Few Questions. Please Need Urgent Help.

[Jigger]

Here are a number of questions that I need answered. Help would be appreciated.

Q1. In ETABS, what if the beam combined fail in Shear and Torsion? Need Solution

Q2. In ETABS, Obtained moments on both ends on simple supported beams. What to do?

Q3. Discuss dependance of foundation on bearing capacity of soil in SAFE model? What options do you have if the Bearing Capacity is very low?

How would you check and find one way and two way shear in SAFE model?

Q4. Why mass and weight are considered separate in ETABS?

Q5. Differentiate b/w P-Delta analysis vs Dynamic Analysis?

Q6. Material properties and strength of Concrete depend on what parameters?

Q7. What limit "1" in punching shows in SAFE?

Even if you know just one answer, please reply. It would be very helpful.

Thank you and Regards.

[EngrUzair]

Aoa.

 

IMHO, following are the answers to your questions:

 

A/Q1: You may need to adopt one or more of the following actions:

          a. increase beam size,

          b. reduce ties spacing,

          c. increase diameter of ties,

          d. use higher yield strength steel for ties

 

A/Q2: You might have used Fixed support on both sides. Try using Hinged support on one side and Pinned support on the other.

 

A/Q3: Required foundation size (area) INCREASES with REDUCTION in soil bearing capacity.

 

          For very low bearing capacity, you might have to go for raft footing or piles.

 

          In SAFE version 8, you may check two-way shear by using 'Design -> Display punching Shear Ratios' Menu option.

 

A/Q4: Mass is used in dynamic analysis and calculated using formula, m = w / g ; where m is mass, w is weight and g is acceleration due to gravity.

 

A/Q5: 'P-Delta Analysis' is carried out to account for length effects in columns (buckling). On the other hand, 'Dynamic Analysis' is carried out to study the effects of time-varying forces (earthquake etc) on the structure.

 

A/Q6: Concrete compressive strength (f'c) is important for calculating various material properties. On the other hand,  strength of concrete depend upon several parameters, like ratio of cement, sand and aggregate; water-cement ratio, age on testing, strength of aggregate, curing method, etc. etc.

 

A/Q7. In SAFE, punching shear results are displayed as a ratio of maximum calculated shear with respect to capacity. A ratio of 1.0 indicates that maximum calculated shear is equal to the maximum capacity of the section.

 

Hope this is helpful.

[Jigger]

Thanks alot Uzair bhai. Keep the helpful posts coming.

 

Q.1 . Don't you think increasing bar size would also help?

[EngrUzair]

Aoa.

 

You may try it. It may help too, but probably not much. To confirm, try various options one by one and observe their effect on overall behaviour of the member, by comparing with previous results. You will yourself understand what difference each option has made, and to what extent.

[Jigger]

Another question,

 

Whats the provision of ACI-318 for Storey drift and Cracking limit?

 

On calculating slab thickness, does room size matter?

 

Whats the difference b/w Working Load and Service Load? (I know the answer but just want to confirm)

 

Thickness of Slab must be greater than?

 

Coefficient of Section modulus in beam is _________ & column is _________

[Jigger]

Differentiate b/w reference plane and reference line in etabs?

Explain importance of self wt. Multiplier in defining static load cases in etabs?

How to check if ALL the loads have been transferred from etabs to safe?

[WR1]

What is the course name for which you are taking the exam...btw?

[Jigger]

What is the course name for which you are taking the exam...btw?

Computer aided drawing... Where the the answers??

[WR1]

 Q1. In ETABS, what if the beam combined fail in Shear and Torsion? 

If beams fails in shear and torsion combined, you should increase the concrete section. Engr Uzair, ties will not help because the combined stresses are more than 8xf'c^0.5 (imperial units). You need to increase concrete section size.

 

 

 Q2. In ETABS, Obtained moments on both ends on simple supported beams. What to do? 

Will update later. This happen sometimes.

 

Q3. Discuss dependance of foundation on bearing capacity of soil in SAFE model? What options do you have if the Bearing Capacity is very low? How would you check and find one way and two way shear in SAFE model? 

Dependence of foundation on bearing capacity of soil? I did not get it. But in SAFE there is no bearing capacity. You have to put modulus of sub grade reaction (you can relate bearing capacity with k as k=120 times the bearing capacity in SI units). See Bowels book or use k from geotechincal report.

 

Two way shear or punching shear can be checked in SAFE from the menu: Design>Punching check

 

One way shear can be checked by showing contours of V13 and V23. V = SRSS of both these components. And phi Vc = 2xf'c^0.5x0.75 in Imperial units or 0.17xf'c^0.5x0.75 in SI units

 

Q4. Why mass and weight are considered separate in ETABS?

 

Mass is used in dynamic and seismic analysis. You should study about excitation of mass and lumped mass from any book on dynamics. 

 

Weight is the normal weight of materials acting as loads on the structure. For example dead, live etc. W=mg as Engr Uzair said.

 

Q5. Differentiate b/w P-Delta analysis vs Dynamic Analysis? 

 

Excessive gravity load buckles the building or column sideways by delta. This delta creates additional moments M=P (gravity) x delta. Thats why this moment is called P-delta moments. If you have not designed for this additional moment, your structural gonna collapse. Ofcourse this happens in very slender columns or building or very heavily loaded columns. Weight or load is involved in calculations.

 

In dynamic analysis (usually done for irregular buildings) you try to capture higher modes. This is done by lumping mass at story levels. There are SDOF (single degree of freedom) and MDOF systems. Read from any book on dynamic analysis. Mass is involved here.

 

 

 

Q6. Material properties and strength of Concrete depend on what parameters?

 

 

Strength of concrete depends on proper curing and mix ratio of ingredients. 

 

 

 Q7. What limit "1" in punching shows in SAFE?

 

 

Punching ratio=1 means, Shear stress is exactly equal to the shear capacity of concrete section.

 

Shear capacity of concrete for punching is calculated from 3 formulas given in code. The least value is used. Open any book on concrete and see punching shear topic.

 

Whats the provision of ACI-318 for Storey drift and Cracking limit?

 

 

In ACI-318;

 

There is no storey drift limitations. However, you can find these limits in ASCE/IBC. Its the same thing.

 

Cracking limit in ACI can be found in chapter 9 (i think) or chapter 10. For water tight structures you need to refer to ACI 350. For detailed cracking limits you need to refer to ACI 224-06. Beaware that ACI 224-06 and 224-01 or 02 and ACI-95 differ in methods 

[WR1]

 

 

On calculating slab thickness, does room size matter?

 

 

Ofcourse,

 

see ACI chapter 9 for calculating minimum thickness of two way slabs and one way slabs. It is Ln/36 etc. Where Ln is the span.

 

Whats the difference b/w Working Load and Service Load? (I know the answer but just want to confirm)

 

 

Working load is the load, a structure can carry safely without failing.

 

Service load corresponds to the serviceability limit state. The load at which a structure or a building or an equipment continues to function properly. For example for your home, ultimate load could be very high which your house could sustain, but some percentage of this load might cause one of the doors in your home to stop working. So the serviceability is disturbed. Load less than that was the serviceability limit state of that door.

 

Thickness of Slab must be greater than?

 

 

I did not get it.

 

There are many things to relate

 

Thickness of slab must be greater than s/2 where s is the main reinforcement spacing in two way slabs or s/3 in one way slabs

 

you can also relate it to the beam stiffness

 

Coefficient of Section modulus in beam is _________ & column is _________

 

Section modulus of beams and columns?

 

Section modulus if a shape property. Check your question again

[Jigger]

Thanks alot for the answers sir. Deeply grateful to both of you.

[Juli]

Hi ,Do you have any Pdf/Link/Video where can I find out every details on Etabs 2013 modeling, I mean not just manual or just example of their premade structures as I already have them. I am searching for those where I will be able to know each function such as details in Define tab( each on when and why will I use pier/ sprandel/functions/modal case/ Pdelta etc ; In assign tab,when to assign what in which cases -I mean when pier, when sprandrel, when modifiers,automesh and manually etc like this. So all I am asking for each details in a pdf or file where there will be a brief explanation on the each functions and each parameters? That would be a great help !!   

full.EDB

[EngrUzair]

Juli!

 

You have come up with a very good question. However, IMHO, you might not be able get reference to a single document to answer your question.

 

The reason is that software design manuals are normally prepared to provide information on 'How to..' use various software commands (through various menu items, or command tabs), for the design of structural elements covered. Whereas, the analysis manuals cover the analytical theory on which the software is based.

 

On the other hand, the example manuals provide methodology for using the software to perform some typical and common type of design tasks, highlighting salient features of the software and locations of ('where to find...') various commands used for the purpose.

 

Unfortunately, however, these manuals DO NOT provide information on specifically 'When to..' use various commands or options.

 

You will therefore have to adopt several approaches to get part answers of you 'When to' question. These approaches may include searching around on the internet, (and elsewhere) for related software training programs, tutorials and forums like this, to learn about the use of software for the situations other than those covered in software manuals.

 

These are my 2 cents. Others members might guide you further, to more specific sources helpful in this regard.

 

HTH

 

Regards.

[Juli]

Thanks EngrUZAIR!!!

Your comment is perfect in that case and I am also agree with you that there is no unique or one piece document that describes that all facts. OKK !! THANKS.

 

Now,let me ask for help to this forum members that Can you please explain the terms of Interaction diagrams that will express why and when as well as how the terms work (i,e include phi, ex phi, inl phi & inc fy, what is fiber model data, MM,PM3 etc all details and when will I apply what in details please? In manual,these are not well described. Again, what is the function of mass source and how to handle with this? Which box is checked/unchecked in what cages in details..And please I desire comments in English.. Thanks !!

 

Before commenting, please see my two attachments !!  And all are in Etabs 2013.