Jump to content
  • Welcome to SEFP!

    Welcome!

    Welcome to our community forums, full of great discussions about Structural Engineering. Please register to become a part of our thriving group or login if you are already registered.

Punching Shear In Safe Very Important Issue


mhdhamood
 Share

Recommended Posts

I have an idea to discuss here related to Punching shear; that is In categorization of columns there are :

1. Interior ,where the distance from each face of a column to the slab edge is at least four times the slab thickness

2. Edge column, where one face of a column in direction of design strip is closer to the slab edge in the same direction by four times the slab thickness .

3. Corner column, where two adjacent faces of a column are closer to their associated slab edges by less than four times the slab thickness. But the issue that is SAFE doesn't consider these definitions so it may give safe results where it may be unsafe .

Please discuss All Regards

Edited by UmarMakhzumi
Fixed font formatting
Link to comment
Share on other sites

SAFE takes all of the above consideration in its calculations. You can simply select appropriate column type if its not taking it automatically. You can assign the column as interior, corner or edge column. If you are specifying corner or edge column there are further four options to select which corner or edge.

Link to comment
Share on other sites

Dear Mr Rana Waseem;
Thank you so much for your response. Exactly I am talking about a case like the following:
1. An edge column has a slab extent less than 4*(depth of slab) of one of it's sides; that mean it shall be taken as edge column and that direction will be    ignored in calculations of parameter of punching except only for a distance of d/2 from that direction will be considered in computing punching perimeter.

2. As ACI papers; wherever the distance from the edge of column to the slab edge is less than 4*(depth of slab), that direction will be ignored in calculating perimeter of  punching except for a distance of d/2.

3. The issue now that : SAFE program for the case mentioned in 1, will not ignore the slab for the direction where distance less than 4*(depth of slab).    Other than it will take that distance in its calculations to the end of slab (Here is the issue, I mean it shall not take that direction because it is neglected as  per  ACI papers except for d/2 distance only........................ why is that? According to any code it works ??? Here to be sure I do the punching  calculations manually but that time consuming).

4. The good news that  SAFE will calculate another case of perimeter as an interior column for the above mentioned case, and takes the case with        smallest perimeter.But still the issue why SAFE take the distance that shall be neglected into its calculations?.

Your involvement is appreciated all.
Regards 
Mohammad

Link to comment
Share on other sites

Okay! SAFE is doing it perfectly. See PCA Notes Fig 16-5 "Edge column" (see attachment).
 
Include the marked dotted area also in calculating punching perimeter. Hope that clears your confusions?

post-133-0-70596500-1428851640_thumb.jpg

Link to comment
Share on other sites

Dear Mr Rana waseem;
Thank you. But I am not talking about what you attached. My case is that there is a distance behind an edge column less than 4*depth of slab( I mean not as perfect case which is =0 as you attached). Now this distance shall be taken only = d/2; not all the distance. This is shown in the following topic Figure3 b http://docslide.us/documents/design-for-punching-shear-strength-with-aci-318-95.html. Note that how that he didnt take the whole distance because it shall be ignored.
Please if you all get my point tell me to proceed .
Thank you all.
Regards 
Mohammad

Link to comment
Share on other sites

The provision you are talking about is performed in other softwares like ADAPT, but I could not find such definition of edge/corner columns in ACI. Can you please share where it is written in ACI code? I dont think there is such provision in ACI.

 

If you read ACI-318 2008 R11.11.1.2, it says

 

"For edge columns at points where the slab cantilevers

beyond the column, the critical perimeter will either be
three-sided or four-sided."
 
So draw punching perimeter around column and see if it lies inside the slab, then take it as interior column. (SAFE does this, if you keep the column location Auto).
 
If any edge of punching perimeter lies outside the slab footprint, ignore that edge.
 
In your case of example attached above, the column should be taken as interior column.
Link to comment
Share on other sites

Thank you Mr Rana Waseem . I say about you you are like an ocean. You introduce a nice discussion.
But let me say that : What is the definition of edge column ?. I guess from your paragraph that it is the one when you draw the perimeter which has three edges.
But as this paper says http://docslide.us/d...aci-318-95.html. that the edge columns is the one has a free edge od less than 4* thickness of slab.

Link to comment
Share on other sites

The document section I have quoted clearly says the clause you were mentioning is for prestressed sections. 

 

Now you have attached the summary that explains the intent of the document that the clauses in this document are written for the design of prestressed and non-prestressed concrete sections (same like ACI). Based on this you cannot say that all what is written inside is applicable to both. Each one of them is treated separately. The section I quoted above is for "Prestressed".

 

Instead of putting links and reference to other items, why don't you show me directly where it is written in ACI the definition of edge column with distance less than d/2?

 

So that we can talk directly on the specific point instead of loop referencing!

 

I have not read the documents you attached the link for, in your last post. Please take a screenshot where it says specifically, and attach it here. 

Link to comment
Share on other sites

And before that, make sure the document is really from ACI? (I also dont know about this clause, so please let me know, I am learning from you).

 

Because the document you are referring says "ADAPT Technical Notes", its does not look like official document of ACI.

 

And remember ADAPT program is used for PT slabs. ( I mentioned this in post#14 as well).

 

Also you still have the option to overwrite punching perimeter (as he said in post#7).

 

 

Show me the edge column definition from some standard ACI paper or code in next post. (Not from the documents you have already mentioned).

 

Thanks.

Link to comment
Share on other sites

If you really want to go in details, then see RISA explanation what it does in finding critical parameter;

 

https://risa.com/risahelp/risafoundation/Content/Common_Design/Punching%20Shear%20-%20Design.htm

 

Goto " Finding the Controlling Case (Interior, Edge or Corner) " section and see how many options are there to find punching perimeter; you can do this manually if the column is very critical.

Link to comment
Share on other sites

The provision you are talking about is performed in other softwares like ADAPT, but I could not find such definition of edge/corner columns in ACI. Can you please share where it is written in ACI code? I dont think there is such provision in ACI.

 

If you read ACI-318 2008 R11.11.1.2, it says

 

"For edge columns at points where the slab cantilevers

beyond the column, the critical perimeter will either be

three-sided or four-sided."

 

So draw punching perimeter around column and see if it lies inside the slab, then take it as interior column. (SAFE does this, if you keep the column location Auto).

 

If any edge of punching perimeter lies outside the slab footprint, ignore that edge.

 

In your case of example attached above, the column should be taken as interior column.

Good discussion. I will just add that Canadian Code CSA A23.3-09 allows a max distance 'dv' to be considered as part of punching shear perimeter where the slab cantilevers off column/ pile.

Thanks.

Link to comment
Share on other sites

Dear,
You have introduced a very nice discussion that reveal your excellent knowledge. Thank you so much. You made a big favor to me and I learned from you. Now I would like to say that I was wrong in:
1. I was very conservative in my estimations to perimeter of punching  because I was ignoring the distance after d/2 when the edge is less than 4*h. 2. I thought that I have to recheck after SAFE program checks for columns near periphery.

But I would like to mention that SAFE define the column according to 5*thickness of slab. Try to overwrite a column location type for a column having a free edge greater than 5*h( which should be treated as interior column) as edge column, then it will give NC (not calculated). 
Best Regards 

Link to comment
Share on other sites

But I would like to mention that SAFE define the column according to 5*thickness of slab. Try to overwrite a column location type for a column having a free edge greater than 5*h( which should be treated as interior column) as edge column, then it will give NC (not calculated). 

Best Regards 

 

I am not sure about 5h provision in SAFE. I will check. Thank a lot!

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
 Share

  • Recently Browsing   0 members

    • No registered users viewing this page.
  • Our picks

    • Hi there,
      I am interested in performing "Performance Based Design" for a 20 story building. 
      I'll be performing "Non-Linear Static Pushover Analysis" for my model. Until now, I have decided to go with "Displacement Co-efficient method". I will be using ETABS 2017 for performing Pushover Analysis. While assigning plastic hinges, I have an option of using ASCE 41-17 (Seismic Evaluation and Retrofit of Existing buildings". I would like to know what would be a better estimate for relative distances for plastic hinges in case of beams, columns. Any input concerning assignment of hinges to beams, columns and shear walls is highly appreciated. Normally it's taken 0.05 and 0.95 or 0.1 and 0.9. What's your opinion on this?
      Secondly, it would be great if someone can recommend me a book or some good source to understand how to characterize building using performance levels. Any sort of help is appreciated.
      I have recently graduated and joined a structural design firm, so kindly guide me, considering me a beginner.

       
      • 2 replies
    • *SEFP Consistent Design*<br style="background-color:#ffffff; color:#272a34; font-size:14px; text-align:start">*Pile Design*<br style="background-color:#ffffff; color:#272a34; font-size:14px; text-align:start">*Doc No: 10-00-CD-0007*<br style="background-color:#ffffff; color:#272a34; font-size:14px; text-align:start">*Date: April 16, 2018*

      1.1. FUNCTION OF JOINT

      Beam-column joint must transfer the forces, such as moment, shear and torsion, transferred by the beam to the column so that the structure can maintain its integrity to carry loads for which it is designed.

      Another function of the beam-column joint is to help the structure to dissipate seismic forces so that it can behave in a ductile manner.

      1.2.WHY DO WE CARE

      During an extreme seismic event, the code-based structure is expected to maintain its load-carrying capacity for gravity loads even after the structure deforms into inelastic range so that it does not pose any life safety hazard. Hence, the joint can go through significant degradation of strength and stiffness, and if it fails in shear, or anchorage, the life-safety objective of code cannot be achieved.

      1.3.CONSEQUENCES OF FAILURE


      1.4.THINGS TO CONSIDER FOR BEAM COLUMN JOINT

      Longitudinal bars of beams, or slab, must be able to develop their yield stress, so that the beam/slab can transfer moment to joint. It means that longitudinal bars must have adequate development length for hooked bars. This implies that the size of the column must be such that bars can develop their tensile forces. If bars can transfer moment, they can also transfer shear as far as monolithic construction is concerned.


      The shear strength of the joint must enable the transfer of moment and shear through it.



      The joint should be Constructible: Congestion of reinforcement is the main concern.

      1.5.DESIGN SHEAR FOR BEAM COLUMN JOINT

      The design shear for beam-column joint depends upon the relative strength of beam and column at the joint.

       
      • 4 replies
    • *Comments/Observations regarding modelling in ETABS*

      *Doc No: 10-00-CD-0006*

      *Date: May 06, 2017*

      Some of the observations made during extraction of results from ETABS (v 9.7.4), for design of reinforced concrete members, are being share in this article.,

      1) Minimum Eccentricity

      ETABS always considers the minimum eccentricity for selecting the design moment of columns irrespective of the probable behavior of the column, whether short or long column. See section 10.10.6.5 and its commentary of ACI 318-08 which deals with minimum eccentricity of long columns. You should always check the design moments that ETABS uses for columns if you want to bring down the cost of construction.

      2) Unbraced/ Braced Preference

      ETABS always performs analysis of frame as if it is un-braced. You should investigate if the storey under consideration is braced, or un-braced (10.10.5.2), and decide appropriate design moments of columns.

      3) Time Period

      ETABS has a tendency to select a time period of the building that is considerably less than the value obtained by the approximate method, Method A, of the section 1630.2.2  of UBC 97. To quote the FEMA 451 document: ''Because this formula is based on lower bound regression analysis of measured building response in California, it will generally result in periods that are lower (hence, more conservative for use in predicting base shear) than those computed from a more rigorous mathematical model". So, there is no need to use the value of time period that is lot less than Ta. One should always check the time period used by the software; ETABS can overestimate the seismic force by more than 2 times.

      Visit the forum link to read the complete article.
      Link: http://www.sepakistan.com/topic/2300-commentsobservations-regarding-modelling-in-etabs/
      • 0 replies
    • The minimum amount and spacing of reinforcement to be used in structural floors, roof slabs, and walls for control of temperature and shrinkage cracking is given in ACI 318 or in ACI 350R. The minimum-reinforcement percentage, which is between 0.18 and 0.20%, does not normally control cracks to within generally acceptable design limits. To control cracks to a more acceptable level, the percentage requirement needs to exceed about 0.60% (REFRENCE ACI COMMITE REPORT 224R-01)



       

       



       

       

      So according to above statement , should we follow 0.60%, to be on more safe side??



       
      • 12 replies
    • Dear Sir/Madam,

      This email is an invitation for the participation in the First South Asia Conference on Earthquake Engineering (SACEE-2019) which will be held on 21-22 February 2019 in Karachi, Pakistan. This conference is the inaugural event in this series of conferences which has been constituted under the auspices of South Asia Earthquake Network (SHAKE). The organisers of the conference include NED University, University of Porto, University of Fuzhou, University Roma Tre and Institution of Engineers Pakistan. The conference website can be visited at http://sacee.neduet.edu.pk/.

      Please note that world leading earthquake engineering experts have confirmed their participation in the conference. These include Prof Abdelkrim Aoudia (Italy), Prof Alper Ilki (Turkey), Dr Amod Mani Dixit (Nepal), Prof Bruno Briseghella (Italy), Prof George Mylonakis (UK), Prof Khalid Mosalam (USA), Prof Humberto Varum (Portugal) and many others. The presence of these distinguished experts allows you to exchange your work/issues with them and discuss possibility of any future collaboration. Please note that participation in the conference is strictly based on registration. Early registration in different categories at reduced rates are available till 10 December 2018. Please visit the conference website to see the details and the link for registration.

      If there are any queries, please do not hesitate to contact the Conference Secretary at the following address

      Prof. Muhammad Masood Rafi
      Conference Secretary- SACEE-2019
      Chairman
      Department of Earthquake Engineering
      NED University of Engineering & Technology Karachi, Pakistan.
      Phone: 0092-21-992-261261 Ext:2605
      Email: rafi-m@neduet.edu.pk
    • What is the Minimum reinforcement For Precast Pile  according to different codes (ACI,BS)??  Pile length is 40 times of pile least dimension . 
      • 1 reply
    • Dear members, I am working on a 10 storied rcc factory building with one basement,  where floor loads are in general 125 psf(Live) . but there are 2 warehouse in the building at ground floor & 10th floor where the Live load of stacked materials are 450psf. I have modeled it and analysed in ETABS. After analysis, seeing the floor displacement for seismic load,  i am in big shock to see the pattern. the displacement pattern suddenly increased hugely & then got normal . if the warehouse load created problem, then why it effected only Ground floor level, not the 10th floor! Please tell me how can i solve it. 
      • 1 reply
    • Asalamualaikum all,

      I have columns which are conflicting with the underground water tank as shown in figure.
       

      So I have decided to make underground water tank base slab as a footing for column. So I import etabs model to safe and just take uniform water load on base slab and point load from columns.

      This is the residential house. The BC is 2tsf. But SAFE is showing tension on the base slab and the thickness from punching is 30''. I believe that thickness is too high. What can be the error? Is this approach is correct for design base slab of ugwt to carry load of two edge columns?
      • 11 replies
    • SAFE perform iterative uplift analysis,any one having experience how to check the results of this analysis???what is the purpose and scope of this analysis???
      • 15 replies
    • Shear wall design
      AOA 

      i am facing problems in shear wall design .what are the pier and spandral ?what will be the difference when we assign pier or spandral? without assigning these the shear wall design is incomplete .

      i am taking about etabsv16

      someone have document about shear wall design plz provide it 

      thank you

       
      • 13 replies
  • Tell a friend

    Love Structural Engineering Forum Of Pakistan? Tell a friend!
×
×
  • Create New...

Important Information

By using this site, you agree to our Terms of Use and Guidelines.