Poster Poster Presentations
Dynamic deformation characteristics of pumice sand
R.P. Orense, M. Hyodo & T. Kaneko
To understand the strain-dependent shear modulus and damping ratio of reconstituted pumice sand samples, a series of dynamic deformation tests was performed using hollow cylindrical torsional shear test apparatus. The effects of confining pressure level and grading characteristics (or fines content) were investigated, and sieve analyses were performed after each test to check if particle crushing occurred. The results showed that the dynamic deformation characteristics of pumice sands were comparable with those of hard-grained sands, e.g., initial shear modulus and shear modulus ratio increased and damping ratio decreased with increase in confining pressure. The effects of fines content were consistent with those observed in other volcanic soils, e.g. Shirasu in Japan. Under undrained cyclic loading, reconstituted pumice sands did not undergo significant particle crushing, resulting in trends in strain-dependent modulus and damping ratio which were similar to those of hard-grained sands.
Dynamic performance assessment of a multi-storey timber building via long-term seismic monitoring and model updating
A.A. Gaul, S.N.R. Jager, P. Omenzetter & H. Morris
The Nelson Marlborough Institute of Technology Arts building is the world's first commercial implementation of a post tensioned Laminated Veneer Lumber (LVL) shear wall system based on EXPAN technology. In order to understand the response of the building in a serviceability level seismic event, System Identification using dynamic monitoring data, Finite Element (FE) modelling, model updating and time history analysis was performed. Several modal frequencies, damping ratios and mode shapes were identified form the seismic response records. Model updating estimated a 16% increase in the stiffness of LVL structural elements, an approximate 90% decrease in concrete, and nearly nil contribution of cladding to stiffness. An estimation of the serviceability response was made based on a single degree of freedom system time history analysis. It was concluded the NMIT building performs well under serviceability seismic loading. The maximum deflection of a 1/25 year event was estimated to be 8 mm.
Consistency of Seismicity and Ground Motion Modelling with the Canterbury Earthquakes
B.A. Bradley
This paper examines the consistency of seismicity and ground motion models, used for seismic hazard analysis in New Zealand, with the observations in the Canterbury earthquakes. An overview is first given of seismicity and ground motion modelling as inputs of probabilistic seismic hazard analysis, whose results form the basis for elastic response spectra in NZS1170.5:2004. The magnitude of earthquakes in the Canterbury earthquake sequence are adequately allowed for in the current NZ seismicity model, however the consideration of ‘background’ earthquakes as point sources at a minimum depth of 10km results in up to a 60% underestimation of the ground motions that such events produce. The ground motion model used in conventional NZ seismic hazard analysis is shown to provide biased predictions of response spectra (over-prediction near T=0.2s, and under-predictions at moderate-to-large vibration periods). Improved ground motion prediction can be achieved using more recent NZ-specific models.
Ground Motion Comparison of the 2011 Tohoku, Japan and 2010-2011 Canterbury earthquakes:Implications for large events in New Zealand
B.A. Bradley
This paper provides a comparison between the strong ground motions observed in the Christchurch central business district in the 4 September 2010 Mw7.1 Darfield, and 22 February 2011 Mw6.3 Christchurch earthquakes with those observed in Tokyo during the 11 March 2011 Mw9.0 Tohoku earthquake. Despite Tokyo being located approximately 110km from the nearest part of the causative rupture, the ground motions observed from the Tohoku earthquake were strong enough to cause structural damage in Tokyo and also significant liquefaction to loose reclaimed soils in Tokyo bay. Comparisons include the strong motion time histories, response spectra, significant durations and arias intensity. The implications for large earthquakes in New Zealand are also briefly discussed.
Estimating post-earthquake welfare and sheltering needs following a Wellington earthquake
K.C. Wright, D.M. Johnston, W.J. Cousins & S.K. McBride
A future earthquake in the city of Wellington will cause widespread building and infrastructure damage, particularly on soft soils. It is also anticipated that all major transport routes (air, sea, rail and road) out of the region and many within the region will be affected. Such impacts create challenges for the provision of welfare and sheltering in the aftermath of an earthquake. A model framework for calculating evacuation numbers, welfare needs and sheltering requirements is proposed based on a variety of damage and non-damage related factors that contribute to evacuation decision-making. A household's decision on whether to evacuate or shelter in place is based on a range of factors, including those directly related to earthquake damage such as structural damage and lifeline utility function, and factors that relate to household or neighbourhood liveability such as access to resources, social networks, mobility or dependency. Multiple factors that contribute to household welfare needs and evacuation decision-making have been included to recognise that post-earthquake evacuation decisions are not based on damage states of buildings or loss of lifeline utility services alone. This paper applies structural damage components of the model and discusses the framework for the non-structural component. Preliminary evacuee and sheltering numbers are derived these will be further refined on applying the non-structural evacuation factors. The outputs from this model will assist those tasked with planning for readiness, response and recovery for a major Wellington earthquake event.
Quantifying Building Engineering Demand Parameters in Seismic Events
H.N. Dantanarayana, G.A. MacRae, R. Dhakal, S.R. Uma & T.Z. Yeow
Engineering Demand Parameters, such as inter-storey drift or floor accelerations, can be correlated to damage within the structure. While current code provisions exist to estimate Engineering Demand Parameters to use in design of components within the structure, such as non-structural elements, these code provisions are not structure specific and their accuracy has not been rigorously quantified. This paper involves a robust and comprehensive study to quantify Engineering Demand Parameters for 180 frame and wall structural configurations. A range of design ductility, design target drift and structural heights are considered. Dynamic inelastic time history analysis is carried out using a suite of ground motion records to obtain the Engineering Demand Parameter of interest. It is found that increasing the flexibility of the structure by either increasing design ductility or target drift increases drift in the first floor columns in the frame structure and on all floors in the wall structure. The code provisions were found to be adequate when considering median values, however drift demands were exceeded at the 84th percentile in several cases. Increasing the flexibility resulted in decreased acceleration demands. All 84th percentile acceleration demands are well within code limits.
Analysis of Liquefaction-Induced Lateral Spreading Data from the 2010 Darfield and 2011 Christchurch Earthquakes
K. Robinson, B.A. Bradley & M. Cubrinovski
The 4 September 2010 Darfield and 22 February 2011 Christchurch earthquakes caused significant damage to Christchurch and surrounding suburbs as a result of the widespread liquefaction and lateral spreading that occurred. Ground surveying-based field investigations were conducted following these two events in order to measure permanent ground displacements in areas significantly affected by lateral spreading. Data was analysed with respect to the distribution of lateral spreading vs. distance from the waterway, and the failure patterns observed. Two types of failure distribution patterns were observed, a typical distributed pattern and an atypical block failure. Differences in lateral spreading measurements along adjacent banks of the Avon River in the area of Dallington were also examined. The spreading patterns between the adjacent banks varied with the respective river geometry and/or geotechnical conditions at the banks.
Torsional Considerations in Building Seismic Design
B. Miranda, G.A. MacRae, T.Z. Yeow & K. Beyer
All buildings are subjected to some degree of torsion which in turn changes the member demands from that of translation only. Torsional effects on buildings subjected to earthquakes are not found directly in structural analysis unless full three-dimensional inelastic dynamic time history analysis is conducted. Since design is often conducted using two-dimensional analysis, these effects are not directly considered. There is currently an understanding of how different parameters may influence torsion, however, the degree to which these factors influence torsion is relatively unknown. Currently there are two simple design recommendations by Beyer/Priestley and MacRae; however, these need to be verified to be used in design. To do this, earthquake ground motions are applied in one direction to single storey structures with different in-plane wall strength and stiffness, rotational inertia and torsional restraint to obtain the inelastic dynamic response considering torsion. A single multistorey analysis is performed to verify the response compared to that of the single storey. It is found that an increase in strength on an element does not increase the demand on any critical element. An increase in rotational mass or a decrease in stiffness eccentricity decrease critical wall displacement. Increasing torsional restraint reduces the critical wall displacement. Beyer/Priestley's prediction is generally non-conservative while MacRae's is conservative. The multistorey analysis was well approximated by the single-storey response. Both single and multistorey structures are recommended to be designed by MacRae's method of which a design example is provided.
Hysteretic Influence on Earthquake Induced Sliding Damage of Contents
R. English, G.A. MacRae & R.P. Dhakal
This paper investigates the influence of hysteretic characteristics of structures on contents damage. The damage to contents considered was limited to sliding induced damage, excluding rocking induced damage. A single storey structure and contents were modelled numerically using non-linear time-history analyses of a multi-spring idealised model. An understanding of the sliding behaviour of contents under impulse loading of a linear elastic structure was developed, against which the performance of non-linear structures was compared. Analyses of the structures were completed using impulse loading and selected earthquake records over a range of natural periods and strength reduction factors. It was found that increasing strength reduction factors directly reduced contents sliding. Increasing hysteretic damping was shown to reduce contents sliding. From impulse analyses a direct relationship between increasing natural period and a reduction in contents sliding was found. This effect was complicated by varying frequency content of earthquakes. It was found that the magnitude of stiffness changes in structures required to produce shock loads on contents was above that feasibly possibly in real structures.
Contents Sliding Response Spectra
S.L. Lin, G.A. MacRae, T.Z. Yeow, R.P. Dhakal & R. English
The importance of building content damage has been recognized again in the recent devastating Canterbury earthquakes as items moved several metres in some cases. Content damage can result in significant economic loss and injuries despite the structural system remaining intact.
In this paper, a simple numerical model is used to simulate the contents sliding behaviour.
After a brief introduction of the methodologies and development of sliding model, the contents sliding behaviour during an earthquake shaking is investigated analytically, followed by the development of the sliding response spectra for contents in structures with different strength reduction factors, coefficients of friction, and structural periods. It is shown that movement of contents is greater when the friction factor is less and when the structure has lower response period and greater strength. An example application of the use of the contents sliding response spectra is provided. Future research directions are also identified.
Design and testing of reinforced concrete frames incorporating the slotted beam detail
J.D.R. Byrne & D.K. Bull
Shortcomings of modern seismic design in reinforced concrete have necessitated the development of new systems capable of addressing these issues. Able to be constructed using existing industry techniques, the slotted beam is one such practicable, economic solution. While earlier research by Au (2010) showed promising results for this system, it also highlighted issues with bond of beam reinforcement within interior joints and understanding of the joint shear mechanism. This paper explains and addresses these issues through a summary of the desktop and experimental research undertaken. The results were encouraging with 2 specimens successfully tested without bar slip and minimal beam elongation.
Loss Estimation in Christchurch CBD followingRecent Earthquakes: Validation and Refinement ofCurrent Procedures
S.L. Lin, S. Giovinazzi & S. Pampanin
Canterbury's recent earthquakes caused devastating losses and resulted in significant damage to buildings in the Christchurch Central Business District (CBD). The already tragic human losses and continuous mounting economic and societal impact reinforce the crucial importance of implementing measures for the reduction of seismic risk.
Earthquake loss estimation procedures, which attempt to predict casualties and losses (direct or indirect) under a given earthquake scenario, either deterministic or probabilistic, can be a very powerful tool in support to the emergency response planning as well as the developing of effective mitigation strategies. Too often the decision to support and initiate a wide implementation of seismic-risk reduction measures is confronted with the perception that the whole operation (e.g. seismic retrofitting of existing earthquake prone buildings) would be too expensive. As a result, passive instead of active policies are typically adopted by central, regional or local government authorities.
In this contribution, a loss estimation evaluation for Christchurch CBD, with focus on reinforced concrete (RC) buildings, is conducted with the main aim to improve the reliability of current procedures to support the aforementioned decision-making process.
Comparisons are made between field observation on the damage of RC buildings of different age and structural types, collected in a comprehensive damage-report, and the post-dicted results of impact assessment obtained using the generated hazard map and fragility relationships. As the work is in progress and the results herein presented are to be considered at this stage indicative of the general features and potential of the approach undertaken, discussion on possible improvements and suggestions for further investigations are presented as well.
Structural Health Monitoring of the Base-Isolated Christchurch Women’s Hospital Following the Canterbury Earthquakes
B. Nigbor, H.P. Gavin, G.A. MacRae, G.W. Rodgers, M. Nayerloo, J.G. Chase, S. Gutschmidt & C. Granger
The September 2010 Canterbury and February 2011 Christchurch earthquakes and associated aftershocks have shown that the isolator displacement in Christchurch Women’s Hospital, which is the only base-isolated structure in Christchurch, was significantly lower than expected. Occupant accounts indicated that accelerations within the hospital were larger than expected for a base-isolated structure and that residual low-level shaking lasted longer following strong-motion events than for non-isolated structures.
To investigate these observations, a multi-university collaboration between the University of California Los Angeles (NEES@UCLA), Duke University, and the University of Canterbury was formed to instrument the Christchurch Women’s Hospital. Five tri-axial strong-motion accelerometers, three uni-axial strong-motion accelerometers and three string potentiometers were utilised to determine the overall building response to the many seismic events of the aftershock sequence. Instruments were installed across the isolation interface in the hospital basement, recording accelerations and relative displacements between the foundation and the base of the superstructure. Accelerometers were also installed in the roof-space to determine structural response and at each end of the structure to investigate any torsional response.
Liquefaction occurred below the main slab of the foundation, which essentially introduced an extra layer of isolation, contributing to a longer observed low-intensity vibration response. Interaction between the isolated Women’s Hospital building and an adjacent non-isolated hospital building was observed, potentially contributing to lower than expected isolation interface displacement. The large vertical accelerations for these events were seen to contribute to the high shaking intensity observed by occupants.
Presentation 086
Impact Mechanics, Damage and Building Pounding: The Effect of Co-efficient of Restitution, Structural Yielding and Gap Ratio
F. Boyer, G. Labrosse, J.G. Chase, G.W. Rodgers & G.A. MacRae
Impact between structures of bridge sections can play a major, unexpected role in seismic structural damage. Linear and non-linear models are developed to analyze structural impact and response of two single-degree-of-freedom structures, representing adjacent buildings or bridge sections. The analyses presented assess probability of impact, displacement change due to impact, and the probability of increased displacement due to impact. These are assessed over a matrix of structural periods for each degree-of-freedom, different impact coefficients of restitution, and a probabilistically scaled suite of earthquake events. Linear versus non-linear effects are assessed using a Ramberg-Osgood non-linear model for column inelasticity. The normalized distance, or gap-ratio (GR), defined as a percentage of the summed spectral displacements, is used to create probabilistic design requirements. Increasing GR and structural periods that are similar (T2/T1~0.8-1.25) significantly decrease the likelihood of impact, and vice-versa. Including column inelasticity and decreasing coefficient of restitution decrease displacement increases due to impact and thus reduce potential damage. A minimum GR~0.5-0.9 ensures that any displacement increases will be less than 10% for 90% of ground motions over all structural period combinations (0.2-5.0sec). These results enable probabilistic design guidelines to manage undesirable effects of impact - an important factor during the recent Canterbury, New Zealand Earthquakes.
Performance Based Design, would it have made adifference in Christchurch?
Will Parker, Josiah Thompson, Paul P. Cordova, Kenneth T. Tam & John D. Meyer
Historically, building codes establish minimum requirements for safety through prescriptive criteria. Critical structures and buildings with higher importance are designed for larger earthquakes that occur less frequently. However, actual performance of the building is rarely assessed. The Canterbury earthquakes showed that building performance varied and that the traditional approach may not deliver the desired results.
In the past decade, Performance Based Design has gained wide acceptance in the engineering community worldwide. Performance Based Design provides a framework to assist a building designer with assessment of building performance, given the potential hazard it is likely to experience. It also allows the owner to understand and choose a range of performance objectives rather than being limited to a building that 'meets code'. In the United States, Performance Based Design concepts have been in use for seismic engineering under the framework outlined in 'ASCE 41 - Seismic Rehabilitation of Existing Buildings'. This paper compares the historical and current approaches to building design in New Zealand with the performance based design approaches currently used in the United States under the framework of ASCE 41. Examples of building performance during the recent Canterbury earthquakes will be used to demonstrate how a performance based design approach can assess performance for buildings and verify equivalent performances using alternative designs. The paper will also show how performance based design can be used to assess the performance required for critical facilities.
Development and Implementation of Buckling Restrained Braces in Taiwan
S.L. Lin, G.A. MacRae, A.C. Wu, P.C. Lin & K.C. Tsai
Buckling restrained braces (BRBs), which are made from encasing a steel core into a steel tube, and confined with infill concrete, have been widely adopted as seismic devices worldwide. In the past decade, many novel concepts and designs of BRBs have been proposed and verified via full-scale components and frame tests in National Taiwan University and National Centre for Research on Earthquake Engineering. Most importantly, the majority of the above technology has successfully been transferred to the industry, and implemented in a range of building applications (e.g. residential, commercial, gymnasium, high-tech factory, and hospital).
In this paper, the basic concept of the BRB is first introduced, followed by a summary of current development of BRBs in Taiwan. The development includes: (i) the investigation of unbonding material, (ii) the proposed novel design of BRBs (e.g. double tube and double core, detachable, and welded end-slot), and (iii) full-scale components and frame tests. Next, several application examples of BRBs in Taiwan are introduced and tabulated. This paper concludes with a discussion and suggestions on how to transfer the technology and experience of BRBs into New Zealand.
Velocity dependence of HF2V devices using different shaft configurations
J.Chanchí Golondrino, J.G. Chase, G.W. Rodgers, G.A. MacRae & C.G. Clifton
High-Force-to-Volume lead dampers (HF2V) have been recently developed through an experimental research program at University of Canterbury, New Zealand. Testing of the device and applications on beam column joints have demonstrated stable hysteretic behaviour with almost no damage. This paper reports testing of HF2V devices with straight, bulged and constricted shaft configurations subjected to velocities of 0.15 - 5.0 mm/s. The effect of the shaft configuration on the hysteresis loop shape, design relationships and the effect of the velocity on the resistive force of the device are described. Results show that hysteresis loop shape of the device is almost square regardless of the shaft configuration, and that devices are characterized by noticeable velocity dependence in the range of 0.15 - 1.0 mm/s.
Behaviour of Asymmetrical Friction Connections using different shim materials
J.Chanchí Golondrino, G.A. MacRae, J.G. Chase, G.W. Rodgers & C.G. Clifton
Asymmetrical Friction Connections (AFC) have been successfully applied in New Zealand. Testing on small components, and beam column joint subassemblies have demonstrated stable, efficient hysteretic behaviour with almost no damage. This paper reports quasi-static testing of full scale AFC specimens using different shim materials: mild steel, aluminium, brass, bisalloy grades 80, 400 and 500. The assembling process and hysteretic behaviour of the connections are described. Effects of different shim materials on the hysteresis loop stability and on the magnitude of the friction force are also discussed. Results show stable hysteretic behaviour and minimum degradation effects using shim materials with high Brinell hardness values ranging from 300BH to 500BH.
Quantification of seismic performance factors for buildings incorporating three-dimensional construction system
M. Mashal & A. Filiatrault
The paper presents an application of the FEMA P695 Methodology for 3D panel construction system composed of sixteen archetypes of different configurations.
The FEMA P695 Methodology is intended for design of new structural systems. It provides a rational methodology of evaluating the seismic performance factors, including the response modification coefficient (R-factor), the system overstrength factor Ω0), and deflection amplification factor (Cd), of a proposed seismic force-resisting system. The Methodology incorporates certain steps for the development, analysis, and the probabilistic assessment of collapse risk of a consistent number of buildings. The Methodology uses nonlinear analysis techniques to characterize nonlinear static and dynamic behavior of a proposed seismic force-resisting system; another advantage of the Methodology is that it explicitly considers uncertainties in ground motion, modeling, design, and test data. The work presented herein calibrates the experimental test data with the analytical results in different steps of the Methodology. Furthermore, it is shown that the Methodology can be directly applied on a series of 3D panel index archetypes, with a significant number of archetypes satisfying the criteria of the Methodology.
Improvements for the Seismic Design of Reinforced Concrete Walls in Chile and Suggestions for the Refinement of Other Seismic Code Provisions
P. Bonelli, J. Restrepo, P.Quintana Gallo, S. Pampanin & A.J. Carr
Recent earthquakes in different parts of the world continue to strike cities where reinforced concrete (RC) structures have been constructed revealing new weaknesses. This is the case of Chile, where a significant amount of mid-rise RC buildings constructed since the 1980's were affected by the 27 February 2010 Maule Earthquake. Even if most of RC buildings remained apparently in the elastic range, showing an acceptable performance, a significant amount of RC walls in stiff and flexible buildings were significantly damaged showing a specific damage pattern not observed or not clearly identified previously. This type of damage was mainly attributed to non-ductile detailing, as the absence of lateral restraint for longitudinal reinforcement to prevent buckling of longitudinal rebar, the excessive initial (gravity) axial load, and the lack of capacity design considerations to protect shear failures, amongst others. In this contribution a summary of recent amendments adopted in the Chilean Seismic Normative (NCh433 seismic design and NCh430 RC design codes) as well as suggestions for further refinement of ACI318 seismic provisions for structural walls are presented in light of the observed damage in RC structural walls after the Maule Earthquake. Finally, the similarity with what was observed in Christchurch after the 22 February 2011 Canterbury Earthquake in structural walls is highlighted.
Temporary Housing Issues following the 22nd Christchurch Earthquake, NZ
Sonia Giovinazzi, Joanne R. Stevenson, Jon Mitchell & Anna Mason
The 22nd February 2011 Christchurch Earthquake damaged or destroyed over 6,000 residential properties forcing thousands to leave their homes. The Natural Hazard Research Platform, NHRP of New Zealand funded a short-term project aiming to inform the Department of Building and Housing, DBH, and the Christchurch Earthquake Response Centre and Recovery Management, CERA, on best practices and methods adopted at international level, to assess and respond to temporary housing needs. Further than this, the project team collaborated with the Council and Statistic NZ on estimating the internal and external population migration caused by the earthquake and its impact on the needs for temporary homes. This paper aims to briefly summarise how the aforementioned agencies responded to the temporary housing needs following the Christchurch earthquake and discuss the successes and issues encountered by the NHRP project to fulfil the overall objective of the project. The lesson learnt to support the planning for temporary housing needs in the occurrence of future events are finally discussed.
Problems of seismic design of the cladding panels of precast buildings
A. Colombo & G. Toniolo
Following the lesson learned from L'Aquila earthquake 2009, the paper presents a systematic definition of the design criteria for the connections of cladding panels of precast buildings, examining the behaviour of the whole system made of structure and panels, and proposes, for the typology of one-storey buildings with industrial destination, some possible alternative solutions that ensure the stability of all the construction elements.
To quantify the design parameters involved in the quoted solutions, some calculations of a typical precast building under seismic conditions are elaborated. The analysis is repeated to compare the different connection systems of the panels to the structure, that is the isostatic solution that allows the structural frame to move independently from the walls, and the collaborating solutions that integrate the wall panel to the resisting structure.
These information are intended to give the base data for a new generation of connection devices compatible with the wall stability under seismic action.
Liquefaction ejecta clean-up in Christchurch during the 2010-2011 earthquake sequence
M. Villemure, T.M. Wilson, D. Bristow, M. Gallagher, S. Giovinazzi & C. Brown
The Canterbury earthquake sequence in New Zealand's South Island induced widespread liquefaction phenomena across the Christchurch urban area on four occasions (4 Sept 2010; 22 Feb; 13 June; 23 Dec 2011), that resulted in widespread ejection of silt and fine sand. This impacted transport networks as well as infiltrated and contaminated the damaged storm water system, making rapid clean-up an immediate post-earthquake priority. In some places the ejecta was contaminated by raw sewage and was readily remobilised in dry windy conditions, creating a long-term health risk to the population. Thousands of residential properties were inundated with liquefaction ejecta, however residents typically lacked the capacity (time or resources) to clean-up without external assistance.
The liquefaction silt clean-up response was co-ordinated by the Christchurch City Council and executed by a network of contractors and volunteer groups, including the 'Farmy-Army' and the 'Student-Army'. The duration of clean-up time of residential properties and the road network was approximately 2 months for each of the 3 main liquefaction inducing earthquakes; despite each event producing different volumes of ejecta. Preliminary cost estimates indicate total clean-up costs will be over NZ$25 million. Over 500,000 tonnes of ejecta has been stockpiled at Burwood landfill since the beginning of the Canterbury earthquakes sequence.
The liquefaction clean-up experience in Christchurch following the 2010-2011 earthquake sequence has emerged as a valuable case study to support further analysis and research on the coordination, management and costs of large volume deposition of fine grained sediment in urban areas.
The effects of soil-foundation interface nonlinearity on seismic soil-structure interaction analysis
M. Moghaddasi, A.J. Carr, M. Cubrinovski, S. Pampanin, J.G. Chase, C.T. Chatzigogos & A. Pecker
This research presents the impact of base fixity on seismic analysis including soil-structure interaction (SSI) considering linear and nonlinear soil-foundation interface conditions. A set of inelastic time history analyses using a yielding single-degree-of-freedom structural system with different fixity conditions at the base are used. The base fixity configurations considered are: 1) fixed-base; 2) linear flexible-base; 3) nonlinear flexible-base without uplift; and 4) nonlinear flexible-base with uplift. A suite of 40 ground motions with large-magnitude and moderate-distance is chosen to ensure robustness of the results across realistic ground motions. The examination of SSI effects on the structural response under a design base earthquake (DBE) level, i.e. 500-year return period event, is carried out for all considered scenarios. In addition, the effects of an increase in the seismic intensity up to a maximum credible earthquake (MCE) level, i.e. 2500-year return period event, are also studied for the case of nonlinear flexible-base with uplift. The results illustrate the degree of residual foundation deformation as well as the impact of SSI on structural acceleration, total displacement and ductility. In this context, the importance of SSI effects for a design procedure as well as the difference between linear and nonlinear SSI considerations is highlighted.
Acoustic Surveying Technology and Research on the Haihe Buried Fault in Tianjin
F. Liu, Y.K. Chen, W.P. Gao, Z.S. Wang & Y.P. Zheng
A Survey was carried out to find the structure of the shallow part of the Haihe River and information on the faulted strata in Haihe Fault in Tianjin using acoustic Surveying methods such as the single-channel seismic technique. The result shows that this method works well in the part where the river is wide and deep. It also shows that in Tanggu area of Tianjin, the upper breakpoint of Haihe Fault is about 30m underneath the riverbed and the corresponding latest active period is Qp3-Qh1, which is consistent with the result of the previous borehole Surveys. In the offshore area of Bohai Sea, the Haihe Fault presents as a NWW-NEE strike dense fault zone and its upper breakpoint is less than 30 m underneath the seabed. It shows that movements of Haihe Fault in Bohai Sea is basically the same as those in Tanggu area.