Abstract: A NDT test, spectral analysis of surface wave (SASW) method, is a
relatively new technique for examining the structural integrity of structural members
of building structures. The SASW method has advantages among NDT methods that
it needs an access from only one side of a testing object and can measure the
dispersive characteristics in layered structures. This study is to model the wave
propagation of stress waves in concrete media using a finite element method.
Experiments using the NDT are to be conducted to investigate the wave behavior in
concrete media. This study also evaluates the surface wave velocity of single layer
cement mortar systems using an experimental analysis of the SASW method, and
examines the corresponding results with numerical results. Specimen models were
single-layer cement mortar slab systems.
Abstract: Chloride penetration into concrete is the main cause of steel corrosion in concrete
structures exposed to chloride-rich environments. In general, conditions on the diffusion process are
dominant among various penetration mechanisms, such as ionic diffusion, capillary sorption, and so
on. In recent analysis of current literature, chloride diffusion is as a simplified one-dimensional
diffusion process. However, for the rebar in the corner zone of concrete beam, the diffusion belongs
to a two-dimensional diffusion. Based on a galerkin finite element method, a two-dimensional
diffusion differential equation is built and solved numerically and the different chloride
concentration is compared to one dimensional diffusion and two-dimensional diffusion process. The
service life of concrete structure members under two-dimensional chloride penetration is predicted
by compared with a critical threshold chloride concentration. Compared with general
one-dimensional chloride attack, the service life is considerably reduced in a corner zone due to
Abstract: Damage of materials is a progressive physical process through which the macroscopic
properties of the material changes and it might end with the final failure of a part and in some cases
can be disastrous. The main mechanism of brittle damage is the nucleation and growth of
microcracks. A way to model the anisotropic damage is to consider its influence on the
compliance/stiffness of the material at the meso-level.
A numerical study of a growing mixed-mode internal crack in a unit cell was undertaken with
the help of a finite element simulation. The model enables us to measure the components of the
elastic compliance tensor modified by damage as the crack grows, showing the evolution of the
anisotropic damage and the evolution of the type of material symmetries. The evolution of the
elasticity tensor shows that the damage associated with a growing elliptical crack changes the virgin
isotropic properties into orthotropic ones and by crack growth the axes of orthotropic symmetry,
initially aligned with the local coordinates of the crack, rotate towards the principle loading axes.
The matrix material of the unit cell is considered to be isotropic linear elastic, homogenous and
the response is perfectly brittle. The characteristic crack size is small compared to the unit cell, so
that the non-interacting crack assumption for the damage models is fulfilled. Crack propagation is
simulated using the stepwise method, which consists of the succession of straight segments and
crack growth is governed by the principle of maximum driving force which is a direct consequence
of the variational principle of a cracked body in equilibrium and considers the effect of all three
stress intensity factors. Without any ad hoc assumption, the crack growth rate is calculated using its
thermodynamic duality with the local maximum driving force.
Abstract: Structural optimization is widely adopted in the design of structures with the
development of computer aided design (CAD) and the development of computer technique recently.
By applying the artificial neural network to structural optimization, designers can gain the design
scheme of structures more feasibly and easily. In this paper, the genetic algorithm (GA) used in the
error back-propagation (BP) network is applied to get the optimization result of the structural
system. And the training pair of BP neural network is obtained from the structural analysis using a
finite element program. The case study of 10 member truss structure using GA and BP will be
helpful to reduce the cost of structures which is related to weight and the dynamic performance of
optimization under the lateral load.
Abstract: This paper reports a parametric stress analysis of various configurations of rack plate
stiffened multi-planar welded KK joints using the finite element method. The KK joint finds
application in the leg structure of offshore Oil & Gas jack-up platforms. The rack plate is a dual
purpose element of the joint because it firstly functions as a stiffener which reduces the stress
concentration at the brace/chord intersection. This could be an immense contribution to the increase
in fatigue life of the joint but other hot spot sites are introduced to the joint. The rack is also used
for raising and lowering of the jack-up hull which gives the jack-up platform its jacking capability.
Over 120 models using a combination of shell and solid elements were built and analysed within
ABAQUS. Non-dimensional joint geometric parameters; β, γ and . were employed in the study
with . being defined as the ratio of rack thickness to chord diameter. Stress Concentration Factors
(SCFs) were calculated under applied axial and OPB (out-of-plane-bending) loading. Three critical
SCF locations were identified for each load case, with each location becoming the most critical
based on the combination of the non-dimensional parameters selected for the joint. This is
important as careful design can shift the critical SCF from an area inaccessible to NDT to one that
can be easily inspected. The SCF values extracted from the models were used to derive six
parametric equations through multiple regression analysis performed using MINITAB. The
equations describe the SCF at the different locations as a function of the non-dimensional ratios.
The equations not only allow the rapid optimisation of multi-planar joints but also can be used to
quickly identify the location of maximum stress concentration and hence the likely position of
fatigue cracks. This in itself is an invaluable tool for planning NDT procedures and schedules.
Abstract: A recent approach based on the local strain energy density (SED) averaged over a given
control volume is applied to well documented experimental data taken from the literature, all related
to steel welded joints of complex geometry. This small size volume embraces the weld root or the
weld toe, both regions modelled as sharp (zero notch radius) V-notches with different opening
The SED is evaluated from three-dimensional finite element models by using a circular sector with
a radius equal to 0.28 mm. The data expressed in terms of the local energy fall in a scatter band
recently reported in the literature, based on about 650 experimental data related to fillet welded
joints made of structural steel with failures occurring at the weld toe or at the weld root.
Abstract: Chloride attacks concrete structures becoming a primary factor that deteriorates the
durability of concrete structures. For this reason, research has been conducted on chloride ion
penetration and diffusion. This research produced an accurate durability life prediction through
reliability assessments and proposes a prediction method for the chloride ion diffusion coefficient of
a concrete applied assessment program for reliability. As a result, test materials were fabricated
using different admixtures and chloride ion diffusion coefficient was calculated by applying an
RCPT test at each equivalent age. Based on these results, reliability prediction formulas were
indicated through the reliability analysis for a durability life design using a Montecarlo method. In
addition, propriety was verified through comparisons and analysis using the proposed formula with
the investigated data for chloride ion diffusion.
Abstract: This paper describes a numerical method for estimating the elastic modulus of cement
paste. The cement paste is modeled as a unit cell, which consists of three parts: dehydrated cement
grain, gel, and capillary pore. In the unit cell, the volume fractions of the constituents are quantified
with a single kinetic function of the degree of hydration. The elastic modulus of cement paste was
calculated from the total displacement of constituents when the uniform pressure was applied to the
gel contact area in cement paste assumed a homogenous isotropic matrix. Numerical simulations
were conducted through the finite element analysis of the three-dimensional periodic unit cell. The
model predictions were compared with experimental results. The predicted trends agree with
experimental observations. The approach and some of the results might also be relevant for other
Abstract: As concrete is a type of porous materials, water or air freely permeates concrete. Therefore
the durability of concrete decreases. However, porous material with a rust inhibitor may allow
permeation of water into concrete. In addition, there may be permeation of water through the rust
inhibitor at the location of steel frames. The objective of the study is to investigate the penetration
depth of concrete under water forced conditions with pressure.
Abstract: Research has been initiated on the effects of high frequency peening methods on the
fatigue strength. These methods combine an improvement of weld toe profile with an initiation of
compressive residual stresses and surface hardening. The effects of two techniques, High Frequency
Impact Treatment (HiFIT) and Ultrasonic Impact Treatemnt (UIT) are compared. Laser
measurements of the weld seam prove that both methods increase the overall weld toe radii.
Further, residual stress measurements verify the introduction of compressive residual stresses at
least up to a depth of 1 mm. The values meet the yield strength combined with an increase of the
surface hardness. These material mechanical effects cause an increased crack resistance. Crack
detection methods prove that the material mechanical effects yield to a retarded crack initiation.
Experimental results show that these effects lead to a significant increase of the fatigue strength and
reduced slopes of the SN-curves.