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Singapore Salary Survey year 2010

Wed, 10 Feb 2010 10:22:52 -0700

PORE STRUCTURE AND DURABILITY OF CONCRETE CONTAINING GBFS

Sabe0001@nospam.com (Sabet Divsholi Bahador) — Sun, 03 May 2009 06:31:46 -0600

INTRODUCTION
The use of Granulated Blast Furnace Slag (GBFS) as
supplementary cementitious material for concrete production
is ecologically and economically very important[1]. High
quality and durable concrete is required to reduce the
rapid deterioration of concrete in severe conditions. It
has been proven that GBFS has perfect performance to
resist chloride induced corrosion[2]. Replacing Portland
Cement (PC) partially by GBFS can improve the fluidity
of fresh concrete, reduce its bleeding and postpone the
setting[3]. The quality of GBFS depends on the chemical
composition, glass phase content and fi neness of GBFS[4].
Using mineral admixtures will result in the consumption
of calcium hydroxide in concrete. In short curing period,
it may increase the carbonation rate of concrete[1]. In this
study, the effect of replacing PC with various percentages
of GBFS on different characteristics of concrete has been
studied. Replacing PC partially with GBFS improved the
characteristic of concrete significantly.

Authors:

Sabet Divsholi Bahador (Sabe0001@ntu.edu.sg)
Jong Herman Cahyadi (CHSjong@ntu.edu.sg)

SUMATRAN MEGATHRUST EARTHQUAKES: WHAT HAS HAPPENED, AND WHAT’S NEXT?

kusno@nospam.com (Kusnowidjaja Megawati) — Sun, 03 May 2009 06:30:35 -0600

Why does Sumatra keep sending earthquakes our way? And
what might be coming next? These are questions that many
Singaporeans are asking recently, as the shaking that began
in June 2000 continues.
The world’s biggest earthquakes and most of its volcanoes
occur where giant tectonic plates beneath the oceans are
diving down under neighbouring landmasses. Singapore is
fortunate to lie several hundred kilometres from the nearest
such “subduction” zone, in the middle of a tectonic plate
that includes all of its Southeast Asian neighbours. Still, the
western edge of that plate, on the other side of Sumatra,
generates such big earthquakes that gentle swaying is
commonly felt in Singapore.
All of the earthquakes we have felt in the past eight years
happened because the upper surface of the downgoing
oceanic plate (called the Sunda megathrust) is sticky. As the
oceanic plate descends northward at about 60 millimetres per
year beneath Sumatra, it clings to Sumatra’s underside along
the megathrust, until it reaches depths of 50 kilometres or
so, where it fi nally becomes hot and gooey enough to slip
steadily into the deep earth.

Authors:

Kusnowidjaja Megawati (kusno@ntu.edu.sg)
Kerry Sieh (sieh@ntu.edu.sg)
Tso-Chien Pan (cpan@ntu.edu.sg)

STRAIN TRANSFER MODELS FOR STRAIN ACTUATORS

cywyang@nospam.com (Yang Yaowen) — Sun, 03 May 2009 06:29:35 -0600

INTRODUCTION
One of the advantages of piezo-composite actuators is to
provide low cost and in-situ actuation with high fl exibility[1].
Actuators as patches made of bulk lead zirconate titanate
(PZT) material are widely used for vibration control of
mechanical structures. However, extremely brittle nature
of the PZT material requires extra attention during the
handling and bonding procedures[2]. Micro fi ber composite
(MFC) has shown its great potential for vibration and
noise control, health monitoring, morphing of structures
and energy harvesting[3]. To explore various applications
of MFC, a reasonable model accounting for the strain
transfer phenomenon between the MFC and the structure
is crucial[4]. There have been a few one dimensional (1-D)
models on strain transfer[5,6,7], but issues still remain on
how accurately these models predict the phenomenon and
how effectively they can be extended to two dimensional
(2-D) cases to increase the accuracy of prediction.
In this work, the existing 1-D Bernoulli-Euler formulation
for bending, coupled bending and extension of isotropic
beams/plates with induced strain actuators is extended to 2-D
cases. Further, it is improved to account for the reduction in
actuation as a result of strain distribution inside the actuator.
The improved 1-D and 2-D formulations are compared with
the uniform strain model which includes the shear lag effects
due to the adhesive layer. A fi nite element model is also
developed to study the strain transfer. Finally, an experimental
test is carried out to evaluate the accuracy and limitations
of the developed models. Results show that the models are
in good agreement with the experiment.

Authors:

Yang Yaowen (cywyang@ntu.edu.sg)
Sabet Divsholi Bahador (sabe0002@ntu.edu.sg)

STATIC ULTIMATE STRENGTH OF CRACKED SQUARE HOLLOW SECTION Y-JOINT

cstlie@nospam.com (Lie Seng Tjhen) — Sun, 03 May 2009 06:28:12 -0600

INTRODUCTION
To validate the fi nite element models of a cracked square
hollow section (SHS) Y-joint[1], a full-scale specimen was
tested under incremental loads up to failure. The Y-joint
was fi rst fatigue cracked using the “Orange Frame” test
rig available in the Construction Technology Laboratory.
The specimen contains a surface crack located at one of
the corners as shown in Figure 1. After completion of the
fatigue test, the crack dimensions were measured using the
Alternating Current Potential Drop (ACPD) technique[2].
The specimen was fabricated from BS4360 structural
steel of grade 50D[3]. The weld profi le and the specimen
preparation were carried out in accordance with the American
Welding Society (AWS) Structure Welding Code–Steel
D1.1/D.1.1M:2006[4] specifi cations. The specimen material
yield stress is 380.3 MPa.

Authors:

Lie Seng Tjhen (cstlie@ntu.edu.sg)
Yang Zhengmao (ZhengMao.Yang@dnv.com.sg)

SCF PREDICTION OF COMPLEX TUBULAR JOINT USING INTERPOLATION APPROACH

ccklee@nospam.com (Lee Chi King) — Sun, 03 May 2009 06:25:58 -0600

INTRODUCTION
In the fatigue assessment of tubular joint, the stress
concentration factor (SCF) is one of the most important
indicators that determine the performance of the joint under
cyclic loading. The variation of the SCF with respect to the
geometrical and loading parameters is always a critical factor
that needed to be considered during tubular joint design. In
most design codes for tubular joints, the variations of the
SCF with respect to the geometrical and loading parameters
are described by some empirical equations. These equations
are normally obtained by applying multi-variable regression
analysis on the numerical modelling results obtained from
parametric studies on a set of identifi ed parameters. For
simple joint types under simple loading condition, these
empirical equations are often able to provide reasonable
predictions. However, for the cases of a more complicated
joint or a simple joint under complex loading, such an
approach would often result in lengthy equations [1].
Furthermore, due to the complexity of the joint and the
presence of many parameters, these lengthy equations would
not be able to give good predictions over the whole range
of parameters. To overcome this problem, a new approach
based on the interpolation method described below was
proposed [1-3].

Authors:

Lee Chi King (ccklee@ntu.edu.sg)
Chiew Sing Ping (cspchiew@ntu.edu.sg)
Lie Seng Tjhen (cstlie@ntu.edu.sg)
Sopha Thong (soph0001@ntu.edu.sg)

DAMAGE DETECTION USING MULTIPLE PIEZO-IMPEDANCE TRANSDUCERS

cywyang@nospam.com (Yang Yaowen) — Sun, 03 May 2009 06:25:05 -0600

INTRODUCTION
Smart materials based structural health monitoring (SHM)
has attracted extensive research attention in the past decade.
Lead zircornate titanate (PZT) impedance transducers,
working on the principle of electromechanical impedance
(EMI), are among the most widely used smart materials due
to their self actuation and sensing capabilities. One single
PZT is sensitive enough to detect incipient damage and
its propagation [1]. However, it is diffi cult to identify the
location of structural damage by a single PZT. Therefore,
in this article, an experimental investigation on damage
location using multiple PZTs is fi rstly presented, followed
by the numerical simulation for verifi cation.

Authors:

Yang Yaowen (cywyang@ntu.edu.sg)
Liu Hui (liuh0019@ntu.edu.sg)

MONITORING VIBRATING STRUCTURES USING PZT IMPEDANCE TRANSDUCERS

cywyang@nospam.com (Yang Yaowen) — Sun, 03 May 2009 06:23:47 -0600

INTRODUCTION
The electromechanical impedance (EMI) method has
emerged as a widely recognized technique for dynamic
identifi cation and health monitoring of structural systems.
The electromechanical admittance response of the smart
system is derived from the dynamic interaction relation
between the lead zirconate titanate (PZT) transducer and
the host structure. For structural health monitoring (SHM)
applications, these spectra may be compared at various times
during the service lifespan of the structure, in which any
change between the spectra is an indication of the presence of
damage or material deterioration. However, the existing EMI
method does not consider the structural vibration caused by
the external excitation other than the PZT actuation, which
means that the existing EMI method is only applicable to
the static structures [1-3]. Unfortunately, many structures
are subjected to vibrations in practice. The vibrations of the
structures will infl uence the results of SHM by causing the
changes in PZT signatures. The changes in PZT signatures
caused by the external excitation and the structural damage
must be differentiated such that the correct information of
structural health state can be obtained. Therefore, this paper
attempts to study the infl uence of the external excitation on
the PZT impedance signature.
For this purpose, a new EMI model is developed for a
simply supported beam structure with external excitations.
Furthermore, an experimental test is carried out to verify
the developed theoretical model.

Authors:

Yang Yaowen (cywyang@ntu.edu.sg)
Miao Aiwei (miao0009@ntu.edu.sg)

ENERGY HARVESTING USING MICRO-FIBER COMPOSITES

cywyang@nospam.com (Yang Yaowen) — Sun, 03 May 2009 06:22:51 -0600

INTRODUCTION
The decreasing energy consumption of MEMS, wireless
sensors and portable electronics invokes the possibility
to harvest energy from ambient vibrations for self power
supply. One simple method for vibration energy harvesting
is utilizing the direct piezoelectric effect. The macro-fi ber
composites (MFC)[1] are featured in their fl exibility of large
deformation, which enables them to harvest energy from
vibrations with little brittle risk and to serve for an unlimited
lifespan. However, the effi ciency of MFC has not been well
investigated. This article focuses on the effi ciency of the
energy harvesting system using MFC attached on a cantilever
beam. The output voltage of the MFC harvester is tested
and estimated using the fi nite element method (FEM). The
procedures of energy storing to the capacitor are simulated
using electronic design automation (EDA) software. By
combining the FEM and EDA simulations, the effi ciency of
the MFC energy harvesting system is estimated.

Authors:

Yang Yaowen (cywyang@ntu.edu.sg)
Tang Lihua (c070073@ntu.edu.sg)