Seismic Analysis and Fragility Curves of Gravity Waterfront Structures

The aim of the study is to propose adequate fragility curves for waterfront/ retaining structures for ground shaking without the presence of liquefaction, using available data from past earthquakes’ damages in Europe and worldwide and numerical analysis of typical cases. Existing fragility curves and damage states are evaluated and their shortcomings and/or limitations are assessed. Typical waterfront structures, with different geometry, foundation soil conditions and seismic excitations, are studied using appropriate numerical modeling. The corresponding damage levels are estimated with respect to the induced residual displacements and the seismic response of the soil-structure system. Considering aleatory uncertainties of the parameters involved, analytical fragility curves are then constructed for the different types of waterfront structures and foundation conditions. The computed analytical fragility curves are compared with the validated empirical ones, in order to propose fragility functions and corresponding damage levels for gravity waterfront/ retaining structures based on European distinctive features

Seismic Hazard and Geophysical Investigations for Architectural Heritage Preservation in Egypt: The Case of Habib Sakakini Palace

The modern architectural heritage of Egypt is rich, and extensively variable. It covers all kinds of monumental structures from palaces, public buildings, residential and industrial buildings, to bridges, springs, gardens and any other modern structure, which falls within the definition of a monument and belongs to the Egyptian cultural heritage. We present herein a comprhensive geophysical survey and seismic hazard assesment for the rehabilitation and strengthening of Habib Sakakini’s Palace in Cairo, which is considered one of the most significant architectural heritage sites in Egypt. The palace located on an ancient water pond at the eastern side of Egyptian gulf close to Sultan Bebris Al-Bondoqdary mosque, a place also called “Prince Qraja al-Turkumany pond”. That pond had been filled down by Habib Sakakini at 1892 to construct his famous palace in 1897. Various survey campaigns have been performed comprising geotechnical and geophysical field and laboratory tests, aiming to define the physical, mechanical and dynamic properties of the building and the soil materials of the site where the palace is founded. All these results together with the seismic hazard analysis will be used for the seismic analysis of the palace response in the framework of the rehabilitation and strengthening works foreseen in a second stage. We present herein the most important results of the field campaign and the definition of the design input motion

Three-Dimensional Stability Analysis of the Central Rotunda of the Catacombs of Kom El-Shoqafa, Alexandria, Egypt

A three-dimensional numerical model has been proposed of the central Rotunda of the catacombs of Kom El-Shoqafa with its six supporting rock pillars, excavated in sandy oolitic limestone deposit. The model was based on a 3D realistic simulation of the problem geometry. The required input for the analysis (strength and deformability of the rock materials) was derived from laboratory tests and empirical assessments. The rock mass in general is normally widely jointed (\u3e 1 m). In the analysis it is considered as an un-jointed homogeneous medium with low strength. Where 2D analysis fails to model properly the column behaviour, we use 3D modeling to evaluate the stress state in the supporting rock pillars of the excavated Rotunda, taking into account their 3D arrangement.. The results of the numerical analysis on the central supporting Rotunda show that some surface subsidence was induced during excavation of the catacombs. In particular, the displacement developed at the surface above the Rotunda reaches a maximum of 3 mm. This numerical result corroborates the observed displacements in the underground structures and the surface subsidence. The first part of this paper presents a comprehensive geotechnical survey undertaken in the archaeological site, comprising geophysical ambient noise measurements along with field and short- and long-term laboratory experiments, in order to define the physical, mechanical and dynamic properties of the soils and soft rock materials. The second part presents the main results of the detailed 3D numerical analysis of these underground monuments, using an advanced soil-rock elastoplastic modelin

Weak Motion Linear Soil Amplification at Aegion, Greece, and Comparison with Seismic Design Codes

We use 473 weak motion surface records from a relatively soft soil site (CORSSA) and 81 from a relatively stiff soil site (DIM) in conjunction with downhole records obtained in rock in order to study linear seismic soil amplification in Aegion, Greece. We estimate peak ‘soil-to-outcrop’ amplification factors in the time domain for the two sites through linear regression of PGA values. We view the results derived from these very weak motion records as indicative of the entire linear elastic range based on the large dataset size. We compare the peak horizontal soil amplification factors we derive from records with those suggested by design codes based on site classification, and find that they define lower boundaries rather than predictions of the average. We also find that, although the vertical component is assumed unamplified, both datasets show a two-fold amplification in its peak value. The results are also compared with previous finite difference analyses. For CORSSA, the amplification values calculated from 2D analyses are quite similar to those based on records, while for DIM they are 35% lower. Finally, while the elastic response spectra are well within the design spectra due to the small PGA values, we normalize them as to PGA in the context of discussing site effects. Spectral shapes do not infer strong site effects at DIM, but they do so for CORSSA, indicating strong surface waves particularly around the site’s fundamental period

Variance reduction and signal-to-noise ratio: Reducing uncertainty in spectral ratios

This paper uses an unusually large dataset to study scatter in site-effect estimation, focusing on how the events that increase uncertainty can be removed from the dataset. Four hundred seventy-three weak motion earthquake records from the surface and bedrock of a 178-m-deep borehole in Aegion, Gulf of Corinth, Greece, are used to evaluate spectral ratios. A simple statistical tool, variance reduction (VR), is first used to identify two groups of events that lie closest and farthest from the average, which is considered here as the initial best estimate of the site response. The scatter in the original dataset is found to be due to the group of events with smallest VR. These events can be removed from the dataset in order to compute a more reliable site response. However, VR is not normally used to choose records for site-effect studies, and it cannot be applied to the usual small datasets available. The signal-to-noise ratio (SNR) is normally used to this end, for which reason we investigate whether SNR can be used to achieve similar results as VR. Signal-to-noise ratio is estimated using different definitions. Data selection based on SNR is then compared to that using VR in order to define an SNR-based criterion that discriminates against events that, according to VR, increase scatter. We find that defining the SNR of a surface record as the mean value over a frequency range around the resonant peak (here, 0.5–1.5 Hz) and using a cutoff value of 5 may be used in this case to exclude most events for which VR is small. This process is also applied to the downhole station, where we obtain similar results for a cutoff value of 3

The Role of Soil and Site Conditions in the Vulnerability and Risk Assessment of Lifelines and Infrastructures. The Case of Thessaloniki (Greece).

Soil conditions and site effects play an important role in the vulnerability assessment of lifelines and infrastructures under strong seismic excitation. Due to the spatial extent of these networks, they are subjected to non-uniform and incoherent ground motion as a result of the variability of soil and geological conditions; consequently their vulnerability assessment depends entirely on the variability of soil conditions and ground motion, known as site effects, for a given seismic scenario. Fragility functions for the exposed elements at risk, composing the different lifelines and infrastructure systems, play an equally important role. The paper presents some selected results of a recent application of a comprehensive methodology assessing the vulnerability of several lifeline systems in Thessaloniki in Greece. The work is part of a large research program, aiming to the development of a general methodology for the assessment of the seismic risk for the building stock, lifeline systems and infrastructures at urban scale. Key factors of the methodology are the inventory, the typology, the specific characteristics and the importance (global value) of the elements at risk, the development of seismic scenarios (seismic hazard) and the geotechnical characterization, with the detailed site response analysis. The methodology and the role of soil and site conditions are highlighted with representative examples of the application in Thessaloniki

Microzonation Study of Duzce, Turkey

Duzce in Turkey was severely damaged during the November 12th, 1999 earthquake (Mw 7.2). The paper presents different surveys and studies performed after the earthquake, which resulted in the microzonation study of the city. At first we collected and analyzed all available geophysical and geological data. Then we performed a well focused geophysical and geotechnical campaign comprising a sufficient number of shallow and deep boreholes, seismic down-hole tests, array measurements of microtremors and ambient noise measurements. The synthesis of all these data resulted in the construction of the seismic geotechnical map and the geometry of the “seismic bedrock” of the city, adequate for site effect analysis. At a second stage we performed a thorough analysis of all available strong ground motion records and we carried out a detailed seismic hazard analysis, which provided the necessary input motion characteristics for the spatial analysis of the seismic ground response. Finally, we conducted a specific site effect analysis for the seismic scenario of the 1999 earthquake with a series of conventional 1D EQL analysis. The processing of the theoretical analysis results led to the estimation and the spatial distribution of the mean acceleration, velocity and displacement response spectra. As a result, Duzce was divided in seismic zones and for each one we proposed the corresponding mean design acceleration response spectra and all other characteristics of the expected ground response

Physical modeling for the evaluation of the seismic behavior of square tunnels

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

Evaluation of seismic hazard for the assessment of historical elements at risk : description of input and selection of intensity measures

The assessment of historical elements at risk from earthquake loading presents a number of differences from the seismic evaluation of modern structures, for design or retrofitting purposes, which is covered by existing building codes, and for the development of fragility curves, procedures for which have been extensively developed in the past decade. This article briefly discusses: the hazard framework for historical assets, including a consideration of the appropriate return period to be used for such elements at risk; the intensity measures that could be used to describe earthquake shaking for the analysis of historical assets; and available approaches for their assessment. We then discuss various unique aspects of historical assets that mean the characterisation of earthquake loading must be different from that for modern structures. For example, historical buildings are often composed of heterogeneous materials (e.g., old masonry) and they are sometimes located where strong local site effects occur due to: steep topography (e.g., hilltops), basin effects or foundations built on the remains of previous structures. Standard seismic hazard assessment undertaken for modern structures and the majority of sites is generally not appropriate. Within the PERPETUATE project performance-based assessments, using nonlinear static and dynamic analyses for the evaluation of structural response of historical assets, were undertaken. The steps outlined in this article are important for input to these assessments

Calibration of strain gauged square tunnels for centrifuge testing

A series of dynamic centrifuge tests were conducted on square aluminum model tunnels embedded in dry sand. The tests were carried out at the Schofield Centre of the Cambridge University Engineering Department, aiming to investigate the dynamic response of these types of structures. An extensive instrumentation scheme was employed to record the soil-tunnel system response, which comprised of miniature accelerometers, total earth pressures cells and position sensors. To record the lining forces, the model tunnels were strain gauged. The calibration of the strain gauges, the data from which was crucial to furthering our understanding on the seismic performance of box-type tunnels, was performed combining physical testing and numerical modelling. This technical note summarizes this calibration procedure, highlighting the importance of advanced numerical simulation in the calibration of complex construction models