Design of Glulam Columns According to Eurocode 5 - Influence of Various Parameters and Methods of Analysis

Sammanfattning: More and more structural analyses today are being conducted with computer-based tools in comparison to traditional methods using hand calculations. The development, according to the Norweigan scientist Kolbein Bell is shifting from using first order analyses with correction factors, to using second order analyses, with computer-based tools. This dissertation mainly compares analyses of glulam columns using first order theory according to Eurocode, to using second order theory, where finite element analyses are conducted with the computer programs Matlab and Calfem. This dissertation consists of two parts. In the first part, a study was performed where different methods of calculation and parameters affecting the load capacity of glulam were analysed. The methods of calculation were then compared to each other, where two columns of reference were used. This comparison was done for only axial loading and simultaneous axial loading and bending moment. In the second part a parameter study was conducted. Some of the tests that were conducted were based on a text, written by Kolbein Bell, where he proposes alternative values for the modulus of elasticity, which takes load duration and moisture content into consideration, for analyses using both first and second order theory. Part of the results, for when a second order analysis were compared to a first order analysis, was that the loading capacity using the design value of the modulus of elasticity according to Eurocode increased with up to 45% using second order theory. Using the design value of the modulus of elasticity according to Bell instead gave an increase of loading capacity with up to 30% which indicates that load duration and moisture content (service class) should be included when a second order analysis is being conducted, in order to not risk making an excessive overestimation in comparison to first order theory. For the most unfavourable conditions (permanent load and service class 3) it shows that when a second order analysis, using the design value of the modulus of elasticity according to Bell is being used, produces almost the same results as a first order analysis, using the fifth percentile value of the modulus of elasticity. The geometry of the column and the difference between buckling in the weak and strong axis turned out to have no effect on the loading capacity, since the same results were obtained from both reference pillars. The initial curvature of the column presented a higher value of loading capacity for standard curvature value of glulam, L/500, when a second order analysis was conducted. Not until the initial curvature exceeded approximately L/240, did a second order analysis give a lower loading capacity than a first order analysis. When the column was analysed for axial loading and simultaneous axial loading and bending moment, second order effects showed a higher impact for large values of axial load. This correlation proved to be correct for both variation of initial curvature and modulus of elasticity. When only a transverse load affected the column, second order effects had no impact.