storefront attachmen

huangyhg

storefront attachment
greetings,
i have a peculiar case which i am trying to analyze and i am lookin for some valuable input.
i have a curtain wall system that attaches to a steel beam. the steel beam has an opening behind it and spans 39'. the opening houses an escalator.
a concrete curb is present to attach the curtain wall. i am trying to use it as a composite section bending about the weak axis, using transformed properties.
please let me know what you think of this.
thanks
anantha
the centroid of your concrete will stay in same vertical position in transformed state, (above the top flange).  the weak axis is not strengthened much by adding concrete cap.  better to flip w shape on side.
a couple of thoughts...
what is the purpose of this concrete curb?  it seems like the connection of the curtain wall to the steel beam will be made more difficult with it present.  
in order to control torsion better, plus give more stiffness in the weak direction, why not use a large tube section instead of a wide flange?
mike mccann
mccann engineering
i also would have started with a tube section, some twisting of the section is likely. also note that the concrete is not reinforced for tension for what you are trying to do. it can stand a percentage of tension shared with the wf up to cracking moment only.
the curb (10 wide x 12 deep) is reinforced with 2#7 ea. side. it has studs staggered at 6" o.c.
i just did a similar detail but i used a large tube with the storefront continuous at the outside face. what is the reason for the curb (concrete beam) on top of the wf?
a couple of others:
how do you plan on attaching this at each end, any twisting accounted for? welding the rebar to the columns?
will this composite beam be shored? i assume so, there is no lateral bracing of the wf.
have you checked the concrete beam for shear?
there will be biaxial stress on the section.
the stiffness of the section will change after cracking.
your studs are working for composite gravity loads plus taking the upper wind force into the composite section, need to check this combined.
some more questions....
why are there two steel columns at the escalator opening? is this an expansion joint?
do these column then span multiple floors with a concentrated load from the wind?
are the outer columns concrete?
how is the steel beam attached to those columns?
1. the curb is to add meat. the curb is required by the architect (!!!). the curb is not attached to the column. all the forces are transferred through the beam into the column.
2. steel beam attached to the column using flange plates welded to the embed plate for fixity. also a detail with top and bottom plates welded to the shear tab (creating an i) to attach to the embed plate
3. columns needed for architectural reason. no expansion joint
4. composite beam is unshored. the beam is intended to span 39' in its weak axis with no bracing.
sorry, i guess i'm not understanding this yet....
the sketch appears to show a horizontal beam running between the rectangular columns. but it looks like this horizontal span is interupted by the pair of steel columns. is 39 feet the distance between the rectangular columns?
i agree with others that the concrete curb seems like a waste of money. it looks like you are trying to resist a significant lateral load on a span of 39 feet. perhaps a wide flange with a cap channel top and bottom.