How to apply Table 9.20.5.2.A. vs Table 9.20.5.2.B

[sunyaer]

This is from Ontario building code part 9:

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9.20.5.2. Lintels or Arches
(1) Masonry over openings shall be supported by steel, reinforced concrete lintels or masonry arches designed to
support the imposed loads.
(2) Except as provided in Sentences (3) and (6), steel angle lintels supporting masonry above openings shall conform to
Table 9.20.5.2.A.
(3) Steel angle lintels supporting masonry veneer above openings shall conform to Table 9.20.5.2.B.
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Table 9.20.5.2.A. & B. are here:

Table 9.20.5.2.A. & Table 9.20.5.2.B.pdf

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The following are 2 questions with answers from a building code training materials:

My questions: why is 9.20.5.2.A. applied in question 1? Is "100 mm brick" in question 1 not veneer, while "90 mm brick veneer" is?

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1. A 2 100 mm opening in an exterior masonry wall and supporting 100 mm brick with no other
load is required to have a loose steel lintel comprising:
a) L-90 mm × 90 mm × 6 mm
b) L-125 mm × 90 mm × 8 mm
c) L-125 mm × 125 mm × 8 mm
d) L-102 mm × 89 mm × 7.9 mm

Answer: d) L-102 mm × 89 mm × 7.9 mm

References:

Sentence 9.20.5.2.(1), (2)→ Table
9.20.5.2.A., Row 4 Column 2


2. A 2 100 mm opening in an exterior wood-framed wall and supporting 90 mm brick veneer
with no other load is required to have a loose steel lintel comprising:
a) L-89 mm × 89 mm × 6.4 mm
b) L-125 mm × 90 mm × 8 mm
c) L-125 mm × 125 mm × 8 mm
d) L-100 mm × 90 mm × 8 mm

Answer: a) L-89 mm × 89 mm × 6.4 mm

References:

Sentence 9.20.5.2.(1), (2) → (3) →
Table 9.20.5.2.B., Row 2 Columns 1, 2, 3, and 5

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[tmurray]

For 100mm brick, your only option is table 9.20.5.2.A. For 90mm veneer, your only option is 9.20.5.2.B.

It's less about the terminology used and more about the size of the material.

 

[sunyaer]

For 100mm brick, your only option is table 9.20.5.2.A. For 90mm veneer, your only option is 9.20.5.2.B.

It's less about the terminology used and more about the size of the material.

Structurally in terms of loading, 100 mm brick would be reasonably assumed to be equal to 90 mm veneer. How would the designer know if the brick or veneer in the tables is hollow or solid? Self weight (loading) of hollow or solid brick / veneer is different.

 

[tmurray]

The designer would be designing based the products specified by the contractor/owner.

 

[sunyaer]

The designer would be designing based the products specified by the contractor/owner.

I think part 9 design tables are like recipe, the designer is not required to do calculation if the span/loading does not exceed the assumptions of the tables. My question would be: how does the designer know the assumption of brick / veneer in terms of being hollow or solid in these steel lintel tables?

 

[tmurray]

I think the assumption would be that the tables are for solid units. I don't see anything discussing equivalent thickness, which would address hollow units. There is certainly nothing prohibiting them from being used for hollow units though.

 

[Inspector Gadget]

Here's a brainteaser for you - how do you size angle iron for structural stone? Because it's required by Code ... but structural stone is often of varied thickness.

 

[tmurray]

In that case you can use the average thickness, assuming that the stone is all of the same density. Next questions:

How many stones to you measure to develop an average density?

How much of a safety factor do you build in?

Ah, statistical analysis of course. You can survey a "statistically significant" amount of stones, put their measurements into statistical analysis software and perform a T Test.

What does everyone normally do? Use the thickest one they can find quickly as a worst case scenario and go from there.

 

[Inspector Gadget]

In that case you can use the average thickness, assuming that the stone is all of the same density. Next questions:

How many stones to you measure to develop an average density?

How much of a safety factor do you build in?

Ah, statistical analysis of course. You can survey a "statistically significant" amount of stones, put their measurements into statistical analysis software and perform a T Test.

What does everyone normally do? Use the thickest one they can find quickly as a worst case scenario and go from there.

That's basically what I did. (FYI, this is my own home, and one of the reasons I got into this biz....)

I also created a "cast in place" concrete lintel behind the stone, 12" thick, bearing a good foot plus on both sides of the opening, with a 15m bar. Because overkill.