Movement Gap

[mijowe]

I have a residential two way PT floor slab with some decent cantilevers and perimeter spans. The skin of the building is a combination of metal panel, precast, and curtainwall, and it is configured in a way that at one floor it may be curtainwall and the next floor above may be precast with punched windows. Sometimes the wall runs past the slab edge, sometimes it is setback and runs floor to floor.

I have been able to design the slabs for the different perimeter loads and zero in on what I would consider reasonable deflections for a floor. My problem is that the finishes change every floor and they are all deflecting differently. The precast deflects the most and can be above a curtainwall level that may actually move slightly up (in theory) if not loaded with live load.

At this point I am a little nervous on how the floors will work together. What is the biggest required gap that i can indicate on my drawings as without creating an impossible detail for the respective exterior skin designers.

 

[ishvaaag]

Someone (may be you) needs to coordinate the requirements that the different constructions areas in the façade require. Once you have that, you will feel reassured you are delivering something that shouldn't cause problems in the future. Make aware of the issue to whom it may concern more close to you, may be your boss, or the architect or engineer of record in order to gain their collaboration to get the proper data, whilst reassuring them that once that is made they will get a satisfactory structure.

 

[hokie66]

How many floors? I don't like the sound of precast being supported on PT floor slab cantilevers. The metal panel and curtainwall systems could be supported full height from the ground (with sliding connections to allow for floor deflection) if this is a low-rise structure, but intervening precast unnecessarily complicates things for the facade engineer. Damn architects!

 

[mijowe]

The building is 18 stories, and the lower floors are parking (open) and retail (all glass)so stacking is not an option.

 

[ishvaaag]

I really don't think the architects are the culprit on this matter. Society once decided that to separate designers from the construction team was rational, necessary and convenient. This was not a fancy of the rulers, they disgusted both the direct relation with rough and rich builders and these themselves saw an opportunity of shedding off responsability many times for a dime.

When this idea of specialization comes to extremes in developed societies' environments sometimes produces extremes of ridiculous results. So it was perfectly possible in Germany till recent years at least (it may be true even now) that a mere draughtsman become an architect even without formal tuition (just a sign of his boss and pass an exam would do); compare this with the situation in Spain in the thirties when one to just enter the school it was customary to have passed two years of "Ciencias Exactas" (mathematics) because if not they rarely would be passing the entry exam.

These things permeate through space and time, and even now we have very variegate degree of training and understanding within what is called an architect all over the world, ranging from fellows with quite deep understanding of some particular matters of architecture and construction (of which structural is one) and true ability in it, and others whose ideas on the same range from vague to directly erroneous. One can muse that the appearance of those entitled "technologists" once adaptively distributed all over the market to earn their bread is not going but to extend this kind of problems for the future.

Since this is what NASA would call a "system's" problem (i.e., the industry or fabrication team is not so well organized as to have resources placed in space and time in an efficient and organized way) we remain more or less obliged to rely in the activity and leadership of people that experience or cause to some degree the system's failure, either out of incompetence or lack of authority and integration of work that could make the things run smoothly.

So, whilst one can understand that awareness gets disgusted in the presence of imposed ignorance, since this is not a matter that typically one can solve (from the given attributions of authorities for the works) it uses to be more rewarding to face the difficulties one meets as challenges than as a cause of nervous breakdown; it may not be without reason that it is said that one should look the things in a "constructive" way, so a timelong acknowledgement that these organizative problems have been living with us already much time, and so instead of insisting on the feelings of self chastisement that the difficulties in course enact, it is better to deal with them as an occasion to exercise the powers of knowledge, logic and persuassion, and why not, of personal enlightment; and even when not able to reconduce the things to the terms of our opinion, see at least that there must be something out there that is causing the objectable issue come to a built state (which can be both a bad example of construction and a loved detail for the seller-owner-user).