HOW TO AVOID A VIBRATION BREACH FINE #tricksofthetrade
Understanding vibration levels and limits accurately is critical. So ensuring the device measuring the vibration is installed correctly is paramount. Our favourite device for measuring vibration in terms of protecting buildings and structures is the AVA-M80 vibration monitor with a tri-axial geophone. This unit will measure the Peak Particle Velocity in 3 directions and provide real-time email and SMS alerts as well as having a long term 8-month battery life.
Vibration limits are mentioned in BS5228-2 for construction and demolition works on open sites. Below are a few steps that should be taken when measuring according to the standard and guideline, in terms of the limits only. These points are general observations of the standard, and you should employee a qualified engineer to make an assessment on project and practice before commencing any works as these notes do not cover all important considerations when measuring vibration.
Identify who or what we are protecting. In BS5228-2, there are two tables with defined limits, one for human perception and one for structural damage. Let’s focus on structural damage only.
Identify the type of building. What are the limits? They are noted in Table B2.
Take note of the frequency range and limits accordingly. Notice how the vibration limits increases with frequency, but generally a lower limit for all is normal used, assuming the vibration sensor is setup to the correctly filter profile and standard. If we know the frequency and the level, potentially we can avoid a breach which is why the AVA-M80 monitor can collect this dataset with vibration waveform data.
In the table you will see at 4Hz the vibration limit is 15mm/s for cosmetic damage right up to 50mm/s at 40Hz.
Note that Figure B.1 refers to cosmetic damage! What is cosmetic damage?
• Cosmetic damage is usually considered as the formation of hairline cracks on drywall surfaces, or the growth of existing cracks in plaster or drywall surfaces; in addition, the formation of hairline cracks in mortar joints of brick/concrete block construction.
In the standard it also documents other types of damage such as:
• Minor damage is considered the formation of large cracks or loosening and falling of plaster or drywall surfaces, or cracks through bricks/concrete blocks.
• Major Damage to structural elements of the building, cracks in support columns, loosening of joints, splaying of masonry cracks, etc.
So, what are the limits for Minor and Major damage? Well as the standard mentions.