Thanks BAretired for the statement. Bending moments of footings are indeed controlled by reinforcement in the form of qu= factored column load / bearing area. So even if the soil capacity increases 5 times fold (from say 150 kpa to 750 kpa). If the shear, moment reinforcement is the same...
Because the designers said they no longer have time to redesign the whole footing just to accomodate the increased bearing capacity.. and they also said 0.5 to 1 meter length increase of the column can be made without changing any of the design... because they have large margin of safety...
What we intend to do is to put the 150kpa designed footing putting right on the rock and just let the designers change the column parameter for the extra 0.5 meter length. We don't want to change the design of the footing anymore. So there is absolutely no problem in putting the 150 kpa footing...
The geotechnical engineer wants to be on the safe side and juse put 150 kpa on paper which is what the designers use (meaning they didn't expect us to dig deeper). Now that we have tuff rock as bottom. Let's say it is really 1000kpa. What is wrong with the footing that is designed for 150kpa...
I don't know your definition of Tuff. You assume it is softer hence less than 150 kpa? I'm talking of tuff rock that is 400 kpa or so. We didn't know the depth of the tuff initially. I'm concerned of your statement that if footing is designed for 150 kpa.. it is not designed for let say 400...
The total footings concrete already reach 60 cubic meter. If we add another 0.5m, it would add another 48 cubic meters for total of 108 cubic meter. The cost would be huge. Do you really implement this? Anyway. I'll just have the columns recalculated to see if additional 0.5 meter would still...
I'm a new construction engineer. I guess I have to ask the structural designers about it. But my fellow construction engineers said for 0.5 meter difference.. they never bother ask the structural designers since 0.5 meter is just short and negligible or within allowance...
It's not exactly overexcavated.. or more done on purpose I mean... it's only found out that 2 meters below are hard rock. so all the footings will be put 2 meters below instead of 1.5 meters. So you think all the columns have to be redesigned for 0.5 meter additional length? But I think this...
BA.. but the footing needs to be put at 2 meters instead of the designed 1.5 meters. Can't put concrete below the footing. Do you redesign the column size and bars or let it remain as it is if it has to go down 0.5m more?
The actual digged or excavated depth is 2 meters to reach certain tuff rock layer, calculated depth of design is 1.5 meters.. what do you normally do in case like this?
1. Increase column size to control deflection
2. Put more bars to control deflection
3. Or nothing at all taking into account...
Problem with grade 60 ties is if the corner bends are brittle and the crews install it without double checking.. so there is advantage in using grade 40 instead of grade 60 column ties... Has anyone here actually make it a point to choose grade 40 instead of grade 60 column ties since the yeild...
We will of course adjust the spacing to accomodate grade 40 stirrups instead of grade 60. I assume there is similarly no hidden problem in using column grade 40 ties with grade 60 main column bars assuming the spacing is recalculated. Correct?
