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I want to know the use of diaphragms in etabs. i discus many people who are use etabs but i can't get justified answer about the application of etabs.

I read the Technical reference  of  Etabs, where they write about Diaphragms. i get two type of diaphragms (plate or shell and joint or beam). 

My question.

1. When do i use Shell diaphragms (if floor present ) 

2.When do i use joint diaphragms ( grade beam level where no slab are provide) 


NB: Diaphragms use to transfer the lateral load to the resisting element ( frame such as column. beam,shear wall) 

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You will assignment diaphragm property to your joints when you are not modeling area elements ( shells, plates or membrane) in the model, but the joints are connected by a horizontal area-member, or some combination of line-members, that will act as a diaphragm in the actual structure. ETABS will use it to distribute lateral forces to all joints based on that diaphragm property.

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  • Our picks

    • Hi guys just to discuss with you my understanding of crack widths in Environmental structures according to ACI. 



      Normal structures



      1. ACI 318-95 based on statistical method of Gergely & Lutz 1968 limits Z based on exposure. We are calculating crack widths here. (Normal structures)


      2. ACI 318-99 proposed limiting the spacing and removed actually calculating the width and also removed the exposure conditions. For example for beams and one-way slabs s (in) = 540/fs -2.5cc or in other words limiting the fs=0.6fy  (For normal structures)


      3. ACI 224R-01 references method 1 and 2 above and 3 european codes.

      The most confusing part is the table in which Nawy suggests 0.1mm crack width for water-tight structures. The whole document is for normal structures except this line. And people are following this line and refer to this document for water tight structures. I mean its just a suggestion and by the way this method 1 is obsolete now since ACI 318-99 (see point 2 above).



      Water tight structures



      1. ACI 318-08 states clearly that for watertight structures ACI 350-06 codes should be used. 


      2. ACI 224.4R-13 also specifically states that for watertight structures walls in section 7.4, we should use ACI 350-06. 


      3. ACI 350-06 for water tight structures does not recommend calculating a number for crack width but rather limiting max steel stress in bars to be 20k ksi or fs=0.33fy for normal conditions.



      To sum it up, 


      Philosophy of crack width control is not to calculate probable crack widths but to limit the max stress in steel bars.


      For normal structures: fs=0.6fy and for water tight structures fs=0.33fy
      • 1 reply
    • Hi

      I want to know the use of diaphragms in etabs. i discus many people who are use etabs but i can't get justified answer about the application of etabs.

      I read the Technical reference  of  Etabs, where they write about Diaphragms. i get two type of diaphragms (plate or shell and joint or beam). 

      My question.

      1. When do i use Shell diaphragms (if floor present ) 

      2.When do i use joint diaphragms ( grade beam level where no slab are provide) 


      NB: Diaphragms use to transfer the lateral load to the resisting element ( frame such as column. beam,shear wall) 
      • 2 replies
    • *SEFP Consistent Design*<br style="color:#272a34">*Pile Design*<br style="color:#272a34">*Doc No: 10-00-CD-0005*<br style="color:#272a34">*Date: Nov 21, 2017*<br style="color:#272a34">

      This article is intended to cover design of piles using Ultimate Limit State (ULS) method. The use of ULS method is fairly new for geotechnical design (last decade). The method is being used in multiple countries now (Canada, Australia etc). The following items shall be discussed:


      Geotechnical Design of Piles (Compression Loads, Tension Loads and Lateral Loads)

      Structural Design of Piles (Covering both Concrete and Steel)

      Connection of Pile with the foundation (Covering both Concrete and Steel)

      Pile Group Settlement

      Things to consider


      1. Overview

      Piles provide a suitable load path to transfer super-structure loads to foundation where shallow foundation are not suitable - this can be due to a number of reasons like existing space constraints or suitable soil strata is not present immediately below structure. Other uses can be to meet design requirements like to have reduced settlement etc.

      This article shall cover the use of straight shaft cast-in-place concrete piles and straight shaft driven steel pipe piles. There are a number of additional piles types like belled concrete piles, precast concrete piles, screw / helical steel piles etc but the discussion to choose a suitable pile type is not in the intended scope of this article. The article is intended  to discuss design requirements for straight shaft piles only (both concrete and steel) . The aforementioned topic about pile selection is a very diverse subject and requires a separate discussion on its own.

      Click on the link to read the full article.
      • 9 replies
    • I am suppose to design a pile foundation for a machine weighing approximately 50 tons and with an operational loading of 100 tons. 
      I ll appreciate your help in terms of guidance & provision of notes...  
      Thank you..
      • 36 replies
    • Material behavior can be idealized as consisting of an 'elastic' domain and a 'plastic' domain. For almost 200 years, structural design has been
      based on an elastic theory which assumes that structures display a linear response throughout their loading history, ignoring the post-yielding
      stage of behavior. Current design practice for reinforced concrete structures is a curious blend of elastic analysis to compute forces and moments, plasticity theory to proportion cross-sections for the moment and axial, load, and empirical mumbo-jumbo to proportion members for shear.


      From the book "Design of Concrete Structures with Stress Fields" by A. Muttoni,  J. Schwartz and  B.Thurliman.

      • 0 replies
    • Dear Fellow Researchers, Academicians, and research students,


      NED University of Engineering & Technology in collaboration with Institution of Engineers Pakistan (IEP) is organizing 9th International Civil Engineering Conference (ICEC 2017) on December 22-23, 2017 at Karachi, Pakistan.

       The congress details are available at its website www.neduet.edu.pk/icec

       Also attached is congress flyer for information and dissemination among your peers.

       Abstracts submission deadline has been extended till October 31, 2017.

      Please click on the link to see the full description.
      • 0 replies
    • AoA all,

      Is it mandatory to do column concreting upto the soffit of the beam in a single pour ?

      What code says about the construction/cold joint location in column ?

      Majority of the contractors are pouring the column concrete upto the soffit of the beam (full height of the column), some contractors leave the column height about 9" to 12" below the beam level and then fill this 9" to 12" column height with the beams & slab concreting. On one site column concreting was stopped at the mid height and the remaining half was filled on the next day.



      • 5 replies
    • 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

      • 10 replies
    • Salam Members,

      Congratulations to Engineers, PEC has become full signatory of Washington Accord, what are the benefits to Pakistani engineers for this agreement. 




      • 3 replies
    • Please clarify the following confusions one by one:-


      1. If we run P-delta analysis in ETABS, then should we ignore stiffness property modifiers for beams and columns? I have heard that if we perform P-delta analysis and apply stiffness modifiers at the same time then the moment magnification process is doubled...?


      2. ETABS considers selenderness of a column by applying moment magnification factors. If we run P-delta analysis also, does it mean that the selenderness of column is being over-estimated? I mean once the moments are magnified in P-delta analysis process and again through moment magnification process?


      Please help me understand the software myth and clarify above confusions.
      • 1 reply
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  • Similar Content

    • By kHURRAM ALI
      aslamwalekum to all,
      when we need semi rigid diaphragm , i normaly take rigid diaphram for beam slab system , i got a vetting project (model made on ETABS 2016) , in which flat slab are used and semi rigid diaphram is assign , A/c to IBC 2006 , concrete slab with thickness more than 1.5 in , not consider as flexible diaphram , here is the code refrence.
      1613.6.1 Assumption of flexible diaphragm. Add the following
      text at the end of Section of ASCE 7:
      Diaphragms constructed of wood structural panels or
      untopped steel decking shall also be permitted to be idealized
      as flexible, provided all of the following conditions are
      1. Toppings of concrete or similar materials are not
      placed over wood structural panel diaphragms except
      for nonstructural toppings no greater than 11/2 inches
      (38 mm) thick.
      2. Each line of vertical elements of the lateral-
      force-resisting system complies with the allowable
      story drift of Table 12.12-1.
      3. Vertical elements of the lateral-force-resisting system
      are light-framed walls sheathed with wood structural
      panels rated for shear resistance or steel sheets.
      4. Portions of wood structural panel diaphragms that
      cantilever beyond the vertical elements of the lateral-
      force-resisting system are designed in accordance
      with Section 2305.2.5 of the International
      Building Code
      here in my case slab is 8 in thick , so can it be act as flexible diaphragm.
      i belive for metal decking , i can use semi rigid diaphram , but not for 8 in thick flat slab
    • By Aye Min Khaing
      What is difference between Rigid and Semi rigid diaphragm. I think if we assign semi rigid, We don't need to consider accidental torsion i.e 5% eccentricity. If we assign rigid, we must consider accidental torsion. And next question is difference between XCM and XCCM in case of rigid diaphragm. What is MassX and MassY. How to calculate XCCM and YCCM. And how they work.
    • By Abdullah Anjum
      Dear All, 
      Could anyone suggest me assigning diaphragm like assigned in attached pic is correct for this building. If it is correct then how could we apply torsional irregularity in static load cases (earthquake case eccentricities override). I can calculate and apply it in simple building but in this building there would be two options of diaphragm( D1 & D2) in eccentricity override option in etabs ( If my assigned diaphragms are correct). which one i need to select.

    • By abdulqadeer29
      While purpose of assigning diaphragm is to transfer inertial forces during earthquake to vertical members . There is general practice which I am following for quite a long time,  that we most of the time don't consider inclined members like stair and ramp. i model them as horizontal slab.
      I have recently observed that there is a difference in the result while considering them as inclined members.
      My question is do we have to assign diaphragm to these inclined members (ramp or stair case)?

    • By BAZ
      *SEFP Consistent Design*
      *Diaphragm Flexibility*
      *Doc No: 10-00-CD-0004*
      *Date: August 07, 2014*

      I am writing this article about a very important, but mostly neglected topic of flexibility of diaphragm. I used to assume that all reinforced concrete slabs can be treated as rigid diaphragms. But as it turns out, only the slab with span-to-depth (depth is length of slab in direction of lateral loads) ratio of less than 3 and without horizontal irregularity can be treated as rigid diaphragm. The more important thing is that the span-to-depth ratio and horizontal irregularity is not the only criteria and one other factor also needs to be kept in mind before assigning rigid diaphragm to concrete slabs in numerical model of building.

      Another important concept that I learned, and it was a moment of epiphany for me, is about TRANSFER diaphragms. I had posted a topic “Amplification Of Forces In Etabs” earlier in this forum but we were not able to reach at a satisfactory conclusion. Now, I have the answer to that query: Back Stay effect. Another article is required to explain it , and this concept is not discussed in this article. This article is about flexibility of diaphragm.

      Diaphragms are horizontal members of the lateral-force resisting system of building structures. Their function is to distribute inertial forces, generated at its own level, as well as other levels, to vertical members of lateral-force resisting system.

      One kind of diaphragm only distributes inertial forces generated at its own level. This kind of behaviour is observed in buildings where there is a continuity of vertical members of lateral-force resisting system: building should not have a setback or podium at lower levels, or below grade levels. The other kind of diaphragm, known as “Transfer diaphragm”, not only distributes inertial forces generated at its own level, but also re-distributes forces coming from upper levels. This type of behaviour is typical of a building having setback or podium at lower levels, or below grade levels. Transfer slabs can attract huge forces due to a behaviour dubbed as BACKSTAY EFFECT.

      Now, coming to the issue of flexibility of diaphragm. According to ASCE 7-10,

      In addition to considering aspect ratio and horizontal irregularity as a basis for assuming concrete slab as a rigid diaphragm, the relative stiffness of adjoining vertical lateral load resisting system. Buildings with shear walls at ends and flexible frames in between are the ones where the assumption of rigid diaphragm leads to underestimation of drifts and erroneous distribution of base shear in vertical as well as horizontal direction (1)(2)(3); shear forces in middle frames can be reduced to 23% if rigid diaphragm is assigned in the model (1) for buildings with this type of structural configuration.

      M. Moeini et al. (2008) (3) conducted a parametric study using numerical analysis and proposed formulae that predicts the error associated with assuming concrete slab as rigid diaphragm. They also concluded that for buildings, without shear walls, rigid diaphragm assumption is suitable for irregular buildings as well. But, for long and narrow buildings with shear walls at ends, the assumption of rigid diaphragm is not suitable.

      The objective of writing this article was to warn engineers about the tendency of blindly assigning rigid diaphragm to concrete slab in any type of building configuration. The result could be underestimation of forces as well as drifts.
      Nakashima, M., Huang, T., Lu, L-W. “ Effect of Diaphragm Flexibility on Seismic Response of Building Structures”, In proceedings of 8th world conference on earthquake engineering. San Luis Obispo, MSc Thesis , “ An Investigation of influence of diaphragm flexibility on building design through comparison of forced vibration testing and computational analysis”, 2010. M. Moeini, B. Rafzey, W.P. Howsen, “Investigation into the floor diaphragm flexibility in rectangular reinforced concrete buildings and error formulae”, In proceedings of 14th world conference on earthquake engineering.
      The article is not finalized and would be completed in coming weeks.
    • By ahsun
      Can anyone tell me while assigning the diaphragm when we have to choose the semi rigid or rigid. What exactly it does with the structure in ETABS? 
      As far my understanding I am applying rigid diaphragm for concrete structure and semi-rigid for steel structures / car park structures.
    • By Waqas Haider
      Assalam o alaikum,
      ACI 21.11.1 tells about diaphragms in seismic zones. My building is in zone 4 and it is frame structure. i have provided SMRF. Is my slab going to act as Diaphragm? Since diaphragm means elements that transfer horizontal forces to vertical elements. and slab becomes cause of major horizontal inertial force and it transfer lateral forces to beams which transfer to columns. Is my slab diaphragm?? 
    • By jammer3425
      what is the purpose of assigning diaphragm b4 running analysis of concrete structure in ETABS and what type of diaphragm is required to be assigned to the structure as it shows us two types rigid and semi rigid. what role does these factors governs or play in the design of the structure?
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