NCMA CMU Lintel Values 1

[scanf1027]

I've been designing some cmu lintels and some configurations I need are not in Table 4 of TEK 17-1B. I created a spreadsheet to design my lintels and checked it against the Table 4 values. What is strange is some Mresisting values match and others are off by a significant amount, say 15,000lb-in. The equation is so simple, I don't believe I have an error.

Has anyone verified the table values? Or does anyone have a suggestion of why my values are significantly higher?

Thanks

 

[ishvaaag]

Maybe the TEK values do not only check for flexural strength, but also limit the width of the cracks, or, even more likely, limit the deflection. The first will give you -when controlling design- a lower moment available for a standing amount of reinforcement, whereas the deflection control won't allow some loads permissible in strength (then some moments) be placed on the dintel due to poor deflection performance.

 

[JLNJ]

Are you looking at both shear and flexure? Shear can be the controlling factor.

 

[scanf1027]

I was speaking about the moment values listed. I know the shear
can control, but I am simply trying to match the table moment values.

thanks

 

[SteveGregory]

They might be using a triangular load assuming that arching action occurs. This is not a good assumption if there is a control joint beside the opening.

 

[msquared48]

Good point Steve.

Mike McCann
MMC Engineering

 

[scanf1027]

Forgive me guys, but Mresisting of a cmu lintel is what it is, regardless of how you assume the load is distributed from above.
Right?

 

[msquared48]

For a certain given amount of steel and grout strength, yes. It depends on how your tables are set up.

Mike McCann
MMC Engineering