Analyzing a 1950 concrete frame 8

[MacGruber22]

I feel a bit over my head in this..

So, I have 3-stories of existing RC-frame garage from 1950. Developer wants 3-stories of apartments above. See attached sketch.

This is what I am being told we are doing by my boss:
1. Ignoring gravity loads on existing RC columns because of the reduction in live load.
2. No geotechincal or other laboratory testing will be performed.

So...how am I supposed to analyze and design the lateral system of a structure like this with no material or reinforcement information?

Also, I am supposed to provide the number of hours for analysis and design (excluding detailing and drafting).

 

[MacGruber22]

Well, JLNJ, a retrofit that is going to support brand new R-2 residential sounds like a reason to be super due-diligent. :/

 

[BAretired]

It seems to me that the assumption has to be: the existing building can carry only the lateral forces arising from wind on the existing building height. Any new lateral force resulting from the new upper tiers must be carried by new lateral bracing; in that way, no reliance is being placed on the existing building to carry additional lateral load.

If the vertical column loads are known to be equal to or less than the original design values then it seems reasonable to accept the columns and their foundations without doing further analysis; if there is even the slightest doubt, columns can be externally reinforced to carry additional load without much trouble and some underpinning can be done under the foundations.

It is still necessary to inspect the existing building to see if there are any obvious deficiencies but with the above assumptions, there seems little point in carrying out any calculations on the existing structure at all.

BA

 

[CELinOttawa]

Now I have to disagree with your there BA; I have done work on structures that were obviously woefully understregth (by analysis and design provisions of ANY era), which had survived simply because they had never seen a full load.

Field service (a la CBD-230 and similar "tricks") is only valid when you know that the loading has been encountered.

The gravity case analysis is a must. Wind I'll take as field tested. Seismic needs to start with a "what do we have now" and go from there, nearly always to a formal upgrade program.