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Journal of Theoretical and Applied Mechanics, Soﬁa, Vol. 48 No. 1 (2018) pp. 46-58

DOI: 10.2478/jtam-2018-0004

NUMERICAL SOLUTIONS FOR NONLINEAR HIGH DAMPING

RUBBER BEARING ISOLATORS: NEWMARK’S METHOD WITH

NETWON-RAPHSON ITERATION REVISITED

A.A. MAR KOU1∗, G.D. MANOLIS2

1Norwegian Geotechnical Institute, Sognsveien 72, Oslo 0806, Norway

2Department of Civil Engineering, Aristotle University Panepistimioupolis,

Thessaloniki 54124, Greece

[Received 10 October 2017. Accepted 04 December 2017]

ABS TRACT: Numerical methods for the solution of dynamical problems in

engineering go back to 1950. The most famous and widely-used time step-

ping algorithm was developed by Newmark in 1959. In the present study, for

the ﬁrst time, the Newmark algorithm is developed for the case of the trilin-

ear hysteretic model, a model that was used to describe the shear behaviour of

high damping rubber bearings. This model is calibrated against free-vibration

ﬁeld tests implemented on a hybrid base isolated building, namely the Solarino

project in Italy, as well as against laboratory experiments. A single-degree-of-

freedom system is used to describe the behaviour of a low-rise building isolated

with a hybrid system comprising high damping rubber bearings and low fric-

tion sliding bearings. The behaviour of the high damping rubber bearings is

simulated by the trilinear hysteretic model, while the description of the be-

haviour of the low friction sliding bearings is modeled by a linear Coulomb

friction model. In order to prove the effectiveness of the numerical method

we compare the analytically solved trilinear hysteretic model calibrated from

free-vibration ﬁeld tests (Solarino project) against the same model solved with

the Newmark method with Netwon-Raphson iteration. Almost perfect agree-

ment is observed between the semi-analytical solution and the fully numerical

solution with Newmark’s time integration algorithm. This will allow for ex-

tension of the trilinear mechanical models to bidirectional horizontal motion,

to time-varying vertical loads, to multi-degree-of-freedom-systems, as well to

generalized models connected in parallel, where only numerical solutions are

possible.

KEY WORDS: High damping rubber bearings; mechanical models; trilinear

hysteretic model; shear behaviour; nonlinear response; base isolation; New-

mark’s method.

∗Corresponding author e-mail: athanasiosmarkou@gmail.com

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Numerical solutions for nonlinear HDRBs 47

1. INTRODUCTION

The ﬁrst time stepping algorithm was constructed by Houbolt [1] within the context

of solving for the dynamic response of aircraft frames using matrix methods of anal-

ysis. It was basically nothing more than a simple central difference method, whereby

velocities and accelerations were written in terms of displacements computed in the

immediately previous time steps. Within the next few years, Newmark [2] published

his landmark paper on what become Newmark’s method for the transient response

of buildings to earthquake-induced loads. His method was versatile because there

were two artiﬁcial parameters (β, γ ) that could be ‘tweaked’ to produce time step-

ping algorithms with different properties. For instance, there was a range of values

that yielded an unconditionally stable numerical integration algorithm, not to mention

that the central difference algorithm could also be recovered as a special case. Since

then, the terminology ‘Newmark-beta’ has been used to demarcate what are explicit

algorithms, in contrast to the newer development of implicit algorithms that over-

shoot the immediately next time step and then move backwards in order to correct it.

A comprehensive review of the truly explosive amount of work done on deriving a

plethora of numerical integration algorithms in structural mechanics as early as the

1980’s can be found in the edited book by Belytschko and Hughes [3].

In here, we focus on the nonlinear response of a class of ‘soft’ base isolators

for earthquake protection of conventional buildings known as high damping rubber

bearings (HDRB). These are becoming widely popular in Europe and there are cur-

rently two large ﬁrms that mass produce them according to speciﬁcations set by the

client. The same holds true in Japan, while in the United States a different category

of base isolators known as friction pendulums are popular. Recently, the authors

have developed a generalized trilinear hysteretic model (THM) that best describes

the mechanical response of HDRB specimens under harmonic excitation of variable

frequency that leads to induced strains of up to 200% [4]. In contrast with the basic

THM and its predecessor, the bilinear hysteretic model (BHM), which can be solved

analytically, this is no longer the case with the generalized THM. Therefore, it is im-

perative to develop variants of the Newmark-beta method that are specially tailored

for highly nonlinear response of a single-degree-of freedom representation. This al-

gorithm needs to be calibrated against experimental results so that its accuracy can

be established.

More speciﬁcally, in the next section, we present the physical model developed

to describe the behaviour of a low-rise building, namely the Solarino building [5],

isolated with hybrid base isolation system (HBIS). Next, the mechanical models for

the isolation system are presented. In the following section, the Newmark method

with the Newton-Raphson iteration scheme is presented for the case of the THM,

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48 A.A. Markou, G.D. Manolis

while in the subsequent section, the comparison between the numerical and semi-

analytical solution is shown and ﬁnally in the last section the conclusions are drawn.

2. PHY SI CA L MO DE L

In 2004 in Solarino, Eastern Sicily two reinforced concrete buildings were retroﬁtted

by using a HBIS and subsequently tested under free vibration excitation, where the

accelerations of the structure were recorded, [5], see Fig. 1. The hybrid isolation

system comprises HDRB with low friction sliding bearings (LFSB), see Fig. 2. The

recorded accelerations were used in order the physical parameters of the system to be

identiﬁed, [6]. Speciﬁcally, the physical model of the structure is a single-degree-of-

freedom (SDOF) system describing the behaviour of the Solarino building is shown in

Fig. 3. THM describes the shear behaviour of HDRB (see Fig. 4), a linear Coulomb

friction model (LDFM) describes the shear behaviour of LFSB (see Fig. 5) and a

linear viscous damping (LVD) accounts for any additional source of damping.

Table 1. Physical parameters of the SDOF system of the Solarino building

HDRB LDSB LVD Mass

kekh1kh2fsucffkfc m

[kN/m] [kN/m] [kN/m] [kN] [m] [kN] [kN/m] [kNs/m] [kNs2/m]

14770 21920 13745 172 0.0285 34 35 197 1284

Fig. 1. The Solarino building.

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Numerical solutions for nonlinear HDRBs 49

Fig. 2. (a) High damping rubber bearing (HDRB) and (b) low friction sliding bearing (LFSB)

of the Solarino building.

Fig. 3. Single-degree-of-freedom (SDOF) system of the Solarino building.

The compatibility, equilibrium and constitutive equations of THM are presented

in Table 2, where fTdenotes the force in THM. The constitutive equation of the

LCFM is given by the following expression:

(2.1) fF= (ff+kf|u|)sign( ˙u),

where fFdenotes the force in the LCFM, udenotes the displacement, ˙uthe velocity,

ffdenotes the force at zero displacement and kfthe slope, see Fig. 5. The rela-

tionships between the mechanical parameters shown in Fig. 4(a) and (e) of the THM

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50 A.A. Markou, G.D. Manolis

Fig. 4. Trilinear hysteretic model (THM) for the description of the shear behaviour of high

damping rubber bearings: (a) mechanical model, (b) force-displacement graph of element 1,

(c) force-displacement graph of element 2, (d) force-displacement graph of element 3 and (e)

force-displacement graph of THM.

Table 2. Compatibility, equilibrium and constitutive equations of THM

Compatibility u=ue+uh

Equilibrium fT=fe1=fe2+fe3

Constitutive law

fe1=keue

fe2( ˙uh6= 0) = fssgn( ˙uh)

fe2( ˙uh= 0) = fe1−fe3

fe3(|uh| ≤ uc) = kh1uh

fe3(|uh|> uc) = (kh1uc+kh2(|uh| − uc))sgn(uh)

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Numerical solutions for nonlinear HDRBs 51

Table 3. Relationships between mechanical and mathematical parameters of the THM, see

Figs. 4(a),(e)

ke=k0;kh1=k1

k0

k0−k1

;kh2=k2

k0

k0−k2

;fs=k0uy;uc= (u3−uy)k0−k1

k0

are given in Table 3. The constitutive equation of the LVD is given by the following

expression:

(2.2) fV=c˙u ,

where fVdenotes the force in the LVD and cdenotes the damping coefﬁcient.

Fig. 5. Linear Coulomb friction model (LCFM) for the description of the shear behaviour

of low friction sliding bearings: (a) mechanical model and (b) force-displacement graph of

LCFM.

3. NEW MA RK ’S METHOD WITH NEW TON-RAPHON ITERATION

Newmark’s method with Newton-Raphson iteration belongs to the group of implicit

time-stepping procedures for nonlinear systems that are based on assumed variation

of the acceleration, see [7]. The original formulation assumes either a constant aver-

age or a linear variation of the acceleration within a time increment ∆t. The general

form of the method is based on a Taylor series expansion of the velocities and dis-

placements, respectively, at time step i+ 1 in terms of the accelerations as follows:

(3.1) ˙ui+1 = ˙ui+ [(1 −γ)∆t] ¨ui+ (γ∆t) ¨ui+1 ,

(3.2) ui+1 =ui+ (∆t) ˙ui+(0.5−β)(∆t)2¨ui+β(∆t)2¨ui+1 .

For the constant average acceleration method, the parameters introduced by New-

mark are set as γ=1

2and β=1

4, while for the linear acceleration method these

are set as γ=1

2and β=1

6. The above equations combined with the equilibrium

equation at the end of the time step iwill permit us to calculate the revised values

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52 A.A. Markou, G.D. Manolis

ui+1,˙ui+1,¨ui+1 . In particular, the equilibrium equation of the SDOF system of the

Solarino building can be written as follows:

(3.3) m¨u+fV+fT+fF=p ,

where pdenotes the external force. Equation 3.3 can be written in incremental form

(3.4) m¨ui+1 +c˙ui+1 + (fT)i+1 + (fF)i+1 =pi+1 .

Solving Eq. 3.1 for ¨ui+1 , we get a relationship with ui+1

(3.5) ¨ui+1 =1

β(∆t)2(ui+1 −ui)−1

β∆t˙ui−1

2β−1¨ui.

Now substituting Eq. 3.5 to Eq. 3.1, we get

(3.6) ˙ui+1 =γ

β∆t(ui+1 −ui) + 1−γ

β˙ui+ ∆t1−γ

2β¨ui.

Equation 3.4 can also be written as

(3.7) (fS)i+1 =pi+1 ,

where

(3.8) (fS)i+1 =m¨ui+1 +c˙ui+1 + (fT)i+1 + (fF)i+1 .

By using the Taylor series expansion to expand the force (fS)i+1 about the displace-

ment ui+1, which is unknown, and by dropping the higher-order terms, we get

(3.9) (fS)(j+1)

i+1 '(fS)(j)

i+1 +(∂fS)(j)

i+1

∂ui+1

∆u(j)=pi+1 .

By differentiating Eq. 3.8 with respect to the unknown displacement u(j)

i+1, we get

(3.10) ∂(fS)i+1

∂ui+1

=m∂¨ui+1

∂ui+1

+c∂˙ui+1

∂ui+1

+∂(fT)i+1

∂ui+1

+∂(fF)i+1

∂ui+1

.

The derivative of ¨ucan be calculated from Eq. 3.5 and the derivative of ˙ucan be

calculated from Eq. 3.6 we recover the relations

(3.11) ∂¨ui+1

∂ui+1

=1

β(∆t)2;∂˙ui+1

∂ui+1

=γ

β∆t.

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Numerical solutions for nonlinear HDRBs 53

Next, from the above two equations, we get the tangent stiffness of the SDOF as

(3.12) (kS)(j)

i+1 =1

β(∆t)2m+γ

β∆tc+ (kT)(j)

i+1 + (kF)(j)

i+1 ,

where

(3.13) (kT)(j)

i+1 =∂(fT)i+1

∂ui+1 (j)

; (kF)(j)

i+1 =∂(fF)i+1

∂ui+1 (j)

.

Note that kTcan be set equal to k0, which is the largest stiffness in the THM, see

Fig. 4, while kFcan be set equal to kf, see Fig. 5. Equation 3.9 can be written as

(3.14) (kS)(j)

i+1∆u(j)=pi+1 −(fS)(j)

i+1 ≡R(j)

i+1 .

Substituting Eq. 3.5, 3.6 in Eq. 3.8 and then in Eq. 3.13, we get

(3.15) R(j)

i+1 =pi+1 −(fT)(j)

i+1 −(fF)(j)

i+1 −1

β(∆t)2m+γ

β∆tcu(j)

i+1 −ui

+1

β∆tm+γ

β−1c˙ui+ 1

2β−1m+ ∆tγ

2β−1c¨ui.

The whole procedure of programming the process of the Newmark method is

presented in Table 4 by following [7].

In order to deﬁne the force in THM, upper and lower limit bounds need to be

established, depending whether the velocity is positive or negative, see Fig. 6. When

the velocity is positive the force cannot be larger than fup

lim, while when the velocity

is negative the force cannot be smaller than flo

lim. In Appendix the pseudo-code for

the deﬁnition of fup

lim and flo

lim is presented.

Fig. 6. Upper and lower limit forces for THM.

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54 A.A. Markou, G.D. Manolis

Table 4. Newmark method: for the SDOF system of Solarino building, following [7]

Special cases

(1) Constant average acceleration method γ=1

2, β =1

4

(2) Linear acceleration method (γ= 1/2, β = 1/6)

1.0 Initial conditions

1.1 Check whether |pi|> ff⇒initiation of motion, set i= 0.

1.2 State determination (fT)0,(kT)0,(fF)0and (kF)0.

1.3 Solve m¨u0=p0−cu0−(kT)0u0−(kF)0u0.

1.4 Select ∆t.

1.5 a1=1

β(∆t)2m+γ

β∆tc;

a2=1

β∆tm+γ

β−1c;

a3=1

2β−1m+ ∆tγ

2β−1c.

2.0 Calculations for each time instant

2.1 Initialize j= 1,

u(j)

i+1 =ui,(fT)(j)

i+1 = (fT)(j)

i,(fF)(j)

i+1 = (fF)(j)

i,

(kT)(j)

i+1 = (kT)(j)

i,(kF)(j)

i+1 = (kF)(j)

i.

2.2 ˆpi+1 =pi+1 +a1ui+a2˙ui+a3¨ui.

3.0 For each iteration j= 1,2,3, . . .

3.1 R(j)

i+1 = ˆpi+1 −a1u(j)

i+1 −(fT)(j)

i+1 −(fF)(j)

i+1.

3.2 Check convergence;

if the acceptance criteria are not satisﬁed, implement steps 3.3 to 3.7;

otherwise go directly to step 4.0.

3.3 (kS)(j)

i+1 =a1+ (kT)(j)

i+1 + (kF)(j)

i+1.

3.4 Solve (kS)(j)

i+1∆u(j)=R(j)

i+1 ⇒∆u(j).

3.5 u(j+1)

i+1 =u(j)

i+1 + ∆u(j).

3.6 State determination (fT)(j+1)

i+1 ,(kT)(j+1)

i+1 ,(fF)(j+1)

i+1 and quad (kF)(j+1)

i+1 .

3.7 Replace jby j+ 1 and repeat steps 3.1 to 3.6; denote ﬁnal ui+1.

4.0 Calculation for velocity and acceleration

4.1 ˙ui+1 =γ

β∆t(ui+1 −ui) + 1−γ

β˙ui+ ∆t1−γ

2β¨ui.

4.2 ¨ui+1 =1

β(∆t)2(ui+1 −ui)−1

β∆t˙ui−1

2β−1¨ui.

5.0 Repetition for next time step.

Replace iby i+ 1 and

implement steps 2.0 to 4.0 for the next time step.

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Numerical solutions for nonlinear HDRBs 55

4. COMPARISON BETWEEN SEMI-ANALYTICAL AND NUMERICAL SOLUTION

The equation of motion, see Eq. 3.3, can be solved semi-analytically as it is shown

in [6]. In this section, a comparison between the semi-analytical and the numerical

solution, provided by the Newmark method, will be presented. The excitation pin

Eq. 3.3 will be

(4.1) p=−0.025mg sin(2πfrt),

where mis the mass of the structure (see Table 1), gis the gravitational acceleration

and fr= 0.41 Hz. It should also be noted that the time step used in the numerical

simulation is Dt = 0.005 sec. The results shown in Fig. 7 show that the results are

identical and the numerical solution is extremely accurate. The difference between

the maximum displacements in the steady-state stage of the excitation is 0.2 mm

(237 mm for the semi-analytical, 237.2 mm for the numerical). In Table 5 the time

required for the solution by the semi-analytical and the numerical solution is pre-

sented. Finally, the results show that the numerical solution requires almost double

implementation time compared to the semi-analytical one.

Table 5. Implementation time required for the solution with the semi-analytical solution and

the numerical one

Semi-analytical Numerical

[sec] [sec]

1.85 3.44

5. CONCLUSIONS

For the ﬁrst time, the numerical solution for the THM model is presented by using

the Newmark method. The numerical solution is compared with the semi-analytical

solution, provided by [6], for the SDOF system of the Solarino building. The results

show that the agreement between numerical and semi-analytical solution is practi-

cally identical. The disadvantage for the numerical solution is that it requires almost

double time to solve the problem. Most importantly, the numerical solution can be

used for extension of the trilinear mechanical models to bidirectional horizontal mo-

tion, to time-varying vertical loads, to multi-degree-of-freedom-systems as well to

generalized models connected in parallel, see [4], where only numerical solutions are

possible.

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56 A.A. Markou, G.D. Manolis

-300 -200 -100 0 100 200 300

u (mm)

-2000

-1000

0

1000

2000

fT (kN)

Numerical Analytical

(a)

0 20 40 60 80

t (s)

-300

-200

-100

0

100

200

300

u (mm)

Numerical Analytical

(b)

-300 -200 -100 0 100 200 300

u (mm)

-50

0

50

fF (kN)

Numerical Analytical

(c)

0 20 40 60 80

t (s)

-1000

-500

0

500

1000

v (mm/s)

Numerical Analytical

(d)

-300 -200 -100 0 100 200 300

u (mm)

-150

-100

-50

0

50

100

150

fV (kN)

Numerical Analytical

(e)

0 20 40 60 80

t (s)

-0.2

-0.1

0

0.1

0.2

a (g)

Numerical Analytical

(f)

Fig. 7. (a) Force-displacement graph of THM, (b) displacement-time graph of SDOF system,

(c) force-displacement graph of LCFM, (d) velocity-time graph of the SDOF system, (e)

Force-displacement graph of LVD, (f) acceleration-time graph of the SDOF system under

harmonic excitation.

ACKNOWLEDGMENT

The authors wish to acknowledge ﬁnancial support from Horizon 2020 MSCA-RISE-

2015 project No. 691213 entitled “Experimental Computational Hybrid Assessment

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Numerical solutions for nonlinear HDRBs 57

of Natural Gas pipelines Exposed to seismic RISK” (EXCHANGE-RISK), Assoc.

Prof. A. Sextos, Principal Investigator.

REFERENCES

[1] HO UB OLT, J. C. A Recurrence Matrix Solution for the Dynamic Response of Elastic

Aircraft. J. Aeronaut. Sci.,17 (1950), 540-550.

[2] NE WM ARK, N. M. A Method of Computation for Structural Dynamics. ASCE J. En-

grg Mech. Div., 85 (1959), No. 3, 67-94.

[3] BE LYTS CH KO, T., T. J. R. HUG HE S. (editors), Computational Methods for Transient

Analysis, North Holland, Amsterdam, 1983.

[4] MA RKO U, A . A., G. D . MA NO LI S. Mechanical Formulations for Bilinear and Tri-

linear Hysteretic Models used in Base Isolators. B. Earthq. Eng., 14 (2016), No. 12,

3591-3611.

[5] OL IVETO , G., M. GRANATA, G. BUDA, P. SCIACCA. Preliminary Results from Full-

scale Free Vibration Tests on a Four Story Reinforced Concrete Building after Seismic

Rehabilitation by Base Isolation, In: JSSI 10th Anniversary Symposium on Perfor-

mance of Response Controlled Buildings, Japan, Yokohama, 2004.

[6] MA RKO U, A. A., G. OL IV ETO , A. ATHAN ASIOU. Response Simulation of Hybrid

Base Isolation Systems under Earthquake Excitation. Soil Dyn. Earthq Eng.,84 (2016),

120-133.

[7] CH OPRA, A. K. Dynamics of Structures: Theory and Applications to Earthquake

Engineering, NJ, Prentice-Hall:Englewood Cliffs, 2012.

APPENDIX

In order to deﬁne the upper and lower limits of the force in the THM the conditions described

in the following pseudo-code (in Matlab/Octave) need to be applied. Note that ujt denotes

the current displacement amplitude.

% C a l c u l a t e f l i m u p −−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−

i f −uy h +2 ∗uy <= u j t && u j t <= uy h

i f uy h >=2∗uy

f l i m u p = Q + k1 ∗u j t ;

e l s e i f uyh<2∗uy

f l i m u p = Fy + k 1 ∗( u j t −uy ) ;

end

e l s e i f u j t >uyh

i f uy h >=2∗uy

f l i m u p = Q + k1 ∗uy h + k2 ∗( u j t −uyh ) ;

e l s e i f uyh<2∗uy

f l i m u p = Fy + k 1 ∗( uyh −u y ) + k2 ∗( u j t −uy h ) ;

end

e l s e i f u j t <−u yh + 2 ∗uy

i f uy h >=2∗uy

f l i m u p = Q + k 1 ∗(−uy h + 2∗u y ) + k2 ∗( u j t −(−uy h + 2∗uy ) ) ;

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58 A.A. Markou, G.D. Manolis

e l s e i f uyh<2∗uy

f l i m u p = Fy −k 1 ∗( uyh −uy ) + k2 ∗( u j t −(−uyh + 2 ∗uy ) ) ;

end

end

% C a l c u l a t e f l i m l o −−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−

i f −uyh <= u j t && u j t <= uy h −2∗uy

i f uy h >=2∗uy

flimlo = −Q + k 1 ∗u j t ;

e l s e i f uyh<2∗uy

flimlo = −F y + k 1 ∗( u j t + uy ) ;

end

e l s e i f u yh−2∗uy <ujt

i f uy h >=2∗uy

flimlo = −Q + k 1 ∗( uyh −2∗uy ) + k2 ∗( u j t −( uy h −2∗u y ) ) ;

e l s e i f u yh<2∗uy

flimlo = −F y + k 1 ∗( uyh −u y ) + k2 ∗( u j t −( uy h −2∗u y ) ) ;

end

e l s e i f u j t <−uyh

i f uy h >=2∗uy

flimlo = −Q−k1 ∗uy h + k2 ∗( u j t + u yh ) ;

e l s e i f u yh<2∗uy

flimlo = −Fy −k1 ∗( u yh −uy ) + k 2 ∗( u j t + u yh ) ;

end

end

%−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−

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