Machine stress rated lumber
Machine stress rated (MSR) lumber is softwood dimension lumber that has had its strength predicted by mechanical means rather than by relying on visual indicators. MSR lumber has traditionally been used for producing engineered wood products such as roof trusses and is now also commonly used in producing glue-laminated (glulam) beams, chords for wood I-beams and webs in stressed-skin panels.
The grading system for MSR lumber is based on the established relationship between the stiffness of a piece of lumber and its bending strength. An MSR machine non-destructively tests each piece of MSR lumber to determine its stiffness so that it can be assigned a permitted design stress. Grades of MSR lumber are assigned “f-E” values (e.g., 1950f-1.7E). The “f” value designates the predicted strength in pounds per square inch (psi) and the “E” value designates the average stiffness measured in millions of pounds per square inch (106 psi).
Products like roof trusses will use different grades of MSR lumber within their structure, depending on the particular stresses experienced by the chords composing each roof truss. Most MSR lumber is 2x4; 2x6 and 2x8. MSR lumber is also produced in smaller quantities.
- Date modified: