Older Masonry Code Provisions 1

[SperlingPE]

I am looking at an existing building designed/built circa 1976. It is a single story building with steel joist roof & metal deck. The perimeter walls are load bearing 6" light weight concrete block. There is no indication of reinforcing in the block on the architectural plans or the structural plans. There are no specification books available. There are no x-braces or other braces or moment frames indicated on the plans. The exterior walls are acting as shear walls.

During this time period, was there a minimum requirement for reinforcing a masonry wall?

 

[MiketheEngineer]

Don't think so

 

[JedClampett]

In the 1985 UBC (the oldest we have), the code required minimum reinforcing for shear walls in anything in a Zone 2 Seismic area or higher. Besides that, nothing.

 

[dik]

I don't know about the US, but in Canada, there was no provision for reinforcing CB except for either fully reinforced or non-reinforced. Partial was not considered. For both types of construction the height was limited by an h/t ratio based on nominal dimensions with an h/t <= 18 for load bearing and h/t <= 36 for partitions.

Dik

 

[msquared48]

In the '73 UBC, the probable code of record here, there were provisions for Unreinforced, Partially Reinforced, and Reinforced Masonry. The masonry stresses were governed by tables.

When I started, the minimum reinforcing we used (for reinforced masonry only as that was all that was allowed in our area due to seismic requirements) was (1)#4 @48 vertiical, and horizontal K-web at 24 (every third course).
Depending on where you are, unreinforced could have been allowed.

Mike McCann
MMC Engineering

 

[BAretired]

I am looking at the Canadian Structural Design Manual 1970. That was back in the good old days when all the codes were in one book including wood, plain and reinforced masonry, plain, reinforced and prestressed concrete, structural steel and aluminum construction.

The first sentence under "Shear Walls" in the masonry code is:
A plain masonry shear wall shall be designed so that no part of the wall is in tension.

BA

 

[SperlingPE]

Thanks for all the answers. Your responses are what I expected.

I am looking at an unreinforced (in all likelihood) masonry shear wall that the owner wants to put windows in to make several shorter unreinforced masonry shear walls that do not work.

On to figure this little problem out.

 

[BAretired]

Maybe the window frames could be made into rigid steel boxes.

BA

 

[dik]

BAretired...
I've still got a copy of the Structural Design Manual, I think that's the title... really good book! I also have a copy of the wind loading booklet that I've scanned and turned into a *.pdf doc. It has some pressure distributions that aren't available elsewhere.

Dik

 

[BAretired]

Hi dik,

I don't think I have that. Maybe you should make it available to the forum. Maybe SlideRuleEra could incorporate it into his impressive library.

BA

 

[NITTANYRAY]

The National Masonry Concrete Association was the governing body for masonry construction in the 1970s. They had design rules for both reinforced and non-reinforced masonry walls.
In areas where seismic or hurricanes loads were not used unreinforced masonry walls were very common.

They produced design tables for unreinforced walls for various wind pressures that varied based on the axial dead load on the wall.

A 6" hollow block wall had a section modulus of 50 in3
and an area of 40.5 in2 per foot of wall.
The allowable tensile stress was 23 PSI for Type S mortar and 16 PSI for Type N mortar. If not otherwise specified Type N in what was used.

It is possible to put new re-bars in the existing walls if you need them for shear. There are design procedures for perforated shear walls for plywood shear walls. The same procedures could be applied to a masonry wall so it can be assumed to act as one large wall at a lower average shear capacity.

 

[SperlingPE]

thanks for all the info....
I will be oming up with a way to reinforce the wall.
I was mostly checking to see if there was a provision in "a code" that said that a minimum amount of reinforcing was required even though the plans had no indication that reinforcing was designed for this particular wall.

 

[steve1]

Where is your building located? Many states and cities had their own building codes in that era.

 

[concretemasonry]

The NCMA was not the governing body for codes since it did not have any legal code standing except being the most responsible organization involved in code activity and masonry research.

During the 1970's they published a document referred to as the "green book" the was titled something like "Tentative Specifications for Engineered Masonry Structures". It was used commonly by engineers because of the documentation and contributing authors (Jim Amrhein(sp?) and others in California and other areas. Much of it was used in the design of many successful loadbearing structures in southern California in the late 1960's and 1970's.

Sperling - If you are looking at a 1970's building it may have been designed by the standards in this document, although it may not have built according to the standard. That will take some "digging".

This document ended up being the major basis for the first ACI 530 when it finally got published initially.

Dick