Beware: Don’t just bolt your beams!

14.12.2018
Blog Post
Builders pointing at beams in the roof

The traditional approach used when two steel beams are provided to support a cavity wall has been to design the beams to each carry half the total load and then connect them with pipe spacers and bolts, even when the loading to each beam was not equal.

This view has been challenged by many structural engineers who say you should not rely on spacers and bolts to fix them together. This becomes more important where the beams are likely to carry different loads, a typical situation in a cavity wall where the inner leaf carries the floor joists, resulting in significantly different loads on the inner and outer beams.

It is common for structural engineers to specify I-beams, also known as Universal Columns (UC), for situations described above. The horizontal elements in an I-beam are called “flanges”, and the vertical element is called the “web”.

I-beams are excellent at resisting vertical loading and bending as these are parallel to the web. However, I-beams are generally weaker in torsion, which may lead to twisting or deflection in the beam, particularly when unevenly loaded – this could result in cracking of masonry above, and in severe cases this could lead to failure of the beams.

So, steel beams and their connection details should always be designed by a competent structural engineer. Depending on the individual situation and the loadings involved, the structural engineer may specify one of several options to connect beams together and reduce torsion, such as:

 

  1. using bolts and spacers at regular centres
  2. welding the beams together or providing a continuous welded plate over the top of both beams
  3. provide web stiffeners between the flanges of each beam

Ideally, onsite welding should be minimised where possible to reduce fire safety risks. If welding is unavoidable, it should be adequately planned and carried out in a safe manner by a competent person – and remember also to check if the client has a ‘hot works permit’ approval process in place before commencing.
 

Want to read more about traditional building techniques and structures?

Take a look at our articles from the "My dad told me about them!" series. Our most popular ones include:

You might also find this article useful: Beware of point loads on beams.

 

Please Note: Every care was taken to ensure the information was correct at the time of publication. Any written guidance provided does not replace the user’s professional judgement. It is the responsibility of the dutyholder or person carrying out the work to ensure compliance with relevant building regulations or applicable technical standards.

This article was updated on 1 August 2022

Comments

No packing of steel

Submitted 3 years 10 months ago

We had a rogue builder who did the steel and didnt pack it and plastered over it, thankfully a family friend caught it in time and we asked him to leave. We have since packed the steel, what would of been the impact if he had got away it, would building have sagged in years to come, there were big gaps between the steel and supporting wall which was the side of our house? As well he put the steel on engineering bricks rather than concrete padstones but we were told while not best practice that this was okay. Any thoughts would be great. Thanks, Matthew.

Why 2?

Submitted 3 years 10 months ago

Can I ask a questions please, why are 2 beams specified, say you have 270mm cavity wall, why not use a single 254UC to span the opening, with both leaves of the wall supported on the top flange?

Why 2?

Submitted 3 years 5 months ago

The weight of 254UC sections starts at 73kg/m and would be a Health and Safety hazard for most builders as wel as beeing more costly.

Similar deflections

Submitted 3 years 10 months ago

Or design pairs of beams to have similar deflections whenever possible (say 152UC for heavily loaded inner leaf and 152UB for outer leaf).

Welded stiff plates between beams seem very excessive and difficult and time-consuming to install.

Pre-loading beams

Submitted 3 years 10 months ago

How do you all feel about the idea of pre-loading beams (thereby inducing the calculated deflection) by using folding steel wedges at the centre of the span before slating and packing under the masonry above.
Then once the acrows are removed there is no cracking ...

Problems with deflection

Submitted 3 years 10 months ago

I'm working on a couple of schemes at them moment where we've been brought in to deal with problems of deflection to the structure and finishes above.
Example: Engineer has assumed load transfer between beams by way of pairs of bolts at 750 ctrs through web with spacers/lock nuts. To me that's no better than a single and provides no load transfer without significant bending or twisting occurring. Engineer has also assumed quarter point restraint via this bolted connection!!
203UB25 spanning 5.8m = big deflection
We always design as follows:
1. Unless wall above is 215mm solid we design the worst case beam.
2. Restraints are used where we have detailed it. So if we need restraint at third points we'll detail strapping to the structure (not to the adjacent beam, this is not adequate).
3. If we do tie the beams together, to restrain both back to the structure, then we detail top flange plates (welded to beam 1, bolted to beam 2, ie no insitu welding needed).
We try not to detail 203 UC due to weight issues, builder will end up splicing which creates it's own set of problems.
Asking a domestic builder to predeflect is not ideal, results will vary!!

July 2014

Submitted 3 years 10 months ago

As from July 2014 all structural steel need to be engineered by an engineer, The engineer is responsible for specifying the Execution Class for the structure (the works as a whole), and for components and details where it is appropriate to specify an Execution Class different to that specified for the structure. Where different, the Execution Class for a component or detail should not be lower than that specified for the works as a whole. The Execution Class for a component or detail should be clearly identified in the execution specification if it is different to the Execution Class for the structure.
All fabricated steelwork should be completed by a ce-marking fabricator.

Universal beam installation

Submitted 2 years 2 months ago

I have just received my load calcs / Pad stone spec regarding the installation of UBS.
I noticed a detailed drawing regarding the fixing the UBs to the pad stone’s Using 10mm resin fixed bolts...is this a new requirement?.

Regards Will

Reply

Submitted 2 years 1 month ago

Hello there

Thanks for getting in touch.

You should take this up with your designer just in case there are issues with the design that we are not aware of.

Kind regards
Barry, LABC

Pads for an I beam.

Submitted 2 years 1 month ago

I have had a 6.5m I beam installed. It is spliced and bolted near the middle, not welded.
The base of the beam is 260mm wide. The beam sits on large plinths about 400mm each end.
The problem is the beam and pad are tilted about 10mm off level across the 260mm width. Nothing has moved it was installed this way.

Is this a problem?
Should I point it out to Building Control or just see if they say anything?

For info, I have not paid the contractor.

Any thoughts

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