Capacity of Existing Precast Double Tees

[tlbse]

I am trying to verify the load capacity of an existing precast double-tee floor in an educaton building for the addition of equipment. The building was constructed in 1963. The double tees are 14" overall depth, 4' wide flange, stems at 2' spacing, spanning 33'-0" with a 2.5-inch concrete topping. The tees are referred to as LEAP #14-DTF-87C, but no required floor loading is provided on the drawings. I am trying to locate manufacturer's load tables from circa 1963 with the same double tee nomenclature to verify original design capacity. Is anyone aware of available load tables or other method to determine capacity short of load testing or invasive inspection?

 

[msquared48]

Where are you located, and where is the closest prestressed casting plant?

Mike McCann
MMC Engineering

 

[Lion06]

If you can't find load tables, just call a local manufacturer and get the skinny on what the nomenclature is. Have you looking in PCI to see if there is anything in there?

 

[tlbse]

We are in northern Illinois. The nearest prestressed plant is in S. Beloit, who I have contacted. They don't produce double tees - so I will check with some others.

 

[tlbse]

I have a call into PCI. I believe the timeframe for this building was prior to PCI producing standardized load tables. Also, the double tees on our project are smaller than current doubles tees.

 

[JAE]

I think a load test is in order. I did one some time ago on an outdoor grandstand which had double tees of unknown capacity. I used ACI 318 criteria if I remember right.

It isn't that difficult of a task, although it helps to have a good contractor help you out on it.

 

[JAE]

Here's a copy of a previous post I wrote once on it:

[blue]I had a number of barrels set up in a specified spacing to load the grandstand to 125% of the required live loading for grandstands (100 psf I think it was). The loading was performed by adding water to the barrels - calculating the volume in each barrel, the resulting weight, and the barrel spacing to mimic 100 psf.

I took vertical elevation measurements of the DT's prior to loading, at 1/4 loading, 1/2, 3/4 and full loading. Then removed the load, took measurements, and then took them again I think at 24 hours later.

ACI provided design criteria for the deflection and deflection-rebound. [/blue]

 

[JD2]

I worked for a pre-stress manufacturer in the early 80's. In our office we had our own computer design program and consequently every Engineer did his own individual design and modified all variables as required for each job and double tee within that job - strand patterns, type of strand (low-lax or stress relieved - don't know what types were available in 1963), pre-stress sequence, concrete release strengths and design strengths, etc. There were no design tables and other than the call out on the double tee ticket (which the guys in the plant used to build the double tee) there was really no correlation with any PCI nomenclature. Unless you could locate the actual shop ticket for the individual double tee(s) that you are looking at and reanalyze the double tee in question, I would be leary of picking a number off a chart regardless of whether you could match a PCI (or even the manufacture's) nomenclature.

I would vote with JAE - load test.

 

[gwynn]

JD2

Were no shop drawings produced by the pre-stress manufacturer? I have dealt with previuosly built precast sections a number of times and have usually been able to acquire the shop drawings of the girders, either from the governing authority, EOR or the manufacturer (assuming they still exist).

Mind you, this was mainly with bridges so differing standards may apply.

 

[JD2]

gwynn

I think what you are calling shop drawings I am calling shop tickets. The engineers produced the design (with the computer output), the draftsmen produced the shop drawing/shop ticket - a separate sheet of paper for each and every design and configuration - both of which were stamped, signed and submitted to the EOR and the CBO for review. The shop ticket showed everything the guys in the field needed to build the product - number and location of strands, holddown points (if required), dimensions, embed plates, mild steel requirements (we used WWF for stem shear reinforcement), type of concrete (lt. wt., normal wt. special concrete color requirements) etc.

The information you mentioned was produced (maybe under a different name, matter of symantics) however it would seem to me that the chances of finding this information from 45 years ago would seem to be very slim.

If they exist and you can find them then you can re-evaluate the original design. If you can't find them, I would be leary of attempting to match up a number designation on a Plan Drawing with a manufacturers chart or a PCI chart (assuming you could find a reasonable match) - there are too many variables that could be altered and not be a part of a load chart.

 

[gwynn]

JD2

You're right, it's just a difference in nomenclature.

We've managed to get a hold of shop drawings/tickets from the late fifties/early sixties, but as I stated before these were for bridges so a different standard of reporting and retention may have been in place.

 

[miecz]

ACI Committee 347 provides a few documents covering load testing of concrete members, available at their web site.