Design of shallow foundations for vibrating machines

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Civil Engineering Team Design of Shallow Foundations for Vibrating Machines By : Le Chi Hung, Ph.D Manager, Civil Engineering team Global Engineering Technology, Seoul, South Korea Website: www.getech.com.sg Email: chlee@getech.com.sg lchhung@gmail.com 12/3/2015 CONTENTS Civil Engineering Team  Machine and foundation types  Design basic  Design criteria  Vibration analysis methods  Design procedure  Analysis tools  Conclusions 12/3/2015 Machine and Foundation types Civil Engineering Team  Machine types  Common foundation types  Rotary machines  Block foundation  Elevated foundation  Reciprocating machines  Block caisson foundation  Piled-foundation  Impact type machines 12/3/2015 Machine and Foundation types Civil Engineering Team  Rotary machine  Example  High speed machine : Turbo generator, rotary compressor, pump  Operating frequency: 3000 -10000 rpm  Reciprocating machine  Example  Compressor, reciprocating engine…etc  Operating frequency < 600 rpm  Produces periodic unbalanced force  Unbalanced for can be approximately considered as sinusoidal in analysis 12/3/2015 Machine and Foundation types Civil Engineering Team  Impact machine  Produces Impact load  Example: Forge hammer  Operating frequency: 60 -150 blows/min  Dynamic loads reach in a very short time 12/3/2015 Design basic Civil Engineering Team  Design: based on the theory of harmonic motion  Assume: (1) Soil-foundation system as an idealized lumped parameter system (single mass, single spring, single damping for each vibration mode), or (2) a circular rigid plate resting on an elastic-half-space media An harmonic motion 12/3/2015 A lumped parameter system A Rigid plate on an elastic media Design basic Civil Engineering Team  Vibrating machine foundation system: resist static, dynamic forces  The dynamic response : Elastic response of the soil-foundation system  Static response: Permanent displacement caused by static and dynamic loads  The basic goal in the design is to limit the dynamic motion, which neither danger the machine nor disturbing working people 12/3/2015 Design criteria Civil Engineering Team  Basic design criteria    For static loads  No shear/bearing capacity criteria  No excessive deformation/Serviceability For dynamic loads:  No resonance (operating frequency and nature frequency should not similar)  Dynamic displacement amplitude must be below the permissible value (given by machine manufacturer)  Minimized unbalance forces and moments (mechanical engineers)  The amplitudes : within the permissible limit (provided by manufacturer)  Vibrating must not be annoying working people and no damage to adjoined structures Other requirements:  Water table should be below the foundation base [minimum below 0.5B (CP 2012-1), otherwise, use piled foundation]  Separated from other structures, component or other machine foundations  Foundation level should be below the level of adjoining structures  Acid-resisting coating needed for foundation 12/3/2015 Design criteria Civil Engineering Team  General considerations  Site condition (soil characteristics, ground water level, topography, seismicity, climate condition….etc)  Machine types (rotating, reciprocating, impact… etc)  Machine configuration (machine size, machine type, operating configuration,…etc)  Loading (static weight, dynamic force, testing, operating, shutdown…etc)  Operational requirements (settlement, vibration amplitude and resonance criteria…etc)  Frequency categories (after Bhatia, 2008):  Very low frequencies: 0-100 rpm  Low frequencies: 100 -1500 rpm  Medium frequencies: 1500-3000 rpm  High frequencies : greater than 3000 rpm 12/3/2015 Design criteria Civil Engineering Team  General flow chart for machine foundation design Soil data (static, dynamic) Trial FND dimension Static loads Dynamic loads Vibration analysis Load combination OK Stability check NG Strength check OK COMPLETED NG 12/3/2015 10 Design criteria Civil Engineering Team  Foundation mass ratio Machine types • Rotary machine • Reciprocating machine • Impact machine Elevated foundation • Top-desk mass • Total pedestal mass 12/3/2015 Values • Ratio = 2.5 – 4.0 • Ratio = 5.0 – 8.0 • Ratio = 2.5 – 3.0 for normal soil condition, Ratio =4.0 – 5.0 for poor soil condition Minimum thickness = m for all Values • Ratio should not lesser than that of machine • Close to the mass of the machine 20 Design criteria Civil Engineering Team  Minimum reinforcement requirement  For block foundation: minimum steel quantity of 25 kg/m3 -50 kg/m3 of concrete  For elevated foundation:    Reinforcement for top-desk: 100 kg/m3 – 120 kg/m3 of concrete  For base : 70 kg/m3 – 80 kg/m3 of concrete Minimum strength of re-bar shall be followed from standards (local codes, ASTM, BS standards…etc)  Longitudinal bars : Rsn = 390 MPa (Grade A–III)  Shear bars : Rsn = 235 MPa (Grade A-I)  Steel welded wire mesh : Rsn = 490 MPa (Class Bp-I) Fatigue factors should be applied to consider the effect of dynamic loads 12/3/2015 21 Design criteria Civil Engineering Team  Vibration amplitude criteria (after Sulu and Nathan, 1976; Bhatia, 2008)  Permissible amplitude by manufacturer is considered at machine level, whereas computed one is at foundation based level  Even calculated amplitude is acceptable for machine, it would be unacceptable for adjoin structures/machines  Similar machine might have different amplitude criteria  If done by foundation designer: must satisfy the general requirements (presented above)  Computed amplitude are always half amplitude, whereas given one are invariably double  Following criteria off vibration amplitude must be applied: 12/3/2015 22 Design criteria Civil Engineering Team  Vibration amplitude criteria (after Richart et al., 1970; Blake, 1964, ACI 351) 12/3/2015 23 Design criteria Civil Engineering Team  Vibration amplitude criteria (after Baxter and Berhard, 1967, ACI 351) 12/3/2015 24 Design criteria Civil Engineering Team  Vibration amplitude criteria (Bhatia, 2008) Foundation for rotary machine 12/3/2015 Permissible vertical amplitude (mm) Low speed rotary machines (100 -100 rpm) • Operating speed 100 -500rpm • Operating speed 500 to 1500rpm • 0.2 to 0.08 • 0.08 to 0.04 Medium speed machine (1500 -3000 rpm) • 0.02 to 0.04 High speed machine ( >3000 rpm) • 0.02 to 0.005 25 Design criteria Civil Engineering Team  Vibration amplitude criteria (after Richart, 1970; Bhatia, 2008) Foundation for reciprocating machine • Operating speed 300 -1500rpm • Operating speed 100 to 300rpm Foundation for impact machine • Hammer foundation Foundation for hammer crusher • Operating speed ≤ 300 rpm • Operating speed > 300 rpm 12/3/2015 Permissible vertical amplitude (mm) • 0.2- 1.0 • 1.0 Permissible vertical amplitude (mm) • 1.0-4.0 Permissible vertical amplitude (mm) • 0.3 • 0.1 26 Design criteria Civil Engineering Team  Vibration amplitude criteria (after Barkan, 1962) 12/3/2015 27 Design criteria Civil Engineering Team  Resonance criteria ± 20% 12/3/2015 28 Design criteria Civil Engineering Team  Resonance criteria  Low for high speed machine and high for low speed machine  Frequency of Soil-FND: minimum ± 20 % far away from the machine frequency  Consideration to avoid possible resonance in practical (Das and Ramana, 2010):  System frequency ≤ 0.5 × machine frequency ( speed ≥ 1000 cpm)  System frequency ≥ 1.5 – 2.0 × machine frequency ( speed < 350-400 cpm)  Increase FND weight  decrease possible resonant frequency  Increase FND area  Increase possible resonant frequency  Increase G of soil (soil improvement)  Increase resonant frequency 12/3/2015 29 Analysis tools Civil Engineering Team  Calculating by commercial software (DYNA N) 12/3/2015 (STAAD Foundation) 30 Analysis tools Civil Engineering Team  Example of calculation using STAAD FND 12/3/2015 31 Conclusions Civil Engineering Team  Based on the machine data given by machine manufacturers and Geotechnical investigation report The foundations for vibrating machines can be designed  Foundations for vibrating machines are subjected to static and dynamic loads  Dynamic forces are much smaller than the static forces, but they are applied repeatedly  Therefore, dynamic (vibration) analysis must be performed to ensure that the soil-foundation system behaves as an elastic material during the life time of the machine Otherwise, the soil-foundation system will be deformed excessively under the dynamic force from the machine  The most important factors are (1) natural frequency of the machine-soil-foundation system, and (2) amplitude of vibration of the machine during operating 12/3/2015 32 Civil Engineering Team Question? 12/3/2015 33 Civil Engineering Team Thank you for your attention 12/3/2015 34 ... foundations for vibrating machines can be designed  Foundations for vibrating machines are subjected to static and dynamic loads  Dynamic forces are much smaller than the static forces, but... reinforcement requirement  For block foundation: minimum steel quantity of 25 kg/m3 -50 kg/m3 of concrete  For elevated foundation:    Reinforcement for top-desk: 100 kg/m3 – 120 kg/m3 of. .. engineer for foundation design should be provided by Machine Manufacturer 12/3/2015 14 Design criteria Civil Engineering Team  Example of machine data and layout for a pump 12/3/2015 15 Design