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USC-000002 · Options & decisions

Compare design options

25% more span, about 144% more deflection: compare the same IPE 300 beam at 6 and 7.5 metres and understand what changes.

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A practical task

Does the same section still meet your target at a longer span? Compare two simply supported beams. Keep the section, material and load per metre fixed. Change only the span.

Inputs & targets

Span
A: 6 m · B: 7.5 m
Section / material
IPE 300 / S235, major axis
Stiffness
E = 210,000 N/mm² · I = 8,356 cm⁴
Total uniform load
12 kN/m including self-weight, without additional load factors
Example target
Deflection at most L/300

How to proceed

  1. Establish the baseline

    Define supports, section, stiffness and total uniform load. Calculate the 6 m option first.

  2. Change the span

    Increase only the span to 7.5 m. Keep IPE 300 and the load per metre of 12 kN/m.

  3. Interpret the results

    Compare moment, deflection and the limit for each span. Keep the deflection assessment separate from resistance and stability.

USC-000002

Same section. Much greater deflection.

The longer option exceeds the chosen deflection target. Although the span increases by only 25%, deflection increases by about 144%. The following values were independently checked analytically.

Analytical comparison for IPE 300 at 12 kN/m
ResultOption AOption BUnit
Span L6.07.5m
Reaction at each support qL/236.0045.00kN
Maximum moment qL²/854.0084.38kNm
Maximum deflection w11.5428.17mm
Example limit L/30020.0025.00mm
w / (L/300)0.5771.1271

A: example target met
11.54 mm ≤ 20 mm

B: example target exceeded
28.17 mm > 25 mm

This assessment only addresses w ≤ L/300. It does not establish beam resistance or stability.

Why the difference is so large

For the same load per metre and flexural stiffness, moment scales with L² and deflection with L⁴. The span ratio 7.5/6 = 1.25 therefore gives 1.5625 times the moment and 2.4414 times the deflection. The example limit L/300, however, increases by only 25%.

w = 5qL⁴ / (384EI)
q = 12 N/mm · E = 210000 N/mm² · I = 83560000 mm⁴

The load per metre stays constant. The longer beam therefore carries a total applied load of 90 kN instead of 72 kN. A comparison with the same total force in kN would be a different task.

The comparison in CALC

These excerpts were captured from the live CALC example on 17 September 2026. CALC calculated the values analytically using Python. The table and deflection values agree with the independent reference calculation.

Original CALC table comparing results for 6 and 7.5 m spans
Live capture: analytical comparison in CALC.
CALC deflection for option A: 11.54 mm
Option A · 6 m span
CALC deflection for option B: 28.17 mm
Option B · 7.5 m span

The CALC diagrams are schematic and scaled separately. Compare the numerical values, not the drawn curve heights. The captures show the German interface.

What you can work with next

You can see why the longer option exceeds the chosen deflection target. Use this result to investigate a stiffer section or a different structural system next.

Scope & prerequisites

Analytical teaching example with a specified total uniform load and Euler-Bernoulli beam theory without shear deformation. L/300 is the chosen example target. Load combinations, actual serviceability requirements, resistance, stability and connections still require verification. No RFEM analysis or section optimization.

Read the workflow in the manual

Your starter task for CALC

Compare two simply supported beams: option A with a 6 m span and option B with a 7.5 m span. Both use IPE 300 in S235, E = 210000 N/mm² and I = 8356 cm⁴ about the major axis. The specified total uniform load is 12 kN/m including self-weight for each option; do not add self-weight again. Calculate analytically using Euler-Bernoulli theory, without shear deformation, load factors or RFEM access. Execute the numerical calculation in Python. Tabulate support reactions, maximum bending moment, maximum deflection, the example target L/300 and the ratio w/(L/300). Show moment and deflection diagrams for both options and the calculation steps. Explain the effects of L² and L⁴. The ratio assesses deflection, not resistance. Identify the remaining EC3, stability and serviceability checks.

Open example in CALC

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Watch the workflow

Video transcript

This silent 40-second explainer uses real CALC screenshots captured on 17 September 2026. It is an edited sequence, not a continuous screen recording. Both options use IPE 300, S235 and a total uniform load of 12 kN/m including self-weight. At a 6 m span, deflection is 11.54 mm, below the example target of 20 mm. At 7.5 m, it is 28.17 mm, exceeding the 25 mm limit. Moment scales with L² and deflection with L⁴. The diagrams are scaled separately. Resistance and stability still require verification; no RFEM analysis was performed.

The next step in your workflow

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