Project contact is Frank Lam at the University of British Columbia
The objective of this project is to develop a large span timber-based composite floor system for the construction of highrise office buildings. This prefabricated floor system could span over 10 m under regular office occupation load, and its use will expedite the construction significantly, converting to multi-million financial savings in a typical 40+ story project, besides the impact on reducing carbon footprint and enhancing living experience.
Highly loaded and large span timber beams are often used for halls, public buildings or bridges.
Reinforcement of beams may be required to extend the life of the structure, due to deterioration or damage to the material/product or change of use. The paper summarises methods to repair or enhance the structural performance of timber beams. The main materials/products cross sections and geometries used for timber beam are presented. Furthermore, their general failure modes are described and typical retrofitting and reinforcement techniques are given. The techniques include wood to wood replacements, use of mechanical fasteners and additional strengthening materials/products.
International Association for Bridge and Structural Engineering Symposium
May 6-8, 2013, Rotterdam, Netherlands
The present paper describes collapses and failures of three large-span roof structures in Switzerland: In February 2009 the steel roof of a three years old gym in eastern Switzerland collapsed. Based on visual findings and on a detailed investigation it could be found that the cause of the collapse was a deficient detailing in each of the seven 26 m long, simply supported main steel plate girders. The collapse was triggered by increasing snow load although at the day of collapse the load was 25% lower than the characteristic value according to the Swiss design code. In November 2003 the roof of a timber multi-purpose hall partly collapsed after a period of rain. The investigations showed that the most relevant reason for the collapse was the incorrect execution of welds at the joints of supporting shoes in conjunction with the marginal design of that detail. From other factors that contributed to the collapse an insufficient drainage system of the roof could be identified as having played an important role. In 2011 a 180 x 1120 mm2 glued-laminated timber beam with a span of 18 m being part of the secondary structural system supporting the flat roof of a DIY superstore near Zurich failed in bending. The failure had been triggered to a considerable extent due to overloading of parts of the roof by a gravel layer compared to other parts of the roof being of higher depth and specific weight. From all three incidents it could be concluded that a closer orientation of the design to available design codes and a strict quality control during design, execution and use of the building would have reduced the probability of collapse / failure of the roof structures considerably.
This PhD research provides a detailed procedure for designing and investigating the short term static behaviour of a proposed long span timber floor system for non-residential applications that meets serviceability and ultimate limit design criteria, with the use of timber as the only structural load bearing part of the system. In this study the behaviour of two types of LVL are investigated through a number of experimental and analytical tests. As a result of the tension and compression tests, a suitable constitutive law is developed which can accurately capture the stress-strain relationship and the failure behaviour of LVL, and it can also be incorporated into FE analysis of any LVL beam with similar structural features to the tested specimens. Further, the results of the full scale four point bending tests on LVL sections are used to identify the behaviour of LVL up to the failure point and to develop a finite element model to capture the behaviour and failure of LVL. Moreover, after investigating the long span timber floors, one system is proposed to be fabricated for the extensive experimental and numerical investigation. The results of the full scale experimental tests together with the numerical investigation provide a robust model for predicting the performance of any timber beams with similar structural features to the proposed system while the dimensions and spans can be varied according to special requirements such as dynamic performance or fire resistance requirements.
The evaluation of damages in large-span timber structures indicates that the predominantly observed damage pattern is pronounced cracking in the lamellas of glued-laminated timber elements. A significant proportion of these cracks is attributed to the seasonal and use-related variations of the internal climate within large buildings and the associated inhomogeneous shrinkage and swelling processes in the timber elements. To evaluate the significance of these phenomena, long-term measurements of climatic conditions and timber moisture content were taken within large-span timber structures in buildings of typical construction type and use. These measurements were then used to draw conclusions on the magnitude and time necessary for adjustment of the moisture distribution to changing climatic conditions. A comparison of the results for different types of building use confirms the expected large range of possible climatic conditions in buildings with timber structures. Ranges of equilibrium moisture content representative of the type and use of building were obtained. These ranges can be used in design to condition the timber to the right value of moisture content, in this way reducing the crack formation due to moisture variations. The results of this research also support the development of suitable monitoring systems which could be applied in form of early warning systems on the basis of climate measurements. Based on the results obtained, proposals for the practical implementation of the results are given.