Load Path Uncertainty in a Wood Structure and the Effect on Structural Reliability

The roof truss bearing points of a light-framed wood house were instrumented with load cells. It was found that under dead load alone, symmetric and theoretically identical truss reactions have significant variation. A similar degree of reaction discrepancy was found under the application of uplift pressures caused by hurricane winds. Analysis revealed that the majority of this discrepancy is caused by inherent uncertainties in load path. Although uncertainties in load magnitude and material resistance are accounted for in design by use of appropriate load and resistance factors, load path is generally taken to be deterministic. In this study, load path uncertainty in a test structure is statistically quantified and the effect on the reliability of wood structural members is investigated. Although large uncertainties in reactions were present, it was found that the resulting influence on reliability was modest, with decreases in component reliability index ranging from 5-15%