Confidence Factor?

Eurocode 8 Part 3 (EC8-3) is devoted to assessment and retrofitting of existing buildings. In order to take into account the uncertainty in the knowledge of structural properties, EC8-3 defines, analogously to the ordinary material partial factors, an adjustment factor, called “confidence factor (CF),” whose value depends on the level of knowledge (KL) of properties such as geometry, reinforcement layout and detailing, and materials. This solution is plausible from a logical point of view but it cannot yet profit from the experience of its use in practice, hence it needs to be substantiated by a higher level probabilistic analysis accounting for and propagating epistemic uncertainty (i.e., incomplete knowledge of a structure) throughout the seismic assessment procedure. This article investigates the soundness of the format proposed in EC8-3. The approach taken rests on the simulation of the entire assessment procedure and the evaluation of the distribution of the assessment results (distance from the limit state of interest) conditional on the acquired knowledge. Based on this distribution, a criterion is employed to calibrate the CF values. The obtained values are then critically examined and compared with code-specified ones. The results pinpoint a number of deficiencies that appear to somewhat invalidate the approach. The methodological significance of the work extends beyond the assessment procedure in EC8-3, since similar factors appear in other international guidelines (e.g., the knowledge factor of FEMA356).     

Floor Spectra of MDOF Nonlinear Structures

In this article, the influence of nonlinear behavior of multiple degree of freedom (MDOF) primary structures on floor response spectra is investigated by means of simple structural models. The cases of shear beam type as well as of capacity-designed plane frames were studied. It is shown that, in general, but not always, nonlinearity of the primary structure has a beneficial effect on floor spectra. However, higher mode response may be amplified due to nonlinear behavior. The issue of a one story structure exhibiting torsionnal response has also been addressed and some important properties are highlighted.     

Ductility of a Structural Wall with Spread Rebars Tested in Full Scale

The experimental work focuses on the ductility of the reinforced concrete (RC) seismic structural walls in buildings of mid-rise height. A full-scale five-story structural wall was tested to obtain results, still scarce in literature, without the influence of size effect. An unusual detailing with large diameter longitudinal rebars uniformly distributed in the wall length was adopted to prevent premature web rebar fracture and shear sliding. The plastic hinge length and deformations were evaluated in detail. The results show the high ductility of the wall that reached a total drift of 2.5%, larger than those usually required in design.     

General Seismic Load Distribution for Optimum Performance-Based Design of Shear-Buildings

An optimization method based on uniform damage distribution is used to find optimum design load distribution for seismic design of regular and irregular shear-buildings to achieve minimum structural damage. By using 75 synthetic spectrum-compatible earthquakes, optimum design load distributions are obtained for different performance targets, dynamic characteristics, and site soil classifications. For the same structural weight, optimum designed buildings experience up to 40% less global damage compared to code-based designed buildings. A new general load distribution equation is presented for optimum performance-based seismic design of structures which leads to a more efficient use of structural materials and better seismic performance.     

Study of Effects of Sediment-Damping,Impedance Contrast,and Size of Semi-Spherical Basin on the Focusing and Trapping of the Basin-Generated Surface Waves

This article presents the effects of sediment-damping, impedance-contrast (IC), and size of semi-spherical (SS) basin on the focusing and trapping of the basin-generated surface (BGS) waves and the spatial-variation of average-spectral-amplification (ASA), differential ground motion (DGM), and average-aggravation-factor (AAF). A frequency-dependent focusing of the BGS-wave is inferred. Increase of ASA, DGM, and AAF with increase of size of the SS-basin with a fixed-shape-ratio revealed that the BGS-wave focusing has counter-balanced the sediment-damping effects. It is concluded that the BGS-wave focusing and trapping in the SS-basin is more sensitive to change of IC as compared to the similar change of sediment-damping.     

Robust Period-Independent Ground Motion Selection and Scaling for Effective Seismic Design and Assessment

A period-independent approach for the selection and scaling of ground motion records aimed at reducing demand variability is proposed for seismic response history analysis. The same set of scaled records can be used to study various structures at the same site regardless of their dynamic characteristics. The statistical robustness of the proposed and current approaches is compared through nonlinear inelastic dynamic analyses performed on single-degree-of-freedom systems and multi-story braced frames. The proposed approach leads to consistent response predictions with a limited number of records. This is advantageous for day-to-day structural design or assessment against code hazard-based seismic demand levels.     

Modification of Ductility Reduction Factor for Strength Eccentric Structures Subjected to Pulse-Like Ground Motions

This article investigates the ductility reduction factors for RC eccentric frame structures subjected to pulse-like ground motions. The structural models are with the strength eccentricities which are much disadvantageous than the stiffness eccentricities during the inelastic response range. A method to determine the ductility reduction factors of the strength eccentric structures is suggested by modifying those of reference symmetric structures through an eccentricity modification factor. The four factors of strength eccentricity ratio, ductility ratio, story number and velocity pulse of ground motions, are investigated to gain insight into this modification factor. It shows that the ductility reduction factors of the eccentric structures are clearly smaller than those of the symmetric structures. The eccentricity modification factor is mainly affected by the strength eccentricity and the ductility ratio, decreasing with the increment of the eccentricity or the decrement of the ductility ratio in a medium eccentricity range. The earthquake pulse-like effect and the eccentricity have coupling influence on the modification factor, while the effect of story number is not apparent. Based on the results of a comprehensive statistical study a simplified expression is suggested, which can estimate the eccentricity modification factors for both pulse-like and nonpulse-like ground motion cases.     

A geometric morphometrics-based assessment of blade shape differences among Paleoindian projectile point types from western North America

Blade shape features in the type definitions of Clovis, Folsom, and Plainview projectile points. However, the accuracy of these assessments has never been evaluated. Here we report a study in which geometric morphometrics and multivariate statistics were used to compare the shapes of the blades of Clovis, Folsom and Plainview points from the Southern Plains of North America. In the course of the analyses, we controlled for the impact of three potential confounding factors: allometry, differences in raw material quality, and resharpening. The analyses show that blade shape distinguishes Clovis points from both Folsom points and Plainview points, but does not distinguish Folsom points from Plainview points. The analyses also show that the similarities and differences in blade shape among the types are independent of allometry, raw material quality, and resharpening. These findings suggest that the type definitions for Clovis, Folsom and Plainview need to be altered. They also have implications for typing specimens that lack other defining characters (e.g. channel flakes, flutes). Lastly, the absence of resharpening effects raises questions about the validity of the reduction thesis.     

The reality of reduction experiments and the GIUR: reply to Eren and Sampson

There is no ambiguity in the existing empirical support for a GIUR as a robust predictor of mass lost from flakes through unifacial retouching. We demonstrate why the GIUR is a reliable method for inferring mass loss, in appropriate circumstances, and why it is a more powerful predictor of mass loss than touted competitors. We explain why Eren, M.I., Sampson's, G. [2009. Kuhn's geometric index of unifacial stone tool reduction (GIUR): does it measure missing flake mass? J. Archaeol. Sci.] arguments are faulty and why researchers should use the GIUR in preference to other methods of estimating the extent of unifacial retouch.     

统计分析在商代陶鬲研究中的应用

统计分析的方法应用于考古学是以定量化的研究代替定性分析的过程。本文将因子分析的方法应用于郑州洛阳地区出土陶器器形的研究中,以描述陶鬲形制的变化,并检验此变化和商文化演进间的关系。