Steel Beams
Common span-to-deflection limits for steel beams are selected according to occupancy, finishes, partitions, vibration sensitivity, and whether the limit applies to total or live-load deflection.
Allowable Deflection Table
L / limit| Application | Limit / Result | Engineering Note |
|---|---|---|
| General floor beams | L/360 | Typical live-load deflection reference |
| Roof members, ordinary finishes | L/240 | Common roof serviceability reference |
| Members supporting brittle finishes | L/480 | Use when finishes are sensitive to movement |
Code note: These are common preliminary serviceability references, not a substitute for the adopted edition of AISC, ACI, Eurocode, or local regulations. Confirm load combination, member type, finish sensitivity, vibration, creep, and long-term effects in the project design.
Reinforced Concrete Beams & Slabs
Reinforced-concrete deflection checks commonly distinguish immediate and long-term effects. Creep, shrinkage, sustained loads, cracking, and non-structural finishes can control the final limit.
Allowable Deflection Table
L / limit| Application | Limit / Result | Engineering Note |
|---|---|---|
| Floor members, live load | L/360 | Typical limit where finishes are not highly sensitive |
| Roof members, live load | L/180 | Common roof live-load reference |
| Members supporting brittle partitions or finishes | L/480 | More restrictive finish-protection criterion |
Code note: These are common preliminary serviceability references, not a substitute for the adopted edition of AISC, ACI, Eurocode, or local regulations. Confirm load combination, member type, finish sensitivity, vibration, creep, and long-term effects in the project design.
Cantilevers
Cantilever deflection is particularly visible and can affect drainage, glazing, partitions, and user comfort. Limits are often expressed using the cantilever length L, measured from the support to the free end.
Allowable Deflection Table
L / limit| Application | Limit / Result | Engineering Note |
|---|---|---|
| General cantilever serviceability | L/180 | Typical preliminary reference |
| Cantilever supporting brittle finishes | L/240 | Use a stricter project criterion where required |
| Sensitive façades or finishes | Project-specific | Coordinate with architect, façade engineer, and code |
Code note: These are common preliminary serviceability references, not a substitute for the adopted edition of AISC, ACI, Eurocode, or local regulations. Confirm load combination, member type, finish sensitivity, vibration, creep, and long-term effects in the project design.
Limit Comparison
The denominator controls the strictness of the limit. For the same span, L/360 permits less movement than L/240 and is therefore the more restrictive criterion.
Allowable Deflection Table
L / limit| Application | Limit / Result | Engineering Note |
|---|---|---|
| 6 m span at L/240 | 25 mm | 6,000 / 240 |
| 6 m span at L/360 | 16.7 mm | 6,000 / 360 |
| 6 m span at L/480 | 12.5 mm | 6,000 / 480 |
Code note: These are common preliminary serviceability references, not a substitute for the adopted edition of AISC, ACI, Eurocode, or local regulations. Confirm load combination, member type, finish sensitivity, vibration, creep, and long-term effects in the project design.