|
|
Vibration Standards
Search Vibrationdamage.com
|
|
|
|
Search Vibrationdamage.com
|
|
Some understanding of ground vibration standards and velocity limits, how they were developed, what they say, how they are properly used and what their shortcomings and limitations might be, especially in construction contexts, is vital to evaluating the reliability of statements based on standards. Following is a relatively non-technical description of vibration standards generally, their important limitations, the standards most commonly used for construction and blasting vibration, the vibration velocity limits they set, how they may be properly applied and what their use might mean for someone whose home or property may have been damaged by construction vibration. Related Information
Vibration Standard Criteria
The one most accepted in the field as an indicator of damage potential is the peak particle velocity (PPV).[12] As the name implies, PPV is a measurement of maximum ground particle movement speed. It is specified in the U.S. in inches per second (in/sec) and in most of the rest of the world in millimeters per second (mm/sec). This quantity is measured in all three perpendicular directions ("axes") of the seismograph's "geophones", as the magnet-in-coil detecting devices, within the silver-gray, cylindrical seismograph transducer head seen in the photos, are termed. PPV is a "vector" quantity (i.e. it has both a value and an associated direction). The peak vector sum (PVS) is usually also quoted; it is simply the square root of the sum of the squares of the
individual PPV
values in all three vector directions measured by the seismograph. PVS is a "scalar" quantity, i.e. one with only a value, which is always larger than the individual PPV vector values.
The three axes (directions) of measurement, the longitudinal (sometimes called "radial", the vector connecting the orientation arrow, as seen at right on the top of the seismograph transducer shown at right, and the source of vibration), transverse (the vector in the same plane as, but perpendicular to, the longitudinal) and vertical (up and down) vectors, are always measured and reported separately. One reason for this is that they have different degrees of importance in causing damage. Structures are built to withstand vertical forces. For that reason, vibrations along the vertical vector are usually of lesser importance in causing damage, though not always benign.[11] Vibrations which differ in different measurement axes have the potential for causing shear in the home structure, which is a major contributor to damage effects. When in shear, different parts of the house move at different speeds or even in different directions, which can cause cosmetic cracking or even structural damage. Vibration standards usually do not take into account directly differences in damage potential between vibration direction components, simply specifying the same limits for all three axes of measurement.[21] Understanding Vibration Standards Vibration standards are set forth by governmental agencies or professional groups to provide guidance to those who might be expected to cause vibration in their work, in order to avoid causing damage. There are different ground vibration standards, which set different vibration velocity limits for varying vibration environments and diverse building types (see below). Thus, a judicious and reasoned choice of which standard to apply in a given situation is critical to proper use of, and benefit from, that standard. Ground vibration standard limits are usually depicted graphically similarly to the U.S. Office of Surface Mining (OSM) blasting standard and USBM RI 8507 blasting study plots at right,[6],[7] using log (logarithmic or non-linear) scales in both the horizontal and vertical directions.
The vibration intensity (peak particle velocity) is on the vertical scale and the vibration frequency is on the horizontal scale. Vibrations deemed "allowable" within these standards fall below the limits indicated by the central lines; "non-allowable" vibrations lie above the lines. Plotting the standards linearly (i.e. with equal intervals between units on the scales) will change the shape of the dividing line separating "allowable" from "non-allowable" vibrations dramatically, but will not change the standards themselves. All scientific studies have limitations, including those of vibration damage. Therefore, standards based on the studies will embody those limitations. Understanding the limitations of scientific work is just as important in using that work properly as is understanding what the work says. Within their scientific limitations, standards and the velocity limits set in them can be invaluable in helping to avoid unnecessary damage by telling contractors and others when their efforts should be of particular concern. They also suggest when and how vibration should be reduced to avoid damage. Using Vibration Standards Because not all vibrations felt by people are damaging to structures, vibration standards attempt to separate those vibration intensities and frequencies which are potentially damaging to structures from those which may be concerning to people, but pose relatively little damage probability. It is important to understand that ground vibration standards are properly used to judge the probability of a single ground vibration of a given size (peak particle velocity), duration and frequency composition causing damage to a collection of houses or buildings of similar construction (see below), rather than the probability of multiple or long-lasting vibrations causing damage to one house or building.[8] This differentiation is especially important in cases of construction vibration, where vibration is usually neither single nor short-lived. One way of stating what the OSM and USBM RI 8507 standard diagrams above really mean scientifically is: "For a given single blasting-caused vibration, lasting less than a few seconds, with ground movement frequency components and velocities (intensities) which fall below the dividing line defining the standard, 95% of essentially intact houses on firm foundations, two stories or less in height, having the dimensions of typical residences, will not be damaged by that single vibration." That might be a mouthful, but that's what the standard and the data really say, at least within the confines of the USBM RI 8507 study which underlies both the standard plots above right. If any of the assumptions or conditions which underlie a ground vibration standard are not met in a given situation, then any use of that standard in that situation is potentially both unwarranted and misleading. Such improper use may also create an unnecessary risk to surrounding structures, if construction activity is based on that improper use. For the blasting settings which have been, by far, the most extensively studied, it has long been recognized that there is no given level of vibration which will or will not cause damage:
Acceptable vibration levels set in vibration standards are based on statistical analyses of damage probabilities, assuming "Gaussian", bell-shaped data probability distributions
like the one shown at left.[15] Given the probability basis of standard limits, the mere fact that a given vibration is of an intensity within the "allowable" regime, even in an appropriately chosen and applied standard, cannot be taken as proof that a vibration of an "allowable" PPV did not or will not cause damage. It is scientifically inaccurate, inappropriate and misleading to say that it is "impossible" for a vibration of a given peak particle velocity (intensity) to cause damage to homes, even if it is within a given standard. If damage occurs from a vibration known to be within the "allowable" regime of a standard, that fact does not imply, by itself, anything about the construction, condition or design of the house(s) damaged. It could reflect an expression of statistical variation, differences between vibration intensities measured at the site of the seismograph and those at the house, local soil or geology conditions, differences in the frequency composition of the vibration, use of an inappropriate vibration standard, or vibration conditions which violate the assumptions behind the standard (e.g. construction vibrations mostly lasting longer than "a few seconds", as described in blasting standards), among several other alternative explanations. Our CVDG Pro chapter, Statistics and Vibration Damage, provides more insight into the role of statistics in setting vibration standards and the proper interpretation of the standards as reflective of probabilities, not certainties. Such statistical limitations don't imply that standards are without meaning, but they require that vibration standards be adopted, applied and interpreted thoughtfully and appropriately. Frequency-Dependent Damage Potential As described in the CVDG chapters, Vibration 101 and Vibration Frequencies, ground vibrations are usually complex, made up of multiple overlapping and interacting frequency components. The frequency components of the vibrations are important determinants of the damage potential. It is well known and understood that structures have natural vibration frequencies, called "resonances", a little like those of a tuning fork.[1] Such resonant vibrations in home and buildings are more felt than heard, due to their low frequencies. At the home's resonant frequency, any repeated or long-lasting vibrations (more than a "few seconds"), like those caused by construction, can add to one another to produce even larger vibrations in the house structure than those occurring in the ground (a process referred to as "amplification"). Thus, the vibration in the house grows, rather than dying away in a few seconds. Even minor components of a vibration which occur at or near the resonant frequency or frequencies are potentially dangerous to the home, if they continue longer than "a few seconds" (e.g. in construction settings). Such resonant phenomena also bring into play so-called "fatigue" (damage caused by repeated flexing) issues. For this reason, most ground vibration standards take into account the frequency dependence of the vibration damage potential, setting more rigorous standards for lower frequency vibrations. The OSM and USBM RI 8507 blasting standards shown graphically above both set lower ground velocity limits near home resonance frequencies than at higher frequencies, but these differences (a velocity factor difference of 2.67 between frequencies above 40 Hz and at 10 Hz) are smaller than the observed amplifications (a factor of up to 4 for corner vibrations in homes, up to a factor of 8 for mid-wall vibrations), even for short-lived blasting vibrations.[9] This difference between the known amplification factors and the smaller velocity factor ratios raises the question whether the velocity frequency factors may be set too low in those standards, even for the blasting vibrations for which they are intended. It is important to note that vibration standards set limits for ground movement velocities, not for velocities of movement in the home. Because of the self-reinforcing nature of vibrations with frequency components near the resonant frequencies, home vibration velocities can be substantially higher than the ground vibration velocities. Long duration, low frequency vibrations associated with construction are much more worrisome from the standpoint of producing resonant amplification of vibrations in the home than the relatively infrequent, short duration, higher frequency ones caused by blasting.[24] Even low velocity vibrations involving repeated ground impacts (e.g. pile driving and some demolition) or other impact-like sources (e.g. tracked equipment movement) are particularly concerning, due to their broad frequency distributions, which assure resonant interaction and amplification in the home. For more discussion of resonance and fatigue effects, see the CVDG chapter, Resonance/Fatigue. Blasting-Related Standards and Studies By far the most commonly used blasting vibration standard in the U.S. is the U. S. Bureau of Mines, Office of Surface Mining (OSM) standard,[1] shown above. It was developed in the early 1980's to address shortcomings of earlier, less stringent standards suggested by OSM. The OSM standard is based largely on the highly respected blasting vibration study done by the U.S. Bureau of Mines, Report of Investigations 8507 (USBM RI 8507) and studies referenced therein. As with most other standards, the OSM explicitly recognizes a frequency dependence of damage potential, with lower frequencies known to be more prone to causing damage. Many U.S. state and Federal agencies use this standard for blasting-related vibrations; others (e.g. contractors, vibration monitoring firms) use it inappropriately for non-blasting construction vibration.
An example of a construction vibration "compliance plot" showing the OSM and USBM RI 8507 limits is just above. It is identical to one appearing in a vibration monitoring report prepared for a road construction contractor; it depicts construction equipment-caused, not blasting, vibration from a videotaped construction operation. Such compliance plots, which can depict any standard chosen, are widely used in vibration monitoring reports. The data points indicate the velocity and frequency properties of various components of one vibration from that job. The vibration depicted in the plot above caused additional witnessed and videotaped damage, specifically correlated to the ongoing construction operation, in a home already damaged by construction. All the vibration frequency/velocity points are well within the "allowable" regime under the central lines for this blasting standard, providing a real-life demonstration that blasting vibration limits are inappropriately applied to construction vibration. Differences Between USBM RI 8507 Safe Blasting Levels and the OSM Standard For frequencies below 15 Hz, two limits are defined in the USBM RI 8507 study, on which the OSM standard is based, one at 0.75 in/sec PPV for "Modern homes, Drywall interiors" and one at 0.5 in/sec PPV for "Older homes, plaster on wood lath". The OSM standard does not explicitly recognize the Safe Blasting Levels of 0.5 in/sec PPV suggested in USBM RI 8507 for "Older homes, plaster on wood lath construction for interior walls" at frequencies below 15 Hz.[5] Instead, it adopts the USBM RI 8507 recommendation of 0.75 in/sec for "Modern homes, Drywall interior" at frequencies below 15 Hz. Thus, if you have plaster walls, the blasting recommendation in the USBM RI 8507 study is lower than the OSM standard. One further comment is in order regarding the USBM RI 8507 recommendations with respect to the 0.5 in/sec limit for houses with plastered walls. Many construction vibration types have sub-40 Hz, higher intensity components.
Often, they are the dominant frequency components (see Resonance/Fatigue). This differentiation is important, since vibratory compactor vibrations in a road construction job
often exceeded the RI 8507 0.5 in/sec blasting limit for plastered wall homes Misuse of Blasting Standards in Construction Settings The OSM standard is based on studies of damage probabilities from single short-lived blasting vibration events, rather than the semi-continuous ones generated by road or other construction using heavy equipment. The USBM RI 8507 study, on which it is based, indicates that continuous vibrations might require a more stringent standard:
Despite these and many other indications that blasting standards are inappropriate in settings with vibration lasting longer than a few seconds, the OSM standard is widely cited, even outside of blasting. It is also misused, despite the cautions to the contrary in the underlying scientific studies, by some governmental agencies, construction contractors and vibration monitoring firms for relatively long-lasting, non-blasting construction vibrations, perhaps because it sets very high limits on ground vibration velocities (intensities). Because such differences in application are so important, one must make certain that the correct and most applicable standards are utilized in a given setting. Construction-based vibration standards must be used for construction
vibrations The Swiss Standards Another set of ground vibration standards that is widely cited worldwide is the "Swiss standards" (SN 640 312a).[19] There are actually three separate "Swiss standards": one for blasting, a more rigorous one for pile driving and a still more rigorous one for machines and traffic. The last of these is the one which is most applicable to road construction and use, as well as most other forms of construction. Construction and Traffic Standards The most relevant U.S. standard in a situation where there are no, limited, inappropriate or inapplicable construction vibration standards in the relevant state or municipality is the Federal Transit Administration (FTA) standard. The Federal Transit Administration's Noise and Vibration Manual (shown at right) is one of the most widely cited sources for vibration standards for road construction and traffic in the U.S. It is well worth reading in detail, as it has a great deal of summary information on vibration, noise and other construction impacts, beyond the vibration standard itself. It defines standard limits for vibration in transportation-related construction situations, which is quite different from, and considerably more restrictive than, the OSM blasting standard. At the risk of some over-simplification, the FTA standard can be characterized as using the four structural categories and limits defined in the Swiss machines and traffic standard (quoted from Chapter 12 of the FTA standard[4], [13], [21] below): FTA Vibration Limits
A typical modern, wood-framed home with drywall ("sheetrock", "gypsumboard") interiors and essentially no prior damage would be considered a Class III building. A home significantly damaged by construction, or any historic home or structure,[14] should be considered as a Class IV structure.[20] While this assignment of damaged homes to Class IV might be disputed by some, both the scientific literature and the damage from the well-documented concrete-dropping incident described above provide support for such an assignment. The FTA standard differs from the Swiss one in that it applies the high frequency PPV limit in the Swiss standard at all frequencies. Thus, this standard is more lenient than the Swiss,[21] particularly at the lowest frequencies
of most concern for resonant interactions with the home. However, it is far more confining on construction vibration than the OSM blasting standard.
A comparison of these FTA vibration limits with the vibratory compactor vibration plot above shows that the vibration levels from the compaction operation exceeded one or more of the FTA standards over 100 times in just an 18 minute period in front of a single home. Most other homes in the area experienced many vibrations which exceeded the FTA standard. Over 600 vibration measurements with velocities in violation of the FTA standards were found in the partial data produced for the road reconstruction project which generated them. Municipal, County, State and Federal Vibration Standards Individual U.S. state and Federal government agencies have set various standards for acceptable vibration velocities in various settings. They tend to be derived from, or identical to, one or more of the basic standards discussed here. Since Federal and some state highway departments have been among the most active in considering construction vibration issues, insofar as they impact road construction, one should survey his own state's DOT web site for information on construction vibration standards specific to road and other construction in that state, if any exist at all.[3] Some municipalities also have vibration standards of their own, which may not be identical to the state standards. You should check on the Internet for vibration standards in your city by using search strings like "[name of city] vibration".[23] Such standards are too often set on the basis of advice from "experts" who do most of their work for construction or mining companies. Predictably, those standards are often based on the scientifically inappropriate, and much more lenient, blasting ground vibration standards, rather than construction standards. One good way to know if a municipal or state construction vibration standard is based on the U.S. OSM standard for blasting is to look for quoted limits of 0.75 or 0.5 in/sec. If these numbers are quoted, there is a high likelihood that the standard is derived from the OSM or USBM blasting standards. If your city has such municipal ground vibration standards based on blasting, their appropriateness in a construction setting involving activities other than blasting can be easily challenged from a scientific standpoint. A discussion about setting state or local vibration standards appropriate for a given locale and type of vibration source can be found in the CVDG chapter, Vibration Regulation. Most developed countries have standards for human-caused (i.e. excepting earthquakes) ground vibration in at least some circumstances.
just to name a few. In addition, there is an
Some of the standards referenced above do not set specific limits on vibration PPV's, but focus on proper procedures for measuring and analyzing vibration data. Others deal with machinery vibrations in factory settings, as well as construction and blasting-caused ground vibration. Most compare human vibration perception with the, often different, vibration levels necessary to cause damage in structures. There are also some separate, far more stringent, vibration standards for areas which house some types of sensitive scientific or medical equipment (e.g. laser tables, MRI machines, spectrometers of various types, electron microscopes, etc.).[17] Just as the OSM standard does not follow all the recommendations of the USBM RI 8507 study on which it is based, vibration standards around the world do not always implement the suggested or lowest allowable levels of vibration found in all scientific studies. For this reason, there may well be studies in the literature which give different limits for a given vibration situation than those quoted in the standards. If your structure or vibration source is significantly different from those covered by the standards, you should search the vibration scientific literature for recommendations more appropriate to your situation. Many of the standards have been updated or reestablished in the last few years, so one should always use the latest applicable version. In the U.S., acceptable peak particle velocities are quoted in inches per second (in/sec), while most other worldwide standards are quoted in metric ("SI" ("Systeme Internationale") or "MKS" ("Meter Kilogram Second")) units of millimeters per second (mm/sec). Divide a standard quoted in mm/sec by 25.4 to convert it to in/sec used in the U.S. A number of the most commonly cited ground vibration standards worldwide are tabulated in the CVDG Pro's Reference chapter, along with numerical parameters for vibration velocity calculations.[21] Of the world vibration standards, the FTA, Swiss, OSM, German, British and ISO standards are the most cited within the ground vibration literature.[22] You can get PDF-format electronic copies of virtually all of them over the Internet, though you may have to pay for some of them. Links to download the FTA, USBM and OSM standards for free are present on our More Information page. Summaries of the PPV limits of the most important standards worldwide can also be found in the CVDG Pro's Reference chapter and in the Reference section of the Vibrationdamage.com Ground Vibration PPV and Safe Distance Calculator, which includes a construction vibration calculator and two different blasting vibration calculators, available free to registered CVDG for Homeowners and CVDG Pro e-books owners, from the direct links provided in their Vibration Analysis Tools chapter.
|
|
|
E-mail to drzeigler@vibrationdamage.com or send online questions or comments about Vibrationdamage.com.
|
Vibration Standards is one chapter of the over 100 page 
The 
Scientific studies have shown that the PPV correlates best with damage potential of all the tested characterizations of ground movement (e.g. PVS, acceleration,
displacement, or strain). Most, though not all, ground vibration standard limits are quoted in PPV values,
The statistical nature of standards means that not all vibrations which are
deemed "allowable" (e.g. below the lines in the center of the standard compliance plots above)
(see left for 
involving heavy equipment use and blasting-based vibration standards for blasting. Use of scientifically inappropriate vibration standards is one of the most common mistakes made when vibration standards are cited.
Such mistakes often lead to damage in nearby buildings.
As with many other standards, acceptable levels of vibration in each of these standards are frequency dependent, with less vibration tolerated at frequencies below 60 Hz (Hertz, cycles per second) and still less below 30 Hz. The
Swiss standards are not commonly used, per se, in the U.S., although they are widely cited and influential in ground vibration discussions and research around the world. 
The Swiss SN 640 312a compliance plot at right above shows the same vibration
in the OSMRE/USBM RI 8507 compliance plot above, caused by repeatedly dropping a large chunk (about 1/2 ton) of concrete on the ground about 6 feet from
the seismograph (see videotape frame at left). It can be seen that the vibration at the seismograph is above several building type limits of the Swiss standard and of the related U. S. Federal Transit Administration standard, discussed
just below.
An expanded and updated version of the FTA Noise and Vibration Manual was issued in 2012 (cover page shown at right)..jpg)
Many of them are derived
from or related to, in some ways, the three discussed above. There are separate standards for:
