Fältmätningar av limträbalkars elasticitetsmoduler
utvärdering av tre mätmetoder
This study investigates three different methods for evaluating MOE,Modulus of Elasticity, in field measurements. The purpose is toinvestigate the possibility to use dynamic measurement methods infield measurements that hitherto (2010) has been performed with staticmethods. The objects of investigation are 20 glulam beams. The firstfield measurement took place in november 2007 and applied a staticmethod based on the standard SS-EN 408. The second measurement,described in this study, took place during summer 2010, and appliedstatic as well as dynamic methods.The MOE of wood is affected by a range different factors. Thesefactors may, due to the complex structure of wood and itsenvironmental response, be very difficult to quantify. Moreover, theaccuracy of each method plays an essential role in evaluating theresults. These conditions altogether make field measurements of MOE acomplex problem.The results show that the average MOE is 97,9% (2010) of the initialaverage MOE 100% (2007). Six of the 20 glulam beams exhibit,somewhat unexpectedly, a higher MOE. This result calls for furtherstudies of the accuracy of the static method.Temperature and moisture content are factors that affect MOE. Sincethese factors differ between measurements made during winter (2007)and summer (2010), it is furthermore recommended to establish arelationship between temperature, moisture content and MOE forspruce (picea abies) and pine (pinus sylvestris) in order to justly comparemeasurements made during different environmental conditions.There is reason to believe, that certain measurement errors arise withthe use of static methods. Possible errors using static methods may, incertain cases, be brought to the surface and questioned by dynamicmethods. Dynamic measurements may also be seen as a verification ofthe results of static measurements.The group of beams treated with oil show a high correlation betweenstatic and dynamic methods, which is an indication that the static anddynamic methods can be approximated. Beams treated with coatinggenerally display a higher MOE in dynamic compared to staticmethods. This may be due to the fact that the coating is included in thedensity, without contributing to the MOE of the beam.Recommendations for future measurements are continued use ofstatic and dynamic methods and evaluations of the accuracy of thesemethods. For dynamic methods, the relationship of coating and density,ivand resonance frequencies should also be evaluated. It is essential totake into account that the reliability of different measurement methodsdue to deterioration of wood, in a long- time perspective might change.