Pre-Eng building over existing building
Pre-Eng building over existing building
(OP)
Our client wishes to design a new PEB spanning over a series of smaller buildings which make up his total operation (automotive dealership). The new building will be about 90’ x 110’ and will cover the existing plus part of the existing vacant lot. The idea is to build the building complete with a new office area and then move into the new office area. Thus he continues to operate during construction without disturbing the office and other operations.
We have not got to the building design stage yet. From past jobs the thrust at the base of the rigid frames may be in the area of 30 – 40 kips (unfactored) depending on the frame spacing. We normally use hair pins or thrust rods base to base to resist the base thrust. With the existing buildings in place neither of those methods can be employed. Obviously there are other ways to accomplish this. Have some of the readers here been involved in something like this? See attached sketch.
We have not got to the building design stage yet. From past jobs the thrust at the base of the rigid frames may be in the area of 30 – 40 kips (unfactored) depending on the frame spacing. We normally use hair pins or thrust rods base to base to resist the base thrust. With the existing buildings in place neither of those methods can be employed. Obviously there are other ways to accomplish this. Have some of the readers here been involved in something like this? See attached sketch.






RE: Pre-Eng building over existing building
Mike McCann
MMC Engineering
RE: Pre-Eng building over existing building
We may be "jumping the gun" until the Arch comes up with the floor plan for the north inmost 50 ft.
RE: Pre-Eng building over existing building
The whole thing sounds like a pretty wild scheme. Lifting heavy structural shapes and building construction in general over occupied space is not without risk. That sounds like one hell of a volume and structure to span the whole space. When some serious architectural planning, some new low-rise additions and some face-lifting on the existing buildings might be more practical and economical. Get complete plans of the existing buildings and foundations, including all mechanicals and any mech. tunnels, etc. So you really know what you’re dealing with. Then, for thrust rods, you could do one of two things: ( 1 ) You could use directional boring, 18" under the existing slab, from frame leg base pier to base pier. Pull a plastic casing through the bore from base location to base location; pull a tie rod through the casing and grout it after some post tensioning. ( 2 ) Depending upon the soil conditions you could drill from each base pier, into and under, the existing buildings, much like they drill, grout and tension tie-backs for tied back retaining walls/whalers in deep excavation work. The boring and casing might be easiest done first and then the piers cast around the casing.
RE: Pre-Eng building over existing building
RE: Pre-Eng building over existing building
In regards to your thrust problem. I would think the easiest solution would be to remove the thrust by installing columns at the ridge in areas where you can. Add a jack beam at the ridge in the area where installing columns may not be possible or possibly "fish" a column through the existing building onto a new foundation. Adding a support in the middle of the frames should almost eliminate the thrust generated by gravity loads.
RE: Pre-Eng building over existing building
This does remind me of one of those projects where you waste a lot of time at meetings entertaining some big-dreaming client, until the owner gets into the meat of the costs and gets scared into buying some cheap land somewhere else and starting new.
And this is purely anecdotal and somewhat off topic, but it seems like here in Florida that any halfway successful car dealership has moved to a new location in the last 5 years or so. There have been a remarkable amount of dealership projects even in a down economy. I pulled into the local Ford dealership to have some work done lately and it was a ghost town, they had moved about a half mile down the same road. Besides a bigger piece of property, they could build the entire new facility with minimal interruption to the original business.
RE: Pre-Eng building over existing building
Thanks for the response. What is going on with dealerships in Florida is just the same as here in Canada. Including your comments about wasting time on a "dream".
J
RE: Pre-Eng building over existing building
http://www.nxtbook.com/nxtbooks/cbp/201309/#/22
RE: Pre-Eng building over existing building
In one project, our office received a call from the contractor after the slab was in asking what the pile of rebar was that they never used. Instead of installing direct ties between the columns per the plans, they bent some small bars and made their own hairpins. As the slab was installed the EOR reviewed and had them install the drag struts on the outside of the building. They became compression struts still using friction to resist the thrust.
You may be able to design a similar system, but it will depend on soil type, exterior grading and access.
RE: Pre-Eng building over existing building
EIT
www.HowToEngineer.com
RE: Pre-Eng building over existing building