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A more common practice when mounting to a concrete pad is to use vibration isolatorsThe two most common types of vibration isolators are steel spring and elastomer padThe primary purpose of vibration isolators is to reduce the noise and vibration which! would be transmitted from the genset to the foundation or supporting structure. A simple and effective method of mounting and applying pad type isolators is to place! non.skidding type isolation pads directly between the sub.base and floorThe number of pads required will be determined by the load bearing capability of the! pads and the genset.s weightFigure 2-1 Typical Installation of Spring Type Isolator ! MN2407 General Information 2-4 . Steel spring isolators are a very effective and commonly used. Steel spring isolators! are typically 95.98% efficient (reduces the transmitted vibration 95.98%) while a pad! type can be 75.88% efficient. Spring isolators also level the genset sub.base in the! event the foundation pad is not perfectly levelSpring steel isolators offer the highest level of vibration isolation, however higher levels! of vibration (although not detrimental) may be seen on some areas of the genset when! mounted on steel springs, due to the (almost) total isolation from the foundation. The! base of most steel spring isolators contains a non.skid pad. The base should be! mounted to the foundation pad as shown in Figure 2-1 or as recommended by the! isolator manufacturer A common practice is to pour a concrete pad directly on top of the floor slab and to! mount the genset on this pad. The purpose of the pad is to facilitate cleaning around! the genset and to provide a more level base. When using this method, floor strength! must support the pad and the genset. The pad should be at least 6in (150mm) thick! and extend beyond the genset in all directions 12in (300mm). Weight Of The Genset! The dry weight of the entire genset is shown on the Generator Set Specification Sheet. The wet! weight includes the fluids (coolant and oil). Figure 2-2 can be used to design the foundation! except in critical situations Figure 2-2 Approximate Weight vs. kW Output ! 2-6 General Informatiom MN2407 Designing An Isolated Foundation! If the genset cannot be mounted directly on a floor slab, or if it is desirable to isolate it from the! floor slab, then a separate foundation slab must be designedA massive concrete foundation is not required. Outside dimensions of the foundation should! exceed the outside genset dimensions by 12in (300mm). ! For single genset installation, the foundation weight should be a minimum of 1.50 times the! genset wet weight. ! For multiple genset installation, the foundation weight should be a minimum of 2.0 times the! genset wet weight. ! Figure 2-3 shows a method to calculate foundation thickness and the soil bearing load of the! foundation and generator set. The soil load bearing capacity under the foundation must equal or! exceed the load from the foundation and genset. If it does not, then a footing, as shown in Figure! 2-4 must be added to spread the load over a larger area Figure 2-3 Calculate Soil Bearing Load (SBL) Capacity ! Figure 2-4 Typical Footing on Foundation in Soil With Low Soil Load Bearing Capacity MN2408!General Information 2-6 Table 2-1 Approximate Load Bearing Capacities of Various Soil Typer Soil TSoil Txod ypeype! Safe Bearing Capacity! lb per ft2!kilo Pascals! Hard Rock . Granite etc50,000 . 200,000!2,395 . 9,576! Medium Rock . Shale etc20,000 . 30,000!958 . 1,436! Hardpan!16,000 . 20,000!766 . 958! Soft Rock!10,000 . 20,000!479 . 958! Compacted Sand and Gravel!10,000 . 12,000!479 . 575! Hard Clay!8,000 . 10,000!383 . 479! Gravel and Coarse Sand!8,000 . 10,000!383 . 479! Loose, Medium and Coarse Sand!8,000 . 10,000!383 . 479! Compacted Fine Sand!6,000 . 8,000!287 . 383! Medium Clay!4,000 . 8,000!192 . 383! Loose Fine Sand!2,000 . 4,000!96 . 192! Soft Clay!2,000!96! Table 2-1 shows approximate load bearing capacities for various types of soil if the actual load! bearing capacity of the soil under the foundation is not known Caution9 Check the local building codes for load bearing capacity requirements Caution9 If the soil is subject to freezing and thawing, the foundation must be extended below the frost! line. Check the local building codes . Reinforce the foundation with No. 8 gauge steel wire mesh placed horizontally on ! 6in (150mm) centers. As an alternative, use No. 6 re.bars on 12in (300mm) centers! horizontally. Minimum cover over the bars should be 3in (76mm). Suggested concrete mixture by volume is 1 part cement, 2 parts sand, and 3 parts! aggregate. Maximum slump of 4in (100mm) and a 28.day compressive strength of! 3000 psi (20,600 kPa). The size of the bolts holding the sub.base to the foundation should be sized to fit the! mounting holes shown on the Installation Diagram . Three.inch (76mm) iron pipe sleeves should be placed around the bolts in the! foundation to allow for any mislocation of the bolts after...

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