Slender timber beams subjected to gravity loads may buckle in the out-of-plane direction. Normally, the same bracing system that is used to prevent lateral movements of the beams, caused by external transversal loading, also serve to increase the buckling strength of the beams. For the idealized case of a perfectly straight beam with full-bracing there is no force in the braces even at buckling because there is no displacement at the brace points. However, in real beams brace forces do develop during loading. This paper describes experimental and analytical studies performed on slender glulam beams subjected to gravity loads laterally stiffened by means of discrete bracing. In particular, the influence of relevant parameters such as i) brace stiffness, ii) brace position, iii) shape and magnitude of initial imperfections on the brace force were investigated.
Although wood is widely used as a construction material, it is mostly limited to low and mid-rise residential construction, partially due to fire code restrictions. This limitation can be overcome by considering hybrid systems which combine wood with non-combustible materials. This research presents an innovative wood-concrete hybrid system, suitable for tall buildings, where a concrete frame with slabs at every third story provides fire separation as well as stiffness and strength to resist gravity and lateral loads. The intermediate stories including their floors are constructed using light-frame wood modules. This approach reduces the environmental footprint of the building, reduces the building weight and therefore the seismic demand on connections and foundation, and speeds up the construction process. For a novel system, numerical modeling is crucial to predicting its structural response to static and dynamic loading. This thesis studies the structural feasibility of the system by developing finite element models and assessing the structural behavior at the component and system levels when subjected to earthquake and wind loads. Nonlinear analyses are performed considering material and geometric nonlinearity using multiple ground motions to estimate the structure’s inter-story drift and base shear. The results demonstrate the feasibility of the proposed wood-concrete hybrid system for tall buildings in high seismic zones.
This paper describes the design of a 12-story apartment building on a single story basement, which has wood floor diaphragms, and structural steel gravity and lateral load resisting systems. The design objective was to develop the most cost-effective structural system while meeting building functionality goals and adhering to code requirements. The main structural and non-structural design issues considered in this all-wood floor building are reviewed: gravity loads, lateral loads imposed by wind and earthquake, floor vibration, acoustics, and changes in wood moisture content. The lightweight structural form proved to be a practical system to lower construction material cost and enable alternative construction techniques to be employed. A comparison with a concrete floor option is briefly made.
A new structural system for multi-storey timber buildings has been developed over the last seven years at the University of Canterbury. The system incorporates large timber structural frames, whereby semi-rigid beam-column connections are created using post-tensioning steel tendons. This system can create large open floor plans required for office and commercial buildings.
Several material properties of the engineered timber used were determined based on small-scale experimental testing. Full-scale testing of beams, connections and frames resulted in a more comprehensive understanding of the behaviour of such systems. Numerical, analytical and framework models also led to the development of design equations and procedures which were validated with the acquired experimental data.
