We always feel traffic vibration is dangerous on the safety of the buildings we are in, but is it, really ?

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Effect of traffic vibration on buildings
€ Sources of Vibration
Vibration in structures can relate to one of three main categories: seismic (ground) vibrations, acoustic
vibrations, and forces applied directly to the load on the working surface.
Seismic vibrations include all sources that make the floor vibrate. Common seismic vibration sources are
foot traffic, vehicular traffic, wind blowing the building, and building ventilation fans, to name a few.
Many of the sources that generate seismic vibrations also generate acoustic vibrations. The difference is
that acoustic vibrations are a measure of the effects of air pressure variations on the experiment.
The final contributor to vibration is forces applied directly to the load on the working surface: Examples
include vibrations resulting from a moving positioning stage with a sample on top of it or the vibrations
transmitted to the working surface via vacuum system tubing. In this article we will discuss the vibration
due to traffic.
€ How Traffic Generates Vibration
Like most vibration problems, traffic vibrations can be characterized by a source-path-receiver scenario
(Figure 1). Vehicle contact with irregularities in the road surface (e.g., potholes, cracks and uneven
manhole covers) induces dynamic loads on the pavement. These loads generate stress waves, which
propagate in the soil, eventually reaching the foundations of adjacent buildings and causing them to
vibrate. Traffic vibrations are mainly caused by heavy vehicles such as buses and trucks. Passenger cars
and light trucks rarely induce vibrations that are perceptible in buildings.
Figure 1: traffic vibrations can be characterized by a source-path-receiver scenario.
€ Factors Influencing Vibration(Level and Frequency)
Road traffic tends to produce vibrations with frequencies predominantly in the range from 5 to 25 Hz
(oscillations per second). The amplitude of the vibrations ranges between 0.005 and 2 m/s2 (0.0005 and
0.2g) measured as acceleration, or 0.05 and 25 mm/s measured as velocity. The predominant
frequencies and amplitude of the vibration depend on many factors including the condition of the road;
vehicle weight, speed and suspension system; soil type and stratification; season of the year; distance
from the road; and type of building. The effects of these factors are interdependent and it is difficult to
specify simple relationships between them. Table1 shows us the velocity of vibration in function of
activity and distance from road.

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Table 1: Approximate generated vibration levels for various sources
Table 2: Vibration and human perception motion

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€ Effect of Vibrations on People
Figure 2: Percentage bothered in the home by type of disturbance caused by traffic
Building vibrations caused by road traffic are not a health and safety concern; they are more a problem of
annoyance. Vibrations may be unacceptable to occupants because of annoying physical sensations
produced in the human body, interference with activities such as sleep and conversation ,rattling of
window panes and loose objects, and fear of damage to the building and its contents. Experience has
shown that people living in houses are likely to complain if vibration levels are only slightly above the
perception threshold, the major concern being fear of damage to the building or its contents. The
tolerance level varies widely from person to person and from area to area.
€ Potential for Building Damage
House owners may complain about damage induced by traffic vibrations, such as cracks in walls and
ceilings, separation of masonry blocks, and cracks in the foundation. However, vibration levels are rarely
high enough to be the direct cause of this damage, though they could contribute to the process of
deterioration from other causes. Building components usually have residual strains as a result of uneven
soil movement, moisture and temperature cycles, poor maintenance or past renovations and repairs.
Therefore small vibration levels induced by road traffic could trigger damage by “topping up” residual
strains. Consequently it is difficult to establish a vibration level that may cause building damage and,
therefore, controversy continues to surround the issue. In some cases, when a building is subjected to
vibration for many years, fatigue damage (that caused by repeated loading) may occur if the induced
stresses in the building are high enough. In addition to damage caused directly by vibration, indirect
damage may result from differential movements caused by soil settlement due to densification. Loose
sandy soils are particularly susceptible to densification when subjected to vibration. Several countries
have adopted standards for evaluating the effect of vibration on buildings.
€ Suggested Solutions and Preventive Strategies
House owners are likely to complain about traffic vibrations if the levels are only slightly above the
perception threshold, the main concern being fear of damage to their property. Building damage may
occur but it is unlikely to be caused solely by the vibrations themselves. Reducing vibrations to an
acceptable level could be difficult and expensive. For existing buildings, the most practical remedial

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measure is road maintenance .For new developments, increasing the distance between buildings and
roads , improvement of soil structure, and in ground pile barriers could prove effective(figure3)
Figure 3: Schematic illustration of an in-ground vibration barrier
Ghada Labaki
Civil engineer trainee