Logo

\

 

IDENTIFYING TYPE OF CRACKS IN STRUCTURES!!

IDENTIFYING TYPE OF CRACKS IN STRUCTURES

CRACKS MAY DEVELOP DUE TO

1. ·         DETERIORATION OF CONCRETE.
2. ·         NATURAL CALAMITIES
3. ·         CORROSION OF REBARS DUE TO POOR CONDTRUCTION PRACTICES
4. ·         INAPPORPRIATE SELECTION OF CONSTRUCTION MATERIALS.
5. ·         TEMPERATURE AND SHRINKAGE EFFECTS.
6. ·         SETTLEMENT OF SUPPORTS.

TYPES OF CRACKS

Ø  STRUCTURAL CRACKS

§  Cause – Incorrect Design, Faulty Construction and Overloading

Ø  NON-STRUCTURAL CRACKS

§  Cause – Stresses induced internally by construction materials.

IDENTIFYING STRUCTURAL CRACKS

THESE TYPE OF CRACKS APPEAR ON STRUCTURSL ELEMENTS SUCH AS BEAMS, COLUMNS,SLABS,ETC.THESE ARE: 

      1.    FLEXURAL CRACKS IN BEAM

2.    SHEAR FLEXURE CRACKS IN BEAM

3.    TORSIONAL CRACKS IN BEAM

4.    TENSION CRACKS IN TIE BEAMS

5.    CRACKS IN COLUMNS

6.    CRACKS IN SLABS

7.    CRACKS DUE TO SETTLEMENT OF FOUNDATION

IDENTIFYING NON-STRUCTURAL CRACKS

1. ELASTIC DEFORMATION-Non uniform Distribution of loads,Excessive Deflection
2. MOISTURE CHANGE
   
   
   
   
   
   
   
3. THERMAL MOVEMENT-Depends on thermal coefficients and dimensions of elements
4. CREEP- Depends on W/C ratio,materials used and shape and size of components.
5. FOUNDATION MOVEMENT AND SETTLEMENT OF SOIL-Due to unequal bearing capacities
6. GROWTH OF VEGETATION-Dehydration is caused by roots leads to settlement
7. CHEMICAL REACTION-Sulphate attack,carbonation,corrosion and alkali aggregate reaction.
   

INSTRUMENTS FOR MEASUREING CRACKS

·         DIGITAL CRACK GAUGE

·         MEASURING MAGNIFIER

·         LOMARO MICROSCOPE

·         CRACK SCOPE

                  

Principles of Concrete Repair & Protection

Introduction to Concrete repairs and protection

Concrete structures under go distress due  various factors during their service life. Identifying the distress, ascertaining the cause of distress and undertaking suitable remediation is essential for safe use of structure.

Reasons for distress.

• Accidental and unanticipated loadings.
• Design errors
• Weathering
• Poor construction practice.
• Corrosive environment.
• Fire damage
• Natural calamities viz. Earth quake, flood
• Use of defective materials

Approach to Concrete repairs

Condition assessment of structure.

• Assess the present condition of structure.
•  In situ parameters of materials.
• Conditions during construction.
•  Original design approach etc.

Consider various options available

• Do nothing.
•  Preserve current state.
•  Partial or total strengthening
• Suggest to demolition 

Selection or repair principle- Focus on main objective of repair.

• Concrete restoration.
• Structural strengthening.
• Protection against chemical ingress
• Others

Remediation methods

• Select remedial method based on the type of repair.
• Based on future service conditions.
• Based on the availability of products.

 Material selection.

• Based on minimum performance characteristics.
• Based on application methods selected.

Properties required for repair materials.

Shrinkage compensated.

Good bond strength with existing substrate.

Compatible Coefficient of thermal expansion with parent substrate.

Should possess sufficient alkalinity to protect steel embedded in concrete.

Low air and water permeability.

Resistance UV rays, heat and aggressive chemical attack wherever required.

Should be non hazardous.

Structural Waterproofing Basics

Introduction to Waterproofing

What is waterproofing?

The treatment of a surface or structure to prevent passage of water under hydrostatic pressure.

Water retaining structures: keeping water in

• Reservoirs and water tanks
• Waste water treatment plants
• Dams
• Secondary containment bund
• Swimming pools
• Sewers and pipelines, etc

Waterproof facilities: keeping water out

Basements

Parking garages

Underground stations and subways

Utility vaults

Reservoirs and water tanks

Marine structures

Tunnels, etc.

 Causes for leakage

• Concrete shrinks and develops micro cracks
• Joints detailing & treatments
• Poor quality of concrete
• Poor workmanship
• High water table
• Water retaining structures
• Structural problems

Why is it required?

Leakage results in

Corrosion and spalling

Life of the structure is reduced

Cannot be utilized as intended

Loss of revenue

Remedial measures are trial & error and very expensive

Selection criteria for basement water proofing.

Usage / utility of the basement areas

Water table level.

Presence of aggressive / corrosive chemicals in ground water.

Area of water proofing application.

Roof slab

Podiums

Balconies

Chejjas

Wet areas

Water retaining  & water treatment structures 

 Waterproofing Range

Ø Liquid applied  

Ø Pre & post applied Membrane

Ø Spray applied

Ø Crystalline

Ø Admixture

Ø Water stops

Ø Thermal insulation cum waterproofing

 

                                                                            

Good Construction Practices-Joining Walls to Roof

Good Construction Practices-Joining Walls to Roof

Connecting walls to roof structure. Join walls and roof to strengthen each other.

·       Column reinforcement has to be protruded from the top of columns and be bent around roof trusses for structural strength, or roof trusses should be strapped with metal ties to the wall structure.

·       Exposed metal must be painted with rust proof paint to avoid corrosion.

An example of binding roof trusses to building structure. Roof trusses should be constructed over columns, and for a concrete column the reinforcement should protrude at the top and be bent over roof trusses to join the roof structure with the wall structure. Metal straps or plates can be used for this role, particularly where the building structure is made of wood.

A good roofing example of column steel reinforcement bent over roof truss to tie house structure to the roof structure. This is an essential detail in areas subject to earthquake and to winds, to keep the roof on the house when a natural hazard strikes the structure. Such exposed steel should be painted with rust-proof paint to minimize corrosion.

 Example of good roofing practice. Steel roof trusses are connected to columns through welding of truss members to column reinforcing steel and purlins are welded with ties to roof trusses. This will hold the roof firmly on the house in storms or other hazards from nature.

 Example of incorrect roofing practice. The roof structure is good, but no connection is made between roof trusses and the building structure. The roof is resting on the top of the house walls and is subject to moving with high winds or other forces of nature.