Bearing plate on brick wall 1

[hokie66]

A steel beam, in the plane of a brick wall, bears on the end of that wall. The beam extends 150mm (about 6") onto the wall, but the bearing stress is too high. In an effort to decrease the bearing stress, a bearing plate is added which is 300mm long, thus projecting 150 past the end of the beam. My contention is that this extension does little or nothing to improve the bearing situation.

Opinions?

 

[rowingengineer]

What is the thickness of the plate and orientation?

http://www.nceng.com.au/

"Programming today is a race between software engineers striving to build bigger and better idiot-proof programs, and the Universe trying to produce bigger and better idiots. So far, the Universe is winning."

 

[hokie66]

In the example which was discussed before, it was 12 mm thick. As I pointed out, the 300 dimension is parallel to the beam and the wall, thus extending 150 past the end of the beam.

 

[rowingengineer]

I guess the assumption is that the beam bears on the end of the wall and not on a pier ect. Yes i would agree that the bearing plate will not have the stiffness or strength to help much if 150mm more bearing is required.

http://www.nceng.com.au/

"Programming today is a race between software engineers striving to build bigger and better idiot-proof programs, and the Universe trying to produce bigger and better idiots. So far, the Universe is winning."

 

[haynewp]

It should be similar to flexible base plate methods, the input to RISA Base (for example) might be able to be tweaked enough for this case to give a decent force distribution over the brick bearing surface since it has flexible base plate capability.

 

[JAE]

The extension helps a little in my view but not much - unless a vertical stiffener is added off the web of the beam (i.e. creating a WT shape) and thus stiffening the extension.

But the bearing stress under the plate would always be triangular - with maximum stress at the end of the wall.

 

[BAretired]

The bearing plate in the original post, posted by the home owner as I recall, was 100x330x12 (all dimensions in mm). The wall was 100mm brick and the steel beam was bearing over a length of 150mm so that 180mm of plate projected beyond the beam. The beam reaction was 47.3kN or about 10.6 kips. The beam was not welded or otherwise connected to the plate and the plate anchorage to the wall was not specified. The engineer changed the plate thickness to 20mm when contacted by the home owner.

I agree with JAE that the bearing will not be uniform under the 100x150 bearing portion of plate. The projecting portion of plate will deflect upward, creating a gap between plate and wall. Extending the beam 150mm would increase the bearing area to 100x300, but the bearing pressure would still be triangular or trapezoidal. This could be fixed by adding a square or rectangular bar between the beam and plate so that the reaction is more or less centered on the plate.

That still leaves the problem of the beam and wall not being connected. I would be concerned about the stability of the wall and beam. The overall design needs to be reviewed by a competent engineer.

BA

 

[Ron]

The stress on the brick is about 460 psi if you consider only the bearing area of the beam. The plate is 12mm thick and twice as long as the bearing length. Yes, the plate will likely "curl", but will not lose complete contact. Assuming half the unloaded plate length remains in contact to help to distribute the load, the stress on the brick is now about 300 psi. There is not enough load, assuming the brick does not completely crush, to cause the plate to "dogleg" upward, thus some contact will remain.

Not an inspired design and I don't particularly like it, but it seems workable.

Yes, the load (10.6k) is a bit high for the application. Not sure that's correct.

 

[msquared48]

With proper stiffeners added to the plate, and a thicker plate, I see no reason why it should not work.

However, the problem exists that the beam would have to be shored during the plate installation to deload the wall, and the entire plate regrouted to attain more uniform bearing once loaded again, otherwise the OP would just be kidding himself with the addition to the plate.

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[hokie66]

I was primarily concerned that a structural engineer, somewhere in the world, had given this person advice that seemed to indicate that the problem was not understood. BARetired says that the engineer, after being queried, increased the bearing plate thickness to 20 mm. As the stiffness of the beam will still be many times that of the plate, I don't think that helps much in this eccentric bearing condition. Sure, if the bearing is concentric, that's what you do, but this plate hanging off one end is not going to help (much). The brick, if overstressed, will still be overstressed.

Agree with BA that stability is probably even more important than the bearing stress, and that the design should be reviewed by a "competent engineer", but I don't think the OP had found that engineer. In this case, the client was better versed than the engineer, and that is sad.

 

[hokie66]

Here is the picture for anybody who still didn't understand.

http://www.physicsforums.com/attachment.php?attachmentid=50131&d=1345743278

 

[msquared48]

So, what's the username and password Hokie?

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[woodman88]

Yesterday I was talking to a fellow engineer. He said that a job he bid on went to someone else. He found out what the winning bid was one third of his bid. He asked me how anyone could do a job for that price. I told him that they just price the bid on what they could grab that worked, even if it was twice what was needed. In hope that once the client got a contractor bid on the job that he would be able to charge for the "value engineering". Thus, actually get paid the full price for the job.
Basically on some of the jobs I have done, if the client called me about whether a 1/2" steel plate worked or not. I would be incline to tell them that we should bump it up to 5/8" or 3/4" before redoing or going over the calculations for him. If another engineer called me about the steel plate not working I would ask them for their building calculations of the load on the steel plate. If they do not have their own calculations on it but were using mine, I would ask them to call back when they have completed their calculations and that we could go over it then.
Whether this is the situation of the original OP or not we really do not have enough information to make a comment on. Whether the original OP'er should get another engineer to look at the job. That is again something we do not have enough information to made a comment on.
Personally for the amount of money that is being spend on buildings and remodeling. I think that a fair price (and not just taking the low bid) for original engineering and having the plans reviewed (by other than the building department) is a very good idea.

Garth Dreger PE - AZ Phoenix area
As EOR's we should take the responsibility to design our structures to support the components we allow in our design per that industry standards.