		2008 NZSEE Conference
	Abstracts

Keynote Address Session 1 Session 2 Session 3 Session 4 Session 5 Session 6 Poster Session Session 8

Visualisation and classification of dynamic structural health monitoring data for assessment of structural condition

O.R. de Lautour and Piotr Omenzetter

The application of time series analysis methods to Structural Health Monitoring (SHM) is a relatively new and emerging technique. Time series methods are inherently suited to SHM where data is sampled regularly over a long period of time. This study focuses on detecting damage by classification of time series model coefficients. Autoregressive (AR) models were used to analyse acceleration time histories from a 3-storey bookshelf laboratory structure and the ASCE Phase II SHM Benchmark structure in both healthy and damaged states. Preliminary inspection of the AR coefficient data to check the presence of clusters corresponding to different damage severities was achieved using two-dimensional projections obtained from either Principal Component Analysis (PCA) or Sammon mapping. Two classification techniques, Nearest Neighbour (NN) and Learning Vector Quantization (LVQ) were used to classify damage into states based on analysis of the AR coefficients reduced in dimensionality using PCA. The results showed that NN classifiers performed well however, small gains could be made using LVQ.

Paper P03: [Read]

Exploring the Feasibility of a Floor System Detached From Seismic Beams in Moment Resisting Frame Buildings

Rajesh Dhakal

In current practice, floor slab and beams in the perimeter seismic frames are monolithically constructed and rigidly connected to each other through starter bars. This rigid connection ensures that the shear friction between the floor and the seismic beam transfers the inertial force resulting from the response acceleration of the floor mass and any superimposed dead loads to the moment resisting seismic frame. But, this rigid connection between the floor and perimeter seismic beams leads to several complications such as: (i) possibility of stronger beam (than columns) because of the slab contribution on the negative moment capacity of seismic beams; (ii) possibility of (unidirectional) plastic hinge forming away from column face; and (iii) the floor-beam compatibility requirement leading to severe damage in the slab as the seismic beams deflect in double curvature and grow in length due to elongation of the plastic hinges at the same time. In a quest to avoid these complications, this paper investigates the feasibility of a floor slab that is detached completely from the perimeter seismic beams. In this system, the slab is rigidly connected to the intermediate beams, which are designed to transfer the inertial force to the columns through shear friction and/or torsional resistance. This idea is conceptually discussed and its validity is scrutinized in the paper.

Paper P18: [Read]

Experimental Investigation on a Hybrid Jointed Precast Frame with Non-tearing Floor Connections

Alejandro Amaris, Stefano Pampanin, Desmond Bull and Athol Carr

The effects of beam elongation in precast frame systems have demonstrated a potential source of un-expected damage to precast floor systems, unless adequate detailing is provided to account for displacement incompatibilities between the lateral resisting systems and the floor.

The Precast Concrete Seismic Structural Systems (PRESSS) research program has shown the efficiency of dry-jointed ductile connections for moment resisting frames in order to reduce damage while sustaining high lateral loads. However, damage to precast floor systems, resulting from a geometric elongation of the beam, has yet to be addressed in detail.

In this contribution an overview of alternative solutions developed for post-tensioned “hybrid” connections is first provided. A series of quasi-static cyclic tests on a major 2-D, 2/3 scale, two story, single bay, precast concrete frame system with an innovative “non-tearing floor” connection is presented. The proposed solution consists of an efficient floor to lateral load resisting connection system which can mitigate the effects of geometric (and material) beam elongation. The response of the “non-tearing floor” solution is compared to alternative more traditional solutions.

Both numerical and experimental results confirm the unique flexibility of the proposed solution and highlight the superior performance under seismic loading sustaining only minor damage to the frame, wall and floor systems under major earthquake events.

Paper P26: [Read]

Architectural characterisation and prevalence of New Zealand's unreinforced masonry building stock

Alistair Russell and Jason Ingham

Unreinforced masonry (URM) buildings remain New Zealand's most earthquake-prone structures. As part of an effort to develop retrofit solutions for upgrading the seismic performance of these structures, research into characterising the national building stock of URM buildings has been conducted.

This research classifies New Zealand URM buildings into typologies, based on their general structural configuration. Seven typologies are presented, and their relative prevalence, age and locations are identified. Based on these classifications, seismic vulnerability assessments will need to be conducted on a regional and national basis.

An estimate of the population and distribution, as well as the construction date, of existing URM structures in New Zealand is also presented. Effort is being developed to further improve the quality of data, in conjunction with exercises currently being conducted by local territorial authorities. The preponderance of these structures were constructed between 1920 and 1930.

Paper P36: [Read]

Design Procedure and Behaviour of the Advanced Flag-Shape (AFS) Systems for Moment-Resisting Frame Structures

Weng Y. Kam, Stefano Pampanin, Alessandro Palermo and Athol Carr

The concept of Advanced Flag-Shaped (AFS) systems, in which alternative forms of energy dissipations (yielding, friction or viscous/visco-elastic damping) are combined in series and/or in parallel together with re-centering elements (un-bonded post-tensioning tendons or Smart memory alloy(SMA) elements), has been previously introduced by the authors. Based on numerical analyses on SDOF-systems, the unique combination of friction or hysteretic dampers in series with viscous dampers, further combined in parallel with re-centering and hysteretic dissipation elements, has been shown to be very effective in controlling both force and displacement responses for either far-field and near-fault ground motions. Experimental validation of the effectiveness of the systems based on shake-table testing on wall systems is presented in a companion paper.

In this contribution, the concept of AFS systems is extended to MDOF systems. Preliminary suggestions for a simplified design procedure for AFS connection systems are given within the framework of a Direct Displacement-Based Design (DDBD) approach. Using case-study prototypes of five-storey moment-resisting frame, incorporating four different connection systems, a comparative MDOF study is carried out by the means of non-linear time-history analyses using suites of far-field and near-fault earthquake excitations. The non-linear time history analysis results for both far-field and near-fault earthquakes provided satisfactory validation of the design procedure, though being, as expected, on the conservative side when dealing with velocity-dependent dissipating systems.

As per the results of SDOF systems, AFS systems appear to be capable of providing beneficial attribute to the response of a MDOF system, particularly when dealing with velocity-pulse earthquake record, typical of a near-field event. In addition to providing reduction of peak displacement/drift response and a negligible residual deformation, floor accelerations and column shears due to the higher mode effects are also lessened. In the global performance matrix, AFS systems would achieve a much higher performance level in comparison to the conventional systems. There is however, less than expected contribution from the excitation velocity on dampers’ energy dissipation up the building heights. Based on these results, an approximation for the velocity-dependent devices’ velocities at a given storey is proposed. In conclusion, a brief discussion on limits and potentials for the practical implementation of AFS systems is given, along with anticipation of ongoing and further investigations.

Paper P38: [Read]

Dynamic Testing of Precast, Post-Tensioned Rocking Wall Systems With Alternative Dissipating Solutions

Dion Marriott, Stefano Pampanin, Alessandro Palermo and Desmond Bull

During the past two decades, the focus has been on the need to provide communities with structures that undergo minimal damage after an earthquake event while still being cost competitive. This has led to the development of high performance seismic resisting systems, and advances in design methodologies, in order respect this demand efficiently.

This paper presents the experimental response of four pre-cast, post-tensioned rocking wall systems tested on the shake-table at the University of Canterbury. The wall systems were designed as a retrofit solution for an existing frame building, but are equally applicable for use in new design. Design of the wall followed a performance-based retrofit strategy in which structural limit states appropriate to both the post-tensioned wall and the existing building were considered.

Dissipation for each of the four post-tensioned walls was provided via externally mounted devices, located in parallel to post-tensioned tendons for re-centring. This allowed the dissipation devices to be easily replaced or inspected following a major earthquake. Each wall was installed with viscous fluid dampers, tension-compression yielding steel dampers, a combination of both or no devices at all – thus relying on contact damping alone. The effectiveness of both velocity and displacement dependant dissipation are investigated for protection against far-field and velocity-pulse ground motion characteristics.

The experimental results validate the behaviour of ‘Advanced Flag-Shape’ rocking, dissipating solutions which have been recently proposed and numerically tested. Maximum displacements and material strains were well controlled and within acceptable bounds, and residual deformations were minimal due to the re-centring contribution from the post-tensioned tendons. Damage was confined to inelastic yielding (or fluid damping) of the external dampers.

Paper P39: [Read]

Qualification of Fibre-Optic Gyroscopes for Civil Engineering Applications

Roberto Franco-Anaya, Athol Carr and Ulrich Schreiber

This paper will outline the feasibility of the use of fibre-optic gyroscopes (FOGs) to measure rotation rates, rotations and displacements of civil engineering structures. FOGs are devices that utilise the Sagnac effect to detect mechanical rotations interferometrically from optical beams. They are compact, easy to install and, unlike conventional potentiometers, do not require a fixed reference frame to operate. In this research, shake table tests were performed on a four-storey one-fifth scale structure equipped with a fibre-optic gyroscope. Four different earthquake ground motions were used in the experimental study. During the seismic testing, the FOG was first attached to one of the first floor columns and then to the third floor of the model structure. Relative displacements at the first floor and rotations at the third floor were calculated from the measurements provided by the FOG. A very good agreement was observed between the measurements obtained with the FOG and those provided by a conventional linear potentiometer. The experimental results validated the accuracy of the measurements recorded by the FOG as well as the dynamic range of the instrument. The FOG was also installed on the Sky Tower in Auckland to evaluate the displacements of the structure. A series of measurements were carried out on the 54th and 60th floors during three days. A sample of the measurements for the 54th floor of the Sky Tower is presented and interpreted.

Paper P42: [Read]

In-plane stiffness of wooden floor

Anna Brignola, Stefano Podestà and Stefano Pampanin

TThe seismic response of existing un-reinforced masonry (URM) buildings is strongly dependent on the characteristics of wooden floors and in particular on their in-plane stiffness and on the quality of the connections between the floors and the URM elements. It is generally well-recognized that adequate in plane-stiffness and proper connections improves the three-dimensional response of the whole system and provides better distribution and transfer of forces to the lateral load resisting walls. Extensive damage observed during past earthquakes on URM buildings of different type have however highlighted serious shortcomings of typical retrofit interventions adopted in the past with the intention to stiffen the diaphragm. Recent numerical investigations have also confirmed that stiffening the diaphragm is not necessarily going to lead to an improved response, sometimes actually having detrimental effects on the response.

The evaluation of the in-plane stiffness of timber floors in their as-built and retrofitted configuration is still an open question and delicate issue, with design guidelines and previous research results providing incomplete, when not controversial, suggestions to the practitioner engineers involved in the assessment and/or retrofit of these types of structures.

In this contribution, a summary of the state-of-the-art related to the role of the in-plane stiffness of timber floors in the seismic response of un-reinforced masonry buildings is presented and critical discussed based on the limited available experimental and numerical evidences. A framework for a performance-based assessment and retrofit strategy, capable of accounting for the effects of flexible diaphragm on the response prior and after the retrofit intervention, is then proposed. By controlling the in-plane stiffness of the diaphragm, adopting a specific strengthening (or weakening) intervention, the displacements, accelerations and internal forces demand can be maintained within targeted levels, in order to protect undesired local mechanisms and aim for a more appropriate hierarchy of strength within the whole system.

Paper P49: [Read]

Liquefaction Remediation by Compaction Grouting

Rolando Orense

After the 1995 Kobe Earthquake, the use of compaction grouting technology gained prominence in Japan due to subsequent retrofitting works, i.e., raising and re-leveling of multi-story apartment buildings which sank or tilted due to soil liquefaction. Following the success of these reconstruction programs, the technology has been used to solve a number of geotechnical problems, including remediation of liquefiable soils. This paper reviews two case histories of compaction grouting application in Japan for liquefaction remediation – the first one under new runways in a busy airport, while the second is under an existing structure. From the experiences derived from these projects, the lessons learned from the grouting process and the merits of compaction grouting as a practical method of liquefaction remediation are discussed.

Paper P50: [Read]

Seismically Induced Landslide Mitigation Using Flexible Slope Stabilization and Protection Systems

Steve Farrand and Anthony Teen

Following earthquake events multiple soil slope failures are observed throughout the structurally fragile soil and rock in North Island Many of these slopes are located in close proximity to various assets including residential buildings and roads, resulting in damage to the structures. Limited mitigation solutions are available to stabilise both the global integrity and surficial slope-parallel instability, along with surficial erosion of the slope. High-tensile steel mesh, combined with an underlying three-dimensional geotextile, provides an effective, economical alternative with a greater design life than shotcrete and massive retaining structures. The flexible mesh is tensioned across the slope with a dimensioned grid pattern of soil/rock anchors that allows the system to be tailored to the site. Special concepts have been developed and are well proven for the dimensioning of the systems to consider superficial instabilities both slope parallel and in between the nails. The mesh promotes re-vegetation or greening of the slope for an aesthetically pleasing, natural looking finish. Numerous cases in New Zealand and internationally confirm that these measures are effective and practical for this application.

Paper P55: [Read]

Lessons from the 2007 Asia Pacific IDEERS Seismic Resistant Design Competition

Rohann da Silva, Dmytro Dizhur, Ronald Lumantarna, John O'Hagan and Quincy Ma

The Asia Pacific IDEERS competition (APEC IDEERS) is an international seismic resistant design competition with the aim of promoting earthquake engineering research to school and university students. The annual competition began in 2001 and is hosted by the National Center for Research on Earthquake Engineering (NCREE) in Taiwan. The competition involved designing and constructing the most efficient multi-storey model structures using the materials provided to resist artificial earthquakes as simulated on the NCREE shake table. In the 2007 competition, the rules for the model were substantially modified to allow for more creative designs and constraints were added to increase the level of difficulty. As a result, the prescribed structure was more complex and design strategies from previous years were no longer applicable

A team of four undergraduate students from the University of Auckland (UoA) represented New Zealand in the 2007 competition. The team competed against 35 other undergraduate teams from universities and polytechnics around Asia and Australia. The UoA team finished first in the competition, the highest placing achieved for a foreign team in the seven years of the competition. The final competition model made use of the conventional weak-beam strong column philosophy and incorporated numerous weight saving features. This paper details the UoA team’s design and testing process prior to the competition and documents the many lessons learnt from the trip.

Paper P61: [Read]

Free vibration tests of a scale model of the South Rangitikei Railway Bridge

Quincy Ma and M.H. Khan

The careful design and construction of a scale model of the South Rangitikei Railway Bridge (SRRB) are reported herein. The model was designed in accordance with stringent similitude requirements and a series of dynamic tests including shake table tests were conducted. This paper presents the preliminary results of the snap back tests only. It was not intended to exactly emulate to the actual SRRB but merely to use the SRRB as a realistic existing example, to investigate the general dynamic behaviour of a rocking structure. Despite this, the snap back tests revealed that the scale model matched previously published natural period of the SRRB prior to pier uplift. Furthermore, experimental results suggest the natural rocking period of the prototype SRRB could vary between 1.73 s and 4.33 s depending on the amplitude of lateral displacement. This reaffirms previous research which hinted the natural rocking period of a rocking structure is amplitude dependent and is a non stationary value.

Paper P62: [Read]

Simple Design for Yielding Structures Subject to Torsion

Eu Ving Au, Gregory MacRae, Didier Pettinga, Bruce Deam and Vinod Sadashiva

Building torsion resulting from building plan irregularity influences the demands on critical elements of a structure during earthquake shaking. Since inelastic torsion is not accounted for directly with the plane frame analysis tools commonly used in design, methods to estimate the likely variation in response due to torsion are required.

A significant body of literature exists related to the torsional response of structures during earthquakes. However, much of it is in a form which is complex, difficult to understand, or unsuitable for design. Perhaps the most simple and easily applied method for consideration of torsion in yielding structures was developed by Paulay in the 1990’s. However, this concept has often been criticized because it does not consider the inertial mass effect or out-of-plane walls, and his techniques are not appropriate for structures undergoing only moderate inelasticity.

This paper extends the concept of Paulay to consider the inertial mass effect as part of the dynamic response of classical single story structures which may or may not have out-of-plane walls. In this method, impulse ground motions are used to obtain general and unique solutions for structures which are appropriate for all levels of inelasticity.

A relationship between the increase in demand considering torsion for different earthquake records and different intensities is then statistically developed based on the general solution. It is shown that the torsional response due to impulse is similar to the average torsional response due to earthquake.

This work is easily understandable, applicable to all levels of inelasticity, and it provides a statistical degree of confidence that the inelastic response is not greater than a specified level. It also forms the basis for a design methodology.

Axial Shortening Effects of Steel Columns in Frames

Christopher Urmson, Gregory MacRae, Warren Walpole, Peter Moss, Karissa Hyde and Charles Clifton

Steel members subject to axial compression and inelastic cyclic displacements, such as may occur during earthquake excitation, exhibit axial shortening due to material inelastic deformation irrespective of the occurrence of buckling. This column axial shortening can cause undesirable effects in the building, especially if it occurs to a different extent in different columns of a seismic-resisting system. This paper summarizes experimental and finite element studies to quantify the axial shortening of columns with known axial forces pushed to inelastic cyclic displacements. A flexural hinge model for a frame analysis program is developed and calibrated against that from experimental and analytical studies. Then, to quantify the effect of axial shortening on realistic moment and eccentrically-braced frames during earthquakes, inelastic dynamic time history analyses were conducted. While axial shortening of more than to 7% of the column length was obtained during experimental testing, the axial shortening was always less than 1% of the column interstorey height in the steel frames studied.

Steel members subject to constant axial compression and inelastic cyclic displacements exhibit axial shortening even before buckling occurs. Buckling exacerbates this column axial shortening. Such shortening, which may occur during an earthquake, can cause undesirable effects in the building, especially if it occurs to a different extent in different columns of a seismic-resisting system.

This paper describes experimental work, in which axial shortening decreases the length of some columns by more than 7%. Analytical studies using the finite element analysis program ABAQUS were conducted which confirm the experimental observations. A simple equation was developed to estimate the axial shortening as a function of the cumulative inelastic column rotation. This equation is independent of the assumed plastic hinge length of the column and it matches experimental and analytical results well.

In order to evaluate the likely amount of axial shortening on realistic frames during earthquake excitation, a moment frame and an eccentrically braced frame designed according to the NZ code, but which expect column yielding, were analyzed. It was found that the amount of shortening was generally less than 5mm in the most critical columns 2 MRF frames and 2 EBF frames analyses with the Los Angeles records scaled to Christchurch and Wellington design levels.

Tsunami Effects on Structures

Michael Hewson, Roger Nokes and Gregory MacRae

A significant body of literature has been developed in the last few years to enable the maximum likely tsunami size at a particular location to be estimated within a certain time period. Also, recommendations for structural design considering tsunami have recently been released. However, these structural design considerations do not consider some of the significant load effects to which a structure may be subject.

This paper presents design equations which may be relevant for New Zealand. Also, the loading effect on a structure which may be open at the side facing the sea, but closed along either side and at the back is described. In this case, the impact of the sea wave on the back wall of the structure may be significantly greater than that on a rectangular structure because the side walls may cause funnelling of the incoming wave. In some cases the back of the structure may be partially open due to the presence of windows or doors which may be smashed as a result of the wave. These too may affect the forces on the back wall of the structure.

Forces on the back wall of a structure open at the front were investigated experimentally. Walls and the back wall were made of clear perspex and the water was coloured, so that when water behind a dam was suddenly released, the level of water at the structure at any interval of time could be captured by a high speed camera. Different initial dam heights, approach roughness, and sizes of opening at the back of the structure were considered. When the opening between the side walls and the back wall was high, it was as though the water was hitting a rectangular wall with no side walls. In addition to the initial impact of the water causing force on the back wall, splash and backwash effects were observed.

It was found that within the limitations of the study, the size of opening did not have a significant effect on the height of water causing pressure on the back wall.

Data Processing of observed damage and reconstruction costs after 2002 Molise Earthquake in Italy

Sonia Giovinazzi and Stefano Podestà

On the 31st October 2002 the Molise Region in Italy was struck by a relatively moderate magnitude earthquake (Mw=5.7). Nonetheless, the earthquake caused a severe level of damage in several villages and towns and the death of 27 children, due to the collapse of a school.

During the emergency and recovery phase, post-earthquake building safety evaluations were performed for all the damaged buildings. The data collected by visual inspection provide a meaningful source of information about the seismic vulnerability of the buildings in that area and the damage undertaken following 31st October 2002 earthquake.

During the reconstruction phase, specific criteria ruled the allocation of funds for the repair/reconstruction of both public and residential buildings. The preliminary design-drawings and the assessment of the reconstruction costs have been therefore produced and provided to the government authorities for all the buildings repaired/reconstructed using public funds.

Reconstruction-costs data, collected during the reconstruction process, and damage and vulnerability data, surveyed during the post-emergency phase, have been processed and used in this paper for comparison, calibration and integration of models currently implemented, within scenario-based earthquake impact assessment approaches, for the vulnerability assessment, damage estimation, cost evaluation and assessment of the needed resources for the reconstruction.

Assessing the resilence of roading organisations to earthquakes

Sonia Giovinazzi, Andre Dantas, Frederico Ferreira and Erica Seville

Recent catastrophic seismic events have demonstrated that the functionality of road transport networks is vital in saving lives, reducing costs and enhancing the resilience of the community to recover from the earthquake event. This is recognised and highlighted by the New Zealand’s Civil Defence Emergency Management Act (2002) enforcing that transport networks need to be able to function to the fullest possible extent during and after an emergency event.

In the framework of a wider collaborative research program between University of Canterbury and Transit NZ, a specific research has been promoted in order to understand the strengths and weaknesses of Transit NZ’s Readiness, Response, Recovery and Reconstruction capabilities in the event of an earthquake.

This paper presents a first insight of the research method that has been widely developed to assess the Resilience of roading organisations to different kind of crisis events in New Zealand. The specific implementation of the proposed method to earthquake events will be performed with reference to two different desktop study cases, namely “Exercise Capital Quake ‘06” and “Exercise Pandora ‘07”, simulating, respectively, a 7.6 Richter Magnitude earthquake on the Wellington fault line and an 8.2 Richter Magnitude earthquake along the Main Alpine Fault.

Keynote Address Session 1 Session 2 Session 3 Session 4 Session 5 Session 6 Poster Session Session 8