First,is the beam strong enough that it doesn't fail by the fibers on the bottom being torn apart, a fiber failure. Second, is the beam stiff enough that there will not be excessive deflection. A bouncy floor, cracked tile or plaster would be examples of this. Third, is the beam strong enough that its fibers don't slip past one another, bend a magazine and watch the pages slide past one another. This is a horizontal shear failure. A SRTB is a Sawn Round Timber Beam. This is defined as a round beam that has been sawn or shaved on one surface such that the sawing or shaving does not exceed 3/10 of the radius at any point. The left output column is for full round beams, the largest diameter required by the three checks is the correct size The right hand output is for SRTB's, again the largest diameter required controls. The full round beams use Hahney's formulas from the "Log Span Tables". Design values and section properties of SRTB's is from "Standard on the Design and Construction of Log Structures" |

Total load on Beam(pounds) | Maximum Allowable Fiberstress in Bending (PSI) | ||

Span of Beam (inches) | Modulus of Elasticity (PSI) | ||

Select Species and Grade | Maximum Allowable Horizontal Shear (PSI) | ||

Full Round Logs | Sawn Round Timber Beams |
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Mid Span Diameter of Unsawn Log Required for Bending | |
Minimum Diameter for SRTB in Bending | |

Minimum Diameter of Unsawn Log Required for L/360 Deflection | |
Minimum Diameter of SRTB for L/360 | |

Minimum End Diameter of Unsawn Log Required for Horizontal Shear | |
Minimum End Diameter for SRTB in Shear | |