Structural Integrity Testing of Trees and Other Solid Structures

Structural Integrity Testing of Trees and Other Solid Structures

The method called "Resistance Drilling Method" is one of the testing method for tree safety inspection. There are also others such as stress wave tomography etc.. The main advantage of the drilling method is that it yields fast measurement and also high local wood / structural condition information which one can get out of the drilling profile.

The drilling device "RESI PD" (PD) has different feed velocities which means that according to the hardness of the tree / structure, the drilling can be performed faster or slower. If there is a very hard tree species we anticipate a needle entering (feed speed) at 25-50 CM/min. If there is a soft surface then the PD can enter up to 200 CM/min.

The amount of drillings per tree / structure depends on damage and cross sectional shape of the tree / structure. The PD has a memory installed which allows for more than 100 measurements to be stored for reference depending on necessity.

Additional recording of the feed curve

The RESI PD also records the compressive force by the feed curve (blue). This is possible as the Power Drill (PD) has two motors – a drilling motor which is responsible for the needle rotation and the compressive motor which pulls the needle into the wood. The feed curve (blue) records the compressive resistance in % amplitude.

This additional recording of the feed curve (compressive force) next to the drilling curve (torsional force) makes it easier to get a better interpretation of the measurement data. The feed curve has a reduced or no shaft friction at all on the drilling needle. Thus, a decrease of the feed curve makes it easier to recognize the distinction between healthy and defective wood.


In this example 1, the drilling curve (green) shows a distinctly increasing drilling trend. At a drilling depth of 35 cm the drilling curve sinks and so it shows a wood defect. However, an interpretation in this increasing area is kind of difficult.

The feed curve (blue) sinks at 31 cm and at 35 cm it even sinks at 0 % amplitude. This indicates a cavity whereas the drilling curve (green) remains distinctly high (at 80 % amplitude) due to the shaft friction.


Resistance drilling devices use a 3 mm thin drilling needle which is being drilled into the wood where the resistances (drilling torque) and the feed force is measured as encountered by the flat needle head. Scientific studies proved that resistance drilling is highly accurate to measure wood density. Sound wood has higher resistance (higher amplitude) than a decayed wood. Changes in wood resistance gets documented on a graph and the changes in amplitude over drilling depth in CM is also noted.

With this method the inspector can determine if there is a decay present in the trees and can also get instantaneous results regarding the wall thickness of the remaining tree (intact wood). This method is used in combination with a visual inspection of the tree to get more accurate and scientific data on tree's structural integrity.

Product Features

  • Easy-to-read, clear display
  • Straightforward and fast digital data collection
  • Prevents fatigue with ergonomic lightweight design
  • High drilling performance with minimum power consumption
  • Rugged, splash-proof aluminium housing
  • Simultaneous recording of the drilling re­sistance and feed speed curve for improved identification of early & difficult to spot decay


  • Compact, battery-powered drilling resistance measuring device with integrated system guidance
  • Electronics in splash-proof housing
  • Easy to use with clear menus and automatic measurement
  • Adjustable feed speed up to 250 cm/min
  • Adjustable drill speed up to 5000 rpm
  • Automatic drill bit retraction
  • Fast and easy changing of drill bit, either automatically or manually
  • Robust, replaceable telescopic guide for drill bit
  • Powerful 18V lithium-ion rechargeable battery

The Power Drill (PD) is equipped with an electronic unit that gives clear support in taking, documenting and evaluating measurements.

Advantages of the electronic unit

  • Large, easy-to-read display (139 x37 mm)
  • Intuitive menu controlled with help of navigation knob
  • USB and Bluetooth interface for connecting to a PC or PDA
  • Measurements stored in internal memory
  • Scaling of measurement curves directly in the electronic unit for better curve interpretation
  • Enter ID number and comments
  • Pre-select drilling depth
  • Automatic Needle Breakage Detection

Display shows the following data:

  • Drilling resistance and feed curve
  • Feed speed and drilling bit rpm
  • Number of measurements stored
  • Free memory remaining
  • ID-number/comment
  • Date, time, battery level
  • Drilling angle
  • Needle Breakage Detection

PD Tool Functional Output:

  • Graphical and numerical cavity detection
  • Detection of decay and incipient decay
  • Flexible and individual adaptation to user specifications and operating conditions
  • Analysis of the feed data
  • Automatic diameter detection allows the automatic withdrawal of the bit after exiting at specific drill angles
  • Test results displayed immediately after the drilling