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alberto

Steel beam to reinforced concrete column/beam connection!

40 posts in this topic

Hello to all!!!!

How do you calculate these type of connections? Are there any Eurocode provisions about them?

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There are clauses in EC2 concerning bearing stress of steel (or other materials) on the concrete but not much else. There are however other published guidelines that aren't code specific, much of which concerns precast construction but there are useful parallel principals with steel-to-concrete. If your connection is moment resisting, it becomes a bit like a moment base plate turned through 90°.

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Ok! If my connections is simply supported can I design it as an ordinary simply supported connection ignoring the concrete?

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Eurocodes say nothing directly for these cases but this is a quite common situation. In general, this type of connection makes sense for pinned supports.

You can design a fixed support but It' s very difficult to satisfy the criteria.

Also for these cases in real life, a fixed support is most probable to turn to a pinned through the years.

Where does your steel beam end? Over the rc column or at its edgeways?

If it's over, things are simple. Check anchorages for shear and pullout failure.

If it's at the edgeways, checks depend more on parameters like: column section dimensions, stirrups distances, cracking and so on.

Anchorage checks are in ETAG guidelines of the European Organization for Technical Approvals.

Steel beam to concrete column/beam connection!

The title is wrong. Steel beam to reinforced concrete column you mean.

Edited by rigid_joint

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The title is wrong. Steel beam to reinforced concrete column you mean.

Yes of course. I hope the admins will correct it.

The steel beams are supported by steel columns and a reinforced concrete beam.

I will simulate the connection as pinned. Do I have to check the pullout failure? I am asking because there is no moment and therefore no tensile force at the bolts of the connection.

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By your first post I understood something different, that a steel beam is supported by rc column.

Anyway, checks still remain the same. Were does this steal beam ends? Over rc beam or edgeways?

If it's edgeways, the checks are more difficult to be satisfied because the cracking parameter is critical. Also, beams usually have a relative small width e.g. 25cm and this circumscription affects on anchorage length limit.

Do i have to check the pullout failure?

In general the answer is still yes due to 2nd order effect moments.

Have also in mind that, in the edgeways case, due to 2nd order effects , there is also a torsional distress on rc beam. Is it critical? I don't know, depends on 2nd order effect values.

A sketch is necessary to understand more.

Edited by rigid_joint

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I just saw your correction above but I'll post this anyway then have another look...

It’s difficult to be specific if we don’t know what kind of connection it is but, you can do all kinds of things.

You can bolt an end plate connection to a column, for example. The bolts can be embedded/drilled, such as resin anchors or mechanical anchors, or they can be through-bolts in sleeves and so on. It is possible to cast bolts or studs in but tolerance is a big issue – if you do this, you would typically use a template and incorporate some tolerance in the steel fittings.

You can also cast inserts into the concrete and these can even be attached to the rebar, by welding for example.

You can bolt on brackets, cleats or fin plates, in a similar way to the way you would with as steel stanchion – this may fit you scenario for a simple supported beam. You just need to make sure that the bolts are OK in shear and in tension (tension due to the eccentricity on the cleats or fin plate).

If you can land your beam on top, you just need to account for bearing and any bolt or anchor tensions into the end of the column. It is also possible to fit a steel ‘stool’ to the top of the column, either by bolting into it or by fixing to projecting and threaded reinforcement bars (again tolerance is an issue but can be overcome with oversize or slotted holes.

If using resin anchors, don’t forget about fire, and with other anchor bolts, edge distance and spacing.

You can assess the interaction of moments and forces between column and beam in the usual way, using stiffness based on the full section, on transformed section or cracked section according to the precision you need.

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Actually I didn't mention anything about column...

The title is "Steel beam to concrete column/beam connection!" because I thought that the design procedure would be the same!

Anyway thanks a lot for your help! The width of the concrete beam is 30cm and unfortunately the beam ends edgeways :(.

I am thinking of using an end plate welded at the beam's cross section and then anchored to the r/c beam.

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I'm confused as I can't visualize your connection.

You could have pull out forces without 2nd order effects - they might simply arise if your connection has a bracket component that has a reaction applied at some distance from the joint interface - just a simple eccentricity effect.

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I am thinking of using an end plate welded to the beams cross section and then anchored to the r/c beam

Whatever you do, anchor checks are in ETAGs. It's a different thing an anchor on tension beam zone and a different thing an anchor in compression zone.

(edit about sketch)

This is what I finally understood. In general seems ok as a bolt grid but only checks could validate it.

Also, there is a minimum distance between bolts, I don't remember the exact value right now but it's at least 5d for preventing pullout out cone interaction.

Edited by rigid_joint

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Thanks a lot rigid_joint! I just found the website with all the ETAG pdf!

Edited by alberto

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This is the connection!

But this isn't a pure pinned support. It's at least semi-fixed.

In fact, It's a fixed connection but beam flexibility turns it to semi-fixed.

But still 1st order moments are at low values due to beam flexibility.

Anyway, for start you have to design a pure pinned support otherwise I don't give much chances for this connection to satisfy checks.

Edited by rigid_joint

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Now it makes more sense...

As rigid_joint says, it is strictly speaking... well, a rigid joint, or nearly!

Now, if the concrete beam was reasonably long and did not have the slab attached to it, it would probably be torsionally flexibly enough to avoid the beam inducing a really large support moment. However, it is restrained by the slab, so it will actually be quite stiff. The support moment could therefore be significant. You could make the problem go away, partly, by designing a 'T' section bracket (or similar arrangement) so that you bolt the T flange to the beam with the T web projecting out in a vertical plane. You could them bolt your beam web to this like in a fin plate connection. If you keep the centroid of the web bolts close to the RC face, the moment due to eccentricity on the bracket may be lower than the moment you would get in the configuration shown. You can also make other sorts of bracket that allow different kinds of freedom.

At present, if you beam is quite stiff, long, or supports a large load, the moment could be enough to generate large bot tensions in your top bolts and pull-out may be difficult to handle.

If the RC beam was a rectangular section, without the slab being in the way, you could bolt right through (missing the rebar!) and avoid pull-out problems. And, yes, in the tension zone you can sometimes have trouble with the bolt pull out forces. Some anchors are not allowed in the tensile cracked zone. Having said that, you have the possibility to put in quite long anchors in the top, as they cannot come out the other side due to the slab - however, getting the resin or grout in becomes difficult.

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Be careful with the ETAG's. You cannot always use them.

1.2 Concrete member

The concrete member shall be of normal weight concrete of at least strength class C20/25 and at most strength class C50/60 to ENV 206 [8] and shall be subjected only to predominantly static loads.

1.3 Type and direction of load

The design methods apply to anchors subjected to static or quasi-static loadings and not to anchors subjected to impact or seismic loadings or loaded in compression.

There is a newer regulation for anchors. Essentially it is the replacement of the ETAG's design method.

DD CEN/TS 1992-4:2009 Design of fastenings for use in concrete

According to DD EN 1992-4-1

1.4.1 Type of loading

Loading on the fastenings may be static, cyclic (causing fatigue failure) and seismic. The suitability of the fastener type to resist either cyclic or seismic loading is stated in the relevant European Technical Specification.

1.5 Concrete strength

This document is valid for members using normal weight concrete with strength classes in the range C12/15 to C90/105 all in accordance with EN 206-1. The range of concrete strength classes in which particular fasteners may be used is given in the relevant European Technical Specification and may be more restrictive than stated above.

This means that you can use the procedure for seismic actions, even for retrofitting old buildings (C12/15) but it is up to you to find and to use a suitable type of anchor.

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MegaTrol, you are right and thank you for the detailed presentation.

However, whatever code or provision alberto is going to use, he has to deal with a more major problem.

He designed a rigid support who thought that it was pinned.

So checks get importance when they are used right.

Edited by rigid_joint

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Don't forget that it could be made into a pinned joint, if that suits the needs of the project, depending on how the steel part is detailed. It could even be made with some capacity to allow movement. However, elaborate connections can get quite expensive.

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Now it makes more sense...

You could make the problem go away, partly, by designing a 'T' section bracket (or similar arrangement) so that you bolt the T flange to the beam with the T web projecting out in a vertical plane. You could them bolt your beam web to this like in a fin plate connection. If you keep the centroid of the web bolts close to the RC face, the moment due to eccentricity on the bracket may be lower than the moment you would get in the configuration shown. You can also make other sorts of bracket that allow different kinds of freedom.

It's your idea, AndyBeeton?

post-1018-14570089578932_thumb.jpg

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Rudi, I think that the anchorage length of the 4 anchors at the bottom of the connection could be smaller.

These anchors might reduce the capacity of the reinforced concrete beam.

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What you show is the kind of thing I was suggesting, yes.

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It's your idea, AndyBeeton?

[ATTACH=CONFIG]327[/ATTACH]

Firstly, of all, this is a connections type used in retrofitting projects, not in a new project. The reason is that the anchor plate (if needed) is placed inside beam before concreting.

Of course, you have to open holes in the formwork and make sure that the bolts will stay in place during concreting.

Secondly, as far as I know, only Americans have done some experimental work over these type of connections and only in static loads. What is its behavior in a recycling loading case? (e.g. vertical seismic component? uplift wind? etc).

Finally, if something is not inside the applying code (whatever design code somebody uses), by following the letter of the law, it needs experimental verification for using it.

Rudi, I think that the anchorage length of the 4 anchors at the bottom of the connection could be smaller.

These anchors might reduce the capacity of the reinforced concrete beam.

Maybe this length is necessary due to uplift wind or vertical seismic component.

But I repeat, it's not so easy (but not impossible, it depends on design loads ) to satisfy the criteria in rc beam case.

In rc column case, it's much easier due to cracking parameter overpass and the much better concrete confinement (closer stirrups).

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Rudi, I think that the anchorage length of the 4 anchors at the bottom of the connection could be smaller.

These anchors might reduce the capacity of the reinforced concrete beam.

Which capacity you mean? For bending, shear or for local detachment?

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Which capacity you mean? For bending, shear or for local detachment?

I thought that the beam has already been constructed!

In general the idea of opening holes in an existed beam doesn't sound good to me...

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All my comments and suggestions are general - I have no idea if this connection is on a project that is anywhere near a seismic area.

With regard to retrofit or not; this kind of connection would not be considered very unusual in new build or retrofit in the UK area. The fixings could be resin anchors, mechanical anchors, drilled right through or cast in, depending on project specifics. It is quite common to have holes through beams and, although we prefer to design them in, they do sometimes get forgotten on site, or a revision to pipework etc. necessitates that they are drilled through. One may do the calculations and frequently verify that it is satisfactory, particularly if the loads and not very great. If the loading is great, then there may be problems. For all I know this application might be a small rafter with a little bit of roof on it.

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Which capacity you mean? For bending, shear or for local detachment?

Let me go one step further. Let's say that you have no capacity problem. Let's say that every check in the paper is satisfied.

Is there anybody to guarantee to the owner that this beam will never appear even a small cracking?

Do you know many owners that will like that cracking?

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