about the thickness requirement at this stage because it will also be governed by the fulfillment of strength requirements, i-e, the design load-moment interaction. I believe that every code has the stability requirements (The slenderness limitation), depending upon the importance of the compression member itself, it may sometimes be less than 100 in some codes, better to check with the code upon which the design is being carried out. I took the height of column as 150 feet and assume "k" as 1.5, which may increase depends upon the boundary conditions at column top. I suggest that a truss type of column be selected and also to keep in mind the workability / Installation process while designing these columns. Wish you good luck

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The statement taken out from ACI document only covers shrinkage cracks in reinforced concrete structures. Hence, it is regarding serviceability limit states. In order to fully understand it, one should know what they mean by 'acceptable level', or 'acceptable design limits'. There must be a paper regarding that, which needs to be studied. You should check latest ACI code; I think. they have not included this provision in the latest code. They are continuing older provision of 0.18/0.2 %. It look like as if they have not taken the recommendation of this committe seriously. It is a confusion.

Thanks for sharing the drawing in pdf format. I am writing down a design approach, and would request everyone to throw their comments and questions. Lets start by: 1) Design Criteria 2) Expected loads on structure 3) Possible limit states 1) Design Criteria I believe that you have been working on this for some time and will be having a design criteria outlining what code do you want to design this structure on, and what material strengths do you intend to use. Please post the design criteria document here. 2) Expected loads on structure The structure is a pair of columns, with motors installed at the top of the that push/ move the chair lift. I would recommend that each column pair would be joined and braced at different levels to provide a stiff support (how far are they ? ; present framing doesn't look to work, I would suggest a truss tower). Possible loads are: Weight of motors. Possible thrusts at starting and stopping of chair lifts or when faced with load shedding. Weight of chair lifts and passengers (considering number of persons and chair lifts at a given time). Wind load on columns. Weight of cable and its reaction on columns. (Cable are eccentric from column center) 3) Possible limit states Apparently, columns need to be laterally stiff enough to maintain tension in the chair lift cables. Uneven support settlement. Utilization of piles to be kept to 60% and under to avoid that. It also depends upon various factors, but I am just throwing in a bullet. Maximum unsupported length of cable. You many wanna do a check on that to make sure things outside your scope don't fail. I remember, we did a problem in Theory of structures for a suspension bridge. Similar concept. Overturning Check. Shear failure of piles. (throwing in a bullet) Anchor Bolt Failure. (from sketch it looks like anchor bolt shown are typical and not designed) Frost Jacking. You can use a higher importance factor as failure can be catastrophic. Some other questions. How good is the geo-technical data ? Please share: what you have done till now. Also list things that you haven't designed and are using typical details. Are anchor bolts designed ? Are piles designed properly ? How are you calculating wind load ? what code ? are you doing any manual checks on that or just software ? What is the seismic class of the site ? Are there any structures near by ? How high is the water table ? What is the confidence level on structural steel available ? Local from a mill or properly tested sections. Is the soil subjected to frost heave ? Are piles and pile cap designed for that ? Are piles concrete or steel ? Do you have more drawings to share ? You foundation looks inadequate ? Free standing columns(present framing) would be out of proportion. I would Suggest having a Truss Tower; load path would be robust and your site construction would be easy and cheap too. I would welcome comments and more questions. Naeem, I am looking forward to your reply. Cheers.