VIBRATION RESISTANCE OF STRUCTURES

The study of the sources and spectral composition of the vibrations at the construction site

An important factor in the vibration stability of the structure is the ratio of its own resonant frequencies and the predominant frequency of oscillations propagating in the soil massif of the foundation. Vibration measurements are performed using a three-component displacement sensors or accelerometers in passive mode. Spectral analysis of records obtained during a sufficiently long period of time (minutes, tens of minutes) in various parts of the building or land design construction allows to identify the maximum frequency of various oscillation modes and their sources (microseisms, traffic noises, vibration, operating of machinery).

Study of the spectral composition of vibrations on the surface of the soil massif

Analysis of the spectral composition of the vibrations obtained along the geophone lines in different frequency ranges (using sweep signals) gives a picture of the responses of the soil massif in different parts of the site to the effect of oscillations of a certain frequency. This makes it possible to evaluate the resonant properties of the layered soil massif in its subsurface part.

  Distribution of the spectral composition of vibrations in soils by depth

Виброграммы, полученные при возбуждении свип-сигнала на поверхности и приеме колебаний на различной глубине в скважине, дают картину распределения энергии различных частотных составляющих сигнала по глубине в грунтовом массиве. Это дает возможность определить глубины заложения фундаментов, опасные с точки зрения возникновения резонансных колебаний. Так максимум энергии колебаний в грунтах на глубине 1-7 м в диапазоне частот 30-50 Гц может быть опасным для устойчивости фундамента при воздействии транспортных шумов.

Definition of impact magnitude

Separate problem of estimating the limiting magnitude of vibration exposure, which causes the actuation of protective system equipment and its disconnection occurs when the event of shock impacts on the ground (pile-driving, drop of heavy loads from height). In this case, the measurements are performed synchronously at different points in the area, ranging from the place of impact to the location of the sensor of the protective system.
To assess the impact force in different parts of the site the velocity of longitudinal and transverse waves propagation in the soil obtained in advance can be used. Depending on the types of sensors, displacements, velocities or accelerations of the soil mass particles are recorded and calculated.