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Ubc Vs Ibc-2003 (For Seismic Calculations)

Sohaib Nazar

By Sohaib Nazar,
in Seismic Design

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Sohaib Nazar Newbie

Sohaib Nazar

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Dear fellows,

i have some queries regarding UBC code and and IBC-2003.

I am carrying out study study in Saudi Arabia, Comparative study for Saudi Arabia maximum and minimum earthquake zones based on UBC and SBC(IBC-2003).

As there is no provision for SBC or IBC in Etabs so I calculated base  shear by hand.(see attached files).Maximum earthquake zoning of Saudi Arabia is 2B according to old SBC(was based on UBC) and S1= 12.6 % and Ss = 43.7 % of g, according to new SBC(based on IBC-2003). There is big difference in values of base shear and lateral forces in both codes.

Please check the files attached.

Can any body suggest and guide me about these results.

(Region 4 in SBC = zone 1 in UBC and Region 6 = Zone 2B in SBC)

 

Also

It is right way to calculate Ss=43.7/100  * 9.81 = 4.26 (which is very big) ?

UBC.docx

SBC.docx

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UmarMakhzumi Enthusiast

UmarMakhzumi

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Posted

Dear fellows,

i have some queries regarding UBC code and and IBC-2003.

I am carrying out study study in Saudi Arabia, Comparative study for Saudi Arabia maximum and minimum earthquake zones based on UBC and SBC(IBC-2003).

As there is no provision for SBC or IBC in Etabs so I calculated base  shear by hand.(see attached files).Maximum earthquake zoning of Saudi Arabia is 2B according to old SBC(was based on UBC) and S1= 12.6 % and Ss = 43.7 % of g, according to new SBC(based on IBC-2003). There is big difference in values of base shear and lateral forces in both codes.

Please check the files attached.

Can any body suggest and guide me about these results.

(Region 4 in SBC = zone 1 in UBC and Region 6 = Zone 2B in SBC)

 

Also

It is right way to calculate Ss=43.7/100  * 9.81 = 4.26 (which is very big) ?

 

All I can understand from your post is that you are doing a comparison between two codes for Saudi and trying to find out quantitative difference of base shear? Also, I believe you want someone to check your numbers?

 

Before you do that you need to understand the differences between UBC and IBC Seismic Design Philosophy; you aren't comparing apples to apples if you just compare numbers. There is a lot different between two codes. Both codes design to a different Maximum Considered Earthquake (MCE). Considering everything is constant, IBC will give you a higher base shear. Read the attached article:IBC and UBC Comparison.PDF

 

Use the method provided in code to identify your seismic response coefficients. Ss=Ground acceleration at short (0.2 second) period, which will allow you to determine Sms and subsequently Sds. Code outlines the procedure to calculate all these components. I don't know why are you calculating Ss like you did. 

 

Documents attached are result output, and calculation is not attached. Without a calculation, no one knows how you came up with the numbers. My best advice to you, to check your numbers is to compare them with a solved example. You can't go wrong.

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WR1 Newbie

WR1

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well this is not always true. Last year I did a similar comparative study in Saudi for one of our projects.

 
UBC-97 gave higher base shear due to the fact that the actual calculated base shear exceeds the maximum allowed value that is independent of time period.
Buildings were in moderate seismic zones and the height of building where the actual base shear was less than the max base shear was 16m for concrete and 18m for steel structures.
These buildings were low rise having 3 stories max.
 
In IBC 2006/ASCE 05 maximum base shear formula has T and actual base shear is constant for all heights. That is the reason max base shear governed  upto 14m height of concrete and 12m height for steel structures.
 
In nutshell IBC 2006 gave us upto 64% reduction in base shear magnitude in concrete and upto 56% reduction in steel buildings as compared to that of UBC-97.
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zenith.international Newbie

zenith.international

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All I can understand from your post is that you are doing a comparison between two codes for Saudi and trying to find out quantitative difference of base shear? Also, I believe you want someone to check your numbers?

 

Before you do that you need to understand the differences between UBC and IBC Seismic Design Philosophy; you aren't comparing apples to apples if you just compare numbers. There is a lot different between two codes. Both codes design to a different Maximum Considered Earthquake (MCE). Considering everything is constant, IBC will give you a higher base shear. Read the attached article:attachicon.gifIBC and UBC Comparison.PDF

 

Use the method provided in code to identify your seismic response coefficients. Ss=Ground acceleration at short (0.2 second) period, which will allow you to determine Sms and subsequently Sds. Code outlines the procedure to calculate all these components. I don't know why are you calculated Ss like you did. 

 

Documents attached are result output, and calculation is not attached. Without a calculation, no one knows how you came up with the numbers. My best advice to you, to check your numbers is to compare them with a solved example. You can't go wrong.

 

The response of Umar Makhzumi is comprehensive, clear and correct.

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zenith.international Newbie

zenith.international

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The response of Umar Makhzuni is comprehensive, clear and correct.

 

In addition, following should be noted.

It is advisable that all designs in Pakistan adhere to IBC rather than UBC-97, which is now considered defunct.

Use of UBC-97 with latest resistance codes for structural concrete (like ACI 318-05, 318-08, 318-11) and AISC codes with publication dates after 1997 is technically incorrect and must be avoided.

 

I hope that structural design community should adapt to the IBC and the appropriate use of resistance codes.

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UmarMakhzumi Enthusiast

UmarMakhzumi

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well this is not always true. Last year I did a similar comparative study in Saudi for one of our projects.

 
UBC-97 gave higher base shear due to the fact that the actual calculated base shear exceeds the maximum allowed value that is independent of time period.
Buildings were in moderate seismic zones and the height of building where the actual base shear was less than the max base shear was 16m for concrete and 18m for steel structures.
These buildings were low rise having 3 stories max.
 
In IBC 2006/ASCE 05 maximum base shear formula has T and actual base shear is constant for all heights. That is the reason max base shear governed  upto 14m height of concrete and 12m height for steel structures.
 
In nutshell IBC 2006 gave us upto 64% reduction in base shear magnitude in concrete and upto 56% reduction in steel buildings as compared to that of UBC-97.

 

 

True, there can be certain cases where UBC gives a higher base shear. However, without knowing basis of study, parameters involved and data points/ no of runs and sensitivity of each parameter quoted results, it hard to conclude. Keeping numbers apart, there are other differences too. IBC considers seismic design category which affects your calculated base shear whereas UBC considers your seismic zone only. While designing a hospital in a lower seismic category, you may end with a higher base shear than for a commercial building with a higher design category, both comparisons being done for IBC.  As I said, it is not an apples to apples comparison, and your results can be different based on what parameters you consider. To me, the whole exercise is pointless, because basis are different. Number crunching.

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zenith.international Newbie

zenith.international

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Dear All:

[1] Please note that Structural Designers in Pakistan are still using DEFUNCT UBC-97. I am a one person team trying to change this practice.

[2] In addition, by using ETABS, they use UBC-97 and latest ACI & ASCE CODES, which is incorrect.

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miqureshi77 Newbie

miqureshi77

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On 12/1/2017 at 11:19 AM, zenith.international said:

Dear All:

[1] Please note that Structural Designers in Pakistan are still using DEFUNCT UBC-97. I am a one person team trying to change this practice.

[2] In addition, by using ETABS, they use UBC-97 and latest ACI & ASCE CODES, which is incorrect.

So what you will do,

will you going to change the Pakistan Building Code?

 

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UmarMakhzumi Enthusiast

UmarMakhzumi

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On ‎2017‎-‎12‎-‎03 at 5:48 PM, zenith.international said:

Let's develop a group of like minded Engineers and make a petition to PEC and KBCA and ACEP.

I will lead but but need numbers.

Please get your petition ready and we will support you through our forum.

Thanks!

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zenith.international Newbie

zenith.international

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I will develop the Text for KBCA bylaws to replace the current clause in Chapter 11 of KBCA by laws. 

 In the mean while need volunteers to develop list of Enginners with email addresses so the revised Text can be sent to them and they Endorse it.

We start with local Bodies, like KBCA and then towards PEC for revising the Building Code of Pakistan Seismic Provisions 2007.

Prof.Dr. Shoaib Ahmad

 

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