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For First Responders · Pedestrian Bridge Vibration

Pedestrian Bridge Vibration for a floor joist

Built for first responders planning or training for real incidents. Run fast what-if scenarios for response planning and training — no software to install in the field. Simulate a floor joist live below — adjust the inputs and watch it respond, right in your browser.

Beam Deflection

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Beam Deflection & BendingLive

Euler-Bernoulli beam theory

Controls

Presets

Span L (m)

Load P (kN)

Flexural rigidity EI (kN·m²)

Euler-Bernoulli theory relates a beam's deflection and internal moment to its load, span, and flexural rigidity EI. Deflection grows with the cube or fourth power of span, which is why doubling a span is far worse than doubling the load. Educational tool — not a substitute for a stamped structural design.

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Data Inspector

Max deflection1.30 mm

Max moment12.5 kN·m

Span/deflectionL/3840

Governing equation

δ = \frac{P L ^{3}}{48 E I} = \frac{10 \cdot 5 ^{3}}{48 \cdot 20000} = 1.30 mm

Reading this result: At L/3840 this beam clears the usual L/360 serviceability limit, so strength (not deflection) is likely to govern the design.

Runs locally in your browser — free forever. Scale to the cloud when reality gets heavy.

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Standing Waves

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Standing Waves on a StringLive

harmonics · nodes & antinodes

Controls

Speed1×

A string fixed at both ends can only vibrate at its harmonics. Each mode n has n+1 nodes (pink) that stay still while the antinodes swing — the physics of every stringed instrument.

Presets

Harmonic n

Fundamental (Hz)

Amplitude (cm)

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Data Inspector

Harmonicn = 3

Frequency330 Hz

Nodes4

Antinodes3

Wavelength2L/3

Governing equation

y = 2 A sin (k x) cos (ω t), f_{3} = \frac{3 v}{2 L} = 330 Hz

Reading this result: 3 half-wavelengths fit the string, so there are 3 antinodes (max swing) and 4 nodes (fixed points). At harmonic n = 3 the string sings at 330 Hz — exactly 3× the 110 Hz fundamental, and the wavelength is 2L/3.

Runs locally in your browser — free forever. Scale to the cloud when reality gets heavy.

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Frequently asked questions

Is this good for first responders?: Yes — this version of "Pedestrian Bridge Vibration for a floor joist" is framed for first responders planning or training for real incidents. Run fast what-if scenarios for response planning and training — no software to install in the field.
Do I need to install anything?: No. It runs in any modern browser, free, with no account required.