This thesis studies the behaviour of diaphragms in multi-storey timber buildings by providing methods for the estimation of the diaphragm force demand, developing an Equivalent Truss Method for the analysis of timber diaphragms, and experimentally investigating the effects of displacement incompatibilities between the diaphragm and the lateral load resisting system and developing methods for their mitigation.
Although shortcomings in the estimation of force demand, and in the analysis and design of concrete floor diaphragms have already been partially addressed by other researchers, the behaviour of diaphragms in modern multi-storey timber buildings in general, and in low damage Pres-Lam buildings (consisting of post-tensioned timber members) in particular is still unknown.
The analysis of light timber framing and massive timber diaphragms can be successfully analysed with an Equivalent Truss Method, which is calibrated by accounting for the panel shear and fastener stiffnesses. Finally, displacement incompatibilities in frame and wall structures can be accommodated by the flexibilities of the diaphragm panels and relative connections. A design recommendations chapter summarizes all findings and allows a designer to estimate diaphragm forces, to analyse the force path in timber diaphragms and to detail the connections to allow for displacement incompatibilities in multi-storey timber buildings.
Seismic damage to floor diaphragms because of displacement incompatibilities are a point of concern in many structures. This paper studies the behaviour of timber diaphragms subjected to frame elongation and rocking of walls in post-tensioned timber buildings. Experimental tests with special connection details between floor panels and between the diaphragm and the lateral load resisting system show that floor damage in severe earthquakes can be avoided by designing for flexibility and proper connection detailing
New Zealand Society for Earthquake Engineering Conference
April 26-28, 2013, Wellington, New Zealand
This paper describes options for seismic design of pre-fabricated timber core-wall
systems, used as stairwells and lift shafts for lateral load resistance in multi-storey timber
buildings. The use of Cross-Laminated Timber (CLT) panels for multi-storey timber buildings is
gaining popularity throughout the world, especially for residential construction. This
paper describes the possible use of CLT core-walls for seismic resistance in open-plan
commercial office buildings in New Zealand. Previous experimental testing at the
University of Canterbury has been done on the in-plane behaviour of single and coupled
Pres-Lam post-tensioned timber walls. However there has been very little research done
on the behaviour of timber walls that are orthogonal to each other and no research into
CLT walls in the post-tensioned Pres-Lam system. This paper describes the proposed test regime and design detailing of two half-scale twostorey CLT stairwells to be tested under a bi-directional quasi-static loading. The test specimens will include a half-flight stair case with landings within the stairwell. The “High seismic option” consists of post-tensioned CLT walls coupled with energy dissipating U-shaped Flexural Plates (UFP) attached between wall panels and square hollow section steel columns at the corner junctions. An alternative “Low seismic option” uses the same post-tensioned CLT panels, with no corner columns or UFPs. The panels will be connected by screws to provide a semi-rigid connection, allowing relative
movement between the panels producing some level of energy dissipation.
This thesis discusses the results of experimental tests on two post-tensioned timber core-walls, tested under bi-directional quasi-static seismic loading. The half-scale two-storey test specimens included a stair with half-flight landings. Multi-storey timber structures are becoming increasingly desirable for architects and building owners due to their aesthetic and environmental benefits. In addition, there is increasing public pressure to have low damage structural systems with minimal business interruption after a moderate to severe seismic event. Timber has been used extensively for low-rise residential structures in the past, but has been utilised much less for multi-storey structures, traditionally limited to residential type building layouts which use light timber framing and include many walls to form a lateral load resisting system. This is undesirable for multi-storey commercial buildings which need large open spaces providing building owners with versatility in their desired floor plan. The use of Cross-Laminated Timber (CLT) panels for multi-storey timber buildings is gaining popularity throughout the world, especially for residential construction. Previous experimental testing has been done on the in-plane behaviour of single and coupled post-tensioned timber walls at the University of Canterbury and elsewhere. However, there has been very little research done on the 3D behaviour of timber walls that are orthogonal to each other and no research to date into post-tensioned CLT walls. The “high seismic option” consisted of full height post-tensioned CLT walls coupled with energy dissipating U-shaped Flexural Plates (UFPs) attached at the vertical joints between coupled wall panels and between wall panels and the steel corner columns. An alternative “low seismic option” consisted of post-tensioned CLT panels connected by screws, to provide a semi-rigid connection, allowing relative movement between the panels, producing some level of frictional energy dissipation.
Long-span timber-concrete composite (TCC) floor systems have the potential to address the design challenges for conventional wooden floors in residential multi-storey timber frame buildings. The aim of this paper is to develop a design approach for long-span timber-concrete composite floor system of 6–9 m. A framework based on value-driven design approach has been developed for integration of results from graphical multi-objective optimisation, spreadsheet-based analysis, structural static and dynamic finite element analysis, and multi-criteria decision making. To verify the developed framework, a residential five-storey timber frame building as a case study has been studied. Optimal design includes optimised thickness of the concrete and optimised smeared stiffness of connectors for three different comfort classes A to C in descending order. TCC floor with span length 7.3 [m] belonging to comfort class A and TCC floor with span length 9.0 [m] belonging to comfort class C has been chosen as optimal solutions. The results indicate that proposed and innovative design approach is a promising tool for developers, architects and structural engineers when designing optimal long-span timber-concrete composite floor system.
New Zealand Society for Earthquake Engineering Conference
April 27-29, 2017, Wellington, New Zealand
With the increasing acceptance and popularity of multi-storey timber buildings up to 10 storeys and beyond, the influence of higher mode effects and diaphragm stiffness cannot be overlooked in design. Due to the lower stiffness of timber lateral load resisting systems compared with traditional construction materials, the effect of higher modes on the global dynamic behaviour can be more critical. The presence of flexible timber diaphragms creates additional vibration modes, which have the potential to interact with each other, increasing the seismic demand on the whole structure. This paper uses a parametric non-linear time-history analysis on a series of timber frame and wall structures with varying diaphragm flexibility to study their dynamic behaviour and to determine diaphragm forces. The analyses results showed that although higher mode effects play a significant role in the structural dynamic response, this increased demand can be successfully predicted with methods available in literature. The parametric analyses showed that the diaphragm flexibility did not significantly increase the shear and moment demand; however, stiff wall structures with flexible diaphragms experienced large inter-storey drifts measured at diaphragm midspan compared with the drift of the wall alone. As expected, the diaphragm forces observed from the time-history analyses were significantly higher than the forces derived from an equivalent static analysis, leading to a potentially unsafe design. The paper presents a simplified approach for evaluating these amplified peak inertial diaphragm forces.
This research investigated the fire performance of unprotected timber floors, focussing on composite joist floors, composite box floors and timber-concrete composite floors. The study of these floors was conducted using the finite element software ABAQUS using a thermo-stress analysis in three dimensions, and with experimental fire tests of floor assemblies. The major goal of this research was to develop a simplified design approach for timber floors, validated against the numerical and experimental work.
Four furnace tests were conducted on unprotected timber floor systems in the full-scale furnace at the BRANZ facilities in New Zealand. A sequentially coupled thermal-stress analysis was conducted to determine the effects of a fire on floor assemblies under load. The thermal modelling predicted the charring damage of the floors tested in the experiments to within a few millimetres of precision, and the simplified assumptions made in relation to fire inputs, boundary conditions, mesh refinement and effective material parameters were accurate to the desired level of precision. A sensitivity study was conducted comparing different mesh sizes, time step sizes, material model approaches and software suites to determine any shortfalls which may be encountered in the analysis. It was found that a material model adopting a latent heat approach was the most adequate for modelling timber in fires using these effective values, and mesh sizes of up to 6 mm produced relatively precise results.
The structural modelling predicted the displacement response and failure times of the floors to within 20% of the experimental data, and the simplified assumptions made in relation to fire inputs, boundary conditions, mesh refinement and effective material properties were once again accurate to the desired level of precision. A modification to the reduction in tension strength at elevated temperatures was proposed to better predict the observed behaviour. A sensitivity study concluded that the material model definition plays a vital role in the output of the modelling. Non-standard fire exposures were also modelled for completeness.
A simplified design method to estimate the fire resistance of unprotected floor assemblies was also developed. The method uses a bi-linear charring rate the assumption of a zero strength layer in the timber. The method was compared to the experimental data from this research and others around the world. The results were also compared to other charring rate methodologies from around the world.
This paper deals with aspects of force- and displacement-based design of multistorey cross-laminated timber (CLT) structures. A method to determine the behavior factors for timber structures based on nonlinear static analyses will be discussed. Different types of analysis models are considered. Results of experimental investigations on connections and CLT wall elements will be presented as a basis for numerical simulations.
Timber-steel hybrid elements are structurally reliable, clean and fast to assemble and disassemble, light, ecologic and economic. Design criteria and a calculation model for beams were developed and a series of real scale tests were carried out in order to check their performance. The results proved to be satisfactory and promising for the final objective of building structural frames for different types of multi-story buildings.
This thesis discusses a novel timber-steel core wall system for use in multi-storey buildings in high seismic regions. This hybrid system combines Cross Laminated Timber (CLT) panels with steel plates and connections to provide the required strength and ductility to core walled buildings. The system is first derived from first principles and validated in SAP2000. In order to assess the feasibility of the system it is implemented in the design of a 7-storey building based off an already built concrete benchmark building. The design is carried out following the equivalent static force procedure (ESFP) outlined by the National Building Code of Canada for Vancouver, BC. To evaluate the design bi-directional nonlinear time history analysis (NLTHA) is carried out on the building using a set of 10 ground motions based on a conditional mean spectrum. To improve the applicability of the hybrid system an energy based design methodology is proposed to design the timber-core walled building. The methodology is proposed as it does not rely on empirical formulas and force modification factors to determine the final design of the structure. NLTHA is carried out on the proposed methodology using 10 ground motions to evaluate the suitability of the method and the results are discussed and compared to the ESFP results.