外文原文
random翻译Response of a reinforced concrete infilled—frame structure to removal of two adjacent columns
Mehrdad Sasani_
Northeastern University, 400 Snell Engineering Center， Boston， MA 02115, United States
Received 27 June 2007； received in revised form 26 December 2007； accepted 24 January 2008
Available online 19 March 2008
Abstract
The response of Hotel San Diego， a six—story reinforced concrete infilled-frame structure， is evaluated following the simultaneous removal of two adjacent exterior column
s. Analytical models of the structure using the Finite Element Method as well as the Applied Element Method are used to calculate global and local deformations. The analytical results show good agreement with experimental data. The structure resisted progressive collapse with a measured maximum vertical displacement of only one quarter of an inch （6.4 mm）。 Deformation propagation over the height of the structure and the dynamic load redistribution following the column removal are experimentally and analytically evaluated and described。 The difference between axial and flexural wave propagations is discussed。 Three—dimensional Vierendeel （frame） action of the transverse and longitudinal frames with the participation of infill walls is identified as the major mechanism for redistribution of loads in the structure。 The effects of two potential brittle modes of failure （fracture of beam sections without tensile reinforcement and reinforcing bar pull out） are described。 The response of the structure due to additional gravity loads and in the absence of infill walls is analytically evaluated.
c 2008 Elsevier Ltd。 All rights reserved.
Keywords： Progressive collapse； Load redistribution； Load resistance； Dynamic response； Nonlinear analysis； Brittle failure
1. Introduction
The principal scope of specifications is to provide general principles and computational methods in order to verify safety of structures。 The “ safety factor ”, which according to modern trends is independent of the nature and combination of the materials used， can usually be defined as the ratio between the conditions。 This ratio is also proportional to the inverse of the probability ( risk ） of failure of the structure。 
Failure has to be considered not only as overall collapse of the structure but also as unserviceability or， according to a more precise。 Common definition。 As the reaching of a “ limit state ” which causes the construction not to accomplish the task it was designed for。 There are two categories of limit state : 
（1)Ultimate limit sate， which corresponds to the highest value of the load—bearing capacity。 Examples include local buckling or global instability of the structure； failure of some sections and subsequent transformation of the structure into a mechanism； failure by fatigue； elastic or plastic deformation or creep that cause a substantial change of the geometry of the structure; and sensitivity of the structure to alternating loads， to fire and to explosions。 
(2）Service limit states, which are functions of the use and durability of the structure。 Examples include excessive deformations and displacements without instability； early or excessive cracks； large vibrations； and corrosion。 
Computational methods used to verify structures with respect to the different safety conditions can be separated into: 
(1）Deterministic methods， in which the main parameters are considered as nonrandom parameters。 
（2）Probabilistic methods， in which the main parameters are considered as random parameters。 
Alternatively, with respect to the different use of factors of safety, computational methods can be separated into: 
(1）Allowable stress method, in which the stresses computed under maximum loads are compared with the strength of the material reduced by given safety factors. 
（2)Limit states method, in which the structure may be proportioned on the basis of its maximum strength. This strength, as determined by rational analysis, shall not be less than that required to support a factored load equal to the sum of the factored live load and dead load ( ultimate state ）. 
The stresses corresponding to working （ service ) conditions with unfactored live and dead loads are compared with prescribed values （ service limit state ) 。 From the four possible combinations of the first two and second two methods， we can obtain some useful computational methods。 Generally， two combinations prevail： 
(1）deterministic methods， which make use of allowable stresses. (2）Probabilistic methods， which make use of limit states。 
The main advantage of probabilistic approaches is that， at least in theory, it is possible to scientifically take into account all random factors of safety， which are then combined to define the safety factor。 probabilistic approaches depend upon : 
（1） Random distribution of strength of materials with respect to the conditions of fabrication and erection （ scatter of the values of mechanical properties through out the structure )； （2) Uncertainty of the geometry of the cross-section sand of the structure （ faults and imperfections due to fabrication and erection of the structure ); 
（3） Uncertainty of the predicted live loads and dead loads acting on the structure; (4)Uncertainty related to the approximation of the computational method used （ deviation of the actual stresses from computed stresses ). Furthermore， probabilistic theories mean that the allowable risk can be based on several factors， such as ： 

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