Maximum bending moment

[foo9008]

Homework Statement

how the author found the maximum moment = 0.29MNm ? is there any formula ? how to find it in this question ?

Homework Equations

The Attempt at a Solution

 

[SteamKing]

Homework Statement

how the author found the maximum moment = 0.29MNm ? is there any formula ? how to find it in this question ?

Homework Equations

The Attempt at a Solution

Of course there's a formula. That's what beam tables are for - too look up things like the maximum B.M. without having to work them out from scratch all the time.

Here is a set of typical beam tables:

http://www.awc.org/pdf/codes-standards/publications/design-aids/AWC-DA6-BeamFormulas-0710.pdf

Your beam is Figure 1, page 4.

BTW, the calculation of the total weight of the wall above has a small error. W = 0.145 MN, rather than 0.145 kN.

 

[foo9008]

Of course there's a formula. That's what beam tables are for - too look up things like the maximum B.M. without having to work them out from scratch all the time.

Here is a set of typical beam tables:

http://www.awc.org/pdf/codes-standards/publications/design-aids/AWC-DA6-BeamFormulas-0710.pdf

Your beam is Figure 1, page 4.

BTW, the calculation of the total weight of the wall above has a small error. W = 0.145 MN, rather than 0.145 kN.

the shape is rectangular cross section , am i right ? why the moment shouldnt' be a(b^3) / 12 ? but , a(b^2) / 8 ?

 

[foo9008]

https://www.google.com/search?q=moment+on+rectangular+object&client=opera&hs=ScO&source=lnms&tbm=isch&sa=X&ved=0ahUKEwiLzvHs7MTNAhWFlZQKHVBgBp8Q_AUICCgB&biw=1536&bih=776#imgrc=dHPa7ZEhoyudlM:

 

[SteamKing]

the shape is rectangular cross section , am i right ? why the moment shouldnt' be a(b^3) / 12 ? but , a(b^2) / 8 ?

The problem is trying to figure out the dimensions of the cross section of the beam so that max. bending stress is limited to 7.5 MPa.

Remember, in bending, σ = M ⋅ y / I

It is postulated that the beam supporting the brick wall is twice as deep as it is wide, or w = b and d = 2 ⋅ b, and I = w ⋅ d³ / 12 and y = d/2