Core requirements for seismic design of quartz sand equipment foundation
installation: a practical plan to withstand an 8-magnitude earthquake
Design standards: Implement the GB 50011-2010 "Code for Seismic Design of
Buildings" and GB 50191-2012 "Code for Seismic Design of Special Structures",
with differentiated responses in areas with a fortification intensity of 7-9
degrees
1. Three core indicators of basic seismic design
1. Bearing capacity requirements
- Concrete strength ≥ C35, foundation thickness ≥ 1/3 of the equipment's
bottom width (ball mill foundations are usually > 1.8 meters)
- Reinforcement ratio > 0.2%, with longitudinal steel bars having a
diameter of ≥ 20mm and a spacing of ≤ 150mm
- Characteristic value of foundation bearing capacity ≥180kPa (pile
foundation reinforcement is required for soft soil layers)
2. Seismic isolation and energy dissipation design
- Deformation of seismic isolation bearing ≥50% (such as lead rubber bearing
LRB800, with a horizontal displacement limit of 400mm)
- Damping ratio is set at 15%-25% (higher value for high-frequency vibration
equipment)
- The width of the seismic isolation trench is greater than 1.5 times the
estimated displacement (with a minimum of 500mm)
3. Frequency avoidance principle
- The fundamental natural frequency and equipment rotational speed should
avoid ±20% (e.g., if the rotational speed of a ball mill is 16rpm, the
fundamental frequency should be >19.2Hz)
- Spring vibration isolators (with a stiffness coefficient of 40-60kN/mm) are
used for large equipment
II. Special design for high-intensity areas with a seismic intensity of over
7
1. Optimization of structural form
- Overall raft foundation: thickness ≥ 2.5 meters, double-layered and
bidirectional reinforcement (Φ25@150)
- Shear key slot: shear keys are pre-embedded in the equipment base plate
(depth ≥ 300mm, spacing ≤ 1.5m)
- Seismic upgrade of anchor bolts:
- Increase the diameter by 2 grades (e.g., M36→M42)
- Embedded depth ≥ 30 times the diameter (M42 anchor bolt embedded depth is
1.26 meters)
- Add a disc spring to the nut for anti-loosening
2. Seismic isolation system configuration
- Triple defense system:
1. Foundation base: rubber isolation bearing (shear deformation 300%)
2. Between equipment and foundation: damping steel spring (deformation
±100mm)
3. Pipeline connection: flexible joint (displacement compensation ≥150mm)
III. Key control points of construction
1. Concrete pouring
- One-time continuous pouring (with an interval of ≤2 hours)
- Temperature gradient < 20℃/m (large-volume foundation with buried
cooling pipes)
- Curing period ≥ 28 days (with moisturizing and covering within 7 days)
2. Installation of seismic isolation bearings
- Levelness error ≤ 1/1000 (calibrated with a laser level)
- Pre-compression treatment: Apply 110% of the equipment's static load for 24
hours
- Protective sleeve seal: Prevents sand and dust from infiltrating the
friction surface
3. Dynamic inspection and acceptance
- Frequency sweep test: 0.5-50Hz sine wave frequency sweep (amplitude
±2mm)
- Resonance point verification: The vibration acceleration at the frequency
corresponding to the equipment's rotational speed is less than 0.2g
- Hammer test: fundamental damping ratio >5%
IV. Post-earthquake emergency checklist
1. Immediate stop inspection items
- Basic crack width > 0.3mm (detected with a crack gauge)
- Anchor bolt displacement > 2mm (measured with a dial gauge)
- Bumping/delamination of seismic isolation bearings
2. Mandatory inspection items within 72 hours
- Foundation settlement difference (measured with a level gauge, with an
alert required if adjacent points differ by >5mm)
- Equipment levelness (measured by laser alignment instrument, deviation
>1/1000)
- Hydraulic oil leakage of damper
V. Case Study of Earthquake Resistance Renovation of a Quartz Sand Factory in
Xinjiang
Background: Cracking of ball mill foundation after earthquake in 8-degree
fortification zone
Renovation plan:
1. Foundation reinforcement: External wrapping with 1.2m thick C40 concrete
(embedded rebar Φ28@200)
2. Seismic isolation upgrade: Install LRB1000 lead rubber bearings (shear
deformation 350%)
3. Pipeline renovation: Replacement of metal hose (compensation length
200mm)
results:
- Passed the simulation of a 9-degree rare earthquake (0.4g acceleration
without damage)
- The vibration value of the equipment has decreased by 60%
- Obtained national earthquake resistance demonstration project
certification
The seismic design of quartz sand equipment must strictly adhere to the
principle of "combining rigidity and flexibility": the foundation's rigid
anchoring provides bearing capacity, while the isolation system's flexibility
dissipates energy to mitigate seismic impacts.