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STRUCTURAL DAMAGE
DETECTION USING
WAVELET APPROACH
Project Guide : PRAKRUTHI GOWD
D. SRAVYA 1602-12-732-049
SAI ANOOP ADITYA.V 1602-12-732-035
CONTENTS COVERED
1)Structural damages:
Damages in concrete
Damages in steel
2)Introduction to SHM
3)Levels of SHM
CONTENTS
Types of slabs
Damages in slabs
Yield line analysis
Non Destructive methods
Introduction to Ansys
Wavelet approach
TYPES OF SLABS
Basic classification of slabs:
One way slab: Length to width ratio is
greater than 2
Two way slab: Length to width ratio is
less than 2
Other types of classification:
Slabs continuous over supports: They
span in one direction & are designed
as continuous beams.
Slabs monolithic with supports: They
may be taken either as continuous
over supports and capable of rotation
or as a continuous framework with
suppports.
Slabs supported on two opposite
edges: They may carry one or more
concentrated loads and bending
moment caused by these loads is
assumed to be resisted by effective
width of slab.
Slabs spanning in two directions at
right angles: They carry udl and is
designed by using coefficients given
below.
Restrained slab with unequal
conditions at adjacent panels: Few
load cases may be similar to that
given in the table and other cases are
calculated seperately.
FAILURES OF SLABS
• Blisters
• Cracking
• Crazing
• Curling
• Dusting
• Efflorescence
• Scaling
BLISTERS
• The appearance of blisters on the surface of a concrete slab during finishing operations is annoying.
• These bumps, of varying size, appear at a time when bubbles of entrapped air or water rising through the plastic concrete get trapped under an already sealed, airtight surface.
• Insufficient vibration during compaction that does not adequately release entrapped air; or overuse of vibration that leaves the surface with excessive fines, inviting crusting and early finishing.
CRACKING
• Cracking can be the result of one or a combination of factors, such as drying shrinkage, thermal contraction, restraint (external or internal) to shortening, subgrade settlement, and applied loads.
• Cracks that occur before hardening usually are the result of settlement within the concrete mass.
• Settlement cracking results from insufficient consolidation , high slumps , or a lack of adequate cover over embedded items.
CRAZING
Crazing, a network pattern of fine cracks that do not penetrate much below the surface, is caused by minor surface shrinkage.
Crazing cracks are very fine and barely visible except when the concrete is drying after the surface has been wet.
The cracks encompass small concrete areas less than 50 mm (2 in.) in dimension, forming a chicken-wire pattern.
The term “map cracking” is often used to refer to cracks that are similar to crazing cracks only more visible and surrounding larger areas of concrete.
CURLING
Curling is the distortion (rising up) of a
slab’s corners and edges due to
differences in moisture content or
temperature be the top and bottom of a
slab.
The top dries out or cools and shrinks
more than the wetter or warmer bottom.
If the curled section of a slab is loaded
beyond the flexural strength of the
concrete, cracks may develop to relieve
the stress.
DUSTING
Dusting the development of a fine,
powdery material that easily rubs off
the surface of hardened concrete.
Can occur either indoors or outdoors,
but is more likely to be a problem
when it occurs indoors .
Dusting is the result of a thin, weak
layer, called laitance, composed of
water, cement, and fine particles
EFFLORESCENCE
Efflorescence can be considered a
type of discoloration.
It is a deposit, usually white in colour,
that occasionally develops on the
surface of concrete, often just after a
structure is completed.
Although unattractive, efflorescence is
usually harmless.
YIELD LINE ANALYSIS
Yield line is a crack in a reinforced concrete slab across which reinforcing bars have yielded and along which plastic rotation occurs.
Yield line design is a well-founded method of designing reinforced concrete slabs.
It uses yield line theory to investigate failure mechanisms at the ultimate limit state.
ADVANTAGES
Economy
Simplicity
Versatility
NON DESTRUCTIVE
METHODS
Variety of NDT methods have been
developed and are available for
investigation and evaluation of
different parameters related to
strength, durability and overall quality
of concrete.
TESTS FOR DETECTION OF
CRACKS/VOIDS/DELAMINATIO
NS
(i) Infrared thermo graphic technique
(ii) Acoustic Emission techniques
(iii) Short Pulse Radar methods
(iv) Stress wave propagation methods
- pulse echo method
- impact echo method
- response method
Other than these tests, few modeling
and analyzing softwares are available
to analyze a structure for damages.
One of such softwares is ANSYS,
MATLAB TOOLBOX that we have
employed in our project to model,
analyze the slab for damages.
INTRODUCTION TO ANSYS
Ansys is a finite element software
which offers engineering simulation
solution sets that a design process
requires.
In our project, we are using Ansys 15
software to understand the behaviour
of slab with different boundary and
loading conditions.
This is a general purpose finite
element modeling package for
numerically solving a wide variety of
problems which include static/
dynamic structural analysis or both.
Ansys is chosen for the purpose of
analyzing of RC slabs because of its
flexibility in geometry and materials
modeling.
Firstly, we give the type of element we
are going to work on which may be
1D,2D,3D,mass element.
Then, the properties of element like
area, moment of inertia are given.
Then, the material properties: Modulus
of elasticity and poisson’s ratio are
given.
After that, modeling is done with the
help of nodes or key points.
Then, meshing is done through which
a finite element model is generated.
The end conditions & load cases are
given according to the problem.
After the element is solved, we can
obtain BMD, SFD, max & min stress
distribution curves.
The structure can be analyzed when it
is subjected to both static and
dynamic loading.
In our project, we subject the slab to
dynamic loading like earthquake
loads, wind loads etc.
The BMD so obtained is imported to
Matlab toolbox for further analysis.
WAVELET ANALYSIS
A wavelet is a waveform of effectively limited duration that has an average value of zero.
Wavelet analysis represents the next logical step: a windowing technique with variable sized regions.
One major advantage afforded by wavelets is the ability to perform local analysis that is, to analyze a localized area of a larger signal.
WAVELET APPROACH
Many a time engineers are given with tasks to build structures which are required to support loads which are dynamic in nature.
For the analysis of such structures wavelet analysis to be used.
The response of such structures recorded and plotted against time is generally known as time history.
This particular signal will contain information about the structure and loads acting upon it in form.