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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 I mean its just a suggestion and by the way this method 1 is obsolete now since ACI 318-99 (see point 2 above).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 Omar Khalid
      While I was modeling a 20 story building with symmetrical concrete slab sections and loads in each story, I noticed that the deflection of the slab increases the more I go higher in elevations despite having the same sections, dimensions and loads.

      I know that floors with symmetrical shapes and loads must endure the same stresses so it has the same reinforcement.

      Can someone explain this behavior or explains why it occurs if I was wrong ?

      Thanks in advance 
    • By waqar saleem
      1-how to calculate deflection for a t-beam?
      2-will it be different from the rectangular beam?
      3-will concrete strength effect the deflection?
    • By Waqas Haider
      Assalam o alaikum,
      For assuring deflection check of flexural members, we compare immediate deflection due to live load with L/180 or L/360. Also we compare total deflection (sum of immediate deflection due live load and long term deflection due to "dead +sustained loads") with L/240 or L/480.
      These deflections are calculated using corresponding effective moment of inertia "Ie" using equation 9-8 of section
      To find out immediate deflection due to dead load we find out it using Ie calculated using cracking moment due to dead loads.
      To find out immediate deflection due to sustained loads we find out it using cracking moment due to sustained loads.
      To find out immediate deflection due to D+L  we find out it using cracking moment due to dead + live loads.
      But to find out immediate deflection due to live load, we don't find it using cracking moment due to live load. We find out it by the difference of deflection due to dead + live load with the deflection due to dead load only.
      as shown by following results of manual calculations (Results from example 10.1 of PCA notes of ACI 318)
      Del.dead = 0.098 in      (calculated using Ma due to dead load only and corresponding Ie came out to be 10648 in4 = i.e. Ig because Ma is less than cracking moment)
      Del.live = 0.0744 (calculated using Ma due to live only and corresponding  Ie came out to be 10648 in4 = i.e. Ig because Ma is less than cracking moment)
      Del.(dead+live) = 0.344 in (calculated using Ma due to dead+live combo and corresponding  Ie came out to be 5345 in4 < Ig because Ma is greater than cracking moment)
      Note that 0.344 is not the simple sum of 0.098(Del.dead) + 0.0744 (Del.live) because here for Del.live, Ie used was based on live only i.e. Ig =10648 in4; for Del.dead, Ie used was based on dead load only i.e. Ig = 10648 in4; and for Del.(dead+live) Ie used was based on (dead+live) load combo i.e. 5345 in4.
      All three "Ie" are different".
      My question is, how to cater this in etabs modeling because in etabs it simply super impose deflections due to dead and live for D+L combo which must not be the case. More over, does modifier 0.35 is enough to cater effect of effective moment of inertia?
    • By Hira Malik
      While checking the allowable deflection in member in ETABS, which deflection is to be considered, absolute or relative? Which one represents the actual deflection of the member?
    • By Ahmad Shabaneh
      I work in a project with large spans (9.2m X 8m) and large service loads (4kn/m^2 SDL+Partitions), (7.5kn/m^2 Live load)
      In modeling the project on ETABS I set the property modifiers for slab (thin shell as 0.25) and this affected the deflection in slabs ( about 5 cm deflection from service loads)
      Hence: Slab thickness is 22 cm and interior beams 50X50 and the owner didn't allowed to increase the thickness
      Any suggestions to solve the problem.  
    • By Nasir Malhi
      Do etabs or sap has allowable deflection checks for beams if it is analysed and designed through these softwares.
    • By Omer Anwaar
      This particular slab (19x18 ft) is expereincing too much displacement, giving rise to very close spacing in slab panel in the middle strip. It has three interior beams placed to carry line load of the walls above. How can this displacement be reduced?
      Slab 19x18.bmp
    • By danny740

      I have a problem with  a simply supported deep beam which has a uniformly distributed load. The beam is simply supported at both ends but I have to consider the results for the following 3 scenarios
      - where the support is at the bottom of each end of the beam
      - where the support is at the mid point at each end of the beam
      - where support is at top of each end of the beam

      I have run this using FEA and I'm finding significantly different deflections and stresses when the beam is supported at the midpoint at its end and the other two scenarios...can anyone explain the exact reasoning for this?

      Sincere thanks
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