9.a Steel and Timber Structures
Experimental studies of the Self-Centering Sliding Hinge Joint
H.H. Khoo, G.C. Clifton, J.W. Butterworth & G.A. MacRae
The Sliding Hinge Joint (SHJ) is a low damage connection that rotates inelastically with minimal damage through sliding of Asymmetric Friction Connections (AFC) in the bottom flange and web bolt groups. When this occurs the joint loses elastic strength and stiffness as the bolts in the AFCs lose tension. Furthermore, the SHJ does not have a recentering mechanism and thus does not always recenter. The self-centering SHJ (SCSHJ) was proposed which incorporates friction damping ring spings (RSs) as a self-centering component. This paper presents experimental studies on 6 full-scale subassembly joints. The joint moment capacities were developed with a combination of AFCs and RSs, and designed as a percentage of capacity generated by the RSs (PRS). The joints produced stable and repeatable hysteretic behaviour, with minimal damage to the floor slab. The joints with just RSs exhibited the ideal flag-shaped self-centering hysteretic behaviour. The SCSHJ had a combination of the SHJ and RS behaviours, with improved self-centering characteristics as the PRS increased. No loading rate effects were observed on the joint response. The SHJ had a 25% reduction in stable sliding capacity under a near fault pulse action due to increased demand on the bolts.
Spectral Design Analysis of Sliding Hinge Joints and HF2V Devices for Seismic Dissipation
F. Kato, G.W. Rodgers, G.A. MacRae & J.G. Chase
Due to the extreme damage seen in several recent earthquakes, several passive energy dissipation devices have been developed with different mechanisms of energy dissipation. Response spectra analysis across multiple earthquake suites is used to investigate the reductions in structural response and base shear forces to probabilistically assess the impact of these devices using suites of ground motions from the SAC project.
Single-degree-of-freedom spectral analysis structures are used with nonlinear models of the sliding hinge joint (SHJ) and HF2V devices. Reduction factors are computed for each device compared to a linear, no-device structure. Force capacity for SHJ and HF2V devices are equivalent. Results are presented as 5th, 25th, median (50th), 75th and 95th percentile responses at each period (0.1-5.0s by 0.1s increments).
Both devices show significant reductions in displacement at all spectral periods of 30-60% (at median). Both increase base shear forces. However, SHJ systems show both a broader 5-95th percentile range, as well as larger increases in base shear due to their different velocity dependence in dissipating energy. The results provide initial design trade-off information in a probabilistic, performance-based framework for these devices.
Measuring the effectiveness of seismic control of steel frames using braces with bilinear and flag-shaped hysteretic characteristics
James B McInerney & John C Wilson
Shape memory alloy materials exhibit flag-shaped hysteretic behaviour, creating the potential for relatively simple yet effective energy dissipation devices for seismic control of structures. In this study, non-linear time history analysis of 1, 2, 4, and 8 storey chevron-braced steel frame models was carried out for braces having flag-shaped hysteresis characteristics. For comparison, the same frames were analyzed with bracing that exhibited simpler bilinear hysteresis behaviour. Each frame was subjected to an ensemble of ground motions to determine their mean responses as measured by several response indices: interstorey drift, residual interstorey drift, column ductility demand, beam ductility demand, storey acceleration, base shear, and absorbed energy. The behaviour of the frames was generally governed by the backbone curve of the brace hysteresis defined by a post-yielding stiffness parameter, a normalized yield force, and a normalized stiffness. Increasing these parameters generally decreased interstorey drift, residual interstorey drift, column ductility demand, beam ductility demand, and absorbed energy. However, this also had the effect of increasing acceleration and base shear. An energy dissipation parameter related to the specific characteristics of each hysteresis model had relatively little effect on the response. In general, frames with flag-shaped hysteretic brace characteristics had responses, as measured by many of the previously listed parameters, which were very similar to frames with simpler bilinear hysteretic brace characteristics. The most significant differences were found to be that frames with bilinear brace characteristics tended to have lower accelerations, and frames with flag-shaped brace characteristics tended to have lower residual drifts.
Ambient and Forced Vibration Testing and Finite Element Model Updating of a Full-scale Post-Tensioned Laminated Veneer Lumber Building
M.L. Worth, P. Omenzetter & H. Morris
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%.
Carterton Events Centre Auditorium Pres-Lam Wall Design and Construction
D. Dekker, S. Chung & A. Palermo
Driven by sustainability, locally available resources and expertise, and economy, the design of the Carterton Events Centre focused on timber for the majority of the main structural and non-structural components. Combined with a client desire for minimization of earthquake damage, dissipative post-tensioned rocking Laminated Veneer Lumber (LVL) shear walls (Pres-Lam) were considered for the lateral load resisting system. During design development various structural forms were explored and tested through costing to determine an economic design solution meeting the project drivers. Advanced numerical analyses carried out by the University of Canterbury validated the design process assuring confidence with the design of the technology.
Seismic performance of a post-tensioned LVL building subjected to the Canterbury earthquake sequence
Tobias Smith, David Carradine, Stefano Pampanin, Rocco Ditommaso & Felice C. Ponzo
The following paper presents the seismic performance of a two storey post-tensioned Laminated Veneer Lumber (LVL) building during the aftershock sequence following the MW 6.3 Canterbury earthquake that occurred on 22nd February 2011. Composed of post-tensioned walls in one direction and post-tensioned frames in the other, the structure under analysis was originally tested quasi-statically in the structural laboratories of the University of Canterbury (UoC), Christchurch, New Zealand. Following testing the building was demounted and reassembled as the offices of the STIC (Structural Timber Innovation Company) research consortium on the UoC campus with several significant changes being made to convert the building from its initial use as a test specimen into a functioning office structure.
Just prior to the start of construction, the MW 7.1, 4th Sept 2010 Darfield earthquake occurred in the Canterbury area, however construction went ahead as planned with the building being almost complete when the more devastating 22 February 2011 event occurred. An array of 3-dimensional acceleration sensors was installed on the building follow completion.
Innovative techniques have been used in the study of the building seismic response allowing clear representation of the buildings dynamic performance. The damage free nature of the building even under its Ultimate Limit State excitation is also clear.