		2007 NZSEE Conference
	Abstracts

Keynote Address 1 Defining Acceptable Performance Criteria Planning for Expected Performance / Improving Existing Performance I Improving Existing Performance II Keynote Address 2 Developments Within Design I Developments Within Design II Developments Within Design III / Understanding the Inputs Assessing Existing Performance Poster Papers

Fully Integrated Performnce Based Design and Retrofit of Existing Buildings : a Case Study

Jonathan Chambers, Trevor Kelly and R.C. Dreyer

The performance based assessment and retrofit of an iconic, 14 storey, historic building in Oakland, California is presented.

The nonlinear dynamic analysis procedure was used in conjunction with FEMA-356 to assess the performance of this early 1900’s, concrete encased riveted steel frame structure.

A ‘fully integrated’ approach was implemented, whereby the calculation of acceptability criteria and assessment of each element is performed at every time step; the performance assessment fully integrated with the analysis engine.

This method overcomes the conservatism inherent in the typical approach, which calculates the performance criteria for certain elements at the end of an analysis using peak results.

In the present case study, the use of the fully integrated approach made it possible to develop a retrofit scheme that met target performance objectives specified by the local authorities without compromising the valuable historic fabric of the building.

Paper P35: [Read]

Estimating Seismic Induced Damage in Buildings

Oliver de Lautour and Piotr Omenzetter

Contemporary methods of estimating the extent of seismic induced damage to structures include non-linear finite element analysis and the use of seismic vulnerability curves. Both these methods however are limited to predicting damage to a certain predetermined structure or class of structures characterized by a small number of parameters. Hence they are unable to generalize damage information to a wider range of other structures (e.g. buildings with a different number of stories and/or bays, or different ground motions). This study presents a generalized method for predicting seismic-induced damage utilizing a simple artificial intelligence tool, namely Artificial Neural Networks (ANNs). ANNs are used to relate a wide set of input parameters, describing both the structure and the ground motion, to a damage index describing the extent of damage in the structure. The proposed method was applied to non-linear computer models of simple 2D reinforced concrete frame buildings. The method was capable of accurately predicting damage to frames varying in strength, stiffness, damping and geometry whilst subjected to a range of ground motions with different peak accelerations, velocities, displacements and spectrum intensities.

Paper P36: [Read]

Performance Evaluation of Bolu Viaducts in Terms of Performance-based Seismic Design of Bridges

Asif Iqbal

Lubricated PTFE sliding bearings and mild-steel energy dissipation devices act together as an elastoplastic seismic isolation system. These systems have been used in seismic isolation of many bridges in Italy and other parts of the world. One case study involving the use of these devices is discussed here to examine their applicability in the performance-based design approach for bridges. The structures are the viaducts on the Istanbul to Ankara Motorway in Turkey.

The design philosophy and application details of the isolation system are studied here. Performance of the isolation system is evaluated for two very strong earthquakes. It is established that pier forces are significantly reduced due to the inclusion of the energy dissipating elements and the level of forces transferred to the substructure can be predicted irrespective of the ground motion. But the absence of a restoring force mechanism also reveals the inherent limitation of the system in which large permanent deformations of the superstructure are created in the event of an earthquake.

A tentative outline of Performance-Based Bridge Design criteria is followed here for the review of the applications. The expected and observed behavior of the isolation system have to be judged with respect to the performance-based requirements. Despite the limitations of the system under discussion, the use of such devices at different performance levels can be rationalized for practical application in bridges.

Paper P57: [Read]

Seismic Assessment and Remediation of the Aviemore Dam Spill and Sluice Gates

Robert Davey, Ken Ho and Jim Walker

In 2006 Meridian Energy completed a comprehensive dam safety programme that evaluated the expected performance of the Aviemore dam under earthquake, and implemented remediation work where required. This programme included investigation of the Waitangi Fault which passes across the dam; derivation of seismic loads and fault rupture movements; assessment of the dam performance under large ground motions and fault rupture displacements; and assessment of the overtopping risk from seiche waves on the lake arising from uplift of the lake floor. This study included evaluation of the dam “appurtenant works”, comprising the intake, spillway and sluice gates; the spillway piers and bridge; the penstocks; the gantry crane and the electrical and control equipment. In this paper we discuss the evaluation and remediation of the spillway and sluice gates.

The spillway and sluice gates are large, steel radial gates. Analyses indicated that these structures will be stressed beyond their yield load under combined hydrostatic and earthquake (SEE) induced hydrodynamic loads. Under the influence of the hydrostatic load, the structures yield when the earthquake response cycle is in the “downstream” direction only, leading to an accumulation of yield displacements in that direction. The resulting large deformations were predicted to fracture the bolts that secure the horizontal girders and skin plate to the radial arms. An innovative remedial solution was developed to avoid this damage and ensure that the gates could be operated following the SEE.

Paper P38: [Read]

Adequacy of Existing House Foundations for Resisting Earthquakes: the Cost-benefit of Ungrading

James Irvine and Geoff Thomas

The past performance of foundations in earthquakes for timber dwellings prompted a practical investigation into the adequacy of existing sub-floor bracing, connection capacity and the overall adherence to NZS3604:1999. Using information gathered from a sample of 80 Wellington dwellings and by using the results from an Earthquake Loss modeller, it was found that the cost of upgrading “at risk” foundations is almost 30 times less expensive than the complete cost of rebuilding dwellings. Potential damage mitigation saves around 5 times the calculated damage costs. This saving has the potential to reduce temporary shelter costs and other large unknown costs of post-earthquake rehabilitation and reconstruction.

Paper P39: [Read]

Seismic Instrumentation of Buildings - a Promising Step for Performance Based Design in New Zealand

Uma Uma

Performance-based earthquake engineering seeks to improve seismic risk decision-making through assessment and design methods that express options in terms that enable stakeholders to make informed decisions as to the level of disruption they are prepared to accept following earthquake attack. The key feature is the definition of performance metrics that are relevant to decision making for seismic risk mitigation. The definition of performance metrics relates the response of buildings and the damage states which in turn need to be supported by knowledge gained from observed data. Instrumentation of buildings with seismic sensors is proven be a successful method to sense and record the data. With the aim of mitigating seismic risk and as a part of scientific research, GeoNet is involved in a national project deploying seismic instruments, including in constructed facilities. The paper discusses the aspects to be considered and the strategies to be followed for an instrumentation program for facilities in New Zealand. These instrumented facilities will act as reference stations for regional accelerograph networks and also give significant information on verification of design assumptions that underpin our standards. Finally, a note on the future developments that can be realised by a strong motion monitoring program to mitigate the seismic risk is presented.

Paper P40: [Read]

Seismic Assessment and Retrofit of Waikanae and Pakuratahi River Bridges

John Wood, Howard Chapman, Gavin Gregg and Donald Kirkcaldie

Seismic strengthening construction work has recently commenced on the Waikanae and Pakuratahi River Bridges assessed as having a high priority for retrofitting. Both bridges are on major State Highways in the Wellington region that carry high traffic volumes. The paper describes the assessment methods and strengthening details used on these two bridges.

Paper P41: [Read]