Finite Element Analysis(FEA)
Mitigating Structural Resonance
Impact Testing & FEA-Based Structural Modification
The Problem
A glass bottle manufacturing facility transports raw materials through silos mounted on a steel support platform. Each silo is equipped with vibration exciters designed to promote material flow during operation.
Over time, two structural “I” beams supporting the platform developed excessive vibration levels. The vibration became severe enough to make the platform unsafe for personnel to stand or perform maintenance activities.
Initial investigations indicated structural resonance as the likely cause — a condition in which a structure’s natural frequency coincides with an external excitation frequency, resulting in dangerously amplified vibrations.
Fig. 1 — Impact test: Mode 2 identified at 25.450 Hz
Key Observation:
The vibration exciters operated at 24.4 Hz.
Impact testing later identified the beam’s second natural frequency at 25.450 Hz, showing near coincidence with the excitation frequency and confirming Mode 2 torsional resonance.
Our Approach
Technomax Middle East LLC conducted a two-stage engineering investigation:
1. Impact Testing
An instrumented impact hammer test was performed on the in-situ beam to experimentally determine its natural frequencies and mode shapes under actual operating boundary conditions.
2. Finite Element Analysis (FEA)
A validated 3D FEA model of the beam assembly was developed to:
Confirm the resonance condition- Correlate experimental results
- Evaluate potential structural modifications before physical implementation
FEA results confirmed the issue:
- FEA Mode 2 Frequency: 24.406 Hz
- Closely matching excitation frequency → resonance condition verifieds
Before: Mode 2 24.406 Hz (resonance)
After: Mode 2 36.411 Hz (safe)
Fig. 2 — FEA Mode 2 torsional shape: before and after modification
The Solution
To eliminate resonance, a structural modification was proposed:
A 5 mm thick stiffener plate was added between the top and bottom flanges of the “I” beam and welded on both sides of the web
This modification effectively converted the open I-section into a closed, box-like configuration, significantly increasing torsional rigidity.
The effectiveness of this modification was evaluated using FEA modal analysis prior to physical implementation.
FEA modal analysis of the modified beam confirmed the effect:
Results
Mode 2 shifted from 24.406 Hz to 36.411 Hz — a +12 Hz increase — moving the beam’s natural frequency well clear of the 24.4 Hz excitation frequency and fully eliminating the resonance condition.
- Before Modification:
Mode 2 = 24.406 Hz (Resonance Condition)
- After Modification:
Mode 2 = 36.411 Hz (Safe Operating Range)
The structural modification produced a +12 Hz frequency shift, moving the beam’s natural frequency well away from the 24.4 Hz excitation frequency, thereby fully eliminating the resonance condition.
Fig. 3 — Isometric view of the modified beam with stiffener plates
Conclusion
Through a combination of impact testing, validated FEA Analysis & modeling, and targeted structural redesign, Technomax Middle East LLC successfully mitigated a critical resonance issue affecting plant safety and operational reliability.
The solution:
- Eliminated hazardous vibration levels
- Improved structural stability
- Enabled safe personnel access to the platform
- Avoided costly structural replacement
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