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Pakistan Journal of Science (Vol. 63 No. 2 June, 2011)

84

NEW SEISMIC PARAMETERS FOR BUILDING CODE OF PAKISTAN AND THEIR

EFFECT ON EXISTING REINFORCED CONCRETE BUILDINGS: A CASE STUDY

M. B. Sharif, A. U. Qazi, M.Ilyas*, N. Mohsin*

Department of Civil Engineering, University of Engineering and Technology, Lahore.*

Strucrual Division Nespak House, LahoreCorresponding author e-mail:[email protected]

ABSTRACT:The large scale devastation caused by the earthquake of October 08, 2005 in NorthernPakistan and Azad Jammu and Kashmir has raised several questions on the adequacy of the present

design and construction practice in the country. Realizing the gravity of the situation, the Government

of Pakistan appointed a Committee of technical experts and Government Officials to supervise and

provide guidance for revision/updating of Building Code of Pakistan, to suggest modifications to the

present codes of practice and to particularly incorporate the recommendations for earthquake resistant

design of buildings. Therefore, It is important to check the adequacy of existing structures especially in

high seismic risk zones according to revised seismic parameters. The National Insurance Complex

Limited (NICL) Building, Jinnah Avenue, Blue Area Islamabad is selected for study. It was

constructed in 1994. In this research seismic analysis has been performed for National Insurance

Complex Limited (NICL) building. These analyses include linear static analysis, response spectrumanalysis, non-linear static analysis and linear time history analysis which are performed using ETABS.

Different analysis approaches have been used to carry out the lateral analysis on the basis of BCOP-

2007 and the time histroy of October 8, 2005 earthquake. The study revealed that base shear is

increased by 7% due to the change in the seismic zoning for the current location of the building. It is

concluded that the change in seismic zoning has not seriously threatened the stability of existing

buildings. The buildings which are then designed according to some recogonized building codes when

analyzed according to BCP-2007 should fall safe. However failure may be expected incase of the

building is not preperly designed or poorly constructed.

Key words: Seismic zone, base shear, drift.

INTRODUCTION

The large scale devastation caused by October

08, 2005 earthquake in Northern Pakistan and Azad

Jammu and Kashmir has raised several questions on the

adequacy of the present design and construction practice

in the country(Ilyas, M & Rizwan,M. 2006). Realizing

the gravity of the situation, the Government of Pakistan

appointed a Committee of technical experts and

Government Officials to supervise and provide guidance

for revision/updating of Building Code of Pakistan, to

suggest modifications to the present codes of practice and

to incorporate the recommendations for earthquake

resistant design of buildings.This committee resulted in

the development of new building code of Pakistan which

is abbreviated as BCOP-2007.It is expected that thestructures constructed under any established earlier

building codes may become nonconforming in relation to

the revised seismic parameters present Building Code of

Pakistan 2007. Proper design and detailing considering

realistic seismic parameters with good construction

practices will reduce the devastation to a much lesser

extent by reducing causalities.

It is essentially important to check the adequacy

of existing structures specially in high seismic risk zones

according to revised seismic parameters. The mainpurpose of the proposed research work is to review the

design of existing reinforced concrete building

considering revised seismic parameters and to ascertain

the adequacy for resistance against adverse effects of

earthquake induced forces. Moreover, to suggest remedy

for different structural components in order to ensure

their safety and stability. An urgent action is needed to

avoid failure of vulnerable structures.

There is a lack of awareness for seismic

protection in many parts of the country. In high seismic

risk zones, time history analysis for high rise structures

must be carried out to depict actual behavior. The

compliance of the specified earthquake resistant designand construction practice must be ensured through

appropriate legal, administrative and technical control.

New buildings must be earthquake resistant in order to

prevent constant addition to existing vulnerable structures

that are already seriously threatened.

Gulten and Calim (2003) studied the torsionally

unbanlanced multistorey RC structures. They found that

by introducing 5% eccentricity an increase of about 10%
mailto:[email protected]:[email protected]


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bending moments in the columns and beams located at

critical locations, occurred.

Erduran and Yakut (2004) studied the seismic

performance for an RC frame system. According to them

detailed assessment procedures generally require a full

blown seismic analysis of the building to determine the

forces and deformations experienced by its components

under a presumed level of earthquake intensity. A

number of widely used such procedures (FEMA 356,

ATC-40 and EUROCODE 8) compare these demands

with the recommended values of member capacities

varying with the level of the performance objectives

employed.

Yun et. al. (2006) presented a procedure for

analyzing the building which was based on non linear and

reliablilty theory. This procedure gives simplified method

for the analysis of steel moment frames with fair

accuracy specially during the non linear analysis. Hugo

(2003) has devised various principles for engineers and

architects for the seismic design of the buildings. It can

be concluded from this report that any building which isdesigned using the principles mentioned in the report of

the author will perform well during an earthquake.

Young et al. (1985) developed the damaged

model for reinforced concrete. They investigated the full

capacity of member which may be used during an

earthquake. Ahsan and Saif (2008) investigated the

failure due to the kashmir hazara earthquake (2005) and

concluded that although knowledgeable and competent

structural engineers are avaialble in Pakistan but the

execution of construction with respect to the design is

very important. They also empahsized that the

recommendations suggested by them are very significant

for new construction. This will help in the reduction ofproperty loss and human lives.

Building description: The National Insurance Complex

Limited (NICL) Building, Jinnah Avenue, Blue Area

Islamabad is selected for study. It was constructed in

1994. The building mainly comprises of two blocks,

Tower block and low-rise block which are separated from

each other by an expansion joint. The Tower block is

mainly used for offices and the low-rise block is used for

parking of vehicles. Tower block has sixteen floors with

two basements and low-rise block has two basements and

two floors. After the earthquake of October 08, 2005

some cracking was observed in the masonry walls which

are non-structural in nature and does not impair strengthof the structural system. Some cracks were also observed

in the construction joints of parapet wall and retaining

wall which do not cause structural instability. The

material properties considered in the design were verified

using non destructive methods.

Structural system: The structural system for the NICL

building is an essentially space frame providing support

for gravity loads and resistance to lateral load is mostly

provided by concrete shear walls and lift-well walls. Slab

system consists of two-way slab with shallow wide Ribs

acting as column strips along the column centre lines.

Flexural effective width of the slab also acts as a wide

shallow beam to transfer gravity and other unbalanced

forces to the columns and shear walls. Reinforcement has

been laid out as for two-way slab system with

concentration of reinforcement in the column strips.

Concrete shear walls and lift-well walls provide lateral

resistance in two orthogonal directions. Structural

members (columns shear walls and lift-well walls) resist

the total seismic lateral loads in proportion to their

relative rigidities with shear walls resisting almost 76

percent of total seismic base shear loads due to their

greater stiffness in the two principal directions. Shear

walls at the periphery of the building are located at each

corner of the building whereas lift-well walls are located

eccentrically with respect to the building center.

Foundation system of the Tower Block building employs

cast-in-place piles with thick pile caps providing load

transfer mechanism from columns and shear walls to thedeep foundations. Low-rise block uses raft foundation.

Seismic parameters: All structures and their components

are analyzed to determine their adequacy to withstand

lateral forces caused by seismic loads. The original

design of the building was based on BCP-1986 with

following seismic parameters:

Z. = Seismic Zone factor = 0.30

I. = Importance factor = = 1.00

Ct. = Numerical coefficient = 0.03

S. = Soil factor = 1.50

Rw. = Numerical Coefficient = 12.0

Above parameters have been revised in the Building

Code of Pakistan 2007. New seismic provisions, which

are based on revised seismic zoning map of Pakistan

which is shown in Figure-1.

Figure-1 Seismic zoning of Pakistan (BCOP-2007)

Few parameters which have been revised by the

BCOP-2007 are shown below.


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Z. = Seismic Zone factor = 0.20

I. = Importance factor = = 1.00

Cv.= Seismic coefficient = 0.32

Ca. = Seismic coefficient = 0.28

R. = Numerical Coefficient = 5.50

S. = Soil profile type = = SD

Material properties: Reinforcement yield strengthconsidered as per original design criteria of National

Insurance Complex Limited building is 60,000 psi.

Following concrete strengths taken from original design

criteria:

Columns 5000 psi

Shear walls 5000 psi

Slab 2500 psi

Beam 2500 psi

Foundation 2500 psi

Dead loads: Dead loads are the vertical loads due to the

weight of all permanent structural and non-structural

components of a building, such as walls, built-in and

moveable partitions, floors, roofs and finishes includingall other permanent construction. Following loads are

used in analysis as taken from original design criteria:

Finishes 30 psf

Partitions 20 psf

Roofing 10 psf

Plaster 10 psf

Live loads: Live loads include loads due to intended use

and occupancy of an area, personnel, moveable

equipments, lateral earth pressures, vehicle and impact

loadings. For National Insurance Complex limited

building, floor live loads are taken as per occupancy and

intended use requirements, from original design criteria

as given below.

Parking Floor 100 psf

Ground Floor 100 psf

Mezzanine Floor 60 psf

First Floor 60 psf

Typical Floor 60 psf

Roof Floor 30 psf

Wind loads: Lateral loads due to wind were imposed on

the building using wind velocity of 80 mph and Exposure

Category-C as per BCP-2007. Wind loads were combined

with other applicable loads as per BCP-2007 load

combinations.

Analytical modeling: The analysis for the study is

carried out using Extended Three Dimensional Analysis

of Building System ETABS Nonlinear Version. The

building is modeled in 3-D with spatial distribution of

masses and stiffness of the structural system. Tower

Block of the building is modeled separately as there is 1inch wide expansion joint separating the two blocks.

Superstructure is modeled by using discrete frame

elements for columns, beams, shell elements, slabs, shear

walls and other concrete lift-well walls. Concrete

dimensions of frame elements were based on sizes of the

structural members provided in the structural drawings.

Materials properties used in the review are as provided in

the original design criteria of the building. In order to

carry out the study different types of computer models

are prepared in software ETABS which are given in

Table-1.

Table-1 Types of analysis and their nomenclature

Model Description

LS-A 86 Building is modeled with 3D space frame, with un-cracked sections considering provisions of BCP 1986.

LS-B 86 3D interior frame of building is modeled with cracked sections considering provisions of BCP 1986.

LS-A 07 Building is modeled with 3D space frame, with un-cracked sections considering provisions of BCP 2007.

LS-B 07 3D interior frame of building is modeled with cracked sections considering provisions of BCP 2007.

RS 86 Building is modeled with 3D space frame, shear walls, lift wells and slab system considering provisions of BCP 1986.

RS 07 Building is modeled with 3D space frame, shear walls, lift wells and slab system considering provisions of BCP 2007.

NLS 86 3D interior frame of building is modeled with beam and column elements considering provisions of BCP 1986.

NLS 07 3D interior frame of building is modeled with beam and column elements considering provisions of BCP 2007.

NLS 01 3D interior frame of building is modeled with beam and column elements.

NLS 02 3D exterior frame of building is modeled with beams, columns and shear wall elements.

TH 01 Building is modeled with 3D space frame considering actual time history record.

TH 02 Building is modeled with 3D space frame considering scaled time history record.

Discussion on results: The different analysis options

which are shown in Table-1 were analyzed on separate

computer model based on the parameters which have also

been mentioned in the previous sections. The main

considerations were given on the story drifts and drift

ratios because the divergence of these values during

different analysis options can comment on the status of

the structure.

The linear static analysis and Response spectra

analysis based on BCOP-86 and BCOP-07 is shown in

figure -2


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Figure-2 Lateral Displacements and Storey Drift Ratios for LS & RS Analysis

The linear static analysis of building due to

revised seismic zoning of Pakistan increases the base

shear by 7%. Due to the increase in base shear maximum

lateral displacement at top of building increases by 32%.It was also observed that the maximum storey drift for

eigth storey increases to 0.42 The structural system of

building shows unsymmetrical distribution of stiffness

which result in additional torsion, due to this reason the

lateral displacements for elastic response spectrum

analysis are on higher side to that of linear static analysis.

It was observed that the maximum storey drift for storey

number seven is having a storey drift ratio of 0.6. Shear

wall and lift wells attract 76% of total base shear and

24% of total base shear is taken by reinforced concreteframe.

The next set of analysis was carried out for non

linear behavior of building. The behaviour of the building

for lateral displacements and storey drift ratios is shown

in Figure-3.

Figure-3 Lateral Displacements and Storey Drift Ratios for NL and LS analysis

Non-linear static analysis of building has shown

that maximum storey drift is experienced by storey

number three with storey drift ratio of 1.1 which is due to

the presence of mezzanine floor in the building. Plastic

hinges are formed at beams only showing strong column

weak beam structure. For revised seismic parameters the

building remains in state of immediate occupancy. Push

over analysis reveal that the beam at third floor will yield

to collapse at base shear of 0.547 times the weight of

structure.

The results of NLS-01 and NLS-02 is shown in

figure -4 and 5. The two analysis differ in a sense that

NLS-01 was without considering shear wall and NLS-02

was with shear wall.

The later displacement for both the cases remains

the same, however the collapse load occur for beams at

story-3 at 0.345W (W= Total weight of structure)

where as in case of NLS-02 the collapse load occurs at

fourth storey at 0.547W as eminent from figure 4 and 5 as

well.


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Figure-4 Lateral Displacements and Storey Drift Ratios for NLS-01

Figure-5 Lateral Displacements and Storey Drift Ratios for NLS-02

Time history record of October 08, 2005 at

Islamabad is collected and TH-01 is prepared in ETABS.

Time history record is shown in Figure -6. Time historyanalysis of NICL building is carried out using ETABS

and buildings response is studied.

TH-01 analysis of NICL building reveals that the

structure suffered maximum displacement at roof with

magnitude of 3.40 inches at time of 71 second and global

drift of 0.13%. At this displacement magnitude and

global drift ratio the structure should not suffer any crack

in non structural walls whereas NICL building actually

suffered cracks in its non structural walls.

Further more the floor acceleration at roof after

TH-01 analysis comes to be 0.033g. At this magnitude of

floor displacement the occupants should not experience

any sever shaking whereas the occupants at top floorexperienced violent shaking. It means that the time

history record is probably scaled down. The displacement

response of NICL building at roof is shown in figure-7

and acceleration response is shown in figure-8.

As the time history record at Nilor for October

08, 2005 earthquake in Kashmir and Hazara seems to be

scaled down so TH-02 is prepared in ETABS. In order to

perform time history analysis of NICL building for scaled

up time history, Original E-W component is scaled up to

achieve the value of global drift of 1.0% and to the reach

peak acceleration of 0.2g to make it compatible with

seismic zone factor of seismic zone 2b. The Scaled up E-W Component of October 08, 2005 earthquake at Nilor is

shown in figure-9.

Figure -6 E-W Component of Kashmir Hazara

Earthquake at Nilore(WAPDA, LAHORE)


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Figure-7 Displacement Response of NICL building at

Roof for E-W Component

Figure -8 Acceleration Response of NICL building at

Roof for E-W Component

Figure -9 Scaled up E-W Component of Kashmir

Hazara Earthquake at Nilore (WAPDA,

LAHORE)

TH-02 analysis of NICL building reveals that the

structure suffered maximum displacement of 30.76

inches at time of 71 second and global drift of 1.13%.

The displacement response at roof of NICL building is

shown in figure 4.21. Further more the peak acceleration

observed is 0.296g at roof. Acceleration response of

NICL building is shown in figure -10.

Figure -10: Displacement Response of NICL Building

at Roof for E-W Component.

Conclusions: It is concluded that the change in seismic

zoning has not threatened the stability of NICL building

which is because of its proper design, detailing and

construction. According to the previous building code of

Pakistan, it is concluded that the buildings which are

designed according to previous building codes when

analyzed according to present building code of Pakistan

with revised parameters should satisfy seismicrequirements. However, if it is not the case then they

were not either properly designed or were poorly

constructed.

REFERENCES

Applied Technology Council (ATC), Seismic

Evaluation and Retrofit of Concrete Buildings,

Vol.1. Report No. SSC 96-01 (ATC-40): (1996)

Building code of Pakistan,section-2, seismic hazard

studies, (1986).

Building Code of Pakistan. Section 5. Seismic design

parameters:(2007).Erduran, E. and A. Yakut. Drift based damage functions

for Reinforced Concrete Columns. Computers

and Structures. Vol. No. 82/2-3: 121-130 (2004)

Federal Emergecny Management Agency. NEHRP

Guidelines for Seismic Rehabilitation of

Buildings, FEMA 273. (1997)

Gulten G. F. and G. Calim. A Comparative Study of

Torsionally Unbalanced Multi-Story Structures


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Under Seismic Loading, Istanbul Technical

University, Civil Engineering Department: 11

19 (2003).

Hugo, B. Seismic Conceptual Design of Buildings, Basic

principles for engineers, architects, building

owners and authorities, Urgent Action Needed.

(2003) http://www. preventionweb. net/english/

professional/ publications/ v.php?id=687

accessed on 15-02-11.

Park Y. and F. Alfredo H.S. Ang. Mechanistic seismic

damage model for reinforced concrete. Journal

of Structural Engineering. Vol. 111(4):722-39

(1985).

Sheikh Ahsan M. and M. Hussain Saif. Pakistan

Earhquake reconstruction and recovery program:

Structural Engineering consideration. (2008)

www.structuremag.org/article.aspx?articleID=7

93 accessed in January 2011.

Yun, S.; R. Hamburger; C.C. Allin and F. D.A. Seismic

Performance evaluation for steel moment

Frames. Postdoctoral Research Associate of

Civil and Environmental Engineering.

University of Illinois, 205N. Mathews Ave., IL

61801, (2006).

Ilyas, M. and M. Rizwan. Devastating effects of

Kashmir-Hazara Earthquake. Proceeding of The

International Conference and Expo on Safe and

Quality Building in Asia Review of Practices .

March 28-29, Lahore, Pakistan. (2006)
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