Free calculator
Padstone bearing calculator
Example values: the 38.7 kN reaction from the steel beam example, bearing at the end of a 100 mm block wall, with a 440 mm padstone. Change them to suit your job.
kN
Use the factored (ULS) reaction when you compare with a design strength.
Beam position and direction
Beam end and wall
Bearing length runs along the wall; the flange sits across it.
mm
mm
mm
Padstone
mm
mm
mm
N/mm²
Your design value, e.g. fd with any enhancement for a concentrated load.
Result
Beam straight on the masonry
Contact area 150 along × 100 across, mm
Bearing stress
2.58 N/mm²
Ratio to the 2.00 N/mm² you entered
1.29 over
On the padstone
Contact area 365 along × 100 across, mm
Bearing stress
1.06 N/mm²
Ratio to the 2.00 N/mm² you entered
0.53 under
Average stress over the contact area. On the padstone the load is taken to spread at 45° through its depth, one way only along the wall, because the beam sits at a jamb or wall end.
How it works
The reaction at the end of a beam is spread over the area of masonry it bears on. Divide one by the other and you have the average bearing stress. With kN and mm, multiply the reaction by 1,000 to get N/mm².
Assumptions behind the numbers:
- Pick whether the beam runs in line with the wall (over an opening, say) or crosses it and lands on it from the side. A crossing beam bears on its flange width along the wall and on its bearing length across the wall, up to the wall thickness. The stress is an average, spread evenly over the contact area. In practice the beam end rotates and pushes harder on the inside edge of the bearing.
- The padstone is taken to spread the load at 45° through its depth. That is a hand-calculation convention for a concrete padstone, not a clause of BS EN 1996-1-1. At a jamb or the end of a wall, the default, the beam sits at one end of the padstone and the load spreads one way along the wall. Part way along a wall the beam is taken to sit in the middle of the padstone and the load spreads both ways.
- The comparison value is yours. The calculator does not work out the masonry strength, the partial factor or any enhancement for a concentrated load.
- It does not check the padstone's own strength, the steel flange on the padstone, eccentricity, or the stress lower down the wall.
- In US mode the reaction is in lb, dimensions in inches and the stress in psi. Match the reaction to the stress you compare with: service loads with an allowable stress, factored loads with a design strength.
Worked example
The beam from the steel beam calculator example has a ULS reaction of 38.7 kN. It is a 203 × 133 UB, with a 133 mm flange, in line with a 100 mm block wall and bearing 150 mm onto the end of it. That is a wall end, so the load can only spread one way. The design strength assumed for the block, for illustration, is 2.0 N/mm².
The bare bearing is 29% over the value entered. With the padstone the ratio is 0.53. Only 365 mm of the 440 mm padstone works, because a 215 mm deep padstone cannot spread the load further from one side. Part way along a wall the same padstone would work over its full 440 mm, giving 0.88 N/mm². That settles the bearing only: the wall and footing below still need checking.
FAQ
How do you calculate the bearing stress under a padstone?
Divide the beam end reaction by the area of masonry the padstone spreads it over. A 38.7 kN reaction at the end of a wall, on a 215 mm deep padstone under a 150 mm bearing, spreads over 150 + 215 = 365 mm of a 100 mm wall: 36,500 mm², so the stress is 38,700 / 36,500 = 1.06 N/mm². Use the ULS reaction when you compare it with a design strength.
When does a steel beam need a padstone?
When the stress directly under the beam end is more than the masonry can take, which is common for steel beams on blockwork. A padstone spreads the reaction over a longer length of wall. In the example on this page, a beam at the end of a wall, the stress falls from 2.58 N/mm² on the bare block to 1.06 N/mm² on a 440 × 100 × 215 mm padstone.
How deep should a padstone be?
Deep enough to spread the load out to its ends. This calculator takes a 45° spread through a concrete padstone, a common hand-calculation convention rather than a rule from BS EN 1996-1-1. With the beam in the middle of the padstone, the load spreads both ways, so a 440 mm padstone under a 150 mm bearing needs to be (440 − 150) / 2 = 145 mm deep to work over its full length. At a jamb or wall end, where the beam sits at one end of the padstone, it spreads one way only and needs 440 − 150 = 290 mm.
What masonry strength should I compare the stress with?
The design value from your code. In the UK that is fd = fk / γM from BS EN 1996-1-1 and its National Annex, which depends on the unit strength, the mortar and the partial factor, increased by the enhancement factor β for a concentrated load where it applies. The 2.0 N/mm² in the calculator is an example only.
If the padstone passes, is the wall fine?
Not necessarily. The padstone itself, the steel flange on the padstone, any eccentricity of the beam on the wall, and the stress lower down the wall once other loads join it all need checking. So does the foundation under the wall or pier.
Check the result
Check against the code and get a qualified engineer to sign off.
A ratio under 1.0 here only means the stress is under the number you typed. Check the bearing against BS EN 1996-1-1 (clause 6.1.3 covers concentrated loads) or your local code, and have a qualified engineer sign it off.
Read more: from beam to foundation, point loads from steel posts and load spread at wall ends.