Micro Drilling in-situ timber test - Incodo, Tauranga New ZealandProcedure for using Micro Drilling for Structural Wood Timber or Beam Damage Assessment
How to assess the structural integrity of wood framing or wood timbers in-situ using micro-drilling
     

  • WOOD BEAM MICRO-DRILLING PROCEDURES - CONTENTS: detailed procedures for using micro-drilling to detect wood damage or rot in wood structural beams & timbers
  • POST a QUESTION or READ FAQs about methods used in testing structural wood members for damage or decay & the role of micro-drilling tests for in-situ evaluation of structural wood beams, timbers, or other framing members in buildings..
  • REFERENCES

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Micro-drilling procedure details used for determining the soundness of wood structural members:

Micro-drilling wood damage testing involves drilling a 2 mm hole in timber members up to 300mm. Drill resistance and related data are processed by computer to provide a graph of wood density and other properties. This article series also compares using micro-drilling with other methods to screen both standing trees and wood structural elements for hidden damage. scribe the relationship between construction details and the occurrence of structural rot in timber frame buildings.

This article series describes the various methods used to test & evaluate the structural integrity of wood-framed buildings where focus is on the condition of structural wood posts, beams and other framing members. We discuss the problems surrounding hidden rot or decay, the presence or absence of moisture or other instrument-detectable clues, and the problem of subjective decisions to replace or not-replace suspect wood structural members.

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How does Micro Drilling Timber Assessment Work?

Paul Probett, Clinton Craig, Blake Probett, Incodo Forensic Building Specialists [1]

This article series on methods for assessing structural wood rot & damage is adapted & expanded from the author's "An Introduction to Micro-Drilling Technology for N. Z. Structural Timber Assessment" and is used with permission. We [DF] have added comments, some illustrations, and additional article citations.

At the references section we include a link to the original article as well as contact information for the authors and Incodo Ltd., a Tauranga, New Zealand forensic engineering firm.

[Click to enlarge any image or illustration]

Our discussion of micro-drilling is divided into three segments. Below is segment 2.

  1. WOOD BEAM MICRO-DRILLING ASSESSMENT - - Incodo study of microdrilling for wood structure assessment
  2. WOOD BEAM MICRO-DRILLING PROCEDURES - separate article, details of how micro drilling is used to assess wood structural member condition
  3. WOOD BEAM MICRO-DRILLING EFFECTIVENESS - separate article, Micro-Drilling: Resistance drill Methods for Wood Structural Member Assessment. Incodo Testing Program of Micro-Drilling for Wood Assessment

Procedure for Using Micro Drilling for Timber Damage Assessment

Testing involves drilling a 2 mm hole in timber members up to 300mm

The drill is computer controlled with drill bit rotation rpms and linear penetration independent of each other and at pre-set levels applicable to the timber species. This is a change from older generation microdrills that had rpm and penetration linked and power applied controlled by the operator.

Results are readable in real time via the onboard display as the graph is formed.

Typical testing for 100 mm p.rad framing is about 15 seconds.

Results are also processed according to developed timber specie parameters and appropriate standards (where applicable) so onboard software instantly gives a preliminary pass, fail or retest assessment of timber. Settings are adjustable to assist with the identifying of quality infractions, decay areas and splits or checks.

Information is then bluetoothed to a draft report and presented in a similar format to the following graphs and charts.





As highlighted in the 2010 RILEM State of the Art Report – In Situ Assessment of Structural Timber by Kasal and Tannert “ If strength values are require(d) the best drills available on the market are required as well as a high level of education and experience. This, proper education of the user is a critical point before applying resistance drilling” quote

Incodo endorse the above and suggest general usage, adjusting programmable settings interpretation and moderation of results is critical.

Micro-drilling In Situ Timber assessment

Test Results: Summary

  • Base of studs where decay transmitted from wet bottom plate – timber frequently found to be sound within 150 - 200 mm possibly allowing splinting of studs rather than full replacement
  • Double timbers joists and studs – frequently decay between members but sound outer faces.
  • Some surface decay has limited penetration
  • External corner studs behind direct fix cladding can have stepped clamping point decay


Test Results: Evaluation and Moderation

Test results indicate appreciable differences between sound and unsound timber. Noticeable anomalies on graphs indicative of issues include:

  1. Partial or Full loss of all or some latewood peaks.
  2. Smoothing of graphs along upper amplitude line affecting normal early wood and latewood norms (lower height of “saw teeth”).
  3. Significant variation across a graph in different area.
  4. General lowering of results in areas on same graph.
  5. Sloping shoulders as graph drops to plateau or valley.
  6. Sloping shoulder to graph at entry and exit points rather than near vertical step within 2-3mm of surfaces.
  7. Acceptable anomalies which are readily identifiable include changes induced by splits, checks, knots, junction between two timber members and pithy cores.

While software is set to handle many of these factors, moderation of individual graphs is part of the testing process and recommendations are that all reports are moderated before being provided.

Micro-drilling Wood Structure Test Protocols

Recommended testing involves checking bottom plates at 1.0m centres and as close as practicable to external corners. In addition testing focuses on high risk details such as window sill corners and points below, balcony to wall connections, base of apron flashings etc and wherever staining or other concern aspects are noted.

Inspection locations are plotted on a WIN 7 tablet using preloaded plans or elevations or on photos taken using the tablet’s main camera. Incodo have developed a suitable template for wirelessly transmitting data from the drill into an open report which can be prepared on the tablet or sent to the office for moderation and review.

Reports are comprehensive and targeted completion for reports is the same or following day after inspection.

Micro-drilling methodology testing for NZ timbers- A Basis

INCODO has undertaken substantial in-house testing to determine suitability of micro-drilling for assessment of low density plantation grown pinus radiata in particular.

Incodo copy of Graph from Bohumil Kasal & Thomas Tannert - Springer 2010Graph highlighting close correlations between X-ray density and resistance drill readings taken using a Resistograph micro-drill.

Quoting:

Profiles of radial X-ray density and drill resistance of the same larch sample.

Rilem - State of the Art Report In Situ Assessment of Structural Timber, Bohumil Kasal & Thomas Tannert, Springer 2010. [3][4][5][6]


 

In addition reliance has been based on studies by others* involving micro-drilling in Europe, USA and Australia related to structural timber in buildings and bridges.

The technology has been used for many years. The big difference is that the PD model is a new generation micro-drill with onboard firmware

*Ref www.printfu.org search “Resistograph” or “Sibtec”

Quote

“Wood density is the property which will be used as an example because of its’ close correlation with timber strength (Dadswell and Nicholls, 1959, Elliot 1970) …and because it is widely held by wood technologists to be the single most important wood variable (de Zeeuw 1965) According to Panshin et al (1963) the relationship between wood density and timber strength is expressed by

S = K (D)n

Where S is any of the strength properties, K is a constant, D is density and n is an exponent which depends on the strength property being considered”

- WOOD DENSITY OF RADIATA PINE: ITS VARIATION AND MANIPULATION – D J Cown, FRI

Note: Above information is copyright, commercially sensitive and is yet to be peer reviewed. It is not to be copied or circulated without the express and written permission of Incodo Limited. Adapted here by InspectaPedia.com, with permission from Incodo 8/5/2012, technical review is in process.

V4a 06/12 - ####

The original authors' article without the expanded discussion added here can be seen at An Introduction to Micro-Drilling Technology for N. Z. Structural Timber Assessment. [PDF]

Additional comments, illustrations, and technical citations addressing wood structure testing technologies have been added. We and the original authors invite and will reply to reader questions and comments using the comments box found at the end of this article. Initial technical review completed 8/6/201

 

 

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