- Determine Design Wind Parameters
- Select the applicable design code or standard (e.g., ASCE 7, Eurocode EN 1991-1-4, GB 50009).
- Identify the basic wind speed for the project location, considering the return period and importance factor.
- Apply terrain category, exposure, and height correction factors.
- Calculate External Wind Pressure
- Compute the wind velocity pressure q(z) at different heights.
- Use the appropriate external pressure coefficients (Cpe) for cylindrical or polygonal silo shapes, considering wind direction and height.
- Determine the design external pressure:
pext(z,θ)=q(z)×Cpe(θ,z)×γwp_text{ext}(z,θ) = q(z) times C_{pe}(θ,z) times gamma_wwhere γwgamma_w is the wind load factor.
- Account for Internal Pressure
- If roof hatches, doors, or vents may be open during high winds, include internal pressure coefficients (Cpi).
- Calculate the net pressure:
pnet=pext−q(z)×Cpip_text{net} = p_text{ext} - q(z) times C_{pi}for both positive and negative combinations.
- Check Overall Stability and Foundation
- Calculate the total overturning moment caused by wind.
- Verify overturning safety factor (typically ≥ 1.5) and check sliding resistance.
- Evaluate anchor bolt tensile forces for uplift conditions.
- Evaluate Silo Wall Buckling
- Assess susceptibility to shell buckling under external suction.
- Compare the net design pressure with the critical buckling pressure of the wall, considering imperfections, wall thickness, and stiffener spacing.
- Strengthen with circumferential or vertical stiffeners if required.
- Roof and Appurtenance Checks
- Verify roof panels, rafters, and connections against uplift forces.
- Check platforms, ladders, guardrails, and ducts for local wind loads and connection integrity.
- Dynamic Effects and Fatigue
- For tall and slender silos, evaluate vortex-induced vibrations and ensure the natural frequency avoids resonance with wind excitation.
- Assess potential fatigue issues in welds and bolted joints due to fluctuating wind loads.
- Serviceability Limits
- Control top displacement, tilt, and ovalization to maintain structural alignment and operational functionality.
- Consider combined effects of wind with snow or ice accretion.
- Construction and Maintenance Considerations
- Ensure sealing strips, coatings, and protective layers resist wind-driven rain and erosion.
- Follow construction tolerances to prevent misalignment that reduces wind resistance.
- Implement periodic inspections for stiffeners, anchor bolts, and corrosion.
- Advanced Evaluation Methods (if needed)
- Perform wind tunnel testing or Computational Fluid Dynamics (CFD) analysis for complex layouts, clustered silos, or challenging terrain.
- Conduct nonlinear finite element shell analysis including imperfections for precise buckling resistance assessment.