I-beam Under Concrete Beam

[NeilL286]

I plan to reinforce a girder beam (there is another beam framing into it at midspan) due to our codes not enclosing the concept of 45 degree compression struts in beam-girder joints and lack of internal hanger stirrups requirements I mentioned in the another thread.

I will use a 12x12 I-beam and metal plates attached to the columns with expansion bolts. I need to know if someone has implemented such design before. Please suggest tips and tell what you encountered along the way. The columns can handle the loads and additional shear from the shorter column effect.

 

[bookowski]

Leave a gap at the top of the steel beam and drypack it to ensure uniform bearing. Depending on your condition you may want to consider pre-loading the steel beam. You can do this by driving steel wedge shims between the concrete beam and top of steel beam to some calculated deflection.

Another obvious one - when drilling into the concrete column consider the reinforcing that you will hit/cut and the impact that has on the column capacity.

 

[structSU10]

I have designed something like this before. I took into account the fact that the concrete beam is fixed-fixed and the steel is pin-pin. It forced me to use a stiffer beam. My case, however, was for the removal of a column so I was trying to not overstress the existing beams. You may not have such a problem, but it may be worth the consideration.

 

[dcarr82775]

I agree with structSU10. The steel beam will need to have a similar or greater EI than the concrete beam or it will not do much good.

 

[BAretired]

I looked at your previous thread507-347413. I suspect that the addition of a steel beam is the wrong approach but must admit I haven't thought through the issue to any extent.

BA

 

[paddingtongreen]

The EI problem goes beyond that though, with the fixed/fixed concrete beam and the pinned/pinned steel beam the deflected shape will vary. Having said that, I know of times when that was ignored quite successfully, but I would expect that, it just eats away some of the safety factor.

Michael.
"Science adjusts its views based on what's observed. Faith is the denial of observation so that belief can be preserved." ~ Tim Minchin