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2014 | Buch

Seismic Evaluation and Rehabilitation of Structures

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SUCHEN

Über dieses Buch

In the past, facilities considered to be at the end of their useful life were demolished and replaced with new ones that better met the functional requirements of modern society, including new safety standards. Humankind has recently recognised the threats to the environment and to our limited natural resources due to our relentless determination to destroy the old and build anew. With the awareness of these constraints and the emphasis on sustainability, in future the majority of old structures will be retrofitted to extend their service life as long as feasible. In keeping with this new approach, the EU’s Construction Products Regulation 305/2011, which is the basis of the Eurocodes, included the sustainable use of resources as an "Essential Requirement" for construction. So, the forthcoming second generation of EN-Eurocodes will cover not only the design of new structures, but the rehabilitation of existing ones as well.
Most of the existing building stock and civil infrastructures are seismically deficient. When the time comes for a decision to prolong their service life with the help of structural and architectural upgrading, seismic retrofitting may be needed. Further, it is often decided to enhance the earthquake resistance of facilities that still meet their functional requirements and fulfil their purpose, if they are not earthquake-safe. In order to decide how badly a structure needs seismic upgrading or to prioritise it in a population of structures, a seismic evaluation is needed, which also serves as a guide for the extent and type of strengthening. Seismic codes do not sufficiently cover the delicate phase of seismic evaluation nor the many potential technical options for seismic upgrading; therefore research is on-going and the state-of-the-art is constantly evolving. All the more so as seismic evaluation and rehabilitation demand considerable expertise, to make best use of the available safety margins in the existing structure, to adapt the engineering capabilities and techniques at hand to the particularities of a project, to minimise disruption of use, etc. Further, as old structures are very diverse in terms of their materials and layout, seismic retrofitting does not lend itself to straightforward codified procedures or cook-book approaches. As such, seismic evaluation and rehabilitation need the best that the current state-of-the-art can offer on all aspects of earthquake engineering. This volume serves this need, as it gathers the most recent research of top seismic experts from around the world on seismic evaluation, retrofitting and closely related subjects.

Inhaltsverzeichnis

Frontmatter
Chapter 1. Surrealism in Facing the Earthquake Risk
Abstract
The possibility of a violent ground motion in a population center poses multiple threats to the safety and continuity of society. It has to be met on multiple planes including the political and the economical. It is not an exaggeration to claim that the construction trades in many parts of the world understood the threat only in twentieth century. In many towns and cities in seismic zones, a strong ground motion can destroy 10 % or more of the existing buildings. To locate the vulnerable, it is necessary to investigate all. If this study is to be done in detail using codified criteria, it may involve an investment that would be unacceptable to a political system that seldom appreciates the risk. That condition constrains the engineering effort to the minimal and requires a procedure that has to be simple and transparent. Above all, data acquisition needs to be within the reach of workers without technical degrees. The paper investigates such a procedure, the Hassan Index, using available information from five earthquake events and finds it imperfect but useful.
Mete A. Sözen
Chapter 2. Rapid Seismic Assessment Procedures for the Turkish Building Stock
Abstract
Seismic performance assessment procedures based on street survey have been developed for low- to mid-rise reinforced concrete and masonry buildings in Turkey. These procedures rely on data that can be collected through visual examination of each building. The data is collected through the forms designed for that purpose. The attributes that are believed to affect seismic performance have been determined and used to evaluate seismic vulnerability. It is important to note that these procedures are not appropriate for determination of seismic vulnerability of individual buildings but to rank a population of buildings according to their relative vulnerability. The primary parameters used for RC buildings include seismic hazard, structural system, number of stories, irregularities in plan and elevation, architectural features and building adjacency. Similar parameters are used for masonry buildings. The procedures developed use the selected attributes to determine seismic vulnerability scores for each building. These scores include a base score that is modified for each attribute to get the vulnerability score. The procedures proposed for rapid seismic assessment were validated and calibrated based on field data and results of detailed assessment procedures.
Ahmet Yakut, M. Altuğ Erberik, Alper Ilki, Haluk Sucuoğlu, Sinan Akkar
Chapter 3. Post-Earthquake Risk-Based Decision Making Methodology for Turkish School Buildings
Abstract
Safety assessment of damaged school buildings is one of the challenging tasks after damaging earthquakes. In this study, a new post-earthquake safety assessment method is proposed for school buildings. The method enables researchers to evaluate the level of risk and to judge the safety of the school building by taking into account the observed level of structural and non-structural damage. First, the vulnerability of the building is identified by considering the relevant damage indicators. Subsequently, the likely consequences of the various performance levels of the school building are identified. The likelihood of a specific consequence is evaluated by jointly considering all failure mechanisms that can lead to the considered consequence. Critical decisions regarding the school are made based on the level of risk and the available resources for risk mitigation. The methodology is expected to be a useful supporting tool for the post-earthquake decision-making process. Using the proposed method, critical decisions, such as continued use, strengthening or decommissioning school buildings can be handled in a rational and consistent way.
Ufuk Yazgan, Reşat Atalay Oyguç
Chapter 4. Proposed Vulnerability Functions to Estimate the Real Damage State of RC Buildings After Major Turkish Earthquakes
Abstract
The Chapter focuses on the applicability of fragility relationships, to predict the seismic vulnerability of existing structures. Since these relationships offer the probability of exceeding a predefined structural response limit in terms of a ground motion intensity parameter, fragility functions are very practical tools to be employed during urban renewal of metropolitan cities with high seismicity. A building ensemble which experienced various damage levels after major Turkish earthquakes is considered herein. Planar structural models for each building are established utilizing DRAIN-2DX computer program and nonlinear dynamic analyses are carried out. The demand parameters are obtained and the capacity is determined in terms of limit states. Finally, fragility relationships recently proposed by various researchers are employed for the building set and compared with the analytical results by means of reflecting the most reliable actual damage state.
Ulgen Mert Tugsal, Beyza Taskin
Chapter 5. Probabilistic Path Finding Method for Post-Disaster Risk Estimation
Abstract
One of the main problems in an immediate post-disaster situation is to find the shortest path between command centres or/and important life care institutions and affected areas, respectively. In this paper, a modified A* search algorithm is proposed, that can find the shortest path between any two points on a map, weighted by the damage probability of the existing infrastructure situated in different locations of an urban area. The proposed approach combines the risk probabilities given by the fragility curves of some relevant constructions located in the disaster area with the deterministic search algorithm. In this case, the real costs provided to the A* algorithm are replaced with expected costs, which are estimated in a stochastic framework. The concept is exemplified on the case study of an urban sample identified in Iaşi, a city of around 300,000 inhabitants, located in the North Eastern region of Romania, exposed to repetitive earthquakes with a recurrence period of around 35–40 years. Thus, probabilistic scenarios can be created for emergency interventions, based on previously recorded local values of Peak Ground Acceleration (PGA). Moreover, the proposed routes for the emergency intervention teams in the post-disaster stage can be visualized on a GIS map, shown actually in our case study. In case of a real extreme event, the information about the proposed routes can be updated in real time, as new data are collected in the field and transmitted to the decision centre.
Florin Leon, Gabriela M. Atanasiu
Chapter 6. Seismic Behavior of Thin-Bed Layered Unreinforced Clay Masonry Shear Walls Including Soundproofing Elements
Abstract
According to the current standards, unreinforced masonry may only be used in regions of low seismicity as the material for the lateral-load resisting system. This requirement may be too safe-sided and leading to not cost-effective solutions for moderately seismic regions. This chapter presents overview of experimental results from shake table tests on unreinforced masonry shear walls carried out in the EQUALS Laboratory of Bristol University, in order to assess, and possibly enhance, the current seismic design rules. The study also includes as additional parameter the presence of soundproofing devices required in buildings with numerous dwellings, in order to achieve the acoustic isolation recommended by recent standards. In practice the required level of acoustic isolation is obtained by locating horizontal rubber layers in the wall. These layers are likely to influence significantly the dynamic response of the wall and hence of the whole structure under seismic actions. Tests are performed on walls realized with masonry units and construction methods typical of North-Western Europe.
Christophe Mordant, Matt S. Dietz, Colin A. Taylor, André Plumier, Hervé Degée
Chapter 7. Assessing Seismic Vulnerability of Unreinforced Masonry Walls Using Elasto-Plastic Damage Model
Abstract
In this paper, the seismic vulnerability of unreinforced masonry walls is assessed by conducting a numerical study on the interaction of axial and lateral resistance. The walls are modeled in an ABAQUS environment, using a plastic damage model originally developed by Lubliner et al. (Int J Solids Struct 25(3):299–326, 1989) and further extended by Lee and Fenves (J Eng Mech ASCE 124(8):892–900, 1998). The model yields interesting interactive collapse mechanisms that occur as the axial loading on the wall is increased. The different modes of failure identified as the axial load is increased include (i) rocking mode, (ii) sliding mode, (iii) staggered head/bed joint failure, (iv) diagonal cracks through wall blocks accompanied by staggered head/bed joint cracking, and (v) crushing of wall blocks or bricks.
Basheer H. Al-Gohi, Cem Demir, Alper Ilki, Mohammed H. Baluch, Muhammad K. Rahman
Chapter 8. Implementation of Experimentally Developed Methodology for Seismic Strengthening and Repair of Historic Monuments
Abstract
The problem of earthquake protection of historic structures and monuments is radically different from that of other structures, due to the priority given to the preservation of the aesthetic, architectonic and historic value, instead of keeping the structure operational. In their effort to protect these structures with the least intervention and the greatest care to preserve authenticity, experts are challenged by the fast development and improved performance of new materials and techniques. However, the implementation of a particular strengthening methodology depends on the extent it has been investigated. Proving the effectiveness of a selected consolidation system can be successfully overcome by design assisted by testing. This Chapter presents the implementation of an original, experimentally verified strengthening methodology in the reconstruction of three very important cultural-historic monuments.
Veronika Shendova, Zoran T. Rakicevic, Mihail Garevski, Roberta Apostolska, Zivko Bozinovski
Chapter 9. Shaking Table Tests of a Full-Scale Two-Storey Pre-Damaged Natural Stone Building Retrofitted with the Multi-Axial Hybrid Textile System “Eq-Grid”
Abstract
This chapter reports about seismic testing on a full-scale two-storey building made of broken natural stones. The dynamic behavior for two stages (a) undamaged and (b) pre-damaged, repaired and strengthened was analysed. All tests took place on the 7 × 5.6 m2 shaking table of Foundation EUCENTRE in Pavia, Italy. The used strengthening technique “eq-grid” was developed over 10 years at the Karlsruhe Institute of Technology (KIT). It consists of a multi-axial hybrid fibre textile embedded in a mortar matrix. In the first years 1:2 scale single masonry walls were quasi statically and/or pseudo-dynamically tested at the KIT lab to identify the adaptability of a mortar-textile-composite for strengthening different kinds of masonry structures including soft lime stone bricks and high strength natural stones. In the end a complete new strengthening system “eq-grid” was developed. To check the results of the conducted wall tests a full-scale two storey masonry building made of high strength natural stones was constructed at Foundation EUCENTRE. The building was uniaxially shaken at different levels of the same earthquake record. In the first stage the unstrengthened building was damaged in such a way that collapse was nearly reached. In the following stage the pre-damaged test sample was repaired and retrofitted using “eq-grid”. As done in practice, the system was applied only on the outer surface of the building. The comparison of the measured and observed dynamic behavior showed a significant increase of the maximum acceleration and ductility. In the end a much better overall dynamic performance of the pre-damaged retrofitted building was achieved. These results fully confirmed the research work based on single wall tests.
Lothar Stempniewski, Moritz Urban
Chapter 10. Application of Mesh Reinforced Mortar for Performance Enhancement of Hollow Clay Tile Infill Walls
Abstract
The use of mesh reinforcement with mortar on existing brick infill walls of reinforced concrete (RC) frames is a recommended seismic strengthening procedure in the Turkish Seismic Code (2007). The premise of the method lies in its ease of application and success in eliminating the out-of-plane failure of existing infill walls. The performance of the mesh reinforced mortar (MRM) application was investigated by pseudo-dynamic (PsD) and cyclic testing. A three-story-three-bay 1:2 scale RC frame with hollow clay tile (HCT) infills in the middle bay was first tested using a continuous pseudo-dynamic test method for three synthetic ground motions compatible with the Düzce city center response spectrum. The test specimen was code complaint. No significant structural damage besides some cracking in the boundary columns was observed but the infill walls almost collapsed. After removing the infill walls of the central bay, a new HCT wall strengthened with MRM was built and the rehabilitated frame was retested under a second series of PsD and reversed cyclic loading schemes. This Chapter reports the findings of the experimental study by placing special emphasis on the seismic response of the code compliant test frame.
Pourang Ezzatfar, Barış Binici, Özgür Kurç, Erdem Canbay, Haluk Sucuoğlu, Güney Özcebe
Chapter 11. Shake Table Tests on Deficient RC Buildings Strengthened Using Post-Tensioned Metal Straps
Abstract
The European research project BANDIT investigated the effectiveness of a novel Post-Tensioned Metal Strapping (PTMS) strengthening technique at improving the seismic performance of deficient RC buildings using shake table tests. A full-scale two-story structure was designed with inadequate reinforcement detailing of columns and beam-column joints so as to simulate typical deficient buildings in Mediterranean and developing countries. Initial shaking table tests were carried out until significant damage was observed in the beam-column joints of the bare frame. Subsequently, the damaged building was repaired and strengthened using PTMS and additional tests were performed. The results of this study show that the adopted strengthening strategy improved significantly the seismic performance of the substandard RC building under strong earthquake excitations.
Reyes Garcia, Iman Hajirasouliha, Kypros Pilakoutas, Yasser Helal, Yaser Jemaa, Maurizio Guadagnini, Mihail Petkovski, Philippe Mongabure, Mihaela Anca Ciupala, Nicholas Kyriakides, Christis Z. Chrysostomou, Alper Ilki, M. Saiid Saiidi, Lluis Torres, Nicolae Taranu, Mihai Budescu
Chapter 12. Bond Strength of Lap Splices in FRP and TRM Confined Concrete: Behavior and Design
Abstract
The effectiveness of Fibre-Reinforced Polymer (FRP) and Textile-Reinforced Mortar (TRM) jackets was investigated experimentally and analytically in this study as a means of confining old-type reinforced concrete (RC) columns with limited capacity due to bond failure at lap splice regions. The local bond strength between lap spliced bars and concrete was measured experimentally along the lap splice region of six full-scale RC columns subjected to cyclic uniaxial flexure under constant axial load. The bond strength of two column specimens tested without retrofitting was found to be in good agreement with the predictions given by two existing bond models. These models were modified to account for the contribution of composite material jacketing to the bond resistance between lap spliced bars and concrete. The effectiveness of FRP and TRM jackets against splitting at lap splices was quantified as a function of jacket properties and geometry as well as in terms of the jacket effective strain, which was found to depend on the ratio of lap splice length to bar diameter. Consequently, simple equations for calculating the bond strength of lap splices in members confined with composite materials (FRP or TRM) are proposed.
Dionysios Bournas, Thanasis Triantafillou
Chapter 13. Finite Element Modeling of Seismic Performance of Low Strength Concrete Exterior Beam-Column Joints
Abstract
This paper presents a finite element simulation to capture the nonlinear response of a typical low strength beam-column joint tested at ITU and also results of the finite element modeling and experimental program conducted at KFUPM for beam-column joints in reinforced concrete construction. Finite element analysis is performed using the software DIANA, simulating the concrete response through Drucker-Prager plasticity with a tension cut-off as failure criterion and using for the reinforcing steel Von-Mises plasticity with multi linear isotropic hardening. The failure mode and deformation response of low strength concrete beam-column joints was predicted with a good correlation between the experimental and finite element results.
Danish Ahmed, Mohammed H. Baluch, Muhammad K. Rahman, Alper Ilki
Chapter 14. FRP Local Retrofit of Non-Conforming RC Beam-Column Joints
Abstract
Recent seismic events have clearly confirmed the vulnerability of existing reinforced concrete (RC) structures. In particular, field observation of structures damaged by L’Aquila earthquake strongly confirmed that premature failure of partially confined (i.e. exterior) beam-column joints was one of the main causes limiting the global structural seismic capacity. Poor attention to details and a lack of adequate transverse reinforcement typically lead to premature brittle shear failure of joints. To provide support to practitioners involved in the L’Aquila reconstruction process, a proper guideline which illustrates the design of local retrofit interventions on structural and non structural elements has been edited by the Italian Civil Protection Department (DPC) and the Laboratories University Network of Seismic Engineering (ReLUIS). In particular, a viable FRP strengthening strategy to increase the seismic performances of partially confined joints (design procedure and installation steps) is widely discussed and presented in the document. To validate the strengthening system recommended in this guideline, an experimental program has been carried out on as-built and FRP strengthened full scale corner RC joints (T shaped joints). After presenting the main guideline recommendations for local strengthening of existing structures, the paper focuses on the experimental program activity; in particular, the specimen design strategy and test setup definition as well as the comparative analysis of the behavior of tested joints.
Andrea Prota, Marco Di Ludovico, Alberto Balsamo, Claudio Moroni, Mauro Dolce, Gaetano Manfredi
Chapter 15. Seismic Rehabilitation of Concrete Buildings by Converting Frame Bays into RC Walls
Abstract
Infilling certain frame bays with RC is popular as a seismic rehabilitation technique. Unless the connection between the old concrete to the new ensures monolithic behavior, this technique is not covered by codes. To avoid penalizing the foundation of the new wall with a very high moment demand, the new concrete should not be thicker than the old frame members. A cost-effective connection of these members to a thin new web is proposed, with design and detailing conforming to current codes for new structures. For practical reasons footings of added walls are often small and weakly connected to the others; so, they uplift and rock during earthquakes. A model is proposed for uplifting footings in 3D, comprising two pairs of nonlinear-elastic springs in a cross layout. It is applied for nonlinear static or dynamic analyses of three buildings with added walls. Analyses of a prototype, regular 4-storey building show the benefits from uplift to the added walls and certain adverse effects on some columns, as well as the lack of a clear positive effect of adding tie-beams. Applications to a 7- and a 2-storey real building with extreme but typical irregularities exemplify the real-life restrictions in the use of added walls and show their limits for the improvement of seismic performance; certain deficiencies in flexure or shear remain in both buildings and are corrected at very low cost with local FRP jackets without new analysis of the building.
Michael N. Fardis, Antonis Schetakis, Elias Strepelias
Chapter 16. Pseudo-Dynamic Tests of 4-Storey Non-Ductile Frames with RC Infilling of the Bay
Abstract
Three 4-storey reinforced concrete (RC) frames at a scale of 3:4 were converted into slender RC walls by filling the bay between the columns with an RC web of the same thickness, which were pseudo-dynamically tested. The specimens were presumed to belong to a non-ductile frame building, the rest of the building been substructured in the test as elastic. Two code-conforming designs were applied to connect the web to the surrounding frame members. Behavior and failure were dominated by flexure, but U-shaped FRP jackets were necessary at the two edges of the composite wall to avoid premature failure near the base due to poor detailing of columns. Slippage or separation at interfaces between the web and the surrounding frame members were minor for both connection details. In one specimen the critical plastic hinge did not form at the base, but in a horizontal band coinciding with the 1st-storey beam of the frame, where the vertical beam stirrups are much weaker than the vertical wall reinforcement; however, this change in failure mode did not adversely affect the global deformation capacity.
Elias Strepelias, Xenophon Palios, Stathis N. Bousias, Michael N. Fardis
Chapter 17. RC Infilling of Existing RC Structures for Seismic Retrofitting
Abstract
The effectiveness of seismic retrofitting of multi-storey multi-bay RC-frame buildings by converting selected bays into new walls through infilling with reinforced concrete (RC) was studied experimentally at the ELSA facility of the Joint Research Centre in Ispra (Italy). A full-scale structure was tested with the pseudo-dynamic method. It consisted of 2 four-storey (12 m tall) three-bay (8.5 m long) parallel frames linked through 0.15 m slabs. The central bay (2.5 m) of each frame is infilled with a RC wall. The frames were designed and detailed for gravity loads only and are typical of similar frames built in Cyprus in the 1970s. Different connection details and reinforcement percentages for the two infilled frames were used in order to study their effects in determining structural response. The results of the pseudo-dynamic and cyclic tests performed on the specimen are presented, and conclusions are drawn.
Christis Z. Chrysostomou, Nicholas Kyriakides, Martin Poljanšek, Fabio Taucer, Francisco Javier Molina
Chapter 18. Hybrid Control of a 3-D Structure by Using Semi-Active Dampers
Abstract
A base isolated three storey 3-D building is semi-actively controlled not to exceed the maximum allowable base displacement. Large displacements are likely to cause failure in the isolation system, and hence, failure in the superstructure is expected. If a base isolated structure is positioned next to a very long fault line, such as the North Anatolian Fault, the structure will mostly undergo far field type excitations. Near field effects will be seen less occasionally, but design considerations should be made to account for both types of excitations. In case of nearby seismic action, the isolated building should be smart enough to modify its isolation impedance to resist against large ground displacement and velocities. For this study, an isolated three storey building model together with four dampers, which are all placed at the base level, is considered. The dampers have controllable orifices (damping coefficients) and the magnitudes of these damping coefficients are assigned by using a linear quadratic regulator (LQR). During an earthquake excitation, the storey displacements and velocities are used as feedback in the calculation of the optimal control force that is producible by viscous dampers, at each time step. This force, however, is applied only at times when critical displacements and/or velocities occur. The performance of the set of controllers is presented via time simulations of the system for three recorded earthquakes. In addition, these records are time shifted five folds to see the effect of near field action. The results indicate that the control effectively reduces the maximum displacements of the isolation system, while maintaining a reasonable isolation to the superstructure.
Gürsoy Turan
Chapter 19. Substructure Pseudo-Dynamic Tests on Seismic Response Control of Soft-First-Story Buildings
Abstract
Soft-first-story structures, such as piloti buildings, are known as vulnerable structures against earthquakes. In this chapter, a simple scheme for reducing the structural damage of such buildings is proposed. Its effectiveness is experimentally examined through substructure pseudo-dynamic tests. In the proposed method, low yield strength steel devices are applied as elasto-plastic dampers at the first story of the buildings to reduce the seismic response and damage. A six-story single-span piloti model, with or without steel dampers, are the subject of the test. The behavior of the two exterior columns at the first story and the steel damper are tested. The substructure pseudo-dynamic tests are successfully performed to investigate the elasto-plastic behavior of the damper and the reinforced concrete columns at the soft-first-story, as well as the overall structural performance. The experimental results show that the seismic damage of piloti buildings can be reduced with steel dampers, which have been found to work as effectively as expected.
Hideto Kanno, Tetsuya Nishida, Jun Kobayashi
Chapter 20. Towards Robust Behavioral Modeling of Reinforced Concrete Members
Abstract
Performance–based seismic design and assessment guidelines promote nonlinear response history analysis of structures using analytical models that can realistically represent the behavioral characteristics of the structural members. For implementation and improvement of such performance–based methodologies, reliable analytical modeling approaches must be used to represent the cyclic nonlinear behavior of the individual structural members in the building, as well as their interaction in the structural system. In this chapter, examples of novel analytical modeling approaches are presented, for simulating the nonlinear response of reinforced concrete structural components, under reversed cyclic loading conditions. Accuracy of the presented modeling approaches are demonstrated via comparison of the model predictions with test results conducted on reinforced concrete wall, column, and panel specimens, with various geometries, material strengths, and reinforcement detailing characteristics. Continuing research efforts on further improvement of the models are also outlined.
Kutay Orakcal
Chapter 21. Earthquake Engineering Experimental Facility for Research and Public Outreach
Abstract
Over the past two decades, important advancements have been made in earthquake engineering practice aimed at reducing seismic risk to urban communities worldwide. Since earthquakes occur infrequently and often in unpredictable locations, the role of experimental research in these advancements has been invaluable. Experimental tests performed under controlled environment can provide high quality data that can advance fundamental knowledge of the behavior of geotechnical and structural elements, validate analytical models, and help explore development of innovative, cost-effective seismic mitigation technologies. It has become evident also that implementation of and investment in seismic risk reduction technologies to vulnerable urban communities requires heightened awareness at all levels of society of the earthquake risk. The authors have found that a shaking table facility while providing valuable research opportunities, is also ideally suited for educational and outreach activities tailored for regional communities and media to heighten their awareness of earthquake risk and demonstrate the important role engineers play in seismic mitigation. The shaking table utilized is uni-directional (1.5 m × 2 m) and has 254 mm peak to peak lateral displacement capacity. The shaking table has been crucial in many research projects in areas such as structural and soil isolation, dynamic interface properties of geosynthetics, seismic permanent deformations, and liquefaction mitigation. The facility is also utilized weekly, as well as at times of heightened public and media interest in earthquake damage, to present various educational modules and carry out shaking table model demonstrations. This paper and presentation will focus on highlights of research conducted using the shaking table and how the facility has been integrated into formal and community-wide educational and outreach programs.
Ece Eseller-Bayat, Seda Gokyer, Mishac K. Yegian
Chapter 22. Physical Modeling for the Evaluation of the Seismic Behavior of Square Tunnels
Abstract
The Chapter summarizes results from dynamic centrifuge tests performed on a rectangular tunnel model embedded in dry sand. The tests were carried out at the geotechnical centrifuge facility of the University of Cambridge, within the Transnational Access Task of the SERIES Research Project (Project: TUNNELSEIS). The experimental data is presented in terms of acceleration and displacement-time histories in the soil and on the tunnel, soil surface settlements, earth pressures on the side walls of the tunnel and internal forces of the tunnel lining. The goal of the experiment is twofold: to better understand the seismic behavior of these types of structures, and to use the high quality and perfectly constrained data to validate the numerical models which are commonly used for the design of rectangular embedded structures. The interpretation of the results reveals (i) rocking response of the tunnel model, (ii) existence of residual values on the earth pressures on the side walls and on the internal forces and (iii) important influence of the tunnel on the shear wave field. These issues are not well understood and are usually not taken into account in the simplified seismic analysis methods.
Grigorios Tsinidis, Charles Heron, Kyriazis Pitilakis, Gopal Madabhushi
Chapter 23. Susceptibility of Shallow Foundation to Rocking and Sliding Movements During Seismic Loading
Abstract
Current design codes prevent the rocking and sliding of shallow foundations during seismic loading despite much research indicating the beneficial nature of allowing such movements. The primary benefit is the partial isolation of the structure from the soil beneath and subsequently the reduced ductility demands on the superstructure, saving money and reducing the risk of collapse. However, further research is required in order to be able to fully model and predict the behaviour of the soil-foundation interface when sliding and rocking is permitted. The results presented in this chapter examine how several different parameters including structural stiffness, aspect ratio, soil relative density and earthquake magnitude affect the level of rotation and sliding experienced by the foundation. Six centrifuge tests were performed to examine how these parameters affected the response of the structure and high speed photography was used to track the movements of the foundation precisely. It was found that structures with a high centre of gravity slid more than structures with a low centre of gravity. Also, stiff structures were found to rotate more than flexible structures and structures located on dense sand rotate more than those located on loose sand.
Charles Heron, Stuart Haigh, Gopal Madabhushi
Chapter 24. Centrifuge Modeling of Liquefaction Effects on Shallow Foundations
Abstract
Earthquake-induced liquefaction is a major concern for structures built on saturated cohesionless soils in seismically active regions, as it often causes failure of critical structures such as bridges and quay walls, which severely restricts post-earthquake emergency response and economic recovery. The destructive consequences of this phenomenon have remarkably increased since it was firstly identified in US and Japan in 1964. This paper describes an investigation on the performance of shallow foundations susceptible to seismic liquefaction, considering the particular vulnerability that this type of foundation has shown in the field during past earthquakes. The research program included three dynamic centrifuge experiments, conducted at the Schofield Centre, University of Cambridge, UK, as part of a SERIES’ TNA Use Agreement focusing on the magnitude of liquefaction effects on shallow foundations, under different conditions, including interaction effects between adjacent structures, and on the assessment of the performance of innovative mitigation techniques, particularly narrow densified zones combined with selectively positioned high-capacity vertical drains.
Andreia Sofia Pedroso da Silva Marques, Paulo Alexandre Lopes de Figueiredo Coelho, Stuart Haigh, Gopal Madabhushi
Chapter 25. Stability Control of Rafted Pile Foundation Against Soil Liquefaction
Abstract
Reinforced concrete (RC) piles are widely used to support structures on soft soil deposits with high liquefaction potential. While the lateral spreading of liquefied soil during earthquakes may cause severe damage to the RC piles, the authors propose using steel sheet pile walls (SSPW) to protect the RC piles from damage and control the overall stability of superstructures. The chapter deals with the nonlinear seismic response and damage evolution and control of multi-storey buildings supported by RC rafted piles on a liquefiable soil. The engineering focus is on the effect of using SSPW to protect existing multi-storey buildings which are supported by rafted pile foundation in a liquefiable soil. The effect of the SSPW embedment length is investigated. Drained and undrained conditions of the soft soil deposits are analytically considered. The results show that the sheet pile wall could improve the overall stability of the reinforced concrete superstructure, but it leads to a higher base shear on the structure.
Ahmed Mohammed Youssef Mohammed, Koichi Maekawa
Chapter 26. Experimental Assessment of Seismic Pile-Soil Interaction
Abstract
Physical modeling has long been established as a powerful tool for studying seismic pile-soil-superstructure interaction. This chapter presents a series of 1-g shaking table tests aiming at clarifying fundamental aspects of kinematic and inertial interaction effects on pile-supported systems. Pile models in layered sand deposits were built in the laboratory and subjected to a wide set of earthquake motions. The piles were densely instrumented with accelerometers and strain gauges; therefore, earthquake response, including bending strains along their length, could be measured directly. Certain broad conclusions on kinematic and inertial SSI effects on this type of systems are drawn.
Armando L. Simonelli, Luigi Di Sarno, Maria Giovanna Durante, Stefania Sica, Subhamoy Bhattacharya, Matt S. Dietz, Luiza Dihoru, Colin A. Taylor, Roberto Cairo, Andrea Chidichimo, Giovanni Dente, Arezou Modaressi, Luìs A. Todo Bom, Amir M. Kaynia, George Anoyatis, George Mylonakis
Chapter 27. Experimental Investigation of Dynamic Behavior of Cantilever Retaining Walls
Abstract
The dynamic behaviour of cantilever retaining walls under earthquake action is explored by means of 1-g shaking table testing, carried out on scaled models at the Bristol Laboratory for Advanced Dynamics Engineering (BLADE), University of Bristol, UK. The experimental program encompasses different combinations of retaining wall geometries, soil configurations and input ground motions. The response analysis of the systems at hand aimed at shedding light onto the salient features of the problem, such as: (1) the magnitude of the soil thrust and its point of application; (2) the relative sliding as opposed to rocking of the wall base and the corresponding failure mode; (3) the importance/interplay between soil stiffness, wall dimensions, and excitation characteristics, as affecting the above. The results of the experimental investigations were in good agreement with the theoretical models used for the analysis and are expected to be useful for the better understanding and the optimization of earthquake design of this particular type of retaining structure.
Panos Kloukinas, Augusto Penna, Anna Scotto di Santolo, Subhamoy Bhattacharya, Matt S. Dietz, Luiza Dihoru, Aldo Evangelista, Armando L. Simonelli, Colin A. Taylor, George Mylonakis
Backmatter
Metadaten
Titel
Seismic Evaluation and Rehabilitation of Structures
herausgegeben von
Alper Ilki
Michael N. Fardis
Copyright-Jahr
2014
Electronic ISBN
978-3-319-00458-7
Print ISBN
978-3-319-00457-0
DOI
https://doi.org/10.1007/978-3-319-00458-7