Generic vibration criteria for vibration-sensitive equipment
The vibration criterion (VC) curves, commonly used in the design of facilities which house vibration-sensitive instruments and tools, were developed by the author and his colleagues, in the early 80's, published by SPIE in 1991 and by IEST in 1993. Each of the criterion curves A through E is associated with a 'line width' or 'detail size' which was an attempt by the authors to describe the capabilities of the tools with which each curve might be associated. In the years since the curves were developed there have been substantial developments in tool design and isolation. In this paper the curves are reviewed in the context of present-day tools and processes. Changes are proposed where these might be justified.
Response equivalent peak velocity: a new method for description of vibration environment for sensitive equipment in buildings
Vibrations that occur within buildings that effect vibration sensitive equipment are of periodic, random or transient nature. The common way to describe a vibration is to transform its information into the frequency domain and show a graph as a function of frequency. The fundamental problem is that there is no obvious way to scale the y-axis in such a graph so that vibrations of the three classes may be compared. A working group within ISO is now presenting a Technical Specification, ISO TS 10811, 'Vibration and shock in buildings with sensitive equipment'. We introduce a new concept to handle all vibration types with only one method. The vibration under investigation is set to excite a single degree of freedom mechanical system with a certain resonance frequency. A sine wave with this frequency is exciting another identical single degree of freedom system. The amplitude of the sine wave is then varied, until both system gets the same maximum response. The vibration under investigation is then characterized for this frequency by the equivalent sine amplitude, given as peak velocity, to be compatible with other methods. The response equivalent peak velocity as a function of frequency, characterizes the vibration.
Experimental investigation of the geotechnical properties and microstructure of lime-stabilized saline soils under freeze-thaw cycling
Abstract The Song-Nen Plain in northeastern China holds one of the three largest expanses of soda saline-alkali soil in the world. Due to its disadvantageous geotechnical properties, the saline soil in this area is unable to meet the needs of construction projects. This study evaluates the stabilizing effect of adding lime to such soils. Specifically, it investigates how the physicochemical and mechanical properties and microstructure of soda saline-alkali soil are altered by lime and how these changes are affected by both freeze-thaw cycling and the duration of curing. The results reveal that adding lime to saline soil transforms clay particles into sand and silt particles and causes the pore size distribution (PSD) to become bimodal, with small-pore and macropore populations. An increase in lime content leads to an increase in the unconfined compressive strength (UCS) but a gradual decrease in both the cation exchange capacity (CEC) and plastic index. Freeze-thaw cycles break up coarse particles and aggregate finer particles, increasing the diameter of macropores and decreasing the USC; however, the effect on specimens with >9% lime is negligible. It is further shown that the geotechnical properties of the soil change immediately after the addition of lime, indicating that the cation exchange reaction takes place very quickly. Furthermore, the pozzolanic reaction leads to an increase in the percentage of sand-sized particles and a decrease in porosity after 28 days of curing. Overall, these results indicate that it is feasible to use lime to improve the engineering properties of soda saline-alkali soil in this area.