www.sefindia.org

[Dr. N. Subramanian]

I read the following message in LinkedIn-which I thought will be useful to some of our members.

Here are some interview questions related to structural engineering that someone faced during recent years.

1) Can A Multi-Storey Structure Be Considered As Statically Determinate In Actual Case ? If Yes How ?<o></o>
Yes. For example a  small steel building with braces in both direction. <o></o>
2) How Do You Define Diaphragms In Etabs ? Rigid Or Semi Rigid ? AndWhy ?<o></o>
Rigid if the thickness is sufficient and no  unusual slabbends. Semi rigid if the building is say for example a residential with many toilet and kitchen sunken portions <o></o>
3) Is Column Beam Joint Rigid Or Pinned ? <o></o>
Depends how you want it to be. No fixed answer. Depends on how designer wants the forces to be transferred/distributed between beam and column. <o></o>
4) Which Column Beam Joint Will Be More Critical In Shear & Bending ? The One With 2 Beams Or 3 Beams Or 4 Beams In Junction ?<o></o>
Cannot be answered unless loading and spans and cross section of individual beams is clear. <o></o>
5) Why Do We Use Response Spectrum Analysis In Etabs & How Is It Done ?
Because we don't have time history ordinates for a future earthquake with us. Secondly response spectrum method is generalised to cover all buildings although i gently disagree with the method. But then that is the closest we have. <o></o>


Note: The Answers are by our Er Kumar Abhishek Singh of Delhi

[VPandya]

Dear  Dr.  Subramanian,

Very interesting post on job interview for Structural Engineers.  I add one more question to the list of questions in the post :

HOW  YOU VALIDATE YOUR  FINAL COMPUTER MODEL OF STAAD/PRO  or  ETABS  RESULTS  SAY OF :  
1) RAFT FOUNDATION  WITH PLATE ELEMENTS  AND SOIL SPRINGS  ELEMENTS .    
2) A 20 story Concrete High Rise Buildings with  Moment Frames and Shear  Walls .

All the new engineers generate quickly a nice RAFT  or  SUPER STRUCTURE computer model and  Design  RAFT THICKNESS  and Reinforcement in the Raft  or  Design  his Beam and Column sizes based on his FINAL COMPUTER  RUN   .  How good are the Moments , Shears , deflections of this FINAL  COMPUTER RUN.   I ask the same question to two STAAD/PRO  instructors in a training session .  Their answer was, we take no responsibility
of your results , depends on the expertise of the project team using our product .
Point is we need an IN HOUSE CHECK LIST to VALIDATE COMPUTER MODEL RESULTS .  
We  all  have seen some very bad
results from  these  FINAL COMPUTER  MODELS  .


Regards .


Vasudeo Pandya  P.E.
Structural Engineer

[Dr. N. Subramanian]

Dear Er. Pandyaji

You are absolutely right. As seen in many posts of this forum also, many engineers simply relay on the computer results. People should know the assumptions on which the computer software they are using  are based and the limitations of the same. They should also check whether the output itself is correct, based on simple checks. For example, the reactions at the bottom of columns should be equal to the loads inputted by the engineer in a particular direction. There should be a smooth uniform profile for the deflection, etc.

Warm regards
Subramanian

[sathyace]

Dear NS Sir & Pandya Sir,

Thank you for posting such a valuable information.

Iam requesting you to post more questions like this and let all young engineers can answer and this will be very helpful to fine tune our knowledge.

As pandya sir said,nowadays all young engineers are taught to depend on computer results and we never cross verify that.

It would be great, if we consider this topic and make it active how we can assess computer results in each and every stage of design.

Thanks & Regards,
Sathya.

[VPandya]

Dear  Er. Sathya ,
In this reply I want to HIGHLIGHT  importance of  Validation/Verification  of  STAAD/PRO or  ETABS  computer  Analyis  and Design results .
The importance of Velidation/Verification is a must if you are going to provide  PROOF  CHECKING  CONSULTANCY  SERVICES  on a project.These two documents are part of  " RECOMMENDED GUIDELINES ON  PROOF  CHECKING  CONSULTING SERVICES  FOR BUILDINGS "  Document 2015/01 .  "    I can not attach full 27 page document for copy protection rules .

You will see from these two attached  documents that  for an experienced  Structural Engineer to  give an PROOF CHECK CERTIFICATE OF COMPLIANCE  ( Annexure- D ) is not easy . He has to be through with all checks . In  USA that Engineer can loose his P.E. and S.E. licenses to practice  Structural Engineering if something goes wrong with the structure .  

One mistake I have seen in STAAD/PRO analysis that most engineers in their computer model put a Command "  PERFORM  ANAYSIS  PRINT  STATIC CHECK " .  Out put file will match all applied loads   LATERAL . VERICAL , OVERTURNING  MOMENTS with REACTIONS from ANALYSIS OUT PUT .    I have worked with engineers who take great comfort in this STATIC  CHECK.  Point is even if you are 100 % off in your input applied  loads , you will still get  this check.   This is hardly a  check .  I can go on having seen some very poor STAAD analysis , but let me stop here.  

Regards.  

Vasudeo  Pandya  P.E.
structural Engineer