Existing Building Risk Assessments.

Read through The Institution of Structural Engineers latest guidance on risk assessments to existing buildings this morning...

https://www.istructe.org/journal/volumes/volume-102-(2024)/issue-1/risk-and-existing-building-assessments/

hmmm....

They're pushing a reduction in safety factors over reliability (which I knew), but here's why we (SPHstructures) won't be adopting that approach and we're going down the reliability route instead.

• Call us old fashioned, but we like more safety within a building rather than less.
• I think its going to be the 'go to' approach for all engineers rather than a last resort and that's pretty dangerous. My worry is they'll negate an understanding of the existing building because a quick reduction in partial safety factors works and they can move on. Its going to be a common argument going forward and people will look to pinch an inch here and there and I don't like the thought of that for one minute.
• Its not in any code - reliability is.
• When you do a search for examples of reducing safety factors you'll find a lot of documents produced by the IStructE, BRE and some UNI papers exploring the idea, but it hasn't been taken up by mainstream codes as yet (happy to be corrected here if I've missed something - either way, we still won't be adopting it for reasons above).
• When you start digging into existing surveys and risk assessments, the main questions you're going to ask yourself is where to draw the line on safety. The code talks about Target Reliability - I love this. It gives you measurable value of where your building should be performing due to its age. Throw in a visual condition survey and you quickly get a measure of the safety of the existing building and what needs addressing, you can also make an estimation on future inspections and draw limits on barrier and mitigation points going forward - this feeds into maintenance requirements under CDM regulations.
• The reduction in partial safety factors is basically the plausibility check (that's in the code), which is when the calculations don't work but the thing is standing up in front of you - so how's it working? That clause encourages you to look at specific critical elements and then leads into a reduction of partial safety factors if need be - you don't just jump straight to the end approach. It usually triggers more investigation work before that anyway which may well show you something that was initially missing.

Ultimately, the assessment of the existing building is the easy bit.

You're going to struggle with any non-compliant building when it comes to disproportionate collapse anyway and clients are going to have to creep into asset and risk management, and they're going to look to us for help with that unless they employ a risk consultant who sits above both us and fire.

That's the tough bit. The management of the risks.

The article talks about the ERIC approach, which is a hierarchy of importance when it comes to managing risk. Great, every Building Control officer in the BSR will be working their way down top to bottom on this. But CROSS have already published a document stating Administrative controls are considered the best form of mitigation in risk management (see Soft Hazards, great publication).

Now that's a fairly low intervention option. But the reasoning is for an accidental event to occur its never just one thing, its a series of smaller events which add up to the larger scenario. So managing the small stuff negates the big stuff.

The one thing the article didn't talk about was next steps. Specifically managing residents expectations. Last year their building was fine, this year its not - so what's happened? Explaining that the legislation has changed rather than the building goes some length.

Clients also need to know their next steps, time frames, costs, comparison with gross disproportion? If you're removing gas from every building are we now expected to add substations into each block to address the additional drain on power now? That comes with its own risks as well.

Do yourself a favour and learn reliability. Its probability based the same as risk, so there's an easy comparison to be made when it comes to ALARP assessments and you'll find it just ties everything together much better - I think the guys writing the codes already knew this.