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In addition to what Makhzumi has said, I would like to add that:- 1) I am not sure if you have to apply soil properties to all of the mat layers, but what I would prefer is to draw drop panels (thick portions of the raft) and then draw the rest of raft (no overlapping). Then as your senior told you to draw thick slabs (stiff property) fro drawing columns over column points in SAFE. But remember do not apply soil properties to these stiff elements. Make thickness of these elements as 1m. 2) You will get concentration of soil pressure and moments near supports (near columns). But do not go for the maximum peak pressure or moments. For bearing pressure, take the contour value just at the face of the column (stiff elements you just have drawn in step 1). Do not read contour values at the edges of elements rather look for the value in the center. 3) For moments and reinforcement design, design for 1m wide strip and average the moments for 1m width. You can do this by applying design strips in SAFE in x and y direction of width = 0.5m and then replicating them every 1m to cover all of your raft. Then after running the analysis you can put in the numbers of bars or dia of bars and the intended spacing of bars to check what reinforcement you require. Do let us know if you find more problems.

I am designing a 2B+G+24 story building. I made the model in Etabs, and ran it, then exported the base reaction to safe for footing design. It has central core walls. When I ran safe (v8), the only version available with the office. It gave me a bearing pressure of about 14 ksf as opposed to allowable of 6 ksf, I increased the thickness from 4 ft to 9 ft gradually but pressure distribution remained same & value only deceased to around 11 ksf. Then I added foundation beams (tied up all columns provided them under all core walls) and assigned line support to them (Kv x width of beam). This run gave me a value of 5.6 ksf bearing pressure which is safe. But I have some questions. I calculated the total area required from total load of the building and its coming out almost equal to the building plot area available. For, punching requirement under single column I at least require a 5.5 ft deep raft thickness. 1. Can I model a raft like this with beams (12" x 72") under all columns (42" x 42") & (36x72") under core walls (24" thick); not inverted beams but beams with top flushed with raft top 3. when we define slab properties do I have to tick the " thick plate" option or not. What is the difference? 4. What is difference between slab types options? slab? footing? mat? 2. Do the slab elements between these beams will have a soil support also assigned to them? 3. Is this type of foundation safe for this high building? or do we have to go for piles or pile/raft interaction? Which would you recommend considering that top of raft is at -19 ft & ground water table is at -11 ft. 4. How to I assign wall supports in safe v8. By placing beams of above property on my raft slab & assigning a wall/line support to them (Kv x width of beam) or Assigning null property to beams and use safe v8 option in which it calculate support stiffness from its size. Kv is the vertical sub-grade modulus. 5. How do we detail thick rafts. Do we provide mid layer of steel. if so can somebody point a reference book or source on how to calculate it. Confused

It is bridge on Lehtrar road; structural configuration of bridge consists of multiple simple spans supported on masonry piers. The bridge has failed, and it cannot be used for traffic. But, there is no sign/warning board on the road which warns people. People ride bikes on this one, and there is no mechanism to stop accidental usage of this bridge by heavily loaded vehicles, especially at night. It is a classic case of "bearing failure". Settlement might also be a contributing factor. .

i got a paper which has somehow explained the shear capacity of circular concrete section http://www.scielo.br/scielo.php?pid=S1983-41952012000600004&script=sci_arttext

W.s Bayan, you should always model node to node. If you don't put beam end on the center of column and that distance is greater than merge tolerence for joints, you will have no load transfer. For cases where beams are placed eccentric to column locations, you can use cardinal points to account for the offset/ eccentricity.

I will try to answer some of your questions: Make sure that when you model your shear/ core wall in ETABS, you have meshed it well, so that the wall has enough well distributed support along the length. Further reading.. 1. Can I model a raft like this with beams (12" x 72") under all columns (42" x 42") & (36x72") under core walls (24" thick); not inverted beams but beams with top flushed with raft top Yes, you can; raft is an inverted slab! 2. Do the slab elements between these beams will have a soil support also assigned to them? Yes they would. Assign them. Further reading... 3. when we define slab properties do I have to tick the " thick plate" option or not. What is the difference? Generically, thick Plate should account for shear deformations in your raft/ mat; Increase your moment and shear. I would suggest you to look into SAFE manual to see the exact difference. If in doubt, keep it checked. 4. What is difference between slab types options? slab? footing? mat? Is your question from a software point of view or general? 4. How to I assign wall supports in safe v8. By placing beams of above property on my raft slab & assigning a wall/line support to them (Kv x width of beam) or Assigning null property to beams and use safe v8 option in which it calculate support stiffness from its size. Kv is the vertical sub-grade modulus. I wouldn't bother assigning any supports to beams. Would just assign area springs to slabs and run it. 5. How do we detail thick rafts. Do we provide mid layer of steel. if so can somebody point a reference book or source on how to calculate it. There is no hard and fast rule and things depend on how thick your mat is. Mid layer can be provided for very thick mats. I have also provided say #5 @ 12" c/c if the mat is very deep for shrinkage control. Make sure you provide skin reinforcement on the sides of the mat and horizontal perimeter bars around it. You will always get areas of high stress under high loads. You can neglect some of the high concentrations by judgement. Also, your mesh size will effect your results and avg stress values. Good Luck!