7.1 Recent Projects
Timber Piles to Mitigate Liquefaction and Lateral Spreading, Aotea Quay Wellington
R.G. Cole
ABSTRACT: The Aotea Quay reclamation was constructed in the north west corner of the Wellington Harbour in the 1920’s and 1930’s. A 10 m high mass concrete seawall was constructed 300 m from the foreshore. The 300 m wide lagoon formed was filled by pumping in silt and sand dredged from the harbour seaward of the seawall.
Under the ultimate limit state design earthquake (rupture of the Wellington fault or similar) extensive ground damage of this reclamation could be expected, including toppling of the seawall, widespread liquefaction of the hydraulic fill, and lateral spreading of the reclamation toward the sea by a number of metres.
The reclamation is currently occupied by port facilities, a road (Aotea Quay) and railway yards. Mainfreight proposes to construct a 150 m x 80 m freight handling building on the landward side of the reclamation. This paper discusses the assessment of potential ground deformation under serviceability and ultimate limit state design earthquakes and how these effects can be mitigated.
Options considered included base reinforcement to limit differential lateral displacement of the building platform, and ground improvement of the reclamation to reduce the potential for liquefaction. The selected option comprises ground improvement of an 8 m wide strip along the seaward side of the building by driving 300 mm diameter timber piles on a 1.2 m x 1.2 m grid. These timber piles stiffen the ground reducing the potential for liquefaction, and penetrate the dense old seabed providing restraint against lateral spreading. The design of the ground improvement and its expected performance are discussed.
Auckland Art Gallery: A Celebration of the New and Old
S.J. Oliver & C.S.M. Mackenzie
ABSTRACT: The performance based assessment and design of aspects of the Auckland Art Gallery Development project are presented. Detailed nonlinear dynamic time history analyses in conjunction with NZSEE Assessment Guidelines and FEMA-356 were used to assess the performance of existing heritage wings. Strengthening of existing heritage building diaphragms with new sheet metal blocked plywood diaphragms is detailed.
Analysis and design of a large glazed atrium tension façade system is summarised. Key design considerations including façade performance requirements under serviceability limit state loads and pre-stressing methodologies are presented. Some aspects of the basement retention design including the influence of the adjacent heritage buildings are discussed.
Studies on the Material Properties of the Aurora Tavern, Auckland
R. Lumantarna, D. Dizhur, P. Liu & J.M. Ingham
ABSTRACT: The Aurora Tavern was one example of many heritage unreinforced masonry (URM) buildings in New Zealand, and therefore like other existing URM buildings, this hotel was vulnerable to damage should a moderate magnitude earthquake occur. Refurbishment and strengthening work was being implemented on the building, during which in-situ testing was performed to investigate the building’s material properties. The URM materials in the Aurora Tavern were generally in poor condition, and water ingress was observed at various locations in the building. In-situ deformability tests and bed joint shear tests were conducted on-site to determine the masonry stiffness and the mortar bed joint shear strength respectively. In addition, individual brick units and irregular mortar samples were extracted for compression testing in the laboratory. Laboratory mortar compression tests and in-situ deformability tests showed that the mortar compressive strength and masonry Modulus of Elasticity were low. However, the brick compressive and mortar bed joint shear strengths were comparable to those of other buildings that were previously investigated by the research team. The Aurora Tavern was demolished on the 18th of November 2010 due to a sudden foundation failure.
Modelling of In-Structure Damping: A Review of the State-Of-The-Art
K. Grinlinton, D. Wood, F. Ayan & P.J. Clayton
ABSTRACT: As part of its HVDC Pole 3 project, Transpower commissioned Beca to provide the detailed assessment and strengthening design for the existing Haywards Synchronous Condenser Transformer building. Earthquake effects up to a 2500 year return period event were considered. Existing schematic studies had concluded that a significant downslope sliding displacement of the whole building was likely, resulting in a preliminary strengthening scheme that included significant anchoring into the slope. Geotechnical investigation and subsequent time history analysis suggested a much more limited extent of sliding. It was also necessary to derive response spectra at the mounting levels of the existing synchronous condensers and the proposed new transformers to limit damage to plant and connections in a severe earthquake. A range of damping levels was considered to estimate the effect of both building and plant damping on seismic acceleration response.
A strengthening solution evolved which balanced the needs of the transformer manufacturer (seismic accelerations limited to achievable levels) with a preference to avoid significant work in confined spaces and/or ground anchoring. The paper describes the time history analysis undertaken and the advantages derived in relation to the building strengthening decision making and the resulting scheme.
SH2 Westshore Bridge Seismic Retrofit
P.S. McCarten, A.S. Chew & N. Lloyd
ABSTRACT: The Westshore Bridge is a typical short to medium span structure located on SH2 within Napier City and was built in 1960. It comprises 3 spans of 20m prestressed concrete T-beam superstructure supported on cap beams that are founded on 406mm octagonal prestressed concrete piles. Critical city utilities including power, telecommunications, gas, sewer and water services are carried on the bridge. Detailed geotechnical assessments identified liquefaction and embankment instability hazards and pushover analyses identified structural vulnerabilities in the pier caps and piles.
The most cost effective option to secure the bridge to the 500 year event level and to prevent catastrophic bridge failure in the 2500 year event was to convert the simply supported superstructure to a rigid diaphragm and enhance abutment stability. The retrofit included installing 12m long sheet pile walls at the abutments with return walls and new capping beam, and, installing 710kN and 590kN yield strength linkage rods in tight working spaces between the outer beams above water at both piers.
Construction challenges included work around the existing sewer and gas services and limiting adverse effects to the bridge structural integrity as a consequence of the seismic retrofit work.
Retrofit Options for Residential House Foundations to Resist Earthquakes
G.C. Thomas & K. McGowan
ABSTRACT: Previous work by Irvine and Thomas has shown that seismic performance of timber framed houses in Wellington is often compromised by poor, no or degraded connections between piles and bearers or foundation walls and joists. The same problems were evident in a number of houses visited in Christchurch after the recent Canterbury earthquake, resulting in avoidable damage. Retro-fit hardware that is cheap simple, easy to install using nail guns or self drilling timber screws has been developed and tested at BRANZ. This hardware is easy to fit, even where space is Ltd restricting the use of hammers, but is ductile in both tension and compression. It is strong enough to develop the maximum passive earth pressure that can readily be achieved under lateral loads for ordinary piles resulting in significant improvement in seismic performance for poorly braced foundations at low cost.