Effective Length of I-Beam 1

[Contraflexure74]

Hi,

I have a steel I-Beam supporting a roof, as per attached detail.

The beam sits on a 100mm inner blockwork leaf at wallplate level. The clear span of the UB is 7m.

My question is can I take the effective length of the beam as 1m as it is laterally restrained by roof structure?

Also do I need to be concerned about destabilising loads?

John.

 

[lemmiwinksownz]

Your braced length/effective length will be the maximum of the spacing of the members restraining the beam. If the roof structure members are spaced 1m, the effective length is 1m.

 

[KootK]

I agree that the roof structure will likely brace the top flange. The other piece of the puzzle is that the connection to the block work also needs to laterally restrain the bottom flange. We'd need to know a bit more about what that detail looks like to comment authoritatively on that.

Also do I need to be concerned about destabilising loads?

Not sure what you mean by this. Can you elaborate?

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[Contraflexure74]

Thanks Lemmiwinksownz,

John.

 

[Contraflexure74]

I guess I can weld a plate to the end of the beam (bottom flange level) and bolt vertically down into the block. At the other end it sits into a wall which runs 90 degrees to the UB so I can build blockwork tight in around the beam end to restrain the bottom flange.

John.

 

[jayrod12]

I would be providing a weld plate at each end of the beam on the masonry wall, regardless of whether the wall is perpendicular to the beam or not. Then I don't have to rely on the mason to fit the block in there tightly around the beam.

 

[Contraflexure74]

Thanks Guys.

John.

 

[KootK]

I agree with jayrod's sentiments regarding the weld plates. I also typically provide 3/4 height stiffeners at the beam bearing locations for good measure.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[Contraflexure74]

Excellent idea on the end stiffeners Kootk.

John.

 

[Hokie93]

Is the beam subject to net uplift? If so, then the unbraced length for that loading condition would be the distance between bottom flange braces or the full span if no bottom flange braces are present.

 

[pappyirl]

The load is not destabilising, the tie ensures this is the case.

Is the beam laterally restraining the block work wall panel under?

The roof is noted as being laterally restrained. How is this achieved, bracing in the roof plane or otherwise? The detail shown in the sketch by itself is not sufficient to provide lateral restraint, although the roof is generally sufficiently braced to transfer the lateral loads.