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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

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.

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)

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.

*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/

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/

*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/

*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/

How to: PARTIAL FIXITY in ETABS


PARTIAL FIXITY IN ETABS
Download article in PDF format

Let’s take the case PARTIAL FIXITY in ETABS. There is no simple option to just release a specific percentage of moments and shear at the supports. The only way is to provide the reduced stiffness of the members. Let’s have a look at different options in ETABS for releases.
You can access these options by clicking: ASSIGN>FRAME LINES>Frame Releases/Partial Fixity



· There are many sets of combinations possible. You can get the details in ETABS help menu. For example it will not allow you to release torsion at both ends.
· The various checkboxes you see in this form are for releasing (making 100% pin connection). One for start point of the section and the other for end point. Important point here is when you select the option either START or END the boxes for spring values will be enabled. By default the values in those boxes is zero which means the stiffness is reduced to ZERO so making it PIN connection.
· To make partial frame releases (say only 50% of the moment), you need to put the“FRAME PARTIAL FIXITY SPRINGS” values in the START and END boxes.


So, WHAT value I put for Fixity Springs

1- First you need to calculate the stiffness of the FULLY FIXED support and this calculated as k=4EI/L
Where k = Fully fixed stiffness of the connection, E=Modulus of elasticity of the member, I=Moment of inertia in the direction of analysis, L=length of the member between supports.
Here the important point is that L is the member length between supports in that particular direction (unsupported length). If the member is divided in let’ say 10 parts, you will not put the length of one part, rather the full unsupported length.
2-After calculating the actual stiffness value of the connection, you need to multiply it by the reduction factor by which you need to reduce the moment, shear etc. The reduction factor is:-


REDUCTION FACTOR = n/(1-n)

Please visit the forum link to view the complete article:
Link: http://www.sepakistan.com/topic/27-how-to-partial-fixity-in-etabs/

Building Drift in ETABS
waseemrana.com
Drift is a very complex topic in structural engineering. It involves too many factors to arrive at a suitable decision. It involves engineering judgment, the phenomenon fresh engineers might not feel. In this article, I have tried to explain what is building drift, allowable limits, ways and means to check in ETABS models and to control the excessive drift. Please keep in mind, this article is not about the building drift as far as structural science is concerned, rather this topic of drift is related to ETABS software.
First of all you must be familiar with the term story drift. For convenience, I am quoting here the definitions from UBC-97 code:-
STORY DRIFT is the lateral displacement of one level relative
to the level above or below.
STORY DRIFT RATIO is the story drift divided by the story
height.

Please visit the forum link to view the complete article.
Link: http://www.sepakistan.com/topic/109-building-drifts-in-etabs/