#82 S.J @ 20ö oc.-1950 1

[JoeBaseplate]

I am assuming that these are 8” bar joists. I’ll need to field verify but the site visit is a couple weeks away. Also the section shows a 2.5” plain concrete (no mention of rebar or mesh) over “steel forming” on top of these SJs with asphalt tiles on top. Did they actually used to use unreinforced concrete for floors

 

[JoeBaseplate]

Is the 75 year SJI manual available online? I googled it and looks like you have to pay to get it.

 

[JD2]

Don't know if it is available on line - but here is the info FYI

Design chart used was dated 1929, updated to 1948 (the chart updated to 1952 is the same except the 14' span goes up to 179 plf and the 15' span goes to 156 plf)

SJ82
8" deep Mr = 52,500"# Allowable End Reaction 1,900#
Approximate weight 4 plf

Span (ft) 10 11 12 13 14 15 16
All. Load (plf) 350 289 243 207 178 155 137

 

[hokie66]

There are a lot of 2 1/2" slabs around, placed on corrugated steel form, and only reinforced with light welded wire fabric. Bar joist spacing was normally 24" or less. These designs never did stack up as adequately reinforced, were based on experience, and I think only worked due to the bond between the concrete and form deck. I have never known of a slab without the welded fabric.

 

[msquared48]

Usually, a true "form deck" is only 1/2" to 3/4" deep, and is placed only to temporarily hold there wet concrete while it is curing, the concrete becoming structural after it cures.

If the "form deck" is 1.5" or greater, then it is a permanent structural item, and perhaps composite with the concrete, depending on the design. There will probably be no shear studs present.

Mike McCann
MMC Engineering

 

[hokie66]

Mike,
Most of these 2 1/2" or 3" slabs included the 1/2" to 3/4" corrugated form in the total depth. I think the only way they work is by composite action, based on bond between the concrete and steel. These slabs were, as far as I know, never designed per ACI provisions, but rather were based just on experience. How do you design slabs on bar joists these days?

 

[msquared48]

Usually the joists are spaced at 5 to 8 feet on center with 1.5" to 3" decking and a composite concrete fill over the deck of 2.5" to 5", reinforced. If bar joists are used, composite action with the joist is not relied upon, but the decking is field welded to the joists and the decking concrete relied upon for the diaphragm action.

Probably similar down under?

Mike McCann
MMC Engineering

 

[hokie66]

No, bar joists are not used in Australia.

 

[JoeBaseplate]

JD2, thanks for the load info. My joist is between 15-16 ft span so that info is exactly what I was looking for.

As far as form deck is concerned, the contractor sent over a pic this morning and indeed there is a form deck. See attached.

 

[JoeBaseplate]

JD2, can I ask what grade steel they may have used?

Thanks!

 

[JD2]

The best that I can tell, prior to 1946 - A9 is the only steel indicated w/ an allowable tensile stress of 18 ksi.

Starting with the 1946 (until 1949) spec, it changed to A7 (the allowable stress stayed at 18 ksi) and says "except that joists or parts of joists formed of strip or sheet steel shall conform to Grade C of ASTM. Tentative Specifications for Light Gage Structural Quality, Flat Rolled Carbon Steel (ASTM A245-44T or A246-44T)"

Starting with the 1949 (until 1951) spec, it stayed with A7 and says "except that joists or parts of joists formed of strip or sheet steel shall conform to Grade C of ASTM A245-48T "Tentative Specification for Heavy Gage Structural Quality, Flat Hot-Rolled Carbon Steel Sheets" or Grade C of ASTM A246-48T, "Tentative Specification for Light Gage Structural Quality, Flat Hot-Rolled Carbon Steel Sheets" or Grade C of ASTM A303-48T "Tentative Specification for Hot-Rolled Carbon Steel Strip of Structural Quality"

Starting with the 1951 (until 1955) spec, it stayed with A7 and says "except that joists or parts of joists formed of strip or sheet steel shall conform to Grade C of ASTM A245 "Specification for Heavy Gage Structural Quality, Flat Hot-Rolled Carbon Steel Sheets" or Grade C of ASTM A246, "Specification for Light Gage Structural Quality, Flat Hot-Rolled Carbon Steel Sheets" or Grade C of ASTM A303 "Specification for Hot-Rolled Carbon Steel Strip of Structural Quality"