Fiber reinforced polymer (FRP) has been proved to be effective to improve the structural strength and ductility for column structures. An experimental study was conducted to investigate the compressive performance of FRP confined glued-laminated timber (GLT) and cross-laminated timber (CLT) columns. A total of 60 column specimens of two dimensions in height using different FRP types, FRP thickness, and laminate types were tested under cyclic axial compression loads. This study focuses on the compressive capacity and ductility of the new FRP composited timber structure. For this purpose, a loading protocol was designed, including a force-dependent pre-load and an amplitude-increasing displacement-dependent cyclic compression load. The results showed that the ultimate compression load of specimens was considerably promoted by the FRP sheets. Wrapping FRP sheets led to an average improvement of 29% and 24% for the FRP confined CLT and GLT specimens, respectively, compared to the initial stiffness of unreinforced specimens. Using the FRP sheets, the energy dissipation capacity of CLT and GLT specimens was increased by 358% and 266%, respectively. In general, GLT specimens had a higher energy dissipation rate compared to the CLT specimens, while CLT specimens showed a better potential for sustained energy consumption if confined with sufficient FRP sheets.
The force-displacement behaviour of structural timber members subjected to axial compression or combined axial compression and bending is distinctively non-linear. This behaviour is caused by the non-linear increase of the deformation due to the increasing eccentricity of the axial load as well as by the non-linear material behaviour of timber when subjected to compression. The present report describes experimental investigations on glued laminated timber members subjected to eccentric compression. The aim of these experimental investigations was to create a data base, which can be used to validate theoretical calculation models and to assess the accurateness of the design approaches given in the design codes for timber structures.
The specimens for the main bunch of experiments were produced using lamellas made of Norway spruce grown in Switzerland. For this purpose, a total of 336 lamellas were available. In the first step, non-destructive tests on the lamellas were performed. These tests aimed at the collection of data in order to characterise the raw material.
In the second step, the lamellas were strength graded. The aim of the grading process was to select two classes of lamellas for the production of the test specimens. The lamellas were selected so that they were suitable to produce glued laminated timber of strength classes GL24h and GL32h. Within the grading process, visual grading criteria as well as machine grading criteria were used.
In the third step, the graded lamellas were used to produce glued laminated timber members. Five tests series were produced. Each of the test series consisted of ten specimens. Three series were made of glued laminated timber GL24h and two series were made of glued laminated timber GL32h. The length of the timber members was varied between the different test series. The lengths were L = 1’400 mm, L = 2’300 mm and L = 3’200 mm respectively. During the production, the setup of the test specimens was recorded. Hence, the position and the orientation of every lamella within the test specimen were documented. Additionally, some non-destructive tests were performed using the test specimens.
In the last step, the glued laminated timber members were subjected to buckling tests. The test specimens were loaded with an eccentric compression force up to failure. During the tests, different measurements were carried out in order to document the experimental investigations as accurate as possible. Amongst others, the applied loads as well as horizontal and vertical deformations were recorded. For a subsample of 20 test specimens, additional local deformation measurements were performed using an optical measurement device.
Conventional cross-laminated timber is an engineered wood product consisting of solid sawn lumber panels glued together. In this study, the structural behavior of solid wood panels of Nail-Cross-Laminated Timber (NCLT) panels connected with nails instead of glue was studied. The failure mode and nail deformation of the novel NCLT panels under axial compression load using eight full-scale NCLT panels was investigated. The effects of four key design parameters, namely, the nail type, number of nails, nail orientation angle, and nail slenderness ratio on axial compression performance of NCLT panels were also analyzed. In addition, a formula for predicting the axial compression bearing capacity of NCLT panels was developed. For calculation of the slenderness ratio, the moment of inertia of the full section or the effective section was determined based on the nail type, number of nails, angle of nail orientation and number of layers of the plate. Results showed that specimens connected by tapping screws had best compressive performance.
Cross-laminated timber (CLT) panels are broadly utilized as structural members in modern timber structures. Variation in the residual resistance of CLT walls after fire exposure may lead to disruption of vertical force transmission and, in turn, structural collapse. To investigate the residual compressive load-carrying capacity of CLT walls after exposed to one-side fire, a series of tests were conducted on 3-ply and 5-ply members: axial compression tests, fire tests, and residual compressive load-carrying capacity tests. Combining the initial geometric defects obtained from the test results and the effect of shear deformation, theoretical formulae describing the compressive load-carrying capacity were deduced. Further considering the different mechanical properties over the residual cross-section model after fire, and the relative position between Region A and CLT orthogonal configuration, the calculation method of the residual compressive load-carrying capacity after fire were derived. The results of the residual compressive load-carrying capacity tests showed that the failure mode of the CLT walls after one-side fire was the eccentric compression, and the nonlinear segments of the load-axial and load-lateral displacement curves after fire accounted for larger proportion than those of axial compression tests. For the same total section thickness, the reduction in residual capacity of the 5-ply walls after fire was less than that of the 3-ply walls. The calculation results of the eccentric compression formulae considering shear deformation and initial geometric defect showed good agreement with the test values of axial compression tests. The residual compressive load-carrying capacity after one-side fire was predicted appropriately, which could be used as reference for assessing the residual load-carrying behavior of CLT elements after fire.
This thesis examines the behaviour of structural timber members subjected to compression alone or in combination with bending. Based on experimental and numerical investigations, the knowledge on the behaviour of these timber members is extended and advanced calculation models are developed. In addition, the accuracy of existing approaches for the design of these members is assessed and modifications are suggested.
By means of extensive experimental investigations, a data base was created which can be used for the validation of calculation models and for the assessment of design concepts. The experimental investigations are carried out on eccentrically loaded compression members made of glued laminated timber. Different parameters such as the strength class of the glued laminated timber or the slenderness ratio of the members are investigated.