Precast Design 3

[khattam32]

I have got to design this precast building,and being new to the precast (never designed precast building before), I am wondering who is actually responsible for designing primary structural members such as precast beams and columns (EOR or precaster's engineer)? Can anyone with precast experience help clarify roles of EOR and precaster in a typical precast building project?

Thanks in advance.

 

[delagina]

i am currently doing a pre-cast bldg. we just provide layout and openings on walls.. upto precast manufacturer to design thickness, rebar, etc...

 

[slickdeals]

You obviously have to provide all loads (gravity and lateral). The precaster is never going to build a 3D model.

 

[delagina]

depends on the precast building maybe. coz the one we have is just a "box" so no load except wind load and roof live load. we did give specification for wind load that they must meet.

 

[delagina]

this is the one we used

http://www.precastbuildings.com/

 

[OHIOMatt]

The following comments are from my expeience with load bearing precast wall panels.

If the intent is for the precast wall panels to act as shear walls, you will have to be very specific in terms of how the shear is transferred. One issue that I have run into is that the precaster will tie some panels together, creating "stiff" elements in the wall line.

Another issue is relates to the use of the panels for girder bearing. If the panels are not designed to transfer load from one panel to the next, you can have greatly varied soil pressures.

 

[keenaseng]

We design the pre-cast (thickness and reo) to satisfy the 'in service' or 'once installed' loads (ie. wind, LL etc).

Any details that relate to the erection of the panels need to be provided by the precast manufacture. Ie. Any lifting eyes or additional reo for lifting etc

 

[khattam32]

Thanks everyone for your input.

The building I am working on has double tee roof with precast columns and pocketed spandrel beams where they support tees. Facade will have architectural precast panels with continuous ribbon windows all around, so I am thinking of making beam-column joints rigid to resist wind and seismic forces. But I am not sure if I needed to design the frame members or precaster would design it. Another dillemma I have is if precaster is responsible to come up with the design, what beam/column sizes I use to perform my lateral analysis. Do I perform a prelim analysis to come up with approx. sizes and use them in my lateral analysis?


Thanks,

 

[steellion]

What does the contract scope of work say?

 

[JD2]

My guess is that it would depend upon the contract, the pre-caster and the capabilities of that pre-caster. I worked as a design engineer for a precast manufacturer in Ft. Worth for about 2 years. We did mostly prestressed/precast parking garages but site requirements sometimes forced us to design other structures (such as retaining or barrier walls). We had a design office that was composed of about 7 structural engineers and a drafting department with about 20 draftsmen as well as a construction yard with all of the formwork, double tee beds, concrete batch plant, etc. required to produce the product. We would design everything (shearwalls, stair towers, L beams, T beams, double tees, columns, etc. including lifting inserts, additional reinforcement for those inserts, etc.) from the foundation up as per the code in force for the location of the project which meant both lateral and gravity loadings as well as the connection designs between the precast elements, the shearwalls and columns to the foundation, etc. We needed to be informed by ether the Architect or EOR of any special loading conditions (I once had to design parts of the top level of a parking garage to support planters that would carry three feet of soil so they could plant small "growies"). We would provide (if requested) gravity loads, reactions, overturning forces, etc. to the EOR for his design of the foundation. In addition to the construction tickets for our own people in the construction yard, we provided stamped design and erection drawings as well as stamped calculations for the review and permit process. The line of separation between us and the EOR was the top of the foundation although, as I said, we did provide the design and detailing for the foundation connections of the precast elements. I'm not sure in the end who was ultimately responsible for the structure since we did provide a stamp for the design of the structure itself - that was above my paygrade at the time. I am sure that in the end, if the lawyers got involved, that it would make no difference - everyone involved would get pulled in to a lawsuit.

If you are talking designing a pre-cast structure as a tilt-up type structure to be built on site, then it is you who designs eveything except that the contractor should be responsible to take care of any modifications to the pieces that may be required for lifting and erection (inserts, stiffeners, etc.).

 

[khattam32]

Ok guys, so I have to discuss regarding SOW with my PM, and take it from there.

JD2, your post helped clear a lot of things, thanks everyone!

 

[hokie66]

How did the project get to this point without a clear understanding of design responsibility? Who made the call that the building structure is to be totally precast as you described?

 

[Brad805]

KH, I act as the speciality engineer for a precast plant in Canada. Do you have a lot of precast suppliers in your area? If not, it can be very helpful to start talking to those that might be considered to bid. If it is a sizable job and they see the potential for a bid, most will help.

It is your job to spec out the general arrangements and the loadings as described. That does include basic sizes, sections and the levels. If you do not have a copy of the PCI manual, you will need one. It has some basic tables, connection details and panel parameters that will probably help.

If you want to give them the flexibility to adjust the sizes for cost efficiencies, you can define that in the bid documents.

As for 3D models, yes some do create them in the US. There are a few that have some incredible websites with all their standard details also. You need to do some research.

A key for success with PC can also be getting them involved sooner in the process than other projects. The one downside of PC is delivery. Our plant is typically reserving space for projects 3months after you sign on the dotted line.

Brad

 

[khattam32]

hokie, The criteria for all precast came from the owner who has another facility of similar construction and they want to match. I understand, the Architect and the owner has been working on it for a while, and the Structural engineer (that'd be me) has just been brought on board.

Brad, thanks for your insight. I actually recently contacted one local precaster, a potential bidder, and got similar input. Great point regarding getting the precaster on board earlier in the process in connection with the schedule. We are thinking along similar lines and going to suggest the owner for the same.

Thanks guys,