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  • [detail] A construction detail problem: L-beam in cast concrete

    First of all: dunno if this is the right section. Sorry if it's not.

    Now, about my problem:
    There is this cast concrete floor of 30cm thick. The corners are to be visible, so we will use a profile / beam thing for that. In the attachment you see the thick line, representing an L-beam. Someone claims that it just has to be cast within the concrete. But I doubt that the beam will hold, because it does not ly IN the concrete, but next to it.

    My idea is that we need a kind of E-shaped beam (missing the top horizontal line), so that the middle horizontal line of the E is cast COMPLETELY INTO the concrete.

    So is this L-shaped possible, or am I right with my doubt about it???...
    Attached Files

  • #2
    It needs some kind of connection to the concrete. It just can't "rest" there. You could achieve this in several ways but one is how you described and I think you would tie the beam piece within the concrete to the rebar (someone back me up on this? or shoot me down ). I am assuming you want the beam surface to be clean? If not you could have bolt connections tied into the concret slab, via the rebar system and them anchor the beam that way. but then you have bolts every so often showing on the surface.

    Structurally do you really need that beam? From what I see I don't think it is neccessary, but I am just seeing a small part of a larger whole. Why not just have the concrete exposed? you could make sure the finish is done right smooth or with texture of some kind...

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    • #3
      Yup, the surface is supposed to be kept clean, so no bolts.
      Attaching it to the rebar is a possibility I hadn't considered yet. I think it's better to do that, just to be safe.

      About the necessity of the beam: there is this system floor of about 15cm above the concrete deck, and the beam was our sollution for a unified look of the total 55cm... That is the use of the beam. Not structural, but esthetical. (cfr attachment: system floor is the blueish thing here)
      Attached Files

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      • #4
        Stijn-
        Wizum asked my question: Why do you need it? And you answered it: you dont but you want the look of steel for the finished appearance.

        If this is the case then you just need enough adhesion to hold the steel to the concrete. This would be best done with some anchors welded to the steel on the inside so they will be cast into the concrete. This is often done with pieces of re-bar or headed studs.

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        • #5
          Seems an awful amount of effort. It would be a whole lot easier just to line it out in plasterboard or MDF.

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          • #6
            If all you want is a uniform appearance, how about something like this? To me it seems a waste of resources to use a valuable steel beam for aesthetic purposes alone.. if that beam was actually carrying weight though, it would seem more reasonable.
            Attached Files

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            • #7
              Why not just render the edge and express the joint between the concrete beam and it's topping as a simple tooled edge, or express it more by reendering up to a small removable batten? It's not clear what's going on on the floor above so this may not be a suitable solution - what are the floor and ceiling systems being used?
              If you're going to use steel then you'll need to anchor it into the concrete with rods that are welded to your 'L' section, which looks like a total overkill as the steel is essentially just there for decoration so why not treat it as such? Personally I'd bend it up over the floor system and make it a design element against the end of the floor. If you carry the lower edge inside the ceiling system you could fix it to the underside of the concrete slab so that it's secure at both ends.
              Last edited by Nick Fox; 24-12-2006, 01:11.

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              • #8
                This is my latest proposal.
                Instead of entering the L-beam into the concrete, I want to screw it afterwards. The connection won't be seen anyway, as it will be hidden by the system floor finishing afterwards...
                Attached Files

                Comment


                • #9
                  This is actually a very doable detail.. On a recent project, we needed to accomplish the same thing. I've attached a sketch of our solution.

                  The nice thing about this detail is that it can hide any number of construction problems such as wavy or non-level concrete forming, out of square conditions, etc. as it's just a face piece that floats over the slab. The finish floor system and the ceiling system all work to the steel cover so everything fits nice and tight.

                  Note that the L shaped piece needs to be fabbed out of 2 pieces of steel plate butt-welded together: Bent plate has a rounded corner, not square. Also, the welding needs to be done in a shop under controlled conditions to keep the heat from warping the plates or spotting the face surface.

                  Take a look at the sketch and let me know if you have any questions...
                  Attached Files

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                  • #10
                    Why did you make that detail? I mean: some of the work seems pointless to me. Why first adding that L in the right top corner, to attach the to-be-visible L with a similar small L to the first small L, if the connection is to be cast out of sight anyway? Couldn't you just attach the second small L to the concrete without the first small L?

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                    • #11
                      Originally posted by Stijn View Post
                      Why did you make that detail? I mean: some of the work seems pointless to me. Why first adding that L in the right top corner, to attach the to-be-visible L with a similar small L to the first small L, if the connection is to be cast out of sight anyway? Couldn't you just attach the second small L to the concrete without the first small L?
                      I really don't get this detail... rough concrete is beautiful (ask Mies)...Way too much work and cost for a "crisp" look...
                      But... if you ask me, I would cast in place the slab with the L-piece inside the formwork... maybe with a couple of welded "studs" perpendicular to the piece on the inside for extra security....

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                      • #12
                        Our particular detail was a cantilevered concrete ramp that was probably going to have some deflection between the time they poured it and the time that we finished the interiors. The purpose of the first upside down L was to give us a steel formed edge to the concrete to attach our steel cover to. Without it, we'd have to drill and epoxy in bolts which would interfere with the finished floor system.

                        Initially, the contractor also though it was too messy and we explained that the detail gave them a lot of protection in case the concrete didn't come out exactly square, plumb, level, etc. and you know what, it didn't! After that, they were glad the detail had the ability to cover up the problems.

                        Comment


                        • #13
                          Originally posted by Stijn View Post
                          This is my latest proposal.
                          Instead of entering the L-beam into the concrete, I want to screw it afterwards. The connection won't be seen anyway, as it will be hidden by the system floor finishing afterwards...
                          This is more or less what I proposed. The only problem I see with it is the exposed top edge that's sure to attract attention from people using the building and I'm sure it would end up being kicked, just for the hell of it. I don't know what your floor finish is but I think that it should either cover that edge or that the edge be folded so that it's under the floor covering. I think you could spot weld an 'L' shaped fixing bracket in the middle of the panel as shown. I'm not all that keen on this detail as it's essentially covering up a problem somebody has created by using this system of construction and if you can avoid it, then I would seriously consider doing so.

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                          • #14
                            You should talk to your structural engineer's about this

                            It could be done very easily and would become the formwork for the slab edge. It would be quite expensive though, and very heavy requiring a crane to place it into position. It would probably need to be hot dip galvanised to stop it from rusting, and to prevent this process from unduly distorting the welded angle it would need to be fabricated from a minimum of 10 plate.

                            Other factors you might need to take into account are:
                            - Accuracy of fabrication and installation.
                            - Transportability of the finished product.
                            - Acceptability of the finish.

                            The Vectorworks drawing below shows how it might be done. The actual design would need to be done by your structural engineer.
                            Attached Files
                            Last edited by mikem oz; 26-12-2006, 08:26.

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