陶器古剂量线性回归方法和误差评估

陶器古剂量P包含等效剂量Q和超线性修正I两个部分,为了提高古剂量测量的准确性,正确地计算古剂量的测量误差,本工作测试了10个古陶片样品,利用线性回归方法计算等效剂量Q和超线性修正I,并对不同的古剂量计算方法进行误差分析和评估。研究表明,线性回归方法(包括归平法和平归法)计算陶器古剂量的准确性优于目前采用的常规法;通过几种不同方法的误差比较和分析,归平法所得误差较其它方法更严谨、合理。该研究在提高古剂量测量的准确性和正确计算古剂量的测量误差两方面具有重要的意义,使得古剂量的测量更加合理,符合数理统计规律。     

Evaluation of IBC Equivalent Static Procedure for Base Shear Distribution of Seismic Isolated Structures

It has been pointed out that the static lateral response procedure for base isolated structures presented in IBC somewhat overestimates the seismic story force [Lashkari and Kircher, 1993 Lashkari, B. and Kircher, C. A. . Evaluation of SEAOC/UBC analysis procedures, Part 1: Stiff superstructure. Proceedings of a Seminar on Seismic Isolation, Passive Energy Dissipation and Active Control. Redwood City, California. ATC Report 17-1.  [Google Scholar]; Constantinou et al., 1993 Constantinou, M. C., Winters, C. W. and Theodossiou, D. . Evaluation of SEAOC and UBC analysis procedures, Part 2: Flexible Superstructure. Proceedings of a Seminar on Seismic Isolation, Passive Energy Dissipation and Active Control. Redwood City, California. ATC Report 17-1.  [Google Scholar]]. In this article IBC equivalent static method for base shear distribution of seismic isolated structures is evaluated. For this purpose one-story to six-story building models are designed according to equivalent lateral response procedure for different elastomeric isolation systems. The results of equivalent lateral response procedure in parameters such as base shear and vertical distribution of base shear are compared with results obtained from dynamic nonlinear analysis and the efficiency and limitations of its application are investigated. In general, the results of equivalent lateral response procedure in base shears are acceptable within the scope of this procedure, but the proposed triangular distribution of base shear is somewhat conservative. So a new formulation for vertical distribution of base shear is proposed which results in a more realistic distribution of shear over the height of isolated buildings. The accuracy of the new formulation is examined by comparing the resulting responses obtained from this study with those calculated by nonlinear time history analysis.     

Direct Displacement-Based Design of Buildings with Different Seismic Isolation Systems

A displacement-based design (DBD) procedure for buildings equipped with different seismic isolation systems is proposed. It has been derived from the Direct Dispaced-Based Design (DDBD) method recently developed by Priestley et al. [2007] Priestley, M. J. N., Calvi, G. M. and Kowalsky, M. J. 2007. Displacement-Based Seismic Design of Structures, Pavia, , Italy: IUSS Press.  [Google Scholar]. The key aspect of the proposed procedure is the definition of a target displacement profile for the structure. It is assigned by the designer to achieve given performance levels, expressed in terms of maximum displacement of the isolation system and maximum interstory drift. The proposed design procedure has been developed for four different idealized force-displacement relationships, which can describe the cyclic response of a wide variety of isolation systems, including: (i) Lead-Rubber Bearings (LRB); (ii) High-Damping Rubber Bearings (HDRB); (iii) Friction Pendulum Systems (FPS); and (iv) Combinations of lubricated Flat Sliding Bearings (FSB) with different re-centering and/or energy dissipating auxiliary devices. In this article, the background and implementation of the design procedure is presented first. It is followed by the results of validation studies based on nonlinear time-history analyses on different design configurations of base isolated buildings.     

Importance of Degrading Behavior for Seismic Performance Evaluation of Simple Structural Systems

This study focuses on effect of degradation characteristics on seismic performance of simple structural systems. Equivalent single degree of freedom systems are used for which the structural characteristics are taken from existing reinforced concrete (RC) frame buildings. Simulation of degrading behavior is achieved by considering actual experimental data. To obtain the seismic response of degrading structural systems, two different approaches are used: inelastic spectral analysis and fragility analysis. According to the results obtained from both approaches, degrading behavior is dominant for mid-rise RC frame buildings as it significantly amplifies seismic demand. Hence, in performance-based assessment approaches, analytical modeling of such degrading structures should be carried out carefully.     

Pushover Analyses of Hand-Loaded Steel Storage Shelving Racks

Among the various types of industrial solutions used to store goods and products, the light duty hand loaded shelving rack (SR) typology represents a very popular solution for domestic applications, libraries and for superstores/markets open to the public. Despite the limited cost, an eventual collapse could result in significant damage of stored goods, injuries, and potentially the loss of human life, with the possible consequence of a long suspension of commercial activities. This reflects directly on the great importance of a correct design that, despite the large use of SRs, is nowadays developed with approaches characterized by inadequate levels of reliability.

A research program on SRs is currently in progress in Italy, with the aim of improving the rules for both static and seismic design and this article presents a combined experimental-numerical study. Both component and pushover tests have been carried out, that are shortly summarized. Overall frame response has been simulated by means of advanced finite element software able to capture key features of the nonlinear response of slender frames with mono-symmetric cross-section members.     

Increasing Seismic Energy Dissipation of Steel Moment Frames Using Reduced Web Section (RWS) Connection

Connections of steel moment frames are vulnerable to brittle failure. Providing a perforation near the beam-ends is suggested as a potential method to improve seismic behavior of these structures. This article presents a numerical study on the energy dissipation of steel moment connections with perforated beam. Models with elongated circular openings of different dimensions and location are analyzed and compared based on the global and local damage indices, predicted failure time and dissipated energy. Results show that an RWS connection with a proper opening size can develop reasonable inelastic deformations and provide an acceptable seismic improvement to moment-resisting frames.     

Equivalent Damping in Support of Direct Displacement-Based Design

The concept of equivalent linearization of nonlinear system response as applied to direct displacement-based design is evaluated. Until now, Jacobsen's equivalent damping approach combined with the secant stiffness method has been adopted for the linearization process in direct displacement-based design. Four types of hysteretic models and a catalog of 100 ground motion records were considered. The evaluation process revealed significant errors in approximating maximum inelastic displacements due to overestimation of the equivalent damping values in the intermediate to long period range. Conversely, underestimation of the equivalent damping led to overestimation of displacements in the short period range, in particular for effective periods less than 0.4 seconds. The scatter in the results ranged between 20% and 40% as a function of ductility. New equivalent damping relations for four structural systems, based upon nonlinear system ductility and maximum displacement, are proposed. The accuracy of the new equivalent damping relations is assessed, yielding a significant reduction of the error in predicting inelastic displacements. Minimal improvement in the scatter of the results was achieved, however. While many significant studies have been conducted on equivalent damping over the last 40 years, this study has the following specific aims: (1) identify the scatter associated with Jacobsen's equivalent damping combined with the secant stiffness as utilized in Direct Displacement-Based Design; and (2) improve the accuracy of the Direct Displacement-Based Design approach by providing alternative equivalent damping expressions.     

Experimental and Numerical Investigation of IPE Reduced Beam Sections with Diagonal Web Stiffeners

A reduced beam section (RBS) is a new type of connection in steel moment resistant frames. In addition to the major benefits, RBS has its own weaknesses, such as web local buckling and lateral torsional buckling. The purpose of this paper is to improve the performance of European I-beam profile (IPE) with an arched cut in the flange, using a diagonal stiffener of the beam web. With the help of laboratory tests and numerical models, it was found that the use of a diagonal stiffener in the area of an arched cut increased the energy dissipation and plastic rotation capacity of RBS connection.     

Pseudo-Dynamic Testing and Analytical Modeling of AAC Infilled RC Frames

Two concrete frames were tested by the PsD procedure. One frame was bare and the other was infilled with AAC blocks in the middle bay. The objective was to determine the effect of AAC infills on the seismic performance of reinforced concrete frames and developing an AAC strut model. Based on the test results, it was found that AAC infill panels did not modify the deformation response of the RC test frame significantly; however, shear in diagonal strut must be considered in boundary column design. A shear design procedure is proposed for the boundary columns in infilled frames. The drift limits of AAC infill panels measured during the tests were 0.005, 0.008, and 0.014 during diagonal cracking, corner crushing, and severe damage states, respectively.     

Frame Semantics

框架语义学是认知语义学的一个新的研究领域。而认知语义学又是认知语言学的一个重要分支。本文简要介绍了认知语言学和认知语义学的联系,框架语义学的由来和相关概念,以及框架语义学理论在应用上取得的最新成果。