A large part of the environmental impact of society today comes from the construction and real estate sector. With the new law on climate declarations for buildings, the interest in building materials with a low climate impact has increased. The only building material, that is considered to be fully renewable and climate neutral, is wood which is widely available in Sweden. However, there are several challenges when wood is used as a construction material, where one has proven to be for the case of structuraltimber in tall buildings. When prefabricated modules are assembled into multi-storey houses, there are challenges to avoid buckling in the strong direction.In this thesis, rotational stiffness in bottom rails of Cross-Laminated Timber (CLT) and structural timber is studied for eccentric load. The aim is to investigate possible advantages in terms of rotational stiffness if a CLT bottom rail is used instead of one made from structural timber. The idea is that a bottom rail with greater rotational stiffness contributes to higher buckling loads. The rotational stiffness is examined through experiments in which four different sets of bottom rails and wooden studs are loaded with six different eccentricities in a hydraulic press. The displacement and deformations of the wooden samples are documented through a digital image correlation system and are then analyzed. The results show that a CLT bottom rail has a higher rotational stiffness than a structural timber bottom rail, which is visible in a studied range based on a calculated theoretical angle-change according to a comparable load case from beam theory. In load case 2 with an initial eccentricity of 20 mm, the bottom rail of CLT in size 40 x 95 mm had a rotational stiffness that was almost three times as high as that of structural timber.The measured rotational stiffness was applied in an approximate calculation model to estimate the contribution of the bottom rail in stabilizing a structural timber stud. By interpreting the results of the calculations according to the second order theory, a relationship was established in which the factor β for effective buckling length was calculated for the different load cases. The calculated factor β shows that the CLTbottom rails contribute to the reduction of the effective buckling length in the order of 28 % for bottom rails with a width of 95 mm and 18 % for the bottom rails of width 170 mm.
| Identifer | oai:union.ndltd.org:UPSALLA1/oai:DiVA.org:kau-95934 |
| Date | January 2023 |
| Creators | Henriksson, Edvard |
| Publisher | Karlstads universitet, Institutionen för ingenjörs- och kemivetenskaper (from 2013) |
| Source Sets | DiVA Archive at Upsalla University |
| Language | Swedish |
| Detected Language | English |
| Type | Student thesis, info:eu-repo/semantics/bachelorThesis, text |
| Format | application/pdf |
| Rights | info:eu-repo/semantics/openAccess |
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