assessment existing concrete structures

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Assessment of Existing Concrete Structures in the

Absence of Drawings

Assessment of Existing Concrete Structures in the

Absence of Drawings

Presented by: John M. Grill, P.E.Senior Engineer

Presented by: John M. Grill, P.E.Senior Engineer

WDP & Associates, PC is a Registered Provider with The American Institute of Architects Continuing Education Systems (AIA/CES). Credit(s) earned on completion of this program will be reported to AIA/CES for AIA members. Certificates of Completion for both AIA members and non-AIA members are available upon request.

This program is registered with AIA/CES for continuing professional education. As such, it does not include content that may be deemed or construed to be an approval or endorsement by the AIA of any material of construction or any method or manner of handling, using, distributing, or dealing in any material or product.

Questions related to specific materials, methods, and services will be addressed at the conclusion of this presentation.

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Copyright Materials

This presentation is protected by US and International Copyright laws. Reproduction, distribution, display and use of the presentation

without written permission of the speaker is prohibited.

© Whitlock Dalrymple Poston & Associates, PC 2011

(WDP & Associates)

A common problem facing design professionals involved in the

modification, repair and reuse of existing structures is how to assess the

capacity of an existing concrete structure when the original design

plans and specifications are not available. The assessment requires an

understanding of the future use, structure type and dimensions,

material properties used in the original construction, the extent of

deterioration present and current building code status of the structure.

This presentation describes methods for assessment of existing

structures with a focus on the assessment of the existing concrete

material properties and structural conditions.

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Learning ObjectivesLearning Objectives

At the end of this program, participants will be able to:

• Identify critical structural parameters and properties that are necessary to obtain,

• Obtain familiarity with industry publications offering guidelines and techniques for obtaining information related to evaluating existing structures,

• Recognize some available test methods (destructive and nondestructive) for sampling and gathering the desired data, and

• Obtain familiarity with how these test methods are applied in practice.

MotivationMotivation

• We have a need to evaluate existing structures

– Repair/rehabilitation is needed

– Change in building use/occupancy

– Sustainable construction

• Drawings are commonly not available

– Lost over time

– Changes in ownership

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Assessment GoalsAssessment Goals

• ACI 364.1R “Guide for Evaluation of Concrete Structures Before Rehabilitation”

• Develop as-built drawings

– Existing geometry

– Structure type

• Identify current conditions

– Deterioration

– Variations/additions to original construction

• Determine material properties

ConsiderationsConsiderations

• Structural assessment

– Current conditions

– Member geometry

– Material properties

• Analysis requirements/limitations

• Building code requirements

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Typical Parameters to DetermineTypical Parameters to Determine

• Verification/identification of current geometry/member sizes

• Location and spacing of embedded items

– Mild reinforcing steel, post-tensioning, conduit, etc.

• Damage assessment

– Corrosion

• Locating hidden flaws and defects (voids, trapped moisture, poor consolidation, etc.)

• Concrete properties

• Reinforcing steel properties

Motivation – Why NDT?Motivation – Why NDT?

Older Structure – some signs of deterioration

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Methods to Verify ConditionsMethods to Verify Conditions

• Measurement

– Direct measurement

– Laser scanning

• Destructive test methods

– Coring

– Cutting

– Drilling

Methods to Verify ConditionsMethods to Verify Conditions

• Nondestructive test methods

– ACI 228.2R “Nondestructive Test Methods for Evaluation of Concrete in Structures”

• Visual Tactile/sounding methods

• Pachometer/eddy current devices

• Surface Penetrating Radar (SPR)

• Impact-Echo (IE)

• Electrochemical corrosion testing

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Visual/Tactile – Sounding SurveyVisual/Tactile – Sounding Survey

• Visual Survey

– ACI 201.1R “Guide for Making a Condition Survey on Concrete in Service”

• Tactile – Sounding Survey

– Used to identify locations and limits of delaminations in concrete

• Chain-dragging or hammer sounding

• Shallow delaminations are identified by a “drummy” or “hollow” sound

Tactile – Sounding SurveysTactile – Sounding Surveys

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Pachometer/Eddy Current DevicesPachometer/Eddy Current Devices

• Used to identify location and approximate depth of embedded metallic objects

• Locate position and spacing of masonry wall ties and steel studs in brick veneer systems

• Location position and spacing of embedded reinforcing steel in concrete slabs and reinforced masonry walls

Surface Penetrating RadarSurface Penetrating Radar

• Uses electromagnetic energy to locate objects, subsurface flaws, or interfaces within a material

– Thickness determination (member sizes)

– Location/orientation/depth of reinforcement or conduit

– Track post-tensioning tendon trajectories

– Locate voids below slabs-on-grade or within CMU masonry

– Identify splice locations

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Surface Penetrating RadarSurface Penetrating Radar

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Post-Tensioning Tendon Rebar Wake

Surface Penetrating RadarSurface Penetrating Radar

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Impact-EchoImpact-Echo

Based on evaluation of stress waves generated by an elastic impact on a concrete surface

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• Applications

– Thickness of members

• ASTM C1383

– Location of internal defects

– Repair quality assurance

– Often used in conjunction with other methods

Impact-EchoImpact-Echo

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Impact-EchoImpact-Echo

Impact-EchoImpact-Echo

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Impact-EchoImpact-Echo

• Summary

– Requires significant experience

– Powerful method for flaw detection

– Applications to quality control

– Verification of results is critical

• Information Sources

– Construction documents

– Construction testing records

– Historical material properties

• CRSI References

– In-situ testing

– Sample extraction and testing

Material PropertiesMaterial Properties

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Material PropertiesMaterial Properties

• Concrete

– Compressive strength

– Durability

• Air content

– Chloride concentrations

– Carbonation

• Reinforcing steel

– Yield strength

– Corrosion damage

Concrete Sampling and TestingConcrete Sampling and Testing

• Chloride content analysis

– Cast in concrete during construction

– Diffusion of de-icing salts

• Carbonation testing

– Reduction in concrete pH

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Concrete Sampling and TestingConcrete Sampling and Testing

• ASTM C42 – “Standard Test Method for Obtaining and Testing Drilled Cores and Sawed Beams of Concrete”

• ACI 214.4 “Guide for Obtaining and Interpreting Compressive Strength Results”

– Corrections for sample conditions

– Number of samples

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Concrete Sampling and TestingConcrete Sampling and Testing

• ASTM C856 – “Standard Practice for PetrographicExamination of Hardened Concrete

– Air content

– w/c ratio

– Cement content

– Aggregate types/sizes/gradation

– Carbonation

– Microcracking

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Concrete Sampling and TestingConcrete Sampling and Testing

Estimation of Concrete StrengthEstimation of Concrete Strength

• ACI 228.1R “In-Place Methods to Estimate Concrete Strength”

– Probe / Pin penetration – ASTM C 803

– Pulse velocity – ASTM C 597

– Rebound hammer – ASTM C 805

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Estimation of Concrete StrengthEstimation of Concrete Strength

• Faster than core testing

– More samples can be tested

– Identify low strength areas

– Require correlation with core samples

Estimation of Concrete StrengthEstimation of Concrete Strength

• Windsor Probe – ASTM C 803

– Utilizes a powder charge to drive probes into the concrete with a known force

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Estimation of Concrete StrengthEstimation of Concrete Strength

Estimation of Concrete StrengthEstimation of Concrete Strength

• Pulse velocity – ASTM C 597

– Measure travel time of an ultrasonic pulse

– Relative compressive strength

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Estimation of Concrete StrengthEstimation of Concrete Strength

Estimation of Concrete StrengthEstimation of Concrete Strength

• Rebound Hammer – ASTM C 805

– Utilizes an internal spring and rod to strike the concrete with a calibrated force

– Easy to use

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Estimation of Concrete StrengthEstimation of Concrete Strength

Reinforcing SteelReinforcing Steel

• Verify yield strength

– 30 to 40 to 60 to ?? Ksi

• NDT Methods

– Not possible

• Grade marks

– Hard to find

• Destructive tests

• Corrosion damages

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Reinforcing SteelReinforcing Steel

Reinforcing SteelReinforcing Steel# 6 Bar

# 4 Bar

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Reinforcing SteelReinforcing Steel

• Yield strength

– ASTM A370 “Standard Test Methods and Definitions for Mechanical Testing of Steel Products”

– CRSI – historical data

Reinforcing SteelReinforcing Steel

• Electrochemical corrosion testing

– Half-cell potential – ASTM C 876

• Likelihood of corrosion

– Concrete resistivity – 4 pin Wenner method

• Concrete’s ability to resist flow of electrons

– Corrosion rate measurement – linear polarization methods

• Current rate of corrosion in reinforcing steel

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Corrosion AssessmentCorrosion Assessment• Polarization Resistance

– Measure of corrosion current

– Based upon evaluation of polarization resistance of reinforcing bar

– Allows measurement of rate of corrosion

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Analysis ConcernsAnalysis Concerns

• Capacity of Existing Structure

– Account for in-situ conditions

– Account for actual material properties

– Account for construction process

• Unbraced length changes

• Shoring

–Loads imposed

• Temporary loads

• Design for “future” loads

Analysis IssuesAnalysis Issues

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Building Code IssuesBuilding Code Issues

• Project specific assessment

• When do current code requirements have to be satisfied?

– Grandfather clause?

– Seismic requirements?

– Energy codes?

• IBC – 5% rule

Concrete Repair CodeConcrete Repair Code

• ACI 318 – Building Code Requirements for Structural Concrete

– New construction

• ICRI Concrete Repair Manual

– Collection of industry guidelines and documents

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Concrete Repair CodeConcrete Repair Code

• ACI 562 – Code Requirements for Evaluation,Repair, and Rehabilitation of Concrete Buildings

– Final stages of development

– Expect completion in 2012

– Parallel to ACI 318 for repair

– Adopt into IEBC or IBC

• Code requirements not guidelines

– Evaluation

– Repair design

– Quality control

SummarySummary

• Existing structures commonly encountered

– Lack of design / construction documents

– Need to preserve / protect these structures

• Assessment

– Numerous methods exist

– Generally project specific

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SummarySummary

SummarySummary

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SummarySummary

• Existing structures commonly encountered

– Lack of design / construction documents

– Need to preserve / protect these structures

• Assessment

– Numerous methods exist

– Generally project specific

• Analysis / Codes

– More involved than new structures

– Repair code to be published in 2012

AIA Continuing Education SystemsAIA Continuing Education Systems

Learning Objectives:

• Identify critical structural parameters and properties that are necessary to obtain,

• Obtain familiarity with industry publications offering guidelines and techniques for obtaining information related to evaluating existing structures,

• Recognize some available test methods (destructive and nondestructive) for sampling and gathering the desired data, and

• Obtain familiarity with how these test methods are applied in practice.

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Resources/ReferencesResources/References

• American Concrete Institute (ACI)

• American Society for Testing and Materials (ASTM)

• Concrete Reinforcing Steel Institute (CRSI)

• International Code Council (ICC)

• International Concrete Repair Institute (ICRI)

Questions?Questions?

This concludes this portion of thethe American Institute of Architects

Continuing Education Systems Course.

Please take a few moments to complete the Evaluation Form.

John M. Grill, P.E. | Senior Engineer703.257.9280 main | 703.257.7589 fax | jgrill@wdpa.com

Keith Kesner, Ph.D., P.E., S.E. | Associate203-354-4503 main | 203-354-4528 fax | kkesner@wdpa.com

Whitlock Dalrymple Poston & Associates, P.C.10621 Gateway Boulevard, Suite 200 | Manassas, VA 20110 | www.wdpa.com