Adding new studs to existing composite steel beams.

[olsont]

I'm currently working on an existing composite concrete and metal deck floor structure which is supported by steel beams with headed studs welded to the beams top flange. My client wants to increase the loading capacity of the floor. In order to increase the capacity, my analysis program indicates that additional studs will have to be added to the beams. The majority of the beams have the studs spaced evenly along the length of the beams top flange. If say an additional four studs need to be added....where should the studs be added on the beam?

 

[ishvaaag]

The analysis program must indicate where is such need. If the studs were apportioned to the elastic shear at the interface, for ordinary simply supported beams the maximum requirement would be at ends and there would be where some adjusted design to lower forces is more likely to get the previous requirement exceeded. If the design is apportioned in the plastic approach, where the total force required in shear for studs in half span is the determinant of a total number and separation of studs, again it would be anyway more effective for a sound behaviour at service level to put the additional studs where the elastic apportionement shows more demand, as said, for common simply supported beams, at ends.

 

[InDepth]

olsont, ishvaaag is correct. Another approach I have used when you only require a few studs is to recalculate the beam based on an expected yield strength of the beam. Depending on the age of the structure you may be able to assume a higher yield and make the beam work without adding studs. You may also want to sharpen your pencil on loads and reduced live loads. Coring to add a few studs is messy and expensive.

You should definately check your connection capacity of the beam. Sometimes this controls.

 

[Structcon]

I would suggest you check the capacity of the beam connections first. Then, if needed, weld up the shear plate to strengthen the connection. Second, check the beam using LRFD to determine if you are overstressed. If so, check the rebar or WWF in the slab and re-calculate the "transformed section", since often that gets me over the top. If not good enough, add a cover plate to the bottom of the beam, but shore the beam first. I would not recommend adding studs to an existing beam.

 

[JoshPlumSE]

I've seen folks weld up a flange plate onto the bottom flange of the beam to give an existing composite beam more strength. I think that ends up being cheaper than coring the slab to add more studs.

 

[paddingtongreen]

There is more to think of here. Does the program know that much of the load is already in the existing composite beam? the extra shear connectors will only share in additional loads after they become effective.

Adding a plate to the bottom flange seems easier if it can be done, in fact, if it is preheated then quickly pushed up to the beam flange and then quickly welded sufficiently at the ends, it can be pre-loaded as it cools; it shrinks and takes on tension loading.

Michael.
Timing has a lot to do with the outcome of a rain dance.