I'm asking this because a company which designs 20-50 storey buiilding and above used entirely ETABS outputs in their calculation sheet. They don't put any formulas.
When doing 2-storey. Of course I use formulas in excel. I don't rely entirely on ETABs. But for the 20-39 storey designers. They...
For those who haven't used ETABS. Try putting just a simple beam supported on a column. Enter the uniform load or point load in the program. You will find out the moments produced by the program is the same as when you calculate it using manual formulas. Now add it it many elements and the...
More than half of local structural engineers I know doesn't use manual computations anymore. They reason it's long process to get for example the biaxial interaction diagram, moments of each columns and beams and their interactions especially if they are designing very tall stories. So they rely...
97% of structural engineers I met haven't experienced doing any combined footings more than 3 meters and most use eccentric footing without making the column stiff enough to handle it so they are not really designed for seismic performance. The reason is cost. If they won't make the eccentric...
I wonder if I can let the contractors weld all the sides so they would be act like 3 meter width full fledge stirrups. The suggestion was just to tie up all the sides with small wires to hold the top bars. Remember in combined footings transverse bars on top was put to take care of moments in...
I talked to the contractor team at length today. I asked how the top bars would be connected to the bottom bars. They said what they do is to extend each transverse and longitudinal bars to the sides and tie up each one of them to create super strong cage for the combined footings (they drew it...
Thanks, ishvaaag. One last concept I needed to know before getting the confidence of letting them handle it. In normal beams above columns (near ceiling). We are concerned about joint shear. For example. If the reinforcement percentage is high like 2.5% or the column small. There would be more...
What can you say about footings rotational restraints? The combined footings width, depth were designed such that rotational restraints in all directions were controlled. However, isn't it the moments have to transfer elsewhere. Meaning, when the period of a building decrease, the elements have...
Instead of using a centering or strap beam. What's wrong if you just combined all the footings into rectangle. This would mean making the footings larger than needed. Is the disadvantage only costs? This is the solution we used. The 3 columns separate only has axial load of 3500 kn. We made...
Hi, thanks for the comments. But one thing I'm thinking is the weight of the concrete itself. In beams above columns (near ceiling). Gravity or sole weight of the concrete can cause shear stress (by the downward force). In combined footings. There is no opposite gravity pulling the footing...
When the shear beam span to depth ratio is less than 2.5. It's supposed to be deep beams. Yet we still use stirrups in above column deep beams (RC). Okay. This is what perflexed me. In combined footings and even normal isolated spread footings. We don't use stirrups because we can increase the...
Oh yes. They will of course still have further say on the contruction. It's just that they won't be working full time on the project. And the thing is combined footings are new to me and my assigned construction engineer.. so I'll just let them change construction engineer. Remember I approved...
hokie66, why.. structural engineers are not connected with the actual constructions. Are you for each of your project? We make and sign and seal plans. It is up to the contractors to build them. I'm coordinating and asking with the engineers who designed it the best way it can be build. But...
Please check out the above combined footings rebars details (slow to load). I was asking the engineer in charged how much was the axial load in each column. He didn't know because it is the program called SAFE that produces all details which are imported from ETABS and they have about 10...
hokie66 and others,
As I have mentioned before. I didn't do the project and I experts handle it. I'm just middleman between them and client. They have designed over a dozen 30 storey buildings which were actually constructed and they are experts in mat foundation. Unfortunately. They rely...
After talking about eccentric footings for 2 weeks. We didn't mention the fact that for columns located at external end. It automatically has moments due to the beams at top (ceiling level) not centered and on one side only even when the column is at center of footing (see above). Now is it not...
ishvaaag and SteelPE. My only concern of standees connecting the top bars to the bottom bars is if there would be unwanted reactions. Can you see any reactions going on between them such as flexures being affected when standees iron held between them or some shear developing from the standees...
ishvaagg, are you talking of the cage collapsing before putting concrete or after it is filled with concrete? If already filled with concrete, how can the cage collapse? The concrete to be used is 4000 psi (or 28 mpa)
do you know the formula when non-linear settlement occurs or the threshold...
Beams have many stirrups at certain distances to avoid shear failure like in following.
But in combined footings.. There are no stirrups like the above. Unless you are saying then that it needs stirrups like above? anyone has actually designed combined footings that use stirrups like above?
Today I was discussing with the contractor engineers of how to support the top bars (longitudinal) in the combined footings like shown above. They haven't encountered anything like it in their years of constructions. This is because in normal footings.. only the bottom bars exist. Now for the...
