CMU Wall Horizontal Section Properties

[jeffhed]

Hello,
I am currently helping a client develop his own masonry block. I have been tasked with developing tables that show the section properties for the block spanning both vertically and horizontally. So for a proof of concept I decided to try to match the wall section properties in NCMA TEK 14-01b. It has worked out well so far, as we can match the values for the walls spanning vertically for both the net section properties and the average section properties. We can also match the net section values for the walls spanning horizontally, but I cannot for the life of me figure out how they are getting the values for the average section properties for walls spanning horizontally. For the walls spanning vertically you basically add in the interior webs that are not considered in the net section properties calculation and you can get the average section properties. But on the spanning horizontally portion, there are no webs to add in, at least the way I am understanding it. If we add in the web on every other course our areas are way high, if we don't add in the web on every other course we get values that are significantly too low. The definitions for the net section properties and the average section properties are defined in the TEK 14-01b as follows:
A Net cross-sectional properties determined from a vertical plane that coincides with the face shells of the units. Net cross-sectional properties are to be used for determining stress and strain resulting from the application of load.
B Average cross-sectional properties determined from two vertical planes calculated as the average of the net and solid properties. Average cross-sectional properties are to be used for determining stiffness and deflection of an element.

So my first question is where are the two planes located for the walls spanning horizontally? I have tried to look at ratios of the different spacings to the solid average section properties and the numbers don't really seem to give me much information. Has anyone tried to duplicated the average section properties for walls spanning horizontally before?

 

[JLNJ]

I presume we are talking about hollow block.

Spanning horizontally I would just use the minimum ASTM allowable face shell thickness to determine the section modulus. Even spanning vertically I don’t count on full mortar bedding of the webs and of course the webs don’t contribute in the horizontal span.

The allowable flexural tension values are different for horizontally and vertically spanning block, so don’t forget to take that into account.

There often is a slight flare to the units to make them easier to pick up. Maybe the NCMA averages this in.

 

[jeffhed]

JLNJ,
We are talking about the average section properties for both hollow and the partially grouted walls. The tables in the NCMA TEK 14-01b state if the mortar bedding is full or just the face shells. I agree that the webs do not count for the walls spanning horizontally. As far as the flexural tension values, we are not considering that right now. We are just trying to duplicate the section properties. If there was a slight flare that NCMA is averaging in, then we would be off on our net section properties, but we are right on on those values. I have been out of town for a week, so maybe I will look at it with fresh eyes today.