s4lmonsushi
Structural
- Apr 1, 2021
- 4
Hi,
I am trying to understand the section modulus Zd, Zu and Zp in AS3700, for an ungrouted, unreinforced masonry wall. The wall consists of 15.01 hollow blocks (390x190x140):
For Zd, it is pretty straight forward - basically section modulus of the block itself viewing from plan, and then multiply by 1000/390 to get the section modulus per m length. Doing a simple hand calculation, I got a Zd value of 2565705mm3/m, which closely matches to what Structural Toolkit Calculates (2398810mm3/m). I believe they used the equation provided in the CMAA MA 55 worked example.
For Zu and Zp though, both toolkit and CMAA MA 55 suggests they are the same as Zd. However, this does not make sense to me - under horizontal bending, the section contributing to the bending strength should only be the face shells (and possibly the perpends), similar to below:
Doing a quick hand calc based on the above section, the Zu/Zp value is 1984167mm3/m. Compared to Zd, there is a 20% reduction, which seems too significant.
Appreciate any input/pointers to the right direction! Many thanks.
I am trying to understand the section modulus Zd, Zu and Zp in AS3700, for an ungrouted, unreinforced masonry wall. The wall consists of 15.01 hollow blocks (390x190x140):
For Zd, it is pretty straight forward - basically section modulus of the block itself viewing from plan, and then multiply by 1000/390 to get the section modulus per m length. Doing a simple hand calculation, I got a Zd value of 2565705mm3/m, which closely matches to what Structural Toolkit Calculates (2398810mm3/m). I believe they used the equation provided in the CMAA MA 55 worked example.
For Zu and Zp though, both toolkit and CMAA MA 55 suggests they are the same as Zd. However, this does not make sense to me - under horizontal bending, the section contributing to the bending strength should only be the face shells (and possibly the perpends), similar to below:
Doing a quick hand calc based on the above section, the Zu/Zp value is 1984167mm3/m. Compared to Zd, there is a 20% reduction, which seems too significant.
Appreciate any input/pointers to the right direction! Many thanks.
