BIZOMAT MAKEOS · Strength
Beam Drop Impact Check (I-Section Properties, Impact Factor, Dynamic Stress)
If a load drops onto this I-beam, what impact factor, dynamic stress and deflection result, and is the section strong enough?
Check of a fabricated or rolled I-section beam struck by a falling load: area, mass per metre, second moment and section modulus of the I-section from its flange and web sizes (as the section properties tool), then the static deflection and stress, the impact factor from the drop height and the dynamic stress and deflection for a simply supported or cantilever beam (as the impact load on a beam tool), against your allowable stress and deflection limit.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Section (I or H) | ||
| Overall depth | mm | Overall depth of the I-section. |
| Flange width | mm | Width of the flanges. |
| Flange thickness | mm | Thickness of each flange. |
| Web thickness | mm | Thickness of the web. |
| Density | kg/m³ | Density of the beam material. |
| Impact | ||
| Support | choice | How the beam is supported and where the load strikes. |
| Falling mass | kg | Mass of the falling object. |
| Drop height above the beam | mm | Height the object falls before it touches the beam. |
| Span (or cantilever length) | mm | Span between supports, or the cantilever length. |
| Elastic modulus | GPa | Elastic modulus. |
| Allowable stress | MPa | Allowable stress for the impact case (often close to yield for an accidental drop). |
| Largest dynamic deflection | mm | Largest deflection you accept during the impact. |
What each input means
Open an input to see what it is, its units, the worked example and the common mistakes, with a small diagram.
Section (I or H)
What this means: Overall depth
- What it is
- The overall depth of the I or H section, from the outer face of the top flange to the outer face of the bottom flange.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 100000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 200 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- A deeper section raises the second moment of area strongly, which lowers static stress and deflection.
- Get it right
- Measure the full depth over both flanges; it must exceed twice the flange thickness.
What this means: Flange width
- What it is
- The width of each flange across the section, measured edge to edge at right angles to the web.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 100000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 100 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Both flanges are taken as equal width; the web thickness must be smaller than this width.
What this means: Flange thickness
- What it is
- The thickness of each flange, measured at right angles to its face; both flanges are assumed the same.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 10000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 10 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- For tapered rolled flanges use the mean thickness from the section table.
What this means: Web thickness
- What it is
- The thickness of the web joining the two flanges, measured across the web.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 10000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 6 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Do not confuse it with the flange thickness; the web is usually the thinner plate.
What this means: Density
- What it is
- The density of the beam material, used to report the mass per metre of the section from its area.
- Units and format
- Enter a number in kg/m³: kilograms per cubic metre. The form accepts 0.000001 kg/m³ to 50000 kg/m³. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 7850 kg/m³ as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Only the mass per metre uses it; the impact calculation ignores the beam’s own mass.
- Get it right
- Take it from the material data sheet; it does not change the impact result.
Impact
What this means: Support
- What it is
- How the beam is held and where the falling load strikes it: simply supported on two supports with the hit at mid-span, or a cantilever struck at its free tip.
- Units and format
- Choose one of 2 options from the list: Simply supported, load at mid-span; Cantilever, load at the tip.
- Example
- The form opens with “Simply supported, load at mid-span” selected as a worked example. Choose the option that matches your case.
- Get it right
- Choose the case closest to the real supports; a cantilever is far more flexible than a simply supported beam of the same length.
What this means: Falling mass
- What it is
- The mass of the object that falls onto the beam, such as a dropped load, tool or component.
- Units and format
- Enter a number in kg: kilograms. The form accepts 0.000001 kg to 10000000 kg. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 20 kg as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Static stress and deflection rise in proportion to the mass; the dynamic values rise too, though the impact factor falls slightly.
- Get it right
- Enter kilograms; the tool converts to weight. Include anything attached to the object that falls with it.
What this means: Drop height above the beam
- What it is
- The height the object falls freely before it first touches the beam, measured from its release point to the contact point.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0 mm to 100000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 100 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- A higher drop increases the impact factor, roughly with the square root of the height for large drops.
- Get it right
- Measure the free fall to first contact, not to the floor; a zero drop still doubles the static values, as for a suddenly applied load.
What this means: Span (or cantilever length)
- What it is
- The distance between the two supports for a simply supported beam, or from the fixed end to the struck tip for a cantilever.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 1000000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 2000 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Static deflection rises with the cube of the length, which changes the impact factor and the dynamic results.
- Get it right
- Use support centres for the span, and the free length beyond the fixing for a cantilever.
What this means: Elastic modulus
- What it is
- The elastic (Young’s) modulus of the beam material, which sets the beam’s stiffness under the impact.
- Units and format
- Enter a number in GPa: gigapascals (1 GPa = 1000 MPa). The form accepts 0.000001 GPa to 1000 GPa. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 200 GPa as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Enter gigapascals, not megapascals. Take it from the material data sheet.
What this means: Allowable stress
- What it is
- The highest stress you accept in the beam during the impact, compared with the dynamic stress, from your design code or the material yield for an accidental case.
- Units and format
- Enter a number in MPa: megapascals (1 MPa = 1 N/mm²). The form accepts 0.000001 MPa to 100000 MPa. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 250 MPa as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Decide with your standard whether the drop is an accidental or a design case; the allowable differs between them.
What this means: Largest dynamic deflection
- What it is
- The largest deflection of the beam you accept at the moment of impact, for example to keep clear of equipment underneath.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 100000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 20 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- This is the peak deflection during the impact, not the permanent set after it.
Method and formulas
- I-section built from two flanges and a web: area, I_x, and c = depth ÷ 2 (as the section properties tool).
- Static deflection δ_st = W L³ ÷ 48EI (simply supported) or ÷ 3EI (cantilever); impact factor = 1 + √(1 + 2h ÷ δ_st) (as the impact load on a beam tool).
- Dynamic stress and deflection = factor × static values.
- Example: I = 20.983 × 10⁶ mm⁴; the impact factor is 161.24, giving 75.358 MPa and 1.256 mm.
Limitations
- Energy method ignoring the beam’s own mass, which lowers the impact factor for heavy beams.
- Local crushing under the impact point and flange buckling are not checked.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Check a beam under a hoist for an accidental drop
- Check a guard or stop beam for a falling part
- Compare beam sections for impact
Who it is for
- Design engineers
- Safety engineers
- Structural designers
What you get
- Section properties
- Static and dynamic deflection
- Impact factor and dynamic stress
Interpreting the result
- A stiffer beam has a smaller static deflection and so a larger impact factor: impact resistance comes from energy absorption, not stiffness alone.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 278, 234–246. Topic reference; no source tables or recommended settings are reproduced.
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Open the Beam Drop Impact Check (I-Section Properties, Impact Factor, Dynamic Stress) calculator