The effect of soil–structure interaction on the seismic risk to buildings

This paper studies the effect of soil–structure interaction (SSI) on the seismic risk estimates of buildings. Risk, in this context, denotes the probability distribution of seismic monetary loss due to structural and nonstructural damage. The risk analysis here uncovers the probability that SSI is beneficial, detrimental, or uninfluential on seismic losses. The analyses are conducted for a wide range of buildings with different structural systems, numbers of stories, and foundation sizes on various soil types. A probabilistic approach is employed to account for prevailing sources of uncertainty, i.e., those in ground motion and in the properties of the soil–structure system. In this approach, probabilistic models are employed to predict the response, damage, and repair cost of buildings. To properly account for the ground motion uncertainty, a suite of nearly 7000 accelerograms recorded on soil is employed. It is concluded that structures on very soft soils are extremely likely to incur smaller losses due to SSI, which is in line with the common belief that SSI is a favorable effect for such systems. However, the results for buildings on moderately soft soils reveal a considerable probability, up to 0.4, that SSI has an adverse effect on the structure and increases the seismic losses.     

A class-oriented mechanical approach for seismic damage assessment of RC buildings subjected to the 2009 L’Aquila earthquake

The simplified mechanical method POST (PushOver on Shear Type models) for seismic vulnerability assessment of RC buildings is used in this study to derive damage scenarios for a database of 7597 RC buildings subjected to the 2009 L’Aquila earthquake. POST allows the evaluation of fragility curves through the determination of the non-linear static response of RC buildings in closed form, assuming the hypothesis of shear type behaviour, and considering the influence of infill panels both in the derivation of structural response and in assessment of building damage, which is defined according to the European Macroseismic Scale EMS-98. The aim of the present study is to provide a much more significant and reliable validation of the methodology, thanks to a much wider database compared to previous studies, and based on a different application of the methodology, i.e. at building class-level instead of single building-level. To this aim, the main geometrical-typological characteristics of the analysed buildings (number of storeys, age of construction, building area) have been statistically characterized based on data collected from post-earthquake AeDES survey forms, considering both the variability of each single parameter and the correlation that exists between one parameter and the other. This also allows to analyse the effectiveness of the adopted analytical procedure in predicting the general trends of observed damage with these parameters, showing a good agreement between observed and predicted trends. The overall predicted damage scenarios are compared with the corresponding observed ones, collected from AeDES survey forms, highlighting, again, a good agreement. Finally, the assumed mechanical interpretation of damage classification of EMS-98 is validated through the comparison between the distributions of damage to vertical structures and infill panels and the corresponding observed post-earthquake damage data.     

Analysis and interpretation of the seismic response of RC buildings in Concepción during the February 27, 2010, Chile earthquake

Observed trends in the seismic performance of eight severely damaged reinforced concrete (RC) structures after the February 27, 2010, Chile earthquake are presented in this article. After a reconnaissance and surveying process conducted immediately after the earthquake, several aspects not conventionally considered in building design were observed in the field. Most of the considered structures showed extensive localized damage in walls of lower stories and first basements. Several factors indicate that damage was brittle, and occurred mainly in recent RC structures supported on soft soils with some degree of vertical and/or horizontal irregularity. Non-ductile behavior has been inferred due to the lack of evidence of spread damage in the structure, and the fact that very similar structural configurations existed nearby without apparent damage. Some key aspects in understanding the observed damage are: geographical orientation of the building, presence of vertical and horizontal irregularities, wall thickness and reinforcement detailing, and lack of sources for energy dissipation. Additionally, results of a building-code type analysis are presented for the 4 most critical buildings, and Demand/Capacity ratios are calculated and compared with the observed behavior. It is concluded that the design codes must be revised relative to wall design provisions.     

Fully probabilistic seismic risk assessment considering local site effects for the portfolio of buildings in Medellín,Colombia

A fully probabilistic seismic risk analysis using a comprehensive approach is conducted for Medellin, the second largest city of Colombia, using a building by building database constructed and complemented from aerial images, considering characteristics such as building use categories, socio-economic levels and replacement values. The seismic hazard used for the analysis corresponds to the most updated study available in the country with the same model that was included in the national building code maps definition. Spectral transfer functions are determined for each of the seismic microzonation zones in order to take into account the dynamic soil response and amplification effects in the risk analysis. Several building types are defined for the city and individual vulnerability functions are assigned to each of them. Risk results are presented in the state of the art metrics such as the loss exceedance curve, probable maximum losses for different return periods, average annual losses and risk maps. The obtained results can be classified by use and socio-economic sectors as well as by structural systems that may help the stakeholders to identify where the risk concentrates.     

Far field damage on RC buildings: the case study of Navelli during the L��Aquila (Italy) seismic sequence, 2009

After the recent Central Italy Earthquake of the 6th April 2009 (Mw = 6.3), the Italian and German engineer and geophysicist Task Force carried out a wide characterization of sites, buildings and damages. In Navelli, a town about 35 km far from epicentre, heavy damage occurred on a reinforced concrete (RC) building that represent an anomalous case of damage, when compared with those occurred in the neighbouring area. In this paper, characterization of the site and damage of the Navelli RC Building is reported and discussed. We performed ambient noise and strong motion measurements, installing one three-directional accelerometer on each floor of the structure and two in free-field, and we have carried out repeated measurements using a couple of three-directional tromometers. In the mean time, a geological survey was carried out and the site response was investigated, with the aid of down-hole measurements. It was thus possible to investigate the structural response and damage taking into account site condition. One of the main results of this work is that repeating analyses using ambient noise measurements show that the main structural frequencies reached after the first damaging shock are constant over time, and then the structural behaviour appears stationary at long term. On the other hand, the strong motion recordings show that the building exhibits a transient non-stationary behaviour as the fundamental frequency changes during each aftershock, then returning to the starting value after each event.     

How well developed is the dynamo theory of flat objects?

Abstract

The existing models of disk dynamos are reviewed and an attempt is made to assess the reliability of their predictions. We analyze key questions such as whether the infinitely extended layer is a proper approximation of the finite disk, or whether it overlooks the possibility of ‘‘forgotten modes'', i.e. whether there is a guarantee that, when the model is used in applications, the mode it predicts as the most easily excited is truly such.

What we find is that all existing models of disk dynamos have shortcomings in these respects, so that the analysis of improved models is worth the effort.     

The stress field variation caused by faulting and the prediction for seismic risk

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Study of crustal seismic velocity in the Weihe fault depression basin by seismic tomographic imaging

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Performance of RC buildings after Kahramanmara? Earthquakes: lessons toward performance based design

Two simultaneous earthquakes occurred in the Kahramanmara?-Pazarc?k and Kahramanmara?-Elbistan districts of Turkey on February 6, 2023, and with magnitudes of 7.7 and 7.6, respectively. These events caused the highest estimated loss recorded in Turkey within the last century from natural disasters. The key reason for the extensive loss was the proximity of eleven cities to the earthquake epicenters. Middle East Technical University teams investigated the building sites in Gaziantep, Kahramanmara...     

Emergency assessment of seismic landslide susceptibility： a case study of the 2008 Wenchuan earthquake affected area

The 8.0 Mw Wenchuan earthquake triggered widespread and large scale landslides in mountainous regions.An approach was used to map and assess landslide susceptibility in a given area. A numerical rating system was applied to five factors that contribute to slope instability. Factors such as lithology, topography, streams and faults have an important influence as event-controlling factors for landslide susceptibility assessment. A final map is provided to show areas of low,medium, and high landslide susceptibility. Areas identified as having high landslide susceptibility were located in the central,northeastern, and far south regions of the study area. The assessment results will help decision makers to select safe sites for emergency placement of refuges and plan for future reconstruction. The maps may also be used as a basis for landslide risk management in the study area.     

Performance of non-structural elements in RC buildings during the L��Aquila, 2009 earthquake

In Italy infills and partitions (non-structural elements) are typically made up of hollow brick masonry, disposed in one or two parallel vertical walls. Many studies have analysed their role on the seismic behaviour of moment resisting framed RC buildings and many seismic codes, all over the world, have provided specific additional measures for them. During the Abruzzo seismic sequence, non-structural damage in RC buildings, both private and public, was extensive, varying from small cracks to collapse, along with minor or no damage to structural elements. This damage involved a number of buildings, both old and recently completed, determining heavy socio-economic consequences, including human casualties, loss of building functionality (particularly important in case of strategic constructions), and unusable buildings. In this paper a review of the most frequent damage patterns is performed, aimed at identifying the main causes of damage and linking them to commonly adopted construction rules. For this purpose, local and global structural configurations frequently exhibiting non-structural damage are described, aside from out-of-plane and in-plane failures. Furthermore, a review of code provisions on non structural elements has been performed in the paper making reference to the most prominent current seismic codes and, finally, some design and construction rules are suggested.     

How useful is the Waldmeier effect for prediction of a sunspot cycle?

Waldmeier effect [Waldmeier M., 1955. Ergebnisse und Probleme der Sonnenforschung. Second Ed., Leipzig, p. 154] states that the rise-time of a cycle depends upon a single parameter, namely the sunspot number Rz(max) at the maximum. Strong cycles have a steeper rise, while moderate cycles rise more slowly. In this paper, using the past data for sunspot cycles 1–23, these aspects are re-examined. It was noticed that the inverse relationship between Rz(max) and rise-time is discernable only when average patterns obtained by superposition of several cycles (separately for strong and weak cycles) are compared. In individual cycles, considerable deviations from the average patterns can occur (several tens of units of Rz and several months of rise-time). For a study of the relationship of Rz(max) with features in the early part of a cycle, the features chosen were Ro (i.e., Rz(min)) and Rz values Ra, Rb, and Rc, 12, 24 and 36 months, respectively, later than Ro (only 12-monthly running means were used). Ro had a moderate correlation (<0.6) with Rz(max), but Ra, Rb, Rc had better correlations. For hindsight predictions for cycles 18–23, the predictions for cycle 19 was grossly erroneous (observed value almost double of the predicted value). For other cycles, the errors were within 25%. For cycle 24, the Rz monthly values up to March 2008 give 12-month running means centered in June, July, August, September 2007 as 7.6, 6.5, 5.8, 6.1. Thus, though we cannot be absolutely sure yet that Rz(min) for cycle 24 has occurred, a tentative, provisional prediction using Rz(min) (i.e., Ro) as 5.8 is Rz(max)=113±19, i.e., in the range 94–132. This is an upper limit, as Ro value may reduce further in coming months, but most probably not very much. For Ro=5.0, the prediction would be Rz(max)= 109±17, while in the extreme hypothetical case of Ro=0.0, the prediction would be Rz(max)=79±14.     

Is the distribution of the lancelet Branchiostoma caribaeum affected by sewage discharges? An analysis at multiple scales of variability

Spatial variation in the density and biomass of Branchiostoma caribaeum was analyzed along a sewage contamination gradient identified by fecal steroids in a subtropical estuary, southern Brazil. Sampling, repeated in the austral winter and summer, followed a hierarchical design nested at four spatial scales (sector > 1 km; area > 100 m; site > 10 m; replicate < 1 m). Density and biomass were significantly lower at sites characterized by high concentrations of fecal steroids. The best combinations of variables that explained the biological similarities among sites involved contamination indicators. Most of the variation of biological data was found at the smallest scales and could be related with the sediment texture. Our study highlighted the usefulness of a multi-scale perspective to evaluate distribution patterns of benthic invertebrates as a biological indication of environmental pollution. Gradient analyses at larger spatial scales may be invalidated by the patchy distribution of benthic fauna if they do not account for such small scale variability.     

In-plane–out-of-plane non-linear model of masonry infills in the seismic analysis of r.c.-framed buildings

The out-of-plane (OOP) behaviour of masonry infills (MIs), inserted in reinforced concrete (r.c.)–framed buildings, is recognized as one of the most important failure modes of this nonstructural element during an earthquake, which may be a consequence of simultaneous or prior in-plane (IP) damage. A five-element macro-model, with four diagonal OOP non-linear beams and one horizontal IP non-linear truss, with an equivalent mass of the infill panel divided between two central nodes, takes into account the IP and OOP failure modes occurring in the event of seismic loading. Pivot hysteretic models predict the non-linear IP and OOP force-displacement laws of the infill panel, based on geometrical rules defining loading and unloading branches. Firstly, a calibration of the proposed IP-OOP interaction model of MIs is carried out considering full-scale experimental results of traditional masonry typologies. Each specimen is initially subjected to in-plane quasi-static cyclic loading, until a maximum drift is reached, and then one-sided OOP cycles are imposed pushing in the horizontal direction and back to zero force. Then a numerical investigation considers masonry infills of an existing six-storey r.c.-framed building designed in compliance with a former Italian seismic code. To evaluate the interaction, the results of simultaneous IP and OOP cyclic tests on MIs at the top, intermediate, and lowest levels of the test structure are presented, assuming different displacement histories: (1) OOP loading faster than IP, at the sixth storey; (2) equal IP and OOP loading, at the third storey; (3) IP loading faster than OOP, at the first storey. Finally, attention is focused on the contribution of masonry infills to the IP and OOP energy dissipation of r.c.-framed structures.     

Quantification of the environmental structural risk with spoiling ties: is randomization worthwhile?

Many recent works show that copulas turn out to be useful in a variety of different applications, especially in environmental sciences. Here the variables of interest are usually continuous, being times, lengths, weights, and so on. Unfortunately, the corresponding observations may suffer from (instrumental) adjustments and truncations, and eventually may show several repeated values (i.e., ties). In turn, on the one hand, a tricky issue of identifiability of the model arises, and, on the other hand, the assessment of the risk may be adversely affected. A possible remedy is to adopt suitable randomization procedures: here three different strategies are outlined. The goal of the work is to carry out a simulation study in order to evaluate the effects of the randomization of multivariate observations when ties are present. In particular, it is investigated whether, how, and to what extent, the randomization may change the estimation of the structural risk: for this purpose, a coastal engineering example will be used, as archetypical of a broad class of models and problems in engineering applications. Practical advices and warnings about the use of randomization techniques are hence given.     

Application of Gumbel mixture extreme theory and maximum likelihood to estimate the seismic risk of the Chinese mainland

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Predicting the distribution of thin bed reservoirs by broad frequency band seismic

Recognition of thin interbedded reservoirs in the middle-shallow strata in the Songliao Basin is a great difficulty. In order to resolve this problem, we present a technique for predicting the distribution of thin reservoirs using a broad frequency band and ultra high resolution seismic. Based on forward modeling, we recognized that a thin bed seismic reflection is characterized by changing amplitude with changing frequency （amplitude versus frequency, AVF）. We calculate the thickness of thin reservoirs from their AVF characteristics and predict the distribution of thin bed reservoir using broad frequency band and ultra high resolution seismic. The technique has been applied in the 3D seismic area of Zhaoyuan in the northern part of the Songliao Basin. The seismic resolution is increased by two or three times over that of conventional seismic and many thin reservoirs have been identified. The technique has extensive application to the exploration and development of oil and gas, such as optimizing the location of exploration wells, the design of wells （especially horizontal wells）, choice of production test layers, analyzing reservoir continuity in development wells, and so on.     

Study on the physical meaning of seismic inhomogeneous degree by rock fracture experiments

Introduction The study of acoustic emission evidenced by rock fracture experiments is the most important field of seismology. By means of the rock fracture technique system, many researchers tried to prove the possible relationship between some parameters such as b value and the stress variation prior to rock fracture using the acoustic emission results from different types of rock fracture ex-periments (MA et al, 2004a, b; Lockner, 1993; JIANG and ZHANG, 1998). In order to investigate th…     

Assessing current faulting behaviors and seismic risk of the Anninghe-Zemuhe fault zone from seismicity parameters

Introduction Strong and large earthquakes are prepared and generated on specific segments of active fault zones, especially on the asperity parts of the zones (Aki, 1984; Wiemer, Wyss, 1997; Wyss, et al, 2000). Therefore, both the faulting-behavior identification and the rupture segmentation mainly based on the method of active tectonics are always important aspects in active fault research (DING, et al, 1993). The purposes of the two aspects of research focus on determining fault units tha…