SEISMIC ANALYSIS OF THE ‘SOUTH GATE’ TALL BUILDING ACCORDING TO EUROCODE 8.pdf

THE STRUCTURAL DESIGN OF TALL AND SPECIAL BUILDINGS

Struct. Design Tall Spec. Build. 14 , 59–67 (2005)

Published online 14 October 2004 in Wiley Interscience (www.interscience.wiley.com). DOI:10.1002/tal.261

SEISMIC ANALYSIS OF THE ‘SOUTH GATE’ TALL BUILDING

ACCORDING TO EUROCODE 8

E. M. WDOWICKA, J. A. WDOWICKI* AND T. Z. B ´ LASZCZY ´ SKI

Institute of Structural Engineering, Poznan University of Technology, Poznan, Poland

SUMMARY

The tallest building designed in Poznan (western part of Poland) is the case study. The analysed building is a

multifunctional ofﬁce centre with the heliport on the top, called the ‘South Gate’. The main structure is the RC

slab and column system with shear walls and cores. After many static analyses the seismic analysis, based on

damage limitation state according to Eurocode 8, was made. The analysis, in which a continuous–discrete

approach and the response spectrum technique were applied, was carried out by means of the DAMB program

Wiley & Sons, Ltd.

1. INTRODUCTION

In tall buildings the lateral loads that arise from effects of wind and earthquakes are often resisted by

a system of coupled shear walls acting as vertical cantilevers. It is possible to perform the analysis of

shear wall structures using either the discrete method or the continuous one (Stafford-Smith and Coull,

1991). In the continuous approach, the horizontal connecting beams, ﬂoor slabs and vertical joints are

substituted by continuous connections. In recent years the use of continuum models in structural analy-

sis has received considerable attention. These models offer an attractive, low-cost method for analysing

large structures and they represent a useful tool for design analysis.

For the dynamic analysis it is convenient to use a hybrid approach based on the analysis of an equiv-

alent continuous medium and a discrete lumped mass system (Aksogan et al ., 2003; Li and Choo,

1996; Wdowicki et al ., 1984; Wdowicki and Wdowicka, 1991). In order to obtain the required ﬂexi-

bility matrix it is necessary to determine horizontal displacements of the shear wall system, subjected

to concentrated loads.

The paper presents results of the seismic analysis based on the above-mentioned method. The subject

of the analysis is the tall building, designed originally in Poznan, which is stiffened by the system of

coupled shear walls. This building is called, because of its elevation shape and its location in the city,

the ‘South Gate’ (see Figure 1). It is a multifunctional ofﬁce centre with a heliport on the top.

After multi-variant static analyses the possibility of seismic location of the designed structure was

taken into account. Seismic analysis was carried out by means of the response spectrum technique

using the DAMB program (Wdowicki et al ., 1995b), as part of an integrated system (Wdowicki

et al ., 1995a). The design spectrum for elastic analysis according to Eurocode 8, Draft No. 6 (PrEN

* Correspondence to: Jacek Wdowicki, Institute of Structural Engineering, Poznan University of Technology, ul. Piotrowo 5,

60-965 Poland. E-mail: jacek.wdowicki@put.poznan.pl

Received December 2003

Accepted March 2004

E. M. WDOWICKA ET AL.

Figure 1. Analysed building: the South Gate

1998-1:200X, 2003) was used. To meet the requirements of damage limitation according to Eurocode

8 the allowable design ground acceleration was evaluated.

2. BUILDING DESCRIPTION

The ‘South Gate’ is designed as a fully smart building designed by the inverse method. The whole

structure is divided by movement joints into three parts: two symmetrical outer parts and one inner

part, because of the building length (about 100 m). The stiffness of each part is designed from the

equilibrium of deﬂection of each one. The ﬂoor layouts of the analysed building are shown in

Figure 2.

The total height of the building is 108·6 m. The main structure is the RC ﬂat slab and column system

with shear walls and cores. The columns are on a grid of 7·5 ¥ 7·8 m or 7·5 ¥ 4·65 m. There are three

basement ﬂoors and 26 ﬂoors above the ground (see Figure 3). Shear walls and cores will be con-

structed in RC, 0·7 to 0·3 m in thickness. They will be slip formed. Continuous ﬂoor RC slabs sup-

ported on columns have a depth of 0·20–0·35 m. The pin connections between columns and slabs have

been designed. RC elements are assumed as B50 (concrete grade) and material properties are taken

to be E = 38·6 GPa, G = 16·54 GPa. The ground at the site in Poznan basically consists of stiff sandy

clay and medium-dense sand. The foundation system under the slab–column part is the slab founda-

tion with a depth of 0·8–1·5 m, but due to bearing capacity of the soil the foundation system under

shear walls and cores is based on RC diaphragm walls and barrettes. External basement walls are also

diaphragm walls.

Struct. Design Tall Spec. Build. 14 , 59–67 (2005)

SEISMIC ANALYSIS OF THE ‘SOUTH GATE’

Figure 2. Floor layouts of the South Gate

3. MODEL AND THEORETICAL BACKGROUND OF ANALYSIS

In the analysed building, lateral loads that arise as a result of winds and earthquakes are resisted by

the three-dimensional system of coupled shear walls (see Figure 4). A single wall or a group of walls

joined in a monolithic way composes a 3D shear wall. The considered shear walls are of the same

height. They are joined by connecting beam bands. The structural properties of shear walls and lintels

are uniform along the building height. A diaphragm action of all ﬂoor slabs is taken into considera-

tion as the effect of their in-plane inﬁnite rigidity and negligible transverse one. Owing to the height-

to-width ratio of the shear walls, there is a possibility of treating each wall as an open thin-walled

beam, according to Vlasov theory assumptions.

The static analysis was carried out on the basis of some variant of the continuous connection method

(Wdowicki and Wdowicka, 1993). In the continuous connection method lintel beams are treated as

the equivalent shear connection medium between shear walls, while the walls are simply regarded as

vertical cantilevers. The technique may be used for both plane and spatial structures, which are essen-

tially regular in form throughout the height. The solution has the merit of being independent of the

number of storeys involved and, in fact, the accuracy increases as the number of storeys rises.

Dynamic solutions have been obtained by treating the structure as a lumped parameter system with

discrete masses in the form of rigid ﬂoor slabs arbitrarily located along the height, having ﬂexural and

torsional inertia (Wdowicki et al ., 1984). A dynamic model with masses in the form of rigid ﬂoor slabs

has been adopted, since over a half of building total mass is concentrated on the ﬂoor levels. Coupled

torsional-ﬂexural vibrations have been considered because the torsional response of buildings during

ambient and earthquake response is signiﬁcant (Hart et al ., 1975). For shear wall multistorey struc-

ture it is more natural to determine the ﬂexibility matrix D than stiffness matrix K. The vibration of

a structure is described by the following relation (Clough and Penzien, 1993):

Struct. Design Tall Spec. Build. 14 , 59–67 (2005)

E. M. WDOWICKA ET AL.

Figure 3. Cross-section of the South Gate

DMx DCx x DF

+ + =

(1)

where D, M and C are ﬂexibility, mass and damping matrices, respectively; x is the d -element vector

of generalized coordinates; d is the number of dynamic degrees of freedom of the calculated struc-

ture; and F is the d -element vector of generalized excitation forces, corresponding to generalized

coordinates.

Calculations were made using the DAMB program (Dynamic Analysis of Multistorey Buildings)

(Wdowicki et al ., 1995b), which provides the possibility of performing linear dynamic analysis of 3D

shear wall structures.

Struct. Design Tall Spec. Build. 14 , 59–67 (2005)

˙˙

SEISMIC ANALYSIS OF THE ‘SOUTH GATE’

Figure 4. 3D structural system of analysed building

The ﬂexibility matrix D is generated from the exact solution of the governing differential equation

for a 3D continuous model. Also mass matrix is generated exactly according to the real distribution

of walls, connecting beams and ﬂoor slabs and including ﬂexural and torsional inertia. The seismic

response of the structure is estimated using the response spectrum technique. The steps involved are

as follows:

(1) determination of natural frequencies and mode shapes;

(2) evaluation of modal participation factors and calculation of modal loading on the structure (using

an appropriate design spectrum);

(3) determination of response estimate taking into account the contribution from the given number of

modes for various parameters of interest (using three methods: SRSS—the square root of the sum

of the squares; CQC—the complete quadratic combination; and DSC—the double sum combina-

tion (Maison et al ., 1983)).

4. RESULTS OF THE SEISMIC ANALYSIS

As a result of the ﬁrst calculation step by DAMB, periods and corresponding mode shapes for the

outer part of the building have been received. The periods of the ﬁrst 10 modes are summarized in

Table 1.

In the analysed case, frequencies of the ﬁrst two translational modes are closely spaced. When the

modal responses for different modes are coupled, according to Eurocode 8 a more accurate procedure

than the SRSS method for the combination of the modal maxima will be adopted. Our previous analy-

sis serves as the basis of choosing the CQC method (Wilson et al ., 1981).

Struct. Design Tall Spec. Build. 14 , 59–67 (2005)

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