Strengthening buildings of stone masonry to resist earthquakes

Stone masonry buildings are common in many areas in the Alpine-Himalayan earthquake zone, and their failure in recent earthquakes has been the cause of many deaths. Poverty and lack of alternatives prevent the replacement of stone masonry with more ductile materials, but the brittleness of unreinforced stone masonry can be considerably reduced by the incorporation of horizontal lacings of timber or reinforced mortar.As part of a joint research project with the Turkish Earthquake Research Institute in Ankara to study low-cost upgrading strategies for rural earthquake protection, full-scale wall elements were subjected to static lateral loading test and dynamic tests on an impulse table. A simple yield-line analysis based on wall overturning was shown to be able to give a useful prediction of the mode of failure and failure load in the static test, and give guidance on the relative performance of unreinforced and reinforced walls in the dynamic test. The results of these tests were used to assess the cost-effectiveness of a large-scale programme of upgrading rural buildings in eastern Turkey.

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Sommario Gli edifici in muratura di pietra sono molto diffusi in ampie zone della regione sismica alpino-himalayana ed il loro crollo ha provocato la perdita di numerose vite umane durante gli ultimi eventi sismici. Spessola poverta' e la mancanza di alternative impediscono la sostituzione della muratura di pietra con materiali piu' duttili: ciononostante il comportamento di tale materiale puo' essere sostanzialmente migliorato incorporando cuciture orizzontali di legno od introducendo elementi metallici nei ricorsi di malta. II progetto di ricerca che si va sviluppando congiuntamente con l'Istituto Turco di Ricerca sui Terremoti di Ankara si propone di individuare una serie di provvedimenti di basso costo per migliorare la qualita' antisimica dell' edilizia rurale. In tale schema sono stati condotti una serie di esperimenti su pannelli murari in scala reale soggetti a carichi statici laterali ed a prove dinamiche su tavola vibrante. Una semplice analisi a rottura basata sul ribaltamento dell'elemento murario si e'dimostrata in grado di fornire accurate previsioni sui meccanismi e sui carichi di rottura nelle prove statiche, e dare utili indicazioni sul comportamento di pannelli semplici e rinforzati sottoposti a prove dinamiche.I risultati di tali prove sono stati utilizzati per una analisi cost-benefici per la definizone di un programma su larga scalla del miglioramento del comportamento sismico di edifici rurali nella Turchia Orientale.

     

Sur les immeubles hyperboliques (On hyperbolic buildings)

The aim of this paper is to give a geometric approach to Tits' amalgam method to construct buildings and to initiate a study of hyperbolic buildings, i.e. whose types are reflexion systems of the real hyperbolic space. We construct lots of examples and study their cohomology at infinity. We construct CAT(–1) polyhedral complexes having big discrete parabolic groups of isometries.     

基于简化模型的超高层结构传感器优化布置

对于自由度较多的超高层结构,传感器优化布置时应考虑多阶模态振型.由于存在空间耦合振动,根据振型质量参与系数难以准确选择出结构弱轴方向的高阶振型.基于等效刚度参数识别法,本文提出了一种将有限元模型沿弱轴方向先简化为等效串联多自由度体系,然后根据简化结构的物理参数来计算弱轴方向振型矩阵的方法,有效地解决了这一问题.以某超高层结构为例,根据计算得到的系统振型矩阵,首先由其转置的列主元QR分解得到传感器的初始布置方案,然后以模态置信度(MAC)矩阵的最大非对角元为目标函数,采用逐步累积算法逐步增加可降低此初始布置MAC非对角元的结构自由度,并考虑经济性因素,最终确定出了传感器的布置方案.     

Dynamic Processes in a Spheroidal Seismic-Damping Mechanism

A mathematical model of a variable-structure system of solids with rolling friction and unilateral sliding friction bonds is described. The model can be applied to seismic isolation mechanisms. Conditions for transition between the possible structures of the equations of state are formulated. The behavior of the system with kinematically defined motion of the base is analyzed as an example__________Translated from Prikladnaya Mekhanika, Vol. 41, No. 1, pp. 119–127, January 2005.     

建筑物周围流场格子Boltzmann仿真

基于格子BGK方程的三维15点格子Boltz-mann模型,对建筑物周围流场进行了数值仿真,对其流场的划分进行了分析,并对不同雷诺数下建筑物周围的流场进行了数值模拟计算,得到了比较满意的结果,为环境质量的评估提供了新的途径.     

Groups acting on buildings, operator K-theory, and Novikov''s conjecture

The paper is devoted to the study of the KK-theory of Bruhat-Tits buildings. We develop a theory which is analogous to the corresponding theory for manifolds of nonpositive sectional curvature. We construct a C ^*-algebra and a Dirac element associated to any simplicial complex. In the case of buildings, we construct, moreover, a dual Dirac element and compute its KK-products with the Dirac element. As a consequence, we prove the Novikov conjecture for discrete subgroups of linear adelic groups. In our study, we develop a KK-theoretic Poincaré duality for non-Hausdorff manifolds.Dedicated to Alexander Grothendieck on his sixtieth birthday     

Universal Covers of Geometries of Far Away Type

The geometries studied in this paper are obtained from buildings of spherical type by removing all chambers at non-maximal distance from a given element or flag. I consider a number of special cases of the above construction chosen among those which most frequently appear in the literature, proving that the resulting geometry is always simply connected but for three cases of small rank defined over GF(2) and GF(4). I also compute the universal cover in those exceptional cases.     

An axiom system for metasymplectic spaces

Metasymplectic spaces are geometries representing Tits' weak buildings of Type F ₄. For metasymplectic and polar spaces an axiom system is given that characterizes them in terms of points and lines.     

The topology at infinity of Coxeter groups and buildings

The connectivity at infinity of a finitely generated Coxeter group W is completely determined by topological properties of its nerve L (a finite simplicial complex). For example, W is simply connected at infinity if and only if L and the subcomplexes (where ranges over all simplices in L) are simply connected. This characterization extends to locally finite buildings. Received: May 3, 2001     

Complete reducibility of subgroups of reductive algebraic groups over nonperfect fields II

Let k be a separably closed field. Let G be a reductive algebraic k-group. We study Serre’s notion of complete reducibility of subgroups of G over k. In particular, using the recently proved center conjecture of Tits, we show that the centralizer of a k-subgroup H of G is G-completely reducible over k if it is reductive and H is G-completely reducible over k. We show that a regular reductive k-subgroup of G is G-completely reducible over k. We present examples where the number of overgroups of irreducible subgroups and the number of G(k)-conjugacy classes of k-anisotropic unipotent elements are infinite.