Poster Poster Presentations
NZS1170.5:2004 Site Subsoil Classification of Lower Hutt
D. Boon, N.D. Perrin, G.D. Dellow, R. Van Dissen & B. Lukovic
ABSTRACT: A 3D engineering geological model of the Quaternary sediments of the Lower Hutt sedimentary basin was constructed using topographic, geological, geophysical, and geotechnical data. The geological and geotechnical data includes 846 borehole records. The shape and spatial distribution of basin units was mapped in 3-dimensions (3D) with seven units identified based on variations in strength and lithology. Shear-wave velocities measured using a range of geophysical techniques were obtained and compared with the 3D model. Engineering geological boundaries in the 3D model corresponded well with observed changes in shear-wave velocity. This allowed a range of shear-wave velocities to be assigned to each geological unit. The 3D engineering geology model was then used to calculate a shear-wave velocity profile on a 25 m2 grid to produce a site-period model for Lower Hutt. This model is used to derive a site subsoil class map in accordance with the preferred methods described in NZS 1170.5:2004. The site subsoil class C/D boundary was determined using the 0.6s contour from the site period model. The minimum and maximum shear-wave velocity values for each unit were used to determine the uncertainty in the location of the C/D boundary. Subsoil class E sites were determined using standard penetration test results and surface geology.
Earthquake Information and Household Preparedness: Results of Interviews with Residents in Timaru, Wanganui and Napier
J.S. Becker, D.M. Johnston, D. Paton & K. Ronan
ABSTRACT: Forty-eight interviews were undertaken with residents in Timaru, Wanganui and Napier in 2008 to explore how people understand and use information about earthquake hazards and preparedness. Three main sources of information were identified during the interviews: passive information (e.g. brochures, TV); interactive information (e.g. community activities; school activities; workplace activities); and experiential information (e.g. experiencing a hazardous event, responding to an event, working in an organisation that deals with hazards). People tended to contextualise hazard and preparedness information around any prevailing experiences and beliefs they had. For example, if they thought safety was an important part of life in general, they would interpret hazard and preparedness information in that context. A number of core beliefs were identified as crucial for helping people consider that preparing is important and motivating actual adjustment adoption. Society also has an influence on how people interpret information and form intentions to prepare. People are often influenced by the opinions of others, and as preparing for disasters is not seen as a societal norm, this can cause people not to prepare. Feeling a responsibility for others (e.g. children) appears to be a big driver of preparedness. Other societal factors such as trust, leadership and sense of community also influence interpretation, dissemination and use of hazards and preparedness information.
The 1948 (Ms 8.2) Lady Caycay Earthquake and Tsunami and its Possible Socio-Economic Impact to Western Visayan Communities in the Philippines
M.L.P. Bautista, B.C. Bautista, I.C. Narag, R.A. Atando & E.P. Relota
ABSTRACT: The Magnitude 8.2 Lady Caycay Earthquake and Tsunami of January 25, 1948 in west-central Philippines is the second biggest earthquake in the 500-year old Philippines earthquake history. According to archives and catalog, 55 Spanish-era churches in Panay Island were damaged, 17 of which totally collapsed. Two persons were said to have drowned along Iloilo Strait because of tsunami. Seismic instrumentation then was also not as well-developed as compared to present. At that time when the earthquake occurred, World War II just ended and most communities were just starting to recover from the disastrous effects of the war. Reports were quite sparse and oftentimes, damages due to war and earthquake were difficult to differentiate. Just using existing reports, there is a incompatibility between intensity distribution and epicenter location and magnitude. Recently, new archival documents have been unearthed that can be used to re-evaluate intensities and consequently re-estimate magnitude. If data is found sufficient, attempts will be done to re-estimate the earthquake's parameters. Then, ground shaking hazard will be modeled and population centers, key economic points and culturally important structures will be plotted to determine possible socio-economic impacts.
Considering Cumulative Seismic Experience and Ageing Effects in Liquefaction Analysis
Philip J. Clayton, René Sonnenberg & Jitendra K. Bothara
ABSTRACT: The comparatively greater liquefaction resistance of older granular soils has been noted by many researchers. One mechanism by which this liquefaction resistance may be gained is through repeated seismic events causing densification.
Analytical methods are used to predict the changes in soil density under repeated seismic events of an initially loose deposit. Indicative changes in liquefaction resistance with repeated exposure to seismic events are provided for deposits in low and high seismicity areas within New Zealand. These results may be of value in the execution of liquefaction risk assessments.
Response of Out-Of-Plumb Structures in Earthquake
T. Masuno, G.A. MacRae, V.K. Sadashiva & A. Wada
ABSTRACT: No building is built perfectly plumb. The out-of-plumb may not just result from construction influences, but it may also occur as a result of permanent displacements after an earthquake. While there are methods to account for out-of-plumb for non-seismic design, such methods do not exist for seismic design, as the effect of different levels of out-of-plumb has not been quantified. It is desirable to know how a new building with a specified out-of-plumb is likely to behave in a earthquake, and how one which is out-of-plumb as a result of a previous earthquake may perform in an aftershock. In this research, the effect of building out-of-plumb is quantified. Simple models of structures with different amounts of out-of-plumb are made. These are designed with different levels of ductility and with different distributions of strength/st
Design of Post-Installed Anchors for Seismic Actions
Gilbert Balbuena, J. Gramaxo & J. Kunz
ABSTRACT: The economic and social costs associated with the failure or interruption of certain services and equipments such as water, energy or telecommunication supply systems and traffic lines are of comparable magnitude to the costs associated with structural failures.
As post-installed anchors are often used to fix these mentioned types of equipment, their adequate design is of crucial importance to guarantee safety and minimize costs associated with seismic events. This paper shows the working principles of different types of anchors, discusses their behaviour under seismic loads, and classifies them according to their suitability for the typical situations occurring in earthquakes such as large cracks in the concrete or alternating directions of the load.
The primary globally established design concept for anchors under seismic loads can be found in the US codes. This paper will describe the principles of the concept. Specific tests qualify anchors for seismic loads. ACI 318 gives a design method for qualified anchors.
The final section of this paper will summarize examples of good detailing of anchorage applications leading to a cost-efficient enhancement of the overall safety of buildings and infrastructures in seismic events.
A Preliminary Analysis on the Response of an Instrumented Building during the 2010 Darfield Earthquake - Significant Effects of Soil-Structure Interaction and Nonlinear Response
John X. Zhao & S.R. Uma
ABSTRACT: We have carried out a preliminary analysis of the strong-motion records obtained from a building array in the Physics building of the Canterbury University, Christchurch, during the 2010 Darfield, New Zealand, earthquake. The reinforced concrete building was designed and built during the 1960’s and has 8 storeys with a half-floor height basement. It is on a deep soil site and is about 20 km away from the nearest part of the fault that produced the MW 7.1 earthquake. The building appeared to have experienced foundation rocking and rotation with respect to the free-field, a result of soilstructure interaction. The building-foundation-soil system also appeared to have developed significant nonlinear response, resulting in a decrease in the stiffness by a factor of 2.
Performance of Concrete Slabs with Different Reinforcing
A. Khanlou, A. Scott, M. Holden, T.Z. Yeow, M. Saleh, G.A. MacRae, S. Hicks & G.C. Clifton
ABSTRACT: This paper describes a test programme at the University of Canterbury to evaluate the performance of elements of concrete slab reinforced in different ways. The reinforcing includes steel fibre, brittle mesh, ductile mesh and two grades of reinforcing bars. The percentage of reinforcing varies. Shear and flexural tests are conducted. The work described is in the initial stages of testing, so this paper concentrates on the methodology for selecting the test types and parameters.
Graphical Interface Toolbox for Modal Analysis
S. Beskhyroun
ABSTRACT: This paper introduces a new toolbox of graphical user interface (GUI) software for modal parameters (eigenfrequencies, damping ratios and mode shapes) identification. The toolbox is a MATLAB software which implements several state-of-the-art techniques for modal analysis. Three frequency domain based techniques: the peak picking (PP) method, the frequency domain decomposition (FDD) method and the enhanced frequency domain decomposition (EFDD) method as well as two time domain based techniques: the Eigen realization algorithm (ERA) combined with the natural excitation technique (NExT) and stochastic subspace identification (SSI) method are adopted in the toolbox. Most of these techniques can be used for experimental (input-output data), operational (output-only data) and combined modal analysis of structures. The program inputs are raw measurement data and if available, the excitation force. The toolbox offers extensive functionalities for the visualization and processing of the data, the determination and visualization of the structure’s modal parameters and comparison of the identified modal parameters. The program is compact, efficient and user friendly, which makes it very intuitive and easy to handle. This paper contains a detailed description of the various modal analysis capabilities of the toolbox, and also shows a sample application which uses the toolbox to extract modal parameters from experimental data from a 3-storey building model.
Residual Stress Effects on the Seismic Performance of Low-Rise Steel Frames
C. Lu & G.A. MacRae
ABSTRACT: In non-seismic plastic design of steel structures, initial residual stresses in members affect the frame tangent stiffness and the lateral strength. This effect can be simply considered by using the Extended Direct Analysis (EDA) approach as part of design process. However, for the design of frames subject to earthquake, the effect of residual stresses is generally ignored, except in the final column design check. This paper looks at the effect of residual stresses on the seismic performance. Pushover and push-pull analyses were performed on a single cantilever column with nonlinear beam-column fibre sections under moderate compressive axial load. In addition, incremental dynamic analyses were performed with 20 SAC earthquake records to consider the dynamic behaviour. The results show that while the initial residual stresses do have some effect on structural behaviour at the first yielding, the post-yielding behaviour is not affected.
Development of Pounding Model for Adjacent Structures in Earthquakes
S. Khatiwada, N. Chouw & J.W. Butterworth
ABSTRACT: Building pounding, a frequently recurrent problem in strong earthquakes, occurs when there is inadequate separation between adjacent structures. Several models have been proposed for the calculation of the resultant impact force, and its effect on the participating structures. This study analyzes two impact models and proposes a new model. The proposed viscous elastoplastic impact element considers the effect of yielding at the contact location of the structures and on the global structural response. A sample numerical investigation is presented for the seismic pounding between two adjacent buildings due to the 1940 North South El-Centro ground motions. The results show that the global response of the participating structures is significantly altered due to the yielding at the contact area.
Experimental Study of Earthquake Sequence Effect on Structures
K.M. Twigden, C.A. Oyarzo & N. Chouw
ABSTRACT: It is common that structures experience sequences of earthquakes. A sequence can consist of a main shock followed by a series of aftershocks which may have a magnitude high enough to induce damage in a structure. Another situation is the history of earthquakes that a structure may experience throughout its lifetime. This study focuses on the effect of a sequence of earthquakes on a structure, especially on the cumulative damage. For this purpose, SDOF scaled models were tested using a shake table. Two specimens made of RC and two specimens of coir fibre RC were considered. Two different sequences of real seismic records are investigated: the Chilean earthquakes representing a series of major earthquakes a structure may experience throughout its lifetime and the Kobe main shock followed by three aftershocks to simulate the effect of aftershocks. Damage assessment is undertaken using as indicators the change in the fundamental frequency obtained from an impact test and the energy dissipated throughout each earthquake sequence by evaluating the accumulated area of hysteresis cycles.
Consequence of Experimental Modelling for Seismic Response of a Multi-Storey Structure
Y. Chen, X. Qin, L. Yan & N. Chouw
ABSTRACT: An equivalent single-degree-of-freedom (SDOF) model has been applied in the study of multi-storey structures in earthquakes for several decades. In this experimental research, the consequence of SDOF and multi-degree-of-freedom (MDOF) modelling for seismic response of a multi-storey building was investigated. The SDOF model was generated by considering only the fundamental mode of the structure and the MDOF model was a simplification of a prototype. Both models were scaled by Buckingham π theorem and excited by different ground motions simulated based on Japanese design spectra. After normalising the obtained results, they are displayed in Fourier domain for discussion. It was found that the SDOF model was able to show the effect of interrelation between structure and ground motion, however, it would underestimate the effect of higher frequency components of the ground excitation.
Modelling of In-Structure Damping: A Review of the State-Of-The-Art
Arun M. Puthanpurayil, Rajesh P. Dhakal & Athol J. Carr
ABSTRACT: System parameters in the mathematical model of a vibrating structure include mass, damping and stiffness; out of which mass and stiffness could defined as a function of the system geometry, whereas damping involves more an observed phenomenon. A consolidated review of the existing current damping models is presented. Earlier studies illustrate considerable issues associated with the use of the conventional Rayleigh model of damping. In this paper conceptual evaluations of the existing formulations are presented and the issues associated with the use or misuses of the models are documented. Despite the inherent complex uncertainties involved, scope for a more in-depth research is identified. A study on the dynamic response of a cantilever beam to a constant force is presented to illustrate the effect of using viscous and non-viscous damping models. Different damping models exhibit different peak responses highlighting the fact that viscous damping might not represent the realistic state of the structure during a dynamic excitation.
Violating Capacity Design in Structures with Viscous Damping and Hysteretic Damping
C.C. Labise, G.W. Rodgers, G.A. MacRae & J.G. Chase
ABSTRACT: Capacity design, while protecting a structure against undesirable energy dissipations, has major implications on member sizes and overall cost. Furthermore, in some situations where protected elements possess some inelastic deformation capacity, it may be unwarranted. One of these situations is when the forces applied to the protected elements result from viscous dampers. This is because when viscous forces cause yielding in an element, the element deforms, so no deformation in the viscous damper is required. If no deformation is requires, the velocity is zero, so there is no force. This implies that very little inelastic yielding is likely to occur in protected elements.
In order to investigate whether or not this is so, a single storey structure was designed and fitted with braces to reduce its response. Both hysteretic and viscous braces were used to obtain the same peak displacement response. The column strength was decreased by a fixed percentage and inelastic dynamic time history analysis was conducted. The amount of energy dissipated in the columns was then compared to determine whether hysteretic braces or viscous braces caused more column yielding so that appropriate over strength values could be developed for different braces types. It was found that the amount of energy absorbed by the column depends on the period but also on the brace design ductility. However, irrespective of the period or design ductility, the column hysteretic energy dissipated by a viscous brace was lower than that dissipated by a hysteretic brace. It follows that column yielding may be significantly less critical for viscous, rather than for hysteresis, braces structures.
A Damage Mitigating Hold-Down Connector for Earthquake Resistant Timber Shear Walls
W.Y. Loo, P.J.H. Quenneville & N. Chouw
ABSTRACT: The slip-friction connector is a type of semi-rigid joint. When implemented in timber shear walls in lieu of standard hold-downs, the slip-friction connector holds the promise of being able to protect the walls from permanent damage during earthquake loading. Slip-friction connectors, originally developed for use in steel framing, rely on the mobilisation of friction across steel plates to resist loading up to a pre-specified threshold. When this threshold is exceeded, sliding occurs between the plates, and the wall is allowed to displace vertically. In this way the lateral forces on the wall are capped to a level in which sheathing, framing, and nail connections are protected from damage. A slip-friction connector developed specifically for use with timber shear walls is proposed, some aspects of its design discussed, and results from numerical modelling presented. It is found that the connector can behave in a highly elasto-plastic manner, with an excellent ability to attain a predefined target slip force. The results from modelling indicate that it will behave fairly robustly when under external force. Experimental testing is in preparation to confirm the proposed design concept.
Analysis of Asymmetric Reinforced Concrete Frame
T. Mahdi & V.Soltan Gharaie
ABSTRACT: In this paper, the seismic behaviour of three concrete intermediate moment-resisting space frames with unsymmetrical plan in five, seven and ten stories are evaluated. In each of these three cases, plan configurations of the structure contain reentrant corners. Nonlinear static and linear dynamic procedures have been used to analyse these structures. To measure the accuracy of these two methods, the non-linear dynamic analysis has been used. Although the differences between the results of these two methods with the nonlinear dynamic procedure are quite wide, the linear dynamic analysis has shown slightly better results than nonlinear static analysis.
A Mechanics Based Approach to Quantify Diaphragm Flexibility Effects
V.K. Sadashiva, G.A. MacRae & B.L. Deam
ABSTRACT: A common assumption made while analysing a building structure under lateral loading, which is not subject to torsion, is that in-plane deformations along the diaphragm length are constant. While this rigid diaphragm assumption may reduce the computational effort involved in analysing a structure, the classifications included in seismic codes of whether or not a diaphragm is flexible is questionable. Past earthquakes and studies have shown that ignoring diaphragm flexibility effects can result in both uneconomical designs and unsafe structures during an earthquake. This paper describes analysis methods to quantify the change in structural response due to different amounts of diaphragm flexibility. It is shown that one-storey structures are the most affected due to diaphragm flexibility. A mechanics based approach is shown to be in good agreement with the results from time-history analyses. A simple equation is proposed that can be used to estimate the fundamental natural period of one-storey structures with flexible diaphragms.
Development of Typical NZ Ceiling System Seismic Fragilities
G. Paganotti, G.A. MacRae & R.P. Dhakal
ABSTRACT: Seismic damage to ceilings can cause significant downtime and economic loss in addition to life safety risk. In order to understand this risk and develop mitigation strategies a small project on non-structural damage was recently funded by the FRST Natural Hazards Platform at the University of Canterbury. This particular project concentrates on two ceiling systems which are commonly used, or applicable, in NZ. This paper addresses the development of fragility functions for the ceiling systems based on component fragilities which are obtained from experimental testing of Armstrong(TM) ceiling components. The ceiling system fragility is obtained through Monte-Carlo analysis using in-plane finite element analysis. Demand parameters include absolute acceleration and displacement. The effect of rigid and flexible sprinklers is also investigated. The acceleration resistance is found to be dependent on the ceiling size. This information is being used directly to estimate both ceiling damage and its contribution to overall building loss.
Wall-Diaphragm Connection Assessment Guidelines for URM Buildings
A.R. Abdul, P.J.H. Quenneville, N.M. Sa’don & J.M. Ingham
ABSTRACT: The connections between walls and diaphragm in unreinforced masonry (URM) buildings typically consist of two major parts. The first part is the wall anchorages and the second part is the diaphragm connections. From the NZNSEE (1995) and FEMA (2006) guidelines, the connection strength values given by both guidelines are apparently related only with the possible failures of the masonry wall anchorages, and no procedures are currently available to identify the strength values related to failure of the timber bolted connections. This latter failure mode is important to consider as the minimum strength value that will govern the wall-diaphragm connection capacity can be acquired from the diaphragm connections. To counter this limitation, this study recommends a set of design equations to assess the strength of the timber bolted connections. By using these equations, in addition to the default connection strength values provided by the guidelines, the expected strength level of wall-diaphragm connections can be accurately assessed.
Damage Mitigation Strategies of ‘Non-Structural’ Infill Walls: Concept and Numerical-Experimental Validation Program
A.S. Tasligedik, S. Pampanin & A. Palermo
ABSTRACT: In the past design codes, infill panels/walls within frame buildings have been considered as non-structural elements and thus have been typically neglected in the design process. However, the observations made after major earthquakes even in recent times (e.g. Duzce 1999, L’Aquila 2009, Darfield 2010) have shown that although infill walls are considered as non-structural elements, they can interact with the structural system during seismic actions and modify the behaviour of the structure significantly. More recent code design provisions (i.e.,NZS4230, Eurocode 8, Fema 273) do now recognize the complexity of such interactions and require either a) consider these effects of frame-infill interaction during the design and modelling phase or b) assure no or low-interaction of the two systems with proper detailing and arrangements in the construction phase. However, considering the interaction in the design stage may not be a practical approach due to the complexity itself and in most cases does not solve the actual problem of brittle behaviour and thus damage to the infills. Therefore, the purpose of this particular research is to develop technological solutions and design guidelines for the control or prevention of damage to infill walls for either newly designed or existing buildings. For that purpose, an extensive experimental and numerical research programme has been planned. The concept, background on infill practice in New Zealand and the research programme will be briefly described in this paper.
Optimization for Performance-Based Seismic Retrofit of Existing Steel Moment Frames using Connection Upgrade
B.K. Oh, S.W. Choi, E.S. Lee & H.S. Park
ABSTRACT: The seismic retrofit research for the connection vulnerability of the steel moment frames constructed before the 1994 Northridge earthquake has been conducted. The seismic retrofit schemes such as connection upgrade, damper, and buckling restrained braces have been developed for the brittle connection of the steel moment frames and applied to the existing buildings. Although the retrofitted steel moment frames satisfy the seismic performances, it cannot be said that these are economically reasonable and efficient seismic retrofit schemes because of the absence of obvious retrofit criteria. Therefore, this paper proposed the performance-based optimal seismic retrofit of the existing steel moment resisting frames using the genetic algorithm based on retrofit costs. Among the seismic retrofit schemes, the connection upgrade which changes the brittle behaviour of the existing connection to the ductile behaviour is selected in this paper. While satisfying the specific performance objective according to FEMA 356, the optimal seismic retrofit technique find the minimum numbers of the connection retrofit and their optimal locations using the optimization method is proposed. The nonlinear static analysis is performed based on the procedure represented in FEMA 356. The optimal seismic retrofit scheme of an example 3story-4bay steel moment frame is proposed using the proposed technique and studied the validity of that scheme.
Behaviour of Coconut Fibre and Rope Reinforced Concrete Members with Debonding Length
M. Ali, B. Nolot & N. Chouw
ABSTRACT: To investigate the feasibility of coconut fibre and rope-reinforced concrete (CFRRC), the effect of bonding between rope and concrete has been considered in this study. The behaviour of five CFRRC column specimens with various rope debonding length configurations under cyclic loading are investigated. For each column, one central coconut fibre rope with a diameter of 4 cm is cast. A polyethylene sheet with multiple wrapping is used along the specific length of rope for eliminating the bond between rope and concrete. Coconut fibre-reinforced concrete is prepared with 5 cm long fibres and 1 % content by mass of concrete material. It is observed that the column with alternate debonding and bonding length has a better behaviour. This study is one of the research steps in finding a proper design of seismic resistant and low cost structure using CFRRC. It is not yet successful, but a workable invention is expected in near future.
A Simple Approach to Real-Time Fault Detection and Diagnosis in Base-Isolation Systems
Mostafa Nayyerloo, Leonardo Acho, José Rodellar, J.Geoffrey Chase & Qi Chen
ABSTRACT: In recent years, base-isolation has become an increasingly applied structural design technique in highly seismic areas. The state-of-the-art practice is to use active or passive magneto-rheological (MR) dampers to limit the base displacement. The crucial effect of likely faults in the base-isolation system on the top superstructure requires that the resulting nonlinear hysteretic system to be monitored in real-time for possible changes in the two most important structural parameters: stiffness and damping.
This paper develops a simple fault detection and diagnosis technique based on comparing the internal dynamics of the base-isolation system with those of a healthy baseline modelto detect faults. Three different cases of stiffness, damping, and combined stiffness and damping faults are studied, in silico, on a realistic base-isolated structure subjected to the Loma Prieta earthquake with a passive MR damper. The simulation results show that the proposed fault detection and diagnosis algorithm is well capable of detecting the existence, determining the type, and quantifying the severity of faults in the system in real-time as the faults occur.
Spectral Analysis and Assessment of a Net-Zero Base-Shear Energy Dissipation Approach for Seismic Energy Mitigation
T. Roland, G.W. Rodgers, J.G. Chase & G.A. MacRae
ABSTRACT: Combining passive and semi-active damping has unique benefits that cannot be achieved through other damping techniques alone. Passive high force to volume (HF2V) lead dampers offer high energy dissipation, but have no ability to customise overall response. Semi-active resetable devices offer adaptability and custom hysteresis loops that can reduce both displacement and base shear, but are Ltd in overall energy dissipation capability. Together, these devices offer a new concept to maximised displacement response reduction, without increasing base shear – a net zero base-shear concept. This paper combines HF2V devices, with design force levels up to 10% of weight, and a resettable device with nominal stiffness of 100% of column stiffness. A spectral analysis is run to size the HF2V device iteratively at each period to achieve maximum reductions in displacement without increasing median base shear.
The results show up to 50% reduction in base shear for the low suite, and up to a 40% reduction for the medium and high suites. Towards longer periods, base shear reduction factors tend to 1.0, indicating net-zero base-shear. This situation is never reached below a structural period of 2.5s, where median base-shear reduction factors are less than 1.0, indicating a reduction in base-shear as well as displacement and structural force. Overall, these results are independent of HF2V device scaling, as analyses using ground motion specific mean velocities and 1m/s mean velocity for sizing the device capacity yield closely similar results. Comparisons are also drawn between the performance of the combined damping system to that of the passive and semi-active systems alone.
Determination of Very Small Strain Shear Modulus of Auckland Residual Soils using Bender Elements
A. Ibrahim, R.P. Orense & M.J. Pender
ABSTRACT: Bender elements test is a convenient technique and frequently employed for shear wave velocity measurement at small strain due to its simplicity and reliability. This paper presents the details of the apparatus setup, preparation and installation of bender elements and soil specimen preparation procedures adopted throughout the experimental processes. Preliminary experimental results on fully saturated undisturbed Auckland residual soil demonstrated consistent shear wave velocities at different frequencies and good quality of triggered and received signals. Furthermore, small strain shear modulus (Gmax) of undisturbed Auckland residual clays measured using bender elements satisfactorily agreed with the Gmax obtained from monotonic small strain triaxial tests.
Field Dynamic Testing of a Large Scale Bridge using Shakers
S.E. Manson, O.H. Woodhouse, B. Li, N. Chouw & J.W. Butterworth
ABSTRACT: Pounding and unseating have been observed as common causes of failure in multi-span bridges in the past major earthquakes. These modes of failure occur because traditional expansion joints cannot accommodate large relative displacements that occur between adjacent bridge spans under earthquake loading. Most of current design practice does not account for the effect of soil-structure interaction (SSI) on the relative response of adjacent spans. The purpose of this research was to create a scale model of a bridge span and perform a field test to incorporate SSI effect. The results will be used for developing modular expansion joints (MEJs). This paper compares the response of the model with an assumed fixed base and with foundation on beach sand under soft, medium and hard soil ground excitations. Spectral analysis of surface waves was performed to obtain the soil stiffness at the test site. It was found that the testing was unable to excite the model in such a way that SSI would occur. Further work needs to be done to refine the model so that SSI will occur.
The “Rapid Earthquake Damage Assessment System (REDAS)” Software
M.L.P. Bautista, B.C. Bautista, I.C. Narag, A.S. Daag, M.L.P. Melosantos, A.G. Lanuza, K. Papiona, M.C. Enriquez, J.C. Salcedo, J.S. Perez, J.T. Punongbayan, E.L. Banganan, R.N. Grutas, E.A.B. Olavere, V.H Hernandez, R.B. Tiglao, M. Figueroa, R.U. Solidum & R.S. Punongbayan
ABSTRACT: The Philippine Institute of Volcanology and Seismology (PHIVOLCS) of the Department of Science and Technology (DOST) developed a software called “Rapid Earthquake Damage Assessment System” (REDAS). The software aims to provide quick and near real-time simulated earthquake hazard map information as a decision support tool for disaster managers during potentially damaging earthquakes. The second aim targets policy makers and local chief exceutives to use it as a tool for mainstreaming disaster risk reduction into the local development planning process.
The software can model four seismic hazards (ground shaking, liquefaction, landslides and tsunami) and since it hosts exposure data, risk elements can also be plotted. Inputs required to produce hazard maps are basic earthquake and fault parameters. To make it multi-hazard in approach, static hazard maps such as volcanic and hydrometeorological are built-in in the software. Its potential to be a risk assessment tool is being enhanced by improving the exposure database, inclusion of a building inventory module, incorporation of vulnerability curves and enhancing its modeling capability to address other natural hazards. Training participants are taught how to build their own risk database using GPS and maps from Google Earth. The software is being continuously improved through feedbacks and inputs from users to make it more attuned to their needs. To date, a total of 14 Philippine provinces, 96 towns and various government institutions had been trained and PHIVOLCS-DOST is determined to disseminate widely the use of this software to local government units.
Development of an Inexpensive and User-Friendly System for Earthquake Exposure Database Building for the Philippines
B.C. Bautista, M.L.P. Bautista, I.C. Narag, A.G. Lanuza, J.B. Deocampo, R.A. Atando, K. Papiona, R.U. Solidum, Trevor Allen, Matthew Jakab, Krishna Nadimpalli, Mark Edwards & Mark Leonard
ABSTRACT: A comprehensive earthquake impact assessment requires an exposure database with appropriate attributes and such detailed database will require years to develop. To hasten the database development, the strategy is to involve as many stakeholders/organizations as possible and equip them with a standardized tool for data collection and management. The most ideal organizations to tap would be the local government units (LGUs) since they have better knowledge of their respective area of responsibilities and have a bigger stake on the use of the database. Such tool is being developed by PHIVOLCS-DOST and Geoscience Australia. Since there are about 1,495 towns and cities in the country with varying financial capacities, this tool should involve the use of affordable hardware and software. It should work on ordinary hardware that can easily be acquired by these LGUs such as an ordinary light laptop or a netbook. The laptop can be connected to a GPS and a digital camera with tethered-shooting features to capture images of structures and their location. The system uses an open source database system such as MySQL and for encoding the building attributes and parameters, a user-friendly GUI with a simplified drop-down menu which contains building classification schema generated from a series of consultations with local engineers, is developed for this system. The resulting national database is integrated by PHIVOLCS-DOST and forms part of another software called Rapid Earthquake Damage Assessment System (REDAS), a hazard simulation tool that is also made available freely to partner local government units.
Adjacent Building Hazard – How Poorly Performing Buildings Endanger Neighbouring Buildings’ Occupants
G.L. Cole, R.P. Dhakal & D.K. Bull
ABSTRACT: The recent Darfield earthquake caused failure of numerous parapets and unreinforced masonry (URM) buildings throughout the Canterbury region. While such collapses continue to be extensively studied, the effects these buildings have on their immediate surroundings are commonly overlooked. The threat local and global building failures pose to public streets and neighbouring buildings are presented in this paper. Examples from the Darfield earthquake are presented to identify a new category of hazard termed ‘adjacent building hazard’. In many instances, the safety of a building’s occupants was found to be primarily endangered by adjacent building hazards. Buildings likely to be at risk from neighbouring parapets or URM buildings are known to exist throughout New Zealand and can be easily identified. The authors argue that the severe consequences of this hazard, and the relative simplicity of identifying susceptible buildings produce a moral imperative to inform the public of adjacent building hazards. A process to inform all stakeholders of the risks from adjacent building hazard is proposed. This process is designed to provide all relevant parties with accurate information and to encourage retrofit of buildings that are likely to put neighbouring buildings at risk during earthquakes. Potential legal and insurance implications of the proposed process are also discussed. Finally, this paper highlights how hazardous buildings greatly endanger people other than the building’s occupants.
Pukerua Bay Overbridge Seismic Retrofit
E.P. Torvelainen, R. Presland & G. Gregg
ABSTRACT: The Pukerua Bay Overbridge crosses the North Island Main Trunk railway line 33km north of Wellington on SH1. The bridge spans a cut forming the two abutment slopes on each side of the rail corridor. The 3-span bridge is 41.2m long and is supported by driven concrete piles. The bridge alignment is at a skew of 45 degrees to the railway and abutment slopes. A previous assessment determined a seismic retrofit of the bridge is required to protect this lifeline route.
A soil nailed slope was designed and constructed to bring the performance of the structure up to an acceptable ultimate limit state design level. The end design was 102, 10m long passive soil nails in the abutment slopes and strengthening of linkages in the bridge deck.
This complex soil-structure interaction problem was critically assessed using a simplified procedure. It compared the relative stiffness of the slope and soil nail system to that of the bridge pier and pile system. The analysis indicated that the soil nail response was significantly stiffer. The effect of the soil nail response on the bridge was considered separately by applying displacements of the slope to the structural model.
The retrofit design is a balance between cost and design level. The design was technically driven by the stiffness and length of the soil nails influencing the structures response. Feasibility wise the design was driven by the remaining design life and replacement cost of the bridge.
Verifying of Different Nonlinear Static Analysis Used for Seismic Assessment of Existing Buildings by Nonlinear Dynamic Analysis
A. Moshref & M. Tehranizadeh
ABSTRACT: The present study is focused on the verifying of non-linear static analysis (Pushover) which is used by two major guidance documents, the New Zealand guideline and the US ASCE 41-06, on the assessment of existing buildings by nonlinear dynamic analysis. The main purpose of the study is to trace the differences in the results produced by these two guidelines. For this, four different moment resisting concrete frames are assessed under these two guidelines to determine the PGA value that causes their collapse. In the next step, these are compared by their similar values which are determined from the nonlinear dynamic analysis.
Comparison of Different Global Optimization Algorithms for Model Updating with an Application to a Full-Scale Bridge Structure
F. Shabbir & P. Omenzetter
ABSTRACT: Due to inherent simplifying assumptions in the finite element (FE) models, the actual behaviour of full scale structures often differs resulting in incorrect detection of the dynamic response under seismic conditions. On site measurements may reveal important differences between measured data and predictions from an FE model. In model updating, dynamic measurements such as natural frequencies, mode shapes and damping ratios are correlated with their FE model counterparts to calibrate the FE model. In this paper, different optimization techniques for model updating have been investigated. Different global optimization algorithms (GOAs), including particle swarm optimization (PSO), genetic algorithms (GAs) and simulated annealing (SA), were used for model updating. The results are compared in terms of accuracy of the updated frequencies. The first part of the paper gives the details of the modal testing of a full scale cable stayed footbridge. The bridge is composed of two spans with composite steel concrete deck, a centrally located steel pylon and six pairs of stays. The bridge was excited using three dynamically synchronized shakers. A dense array of sensors was employed to measure the response. The second part describes model updating of the bridge FE model. The aforementioned GOAs were used to calibrate the FE model with the experimental results. The paper concludes with a discussion on the efficacy of using the different GOAs to obtain a representative FE model.
Experimental Investigation of Nonlinear Structure-Foundation-Soil Interaction
X. Qin, Y. Chen & N. Chouw
ABSTRACT: In current design practice, structure and foundation are considered separately. Only plastic hinge development in structures is accepted. Structural rotation resulting from possible excessive soil deformation is considered as a potential of structural collapse. To avoid plastic deformation of supporting soil and temporary separation between footing and ground, an oversized footing is often selected. Study of structure-foundation-soil interaction (SFSI) in the past revealed that nonlinearities in the soil and foundation-soil interface can be beneficial to the structural seismic performance. Hence, an oversize foundation is not required and the structural ductility demand can be reduced. In this work, the possible beneficial effect of nonlinear SFSI was investigated. Plastic deformation in structure and soil as well as separation between footing and soil were considered simultaneously. The ground excitation was applied via shake table, and the soil was represented by a box of sand. Structure and earthquake with different dynamic properties were considered. The interrelation between earthquake dominant frequencies and structural fundamental frequencies is discussed.
Nonlinear SSI Effect on Adjacent Bridge Structures with Pounding
E.M. Behrens & N. Chouw
ABSTRACT: Past investigations of pounding responses of adjacent bridge decks are performed mainly under the assumption that the considered bridge structures are fixed at their base. If the subsoil is considered at all only linear soil is considered. In this work the nonlinear interaction between adjacent bridge structures and subsoil is incorporated in the numerical analysis. The plastic deformation in the ground with the structural footing is simulated by a macro element and the bridge structures by a lumped mass model. Spatially uniform ground excitation is assumed. The results show that nonlinear structure-foundation-soil interaction can significantly alter the relative response of adjacent structures and consequently the pounding response of bridge girders.
Evaluation of Variation in Dynamic Response of Two Instrumented Buildings under Seismic Excitations
F. Butt & P. Omenzetter
ABSTRACT: Natural frequencies and damping ratios are very important parameters characterizing the dynamic response of buildings. These dynamic characteristics of building structures are observed to vary during different earthquake excitations. To evaluate this variation, two instrumented buildings were studied. One of the buildings is a three storey reinforced concrete (RC) frame building with a shear core, while the other is a three storey RC frame building without shear core. Both the buildings are part of the same large complex but are seismically separated. One of them is instrumented with five and the other with four tri-axial accelerometers. The dynamic properties of the buildings were ascertained using a time domain state-space subspace system identification technique considering 50 recorded earthquake responses. Relationships between identified natural frequencies and damping ratios, and the peak ground acceleration (PGA) at the base level and peak response acceleration (PRA) at the roof level were developed. It was found that response of the buildings strongly depended on the excitation level of the earthquakes. A general trend of decreasing fundamental frequencies and increasing damping ratios was observed with increased level of shaking and response. It is concluded from the investigation that knowledge of variation of dynamic characteristics of buildings is necessary to better understand their response during earthquakes.
Seismic Behaviour of Column-To-Foundation Connections with Cast-In and Post-Installed Rebars. Phase I: Deterioration of Bond between Reinforcing Bars and Concrete Subject to Cyclic Loads and Cyclic Cracks
C. Mahrenholtz, R. Eligehausen & S. Pampanin
ABSTRACT: The load transfer in connections between concrete structural members often strongly relies on the bond along the anchorage of the reinforcement. Therefore, the bond characteristic between reinforcing bars and concrete can have a significant influence on the specific deflection and cracking of the entire structure.
In case of a seismic event, the structure and thus the main reinforcement is cyclically loaded. At the same time, cracks along the reinforcement anchorage open and close due to the cyclic response of the structure. Both, cyclic loads and cyclic cracks progressively damage the bond strength.
As first part of a more comprehensive research program on seismic behaviour of column-to-foundation connections with post-installed reinforcing bars, the effect of simultaneous load and crack cycling was experimentally investigated in simulated seismic tests, at the Laboratory of the University of Stuttgart, to determine a bond stress-displacement model.
Predicting Structural Response with On-Site Earthquake Early Warning System using Neural Networks
Chu-Chieh Jay, Zhe-Ping Shen & Shieh-Kung Huang
ABSTRACT: The on-site earthquake early warning system is under development for the area near the earthquake epicenter to provide information such as earthquake magnitude, the arrival time and the intensity of the strong shaking for free field as well as the structural response, etc. The real-time strong motion signals recorded from Taiwan Strong Motion Instrumentation Program (TSMIP) were used to train neural networks and the characteristics of the sensed earthquake accelerograms were learned. The neural networks provide a seismic profile of the arrival ground motion instantaneously after the shaking is felt at the sensors by analyzing the three components of the earthquake signals. Each data sample, consist of the first 1~10 second envelope of the complete earthquake accelerogram, was used as the input of the neural networks. The output of the neural networks provides estimates of the structural response and the time for emergency action. The neural network based algorithm is trained with 50149 accelerograms from 2505 earthquakes recorded in Taiwan. By producing informative warnings, the neural network based methodology has shown its potential to increase significantly the application of earthquake early warning system (EEWS) on hazard mitigation.
Evolutionary Strength Domains of Unreinforced Masonry Spandrel Panels Including Strain Softening
F. Parisi & N. Augenti
ABSTRACT: Post-earthquake reconnaissance reports and experimental programs have shown that spandrel panels, i.e. the horizontal structural components between consecutive piers, play a key role in the in-plane nonlinear response of unreinforced masonry (URM) walls with openings to lateral seismic actions. This paper investigates the bending moment capacity of URM cross-sections through the development of simplified moment - axial force interaction equations including the strain ductility of masonry to capture strain softening effects. A constitutive model for masonry subjected to uniaxial compression parallel to mortar bed joints was processed to get flexural strength domains at both elastic and ultimate limit states. Evolutionary strength domains were also developed to be used in seismic assessment of masonry buildings based on static pushover analysis. They account for moment capacity increase/degradation under increasing strain ductility demand on the URM cross-section. The proposed limit strength domains are compared to those corresponding to other constitutive models typically used for masonry structures. Ultimate strength domains are compared to experimental data available in the literature. It is shown that more conservative estimations of ultimate moment capacity are obtained if the proposed equations and those corresponding to elastic-perfectly brittle constitutive model are used.
Results of Pseudo-Static Tests with Cyclic Horizontal Load on Cast in Situ Sandwich Squat Concrete Walls
T. Trombetti, G. Gasparini, S. Silvestri & I. Ricci
ABSTRACT: In recent years, the seismic behaviour of structural systems composed of squat concrete walls has been the object of a renovate interest. This paper presents the results obtained in a wide experimental campaign carried out as a joint effort between the University of Bologna and the Eucentre labs in Pavia. This effort was devoted at the assessment of the seismic performances of cellular structures composed cast in situ sandwich squat concrete walls. In order to obtain a full characterization of seismic behaviour (stiffness, strength, ductility, energy-dissipation) of such structures, a number of tests were performed upon two dimensional (3.0 m by 3.0 m) cast in situ sandwich squat concrete walls (with and without openings). In the experimental tests a number of horizontal in-plane loading cycles were imposed to the specimens, while the vertical load was kept constant. The results obtained have shown that the tested elements are characterized by: (i) absence of a real failure; (ii) high values of the maximum horizontal load applied to the structural systems (higher than the applied vertical load); (iii) residual bearing capacity w.r.t. the vertical loads, also when large lateral deformations were developed; (iv) a good degree of kinematic ductility.