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Research papers, The University of Auckland Library

A review of the literature showed the lack of a truly effective damage avoidance solution for timber or hybrid timber moment resisting frames (MRFs). Full system damage avoidance selfcentring behaviour is difficult to achieve with existing systems due to damage to the floor slab caused by beam-elongation. A novel gravity rocking, self-centring beam-column joint with inherent and supplemental friction energy dissipation is proposed for low-medium rise buildings in all seismic zones where earthquake actions are greater than wind. Steel columns and timber beams are used in the hybrid MRF such that both the beam and column are continuous thus avoiding beam-elongation altogether. Corbels on the columns support the beams and generate resistance and self-centring through rocking under the influence of gravity. Supplemental friction sliders at the top of the beams resist sliding of the floor whilst dissipating energy as the floor lifts on the corbels and returns. 1:20 scale tests of 3-storey one-by-two bay building based on an earlier iteration of the proposed concept served as proof-of-concept and highlighted areas for improvement. A 1:5 scale 3-storey one-by-one bay building was subsequently designed. Sub-assembly tests of the beam-top asymmetric friction sliders demonstrated repeatable hysteresis. Quasi-static tests of the full building demonstrated a ‘flat bottomed’ flag-shaped hysteresis. Shake table tests to a suite of seven earthquakes scaled for Wellington with site soil type D to the serviceability limit state (SLS), ultimate limit state (ULS) and maximum credible event (MCE) intensity corresponding to an average return period of 25, 500 and 2500 years respectively were conducted. Additional earthquake records from the 22 February 2011 Christchurch earthquakes we included. A peak drift of 0.6%, 2.5% and 3.8% was reached for the worst SLS, ULS and MCE earthquake respectively whereas a peak drift of 4.5% was reached for the worst Christchurch record for tests in the plane of the MRF. Bi-directional tests were also conducted with the building oriented at 45 degrees on the shake table and the excitation factored by 1.41 to maintain the component in the direction of the MRF. Shear walls with friction slider hold-downs which reached similar drifts to the MRF were provided in the orthogonal direction. Similar peak drifts were reached by the MRF in the bi-directional tests, when the excitation was amplified as intended. The building self-centred with a maximum residual drift of 0.06% in the dynamic tests and demonstrated no significant damage. The member actions were magnified by up to 100% due to impact upon return of the floor after uplift when the peak drift reached 4.5%. Nonetheless, all of the members and connections remained essentially linearelastic. The shake table was able to produce a limited peak velocity of 0.275 m/s and this limited the severity of several of the ULS, MCE and Christchurch earthquakes, especially the near-field records with a large velocity pulse. The full earthquakes with uncapped velocity were simulated in a numerical model developed in SAP2000. The corbel supports were modelled with the friction isolator link element and the top sliders were modelled with a multi-linear plastic link element in parallel with a friction spring damper. The friction spring damper simulated the increase in resistance with increasing joint rotation and a near zero return stiffness, as exhibited by the 1:5 scale test building. A good match was achieved between the test quasi-static global force-displacement response and the numerical model, except a less flat unloading curve in the numerical model. The peak drift from the shake table tests also matched well. Simulations were also run for the full velocity earthquakes, including vertical ground acceleration and different floor imposed load scenarios. Excessive drift was predicted by the numerical model for the full velocity near-field earthquakes at the MCE intensity and a rubber stiffener for increasing the post joint-opening stiffness was found to limit the drift to 4.8%. Vertical ground acceleration had little effect on the global response. The system generates most of its lateral resistance from the floor weight, therefore increasing the floor imposed load increased the peak drift, but less than it would if the resistance of the system did not increase due to the additional floor load. A seismic design procedure was discussed under the framework of the existing direct displacement-based design method. An expression for calculating the area-based equivalent viscous damping (EVD) was derived and a conservative correction factor of 0.8 was suggested. A high EVD of up to about 15% can be achieved with the proposed system at high displacement ductility levels if the resistance of the top friction sliders is maximised without compromising reliable return of the floor after uplift. Uniform strength joints with an equal corbel length up the height of the building and similar inter-storey drifts result in minimal relative inter-floor uplift, except between the first floor and ground. Guidelines for detailing the joint for damage avoidance including bi-directional movement were also developed.

Images, UC QuakeStudies

A photograph submitted by Raymond Morris to the QuakeStories website. The description reads, "This painting of the ‘Frame workshop’ 456 Colombo St. Sydenham is by artist Raymond Morris. It is one of many paintings he has done of buildings demolished in the earthquakes 2010-2011.".

Images, UC QuakeStudies

A photograph of the earthquake damage to the Christchurch Chinese Methodist Church on Papanui Road. The gable wall has crumbled, the bricks and window frame falling onto the ground. Wire fencing has been placed around the building as a cordon.

Images, UC QuakeStudies

Damage to a house in Richmond. The brick wall is badly cracked and twisted, and some bricks have fallen, exposing the lining paper and framing below. The photographer comments, "These photos show our old house in River Rd and recovery work around Richmond and St Albans. I think it's broken".

Images, UC QuakeStudies

Damage to a house in Richmond. Bricks have fallen from the walls, exposing the wooden framing beneath. Power lines between the house and a power pole have been stretched taut. The photographer comments, "The house and power pole have moved, stretching power lines taut as a guitar string".

Images, UC QuakeStudies

Samo Coffee Lounge signs decorate the front of The Loons Circus Theatre Company building on Canterbury Street in Lyttelton. The facade of the building is propped up by a timber frame and concrete blocks. Samo Coffee Lounge was run inside the Loons building by a group of former Lyttelton Coffee Company staff.

Images, UC QuakeStudies

Damage to a house in Richmond. The brick wall is badly cracked and twisted, and some bricks have fallen, exposing the lining paper and framing below. The driveway is cracked and covered in liquefaction. The photographer comments, "These photos show our old house in River Rd and recovery work around Richmond and St Albans. Does that wall look straight to you?

Images, UC QuakeStudies

Damage to a house in Richmond. The brick wall is badly cracked and twisted, and some bricks have fallen, exposing the lining paper and framing below. The driveway is cracked and covered in liquefaction. The photographer comments, "These photos show our old house in River Rd and recovery work around Richmond and St Albans. More shaking damage on the east wall of the living room at our house".

Images, UC QuakeStudies

Two people examine damage to a house in Richmond. The brick wall is badly cracked and twisted, and some bricks have fallen, exposing the lining paper and framing below. The photographer comments, "These photos show our old house in River Rd and recovery work around Richmond and St Albans. The near wall is leaning at an alarming angle. I didn't like walking past it".

Images, UC QuakeStudies

Damage to a house in Richmond. Bricks have fallen from the walls onto the driveway, and a large gap between the concrete foundation and the wooden framing shows how much the house has moved. The photographer comments, "The foundations and brick cladding moved, but the timber wall remained in position. The gap grew to over 400mm by the time the house was demolished.