Structural Engineering and Mechanics, Vol. 41, No. 1 (2012) 67-81

67

Differential quadrature method for free vibration analysis
of coupled shear walls
K.B. Bozdogan*
Department of Civil Engineering, Cumhuriyet University, Sivas, Turkey(Received January 6, 2011, Revised July 17, 2011, Accepted November 30, 2011)
Abstract. Differential Quadrature Method (DQM) is a powerful method which can be used to solve
numerical problems in the analysis of structural and dynamical systems. In this study the governing
equation which represents the free vibration of coupled shear walls is solved using the DQM method. A
one-dimensional model has been used in this study. At the end of study various examples are presented toverify the accuracy of the method.
Keywords: differential quadrature method; coupled shear wall; free vibration; continuum model; sandwich beam

1. Introduction
Shear walls are structural systems commonly used in the construction of high rise buildings toincrease resistance to horizontal loads, such as wind and seismic loads acting on the buildings. They
are specifically designed to react to these kinds of loads, by taking into consideration theenvironmental features and stipulated building codes of the country. Shear walls which have
openings and vertical rows for windows and doors, due to architectural concerns, are called coupledshear walls.
There are a great number of studies dealing with the vibrational analysis of high-rise buildings
containing coupled shear walls in their structure (Rosman 1964, Smith 1970, Cheung et al. 1977,
Basu et al. 1979, Coull and Smith 1984, Chaallal 1992, Kwan 1993, 1995, Li and Choo 1996,
Chaallal and Ghmallar 1996, Chaallal et al. 1996, Kuang and Chau 1998, Ha and Tan 1999, Rashed2000, Kim and Lee 2003, Aksogan et al. 2003, Zeidabadi et al. 2004, Wang and Wang 2005,
Aksogan et al. 2007, Bozdogan et al. 2009, Resatoglu et al. 2010, Takabatake 2010).
Rosman (1964) proposed a continuous medium method for a pair of high rise coupled shear walls.
Basu (1979) presented the seismic design charts for buildings containing coupled shear walls. In the
study of Li and Choo (1996) a hybrid approach that is based on the analysis of equivalent continuous
medium and a discrete lumped mass system for free vibration analysis of stiffened pierced walls on
flexible foundations was proposed.
On the other hand several modeling approaches and numerical solutions are suggested in these*Corresponding author, Ph.D, E-mail: kbbozdogan@yahoo.com.tr

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K.B. Bozdogan

studies and in the literature for free vibration analysis of the buildings that contain coupled shear
walls in their structures. Most of them make use of numerical differentiation in calculations. Althoughcomputational power and the speed of computer technology is increasing rapidly, numerical methods
and algorithms should meet the increasing amount of data. The finite difference method is a wellknown numerical method used to approximate the derivatives of differential equations. Howeverconvergence to the solution is slow.
In this study, we propose a method that employs Differential Quadrature Method (DQM) for freevibration analysis of structures containing coupled shear walls based on the continuous system model.
Similar studies in the past used conventional numerical methods, such as the Finite Difference(FE) Method to approximate the derivatives of the differential equation that describes the dynamical
behavior of the structures with coupled shear walls. The proposed method improves upon past studies
by utilizing DQM, which is designed for free vibration of the buildings having coupled shear walls
under horizontal loads thereby converging to the solution faster than the methods presented inliterature. In addition, DQM solutions are the most accurate among the solutions proposed so far.

2. Differential quadrature method
DQM rapidly converges to a fairly accurate numerical solution of differential equations in engineering
problems. There are numerous (numerical) approximation of derivatives in numerical analysis;
however, most of them lack simplicity and efficiency in algorithmic construction and computation
aspects. Unlike conventional methods such as Finite Differences (FD) and FE, DQM requires lessgrid points to obtain acceptable accuracy. Proposed by Bellman et al. (1971, 1972), DQM is an
accurate method for solution of nonlinear differential equations in approximation of the derivatives.
The successful application of DQM in mechanics has been demonstrated numerous researchers(Bert et al. 1987, Striz et al. 1988, Shu and Richards 1992, Bert et al. 1993, Striz et al. 1995, Bert
and Malik 1996a, Bert and Malik 1996b, Shu and Hue 1997, Liew et al. 1999, Liew and Teo 1999,
Liew et al. 2001, Karami and Malekzadeh 2003, Civalek 2004a, Civalek and Ülker 2004, Civalek
2005, Malekzadeh and Farid 2007, Kaya 2010, Efthekhari and Jafari 2011).
Another advantages of DQM is that it transforms the differential equations into a set of analogous
algebric equations in terms of the unknown function values at the resampled points in the solution
domain (Civalek 2004b).

3. System model
Coupled shear walls do not exhibit Timoshenko or Euler Bernoulli beam behavior. Rather, they
behave as a beam having a combination of the two. A beam exhibits both is defined as sandwich
beam (Fig. 1).

4. Governing equations and boundary conditions
The governing equations of coupled shear walls can be written as

Differential quadrature method for free vibration analysis of coupled shear walls69

Fig 1. Physical model of coupled shear wall2

4
2
∂ Ub ( z, t ) ∂ 2 U ( z, t )∂ U ( z, t )∂ U ( z, t )K–-------------------+
K- + p --------------------=0
EI -------------------ss ---------------------4
2
2
2
∂z
∂z
∂t
∂z

(1)

where p is the mass per unit length, U represents the total shape function, z represents the verticalaxis, dUb/dz represents the rotation angle of bending of coupled shear walls
U and Ub are to be a function of circular frequency ωU(z, t) = X(z)sin(ω t)(2a)

Ub(z, t) = Xb(z)sin(ω t)(2b)

When the Eq. (2) is substituted into Eq. (1), the resulting Eq. (3) is
2

4
2
Xb
dX
2
X+K d
-------- – pω X = 0
EI --------4 – Ks ds ---------2
2
dz
dz
∂z

(3)

The shear force equilibrium for beam on the right side (Fig. 1) can be written as
3

dX
d Xb
dX
- + Ks ------ – Ks --------b = 0
D ---------3
dz
dz
dz

(4)

Ks is the equivalent shear rigidity of coupled shear walls (Fig. 2) and can be calculated as (Potzta
and Kollar 2003)
1
Ks = ----------------------1 1⎞⎛ ----- + ----⎝ Rw Rb⎠(5)

where Rw is
n 12EI
pj
Rw = ∑ -------------2
j = 0 hi(6)

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K.B. Bozdogan

Fig. 2 Coupled shear wall

For coupled shear walls which consists of n walls and n−1 connecting beams, Rb can be calculated
from Eq. (7) (Potzta and Kollar 2003)
2

2

n – 1 6EI [ ( d + s ) + ( d + s
bjjjj
j + 1) ]Rb = ∑ ------------------------------------------------------------------12kEI
3 ⎛
bj⎞
j=1
dj h 1 + -----------------2⎝
GAbj dj ⎠(7)

where, h is the height of the storey, dj and sj are the length of the jth wall (Fig. 2).
EIbj and GAbj represent the flexural rigidity of the connecting beam and the shear rigidity ofconnecting them, respectively. k is the constant that depends on the shape of the cross-section of thebeams (k = 1.2 for rectangular cross-sections).
EI is the total bending rigidity of the shear walls and D represents the global bending rigidity of
the coupled shear wall that can be calculated asn

D = ∑ EAj rj

2

(8)

j=1

where Aj is the cross sectional area of the jth shear wall, n is the number for walls and rj is the
distance of the jth shear wall from the center of the cross sections.
The non-dimensional form of the governing Eqs. (3) and (4) can be written as
2

4
2
dX
X 2d X--------4 – k2 d--------2 + k ----------2-b – mX = 0
dξ
dξ
dξ

(9)

3

dX
2 dX
----------3-b + s2 dX------ – s --------b = 0dξdξdξThe parameters ξ, k, s and m are defined in Table 1.

(10)

Differential quadrature method for free vibration analysis of coupled shear walls

71

Table 1 The Parameters used in the problem and their definitions
Parameter

Definition

ξ

z
---H

k

K
H -----s
EI

sK
H -----s
D

m

p 4 2
-----H ω
EI

The boundary conditions of a coupled shear wall can be written as
X(0) = 0(11)dX ( 0 )-------------- = 0
dξ

(12)

dXb ( 0 )---------------- = 0
dξ

(13)

2

d X(1)---------------=0
2
dξ

(14)

2

d Xb ( 1 )-----------------=0
2
dξ

(15)

d
X ( 1 ) 2 ⎛ dX( 1 ) dXb ( 1 )⎞---------------– k -------------- – ---------------=0
3
⎝
dξ
dξ ⎠
dξ

(16)

3

5. Solution of the governing equations for wall-frame structures using DQM
We consider a one- dimensional problem, as shown in Fig. 3. It is assumed that the function X(ξ)
is smooth over the whole domain.
If it is assumed that X and Xb are polynomials of degree n − 1, the function of X can be written as(Shu 2000)n

X = ∑ ai – 1 * ξ
i=1

i–1

(17)

72

K.B. Bozdogan

Fig. 3. Discretization of one dimensional problemn

Xb = ∑ bi – 1 * ξ

i–1

(18)

i=1

where ai−1 is the coefficient vector and n is the number of nodes.
Using Eq. (17) and Eq. (18), the derivatives of X and Xb of ξ can be written asndX------ = ∑ ( i – 1 ) * ai – 1 * ξ i – 2dξ i = 1

(19)

n
dX
--------b = ∑ ( i – 1 ) * bi – 1 * ξ i – 2
dξ
i=1

(20)

n
dX
--------2 = ∑ ( i – 1 ) * ( i – 2 ) * ai – 1 * ξ i – 3
dξ
i=1

(21)

2

2

n
d Xb
----------2- = ∑ ( i – 1 ) * ( i – 2 ) * bi – 1 * ξ i – 3
dξ
i=1

(22)

n
dX
--------3 = ∑ ( i – 1 ) * ( i – 2 ) * ( i – 3 ) * ai – 1 * ξ i – 4
dξ
i=1

(23)

3

3

n
d Xb
----------3- = ∑ ( i – 1 ) * ( i – 2 ) * ( i – 3 ) * bi – 1 * ξ i – 4
dξ
i=1

(24)

n
dX
i–5
-------( i – 1 ) * ( i – 2 ) * ( i – 3 ) * ( i – 4 ) * ai – 1 * ξ
=
∑
4
dξ
i=1

(25)

4

Differential quadrature method for free vibration analysis of coupled shear walls

73

4

n
d Xb
----------4- = ∑ ( i – 1 ) * ( i – 2 ) * ( i – 3 ) * ( i – 4 ) * bi – 1 * ξ i – 5
dξ
i=1

(26)

Then the functional values in the whole domain are
X1 = X(0) = a0

(27.1)

Xb1 = Xb(0) = b0

(28.1)n

X2 = X(h) = a0 + a1h + ...... + a1h(27.2)

Xb2 = Xb(h) = b0 + b1h + ...... + b1hn

(28.2)

Xn = X(n*h − h) = a0 + a1*(h*n − h) + ...... + an*(h*n − h)n(27.n)

Xbn = Xb(n*h − h) = b0 + b1*(h*n − h) + ...... + bn*(h*n − h)n(28.n)

Where h is the distance of two grid points and is equal to 1/(n − 1).
Eq. (29) represents the matrix form of Eqs. (27.1), (27.2)….. (27.n)
X1

1

0

. . . .

0
n

X2

1

h

. . . .

h

.

.

.

. . . .

.

.

= .
.

.
.

. . . .
. . . .

.
.

.

a0

a0

a1

a1

.

.
=A

.

(29)

.

.

.

n

n

an – 1an – 1

n

n

an

an

b0

b0

b1

b1

Xn – 11 ( n – 2 )*h . . . . ( n – 2 ) *hXn

1 ( n – 1 )*h . . . . ( n – 1 ) *h

Eq. (30) shows the matrix form of Eqs. (28.1), (28.2)….. (28.n)
Xb1

1

0

. . . .

0
n

Xb2

1

h

. . . .

h

.

.

.

. . . .

.

.

= .
.

.

. . . .

.

. . . .

.

.

.

.

.
=B

.
.

.

n

n

bn – 1

bn – 1

n

n

bn

bn

Xb(n – 1)

1 ( n – 2 )*h . . . . ( n – 2 ) *h

Xbn

1 ( n – 1 )*h . . . . ( n – 1 ) *h

(30)

.

Using Eqs. (19), (20) and (23), Eq. (10) can be written asn∑ ( i – 1)*( i – 2 )*( i – 3 )*bi – 1 *ξ
i=1

i–4

2

n

+ s ∑ ( i – 1 )*ai – 1 *ξi=1Using Eq. (31), Matrix Eq. (32) can be written as

i–2

2

n

– s ∑ ( i – 1 )*bi – 1 *ξ
i=1

i–2

=0

(31)

74

K.B. Bozdogan

C

a0

b0

a1

b1

.

.

.

=D

.

.

.

an – 1

bn – 1

an

bn

(32)

The elements of matrices C and D can be written as
C(1,1) = 1(33)

C(i, i) = s2*(i− 1) i = 2......n(34)

C(i, j) = C(j, i) = 0 i ≠ j(35)

D(1,1) = 1(36)

D(i, i) = s2*(i − 1) i = 2......n(37)

D(i, i + 2) = −(i + 1)*(i)*(i − 1) i = 2......n(38)

D(i, j) = 0 i ≠ j and j ≠ i + 2(39)

Using Eqs. (25), (21), (22), (17) in Eqs. (9) and Eq. (11), (12), (13), (14), (15), (16); Matrix Eq.
(40) is formed as given in the equation

E

a0

b0

a1

b1

.

.

.

=F

.

.

.

an – 1

bn – 1

an

bn

(40)

The components of the matrices E and F are to be as follow.
E(1,1) = 1(41)

E(1, i) = 0 i = 2......n(42)

F(1, i) = 0 i = 1......n(43)

E(2, 2) = 1(44)E(2, i) = 0 i = 1, 3., 4......n(45)

Differential quadrature method for free vibration analysis of coupled shear walls

75

F(2, i) = 0 i = 1......n(46)

F(3,2) = 1(47)

F(3, i) = 0 i = 1, 3., 4......n(48)

E(3, i) = 0 i = 1......n(49)

E(n − 2, i) = (i − 1)*(i − 2) i = 1......n(50)

F(n − 2, i) = 0 i = 1......n(51)

F(n − 1, i) = (i − 1)*(i − 2) i = 1......n(52)

E(n − 1, i) = 0 i = 1......n(53)

E(n, i) = (i − 1)*(i − 2)*(i − 3) − k2*(i − 1) i = 1......n(54)

E(n, i) = − k2*(i − 1) i = 1......n(55)

E(j, i) = (i − 1)*(i − 2)*(i − 3)*(i − 4)*(j*h − h)i−5 − k2*(i − 1)*(i − 2)*(j*h − h)i−3 − m*(j*h − h)i−1 (56)F(j, i) = − k2*(i − 1)*(i − 2)*(j*h − h)i−3(57)

Using Eq. (32), Eq. (58) can be written as
b0

a0

b1

a1

.

.
–1

=D C

.
.

(58)

.
.

bn – 1an – 1bnan

By using Eq. (58) in Eq. (40)
a0

a0

a0

0

a1

a1

a1

0

.

.

.

= .

.
E

.

.
–1

= FD C.

–1= ( E – FD C )

.

.

.

.

an – 1an – 1an – 1

an

an

an

0
0

are obtained.
Finally, using Eq. (29) and Eq. (59), Eq. (60) can be obtained

(59)

76

K.B. Bozdogan–1( E – FD C )A

–1

X1

X1

0

X2

X2

0

.

.

.

.

= .

.

.

Xn – 1

Xn – 1

.
0

Xn

Xn

0

.

=Z

(60)

The values of ω which set the determinant of Z matrix to zero, which include the weight coefficients,
are the circular frequencies.

6. Numerical examples
In order to verify the presented method, three numerical examples have been solved by a program
written in MATLAB. The results are compared with those found in literature.

Fig. 4. A 20 storey coupled shear wall

Differential quadrature method for free vibration analysis of coupled shear walls

77

Table 2 The numerical data for the coupled shear wall (Example 1)
Geometric and Structural Properties of Coupled Shear Wall
Young Modulus

3.6*1010 N/m2

Mass Density

2.4* 103 kg/m3

Poisson Ratio

0.15

Total storeys

20

Total Height

56

Thickness of Left Side Wall

0.3

Width of Left Side Wall

5.0

Thickness of Right Side Wall

0.3

Width of Right Side Wall

7.0

Thickness of Lintel

0.3

Height of Lintel

0.4

Length of Lintel

2.0

Table 3 Natural frequencies for Example 1 (rd/s)
Mode

NASTRAN
Takabatake (2010)

DQM (n = 13)

DQM (n = 15)

1

13.09

12.94

12.94

2

55.55

57.63

57.57

3

129.00149.63140.864224.90-254.72

Example 1
A 20-storey building with coupled shear wall system (Fig. 4) is analyzed in this example. The
numerical data for the coupled shear wall are given in Table 2. The first four natural frequencies arecalculated by using DQM and compared with those found in the literature (Takabatake 2010) in
Table 3. In the study of Takabatake (2010) NASTRAN is used to solve the problem.
Example 2
Consider the coupled shear wall system shown in Fig. 5. The coupled shear wall with three bays
consists of 12 storeys, has the following properties: E = 20*1010 kN/m2, p = 24 kN/m3.
The height of each connecting beams is 31 cm and the thickness of the wall is 16 cm everywhere.
The coupled shear wall is taken from the study of (Aksogan et al. 2007) and the problem in the
study is analyzed in both aspects using continuous connection and finite element methods. Freevibration analysis is carried out and it is compared to those found in the literature (Aksogan et al.
2007) (Table 4).

78

K.B. Bozdogan

Fig. 5 Geometric properties of structure in Example 2
Table 4 Comparison of natural frequencies in Example 2 (Hz)Mode

SAP 2000
Aksogan et al. (2007)

DQM (n = 13)

DQM (n = 15)

1

3.030

3.042

3.070

2

12.00412.512

12.2883

25.96927.46226.536442.884-42.739

Example 3
A twenty-six storey building, with coupled shear walls, is designed by taking into consideration
the seismic loads of the zone it is built in (Fig. 6).
The horizontal loads are counteracted by six parallel coupled shear walls whose properties are
given as follows:
The thickness of the shear wall is 0.305 m and the thickness of the floor slab is 0.203 m. Also
d1 = 1.68 m, s1 = s2=7.32 m, H = 71.32 m, h = 2.743 m, E = 25*106 kN/m2. The distributed mass ofthe building (per unit height) is estimated to be 327.3*103 kg/m.

Fig. 6 Floor plan of 26- story flat- slab shear wall building (Example 3)

Differential quadrature method for free vibration analysis of coupled shear walls

79

Table 5 Comparison of natural frequencies in Example 3 (Hz)Mode

Chai and Chen (2009)

DQM (n = 13)

DQM (n = 15)

1

1.599

1.600

1.600

2

0.358

0.357

0.358

3

0.148

0.141

0.149

In this example the first four periods of the building are approximated and compared to the study(Chai and Chen 2009) in Table 5.

7. Conclusions
In this study the governing equations for the free vibration analysis of coupled shear walls areformulated and solved numerically using DQM. The whole structure is modeled as a sandwich beamin this method. The governing differential equations of the sytems given in the examples are solved
using DQM.
It is observed that the DQM provides satisfactory results. When n is 15, the error for the firstmode is less than 1.32% when DQM is used. This method is suitable for the first three modes.
DQM converges faster than FD and FM even though less grid points are used. Also the results are
better compared to those achieved by using other methods. The main advantages of the Differential
Quadrature Method are its inherent conceptual simplicity and the fact that it is easily programmable.
Therefore, it can be used at the concept design stage.

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