David Carradine

Post-Tensioned Glulam Beam-Column Joints with Advanced Damping Systems: Testing and Numerical Analysis

This article describes tests investigating a feasible source of passive damping for post-tensioned glue-laminated (glulam) timber structures. This innovative structural system adapts precast concrete PRESSS technology [Priestley et al., 1999] to engineered wood products combining the use of post-tensioned tendons with large timber members. Current testing is aimed at further improvement of the system through additional energy dissipation. Testing has favorably compared glue-laminated timber (not previously implemented in this way) with laminated veneer lumber (LVL) used in New Zealand. After initial benchmark testing with post-tensioning only, a simple, minimally invasive and replaceable type of hysteretic damper was added.

In-Plane Experimental Testing of Timber-Concrete Composite Floor Diaphragms

Recent advances in multistory timber building design have led to new structural systems that allow open floor plans with large spans between frames and/or walls. Timber-concrete composite (TCC) flooring can achieve the spans required but has the potential to be flexible under diaphragm actions, which can significantly alter the seismic response of a building. In-plane experimental tests on a 3 m by 3 m one-third scale TCC floor were performed using quasi-static earthquake loading simulation. The experimental results indicate that the deformation between the floor and lateral load resisting systems (LLRS) is much greater than the in-plane deformation of the floor diaphragm. Hence, a floor system with similar aspect ratio can be modeled as a single-degree-of-freedom for future structural analyses. Different connections were considered between the floor unit and lateral restraints, which simulate the LLRS. The connection was either timber-to-timber or concrete-to-timber and incorporated screws or nails acting as dowels or inclined at 45°. Each connection type performed differently in terms of stiffness, strength, ductility capacity, and induced damage. Screws that were oriented at 45° to the connection interface were significantly stiffer than fasteners aligned orthogonal to the interface. There was little difference in the initial stiffness for the concrete-to-timber connection compared to the timber-to-timber connection. The testing indicated that a timber-to-timber interface is more desirable because of construction ease and reparability. The in-plane response of the floor system is modeled using finite elements and compared to experimental results. Design recommendations are provided for the cyclic strength of inclined wood fasteners.

Design of Timber-Concrete Composite Floors for Fire Resistance

This research investigated the fire performance and failure behaviour of timber-concrete composite floor systems currently under development in New Zealand, resulting in a design method for evaluating the fire resistance of these floors with different types of connections. Furnace tests were performed on two full-size floor specimens at the Building Research Association of New Zealand (BRANZ). Both floor specimens were 4 m long and 3 m wide, consisting of 65 mm concrete topping on plywood formwork, connected to double LVL (laminated veneer lumber) floor joists. They were tested over a 4 m span, subjected to a nominal design live load of 2.5 kPa. Both floors were subjected to the ISO 834 test fire for over 60 minutes. Two separate connection types were tested; concrete notches cut into the timber beams with an incorporated shear key, and metal toothed plates pressed between the double beams.It was found that the reduction in section of the timber beams due to the fire governed the failure mode of the floor...

Development of constitutive model for laminated veneer lumber using digital image correlation technique

This paper describes the development of a three-dimensional constitutive model for laminated veneer lumber (LVL) needed for new developments using this material. The LVL was manufactured in New Zealand from Radiata Pine. Experimental testing has been performed according to European timber testing standards. Block compression testing has resulted in modulus of elasticity values in the three material directions. Digital image correlation (DIC) technique has been used to determine the six Poisson’s ratios. Shear testing, whereby timber specimens were glued between two steel plates, has given stiffness values using DIC measurements. Experimental testing results have been compared with values found in literature. Results from this experimental testing programme have made it possible to create a three-dimensional elastic material model of LVL for the use in finite element analysis programmes. Although the material properties do not result in a symmetrical constitutive matrix, only minor adjustments are needed to gain the benefits of a symmetrical matrix.

Gravity Design of Post-Tensioned Timber Frames for Multi-Storey Buildings

This paper describes the use of post-tensioning for timber gravity frames. These frames can be used for multi-storey commercial and office buildings. Two different configurations are described, one with prefabricated post-tensioned timber beams and one with post-tensioning through the full length of the frame. In the latter, beam-column connections are created by the clamping force due to the posttensioning. It is shown that post-tensioning of timber beams can create a precamber which helps to satisfy deflection criteria. This makes it possible to create long span timber beams while limiting the section height. Key design issues including deflections, tendon profile, deviators and tendon anchorage are addressed. The behavior of these connections is presented and the three deformation components of the connection are explained. A design example of a post-tensioned timber frame is also included.

Modelling the fire performance of structural timber-concrete composite floors

This paper describes numerical modelling to predict the fire resistance of engineered timber-concrete composite floor systems. The paper describes 3D numerical modelling of the floor systems using finite element software, carried out as a sequential thermo-mechanical analysis. Experimental testing of these floor assemblies has also been undertaken to validate the models, with multiple full scale tests conducted to determine the failure mechanisms and assess fire damage to the system components. The final outcome of this research is the development of simplified design methods for calculating the fire resistance of a wide range of engineered timber floor systems, as part of a larger research project on multi-storey timber buildings.

Experimental Testing of Posttensioned Timber Frames under Gravity Loading

AbstractThis paper describes the experimental testing campaign of one-bay and two-bay posttensioned timber frames under gravity loading. Long-span box beams, made of radiata pine laminated veneer lumber, were connected to columns using only the compressive force introduced by posttensioning tendons. The use of tendons with a draped profile resulted in not only semirigid beam-column connections, but also an initial precamber. Both aspects helped to satisfy deflection design limits. The load-deflection behavior of the beams, the increase in posttensioning force during testing, and the connection behavior are evaluated. Of particular interest is the gap opening of the connection, which showed a distinct bilinear moment-rotation behavior. The application of posttensioning tendons to timber frames can more than double the load-carrying capacity at serviceability limit state.

Structural Behavior of Longitudinally Posttensioned Timber Beams under Serviceability Gravity Loading

AbstractThe scope of this paper is to quantify the advantages of using unbonded longitudinal posttensioning for long-span timber beams. This sustainable system can be a suitable alternative to more...

Long-Term Behavior of LVL Posttensioned Timber Beams

AbstractThe long-term behavior of unbonded posttensioned laminated veneer lumber (LVL) timber beams was investigated for four years under uncontrolled environmental conditions. Two full-scale simpl...