2CL404 Civil Engineering ProjectStrain Measurement in RCC

Structure By:

Ankit Ahir 11BCL003

Rekan Gadhecha 11BCL009

Nakul Gami 11BCL010

Nisarg Gandhi 11BCL011

Guided By:

Prof. Digesh Joshi

CONTENTS

• INTRODUCTION

• OBJECTIVES & SCOPE OF PROJECT

• NEED OF PROJECT

• LITERATURE REVIEW

• APPROACH

• TASKS PERFORMED

• TASKS TO BE PERFORMED

STARTING WITH THE BASICS…

• What Is Strain?

When External Forces Are Applies On A Object Made Of Elastic Material It Tends To Change Its Shape And Size

The Relative Change In Shape Or Size Of An Object Due To Externally Applied Forces Called Strain

• What Is Stress?

The Internal Resistive Force Developed In The Body Due To Strain Is Called Stress

STARTING WITH THE BASICS…

• Relation Between Stress And Strain

Initially The Stress And Strain Are Directly Proportional (Up to Point A)

Then As The Strain Increases There Is Some Permanent Deformation In The Body

The Region Till Point B Is Called Elastic Region And The Region Further Is Called The Plastic Region

STARTING WITH THE BASICS…

• What Is Strain Gauge?

A device for indicating the strain of a material or structure at the point of attachment.

There are some materials whose resistance changes when strain is applied to them or when they are stretched and this change in resistance can be measured easily

It is basically of two types

1) Mechanical strain gauges

2) Electrical strain gauges

STARTING WITH THE BASICS…

• MECHANICAL STRAIN GAUGE

It is  made up of two separate plastic layers. The bottom layer has a ruled scale on it and the top layer has a red arrow or pointer. One layer is glued to one side of the crack and one layer to the other. As the crack opens, the layers slide very slowly past one another and the pointer moves over the scale. The red crosshairs move on the scale as the crack widens. 

STARTING WITH THE BASICS…

• Electrical STRAIN GAUGE

When an electrical wire is stretched within the limits of its elasticity such that it does not break or permanently deform, it will become narrower and longer, changes that increase its electrical resistance end-to-end.

Strain can be inferred by measuring change in resistance.

WHAT IS OUR PROJECT?

• Our Project Is Basically To Measure The Strain In RCC Structures

• Our Main Aim Is To Measure Strain In The Concrete Beam As Well As In The Steel Reinforcement Of The Beam

WHAT IS OUR PROJECT?

• Consider A Simply Supported Beam As Shown In The Figure

• A Concentrated Load F Is Applied At The Mid Span Of The Beam

• The Beam Will Undergo Sagging

• So As Shown In The Figure Surface 1 Will Be Under Compression And Surface 2 Will Be Under Tension

• We Measure The Strain In This Two Surfaces And The Strain In The Reinforcement Of These Two Regions

PURVIEW OF THE PROJECT

• The Project Extends To The Study Of Working, Construction And Experimental Usage Of Mechanical And Electrical Strain gages For The Measurement Of Strain

• It Also Covers The Casting And Testing Of PCC Cubes, Beams And Cylinders And To Measure The Strain Electrically And Mechanically

• It Also Includes The Casting And Testing Of RCC Beam And To Measure The Strain Electrically And Mechanically

WHY IS THE PROJECT REQUIRED?

• Strain Can Be Calculated Analytically By Various Methods In The RCC Structure But Those All Calculations Are Based On Some Assumptions And Can Be Erroneous

• Thus This Experiment Exactly Helps To Calculate The Strain Practically As Well As Analytically And The Error In Both Can Be Calculated

• Also It Will Help To Decide Weather The Reinforcements Of Lower Diameter Can Be Used For A Given Load To Resist The Allowable Deflection.

• These Project Helps To Understand The Behavior Of Various Elements Of The RCC Structure Due To Applied Load

WHAT WE REFERRED?

• We Studied Various Articles And Reports On The Working Of Strain gages

• We Emphasized On The Working Of Electrical Strain gages

• We Also Studied The Procedure To install Electrical And Mechanical Strain gages On The RCC Structures And The Procedure To Take Readings Of The Strain

• We Studied In Detail:

1. The Type Of Electrical Strain gages Available In The Market

2. The Type Of Electrical Strain gage To Be Used For Measuring Strain Concrete

3. The Type Of Electrical Strain gage Required To Measure Strain In Steel

WHAT WE REFERRED?

• Student Strain Gage Manual-published By Vishay Measurements Groups Inc.

This Literature Talked All About Various Types Of Strain Gages And Its Use In Various Criteria

It Says That The Installation And Operating Characteristic Depend On

1) Backing Material

2) Gage Length

3) Gage Pattern

WHAT WE REFERRED?

• Strain gages And Instrumentation: Application Note TT-661

This Note Refers To Strain gage Installation For Concrete Structures

It Describes The Procedure To Install Electrical Strain gage

It Includes Following Steps1) Degreasing 2) Conditioning 3) Filling 4) Layout Lines5) gage Bonding 6) Soldering

WHAT WE REFERRED?

• Report on Direct Tensile strength on concrete by Raghuraj Ranjendra Vaidya(11MCLC18)

The whole report had different tests and results of direct tensile test on concrete

It also describes the installation and testing by mechanical strain gage

It enumerates some basic steps to get readings from a mechanical strain gage

APPROACH TO THE PROJECT

• To Achieve Our Aim Of Getting Strain In RCC Structures

We Will Study The Working & Installation Of Electrical And Mechanical Strain gages

We Are Going To Cast As Per Given In The Table For M25 Grade Concrete

We Will Attach The Electrical Strain gage And Measure The Strain In Each Of The Structure Electrically And Mechanically

We Will Compare The Readings Obtained Analytically And Experimentally

Specimens Nos

PCC Cubes 6

PCC Beams 6

PCC cylinders 6

RCC beams 6

What we have done till now..

• We have studied various literature related to our objectives as discussed in literature review

• We calculated the mix design for M25 grade of concrete

• We also designed RCC beams with under reinforced and over reinforced section

• Then we casted cubes, beams & cylinders from the designed plain concrete mix

• We also casted 3 cubes extra from each batch to test it for the required designed strength

Casting of beams Casting of cylinders

Casting of cubes

What we have done till now..

• Then we tested the cubes for 28 days strength

• The results are as shown in the table

Batch Strength (Mpa) Average strength

Batch 1 22 22.3

22.9

22

Batch 2 23 22.5

22

22.5

Batch 3 22 23

23

23

Batch 4 23 23.23

23.2

23.5

Batch 5 22 23.67

25

24

Batch 6 23 23.83

24

24.5

What we have done till now..

• As the results were not satisfactory, we have casted new cubes, beams & cylinders with different cement and some corrections in the mix design

What we will do further…

• We will place an order for the electrical strain gages and the protective coating required to be done to protect the strain gages while concreting

• After 28 days we will measure the strength of the new cubes casted

• After getting satisfactory results we will install the electrical strain gage on the PCC specimens and measure the strain electrically and mechanically

• Meanwhile we will construct the reinforcement cage for the RCC beams for over-reinforced and under-reinforced structure

What we will do further…

• We will design the formwork for the beam as per our required dimensions

• We will install the electrical strain gage on the reinforcement at predefined critical places

• Then we will cast the beam with M25 grade of concrete

• We will then install electrical strain gages on the surface of concrete

• And hence we will measure the strain in the beams electrically and mechanically

• Then we will compare the results obtained by analytical calculations and our experimental results

THANK YOU