The balcony rail itself can be designed to any number of structural codes depending on what material you have in mind ie timber, steel, aluminium, plastic etc.

Th fix it to the slab it wil usually be bolted either to the top surface of the balcony slab at the front edge, or onto the front downstand face of the concrete slab.

The anchors wil usually be mechanical wedge anchors or resin anchors, both of which are drilled and fixed into the concrete.  The design of the fixings are usually given as standard design examples in the product literature of the bolt manufacturer.  These manuals are often given out free or are on the web.  the companies which you should probably visit first are:  Hilti, Spit, Rawlplug, Parabolt, Fischer.

Regards

Andy Machon

 
 

Another possible detail for attaching a handrailing to the concrete slab is to cast weld plates or pipe sleeves into the concrete slab.  This requires some good layout work when forming the concrete, although you can cast the items in the slab and measure them inplace afterward. Then, shop fabricate the railing to match the weld plates or sleeves.

Just another way to get the job done.

avoid expansion anchors, and corrosion resistance is a good thing especially for high rise balconies.

Best to fix down thru' the slab & not on the edge because a)fixing on the edge of the slab will give you limited edge distance, thus reducing the allowable pull out on the anchors-see trade literature... b)you have to resist a moment from a force being applied at balcony rail level horizontally (say 1100mm above floor level) and take this out using the resistance from your base connection, which may have a limited lever arm, perhaps only the distance between anchors(say 150mm).To answer your question, design your base connection to resist overturning moment from horizontal load at top of rail (or infil panel) ref. local codes, & this load as direct shear at base level.

Let's make two assumptions first (and hope they are correct!)...(1) the slabs have been designed to accept the anticipated loads, and (2) you are only talking about a perimeter handrail, not an additional balcony (separately loaded) to bear on the existing slab.

Now the issue is one of designing and anchoring the handrail.  First the handrail has to withstand a lateral concentrated load by most codes.  Further, both a lateral distributed load and vertical distributed load must be accommodated by most codes.  Don't forget to check the wind load...it can be significant, particularly at upper elevations and near coastal applications.  Don't forget the little things like picket spacing...must typically comply with a life safety codes as well as building codes.

Next consider the materials for the handrail.  If aluminum, be careful of dissimilar metal contact, contact between the aluminum and the concrete, and "electrical" continuity between the rail, the fasteners, and the reinforcement in the concrete.  If steel, less problem, but still a consideration.

Then comes the anchoring....wedge?, epoxy?, embedment?
All will work, just different considerations for each.  Near the edge, wedge anchors have lower capacity than epoxy anchors because of compensation for "blow-out" at edge.  For rail post embedment, be sure not to trap water or even condensation in the post or on the surface surrounding the post.   This will lead to corrosion and premature failure.  Horror stories abound, including death!

Thanks for all the suggestions. I am actually design the whole steel balcony which will have to cantiliver off the edge of the slab. The balcony frame will be assembled on ground and lifted into position by crane. I'm just not familier with connecting steel members to concrete.

oh boy, the whole balcony is attached to the slab...just how thick is your slab and how far does the balcony project out from the slab edge??? handrail is simple in comparison!  How many floors require balconies.  you may want to do some pull testing on some anchors (epoxy) to determine the concrete strength and condition (existing I'm assuming) before you do any design.  could be difficulty with existing reinforcing in the slab at the edge for anchors and drilling ....

by the way if your not to familiar with 'connecting steel members to concrete' you better get 'familiar' because by the sounds of it in this case thats what its all about !!!  you've got a slab edge, which will limit the number of anchors vertically, which must resist the moment, combined tension and shear resulting from your balcony load, simple statics, very complicated anchorage.

suggest also looking at Blodgett "Design of Welded Structures' section 3.3 Column Bases, and ASCE Paper no. 2852 ' Moment Rotation Characteristics of Column Anchorages' to look at stiffness of base plates and anchor bolts and assumption of concrete/reinforcing type stress blocks .... sorry your problem worries me i think i must not understand your description properly.

Rcslab,

I assume that you have checked the existing concrete slab for the new balcony load.

My preference for fixing in such cases is to extend the new steel beams as far under the existing balcony as possible so as to maximise the favourable lever-arm. Also, at the slab edge fix into the vertical slab face rather than underneath so that the bolts are working in shear rather than pure tension.

I also assume that this work will be checked by an experienced structural engineer.

If you are retrofitting the balcony to an existing structure and anchoring it to the existing slab, the best way, in my opinion, is not to design the balcony as a cantelever.  

Anchor the member (e.g., a channel) to receive the framing to the slab edge with undercut anchors or epoxy anchors. Follow the embedment, edge distance, shear strength, pull-out strength, spacing, etc. requirements for the anchor you choose.

The projected edge of the balcony is supported by tension rods tied back to the floor above (connected to the channel of the floor above, which is tied to the slab).  This way, no momemt connection is needed at the slab edge to support the balcony steel, and the connections are simpler.

When detailing, pay attention to the effect of water and freeze/thaw over the long term.  You do not want water to damage the slab edge or the anchors and compromise the strength of your connections.