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Turkish Hello, in the project entered in ide 6, the ground safety: 0.77 (7.7), 50% increase cannot be made because the ground group is D. For the beamless raft solution, the system requires too much cantilever in the floor area, otherwise the ground safety stress does not recover compared to the average stress. Building B+Z+5 floors. What are your suggestions?
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Beamless raft ground stress
- Thread starter tuvenan
- Start date
The pile foundation system is very costly. The building consists of a rectangle that covers 240 square meters in the basement and ground, and 310 square meters in the normal floors. It consists of 12 flats in total. A pile system is unthinkable for it to be economical. Thanks for your answer
HakanŞahin
Administrator
If you add the project, maybe some suggestions for your goal may come...
HakanŞahin
Administrator
Hello, In the roughest calculation, if we divide the total weight of the structure by the raft area, the floor safety is insufficient. It is obvious that much more floor area is needed in case of earthquakes... AverageSoil Stress = Structure Weight/Rat Area 2453/293 = 8.3 t/m2 > 7.7 t/m2 According to this calculation, you need at least 320 m2 raft area from only vertical loads. Your ground values are low, so ground improvement should be done or other foundation system alternatives should be evaluated...
As you said yes, the ground safety remains negative. I would like to pose a general question when I solve the system with beams. When a raft foundation is defined to the area between the continuous beams, if the area is small, the floor safety may be negative. however, when the area surrounded by continuous foundation beams is large, the floor is safe (because the floor area you mentioned grows). however, even if the continuous foundation beams and columns are not connected to each other, leaving the area large is enough to save the foundation. Isn't this situation statically objectionable? In other words, since the floor area of the building does not change, why the number of continuous foundation beams passed through that area and the small or large raft floor areas that separate the floor area affect the floor safety.
HakanŞahin
Administrator
Partial slab and foundation beams cannot be defined together... (However, they can be defined apart from each other) In rafter raft foundation systems, you must connect all columns with continuous foundation beams and form slab eyes. Defining beams on one side or certain parts of the system and defining a single floor is not in accordance with data entry rules.
I guess I was misunderstood. I agree with what you said about the design of the system, there is no such thing. I am sending an example attached. beamed raft version of the previous project. When I define the continuous foundation beam between the s07-s10 columns and the s08-s11 columns, the raft flooring in that area does not save the ground tension, but when I do not it saves it. Good work
HakanŞahin
Administrator
Maximum ground stress control in the rafter raft depends on the size of the area of the slab cells... When you do not insert those beams, you reduce the magnitude of the ground stress falling on the slab chamber. It would be more convenient to insert those beams and even connect TK12 and TK13 beams to S10 and S11 columns...
Greetings.. Having a basement in your building is a very good advantage for you. I don't know if you have taken into account the soil characteristics at the lower level of your foundation, but removing the ground load up to the lower level of the foundation means that half of your structure is covered. If your problem is only exceeding the soil safety stress, I think you should look at the ground stress value at the bottom of the foundation and the net ground stress at that point, taking into account the weight of the lifted ground.
Hello; After the analysis in the beamed raft foundation project I sent attached, I wanted to review the soil stresses from the reinforced concrete/continuous foundation menu. But the screen is completely blank. Values do not appear when selecting combinations. Only the minimum, average and maximum values appear. I have another question. I chose the raft floor thickness of 50 cm, the coating load of 0.15 tons/m2 and the live load of 0.2 tons/m2. After the analysis, the raft slab loads changed. The G, Q values of each raft differ from each other, with G varying around 20 tons/m2, and Q around -4 tons/m2. I couldn't figure out the logic of this. I'm waiting for your help.
HakanŞahin
Administrator
Hello, It is normal for the G and Q values to change in each cell in the rafter raft system, because the loads coming from the columns to each raft slab are calculated separately for each slab and then from the slabs. distributed to continuous foundation beams with finite elements Opportunity to examine stress values in 3d frame mode on rafter raft being in the program You cannot see those values. Good work..."civil1979":1ctlfenx" said:Hi, I wanted to review the soil stresses from the reinforced concrete/continuous foundation menu after the analysis in the rafter raft foundation project I sent attached. However, the screen came up completely blank. When I select the combinations, the values do not appear. Only the minimum, average and maximum values appear. Another question is. I chose the raft floor thickness of 50 cm, I chose the coating load as 0.15 tons/m2 and the live load as 0.2 tons/m2. After the analysis, the raft floor loads changed. The G, Q values of each raft are different from each other, G 20 tons/m2 , Q and it changes around -4 tons /m2. I couldn't figure out the logic of this. I am waiting for your help.
The ground safety stress value obtained from the drilling made by the geological engineer considering the foundation depth in the foundation analysis. Can you expand on this sentence "Removing the ground load up to the bottom of the foundation means that half of your structure is covered"? Thank you, good work"onda":1ijz0e5t" said:Greetings.. Having a basement in your building is a very good advantage for you. I don't know if you have taken into account the ground characteristics at the lower level of your foundation, but removing the ground load up to the bottom of the foundation means that half of your building is covered. If your problem is simply exceeding the ground safety stress, I think you should look at the ground stress value at the bottom of the foundation and the net ground stress at that point, taking into account the weight of the lifted ground.
mhanifiata
New Member
In the foundation analysis, the soil safety stress value obtained from the drilling made by the geological engineer considering the foundation depth is used. Can you explain this sentence a little more, "Removing the ground load up to the bottom of the foundation means that half of your structure is covered"? Thank you, good work[/quote] I think that sentence is used to mean "the soil layer at the foundation depth normally carries the ground above it before excavation. Since this is removed after excavation, it is necessary to remove the load from that layer"
Greetings I tried to explain as the previous friend understood, but I think I misused the word half of the structure, I should have said part of the structure load there. In our conversations with geological engineers, it is necessary to evaluate the data on the layer where the foundation will sit, and I wanted to point out that the net ground stress should be calculated from the soil load removed as a result of excavation and the load difference we transferred at that level. Take it easy, I wish you good work.