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Comparison of UBC-1997 And IBC-2021 For Earthquake Resistant Design of

High Rise RCC Building

Conference Paper · February 2023

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 2nd International Conference on Advances in Civil and Environmental
Engineering (ICACEE-2023)
University of Engineering & Technology Taxila, Pakistan
Conference date: 22nd and 23rd February, 2023

Comparison of UBC-1997 And IBC-2021 For Earthquake Resistant Design of High Rise
RCC Building

Asad Ullah Khan, Adil Khan

University of Engineering & Technology Peshawar, Pakistan
asadullahk636@gmail.com, 18pwciv5027@uetpeshawar.edu.pk
Warda Zulhaj, Salwa Shaheen, Muhammad Ali Raza, Mohid Irfan
wardazulhaj2000@gmail.com, civilianuet222@gmail.com, tkhcollege786@gmail.com
18pwciv5184@uetpeshawar.edu.pk

ABSTRACT
This manuscript covers a study on the comparison between different aspects of reinforced concrete
buildings designed according to two different codes in the specific seismic zone. The dimensions,
configurations, and material properties are selected according to the usual practice in the area. For
the purpose of this study, two to ten-story buildings were selected. The numerical models of
selected reinforced concrete buildings were prepared in the finite element method-based software
ETABS (Version 19). The seismic analysis and design of these structures were carried out for
seismic zone 2B of UBC-97 and risk category III of IBC-21. After this, the design optimization
study and cost comparison analysis has been done. The manuscript provides an idea about two
different building codes i-e UBC-97 and IBC-21.

KEYWORDS: ETABS, UBC-97, IBC-21

1 INTRODUCTION

Humans started to fight against natural disasters from their first day on earth till now like
earthquakes, floods, tsunamis, etc. To fulfill the needs of mankind, the development of the world
started in every field of life. With the development of mankind, structures were constructed rapidly
[1]. Now everyone can see hundreds of skyscrapers, bridges, and other fascinating structures
across the world. To cope with the disaster of earthquakes, people started considering the
earthquake-resistant structure in the design [2]. Earthquakes do not kill people but actually, people
are killed by the collapse of badly designed and constructed buildings. The Kashmir earthquake of
October, 2005 had devastating effects on the area with many buildings damaged or collapsed.
Many people lost their lives [3]. It is almost impossible to exactly predict the occurrence of an
earthquake but the histories of previous earthquakes make it possible to a great extent and with the
different types of new materials available in our inventory, it is possible to construct an earthquake-
resistant building [4]. Many structural typologies shall be analyzed to provide a solution to a
problem that shall not only be efficient and cost-effective but also acceptable to the locality [5].

Page 1 of 8
 2nd International Conference on Advances in Civil and Environmental
Engineering (ICACEE-2023)
University of Engineering & Technology Taxila, Pakistan
Conference date: 22nd and 23rd February, 2023

2 METHODOLOGY

1. Selection of Building SAFE

2. E-TABS modelling 4. Detailing in REVIT
3. Footing analysis and design in 5. Comparison on different levels

2.1 Selection of Building

Our project is about the earthquake resistant design and comparison of reinforced concrete
buildings designed on UBC-97 and IBC-21 [6,7]. The hypothetical buildings of ten storeys having
uniform grid of 96’x96’ were selected and were designed in the software E-tabs and from there
suitable sizes of structural members were selected after analysis. The dimensions of both buildings
designed on UBC-97 and IBC-21 [6,7] having ten storeys, the beams are of size 15”x24”, the
columns provided are 30”x30” and slab thickness is 6.5”.

2.2 ETABS Modelling

Two types of finite elements are used in creating the ETABS model; frame elements to model
beams and columns and shell elements to model slabs and foundation.
The structure in ETABS is analysed and designed by performing the following steps.
1. First of all, we define the grid for the software itself. Live load = 40 psf (as per
structure. Grid size used is of 4’ x 4’. The code) (on all floors except roof) Live load =
number of bays in both directions are 4. 20 psf (as per code) (on roof only)
Superimposed dead load = 90 psf (from
2. Number of stories = 10 and Height of each
floor finishes and wall loads) (on all floors
story = 11’.
except roof)
3. The materials used in the project are: Superimposed dead load = 40 psf (from
Concrete = 3000 psi (for beams and slab) floor finishes and wall loads) (on roof only)
Concrete = 4500 psi (for columns and
8. The seismic loading parameters are defined
foundation) Rebar = Grade 60 = 60000 psi
as per the code. These values are specific to
4. Various sections are defined for slabs, Peshawar City.
beams and columns. After much trial and
9. Mass source is defined as per code for the
error, we got the final sections as; Beams =
application of seismic forces to the model.
15” x 24”, Columns = 30” x 30’’, and
The dead loads are used in mass source.
Slabs=6.5” (thick)
10. A rigid diaphragm is assigned to the model.
5. After defining all the sections, the structure
is drawn using drawing commands. 11. The Mat footing is modelled in SAFE.
6. The load patterns and load combinations are 12. The soil subgrade modulus is defined for
defined as per the code. the value of spring constant for the design
7. The loads applied to the structure are; Dead of foundation.
load = Weight of the structure taken by the
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 2nd International Conference on Advances in Civil and Environmental
Engineering (ICACEE-2023)
University of Engineering & Technology Taxila, Pakistan
Conference date: 22nd and 23rd February, 2023

13. The soil subgrade modulus for the design of b) The “run” button is now pressed to run the
footing is calculated as: analysis.
a) K = 12 x S.F x Bearing Capacity = 12 x 3 x
2.5 = 90 k/ft3 = 90000 lb/ft3

3 ANALYSIS

After carrying out the analysis the major outputs of structural analysis are the:
(1) Shear force diagrams, (2) Bending moment diagrams, and (3) Axial force diagrams

3.1 Shear Force Diagram

The SFD of the models using both the codes are given below in Figure 1 and 2. The values below
are in the units of “kip”.

3.1.1 UBC-97: 3.1.2 IBC-21

Figure 2: Shear force diagram (UBC-2021)

Figure 1: Shear force diagram (UBC-1997)

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 2nd International Conference on Advances in Civil and Environmental
Engineering (ICACEE-2023)
University of Engineering & Technology Taxila, Pakistan
Conference date: 22nd and 23rd February, 2023

3.2 Bending Moment Diagram

The SFD of the models using both the codes are given below in Figure 3 and 4. The values below are in
the units of “kip-in”.

3.2.1 UBC-1997: 3.2.2 IBC-2021:

Figure 3: Bending moment diagram (UBC-97) Figure 4: Bending moment diagram (UBC-21)
3.3 Axial Force Diagram
The Axial force diagrams of the models using both codes are given below in Figure 5 and 6. The values
below are in the units of “kip”.
3.3.1 UBC-97: 3.3.2 IBC-21:

Figure 5: Axial force diagram (UBC-97) Figure 6: Axial force diagram (UBC-21)
Page 4 of 8
 2nd International Conference on Advances in Civil and Environmental
Engineering (ICACEE-2023)
University of Engineering & Technology Taxila, Pakistan
Conference date: 22nd and 23rd February, 2023

4 RESULTS AND DISCUSSION

4.1 Base Shear Comparison

Base Shears are computed according to both the codes i.e. UBC-1997 and IBC-2021.
4.1.1 UBC-1997:
Base Shear computed from the Static lateral force procedure according to UBC-1997 is given by:
𝐶𝑣𝐼
𝑊 𝑉=
𝑅𝑇
i. Cv = Coefficient of velocity I = iv. W = Seismic weight of the structure
Importance factor v. The total design base shear shall not be less
ii. R = Response modification coefficient than the following:
iii. T = Time period 𝑉 = 0.11𝐶𝑎𝐼𝑊
2.5𝐶𝑎𝐼
Now: 𝑉= 𝑊 and 𝑇 = 𝐶𝑡(ℎ𝑛)3/4
𝑅

Finally, by putting all the values in these equations the Base Shear, V = 968.66 kip

4.1.2 IBC-2021:
Base Shear computed from the Static lateral force procedure according to IBC-2021 is given by:

𝑆𝐷𝑆𝐼
𝑉=𝑊
𝑅
i. SDS = Two-thirds of the maximum ii. I = Importance factor
considered earthquake spectral response iii. R = Response modification coefficient
accelerations for short period (0.2s) iv. W = Seismic weight of the structure
2 2
𝑆𝐷𝑆 = 3 𝑆𝑀𝑆, and 𝑆𝐷1 = 3 𝑆𝑀1
But, 𝑆𝑀𝑆 = 𝐹𝑎𝑆𝑆 and 𝑆𝑀1 = 𝐹𝑣𝑆𝑆
For Peshawar City, Ss=0.6 to 0.8 and S1=0.25 to 0.3
i. SMS = maximum considered earthquake iii. Fa = Site coefficient for short-period
spectral response accelerations for short- accelerations
period iv. Fv = Site coefficient for 1-second period
ii. SM1 = maximum considered earthquake accelerations
spectral response accelerations for 1
second period
𝑆𝐷1𝐼
Maximum Base Shear = 𝑉 = 0.01𝑊 and Maximum Base shear = 𝑉 = 𝑅𝑇 𝑊
Finally, by putting all the values in the equations the Base Shear, V = 954.35 kip

4.1.3 Comparison
On comparing the Base Shears calculated from both codes there is not any significant difference between
the two. Base Shear from IBC-2021 is slightly less than the Base Shear calculated from UBC-1997.

Page 5 of 8
 2nd International Conference on Advances in Civil and Environmental
Engineering (ICACEE-2023)
University of Engineering & Technology Taxila, Pakistan
Conference date: 22nd and 23rd February, 2023

4.2 Shear Force and Bending Moment Comparison

The shear forces and bending moments in a particular beam designed for both codes are given
below in Figure 7 and 8.
4.2.1 UBC-1997 4.2.2 IBC-2021

Figure 7: Shear force and bending moment Figure 8: Shear force and bending moment
diagram (UBC-1997) diagram (IBC-2021)
Let’s take a beam at level 5 of the building i.e. Beam B22 is analyzed for the maximum load
Beam B22 and analyzed it for the maximum combination according to IBC-2021. Its shear
load combination according to UBC-1997. Its force and bending moment diagram is given
shear force and bending moment diagram is below:
given below:
So from the figure it is shown that the
So from the figure it is shown that the maximum shear force and bending moments in
maximum shear force and bending moment in this beam are:
this beam are: Maximum shear force V = 30.197 kip
Maximum shear force V = 34.328 kip Maximum bending moment M=2103.71 kip-in
Maximum bending moment M=2422.81 kip-in

Page 6 of 8
 2nd International Conference on Advances in Civil and Environmental
Engineering (ICACEE-2023)
University of Engineering & Technology Taxila, Pakistan
Conference date: 22nd and 23rd February, 2023

4.2.3 Comparison
On comparing the maximum shear force and maximum bending moment developed in the beam,
we can observe that the shear force and bending moment in the beam designed according to the
IBC-2021 is slightly less than the shear force and bending moment in the beam designed according
to the UBC-1997.

4.3 Axial Force Comparison

4.3.1 UBC-1997 4.3.2 IBC-2021

Let’s take the middle column at level 1 of the Column C11 is analyzed for the maximum load
building i.e. Column C11 and analyze it for the combination according to IBC-2021. Its axial
maximum load combination according to UBC- force diagram is given below in Figure 10:
1997. Its axial force diagram is given below in
Figure 9:

Figure 9: Axial force diagram (UBC-1997) Figure 10: Axial force diagram (IBC-2021)
So from the figure it is shown that the So from the figure it is shown that the
maximum axial force P = 1110.285 kip maximum axial force P = 995.115 kip

4.3.3 Comparison
On comparing the maximum axial force developed in the column, we can observe that the axial
force in the column designed according to the IBC-2021 is slightly less than the axial force in the
column designed according to the UBC-1997.
Page 7 of 8
 2nd International Conference on Advances in Civil and Environmental
Engineering (ICACEE-2023)
University of Engineering & Technology Taxila, Pakistan
Conference date: 22nd and 23rd February, 2023

5 CONCLUSION
1. UBC-97 estimates 1.5 % more base shear than IBC-21
2. UBC-97 estimates 13.68% more maximum shear force than IBC-21
3. UBC-97 estimates 15.16% more maximum bending moment than IBC-21
4. UBC-97 estimates 11.57% more maximum axial force than IBC-21.

REFERENCES
1 Swenson, Alfred; Chang, Pao-Chi. History of Building (PDF). Archived from the original (PDF) on 2016-03-
04.
2 Emerging techniques to simulate strong ground motion. Sandeep, ... A. Joshi, in Basics of Computational
Geophysics, 2021
3 "Pakistan: A summary report on Muzaffarabad earthquake" ReliefWeb, 7 November 2005. Retrieved 23
February 2006.
4 O. Gunes, Turkey's grand challenge: Disaster-proof building inventory within 20 years, Case Studies in
Construction Materials, Volume 2, 2015, Pages 18-34, ISSN 2214-5095,
https://doi.org/10.1016/j.cscm.2014.12.003.
5 Wenjun Gao, Xilin Lu, Shanshan Wang, Seismic topology optimization based on spectral approaches,
Journal of Building Engineering, Volume 47, 2022, 103781, ISSN 2352-7102,
https://doi.org/10.1016/j.jobe.2021.103781.
6 UBC-1997
7 IBC-2021
8 ASCE 7-10
9 Design of Concrete Structures by Darwin

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