Ayesha

Dear All,
Salam and Hope all are fine,
Very happy to see this platform because several time I tried myself to create such kind of Platform but due to Un avoidable Circumstance, I was not able to Create.
Several time I have asked from teachers and co related friends about Pakistan building Code.
I'm not sure whether it is being used or not or whether it is fully created or not ? can any one tell me regarding that, I will be thankful
2ndly I have a Question regarding Software which we use for Analysis such as Etab, there is no any option for our Country I want to ask ( Why, When, Where ???)????

Thank you for your reply.
The issue seems to come up randomly. I contacted the technical support and sent them my model via email but they were unable to reproduce the issue.
 
 

First of all my apologies, if my question seems stupid because of my unfamiliarity with the topic.
When defining response spectrum load case in ETABS, we have three directions; u1, u2 and u3.
Lets assume the excitation angle = 0 and building principle direction is u1
So I will apply response spectrum function (per IBC 2006) in u1 direction by a scale factor.
My question is why we don't apply u2 and u3 in the SAME LOAD CASE.
My understanding is, according to WILSON in his book on STATIC & DYNAMIC ANALYSIS, CHAPTER 15. The response is calculated for each direction separately. Then this response is combined by different methods (CQC, SRSS etc) which is called MODEL COMBINATION.
In CQC method response in 2 directions is assumed to be a portion of 1 direction means S2=a.S1
Where a = 0 to 1.0, recommended value is 0.50 to 0.85
I know in EQ building has only one principle direction. Although EQ can hit from any direction but there is always one major direction. or you can say major acceleration in 1 direction. Lets say u1.
As in CQC method the response in other direction will be some portion of response in major direction. I also know that If we have equal spectra CQC is reduced to SRSS method which is independent from the excitation angle theta.
My confusion is we will do MODAL COMBINATION (cqc or srss) only when we want to combine u1, u2 and u3 at the same time. But if we are applying only u1 in one response spectrum load case, then we DONT have to do modal combination. It is the same thing as in CQC S2=a. S1. Now in this case a=0. so S2=0. All we have is only response in u1 direction.
Then in my building models what i do? include u1 and u2 both in one load case or in separate load cases?

Just found an amazing website with lectures on Structural Dynamics and Earthquake Engineering in Pakistan.
https://structurespro.info

Thank you Umar

W.salaam,
My suggestion would be that you still use the minimum specified yield strength of 460 MPa, as you are testing limited number of bars out of of thousands of bars that will be used for the structure. Also, it is good to keep some contingency as there are a lot of assumptions and limitations involved.
Thanks.

Time period is still based on uncracked properties as that would result in a shorter period ; more stiffness; higher seismic load. There are multiple very rigorous discussion on the forum about time period. Below is one thread, you can search others.
 

If beams are fixed, you have moment connection. The frame has lateral rigidity. If beams are pinned, all the lateral load would need to go to a bracing system or shear walls.
Providing fixity increases stiffness and also allows you to use smaller sections to satisfy gravity deflection limits apart from lateral stuff.
 

Read chapter 10...Actually concrete cracks just after it reaches its tensile strength (about 7.5 to 10 or 12% of its compressive strength). before that the reinforcement is not taking action. So once concrete starts cracking...(when concrete cannot take tension) reinfrocement starts taking the tension. Now obviously when concrete cracks...we cannot analyze our section based on full inertia...so we have to reduce the stiffness, because its in reality. like this..
Now how we can reduce its properties? there are many methods...like the one given in chapter 10 of the code (ACI). like we reduce beam stiffness by 35% and column by 70% (uncracked) ... this is all relative.. I mean if you have only all the beams. even if you dont reduce stiffness it will be ok! but why we reduce stiffness is to redistribute internal forces from less stiff to more stiff areas like from beams (35%) to columns or walls (70% reduction).. So this way it ensures proper load path and distribution of loads based on stiffness

I think both ETABS and UBC 97 provisions are correct.
As ETABS completely follows UBC97 therefore only UBC's provisions are elaborated below.
UBC seismic design philosophy limits the minimum time period (in the form of maximum base shear ) to Ts (UBC response spectrum) which is equivalent to Cv/2.5Ca.
For elaboration ,
V=CV.I.W/R.T
Substitutue T=Ts=Cv/2.5Ca in above eqn
therefore 
V=(CV.I.W/R)X(2.5Ca/Cv)
i.e V=2.5Ca.I/w (the maximum base shear that ETABS and UBC97 uses)
Therefore time period regardless of its shorter value below Ta cannot be lesser than Ts which is in contrast with UBC97 provisions that are inherent in ETABS.
However, analysis indicating time period lesser than Ta indicates a over stiff/over design structure, therefore it is recommended to maintain a natural period closer to 0.1x (no of floors).
 
 
 
 

Part of the reason the forum went quiet as I found out recently was our Anti-Spam system. Almost all new users that registered on the website are now tagged for manual approval by Admins. Since that takes some time, therefore, the new users don’t get approved right away and by the time they get approved, the question for which they wanted to come to the forum is probably solved. We are looking into it. Apart from that, this forum focuses on a very small subset of Civil Engineering professionals - we also do admit that participation level is low as target audience is very limited and there are some challenges that we need to overcome. 
Thanks. 

There is one tutorial on CSI Wiki for SAP2000. You can see if the same feature is in ETABS. I can't check as I don't have ETABS copy with me.
https://wiki.csiamerica.com/display/tutorials/Radial+point+load
Please download the attachment, report.pdf and read it.
Thanks.
 

The project I am working on is kind of an assessment. It is my first time so I want to explore different options and alternatives to expand my engineering knowledge. I am very thankful to all of you for your guidance and deep insights. I am very happy to find you guys who can guide me regarding the problems faced by structural engineers in Pakistan. I hope to benefit from you guys in the future.
I am using ACI. Slab thickness is 6" and fc' is 3000psi.

These Type of problems and Deep technical Ambiguites should/must be shared  to get the Experience Str Engineers opinions . I appreciate you on highlighting this issue and Thanks to all the Engineers who responded to your post

Designing buildings via such forums can lead to engineering failures - its a dangerous thing.
This forum is for general advise, and then you as the engineer need to make the necessary engineering judgement based on your knowledge and experience.
However, as rules of thumb:
1. Which code are you designing the concrete to? American or European?  Follow the rules given in the code!!
2. Here is general advice, based on European Codes.
For say 30N/mm2 concrete strength, and straight ribbed bars:
ANCHORAGE:
Good concrete/rebar bond conditions, good quality control: 40 x bar diameter;
Poor concrete/rebar bond conditions, poor quality control: 60 x bar dai
 
LAPS: 30 N/mm2 conc
Bar laps, good bond, good conc quality control on site: 60 x bar dia
Bar laps, poor bond, poor quality control on site: 90 x bar dia
 
Below are defined "good" and "poor bond" conditions. If your slab is less than 250mm thick, then you have good bond condition, provided there is good concrete quality control regime on site. Quality is not something Pakistan construction sites are renowned for from my limited experience.

 
 
 
 
 

You can do the same for section B-B

This does not mean you need beam under the line load. The line load at the end will act as point load per unit width of your balcony. The line load at sides can be treated as line for that unit width of balcony. No  beams are needed,which means you will not have forces which need enlarged cross-section. Do your calculations; figure out bending moment and shear at critical section;  you will know.

Good points made by BAZ & Umar.
Just to add, there is more than one way to skin an animal, as they say – here is another approach to take.
The third option would be not to put in "releases" and to "detail" the beam appropriately for torsion - this means the longitudinal bars in the beam may increase in size, and the links (stirrups) are detailed as torsion links. Transferring “releases” from computer software to the steel fixer on site can be tricky. Concrete behaves as you detail it!
It is the combination of vertical shear and torsion that induce cracking and failure - unless the reinforcement (longitudinal & links/stirrups) are detailed to cater for it for it. In the beam there will be additional longitudinal reinforcement in the top, bottom AND SIDES to cater for any torsion.
The figures below may help you understand the "practical" on site concept of catering for torsion with properly detailed reinforcement.
1.     What is torsion:
 
2.     Below is a torsion "link" or "stirrup" shape – what it looks like:
 
 
Below is a torsional situation: In Pakistan always include a bar in bottom (shown red) of cantilever balcony ALSO, same shape as top bar, but bend up and around towards to top of beam/slab, to allow for load reversal during an earthquake!
 
 
When I built my house in Pakistan, the steel fixer managed to bent one bar thus for the balcony - the workers in Pakistan (where material is expensive and labour is cheap) are very talented, but do not have the technical know-how sadly..... that's the challenge for the likes of you the structural engineer to disseminate down!
 
 
Keep an eye on this forum. There is Pakistan RC Building Reinforcement Detailing Manual in preparation and will include this torsion detail now that it has come up here! This Manual be an advisory document but will assist both "young" structural engineers and reinforcement detailers (draftsmen) to understand reinforcement detailing and fixing!
Passing down knowledge – think of it as “zakat”, then it gets easier then to give and share!
 
 

Assalam O Alykum
I have seen the attached video on the CSI web for Etabs. Totally new for me its walk inside the structure.
I wish if design engineers can see it as well whenever they have free time. Its amazing.
Thank you
 
etabs_-_27_visualization_tools_0.mp4

Calculate your base shear.. delete everything from the model except for shear wall and apply the seismic load manually on the wall. That is one way to do it.

Normally, we run all load combinations and then in result summary see which load combo is governing and check that one.
 

You should select "Include special seismic" and in DL multiplier use the value of 0.2SDs. When you do that, your automatic load combos would always be correct and will have the vertical component of earthquake added. Do it, and check manually. Code requires you to apply earthquake loads at a eccentricity of plus minus 5%. When you define a load case, say Eqx it is defined in X direction. you need to select EQX + ECCEN Y(5%y) instead of EQx only(see above image). Similarly, define a new load case in EQX -ECCENY(5%y) to satisfy that code provision. Repeat same for other direction.
Its great to see more female engineers joining the forum. Zoya do tell your other friends too who are in the same field and lets make this place more active and more productive.

The seismic data for IBC for major cities of Pakistan is provided in this thread that I posted above. 

Calculate your base shear.. delete everything from the model except for shear wall and apply the seismic load manually on the wall. That is one way to do it.

1) Self Study.
2) Ability to visualize what is on a 2-D Drawing.