Effect of proof loading on the strength of lumber
A Monte Carlo simulation program was used in this study to evaluate the performance of No.2 and better grade combination of 38 mm x 140 mm Western Hemlock lumber proof loaded in bending. Two proof load magnitudes of 19.54 MPa and 23.05 MPa representing the 2nd and 5th percentile load levels of th...
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| Language: | English |
| Published: |
2009
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| Online Access: | http://hdl.handle.net/2429/12077 |
| Summary: | A Monte Carlo simulation program was used in this study to evaluate the performance of
No.2 and better grade combination of 38 mm x 140 mm Western Hemlock lumber proof loaded
in bending. Two proof load magnitudes of 19.54 MPa and 23.05 MPa representing the 2nd and
5th percentile load levels of the short-term strength respectively were selected for the proof
testing program to investigate the impact of proof loading. The rate of loading for all the testing
programs was 2679 MPa/hr.
The Canadian damage accumulation model was incorporated into the simulation program
to calculate the probability and time-of-failure of every member as well as the strength of the
survivors after testing at the two proof load magnitudes. Damage accumulated in a member was
quantified based on the strength of the weak survivors. It was found that damage accumulated
appears to be greater in the weaker survived members tested at the 2nd percentile load level
compare to the weaker survivors tested at the 5th percentile load level. Forty pieces of the 2000
members tested at the 2nd percentile load level broke during proof loading whereas 101 pieces
failed when the 2000 members were proof loaded at the 5th percentile load level.
Plots of cumulative probability distributions indicated no significant difference between
the original short-term strength and the strength of the survivors tested at both proof load levels.
However, approximately 11% damage was accumulated in the weakest survived members proof
loaded at the 2nd percentile proof load level compared to a damage level of 1.2% experienced by
the weakest survived member proof loaded at the 5th percentile load level.
It appears damage did not accumulate in the survivors with bending strength values
beyond 20.69 MPa and 24.48 MPa for the 2nd and 5th percentile proof load levels respectively.
Therefore, when a proof load magnitude of 23.05 MPa is selected to evaluate the performance of
38 mm x 140 mm Western Hemlock lumber in bending, more reliable survivors may be obtained
compare to a proof load magnitude of 19.54 MPa. |
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