Why do buildings shake

Vibration can be disturbing to building occupants. Recent trends in office design have aggravated the problem. More and more offices are laid out as open plans, with the absence of full-height, floor-to-ceiling partitions. Consequently, there is less live loading in the building and less damping.

In the past, structural engineers designed first for strength and then used established procedures based on slab stiffness and the percentage of damping to check for vibration acceptability or serviceability. One leading authority in the field of perceptible vibration now holds that it may be preferable to design for serviceability first, and then verify strength.

Another approach is the judicious use of concrete reinforcing steel. This method was used successfully in the construction of a mechanical room on a foot span above an operating room of a hospital. Although the original design resulted in a floor natural frequency of 3 Hz, a frequency of 6 Hz was needed to isolate the vibration of the mechanical equipment.

Doubling the amount of concrete reinforcing steel doubled the stiffness of the floor and diminished the vibration, without increasing the cost of the structural steel or reducing the floor-to-ceiling height. Another alternative is to use a damping compound in the concrete, which increases the natural damping of the concrete and cuts the amplitude of vibrations by a factor of four.

Sign up for our Newsletter! Mobile Newsletter banner close. Mobile Newsletter chat close. Mobile Newsletter chat dots. Mobile Newsletter chat avatar. Mobile Newsletter chat subscribe. Prev NEXT. Structural Engineering. In addition to strengthening a building against earthquake shocks, engineers can actually reduce the force a building is subjected to. They install what are called base isolators , which isolate the base of the building from the earth's movements. Most are one of two forms.

Some are like giant hockey pucks that squish and deform as the building rocks atop them, absorbing some of the energy of the shaking. Others are sets of two horizontal surfaces, plates made frictionless so that they will slide past each other.

The building sits on the top plates, the bottom plates rest on the ground. When the earth lurches, only the bottom plates move, sliding back and forth under the top plates. Location, location, location Sometimes the characteristics of a particular earthquake and the ground a structure is on coincide in just the right or wrong way, and the quake is particularly devastating.

Occasionally, a seismic wave hitting a building will have a frequency that just matches that structure's natural sway. In physics terms, the building has the same resonant frequency as the wave. When this happens, multiple waves at the resonant frequency pass through the structure, their effects amplifying each other.

This makes for a very destructive force. The impact of resonance was very apparent after a large quake in Mexico City in Mid-range buildings of stories were in resonance with the seismic waves, causing those buildings to sufer more damage than shorter or taller ones. As quake waves pass through the earth, they are filtered in different ways by different kinds of soils. Some small scale materials tests can be done to verify the installed material matches the design specifications by taking samples and testing in a laboratory.

They would typically publish a report summarizing what they did, what they observed and their findings. While such reports are quite technical by nature, the main gist of it should be comprehensible to any reasonably intelligent person without an engineering background.

It's impossible to say if you overreacted since I was not there. While there is certainly cause for concern, imminent collapse World Trade Center style is highly unusual. I've seen many obviously failed buildings in developing countries in which squatters live without incident for years.

Yet one would have to be truly desperate to spend time in such buildings, as sudden catastrophic collapse does remain a possibility. I've encountered a vast range of vibrations in multi-dwelling buildings I have lived. Hear are the ones I can remember:. Note that all these sources are not the building structure itself, and are fairly easy to track down. I can't remember encountering a source of vibration or shaking whose source I could not pinpoint with a small amount if work.

If you still cannot pinpoint the source after putting some earnest effort into finding the source, it may actually be the building structure itself. This is not that far fetched if the building was not engineered building inspectors usually defer to a professional engineer for structural issues. Even if the building doesn't collapse, you will have made the correct decision with the information you had at hand at the time. Thereafter maintain a daily log with times, degree of movement and any other relevant information.

Get your friend to stay and report on a cell phone the movement while you are outside checking the source. If it still does not help a good engineer would be useful but very expensive. But if you are not having the peace of mind, leave the place and take action to get the deposit back and inform the owners and the authorities. Sign up to join this community.

The best answers are voted up and rise to the top. Stack Overflow for Teams — Collaborate and share knowledge with a private group. Create a free Team What is Teams? Learn more. My 5th top floor apartment is shaking; what might cause this? Ask Question. Asked 8 years, 10 months ago. Active 7 years, 2 months ago.