A simplified design method for estimating the fire performance of structural timber floors

The widespread use of structural timber in tall buildings is often inhibited because timber is a combustible material and is commonly perceived to behave poorly in fires. This research develops a simplified design approach for the fire performance of different types of prefabricated timber floors used in multi-storey buildings. The floor types under investigation include several different geometries of box-shaped and T-shaped timber floors made from Laminated Veneer Lumber (LVL). The investigations were carried out with numerical simulations and four experimental fire tests. A simplified design method to estimate the fire resistance of unprotected timber floor assemblies is proposed and calibrated against the numerical and experimental work. The method uses a bi-linear charring rate and the assumption of a zero strength layer in the timber. The method is compared to the experimental data from this research and others around the world, as well as charring rate methodologies from around the world

Sustainable timber use in residential construction: Perception versus reality

© 2014 WIT Press. Close to 90% of new project homes in NSW, Australia are constructed with reinforced concrete flooring and brick veneer envelope whereas many traditional Australian homes were built of timber floor structures with timber walls and cladding. The adoption of concrete and brick homes originated from a perceived advantage of longevity, low maintenance and thermal comfort. Innovation in wood treatments, wood protection and insulation have provided solutions to these issues so that timber is once again a viable option with added benefits such as environmental sustainability and erection speed. This paper reviews literature and analyses the results of a home occupants’ survey on the perception of timber use in new homes in NSW, Australia. It also investigates the comparative performance of a timber veneer/structural timber home to a concrete floor/brick veneer home to evaluate whether perception of timber performance matches reality. This paper highlights Australian homeowners’ reluctance to use timber as a sustainable building product for homes even when they are willing to pay for a more environmentally sustainable home. It also discusses the time and environmental advantages of a timber home over a concrete and brick home based on the results of a test case study

A comparative life cycle assessment approach of two innovative long span timber floors with its reinforced concrete equivalent in an Australian context

The building sector contributes 24% of the total greenhouse gas emissions in Australia. This is expected to rise by 110% by 2050. Consequently, there has been an increased demand for more sustainable building materials which can play a significant role in reducing carbon emissions. Engineered timber wall and floor panels are being seen as a viable alternative for multi-storey buildings for both strength and environmental purposes and are gaining popularity in Europe, North America and New Zealand. A number of previous Life Cycle Assessments (LCA) comparing timber and concrete mid-rise buildings have highlighted the environmental benefits of using timber, particularly during material production and on-site construction stages. Furthermore, the choice of endof-life scenario had a significant effect on the LCA outcome. The objective of this paper is to compare the environmental impacts associated with alternative designs for a long span floor in a multi-storey building in Australia. The comparison, using an LCA approach, is based on a recently built long span Timber Concrete Composite (TCC) floor in a University building in Sydney. Three design options are considered: the original design of TCC, a Cross Laminated Timber (CLT) panel, and a traditional in-situ reinforced concrete (RC) slab. The CLT and RC designs were conceived with reference to the floor plans and structural loads obtained from issued-for-construction drawings. With this evaluation, recommendations for increasing the competitiveness of CLT and TCC within the Australian market are made

Forest floor vegetation in Sweden

In boreal forests, dwarf-shrubs (Vaccinium spp.) often dominate the forest floor and are key-stone species in ecosystems due to their importance for nutrient cycling and as a major food source for herbivores. Forestry affects the vegetation both directly through management and indirectly by altering the forest structure. Forest fertilization with N at the end of the rotation period is a common practice in Swedish boreal forests. Even higher timber production can be achieved if fertilization with multi-nutrient fertilizer is applied early in the rotation period, but the effects on forest floor vegetation have not been studied. The objectives of this thesis were to increase knowledge regarding how 1) intensive fertilization in young forest affects forest floor vegetation; 2) background deposition of N influences the effects of N addition; and 3) to relate observed changes in common species abundances to changes in forest structure. Fertilization decreased the abundance of many common forest plant species while only few species increased (I). Surprisingly, also species known as nitrophilous decreased in abundance. Paper I shows that the decrease in availability of light induced by fertilization is a crucial factor behind this change. Consequently, fertilization reduced both species richness, species diversity and the between site (β) diversity (II). In areas where the background N deposition was low (4 kg ha-1 yr-1), the effects of N addition were larger than in areas with intermediate (16 kg ha-1 yr-1) deposition (III). Key-stone species among the forest floor vegetation of boreal Sweden (e.g. Vaccinium myrtillus) were found to decrease in abundance (IV). These species are strongly dependent on aspects of forest structure, such as forest density and age, and likewise, temporal changes in species abundance coincided with corresponding changes in forest structure (IV). In conclusion, in large parts of Sweden the prevailing forest management is incompatible with a productive forest floor vegetation possessing a high diversity of plant species, and this situation will only be exacerbated by more intensive use of fertilization regimes. To avoid associated cascading effects from the decreased abundance of key-stone species, forestry intensity needs to be relaxed on the landscape level which would likely result in a considerable loss of timber production. Compensation for this loss through intensified forestry on other areas would indicate the need for altered forest zoning

Derivation of fragility curves for traditional timber-framed masonry buildings using nonlinear static analysis

Recent earthquakes and two experimental campaigns on timber-framed masonry walls have shown that timber-framed masonry buildings possess a good displacement capacity and hence can withstand severe earthquakes without collapse. In the present paper, timber-framed masonry panels with diagonal braces are studied. Using a simplified model based on non-linear (NL) lumped plasticity strut elements, NL analyses are carried out of typical traditional buildings in Lefkas (Greece) with diagonally braced timber-framed masonry walls in their lateral load resisting system. Furthermore, an investigation is carried out regarding the foundation of the buildings. The key feature of the Lefkas buildings is their dual structural system. The primary system consists of a stone masonry ground floor and all upper floors are made of timber-framed masonry walls. Timber posts in the ground floor, a few centimetres apart from the stone masonry, constitute the secondary structural system which is connected to the upper floors. This latter system is activated once the ground floor stone masonry piers fail. Two different structural models are developed to simulate each system. Pushover curves are derived from the NL analyses of the buildings and are then converted into capacity curves assuming the fundamental mode dominates. On these curves four damage states (slight damage, moderate damage, heavy damage and collapse) are defined on the basis of criteria related to the actual response of the building. The first three damage states are defined on the capacity curve of the primary system, whilst the ultimate damage state is related to the response of the secondary system. Then, fragility curves in terms of spectral displacement are generated, adopting a log-normal statistical distribution of the probability of damage

Structural health monitoring of an innovative timber building

A main focus in timber construction research is the development of innovative, sustainable and reliable structures. In order to determine the long-term structural behaviour of these novel structures, structural health monitoring is a valuable tool. In the past two years an innovative timber-hybrid pilot building has been conceived, designed and realized at ETH Zürich. The building contains four innovative structural systems, a post-tensioned timber frame, two timber-concrete hybrid floor systems using beech LVL, and a biaxial pure timber floor in beech wood. In order to fully understand the combined structural behaviour of these innovative systems an extensive monitoring system was set up. The dense sensor network was implemented along with the construction progress, in order to also quantify the effects of important construction stages on the structural behaviour (addition of significant loads, addition of stiffening elements, extreme changes in environmental climate, etc.). The installed setup includes 16 load cells, measuring the changes in the post-tension force in the frame, absolute deformation measurements, temperature and relative humidity sensors, as well as measurements of the moisture content of timber. The monitoring campaign is planned to be continued for several years beyond the completion of construction, in order to quantify the long-term behaviour during the use phase of the building

Investigation of a proposed long span timber floor for non-residential applications

University of Technology, Sydney. Faculty of Engineering and Information Technology.Design of floor systems for commercial and multi-residential buildings in many parts of the world is currently dominated by the use of structural materials other than timber, such as reinforced concrete systems. Recent research in Australia has shown that the major barriers to using timber in non-residential buildings are the fire performance and the lack of designer confidence in commercial and industrial timber-based constructions. In this regard, significant research initiatives have commenced in Australia and New Zealand with the aim of developing timber and timber hybrid systems for large span commercial and industrial applications. 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. The specimen’s responses to long-term loading, in-plane loading, dynamic excitation, cyclic loading and loading history are outside the scope of this PhD research. Moreover, other aspects of performance such as assessment of acoustic performance, dynamic performance and the possible interconnection systems alongside floor modules are not covered in the scope of this research project. 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 experimental investigation involved subjecting the full scale proposed floor modules (6m and 8m clear span LVL modules) to both serviceability and ultimate limit state static loading to assess the strength and serviceability performance of the proposed system. A continuum-based finite element model is also developed to capture the behaviour and failure of the long span LVL modules and to adequately predict the serviceability and ultimate limit performance of the proposed floor system. To evaluate the partially-composite strength and serviceable performance of LVL floor system, a series of push-out tests are conducted on the fabricated timber connections using normal screws as the shear connectors, and the stiffness of the connections are assessed at serviceability and ultimate limit state. A number of LVL beams (3.5m “T” shaped beams) were also fabricated using only normal screws as the load bearing shear connectors at the interfaces, and are tested under serviceability and ultimate limit state loads with different screw spacing. Furthermore, a closed-form prediction analysis is conducted to calculate the partially-composite ultimate load of the beams. A comparison between the experimental results and the closed-from predicted results is undertaken, and the results are used for predicting the partially-composite behaviour of long span 6m and 8m LVL modules. 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

Vibrational Modal Frequencies and Shapes of Two-Span Continuous Timber Flooring Systems

Based on classic vibrational bending theory on beams, this paper provides comprehensive analytical formulae for dynamic characteristics of two equal span continuous timber flooring systems, including frequency equations, modal frequencies, and modal shapes. Four practical boundary conditions are considered for end supports, including free, sliding, pinned, and fixed boundaries, and a total of sixteen combinations of flooring systems are created. The deductions of analytical formulae are also expanded to two unequal span continuous flooring systems with pinned end supports, and empirical equations for obtaining the fundamental frequency are proposed. The acquired analytical equations for vibrational characteristics can be applied for practical design of two-span continuous flooring systems. Two practical design examples are provided as well

Assessment of dynamic and long-term performance of an innovative multi-story timber building via structural monitoring and dynamic testing

Peer reviewedPostprin

The Design of a semi-prefabricated LVL-concrete composite floor

This paper describes the design of a novel semi-prefabricated LVL-concrete composite floor that has been developed in New Zealand. In this solution, the floor units made from LVL joists and plywood are prefabricated in the factory and transported to the building site. The units are then lifted onto the supports and connected to the main frames of the building and to the adjacent units. Finally, a concrete topping is poured on top of the units in order to form a continuous slab connecting all the units. Rectangular notches cut from the LVL joists and reinforced with coach screws provide the composite action between the concrete slab and the LVL joists. This system proved to be an effective modular solution that ensures rapid construction. A design procedure based on the use of the effective flexural stiffness method, also known as the “gamma method” is proposed for the design of the composite floor at ultimate and serviceability limit states, in the short and long term. By comparison with the experimental results, it is shown that the proposed method leads to conservative design. A step-by-step design worked example of this novel semi-prefabricated composite floor concludes the paper