Forensic Evaluation Techniques For Masonry Construction

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Forensic Evaluation Techniques For Masonry
Construction
Gerald A. Dalrymple, P.E.
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TOPICS

• INFRARED THERMOGRAPHY (IRT)
• SURFACE PENETRATING RADAR (SPR)

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CAPABILITIES

• Location Of Voids In Grouted Reinforced Masonry
• Location Of Voids In Composite Barrier Wall
  Systems
• Location, Position Spacing Of Structural
  Reinforcement
• Location Spacing Joint Reinforcement
• Location Of Embedded Conduits, Pipes, Chases, etc.

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NDT ADVANTAGES

• Investigations Generally Benefit From NDT Methods
• More Data
• Rapid Data Collection
• Better Representation Of Conditions
• NDT Methods Offer Quick Results With Minimal
  Disruption
• NDT Can Be Beneficial During Construction For
• Mock-up Evaluation
• Quality Assurance Tool During Construction
• Evaluation Tool For Completed Construction

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NDT DISADVANTAGES

• More Than One NDT Method May Be Required To
  Define Conditions
• NDT Methods Selected Are Largely Dependent On The
  Type Of Masonry Construction
• Composite Wall, Cavity Wall, Hollow Units, Solid
  Units
• Environmental Conditions May Effect Or Distort
  Results
• Construction Details Building Components May
  Effect Or Distort Results
• Some Conditions Cannot Be Reasonably Determined
  Without Destructive Testing As Verification

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INFRARED THERMOGRAPHY

• Operates In The Long Wave Infrared Range Of The
  Electromagnetic Spectrum (8-14 um)
• Converts Differing Amounts Of Infrared Energy To
  Corresponding Intensities Of Visible Light
• Image Is Influenced By Temperature And Emissivity
  Of Object

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INFRARED THERMOGRAPHY

• WHAT IS INFRARED ENERGY?
• Infrared energy is more commonly known as "heat".
• Heat is a form of light invisible to our eyes but
  detectable with our skin.
• Infrared light occurs at wavelengths just below
  red light, hence the name, infra- (below) red.
• Near-infrared is the "color" of the heating coil
  on an electric stove just before it glows red.

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ELECTROMATIC SPECTRUM
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INFRARED THERMOGRAPHY

• ADVANTAGES
• Completely Non-destructive With Very Rapid Output
• Digital Data Record To Memory Card Or Video Tape
• DISADVANTAGES
• Completely Dependent On Environmental Conditions
• Data Can Be Obscured By Building Components
• Not Effective For Some Types Of Masonry
  Construction

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SINGLE WYTHE CONCRETE MASONRY
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DOUBLE WYTHE CONCRETE MASONRY
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DOUBLE WYTHE CONCRETE MASONRY
IRT Signature
No IRT Signature
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INFRARED THERMOGRAPHY

• THERMAL ENERGY MUST BE PRESENT
• Solar Energy
• Applied Heat Source
• Infrared Signatures Are Captured Through The
  Lens Of An Infrared Camera
• With The Aid Of A Camcorder And Computer
  Software, The Image Can Be Recorder And Printed

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INFRARED THERMOGRAPHY

• ENERGY SOURCES
• Solar
• Direct Sunlight
• Heat
• Temperature Differentials
• Environmental
• Artificial Heat Sources

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INFRARED THERMOGRAPHY
Temperature Differentials Heat energy is
transferred and emitted (reflected) differently
through grouted and hollow masonry unit cells or
collar joints.

• When subjected to temperature differentials, heat
  is transferred through the masonry wall.

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INFRARED THERMOGRAPHY
Temperature Differentials Heat energy is
transferred and emitted (reflected) differently
through grouted and hollow masonry unit cells or
collar joints.

• Grouted cells transmit the majority of the energy
  and appear cold (Dark Gray).
• Hollow cells emit (reflect) the majority of the
  energy and appear hot (Light Gray).

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INFRARED SIGNATURE
Grouted Cells Appear Dark Gray Or
Cold Ungrouted Cell Appears Light Gray Or
Hot
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INFRARED THERMOGRAPHY
Solar Thermal Loading
Thermal equilibrium occurs during mid-day and the
middle of the night.
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INFRARED THERMOGRAPHY
Solar Thermal Loading

• Temperature Gradient As a rule of thumb a 10F
  temperature change in a 4-hour period is
  necessary to obtain reliable data.

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INFRARED THERMOGRAPHY

• LIMITATIONS
• Moisture Free moisture on masonry will
  significantly alter results due to the
  evaporative cooling effect on the surface of the
  masonry walls.

• LIMITATIONS
• Moisture Free moisture on masonry will
  significantly alter results due to the
  evaporative cooling effect on the surface of the
  masonry walls.
• Wind Convection losses, particularly around
  corners and parapets of buildings, can reduce the
  contrast and clarity of infrared images.

• LIMITATIONS
• Moisture Free moisture on masonry will
  significantly alter results due to the
  evaporative cooling effect on the surface of the
  masonry walls.
• Wind Convection losses, particularly around
  corners and parapets of buildings, can reduce the
  contrast and clarity of infrared images.
• Solar Discrepancies Solar exposure can vary
  significantly along or between walls. Solar
  energy effects the rate of loading based on
  exposure and angle of incidence.

• LIMITATIONS
• Moisture Free moisture on masonry will
  significantly alter results due to the
  evaporative cooling effect on the surface of the
  masonry walls.
• Wind Convection losses, particularly around
  corners and parapets of buildings, can reduce the
  contrast and clarity of infrared images.
• Solar Discrepancies Solar exposure can vary
  significantly along or between walls. Solar
  energy effects the rate of loading based on
  exposure and angle of incidence.
• Obstructions Staging, construction vehicles,
  trees and ongoing construction operations can
  obscure the target.

• LIMITATIONS
• Moisture Free moisture on masonry will
  significantly alter results due to the
  evaporative cooling effect on the surface of the
  masonry walls.
• Wind Convection losses, particularly around
  corners and parapets of buildings, can reduce the
  contrast and clarity of infrared images.
• Solar Discrepancies Solar exposure can vary
  significantly along or between walls. Solar
  energy effects the rate of loading based on
  exposure and angle of incidence.
• Obstructions Staging, construction vehicles,
  trees and ongoing construction operations can
  obscure the target.
• Architectural Features Metallic objects can
  affect the thermographic images of surrounding
  masonry.

• LIMITATIONS
• Moisture Free moisture on masonry will
  significantly alter results due to the
  evaporative cooling effect on the surface of the
  masonry walls.
• Wind Convection losses, particularly around
  corners and parapets of buildings, can reduce the
  contrast and clarity of infrared images.
• Solar Discrepancies Solar exposure can vary
  significantly along or between walls. Solar
  energy effects the rate of loading based on
  exposure and angle of incidence.
• Obstructions Staging, construction vehicles,
  trees and ongoing construction operations can
  obscure the target.
• Architectural Features Metallic objects can
  affect the thermographic images of surrounding
  masonry.
• Age of Construction At early ages, heat of
  hydration of the grout or water absorption by the
  masonry can affect the data.

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INFRARED THERMOGRAPHY
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RETAIL SHOPPING CENTERHOLMDEL, NEW JERSEY
Single Wythe Reinforced Concrete Masonry

• Location And Delineation Of Grout Voids Using IRT
• Verification Of Reinforcement Spacing And Splice
  Conditions

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WALL PANEL
INFRARED IMAGE
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WALL PANEL
INFRARED IMAGE
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WALL PANEL
BLOCKAGE
Blocked Cell
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EXPOSED VOIDS
BLOCKAGE
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FACE SHELL REMOVED
REINFORCEMENT INSTALLED
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GROUT PORTS INSTALLED
GROUTING IN PROGRESS
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REINFORCEMENT INSTALLED
IMAGE AFTER REPAIR
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INFRARED THERMOGRAPHY SUMMARY

• Requires Adequate Thermal Loading to Be Effective
  (Gain or Loss)
• Works Well on Grouted Single Wythe or Grouted
  Collar Joint Construction
• Air Spaces, Insulated Cavities, Acoustic
  Treatments And Water Obscure Results
• Data Can Be Gathered Quickly Provided There Is An
  Adequate Thermal Window
• No Data Related To Reinforcement Installation Is
  Obtained. Reinforcement Data Must Be Gathered By
  Other NDT Methods.
• Can Be Used As Part Of A QA/QC Program During
  Construction

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SURFACE PENETRATING RADAR
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SURFACE PENETRATING RADAR

• ADVANTAGES
• Continuous Data Collection At Walking Speed With
  Real Time Visual Output
• Does Not Disturb Finishes - Penetrates Surface
  Coatings, Carpet, etc.
• Requires Access From Only One Side
• Separate Antennas Available For Different
  Penetration Depths
• Ability To Distinguish Closely Spaced Targets
• Very Sensitive To Steel
• No Radiation Hazard - Transmitted Power Is Less
  Than A CB Radio

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SURFACE PENETRATING RADAR

• DISADVANTAGES
• Very Sensitive To Steel Air
• Post-tensioning, Rebar And Steel Conduits Produce
  Similar Signals
• Loss Of Resolution Vs. Penetration Depth (Deeper
  Penetration Less Resolution)
• Signal Interpretation Requires SPR Experience And
  Knowledge Of Construction Materials Methods

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SURFACE PENETRATING RADAR
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SURFACE PENETRATING RADAR
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SURFACE PENETRATING RADAR
Post-Tensioning Tendons at Profile High Point
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SURFACE PENETRATING RADAR
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SURFACE PENETRATING RADAR
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SURFACE PENETRATING RADAR

• CONCRETE APPLICATIONS
• Reinforcing Bar Location, Depth Slice Length
• Post-tensioning Tendon Location
• Conduit Location
• Void Location
• DISADVANTAGES
• Resolution Decreases Depth Of Penetration
• Water In The Section Can Obscure Readings
• Delaminations Can Obscure Readings

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SURFACE PENETRATING RADAR

• MASONRY APPLICATIONS
• Reinforcing Bar Location, Depth Slice Length
• Voids in Grouted Cells or Collar Joints
• Joint Reinforcement Location Depth
• Conduit and Chase Location
• DISADVANTAGES
• Cannot Penetrate Air Spaces or Cavities
• Water in Wall Can Obscure Readings
• Masonry Unit Cores or Cells Can Obscure Readings

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SURFACE PENETRATING RADAR
Anatomy of A Radar Signal In Masonry
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SURFACE PENETRATING RADAR
Anatomy of A Radar Signal In Masonry
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SURFACE PENETRATING RADAR
Back Face of Wall
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LOADBEARING MASONRY HIGH SCHOOL LANCASTER, PA

• Identify Grouting Reinforcing Deficiencies
  Using Surface Penetrating Radar (SPR)
• Development of As-Built Drawings Using SPR Data
• Produce Repair Design Documents
• Manage Repair Construction

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WALL REINFORCEMENT GROUTING
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WALL REINFORCEMENT SPLICES
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WALL REINFORCEMENT SPLICES
Course Above Splice
Course At Splice
Course Below Splice
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COLUMN REINFORCEMENT GROUTING
Level A Column T/3 Column Type C6 Column Design
Load 187 kips Design Reinforcement (8) 11
Bars
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COLUMN REINFORCEMENT GROUTING
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LOAD TRANSFER AT PRECAST PLANK
Dowel Bars
Wall
Topping Slab
Precast Plank Cross Section
Bond Beam
Plank Cores
Individual Bearing Pads 3-1/2 x 3-1/2
Masonry Wall Vertical Reinforcement Not Shown
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LOAD TRANSFER AT PRECAST PLANK
Axial Wall Load
CMU Face Shell Mortar Bedded
Grout Column In Void Cell Receives Little Load
Plank Floor Load, Each Face Transferred Through
Legs
Bearing Stress on Supporting Wall
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LOAD TRANSFER AT PRECAST PLANK
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LOAD TRANSFER AT PRECAST PLANK
Void Core Signal Reflection
Scan From Floor Surface
Black
White
Black
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LOAD TRANSFER AT PRECAST PLANK
SPR Scan of Precast, Hollow Core Planks Room
B113 Column Line H Scan Direction South to
North Scan Location Level B Floor, 2.5 from
face of wall
Voided Plank Core, Typical
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QUALITY ASSURANCE CMU BEARING WALLS
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US TREASURY BUILDINGWASHINGTON, D.C.
Multi-Wythe Brick Masonry Wall

• Identify Existing Chimney Flues Using Surface
  Penetrating Radar
• Development of As-Built Drawings Using SPR Data

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EXISTING CHIMNEYS AND FLUES
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TYPICAL SPR SCAN OF MASONRY WALL
(B-W-B)
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LOCATION OF FLUES IN WALL
Floor
4th
3rd
2nd
1st
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SURFACE PENETRATING RADAR SUMMARY

• Penetration Depth
• Minimum depth of objects resolvable is
  approximately one-half the wavelength from the
  antenna surface. For typical concrete and masonry
  materials, this translates to a minimum depth of
  1 to 1½ inches when using a 1500 MHz antenna.
• Maximum depth varies depending on material and
  antenna frequency. Maximum penetration is
  approximately 16 inches for plain concrete or
  solid masonry with a 1500 MHz antenna.
• Depth of penetration below the level of the rebar
  is approximately one-half the spacing between
  parallel bars. Welded wire mesh or congested
  rebar placed close to the surface can severely
  limit the ability to resolve deeper targets.
• Radar cannot penetrate electrically conductive
  materials such as metals or salt water. These
  materials act as reflectors.

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SURFACE PENETRATING RADAR SUMMARY

• Detecting Targets
• Minimum layer thickness or minimum distance
  between interfaces is approximately one-half the
  wavelength. For an air void in concrete or
  masonry, this corresponds to a minimum depth of
  approximately 1 inch for a 1500 MHz antenna. This
  means that most cracks and delaminations are not
  easily detected by radar.
• Embedded steel reinforcement as small as ¼ inch
  diameter can be detected due to the reflective
  property of metals and other conductive
  materials. Plastic conduit can be detected
  because of the annular shaped void that it
  creates not by the thin plastic walls of the
  conduit. Similarly, a ½ inch diameter unbonded
  monostrand tendon appears the same as a 4 rebar
  because the sheathing is too thin to detect.

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SURFACE PENETRATING RADAR SUMMARY

• Detecting Targets
• Radar waves attenuate in air, making it difficult
  to detect targets within large (deep) air voids.
  For example, rebar located in the hollow cell of
  a CMU will not usually be detected by SPR.
• To resolve discrete targets, such as individual
  steel rebar, the minimum spacing between bars
  must be at least 4 times the bar diameter.
• Because radar cannot penetrate metal, hollow
  steel objects, such as conduits, generate the
  same signal as a solid steel rebar or an unbonded
  monostrand tendon (provided the diameters are
  similar).
• Minimum length of survey area is approximately 24
  inches. The length of the antenna is
  approximately 6 inches, which leaves a minimum
  length of 18 inches for the data record. Scans
  which are shorter than 18 inches should not be
  used because the characteristic patterns
  necessary for data interpretation will not be
  fully developed.

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SPR RESOLUTION LOSS
Top of Slab
Bottom of Slab
Closely Spaced Reinforcing Bars
7 - 4
7 - 4
D Column Strip
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SPR TARGET IDENTIFICATION
Tendon Profile At Support
Tendon Profile At Mid-Span
E
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QUESTIONS?