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Dear All,

The forum has been updated today with a lot new features.

You can find the list of all the new improvements by visiting this website.

Some highlights are:

1) Improved Search Features


2) Emoji

Emoji support is now available in all editors.


Do check out the link posted above for the complete list.

One additional announcement that I would like to make is that with reference to last forum update post (read below),  @Rana and @BAZ are forum Admins now. I think it was important to do as it brings more transparency for the forum and also helps spread the responsibility. The forum belongs to the members so it never made sense for one person to be Admin,

As always, feedback is much appreciated.

Thanks for taking the time out to read this update.

Cheers!

 
  • 2 replies

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 I mean its just a suggestion and by the way this method 1 is obsolete now since ACI 318-99 (see point 2 above).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:

Overview


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

9th International Civil Engineering Conference (ICEC 2017), December 22-23, 2017, Karachi, Pakistan
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.

Thanks

 

 
  • 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. 

 

Regards   

 

 
  • 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

Development Length Of Standard Hooks
Assalam o alaikum.
According to ACI 12.5.2,
development length for fc' = 3000, fy=60000, for normal weight concrete and epoxy less reinforcement, The required development length comes out to be
for #3 = 8.2 inch
for #4 = 10.95 inch
for #6 = 16.42 inch
for #8 = 21.9 inch
 
And if in my case, ACI 12.5.3 is not fulfilled, it means now i have to provide ldh as mentioned above. ldh is STRAIGHT EMBEDMENT LENGTH + RADIUS OF BEND + ONE BAR DIAMETER as shown in figure attached. Now my question is, if in my case, main reinforcement of beam is of #6 and #4, minimum column size required will be 18 inch and 12 inch respectively. Lets say by any means, i can not select #4, #3 bars and size of column where bars are to be terminated is 12 inch, how to fullfil this development length???
  • 11 replies

ShearWall - Temperature Design in ETABS
Dear all,

I am trying to design shearwalls through ETABS with temperature load applied over shell. At various location, spandral section fails in Shear due to temperature and piers (sometime in shear, mostly in flexure).  (See Attached Image)

Certainly all the problem in Shearwalls are due to temperature. I don't want to increase cross section of spandral or pier at some location just due to temperature load case as it will appears non-uniform with rest of the wall. 

I have seen stiffness modifier affect distribution of forces and also rigid/semi rigid daiphragm assumption. 

 

Can anybody guide how to properly design the shear wall with temperature load applied in ETABS or share any similar experience. Thanks in Advance.    
  • 15 replies

Etabs Manual Meshing Problem
ENGINEERS;
I WILL LOOSE MY BRAIN FROM ETABS. 
I DECIDED TO MAKE MANUAL MESHING FROM AREA ELEMENTS BESIDE EACH OTHER AND EVERY HING WAS FINE .
BUT AFTER DEVISION SAY 7*7 ELEMNTS FOR EVERY BIG ELEMENT AND MAKING ETABS CHECH..................THEN 500 ERROR MESSAGE THAT ALL ELEMNTS ARE CLOSE TO EACH OTHER.  WHAT ARE GOING...... SOMEONE TELL ME PLEASE...... I WILL LOST MY WORK
  • 6 replies

Shear Reinforcement In Etabs
Assalam o alaikum.
I have just designed a frame structure with SMRF. The out put of shear seams weird to me. Column reports design shear Av/s as 0.045. (Images are attached). but when i right click the member, it must show me the most critical case HIGHLIGHTED AUTOMATICALLY. But it highlights load combo 38 (auto-generated combos have been used) which reports Av/s as 0.038. And 0.045 value is at combo 32. Is their any logic behind it?? More over how to interpret this Av/s?? means 0.045 in kip-in units means what? How can i convert this into spacing?? 
  • 9 replies

Hello everyone, I hope all of you will be fine. In etabs when we apply Response Spectrum loading on a multistoried building with 2 basement floors. At what floor level this loading will be applied as in equivalent static seismic analysis, we can apply EQX & EQY on any floor we like as this option is available in etabs but the problem is with response spectrum and time history analysis. please if someone knows and have the experince, share it i shall be very thankful.  
  • 5 replies

Salaikom dear professionals,
First of all I would like to express my sincere thanks to the initiators of this forum for establishing such an exceptional atmosphere for knowledge/experience sharing, I it is really useful, In fact since I have found the forum I am mostly online and busy reading the posts. I would also like to thank the members for their professional comments and advice.
As my first post in this forum I would like to ask the following queries:
1-After running the analysis and design when I check the DESIGN DATA through Display >> Show Tables >> DESIGN DATA >> Concrete Frame Output, there is no specific message in Column Summary Data and Beam Summary Data, but in Joint summary data it is showing that “Joint B/C check not done”. Does anyone has any idea? I am sharing the ETABS model for your information and easy reference.
ETABS MODEL.zip
2- ETABS provides greater area of steel in the upper column than the column at BASE, perhaps due to higher moment. Could someone explain why this is so? In practice should we maintain maximum steel in both stories? Or we shall follow what the software suggests?
3- Beside considering the minimum thickness required for deflection control of Beam as per Table 9.a Chapter 9 ACI-318 , using concrete crack behavior in ETABS and checking story drift, Do we have to check the deflection of beams for the serviceability propose elsewhere in ETBAS? If yes, Could anyone explain it?
Regards, and look forward to any explanation
  • 13 replies

Posting this thread to break the ice. Modelling domes is very easy in Etabs/SAP. All you need to do is to draw the curvature of the dome in elevation by a series of straight lines, but draw only the one half. Then using the apex at centre point, radially extrude the line say 24 times at 15 degree intervals (or 48 times at 7.5 deg intervals. This feature is under Edit> Extrude Lines to areas. You can further use this geometry for Finite Element Analaysis.
  • 22 replies

Hello,
 
I am designing the mosque in zone 4 . The roof of the mosque is a Truss.I have following questions 
 
1. Do truss rest on the beam ? if yes .? do i have to assign any support conditions ? or etab will selelct by default.
2. what will be the grade of steel for the truss ? yield or tensile strength. some one told me go for A 36 ( 36,58)
  • 15 replies

I accidentally came across these useful case studies, which, I would like to share. You can use them if you are working on a commercial or residential building retrofitting project. These case studies provide insight about seismic retrofitting and also on analytical methods, that are used for building assessment. I would also like to give due credit to people who are involved in these studies. All these studies were performed under a US-Pakistani Joint Cooperation Project. The details for the project are.

 





 

6-Storey Mixed Use Building in Karachi.pdf

10-Storey Office Building in Karachi.pdf

RS-4 Storey Academic Building in Karachi.pdf

Five Storey Residential Apartment.docx

Please visit the thread to download the attachments.
  • 2 replies

*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”,

Read more: http://www.sepakistan.com/topic/1480-diaphragm-flexibility/

  • 4 replies

Dear Engineer,

KPK Seismic Field Practicing Manual is attached. 

Field Practice Manual on basics of good construction practices.pdf

Thanks.

Please visit the forum link to download the attachment.
Link: http://www.sepakistan.com/topic/2179-kpk-seismic-field-practicing-manual-urdu/
  • 4 replies

*SEFP Consistent Design*
*1997 UBC vertical earthquake term*
*Doc No: 10-00-CD-0002*
*Date: May 30, 2013*
*Article is ripped: Good one to share though* 
 
For Strength Design, Ev has the effect of increasing compression and tension/uplift effects on vertical load carrying systems. Ev is not applicable for Allowable Stress Design. The new term, Ev, was introduced in the 1997 UBC. UBC Section 1630.1 defines Ev as the load effect resulting from the vertical component of the earthquake ground motion.
 
For Strength Design, Ev is defined as 0.5CaID. For Allowable Stress Design, Ev is defined as 0.

Ca= seismic coefficient from UBC Table 16-Q

I = importance factor from UBC Table 16-K

D = dead load
 
UBC Section 1630.1.1 defines the earthquake load, E, as the earthquake load on an element of the structure resulting from the combination of the horizontal component Eh and the vertical component Ev.

E = Rh*Eh + Ev (UBC 30-1)Rh= redundancy factor defined in UBC Section 1630.1.1Eh = earthquake load resulting from either the base shear, V, or the design lateral force, FpSubstituting the definition of Ev into this equation results in:E =Rh*Eh + 0.5CaID (Modified 30-1)The 1997 UBC defines load combinations in Section 1612. Strength load combinations 12-5 and 12-6include E.1.2D + 1.0E +(f1L + f2S) (UBC 12-5)0.9D (1.0E or 1.3W) (UBC 12-6)Substituting modified equation 30-1 into these equations results in:1.2D + 1.0 Eh + 0.5CaID + (f1L + f2S) (Modified 12-5)(0.9 + 0.5CaI)D + Eh (Modified 12-6a)(0.9 - 0.5CaI)D - Eh (Modified 12-6b)

Please visit the forum link to view the complete article.
Link : http://www.sepakistan.com/topic/1339-1997-ubc-vertical-earthquake-term-ev/
  • 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

*SEFP Consistent Design*
*UBC Seismic Drift Limits*
*Doc No: 10-00-CD-0003*
*Date: June 04, 2013*
 
The goal of this tutorial is to demonstrate how to evaluate building drifts and story drifts using UBC 97 guidelines. The philosophy behind Story Drift Limits is “Deflection Control”; In UBC 97, deflection control is specified in terms of the story drift as a limit on the lateral displacement of one level relative to the level below. The story drift is determined from the maximum inelastic response, ΔM.
 
Let’s start by defining the design-level response displacements. The elastic deflections due to strength-level design seismic forces are called design-level response displacements. These are denoted by ΔS, where the subscript ‘s’ stands for strength design. Design level response displacements are what you get out of your software, when you run analysis. Please note that structural analysis softwares may provide these values in different formats; say a percentage of height or a direct output.
 
Well, to calculate your story drifts, first you need to find maximum inelastic response displacements from your design-level response displacements. The maximum inelastic response displacement is defined as:
ΔM = 0.7RΔS
Where, R is the structural system coefficient, the subscript ‘m’ in ΔM signifies that we are calculating a maximum value for the deflection due to seismic response that includes inelastic behavior.
 
Visit the forum link to view the complete article.
Link: http://www.sepakistan.com/topic/1341-ubc-seismic-drift-limits/

  • 10 replies

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    • Could you help me understand how moment will be distributed in two ends of beams if one end of beam is fixed and other end is partially fixed? Say, previous 24ft beam with 15k/ft udl....FEM are -720 k-ft both sides.....now one of end has been partially released so that it can develop 360k-ft how will moment be distributed to other end...I am getting 900 k-ft at fully fixed end and shears at 2 ends became 157.5 and 202.5 kips..., I fail understand how to solve this indeterminate beam with one partial fixed end...   Thanks for your help
    • The settlement is likely due to weakening of soil support beneath the columns. There may be several reasons for this, like ingress of moisture in the underneath soil, sudden subsidence of some underground cavity etc. This may be investigated through some geotech engineer. Underground water tank, some nearby leaking water supply or sewerage line might also be the reason for weakening of the soil. To start with, these should also be checked & any leakage observed should be promptly & properly rectified.  Futher advice can be given on knowing the results of geotechnical investigation, carried out for determining the most likely cause of settlement.
    • Thanks for your reply. Actually your blog was one of the first I studied before doing it. 
      I understood it now. ETABS is using equation like M=(n/(n-1))*4EI/L*theta. so rotational stifness constant k=(n/(n-1))*2EI/L. If you are reducing stiffness on both sides consider using spring constant of (n/(n-1))*2EI/L n=% of moment to be resisted.....for n=1 we will get fully fixed, for n=0 we will get fully hinged.  The graph can be considered to be n(Y-Axis) and (n/(1-n))*2 as X axis. The data makes sense now. i am worried about 3D now, I have 55 story building in which i have to model connection loss in terms of decrease of stiffness. I don't know if I could use 
    • What kind of foundation system is there. you can consult a geotechnical engineer as well to get some option interms of soil improvement etc. From a structural point of view, you can  always introduce more columns and reduce load per existing column to reduce settlement. Thanks. 
    • plz help me out of this problem.. the foundation is settling down week by week. it is a warehouse. a big  Under ground water tank is adjacent to the failed column. we have only little space to work. this is in dubai. Suggestions please what so i can do. plz do reply
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