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.