This paper presents an investigation of possible disproportionate collapse for a nine-storey flat-plate timber building, designed for gravity and lateral loads. The alternate load-path analysis method is used to understand the structural response under various removal speeds. The loss of the corner and penultimate ground floor columns are the two cases selected to investigate the contribution of the cross-laminated timber (CLT) panels and their connections, towards disproportionate collapse prevention. The results show that the proposed building is safe for both cases, if the structural elements are removed at a speed slower than 1 sec. Disproportionate collapse is observed for sudden element loss, as quicker removal speed require higher moments resistance, especially at the longitudinal and transverse CLT floor-to-floor connections. The investigation also emphasises the need for strong and stiff column-to-column structural detailing as the magnitude of the vertical downward forces, at the location of the removed columns, increases for quicker removal.
The characterization of the behaviour of connectors used in Cross-laminated Timber (CLT) structures is an important aspect that needs to be considered in their seismic design. In this paper, the data from shear and axial tests conducted on connectors have been used to define their force-displacement curves under cyclic loads using the SAWS model in OpenSees. The component curves were then incorporated into the corresponding wall models and the results were compared with their experimental counterparts, in order to determine the validity of the finite element model. Thereby, the non-linear behaviour was restricted to the connectors while the walls themselves were composed of linear orthotropic shell elements. The models were found to provide a good estimate of the initial stiffness and maximum load capacity of the wall specimens. The effects of vertical loading and the presence of openings were determined based on analyses run on the calibrated model.
Guadua angustifolia Kunth (Guadua) is a bamboo species native to South and Central America that has been widely used for structural applications in small and large scale buildings, bridges and temporary structures. Guadua remains a material for vernacular construction associated with high levels of manual labour and structural unpredictability. The aim of this work is to develop standardised industrial structural products from Guadua and to measure and predict their mechanical behaviour. Cross laminated Guadua (CLG) panels comprised of three and five layers were manufactured and their mechanical properties evaluated by testing small and large specimens in compression and shear. The digital image correlation (DIC) method was used to measure strain variations in the X, Y and Z axes on the surface of small CLG panels with strain gauge measurements on the reverse face. The deformation of large CLG panels was measured using DIC on the front face and transducers on the reverse face. The results from mechanical tests and DIC were compared and a finite element (FE) model developed that predicts the response of the material. Overall, this study provides guidelines for structural design with engineered bamboo products which are of key importance for their mainstream use.
New Zealand Society for Earthquake Engineering Conference
April 13-15, 2012, Christchurch, New Zealand
The Nelson Marlborough Institute of Technology Arts and Media building was completed in 2011 and consists of three seismically separate complexes. This research focussed on the Arts building as it showcases the use of coupled post-tensioned timber shear walls. These are part of the innovative Expan system. Full-scale, in-situ dynamic testing of the novel building was combined with finite element modelling and updating to obtain an understanding of the structural dynamic performance within the linear range. Ambient testing was performed at three stages during construction and was combined with forced vibration testing for the final stage. This forms part of a larger instrumentation program developed to investigate the wind and seismic response and long term deformations of the building. A finite element model of the building was formulated and updated using experimental modal characteristics. It was shown that the addition of non-structural elements, such as cladding and the staircase, increased the natural frequency of the first mode and the second mode by 19% and 24%, respectively. The addition of the concrete floor topping as a structural diaphragm significantly increased the natural frequency of the first mode but not the second mode, with an increase of 123% and 18%, respectively. The elastic damping of the NMIT building at low-level vibrations was identified as being between 1.6% and 2.4%
This paper deals with a certain type of C.L.T. (Cross Laminated Timber) construction, in a residential building in Fristad, Sweden. The objective is to study impact noise transmission, at the lower frequency range (10-200 Hz), where wooden dwellings perform inefficiently, in terms of acoustic quality. The vibrational behavior of lightweight structures and specifically a multilayered floor separating two vertically adjacent bedrooms are investigated. A numerical model of the multilayered test plate, which includes sound insulation and vibration isolation layers, is developed using the Finite Element Method (F.E.M.) in commercial software. The design process, the analysis and improvement of the calculated outcome concerning accuracy and complexity are of interest. In situ vibration measurements were also performed so as to evaluate the structures dynamic behavior in reality and consequently the validity of the modelled results. The whole process from design to evaluation is discussed thoroughly, where uncertainties of the complex F.E.M. model and the approximations of the real structure are analyzed. Numerical comparisons are presented including mechanical mobility and impact noise transmission results. The overall aim is to set up a template of calculations that can be used as a prediction tool in the future by the industry and researchers.
Connections are critical parts of timber structures, transmitting static and dynamic forces between structural elements. Extensive experiments were conducted and detailed Finite Element (FE) models were developed. The experimental results showed that the stiffness and load-bearing capacity of the joints is reduced by post-fabrication wetting and is increased by post-fabrication drying. It was clear from those test results that changes in mechanical properties were greater than could be explained by effects moisture content changes have on material properties. Three-dimensional (3-D) continuum FE models for connection loaded parallel to grain were successfully developed based on analysis of connections having a single ½ inch (12.7 mm) or ¾ inch (19.1 mm) diameter bolt. The model included the nonlinearity of material and contact analysis between wood and steel and revealed that the connection capacity can be well predicted by using FE techniques.
This research project presents both innovative multi-scalar modelling methods and production processes aimed at facilitating the design and fabrication of free-form glue-laminated timber structures. The paper reports on a research effort that aims to elucidate and formalize the connection between material performance, multi-scalar modelling (Weinan 2011), and early-stage architectural design, in the context of free-form glue-laminated timber structures. This paper will examine how the concept of multi-scalar modelling as found in other disciplines can also be used to embed low-level material performance of glue-laminated timber into early-stage architectural design processes, thus creating opportunities for feedback across the design chain and an increased flexibility in effecting changes. The research uses physical prototypes as a means to explore and evaluate the methods presented.
The thermal refurbishment of the building stock is one of the most fundamental challenges of sustainable urban development. Particularly the use of natural and local materials gets an increasing relevance, regarding the embodied energy. The focus of this work is the development of systematised solutions for thermal refurbishment with...
A candidate CLT diaphragm analysis model approach is presented and evaluated as an engineering design tool motivated by the needs of seismic design in the United States. The modeling approach consists of explicitly modeling CLT panels as discrete orthotropic shell elements with connections between panels and connections from panels to structural framing modelled as two-point springs. The modeling approach has been compared to a developed CLT diaphragm design example based on U.S. standards showing the ability to obtain matching deflection results. The sensitivity of the deflection calculations to considering CLT panel-to-panel connection gap closure is investigated using a simple diaphragm example. The proposed modeling approach is also applied to the candidate floor diaphragm design for the Framework project, one of the two U.S. Tall Wood Building Prize Competition winners, currently under design. Observations from this effort are that the proposed method, while a more refined model than typically used during building design, shows promise to meet the needs of innovative CLT seismic designs where appropriate simpler diaphragm models are not available.