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.
spIn this report, the seismic performance of 6-storey wood frame residential buildings is studied. Two building configurations, a typical wood-frame residential building and a building to be tested under the NEESWood project, were studied. For each building configuration, a four-storey building and a six-storey building were designed to the current (pre-April 6, 2009) 2006 BC Building Code (BCBC) and to the anticipated new requirements in the 2010 National Building Code of Canada (NBCC), resulting in four buildings with different designs. The four-storey building designed to the current 2006 BC Building Code served as the benchmark building representing the performance of current permissible structures with common architectural layouts.
In the design of both four-storey and six-storey buildings, it was assumed that the buildings are located in Vancouver on a site with soil class C. Instead of using the code formula, the fundamental natural period of the buildings was determined based on the actual mass and stiffness of wood-based shearwalls. The base shear and inter-storey drift are determined in accordance with Clauses 126.96.36.199.(3)(d)(iii) and 188.8.131.52.(3)(d)(iv) of BCBC, respectively.
Computer programs DRAIN 3-D and SAPWood were used to evaluate the seismic performance of the buildings. A series of 20 different earthquake records, 14 of the crustal type and 6 of the subcrustal type, were provided by the Earthquake Engineering Research Facility of the University of British Columbia and used in the evaluation. The records were chosen to fit the 2005 NBCC mean PSA and PSV spectra for the city of Vancouver.
For representative buildings designed in accordance with 2006 BCBC, seismic performance with and without gypsum wall board (GWB) is studied. For representative buildings designed in accordance with the 2010 NBCC, the seismic performance with GWB is studied. For the NEESWood building redesigned in accordance with 2010 NBCC, seismic performance without GWB is studied. Ignoring the contribution of GWB would result in a conservative estimate of the seismic performance of the building.
In the 2006 BCBC and 2010 NBCC, the inter-storey drift limit is set at 2.5 % of the storey height for the very rare earthquake event (1 in 2475 year return period). Limiting inter-storey drift is a key parameter for meeting the objective of life safety under a seismic event.
For 4-storey and 6-storey representative wood-frame buildings where only wood-based shearwalls are considered, results from both DRAIN-3D and SAPWood show that none of the maximum inter-storey drifts at any storey under any individual earthquake exceed the 2.5% inter-storey drift limit given in the building code. With DRAIN-3D, the average maximum inter-storey drifts are approximately 1.2% and 1.5% for 4-storey and 6-storey buildings designed with 2006 BCBC, respectively.
For the NEESWood wood-frame building, none of the maximum inter-storey drifts at any storey under any individual earthquake exceed the 2.5% inter-storey drift limit for 4-storey building obtained from SAPWood and 6-storey building obtained from DRAIN-3D and SAPWood. For any 4-storey building analysed with DRAIN-3D, approximately half of the earthquakes resulted in the maximum inter-storey drifts greater than 2.5% inter-storey limit. This is partly due to the assumptions used in Drain-3D model in which the lumped mass at each storey is equally distributed to all the nodes of the floor. As a result, the total weight to counteract the uplift force at the ends of a wall would be much smaller than that anticipated in the design, thus causing hold-downs to yield and large uplift deformations to occur.
Based on the analyses of a representative building and a redesigned NEESWood building situated in the city of Vancouver that subjected the structures to 20 earthquake records, 6-storey wood-frame building is expected to show similar or smaller inter-storey drift than a 4-storey wood-frame building, which is currently deemed acceptable under the current building code.
Building construction - Design
Building construction - Specfications
Earthquakes, Effect on building construction
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.
This paper discusses the impact of the natural frequency of multi-storey timber structures, focusing on force-based seismic design. Simplified approaches to determine the frequency of light-frame and cross-laminated timber structures are investigated. How stiffness parameters for simple two-dimensional analysis models can be derived from the different contributions of deformation...
This paper investigates the risk of disproportionate collapse following extreme loading events. The methodology mimics a sudden removal of a loadbearing wall of a twelve-storey CLT building. The ductility-demand from the dynamic simulation is checked against the ductility supplied by the structural components and their connections. The analyses focus on rotational stiffness (k) of the joints by considering three different sub-structural idealisations according to the required modelling details and the feasibility of model reductions. To resist the imposed dynamic forces, the required k-values may be too large to be practically achieved by means of off-the-shelf brackets and screw connections. Improved structural detailing as well as adequate thickness of structural elements need to be considered in order to reduce the probability of disproportionate collapse.
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 paper presents a study on the seismic design of hybrid multi-storey wood buildings made of CLT and Light-Frame shear walls acting at the same level. Within the framework of the force-based method, the aim of this study is to propose a simple formulation in order to establish the value of the q-factor of the hybrid system which could be also implemented in seismic design codes such as Eurocode 8. This was achieved by analysing the results of nonlinear dynamic (time-history) analyses performed on a four storey case-study building with different combinations of CLT and Light-Frame shear walls.