Simulated Portfolio for the Seismic Risk Assessment of Composite Structures
Assessment of damage costs due to an earthquake is an important issue for the insurance industry, yet it currently lacks real damage data for realistic pricing of individual risks. Sophisticated numerical tools, which are widely used to assess structural behavior in great detail (like FEM), may be used with confidence in modeling damage and therefore, they may be suitable in seismic risk assessment for insurance purposes. To produce a virtual damage database, the “Simulated Building Portfolio”-Tool (SBP-Tool) was developed at the University of Kassel in cooperation with the Munich Re. This paper presents the first virtual portfolio for steel-concrete composite frame structures. The SBP-Tool uses beam elements for the composite columns and steel girders, and shell elements for the concrete slabs. Shear springs are automatically created to model the composite action between concrete slabs and steel beams. Rotational springs model the semi-rigid beam-column connections. INTRODUCTION The assessment of damage losses due to an earthquake is an important issue for the insurance and reinsurance industry, but it currently lacks the level of detail that is required for realistic pricing of individual risks. Once again, the recent earthquakes that stroke Chile (Maule, Mw 8.8, February 6, 2010), New Zealand (Darfield, Mw 7.0, September 3, 2010 and Lyttelton, Mw 6.1, February 21, 2011) and Japan (Honshu, Mw 9.0, March 11, 2011) in the last three years proved the strategic importance of this kind of industry and renewed the crucial question of how to develop a resilient concept for society. Any further advancement in that respect is strictly related to the capabilities of creating reliable models to predict seismic risk. This process implies a better understanding of the hazard, of the vulnerability and of the exposure that is involved. Even if important on-going projects, like the Global Earthquake Model (GEM), are aiming at sharing and improving our knowledge, the “state-of-the-art” of the empirical data-set regarding earthquake’s economic losses presents a severe non-uniformity. The worldwide information available is extremely different from both the quality and the geographical points of view. Since earthquakes are rare events, the situation will not likely change significantly in the foreseeable future. It is therefore necessary to further investigate the development of innovative concepts based on consolidated numerical simulation techniques. This paper presents how to simulate a first portfolio consisting of steel-concrete composite structures, which can be used in combination with detailed wave propagation models to estimate the damage and the resulting damage costs. [Mazzieri 2013] shows how to describe a spatial variability of strong-ground motions through large-scale 3D simulations of wave propagation in near-surface soils. He developed complex 3D FE-models for a region of 1 km x 1 km and a depth of 50 m. More than 1.000.000 Finite Elements are typically required to simulate the wave propagation in a particular soil system. Using these complex soil models, Mazzieri assessed the response of buildings due to the simulated wave propagation by modeling them as rigid bodies (Figure 1). This neglects the dynamic characteristics and the non-linear structural behavior of buildings despite being the controlling factors for the response of buildings under seismic actions. Fig.1 Left: 3D-model of the soil and the buildings in Christchurch CBD, [Mazzieri 2013] Right: Snapshots of the simulated displacement of the buildings of the Christchurch CBD, [Mazzieri 2013] A combination of such detailed wave propagation models with sophisticated structural models for the buildings in question is required, if reliable data for seismic risk analysis is to be provided. THE SBP-TOOL FOR GENERATING A VIRTUAL PORTFOLIO To create this kind of building models, the so-called “Simulated Building Portfolio-Tool” (SBP-Tool) was developed at the University of Kassel in cooperation with the Munich Re, [Mühlhausen 2011, 2012]. It provides a virtual portfolio of realistic buildings by using a set of global building criteria provided by the user in a configuration file. A statistical process automatically generates each individual building for the portfolio using the given range for each criterion. Fig. 2 Import new routines to generic SBP-Tool The program is written in ISO C99 and features a modular design (Figure 2). This allows for easy adaptation to different structures (masonry, steel frames, rc-frames with masonry infill, etc.) and inclusion of additional building features, like stairs or penthouses. Currently, the SBP-Tool is used to generate 3D linear FE-models of masonry buildings (Figure 3) and as a recent addition, steel-concrete composite frame structures. A detailed description of how to generate the sophisticated steel-concrete composite frame structures with the predesign (static) module is given in the following chapter. Fig. 3. A regional portfolio of 3D FE-models for masonry buildings simulated with the SBP-Tool. This can be combined with any seismic input, e.g. wave propagation models Whereas the first file (a configuration file) does not depend on any particular FE-software, the second one, the output, must be adapted to its specific commands. This allows the use of other FE-software (Ansys, Open Quake, SLang etc.) without interfering with the initial generation process of the buildings. SLang imports the ASCII files and, by executing the commands, it creates the mass and stiffness matrices. They are exported as two additional output files. Furthermore, SLang creates a file with all the information associated with each DOF. Thus, a set of 4 files is created for each building generated containing all the necessary information to perform a dynamic analysis, and in particular a time history analysis. In general (e.g. non-linear structures) around 500 time histories are required to determine the standard deviation of a local variable with an accuracy of greater than 99 % according to the central limit theorem. That means for a given portfolio like the one in figure 4 with 65 buildings and approximately 1.700.000 DOFs, 8.500.000 time histories are required. To compute 8.500.000 time histories in a short period of time, the use of an efficient algorithm in combination with parallel computing is necessary. In the case of linear structures, the use of power spectra provides an efficient way to calculate the required statistical values of local variables, which can be obtained by multiplying the transfer function of the local variable with the power spectrum of the input process (ground motion). STEEL-CONCRETE COMPOSITE FRAME STRUCTURES WITHIN THE SBP-TOOL A composite structure combines two or more materials with each other and is a widely used structural system in buildings and bridges. Nowadays, a wide range of materials can be used in composite structures, like wood and concrete (especially ultra high performance concrete), but the most common way is combining steel and concrete for manufacturing composite columns, composite beams and composite slabs. The main purpose of combining different materials is to take advantage of the strengths of each material despite the different mechanical properties and their individual weaknesses; for example while one material can be efficient in tension (e.g. steel) the other one (like concrete) would be efficient in compression. Further advantages of using steel-concrete composite structures are that concrete provides a good protection against corrosion and high temperature (fire). The use of steel-concrete composite structures can result in a more efficient design in comparison with steel or concrete structures alone. Usually, larger spans can be reached when a concrete-steel composite system is chosen [Bode,1998, Huber, 2000]. Fig. 4 – A sketch of a steel-concrete composite slab, [Duowei webpage] Concrete Slab Profiled steel decking Shear studs
Virtual portfolios for earthquake insurance related risk simulations
Seismic Risk, a combination of Hazard, Vulnerability and Loss, is becoming a mainstream topic due to an increase in the losses and damage caused by earthquake related effects worldwide. Therefore, it has become an important aspect for insurer and reinsurers since it is extremely difficult to assess due to the lack of the necessary data compared, for example, to car insurance (chapter 1). As described in chapter 2, where the state of the art of seismic risk assessment and simulation is described alongside a more refined approach to seismic risk, current Vulnerability models are oversimplified and do not provide enough accuracy in predicting the damage. Due to the fact that little information on the behavior of real buildings under earthquakes is known, the buildings are vulnerable, and real datasets of observed damages at structures due to earthquake are rare and vary greatly in terms of quantity and quality. The scope of this thesis, Vulnerability modelling, is presented in more detail in chapter 3. In order to cover the demands of the insurance industry, a tool for generating 3D buildings which are then exposed to several hazard scenarios is needed. This tool has been developed in a general way with clear interfaces between the risk components Hazard, Vulnerability and Loss, and it is able to produce realistic 3D buildings quickly and easily. Its global aim is the generation of a statistically equivalent district of a city or a particular insurance Virtual Portfolio. Therefore, in this thesis, the Sophisticated 3D vulnerability modelling for Seismic Risk Simulation (3D-SRS) concept (chapter 4) has been developed to better capture observed damages. It defines the seismic risk in terms of estimating structural damage areas under an seismic excitation in order to be the base for a more realistic pricing from the point of view of insurers and reinsurers. The 3D-SRS consists of sophisticated numerical 3D Virtual Portfolios, a group of buildings with detailed local models. Although only linear covered by taken in this thesis, the concept is open to non-linear approaches as discussed at the end of that chapter. In terms of seismic risk, this is the first study with such complex local models for Vulnerability. For the purpose of generating Virtual Portfolios, the Simulated Building Portfolio-Tool (SBPTool) was developed in cooperation between the University of Kassel and the Munich Re, and it generates hundreds of numerical 3D-FE buildings in an automatic fashion, based on a set of global building parameters. It is also able to model local pre-damages around the foundation, windows or roofs in order to take into account a more realistic building stock. In chapter 5, the SBP-Tool is used to generate the geometry of an Unreinforced masonry building and it is modeled with geometrically linear shell elements and orthotropic material laws. The shaking table test of a two storey URM building from LNEC in Portugal is used to validate the method by comparing observed and estimated damages. The Mechanical Damage Indicator is used in order to link the principal stresses and mechanical damage. As a first assumption, a limit of using linear elastic models is proposed using the linear model approach. Chapter 6 demonstrates the use of 3D-SRS with the clear interfaces. During the evaluation of the estimated damages, a multivariate test of different building parameters was performed by using a Linear discriminant analysis in order to study the effect as well as the influence of different building parameters on the damage. At the end of this study (chapter 7), a comparison of the well-known and widely used ParkAng Damage Index between local models, those generated with the SBP-Tool and global models (SDOF) is made. This comparison basically reflects the damage distribution. By using local 3D models, real observed damages can be reflected, whereas the damage distribution of the global models shows no correlation to observed damages.
Inquiring "Tree of Life" at Home: Persian Classic Literature in English Classes.
The recent decades of English Language Teaching (ELT) appear to be particularly concerned with the marginalisation caused by English linguistic, cultural, and academic colonisation and imperialism. Bold footprints of this academic monopoly can be seen in the wide incorporation of abridged or unabridged British and American literary works in foreign language settings. Such literary products are often legitimised as authentic materials authored by native speakers. Inspired by the idea of incorporating non-native literature and translated first language literature into English classes, the authors of this article sought to explore the possibilities of opening spaces for English translations of Persian classic works of literature in English as foreign language classrooms and tracing the language events that unfolded as a result of incorporating such literature. The participants of this two-semester long action research project were non-English major Iranian female university students, majoring in various fields at Alzahra University, Tehran, Iran. The sense of familiarity the students had with such national literary works led to the emergence of language instances lightened by sparks of virtue, vision, life and art.