Padstone Sizes 4

[DaveHolder]

Can anyone please explain how these maximum allowable loads have been worked out.

I am going to use as an example of Blockwork strength 3.6 N/mm2 , length 215mm and 100mm width.

To work out the maximum shear for the blockwork = (3.6 x 1.25/3) x (215 x 100) = 32.25kN, it is not as shown in the table 23KN.


thanks

 

[HTURKAK]

Padstones are used to spread the load at the bearings of steel or RC beams on masonry walls.

This table apparently for the maximum allowable load vs padstone size and seems to be a supplier's table . One of the masonry type London Brick implies , the allowable load is calculated using the factors at BS 5628.

Design compressive strength =fd =ß Xfk /(ϒm )

ß =capacity reduction factor Table 7, BS 5628 =0.88 for eccentricty =0.1 t and slenderness ratio ≤ 10

For your case , Blockwork strength 3.6 N/mm2 , length 215mm and 100mm width Design compressive strength = 0.9*3.6/3=1.08 MPa.

maximum allowable load Nr=1.05*215*100=23.22 kN. rounded to 23kN.

I will suggest you to look

https://www.eurocode6.org/Published support material/Design Guide 2.pdf

and more info at

https://www.eurocode6.org/index.htm

 

[DaveHolder]

Thank you buddy,

One more question. How can you determine how many courses are needed? is 23kN for 2 course means 23/2 =11.5 kN per course ?

Thanks

 

[HTURKAK]

You will determine the plan area of the padstone by the permissible concentrated bearing stress on the masonry.
The above data proposes 1.25 which is bearing type 1. The local design strength (bearing strength) fb=1.25*fk /(ϒm )

for blockwork strength 3.6 MPa, fb=1.25*3.6/3=1.5 MPa. Using this value determine the area of padstone .

The depth of the padstone is based on a 45° load spread from the edges of the steel beam / RC beam on the padstone
until the padstone area is sufficient that the bearing stresses are within permissible limit.

The following picture depicts the stress distribution at padstone taken from ( Design of Structural Elements , W. M. C. McKenzie )

 

[DaveHolder]

Thank you buddy!

Just need little clarification using an example!

I got 120kN beam steel reaction 100 bearing on parallel wall 215mm thick , 3 meter high!

If I want use Engineering brick 3 course, would be sufficient to handle the stress?

I’m not sure what is the compressive strength of Engineering brick!

I have seen worked example before was using 13Mpa but I’m not sure if that is correct!

In case, it is correct fk would be 13 x 1.25/3 =6.5

So the bearing area required 120 x 1000/ 6.5 =18461mm2

 

[DaveHolder]

Can you please work out and elaborate using the following example.

I have 140kN load reaction from UB254 x 146

3 meter height of Wall stone 440mm thickness parallel to the beam.

The beam bear 215mm onto 440mm long x 215mm wide 3 No courses of A Engineering break.

So stresses under the beam = 140x1000/(146x215) = 4.46Mpa this should be less than the compressive strength of Engineering brick A = 1.25fk/3 Mpa I am not sure what the figure.


Now working out the stresses under the pad stone = 140 x 1000/ (215 x 440)= 1.48Mpa which should be less than what exactly?



Thank you for your help.

 

[BAretired]

Seems like a lot of confusion over something which ought to be very simple.

BA

 

[HTURKAK]

Dear Moonknight (Structural), the beam is UB254 x 146 . That is, (if there is no additional base plate ) , the bearing width shall be 146 mm.

If the reaction of UB254 x 146 140kN is factored load, and if the padstone is engineered brick fk= 13 MPa, Local strength = 1.25fk/(ϒm ) (for bearing type 1)

Local strength = 1.25*13/3= 5.4 MPa.

The bearing area will be Ab ≥ 140000/ 5.4 = 26000 mm2 Y=146 mm, X=26000/146= 180 mm. if the wall thickness t=440 mm,

Bearing length X ≥ t/2= 220 mm. Final bearing area Ab= 146X 220 mm . In order to determine the depth of padstone, we shall know the masonry wall blockwork strength.

Assume Blockwork strength 3.6 N/mm2 , Design compressive strength = 0.9*3.6/3=1.08 MPa. and the depth of the padstone will be determined using this Design compressive strength .

Assume there is only beam reaction load Ved= 140kN the area of the padstone will be = 140000/1.08=130000 mm2. If we assume the length of padstone y =440 mm (wall thk). the width x = 300 and bearing width 146 mm, with 45 degree dist. 73+ H= 150
H≥ 77 mm . round to H=100 mm .

Padstone final size= 220X 440 X 100 H.

This calc. for info only . the refined calc. shall consider available material properties and the other loads applicable to wall .

 

[DaveHolder]

Thank you HTURKAK,

You have been more than helpful.

Just one thing

73+H=150?

73 is half bearing width + H = half of bearing length 300/2?

Is that correct

 

[HTURKAK]

True...The depth of the padstone shall be calculated with a 45° load spread from the edges of the steel beam on the padstone
till the padstone area is sufficient that the bearing stresses are within permissible values of masonry wall.

Padstone dimensions should be multiples of the coordinating size of the available brick . Standard UK brick size 215 × 102 × 65 mm and gives co-ordinating size 225 × 112 × 75 mm. The selected height of the padstone should fit with this dimensions.

 

[DaveHolder]

Thank you very much HTURKAK you are a star!

I am not sure about the rules here but would like to connect with you.

Thanks again

 

[Ron]

@BAretired....Yep!