Design of Steel Portal Frame Buildings for Fire Safety

This paper describes a study into the fire behaviour of steel portal frame buildings at elevated temperatures using the finite element programme SAFIR. The finite element analysis carried out in this report is three dimensional and covers different support conditions at the column bases, the presence of axial restraints provided by the end walls, different fire severities within the building, different levels of out-of-plane restraint to the columns and the effect of concrete encasement to the columns. From a large number of analyses, it is shown that the bases of the steel portal frames at the foundations must be designed and constructed with some level of fixity to ensure that the structure will deform in an acceptable way during fire, with no outwards collapse of the walls. The analyses also show that to avoid sidesway (i.e. collapse outwards) it is not necessary for steel portal frame columns to be fire-protected unless the designer wishes to ensure that the columns and the wall panels remain standing, during and after the fire

Effect of aspect ratio on fire resistance of hollow core concrete floors

Previous studies have shown that the fire performance of hollowcore units is significantly affected by the end support conditions, but it has not been clear how the fire resistance of the overall floor system can be improved by providing side supports. The previous studies used beam grillage and shell elements to separately model the hollowcore units and the topping concrete slab using the platform of the non-linear finite element program SAFIR. The modelling method required a lot of computational resources and is not ideal to model a large floor area. This paper describes the effect of the side supports and the aspect ratio of the floor on the predicted fire resistance. It also compares the efficiencies of shell elements and short beam elements for finite element modelling of the topping concrete in fire conditions. The results show that integrating the topping concrete slab into the beam grillages reduces the complexity of the model and also provides satisfactory results. Side supports can increase the fire performance of hollowcore floor slabs provided that the spacing of the side supports does not greatly exceed the span length

NMIT Arts & Media Building - Damage Mitigation Using Post-tensioned Timber Walls

Paper 090The NMIT Arts & Media Building is the first in a new generation of multistorey timber structures. It employs an advanced damage avoidance earthquake design that is a world first for a timber building. Aurecon structural engineers are the first to use this revolutionary Pres-Lam technology developed at the University of Canterbury. This technology marks a fundamental change in design philosophy. Conventional seismic design of multi-storey structures typically depends on member ductility and the acceptance of a certain amount of damage to beams, columns and walls. The NMIT seismic system relies on pairs of coupled LVL shear walls that incorporate high strength steel tendons post-tensioned through a central duct. The walls are centrally fixed allowing them to rock during a seismic event. A series of U-shaped steel plates placed between the walls form a coupling mechanism, and act as dissipators to absorb seismic energy. The design allows the primary structure to remain essentially undamaged while readily replaceable connections act as plastic fuses. In this era where sustainability is becoming a key focus, the extensive use of timber and engineered-wood products such as LVL make use of a natural resource all grown and manufactured within a 100km radius of Nelson. This project demonstrates that there are now cost effective, sustainable and innovative solutions for multi-story timber buildings with potential applications for building owners in seismic areas around the world

Environmental Impacts of Multi-Storey Buildings Using Different Construction Materials

The Research Goals and Objectives for this project were set out in the Ministry of Agriculture and Forestry (MAF) RFP POR/7811, April 2007. The University of Canterbury responded with a collaborative research programme ‘to fill the information gap about what is the greatest amount of wood that can be used in the construction and fit-out of commercial, large-scale buildings in New Zealand (and) …… to provide Life Cycle Assessment (LCA) information about the benefits of maximising the use of wood in sustainable buildings’. This research project modelled the performance of four similar office building designs – Concrete, Steel, Timber and TimberPlus – all based on an actual six-storey 4,200m2 building, to investigate the influence of construction materials on life cycle energy use and global warming potential (GWP). All four buildings were designed for a 60 year lifetime, with very similar low operational energy consumption. The Concrete and Steel buildings employed conventional structural design and construction methods. The Timber buildings were designed with an innovative post-tensioned timber structure using laminated veneer lumber (LVL). The TimberPlus design further increased the use of timber in architectural features such as exterior cladding, windows and ceilings. All timber materials are renewable and durable, sourced from sustainably managed forests. Predicted construction times for all four buildings are similar. The LCA study by Scion considered the full life cycle of the buildings including initial embodied energy of the materials, and maintenance, transport, operational energy and two endof- life scenarios, where deconstructed materials were either landfilled or reutilised. Increasing the amount of timber in the buildings decreased the initial embodied energy and GWP of materials and also decreased the total energy consumption and GWP over the 60 year lifetime. The TimberPlus design clearly had the lowest environmental impacts, whilst the Steel building had the highest impacts. A significant benefit could be obtained in the Steel, Concrete and Timber buildings by replacing high embodied energy components (especially aluminium windows and louvres) with timber. The final destination of deconstruction waste at the end of the 60 year life-cycle is extremely important. Landfilling of timber waste, with the permanent storage of most of the carbon in the timber, was slightly more beneficial than burning of wood waste for energy. The benefits of landfilling timber waste will increase as modern and future landfill construction and management capture and utilise more of the methane generated by decomposition. Recycling of steel and concrete is more beneficial than landfilling. It is important to note that looking at a single environmental indicator, such as GWP, could lead to unintended outcomes. For example, for the TimberPlus building the landfilling scenario would be slightly better in terms of climate change. However, looking at the energy results alongside the GWP results, the reutilisation scenario shows both an energy reutilisation benefit, as well as still being beneficial to climate change. Therefore, the use of multiple indicators may be necessary to inform the environmental decision-making process.An alternative end-of-life scenario which assumed permanent storage of carbon in wood materials showed that net total GWP for the materials in the TimberPlus building is negative, because the long-term storage of over 630 tonnes of carbon dioxide removed from the atmosphere more than cancels out all the greenhouse gases emitted in the manufacture of all the other building materials. In this scenario, the TimberPlus building could be considered to be ‘carbon-neutral’ for at least the first 12 years of its operation. With NZ-specific energy and GWP coefficients now available, a simple model can be developed for assessing the energy and GWP impacts of individual buildings. This study shows that the Green Star Office rating tool does not capture all the benefits of using more wood in buildings which are identified by the simple model or a full LCA study. Support of on-going research is essential to further develop the potential for Timber buildings to be more widely used in NZ, with subsequent reductions in greenhouse gas emissions

Parametric study of modelling structural timber in fire with different software packages

In a bid to accurately model structural behaviour of timber buildings in fire, a number of obstacles have been identified which must be fully understood before advanced computer modelling can accurately be used to represent physical behaviour. This paper discusses the obstacles, with suggestions on how to mitigate them, incorporating the challenges of using general purpose finite element software. The paper examines modelling with ANSYS, SAFIR and ABAQUS and the individual and collective challenges related to thermal analyses of timber structures in fire conditions. It considers the effects various model parameters (thermal and structural) may have on physical interpretation of experimental data in comparison with the accuracy of numerical solutions. In detail, the study looks at the effects of 1D and 2D heat transfer analyses, finite element mesh sizes, time steps and different thermal property approaches on thermal models of timber members in fires. It further recommends how best to model these structures using the different finite element software packages

Performance of Timber, Masonry and Earth houses in the Christchurch earthquakes New Zealand September 2010 and February 2011

Two earthquakes struck close to Christchurch city in New Zealand generating high level ground excitations that caused severe geotechnical effects and widespread structural damage. This paper focuses on damage to timber and masonry that resulted from the geotechnical effects experienced including liquefaction, lateral spreading, rock fall, horizontal and vertical ground accelerations. Light timber framed construction performed well for life safety but there were a large number seriously damaged, heavy masonry caused significant problems when inadequately reinforced. Changes to the construction standards are needed to improve foundation requirements and lateral wall bracing. Earth building damage to modern houses is discussed in reference to the New Zealand Earth Building Standards, and particularly the non-specific design clauses which specify a consistent reinforcing approach. Double skin pressed earth brick and earth brick veneers performed badly and will be excluded in a future revision. Historic unreinforced earth buildings suffered serious damage that was typical for the level of shakin

New exact solution of Dirac-Coulomb equation with exact boundary condition

It usually writes the boundary condition of the wave equation in the Coulomb field as a rough form without considering the size of the atomic nucleus. The rough expression brings on that the solutions of the Klein-Gordon equation and the Dirac equation with the Coulomb potential are divergent at the origin of the coordinates, also the virtual energies, when the nuclear charges number Z > 137, meaning the original solutions do not satisfy the conditions for determining solution. Any divergences of the wave functions also imply that the probability density of the meson or the electron would rapidly increase when they are closing to the atomic nucleus. What it predicts is not a truth that the atom in ground state would rapidly collapse to the neutron-like. We consider that the atomic nucleus has definite radius and write the exact boundary condition for the hydrogen and hydrogen-like atom, then newly solve the radial Dirac-Coulomb equation and obtain a new exact solution without any mathematical and physical difficulties. Unexpectedly, the K value constructed by Dirac is naturally written in the barrier width or the equivalent radius of the atomic nucleus in solving the Dirac equation with the exact boundary condition, and it is independent of the quantum energy. Without any divergent wave function and the virtual energies, we obtain a new formula of the energy levels that is different from the Dirac formula of the energy levels in the Coulomb field.Comment: 12 pages,no figure