UmarMakhzumi

I am glad that you have set up everything and results are with you. I am not sure if your Time History load case is correct since I don't use periodic Time History function. Also, your modal damping looks high. Anyways, you have completed your analysis. Good. Now do your resonance runs and you are done.

Sir, are you doing a modal analysis? If you make your structure stiffer the seismic force would increase in that case. As smaller the T, the bigger the force Also, do you get a constant distribution of base shear when for stories below ground when you specify your lowest level in ETABS load case to be ground? Thanks.

In base shear calculations hight of the structure is what is above ground, also called Tn. Sir, what if you try the same model with your base supports at ground level and all basement levels deleted. Do you get the same distribution ? Thanks.

Suarez, I have gone through all your attachments. Here are a few things that you should consider: Time History Function & Load Case: You have applied the loads but you have to associate your loads with some function that would make it a dynamic load. The loads that vendor provided are normally called machine unbalanced forces and they are function of machine speed. What you do is set-up a time history load case and specify load patterns which contain your dynamic load along with sine and cosine functions and link them to your TH load case. Read through tutorial to understand how to define a TH Load Case for machine operating. See attached Image from CSI Example . COM Location: I'm assuming that LOAD POINTS provided by vendor are aforementioned CoM-locations. In that case, I have applied static & dynamic loads at these locations and have run TIME-HISTORY FUNCTION, which yielded into results posted earlier You should not assume and ask vendor to provide you the COM locations. COM locations are always higher than the supporting structure. Image that you provided above (TTF-zip-file ) there are no joints defined above the top platform, so I cann't say that you are applying your loads at the correct locations. See attached Image from CSI Example. Results: The results posted by you do not mean anything. You have posted 5634 lines of output. Before you proceed, ask your vendor, what is the location where the amplitude needs to be satisfied. Is it the COM locations? Is it the Top of Concrete Table Top? and then check your maximum vibration at that level. Tutorial shows you how to check amplitudes too.See attached image. What is stopping you to complete your calc correctly? The machines your are designing the concrete table top foundation operate at 2 different speeds. You need output for both machines independent at the points of interest and then you need to superimpose that output. Let it be displacement or velocity. Another reason why you need to do that is your pile impedance for both operating speeds is different.First you establish that at the machine speed your vibrations are less than 30 microns, then you proceed to check your resonance runs (for all modes between 0.8 to 1.2 * Operating Speed). Going Forward: You have to realize that you have a complete example with you, and if you go through all my replies, I have provided you with all general and some specific information that you would need to complete the analysis. You have to take your time and understand things that you are trying to design. I can't review or vet models because of my work load, but I can tell you what to do. I can't check anything.

In a no diaphragm scenario, your walls are independent, something we don't want in seismic design, and the purlins may be subjected to some force if they have a fixed connection with wall. The force would come from the out of plane bending and in-plane movement of wall. But the limit state that would govern would be wall failure rather than purlin, so I wont worry about the purlins but care more about providing a diaphragm and ensuring that load path to foundation is satisfactory. Wall stability is critical here. You could ensure better wall performance by providing continuous plinth band, sill band, lintel band and tie beam on top of wall. Thanks.

You need to do base shear calculation. From Load Bearing I would assume Masonry Walls. All you need is a sample calculation that could show you how to distribute the load to walls based on their stiffness. What is the roof made of? Is it a single story house with wood/ steel purlins and metal sheeting on top? For purlin design, if your purlins are acting as a diaphragm, then you need to consider it. But I doubt if that would be the case. I did a project for Azad Kashmir, where an old hospital was retrofitted for seismic loads and had a typical Truss with metal sheeting on top. The final recommendation in that case was to provide a diaphragm made up of C Channels, since the slopped trusses failed to act as one. Please share the details of what roof is made of and how purlins support the roof. Thanks.

Okay, lets go step by step. What are the points where you are checking the max vibrations? CGs? Provide a table where you report maximum vibrations due to load case at cg locations only and also what machine caused these vibrations? Also, what are your maximum limits in microns? Thanks.

I am not clear about the question Sir!

I would design the basement and below for over strength for seismic forces. Thanks.

Your spreadsheet is showing acceleration. You need to look at either velocity or displacement. Have a look at the tutorial I posted the link to. It explains how you can check specific nodes for vibration limit. Once you do that, then you could run resonance runs and find your final amplitudes. Thanks.

Before going in modes, did you check what your maximum vibration is due to both machines operating?

CSI has made an example which may help you understand how to apply loads and analyse rotatory equipment. Its attached with the post. Thanks. Vibrating machinery steel skid on piles.pdf

I would like to see the definition of your Time History Function? Explain to me how are you applying your loads in SAP2000 for the given frequency of operation and that would contain answer to Moreover, attach snapshots of your SAP200 file so that I can see if you are modelling it correctly. Thanks.

12 Modes are very few and I believe is the default number in settings. You should run your modal analysis for at least 300 modes or 95% of Static Dead. Check your magnitudes for cases of Turbine Operating and Generator Operating and superimpose them to see if the total doesn't exceed vendor limit at points specified by vendor. Since your operating frequencies are different for both turbine and generator, you should have two files for each case operating with pile impedances referring to the speed of forcing function. Regarding Modal Analysis, You have to see two bandwidths. First one is from 0.8-1.2 of your Generator Operating Speed; which would be 20 Hz to 30Hz and the second bandwidth will be from 0.8-1.2 of Turbine Operating Speed. For each case, note all the modes that fall into the bandwidth. Then run Modal Time History Function by equating your forcing function to the frequency of the mode(that's how you check resonance). Superimpose the results for each operating case and if they are below the vendor allowable limit at the points vendor has specified. you are good. Thanks.

Depends upon what kind of analysis you are doing and what parameters are you looking for, e.g. If you are checking pump vibrations on a steel skid, it doesnt matter what your modal mass participation is and what your primary modes are. All you care is what modes fall closer to the forcing function that would resonate the pump.

You need DYNA5 to get pile impedance(stiffness + damping) values. DYNA5 would calculate these values for your pile group considering group effects. You should convert the group values to single pile, and use them in SAP2000 as a One Node/Joint link and do the Modal Time History Analysis. Find your critical modes and check structure for resonance. If your amplitudes are lower than vendor allowable, you are good. Tell you company to buy DYNA5.

Use the vendor provided unbalanced load and perform a Modal Time History Analysis in SAP2000 to see what your vibrations are.

You need to calculate the unbalance load and apply that as a dynamic force based on the speed of machine. What kind of company you work for and what software are you using ? Thanks.

Generally that is correct. However, Torque is considered as a static load too and is reported with other static loads.

I havent tried it but I guess Etabs wont do any calcs related to seismic distribution. Also, center of mass and rigitity calculations are purley based on diaphragm assignment.

Concrete is poor in tension and effectively in a RCC brace, all tension would be taken by re-bars. However, concrete bracing can be designed, but hard to pour, construct and place and may not be feasible where tension forces are huge. Regarding ETABS comment, you can take ETABS forces and design it manually. Method of Strain Compatibility would be of choice is such a case. MacGregor has an example on that.

I personally don't agree to what your senior in office told you. Here are some things that you should consider:1) You should challenge your results because area for pressure distribution remains same as before. Ask yourself that why did your results improve? 2) (update later) 3) Lean concrete has no structural use and shouldn't be modelled in SAFE v8. If your slab/ raft/ mat was 8" inch, I would accept a 6" concrete layer for pressure distribution but considering the thickness of lean concrete layer to be <<< than that of mat, I wouldn't consider it. 4) Please watch CSI WATCH and LEARN Series for SAFE v8 to see how to model drop panels in SAFE. 5) Do consider cracked section properties for your mat/ raft foundation flexural and shear design. It would be 0.25*I 6) Plot your moment contours for all load combinations. Select a reinforcement in slab and check your section capacity for maximum moment. Visually compare the contours with the max capacity that you calculated manually. That would allow you to assess if your foundation capacity is meeting the demand. For general information, when you increase your foundation thickness, your pressure distribution contour peak drops, and the reason is that you raft/ mat becomes more rigid and load distribution becomes more even. Thanks.

There are options that allow you to specify cardinal points (I don;t remember exactly) but I think that was what it was called. Look them up.

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!

I believe that by steel you mean rebar. If you generate your drawings through a software, mostly a material take off option is there that reports that information. You can also set up an excel sheet to do the job for you.