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The first thing you need to check is if you have done a modelling mistake or not. ETABS and Manual results shouldn't be off by more than 2%. Here are a few items that you should check and then get back to us.
1. Check Total Gravity Load
The easiest way to do it is that to check vertical reaction (gravity only) at a column. If the manual and ETABS column reactions for gravity load are same at different locations in your model, then you can assume that your loading input is correct. As a rule of thumb, you centre columns with biggest tributary areas should have higher reaction than corner and edge column assuming constant grid framing.
2. Check Load Combinations
The next step is to check the load combination and that if the loads have been correctly assigned to each load category. The best way to do that is to print your load combinations and check them on paper. Similarly, load cases assignments can be checked as well. Pay attention to signs of +ve and -ve.
3. Check Units
When checking assigned load cases, you need to make your that you have applied the loads in the correct units. It is very common to juggle the units while multi-tasking. Verify all units.
4. Check Material Properties
I have checked a lot of models where everything was correct except for material properties. Sometimes, the design engineer enters wrong unit weight and it messes all the reactions and design. Be sure to verify material properties.
5. Check Stiffness Modifiers
If you are assigning stiffness modifiers, please check them to ensure they are correct.
6. Check Slab Thickness
Make sure your slab thickness is correct and not in wrong units.
7. Check member sizes
Make sure that the members are correctly modelled.
8. Check Model for Errors
You need to make sure that your model is stable. If your model is unstable your results would mean nothing. I don't know what the latest version of ETABS does in-terms of instability warnings but SAP2000 would never give you instability warning. You will have to go in the analysis log and check if the model is stable or unstable. A lot of junior engineer just get their results from unstable models which is dangerous. Check the analysis log and check model for all error including meshing.
After you have completed all these steps, you will have more confidence in stating the discrepancy between ETABS and Manual Calcs.
What is the angle of the backfill with the horizontal? After I know that I might be in a better position to comment in detail but as a matter of general approach, since backfill pressure on the wall is applied considering soil as a fluid (Gamma*H), the lateral load due to backfill should stay the same as your maximum height stays the same. This is my opinion and if someone else had a different one, I would love to hear that as well. The image below explains the same thing.
Also what is the utilization of this wall. I mean why are you making it. What land use would be for the area on the non-backfilled face of the wall?
You have mentioned that the wall is 30 feet high. Is the backfill slope lowest point 30 feet as well or it goes much further below? Depending on that, there might be an alternate sliding plane.
In manual calculation we do 2D analysis of structures using different method of analysis than stiffness method. So somewhat difference will always be there while you compare results of manual vs Etabs in Systems.. For individual elements, they are 100% same.... More over, be sure to make modifiers of slab to 0.0001 to nullify slab stiffness because in manual analysis, might be u are assuming only rectangular beam and applying line load to this beam. but in etabs you are modeling slab with beam making system a bit stiffer due to slab stiffness. If you will reduce slab stiffness to negligible value, than results will be near to each other. Still there will be some difference because we might be using force methods idealizing 2D structure while etabs performs 3D analysis using direct stiffness method.
As per discussion with my senior in office, we have concluded that since soil slope angle is already lesser than angle of repose of soil, so soil will not slide to that slope. Wedge of soil will be exerting pressure on wall because at wall we are forcing soil to stand at larger angle than its angle of repose. So i was wrong than we should take lesser backfil load than total height. We should take ful height or at least the height of soil which cantilever heal is bearing.... This is what we think.. If we concluded wrong, kindly correct. thanks.
Having more than one email addresses is normally not a good idea, in that you need more time to in order to check all the email accounts regularly. However, with the option of using the forum email as forwarding email only, it is really a good idea especially with reference to promotion of the forum.
IMHO, all those eligible, must get the forum email addresses and start using it more than their other email addresses, so that more and more people get familiar with the forum.
Assalam o alaikum,
If a retaining wall is retaining horizontal backfill, It will experience soil presure due to full height of backfill because we are forcing soil to retain at an angle larger than its angle of repose and hence failure wedge will cause force on full height.
But if a retaining wall is retaining backfill having sloppy face( for insulation purposes lets say), then it should not experience the pressure due to full height in my opinion. Because soil is having slope on opposite side, (away from wall) and hence if a failure plan would occur, it will cause soil to slide away from wall, not towards wall. This is what i think. Pictures are also attached. In my case the wall height is 30 ft but it is retaining a backfill with slope. So i wonder if i should take load due to full 30ft height. I think i can take 25 ft height(or some other reduced value). Can any one guide me how to calculate backfill load due to such type of backfill? Thanks.
I was browsing through my archives are noticed a bunch of articles written by NICEE (National Information Centre of Earthquake Engineering (NICEE) was established in IIT Kanpur with the mandate to empower all stakeholders in the building industry in seismic safety towards ensuring an earthquake resistant built environment. NICEE maintains and disseminates information resources on Earthquake Engineering. It undertakes community outreach activities aimed at mitigation of earthquake disasters. NICEE’s target audience includes professionals, academics and all others with an interest in and concern for seismic safety).
The articles are free to publish as long as original content stays unchanged. These articles are good for fresh structural engineers and Civil/ Structural Engineering Students. The best thing about them is that they are only 2 pages and full of images. It literally takes less than 5 min to go through each.
How architectural features effect buildings.pdf
How buildings twist during earthquakes.pdf
How do Beam-Column Joints in RC Buildings Resist Earthquakes.pdf
How do Brick Masonry behave during Earthquake.pdf
How do Columns in RC Buildings Resist Earthquakes.pdf
How do Earthquake Affect Reinforced Concrete Buildings.pdf
How Flexibility of Buildings affect their earthquake response.pdf
How the ground shakes.pdf
How to make building ductile for Good Seismic Performace.pdf
How to make Stone Masonry Buildings Earthquake Resistant.pdf
How to Reduce Earthquake Effects on Buildings.pdf
What are magnitudes and intensity.pdf
What are seismic effects on structures.pdf
What causes earthquake.pdf
What is seismic design philosophy of Buildings.pdf
Why are Buildings with Shear Walls Preferred in Seismic Regions.pdf
Why are horizontal bands necessary in masonry buildings.pdf
Why are Open Ground Storey Buildings Vulnerable in Earthquakes.pdf
Why are Short Columns more Damaged During Earthquake.pdf
Why is vertical reinforcement required in masonry buildings.pdf
Why should Masonry Buildings have simple Structural Configuration.pdf