Floor vibration
From Wikipedia, the free encyclopedia
In the design of floor systems in buildings vibrations caused by walking, dancing, mechanical equipment or other rhythmic excitation may cause an annoyance to the occupants or impede the function of sensitive equipment. A calculation procedure to analyze steel framed floor systems is given in a design guide published by the American Institute of Steel Construction.
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[edit] Dance-Floor Vibration
Women appear to be able to detect the feel of a dance-floor more-so than men, this may be because men have tougher shoes, or are more comfortable than a woman in high-heels where a lack of "spring" in the floor is more likely to be noticed. (Some women even discount this and suggest it's nothing more than not having enough dances.) The serious side of this is: In the past (1940's) dancing was very popular and most hotels had a "ballroom" with used to be known as a Sprung Maple Floor. Now, in 2007, there are many techniques for making floors and the cheapest will often get the contract. Many "ballroom" dances are progressive, or require "progression" ( that's moving around the room), therefore the surface needs to be free from any stickiness. Modern concrete under-floors often specify a 3mm layer of sound-deadening material above(is it foam plastic like ethaline - something with a long-life since it will be expensive to replace). Another issue with dance floors is noise.
[edit] How to Build Dance-Floors Cheaply: PART ONE
The Building industry has often developed ideas which don't make it any further for many reasons. Ordinarily this will be perfectly okay, since there are many tiny nails each holding-on. However, a concern is the fact the wood is quite thin, maybe 20mm, and will dry-out in summers future. This being the case the grip will reduce and one can imagine that as wind twists the roof, the plates start to work loose. At some point they can fall out and the truss falls apart, with serious consequences. A solution - insist the plates are screwed together, so they exert a retaining force either side of the wood (ie a plate each side, bolted through the wood). The nailplate might need reinforcing by the hole but a large thick threaded washer would achieve this. The thread-ends would be knocked-over so they cannot unscrew. This principle is expanded below, with floors.
[edit] How to Build Dance-Floors Cheaply: PART TWO
The first requirement is a basic concrete floor set below the finish height. Secondly, there must be timbers of sufficient length to span the floor - this is where lamination comes in - by laminating the joists considerable spans can be accommodated with cheaper timbers and without the risk of warping/twisting (by careful matching ). One issue remains that lighter timbers cannot support a great weight, so it has to be supported along the length - this is where I have no experience but suspect a brick pier (even 1-brick high) will be too solid, and could give rise to regular points on the floor where it is "soft" and dead-hard....most unpleasant. The ideal would be a degree of spring equal over the floor. Two ways to do this would be:
ONE: Static A weight is applied (like bricks) until the surface drops 1 mm. Hardly a dangerous deflection and one that's easily measured with a vernier gauge, or some optical device/laser. By comparing this weight at different points it should be possible to conclude when it is right-enough. With some care a heavy man might become skilled to use a personal weighing machine taking the weight reading when the floor is suitably depressed. A pair of holes drilled into the metal casing can serve as alignment, for a laser-based system like that used with laser-levels.
TWO: Dynamic This relies upon a weight being dropped on the floor (like a cricket-ball) and recording the damped waveform (ie the resonance, or bounce). This will vary also and will tend to be higher where the static deflection is less...rather like tapping on the walls of an old castle, seeking secret passages.
[edit] How to Make it Even
Many places of support will tend to make for fewer variations....clearly if the floor was directly on the concrete it would be very even, but it would be uncomfortable...introducing some foam underlay might be sufficient, but this might deaden the floor, causing a lack of communication between dancers (and this could be important). An idea to possibly prevent this problem is to use laminated timbers (vertical joints) to span across brick supports - this allows ventilation and debris to be clear.....with elongated slots in the timber where there is support below. This will allow some static deflection since even at the point of support the upper part of the timber is only supported at a short distance. A series of bored boles should suffice although I'm sure some clever person can design a simpler scheme that performs better, whilst being less costly and easier to create.
[edit] Surface finish
Traditionally wood is used; it has a long-history of acceptance and has survived the test of time. There is no reason why there cannot be an underfloor of MDF, or bonded-fibreboard like chipboard provided it is protected from water, whether this is flood from below or a spillage from above. These issues alone may exclude such material as it is difficult to be certain. An under-floor of light timbers (Laths) could serve the same purpose as it will add strength to the expensive finish whilst being a lot cheaper. The upper finish should be "real wood" but as a temporary experiment a laminate could be tried - this may show signs of local wear, so there may be some advantage in laying it in zones, or use a better flooring close to doorways and certainly near toilets or kitchens where the risk of water damage will be greater. The entrance area to halls should trap dirt and stones as well as provide sound-deadening from the street, for this reason a strong carpet, or fibre-matting will be appropriate and consideration should be given to using "squares" that can be taken-up replaced or moved as they show signs of wear. Large coil mats to trap dirt are a good investment and need to be lit well to achieve their purpose. There are many sealants that should be applied to wood floor and this will depend on the supplier suggestions. Bear in mind the use so that you avoid a varnish which will show scratches. Tables and chairs should be provided with protectors to spread the load on the floor, to avoid damage to the wood fibre. If tubular-steel is used the end needs to be blind - not just covered up, as this will soon punch-through. Retro-fitting chairs might be a useful community job and its long term benefit should last several generations of done well. The support area of a steel tube is quite small, by filling-in the hole it is many times greater which lets the protector do its job much better. Adapted chairs will suffer less damage when used on grass, in the summer. Small dried branches are rough-tapered, banged-in and cut carefully to length. A final wallop makes them flush, apply protector with some glue. Paint at least one leg to identify the construction group.
