AS3700 Unreinforced Brick Horizontal Bending - Section Modulus Issue

[geopat69]

HI all

I have an issue i can not resolve in my head regarding AS3700 unreinforced horizontal bending. I have been thru the Thinkbrick manuals and the National Masonry manuals...and whilst they prescribe what to do for designers, they do not provide insight into the origin of the section modulus!

In reference to Cl 7.4.3.2 equation (iii), this formula gives the horizontal capacity (Mch) of an unreinforced brick wall with a Vertical straight line failure thru the perpends and brick unit-> Hence the reason Zu and Zp are used in this equation:

Mch = phi x (0.44 x f'ut x Zu + 0.56 x f'mt x Zp)


However, since the units are mm3/m for Zu and Zp, has anyone delved into the logic of this? I mean, if a brick wall (made up of 110mm wide by 76mm high bricks)is spanning horizontally, the AS3700 requires that the capacity and actions be determined on a basis of per meter (which mean Zp and Zu are mm3/m). So simplistically, this means there will be 6.58 bricks vertically and 6.58 perpends vertically. Thus, 6.58 x 76 = 500mm of brick, and, 500mm of perpend.

But clearly the section modulus of Zu is per meter(not per 500mm) and Zp is per meter(not per 500mm).

Can anyone explain how the code derived Cl 7.4.3.2 on the basis that only half the section modulus of the unit and perpends are used.???

 

[Settingsun]

The 0.44 and 0.56 factors: 440mm and 560mm.

 

[geopat69]

Good response Steveh49.

I see where its from. 1000/86 = 11.63.

Then 11.63 / 2 = 5.81

Thus 5.81 x 76 high brick is 441mm and 5.81 x (76 +10perpend +10perpend) =560mm

and they are the factors in the As3700 formula.

Interestingly, those factors are slightly different for bricks manufactured as double height!!!

regards and thanks