Having just posted a reply to a question on the forum. This got me thinking about something that's been niggling me for a while. This affects all of us that design & specify outdoor structures.
What information & warnings do give clients about over loading the materials you specify? Examples:
Driveways
A domestic driveway with 50mm blocks 50mm sand 150mm MOT, would be suitable for loads up to 3.5 tonnes gross 7.5 tonnes at a push, evenly distributed. I have seen vehicles of 32 tonne tipping on drives, with the minimum of protection against the point loading. Do you specifie a maximum vehicle weight for such structures?
Decking
For domestic deck I follow TRADA span tables, using C16 rated timber. this gives a design strength of 1.5 kN/m2 evenly sistributed. What about that party, were every one gets up to dance on the new deck? These limits could easily be exieded and the structure fail. Injuries & fatalities have resulted from deck failures in the past. All first floor decks should always be installed with the advice of a structural engineer.
What other situations would you bring in a structural engineer? Landforms? Retaining walls?
How do you limit your liability? Should you put up notices on the drives & decks 'Maximum load...'?
Clive
www.thehandmadegarden.com
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this is a good post now that evrything is health and safty mad and people reching for the solicitor to sue the second something gose wrong
when i used to do landscaping i would specify the requirments of the structure i was building in the quote ie
double drive to hold 3 average familie cars useing .......... materials and ..... dimensions
kind of coverd my self for if some one decided to park there works 7.5 truck on there or have things deliverd by a building supplies place who didnt put any blocks down to spread waight properly.
as for warning signs and waight limmits being displayed etc the chance is that will be something which would have to be done soon if things keep going in the direction they are now
Could there be two parts to this ? Those issues that affect the initial design & build, then those issues you need to have the client understand/respect to limit your liability.
My concerns have always been around cut & fills and wall lodgings.
At what point do you say woah....we need a structural engineer on this one...( much to disgust of clients).
Would like to come back to this when I've more time away from site.
Good point Neal I remember years ago giving evidence for a landscaper, that had installed a lawn that had failed. The customer said he wasn't told he had to keep cutting it and won his case. You cant take anything for granted!
Gary excuse my ignorance but what's a wall lodging?
The problem is, as we design and specify gardens, this is a broad church, always pushing ourselves to use new materials. Doing things in different and imaginative ways, that push the envelope 'Those that never fail never try' But we live in an ever litigious world. We also need to have in mind those that will use the spaces we create, irrespective of there abilities. To ensure that are protected from unnecessary risk.
Should be 'wall loading' .....
We have always used a consolidated lean mix concrete base for our block paved drives. Our first one was in 1985 and had 5 follow-ups in the same road within a year. ALL are still there, no ruts, no 'proud' man holes etc.
Good topic.
A few years ago a client told me they wanted to put a temporary circular swimming pool on the new deck I'd built for them (approx. 3.5 to 4m square). I calculated the volume of the pool they were looking at and realised that if they filled it to the top the water alone would weigh about 11 tonnes. Obviously I dissuaded them and suggested the lawn might be better and would grow back eventually. Luckily the deck wasn't raised by much so wouldn't have collapsed far, but it did make me think about how clients will use the structures you build after you're gone. Attaching swings to pergolas for example. Should you build to accomodate different uses or just warn the client that they should only use the structure for the intended purposes?
I tend to over design the structural integrity of my designs as my original degree was in civil engineering where I learnt to assume worst case scenarios and add a safety margin. However I don't think my decks would survive a metre deep pool on top!
I built an underground wine cellar in 1991.
I say underground but it was cut into a steep hillside , a reinforced concrete block wall construction with a beam and block roof topping it off.
Once the roof was in place we then covered the roof with a dpc membrane and then 600mm of the soil we'd excavated pre-construction. I do not remember the technical specification but we were able to drive a 2 tonne dumper and a mini excavator over the top.
Even though I designed the wine cellar I had all of the loading calculations done by a structural engineer.
Just as an update on this thread. I recently came across this article. The consequences of exceeding the designed loading of a structure, even temporarily can have tragic consequences. This scenario is one that we could very easily see played out on a landscape site.
Builder jailed over toddlers death
Gary this looks like exactly one of those situations you spoke of.
yeah, shouldn't just assume people will be sensible - who thinks about the strength of a decking before they invite 150 people over for a wedding in the back garden?
i did a large raised deck a couple of years ago and the guy i was working with who's brother the deck was for was forever shaking his head and complaining about the cost and quantity of the fixings we were using and the amount of timber we used - too expensive and over engineered was his view, i did point out that the collapse of the deck under the weight of a wedding party could be a major disaster, but he seemed to keep putting that to the back of his mind.
if i'd had my way it would have been even more substantial considering that with 2 daugthers of a certain age, it is likely that that deck will have a couple of hundred people/wedding guests on it at some point.
there's nothing wrong with getting hold of a copy of the timber decking association guidlines and building to them - bearing in mind that a lot of decks actually require planning permission and building regulations, it's the least we should do
as for the lean mix sub base, that's an interesting idea, i did a lean mix access road once and it worked well. never thought of using it for a driveway base before though. thanks for the tip.
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