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Thread: Very basic civil engineering question

  1. #1
    Associate Engineer
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    Very basic civil engineering question

    I'm designing a concrete pad for an elevator that will be built on the outside of a two-story concrete block building. I would like to get some feedback on the design of the pad. Specifically, I would like to know the following.

    * Should I have a foundation around the outside that goes below the frost line, to keep the pad stable? The frost line defined in the building code in this jurisdiction is 18 inches below ground level, so that would not be difficult or expensive.

    * How thick should the floor part of the pad be?

    * Anything else important I might have missed.

    Background and Detail

    I work for the company that builds the elevators, but we are all mechanical and electrical engineers and have no experience with concrete and structures. We have the agreement of the building owner to install the elevator, but he doesn't want us to pin the concrete to his structure since it is only temporary. (It's a test and development unit.) So it will be a stand-alone pad adjacent to the building. However, we also want to minimize any relative movement between the building and the elevator, so we want to be sure that the concrete pad settles or moves around as little as possible.

    I've attached a sketch of the proposed pad. It has a raised lip about 8 inches high on the three sides that aren't adjacent to the building, so that the elevator sits in an 8 inch deep pit. The elevator rail system, which supports all the weight, sits on the raised rectangle on the floor of the pit. The pit floor has a slight slope, for drainage, which goes out to ground through a small pipe. There is an enclosure that sits on the top of the lip, and the mass of the enclosure is transferred to the concrete through the four corner posts.

    Here are the approximate masses.

    Elevator, rail system, and payload: 2,500 kg/5,400 lb
    Enclosure: 1,900 kg/4,200 lb

    PadDetails_Forum.jpg

  2. #2
    Associate Engineer
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    I got an important detail wrong. The corner posts that support the enclosure (1,900 kg) rest just inside the pit, on the floor of the pad, at each corner.

  3. #3
    Lead Engineer Cake of Doom's Avatar
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    To be honest, I would design this to resist the elevators maximum buffer load (with a factor of safety), and then add either concrete mass or reinforcement for thermal cracking/shrinkage from there. Once you've designed for the buffer loads, you'll probably find that everything else falls into place.

    The geotech report will be able to tell you if you need additional foundation area for the ground to resist the loads. There are lots of fancy ways to size these things but without the maximum loadings, its hard to give an informative answer.

  4. #4
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    Hi everyone,
    Is there anyone that help me to find out the answer of this question?
    Life Cycle Assessment practitioner wants to compare environmental performance of two diferent models of refrigerators. What functional unit should he select to enable an accurate compraison?

  5. #5
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    sarahblue, you need to start a new thread of your own under the appropriate title for this subject.
    Last edited by Kelly Bramble; 10-15-2014 at 12:30 PM. Reason: Spelling

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