UmarMakhzumi

Please see this: 

Thanks.

The only way I can think of is very tedious. Model shell elements in layers and introduce compression only links between them. What are you trying to do here- just curious !

Thanks.

Hani,

The embedment looks shallow for such case as it takes a lot of structure movement to mobilize “passive soil resistance”. Your pole might have tilted by then - a serviceability failure.
 

I mean look at nature, the taller the tree, the deeper the roots. Same goes for mountains. Generally it is said that the height the mountain extends above ground, the same footprint is present inside the ground too. For such case, you are better off to provide pile(s) under poles.
 

Shallow embedment is also tricky as top soil layer can be subjected to frost, adfreeze, erosion, soil run off etc. I would provide a pile and design accordingly. How tall are the poles for which you are providing this solution?

Thanks.

15 hours ago, sardarali said:

I have a problem I have a slab with two portion and they are not with global as in image bellow  how i can get the the direction of rebar

Please read the discussion above as it answers your question.

Thanks.

Normally analysis for such cases is better suited considering Abaqus or other FEA softwares that can allow you to model the interface between CFRP and existing material. Frame analysis can be done by defining custom properties for locations where such reinforcement is used and then you can use the forces at that location to analyze the location in Abaqus or any other FEA software for limit state that you are interested in.

21 hours ago, Zeeshan Ahmad said:

i need guidance in modelling overhead water tank in etabs. For Top Slab, the spans are 30'x30'. Should i provide beams to support the slab.

Yes, beams are always a good idea as  adding beams would make slab design light and help you manage and design for crack control reinforcement requirements.

21 hours ago, Zeeshan Ahmad said:

Further, normally we dont see columns extending to the top and terminates at the verge of shear wall. should i extend the columns beyond the last level and extend it in the water tank walls to support the beams.

Your columns are like boundary elements so you should extend them. Regularity, redundancy & Symmetry should be provided by default for all layouts.

21 hours ago, Zeeshan Ahmad said:

Further, if beams are necessary they will cross each other in the middle but will be without any support due to water tank.

This is okay. However, since your layout is square so important to detail beams rebar as continuous.

21 hours ago, Zeeshan Ahmad said:

lastly, what should be the preferred foundation type. also detailing of RCC wall

Depends on your Geotech Report & Engineer. What is the recommendation by the Geotech? Just check your strength and serviceability limit states (settlement etc) for foundation and go with the one that can meet the demand. Detailing for RCC walls, you can look up either a detailing manual or contact people in the forum if they would like to share go bys with you.

Thanks.

Zeeshan,

Thank you for posting this question. For wall design and understanding ETABS output, there are excellent videos made by CSI that can serve as the starting point. I would suggest watching Tutorial Video 08, 09 & 18 for ETABS Watch and Learn Series. The link is provided below.

https://www.csiamerica.com/products/etabs/watch-and-learn

Moreover, this topic has been discussed in very detail in the forum. You can search the forum. I am just posting a few references that you will find useful.

Shear Wall Results -

https://www.sepakistan.com/topic/2303-shear-wall-design/

https://www.sepakistan.com/topic/2226-pier-forces-and-story-forces/

Boundary Elements -

https://www.sepakistan.com/topic/2420-modelling-of-boundary-elements-incorporated-walls/

Thank you.

Abraham,

Thank you for your question. Would it be possible to provide a more specific question as I believe a lot of contributors on this forum are working engineer and they might not have the time to figure out and what to look for in your model.

Thanks.

Intuitive,

The results you are getting are correct and "evening out" is expected. Generally the following approach is used for piled raft foundation analysis and design using a software.

1) To get pile reactions for pile design, use pinned support or a very high vertical spring stiffness. This will give you higher pile reactions and the case is conservative for pile design.

2) For designing the mat/ raft foundation, use softer springs at that would give you a higher reinforcement in the raft/slab. Conservative case for flexural, but not for shear. Though you can do additional runs for shear using stiffer spring.

On a recent project, I was reviewing a calculation with similar situation and I asked the engineer to calculate the range of springs (Stiff, soft) based on variability in soil properties and settlement of pile group and we used the springs as explained above.

Thank you.

Tufail,

Thank you for the feedback. Since we are just a website and the website is mobile friendly so app development has been put to rest. If you have other ideas, please do post. We always love to hear from our members.

Thank you! 

Sushan,

Corner frames are considered mostly. You can spot check the interior ones. Unless you have flexible diaphragm, the corner frames should also give you the max displacements.

Thank you.

On 12/14/2020 at 10:02 PM, ANStructs said:

In the computer model, if a designer has assumed that the stairs do not provide any lateral stiffness, then it is the responsibility of the designer to detail the connection such that it reflects the behavior of assumed connection in the model.

Thank you for this. Yes, the comment goes both ways!

I think in Pakistan as long as your formwork is multiple of 3", the contractor should be able to do it.

You should put on drawing what you need based on analysis and it is always a good idea to keep some margin.

Thanks.

Usman,

You can look up papers or articles published using shaking table data and contact the authors to request the same data.

That would be one way. I think University of Peshawar has a shaking table or something similar. Reach out to them. Some of the forum members are Peshawar and you can contact them as well.

Good share. Looks like a concrete breakout failure.

Thanks.

Tufail,

I am not sure if ETABS does it but back in the day, SAFE would be the go to program for Slab design. Both programs are integrated so you can import and export from one software to another.

You can check SAFE to see if it allows you to design hollow slabs. I think SAFE does design Waffle Slabs so hollow might be a possibility. Anyway, as an alternative, you can use rigid diaphragm in your analysis and design the slab manually. That option is always available. 

Thanks.

Saugat,

Static base shear is based on first mode so it is kind of conservative.

Thanks,

Tufail,

Can you also please attach the design output summary for any beam/ column where reinfo is shown as zero?

Thank you.

Saugat,

I am not familiar with (I*g)/2R term. It might be correct but I haven't come across it. There is a tutorial on the forum that you can follow for scaling static loads. Please see the link to the thread below.

Thanks.

Ayman,

You will need to see the mass participation per mode and then make sure you have enough modes (sum up the mass participation for each mode) to meet your building code requirement (90% or something varies from Code to Code).  If you didn't have enough modes when you sum up the modal mass participation per mode, then you need to increase the number of modes thill you sum hits the magical number as specified in the code. The table above is showing displacements per mode is different than what you should be looking at.

Thanks.

A structural model should be representative of the stiffness, mass and damping characteristics of the structure. For static analysis, stiffness and mass should be accurately modelled. This is the fundamental. Based on this:

1) No. Modelled together.

2) Should be modelled. This has been discussed in the forum to death. Search backstay effect.

3) Pro is accuracy. Cons are hard to quantify as you don't know what you don't know.

Thanks.

SAL9000,

There are different opinions on it.

One opinion is that Stair cases should be modelled as they can alter the response of your structure. Seismic Design of Reinforced Concrete and Masonry Buildings sheds some light on it. You can model them by inclined shells. If you model staircases, then you have to detail them for the force they attract. Very important.

Other opinion is that they shouldn't be modelled as they are not detailed to take the seismic force. The normal practice in Pakistan is not to model them. 

If you ask my personal opinion, I would suggest modelling them.

Thank you.

Waqar,

One thing that comes to my mind is that if there is a possibility to have another building being constructed adjacent to yours. By adjacent I mean side by side. The can probably result in some excessive settlement down the road. Just a thought.

Thanks.

On 11/16/2020 at 10:41 PM, Simple Structures said:

It is common for geotechnical engineers to allow 20% overstress on bearing pressure due to transient (non-permanent) loading, i.e wind.

Excellent reply here. Just to add that this is allowed in some code and not allowed in others for Transient Loading (temporary like Seismic and Wind). Not sure what is the basis for Waqar's design but he can confirm and check with geotech if he can use the extra 20 or 30 percent.

Thanks.

12 hours ago, waqar saleem said:

Salam,

I have a raft modeled in Safe based on Etabs, edges show too high stresses and soil pressure, i have reasonable offset from the column grids. How i could resolve this issue.

Thank you in Advance.

Waqar,

You can change your column framing by adding more columns so load on edge columns is smaller than what you have now. Also review your load input and sharpen the pencil to see if there is any conservatism in the loads and take them out.

Thanks.