Structure Adequacy Analysis of A Building using Non-Destructive Testing Technology

Structure Adequacy Analysis of A Building using Non-Destructive Testing Technology

Rakesh Kumar

M. TECH

(STRUCTURAL & FOUNDATION ENGINEERING)

Department of Civil Engineering AL-FALAH UNIVERSITY, Faridabad INDIA

Aftab Alam

(Assistant Professor)

Department of Civil Engineering Manav Rachna International Institution of Research and Studies, Faridabad INDIA

Abstract In order to assess the condition of the RCC structure, a thorough evaluation was performed. The evaluation determined the structural condition, the need for repair or maintenance and provided an indication as to the safety and expected remaining service life of the structure. The testing consisted of:

1. A visual inspection of the exterior exposed elements to determine if there were any obvious signs of distress, deflection or deterioration in the structure.

2. The inspection of the structure to determine the condition of the structure. This is essential as we found that the structure can appear to be in a very good condition from outside, but could be suffering from extreme structural distress from inside.

3. Selective concrete/steel removal to examine the condition of the underlying reinforcing steel.

4. Materials testing to determine steel/concrete compressive strength, carbonation, chloride content. Objectives of the overall investigation:

The overall objective of the investigation carried out for the structure is to obtain an up to date account of the health condition of the structure so that appropriate repair measures can be taken up to make up for the damages sustained. Keeping this in view the basic objectives of the investigation formulated are as given below.

1. To assess the existing condition of the structural elements.

2. To determine the extent of damages in the structure, so as to undertake suitable remedial measures for rehabilitation of the structure.

Planning and Survey and Methodlogy

Walk over survey: First and foremost activity in a condition survey and structural investigation, especially in distressed superstructure, is a walk over survey or systematic visual inspection so as to gather readily available information about the structure in question. Further, careful visual observation of typical crack pattern and the nature of the spalling can furnish valuable information regarding the distresses. This in turn provides an idea about the degree of damage encountered in the concrete and hence the extent of repair required. A systematic visual observation has been recorded in this investigation and the findings are presented in later part of this report.

Selection of tests: Tests are selected on the basis of the requirements of the overall objectives of the investigation and the observations made during a quick walk over survey. In this investigation, following in-situ and laboratory tests were considered necessary for achieving the overall objectives stated earlier for the structure. Various Test were Conducted for the evaluation of the Structure:

METHODLOGY

1. Visual Survey

2. Test Plan

3. Sample and Data Collection

4. Structure Stability Analysis & Retrofitting

   1. INTRODUCTION

      The Existing structure is Family Wing Building of Military Hospital, Mathura (U.P) having G+1 stored with two corridor & number of rooms as mention in rough sketch of Building. Condition health assessment of Family Wing Building of Military Hospital, Mathura (U.P) by using Visual Inspection & Non-destructive testing. This report pertains to the stated safety appraisal & health assessments.

      In order to assess the condition of the RCC structure, a thorough evaluation was performed. The evaluation determined the structural condition, the need for repair or maintenance and provided an indication as to the safety and expected remaining service life of the structure.

      Primary Evaluation:

      A visual inspection of the exterior exposed elements to determine if there were any obvious signs of distress, deflection or deterioration in the structure.

      Selective concrete removal to examine the condition of the underlying reinforcing steel.

      In-Situ and laboratory testing is perform to determine concrete homogeneity, compressive strength & condition of steel and RCC structure.

      Walk over survey:

      First and foremost activity in a condition survey and structural investigation, especially in distressed superstructure, is a walk over survey so as to gather readily available information about the structure in question. Further, careful visual observation of the nature of the crack & spalling can furnish valuable information regarding the distresses. A systematic visual observation has been recorded in this investigation and the findings are presented in later part of this report.

      Visual survey of the structural members and documenting the damage if any with the help of photographs

      1.1 Visual Survey

   2. TEST PLAN

Selection of Tests:

On behalf of primary evaluation further In-situ and laboratory testing was selected to know the nature of the Crack, Spalling, Compressive Strength, Cover etc. As per surface condition, test locations were decided to cover the secondary evaluation of overall structure.

Secondary Evaluation:-

The various Non-Destructive Tests proposed to be carried out for condition survey of the structure are listed below:

1. Ultrasonic Pulse Velocity Test as per IS: 13311 (Part- 1)-1992 for ascertaining the quality of concrete, soundness and density of concrete.

2. Rebound Hammer Test: For determining the estimated compressive strength of concrete and uniformity of concrete in terms of surface hardness as per IS 13311 (Part-2)- 1992.

3. Carbonation Test as per BS EN: 14630 Measurement of carbonation depth by phenolphthalein spray test at selected locations on RCC members of the structures covered under the study to see the depth of carbonation.

4. Core Extraction: IS: 516, concrete extraction for exact in-situ compressive strength evaluation of concrete, grade and fck value of concrete.

5. Chloride content as per IS: 456: 2000,IS: 14959 (Part 2) 2001, B.S. 5328, ACI 201.2R-92

6. PH Test on Concrete sample to determine the acidic or alkaline nature of concrete

7. Tensile Strength Analysis of existing Steel Members:- To analyze the tensile strength of existing steel members/steel bar; how much tensile strength has been lost by member during the corrosion along with time.

8. Structural Drawings Preparation: Preparation of structural drawings with complete RCC details, section sizes and steel percentage by using profometer or GPR based scanner, it will give detailed cover depth and existing protecting layer of steel rebar, diameter of steel and number of steel bar.

9. Structure Analysis: To Analysis for additional one floor as per IS 456:2000,IS 800:2007 and IS 1893 in Seismic Zone.

10. Retrofitting Design: Design the retrofitting methodology to increase the load carrying capacity of the structure as per IS 13935-2009.

Number of Tests performed:- Ultrasonic Pulse Velocity-14 Nos Rebound Hammer Test- 40 Nos. Cover Meter & RCC Scanning- 3Nos. Carbonation, Core, pH Test- 3 Nos.

Crack Pattern Analysis- 10 Nos.

concrete.

Ultrasonic pulse velocity is a means of assessing variations in the apparent strength of concrete.

The quality gradation of concrete can be appraised at best qualitatively as `excellent', `good', `medium' or

`doubtful'. The meanings of the term `excellent', `good',

`medium' and `doubtful' are based on ultra sonic pulse velocity measured at site and are as per the nomenclature of IS 13311(part-1): 1992. To strike balance between the reliability, speed and damage to structure, core test have to be used to establish a correlation between rebound number index and the estimated in-situ strength with the USPV test results in the investigation.

Objective of testing:-

Ultrasonic pulse velocity test is used to establish the following:

Homogeneity of concrete

Presence of cracks voids, honeycombing and other imperfections

Changes in the structure of concrete which may occur with time.

Quality of one element of concrete in relation to another i.e. comparative quality analysis and gradation of concrete.

The values of dynamic elastic modulus of the concrete. References:-

BS 6089:1981 and BS 1881:Part203 IS 13311:Part1:1992

ASTM: C597-83.

Results of Ultrasonic Pulse Velocity Test

*Note: Total no of test sample = Sum of frequency

3.2 REBOUND HAMMER TEST:-

Purpose:-

This test gives a measure of the surface hardness of the concrete surface. Although there is no direct relationship

between this measurement of surface hardness and strength, an empirical relationship exists. Rebound hammer is the best known methods of comparing the concrete in different parts of a structure and indirectly assessing concrete strength. The rebound hammer should be considered as a means of assessing variations of strength within a structure rather than an accurate means of assessing the strength. Objective of testing:- Rebound hammer test is performed to determine the following:

Surface hardness

Uniformity of concrete over the structure Grade of concrete

Estimated strength which is derived from establishing a relationship between in-situ core strength and rebound number.

References:-

BS 6089:1981 and BS 1881:Part 202, IS13311(Part2):1992

ASTM C 805-02

Results of Rebound Hammer Test

*Note: Total no of test sample = Sum of frequency

3.3. COVER AND CARBONATION TEST:-

Carbonation Depth:-

Concrete cover layer acts as a good protective layer for the reinforcement. When whole Protective layer/cover depth is carbonated as per carbonation (B.S 4248) deterioration of structure will fall in deterioration period with linear rate. So full carbonated cover depth removal is mandatory to protect the steel bar from further corrosion and we have to increase the thickness of cover depth to protect the steel from futuristic corrosion.

Results of Cover and Carbonation Test:

Whole Protective layer is carbonated in present case. Carbonation depth is greater than depth of cover

1. CORE DRILLING METHOD FOR IN-SITU COMPRESSIVE STRENGTH ANALYSIS OF CONCRETE CORE IN LAB:-

   Purpose:-

   This test is known as a confirmatory test to get the idea about the compressive strength of the existing concrete. Core compressive strength is the best known methods of getting the in-situ concrete compressive strength in different parts of a structure at present time and indirectly assessing the fck value of concrete.

   Objective:-

   Compressive strength (Grade) of concrete fck value of concrete

   Estimated strength which is derived from establishing a relationship between in-situ core strength and rebound number.

   References:- IS516:1959 IS1199:1959 IS456:2002

   Results of Core Cutting Test:

2. Chemical Test

   Generally cast-in chlorides are chemically bound within the cement matrix and dont migrate through the concrete, while chlorides in-grassed are substantially free to move and diffuse through the pore solution into cement matrix and leads to

   corrosion in RCC. It is important to note that whether free chloride ions are leading to chloride-induced corrosion of the reinforcement or not.

   Chloride (water soluble) % mass of concrete (IS: 14959 (Part 2) 2001, B.S. 5328)

   Results of Chemical Test

3. CORROSION ANALYSIS ON THE BASIS OF HALF- CELL POTENTIAL TEST RESULTS:-

   Permeability of concrete has an inverse relationship with the concrete cover depth and is directly related to the corrosion of the reinforcement. The tendency of any metal to react with an environment is indicated by the potential it develops in contact with the environment. In reinforced concrete structures, concrete acts, as an electrolyte and the reinforcement will develop a potential depending on the concrete environment, which may vary from place to place. The schematic diagram for reinforcement corrosion mechanism is shown below: ASTM C876 standard provides information on the probability of reinforcement corrosion based on measured HCP values. The difference in voltage between the reinforcing steel and the current source can be correlated to the amount of corrosion.

   At most of locations steel are suffering from 95% risk of corrosion which clearly shows that risk of active corrosion is high which is not under permissible range. So we can say that reinforcement has lost its tensile strength due to corrosion.

4. STRUCTURAL STABILITY ANALYSIS FOR MILITARY HOSPITAL FAMILY WING BUILDING USING NON DESTRUCTIVE TECHNIQUE TESTS RESULTS AND INTERPRETATIONS

   Method of structural adequacy analysis and design parameters:-

   The seismic safety of a reinforced concrete building will depend upon the initial architectural and structural configuration of the total building, the quality of the Structural analysis, design and reinforcement detailing of the building frame to achieve stability of elements and their ductile performance under severe seismic lading. Proper quality of construction and stability of the infill walls and partitions are additional safety requirements of the structure as a whole. Any

   weakness left in the structure, whether in design or in construction will be fully revealed during the postulated maximum considered earthquake for the seismic zone 4 in the earthquake code IS: 1893.

   Assumptions in static analysis

   The basic assumptions in static analysis methodology are as follows:-

   1. The behavior of the structure is assumed to be perfectly liear and deformations are small

   2. All joints are rigid

   3. The members are subjected to axial, flexural and shear deformations

   4. The force deformation relationship remains linear during the entire load regime.

   5. Plinth beams are assumed Mathematical Modeling

   The structure is idolized as a 3-D space frame model. The beams and columns are considered as members. The floor slab load is given on beam members. The brick wall is used as a filler wall and is not casted monolithically with structure; hence this load is also given on beam members. The columns are assumed to be fixed at the foundation level.

   Loads for Superstructure and Sub structural elements:

   1. Grade of Concrete: M15 ( As per NDT Test )

   2. Steel: Fe415

   3. Slab thickness: 150mm

   4. Density of Concrete: 25kN/m³

   5. Density of Brick: 20kN/m³

   6. Ground floor to First floor level height = 3.65m

   7. Live load on other floors: 4kN/m²,

   8. Live load on roof : 1.5 kN/m², Dead Loads:

   9. Floor load: 4.75kN/m² (all dead load included in it like tiles, False ceiling and others)

   10. Top Floor load: 6.35kN/m² (all dead load included in it like top profile, False ceiling and others)

   Materials properties data for static analysis: (as given in test certificates of reports)

   1. Concrete

      1. Concrete grade: Grade of concrete: M 15

      2. Static modulus of elasticity : 5000fck

      3. Poissons ratio : 0.17

      4. Unit weight of R.C.C: 25 kN/m3

      5. P.C.C: nominal mix of 1:4:8

   2. Reinforcement Steel

   Yield strength Fy: 415 N/mm2 Conforming to IS 1786 -1985

   Static modulus of elasticity : 2 x 105 N/mm2

   Load combinations

   Combination of Loads considered in analysis: The structural design has been carried out in accordance with the provisions of the codes IS 456 2000 and IS 1893 2002 for Normal design conditions

5. Analysis Summary

   Beams Analysis Results

   Columns Analysis Results

   Foundations Analysis Results

   During Analysis the foundation size are found to be insufficient as per the SBC soil report. Hence need to be retrofit.

6. Retrofitting Methodology For Columns

1. Removal of loose concrete from the member so as to prevent from the deterioration or de-bonding issues that entire loose particle from the concrete should remove around 25- 50mm from all the sides of columns. After removal of loose concrete entire surface should be wetted by spraying water. Propped the slab during chipping by hydraulic jacts at 1

   @1sqm each.

2. After the removal of the loose mass of concrete for surface preparation the existing reinforcement is exposed to the atmosphere which is treated with the anti-corrosive treatment to avoid corrosion in the steel.

3. Based on the design aspect additional reinforcement is added to concrete with maintaining of proper alignment and cover with a lap length of 50Xdia of bar= 1 meters.

4. After anti-corrosive treatment to existing reinforcement, the Nito Bond EP Chemical is applied to the old concrete to prepare a bond between the old and new placed concrete.

5. After the application of the nito bond ep the the ties and shear connector should be laid as per design.

6. After the placing if ties and shear connector immediately shuttering is fixed, the shuttering is carried out to provide the desired shape and size to the structure after jacketing.

7. Pouring of Concrete is carried as per required thickness based on design aspect, and proper part that pouring should be done and also to be compacted properly by manual condition using needle vibrators.

8. Once the pouring done after period it should be de-shutter the joints of the shuttering occurs in column it should be filled with cement mortar layer.

9. For imparting durability water should be properly cured to casting surface that it should achieve strength. At suitable intervals curing of the surface to be done.

For Beams

1. Removal of loose concrete from the member so as to prevent from the deterioration or de-bonding issues that entire loose particle from the concrete should remove below upto 25mm from beams junction. After removal of loose concrete entire surface should be wetted by spraying water. Propped the slab during chipping by hydraulic jacks at 1 @1sqm each.

2. After the removal of the loose mass of concrete for surface preparation the existing reinforcement is exposed to the atmosphere which is treated with the anti-corrosive treatment to avoid corrosion in the steel.

3. Based on the design aspect additional reinforcement is added to beam with maintaining of proper alignment and cover with a lap length of 50Xdia of bar= 1 meters.

4. After anti-corrosive treatment to existing reinforcement, the Nito Bond EP Chemical is applied to the old concrete to prepare a bond between the old and new placed concrete.

5. After the application of the nito bond ep the the ties and shear connector should be laid as per design.

6. After the placing if ties and shear connector immediately shuttering is fixed, the shuttering is carried out to provide the desired shape and size to the structure after jacketing.

7. Pouring of Concrete is carried as per required thickness based on design aspect, and proper part that pouring should be done and also to be compacted properly by manual condition using needle vibrators.

8. Once the pouring done after period it should be de-shutter he joints of the shuttering occurs in column it should be filled with cement mortar layer.

9. For imparting durability water should be properly cured to casting surface that it should achieve strength. At suitable intervals curing of the surface to be done.

For Foundations

1. Removal of loose concrete from the member so as to prevent from the deterioration or de-bonding issues that entire loose particle from the concrete should remove around 50- 75mm from all the sides of foundation. After removal of loose concrete entire surface should be wetted by spraying water.

2. After the removal of the loose mass of concrete for surface preparation the existing reinforcement is exposed to the atmosphere which is treated with the anti-corrosive treatment to avoid corrosion in the steel.

3. Based on the design aspect additional reinforcement is added to concrete.

4. After anti-corrosive treatment to existing reinforcement, the Nito Bond EP Chemical is applied to the old concrete to prepare a bond between the old and new placed concrete.

5. After the application of the nito bond-ep the ties and shear connector should be laid as per design.

6. After the placing if ties and shear connector immediately shuttering is fixed, the shuttering is carried out to provide the desired shape and size to the structure after jacketing.

7. Pouring of Concrete is carried as per required thickness based on design aspect, and proper part that pouring should be done and also to be compacted properly by manual condition using needle vibrators.

8. Once the pouring done after period it should be de-shutter the joints of the shuttering occurs in column it should be filled with cement mortar layer .

9. For imparting durability water should be properly cured to casting surface that it should achieve strength. At suitable intervals curing of the surface to be done.

For Slabs

• Concrete Removal and Surface preparation

  The general procedure for marking area to prepare the surface of spalled area for carrying out repairs

  Fig Recommended Layout of Surface Repairs.

  Prior to preparation of concrete surfaces, exposed renforcement should be inspected for access clearance, cross- sectional area and location. Reinforcing bars must be further exposed if the remaining concrete is de-bonded from the reinforcing steel. Removal must be continued to completely expose the bar if more than half of a reinforcing bar perimeter has been exposed. For completely exposed reinforcing bars, a minimum average clearance of 25 mm or nominal maximum size of aggregate plus 5mm, whichever is greater, must be provided between the reinforcing bar and surrounding concrete.

  The process of Surface preparation is illustrated stepwise (Step 1 to 3) in Fig. The general procedure in preparing concrete and reinforcement surfaces for optimum bonding is to sandblast the surfaces and then remove dust and debris by air blasting,

  low-pressure water blasting, or brooming. If the damage is due to corrosion, a suitable coating may be considered after removal of total rust from its surface to protect the exposed reinforcing steel. Final inspection of the prepared area including remedying any deficiencies should be completed just prior to batching the repair material.

  • Apply Bonding Coat and Repair Application Polymer Modified Cement Mortars are used for repairs on old hardened concrete for repairing defects on exposed concrete surface only.

REFERENCES

Codes:

1. IS516:1959

2. IS1199:1959

3. IS456:2002

4. BS 6089:1981 and BS 1881:Part203

5. IS 13311:Part1:1992

6. ASTM: C597-83.

7. IS: 14959 (Part 2)

BIOGRAPY