The effect of floor flexibility on the seismic behaviour of post-tensioned timber buildings

This report describes in-plane experimental testing and numerical modelling of timberconcrete floor diaphragms. The experimental tests investigated the in-plane stiffness of the diaphragm and the stiffness and strength of different connections between the diaphragm and the lateral load resisting system. The test model was 1/3 scale and three meters square in plan. Seven tests with a different kind of connection between the floor and the rigid lateral supports (which simulated a timber lateral load resisting system) have been performed. The results of the experimental testing are used to calibrate numerical models which are used to investigate the effects of the floor flexibility on the seismic behaviour of post-tensioned timber buildings. For the experimental tests, screw and nail fasteners were used to connected to floor unit to the lateral supports. These fasteners were embedded into the concrete slab or timber edge joints at different orientations. The stiffness of the diaphragm connections was vastly different for each detail. Screws installed at a 45? angle (inclined) to the lateral supports were four times stiffer than the screws installed orthogonal to the lateral supports. The initial stiffness of the inclined fasteners was similar for timber-to-timber and concrete-to-timber connections. For the timberto- timber connections the orientation did not seem to influence the strength of the connection. The tested diaphragm had an uncracked stiffness of 4000 kN/mm and a cracked stiffness of 300 kN/mm. For the tested floor unit it was concluded that the influence of the diaphragm flexibility was negligible compared to the connector flexibility. The floor flexibility can be idealized as three different parts, the deformation of the connectors, the shear deformation of the diaphragm and the flexural deformation of the diaphragm. The numerical analyses showed that in most perceivable situations the connection deformation will govern the in-plane seismic response of the floor. Hence, it is justified to model it as a single-degree-of-freedom (SDOF) element. The influence of the floor flexibility on the seismic response of post-tensioned timber buildings is small. In most cases neglecting the floor flexibility is a conservative approach for the structural design of the building. However, structures with stiff walls and long floor spans there can be a significant amplification of the seismic response. For that case, a simple SDOF representation is proposed. Code-based recommendations for predicting the peak floor accelerations are found to be inadequate. A methodology is proposed to more accurately predict the expected peak floor accelerations for desig

Structural Performance of Post-tensioned Timber Frames under Gravity Loading

A new structural system for multi-storey timber buildings has been developed over the last seven years at the University of Canterbury. The system incorporates large timber structural frames, whereby semi-rigid beam-column connections are created using post-tensioning steel tendons. This system can create large open floor plans required for office and commercial buildings. Several material properties of the engineered timber used were determined based on small-scale experimental testing. Full-scale testing of beams, connections and frames resulted in a more comprehensive understanding of the behaviour of such systems. Numerical, analytical and framework models also led to the development of design equations and procedures which were validated with the acquired experimental data

Effects of "Visual Schema Displacement Therapy" (VSDT), an Abbreviated EMDR Protocol and a Control Condition on Emotionality and Vividness of Aversive Memories: Two Critical Analogue Studies

Visual Schema Displacement Therapy (VSDT) is a novel therapy which has been described as a treatment for stress and dysfunction caused by a traumatic event. Although its developers claim this therapy is quicker and more beneficial than other forms of trauma therapy, its effectiveness has not been tested. We compared the efficacy of VSDT to an abbreviated EMDR protocol and a non-active control condition (CC) in two studies. In Study 1 participants (N = 30) were asked to recall three negative emotional memories under three conditions: VSDT, EMDR, and a CC, each lasting 8 min. Emotional disturbance and vividness of the memories were rated before and after the (within group) conditions. The experiment was replicated using a between group study. In Study 2 participants (N = 75) were assigned to one of the three conditions, and a follow-up after 6-8 days was added. In both studies VSDT and EMDR were superior to the CC in reducing emotional disturbance, and VSDT was superior to EMDR. VSDT and EMDR outperformed the CC in terms of reducing vividness. Results need to be replicated in clinical samples. It is unclear how VSDT yields positive effects, but irrespective of its causal mechanisms, VSDT warrants clinical exploration. [Abstract copyright: Copyright © 2018. Published by Elsevier Ltd.

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. © 2010 ASCE

Effects of “Visual Schema Displacement Therapy” (VSDT), an abbreviated EMDR protocol and a control condition on emotionality and vividness of aversive memories: Two critical analogue studies

Background and objectives: Visual Schema Displacement Therapy (VSDT) is a novel therapy which has been described as a treatment for stress and dysfunction caused by a traumatic event. Although its developers claim this therapy is quicker and more beneficial than other forms of trauma therapy, its effectiveness has not been tested. Methods: We compared the efficacy of VSDT to an abbreviated EMDR protocol and a non-active control condition (CC) in two studies. In Study 1 participants (N = 30) were asked to recall three negative emotional memories under three conditions: VSDT, EMDR, and a CC, each lasting 8 min. Emotional disturbance and vividness of the memories were rated before and after the (within group) conditions. The experiment was replicated using a between group study. In Study 2 participants (N = 75) were assigned to one of the three conditions, and a follow-up after 6–8 days was added. Results: In both studies VSDT and EMDR were superior to the CC in reducing emotional disturbance, and VSDT was superior to EMDR. VSDT and EMDR outperformed the CC in terms of reducing vividness. Limitation: Results need to be replicated in clinical samples. Conclusions: It is unclear how VSDT yields positive effects, but irrespective of its causal mechanisms, VSDT warrants clinical exploration