Analytical Collapse Study of Lightly Confined Reinforced Concrete Frames Subjected to Northridge Earthquake Ground Motions

Review of older non seismically detailed reinforced concrete building collapses shows that most collapses are triggered by failures in columns, beam-column joints, and slab-column connections. Using data from laboratory studies, failure models have previously been developed to estimate loading conditions that correspond to failure of column components. These failure models have been incorporated in nonlinear dynamic analysis software, enabling complete dynamic simulations of building response including component failure and the progression of collapse. A reinforced concrete frame analytical model incorporating column shear and axial failure elements was subjected to a suite of near-fault ground motions recorded during the 1994 Northridge earthquake. The results of this study show sensitivity of the frame response to ground motions recorded from the same earthquake, at sites of close proximity, and with similar soil conditions. This suggests that the variability of ground motion from site to site (so-called intra-event variability) plays an important role in determining which buildings will collapse in a given earthquake.     

Shear Modulus and Damping Ratio of Cohesive Soils

This article presents results from a laboratory investigation into the dynamic characteristics of reconstituted and undisturbed cohesive soils by means of resonant-column tests. In particular, results showing the influence of various soil parameters, such as confining stress, overconsolidation ratio, void ratio, plasticity index, calcium carbonate content, and time of confinement on shear modulus and damping ratio at small and high shear strains are presented and then discussed. Relationships for the small-strain shear modulus, the degradation of shear modulus at high strains, and the increase of damping ratio at high strains over its small-strain value are proposed. Finally, the practical implications of the results in the context of seismic site response analysis are discussed.     

Study on Response Spectral Acceleration from the Great Wenchuan,China Earthquake of May 12, 2008

The M _w7.9 Wenchuan earthquake produced a rich set of over 1,400 accelerograms, which helped us to better understand strong ground motions from such a large event. Using the abundant data, we investigated the characteristics of response spectral accelerations from this event. This study includes: the spatial distribution of spectral amplitudes at three periods selected to represent ground motions at short, short-middle, and middle-long period ranges; attenuations of response spectral accelerations at periods between 0.05 and 10 s; comparison between the observed ground motions and predicted motions from empirically based equations [Abrahamson and Silva,1997 Abrahamson, N. N. and Silva, W. J. 1997. Empirical response spectral attenuation relations for shallow crustal earthquakes. Seismological Ressearch Letters, 68: 9–23. [Crossref] , [Google Scholar]; Boore et al., 1997 Boore, D. M., Joyner, W. B. and Fumal, T. E. 1997. Equations for estimating horizontal response spectra and peak acceleration from Western North America earthquakes: a summary of recent work. Seismological Ressearch Letters, 68: 128–153. [Crossref] , [Google Scholar]; Campbell, 1997 Campbell, K. W. 1997. Empirical near-source attenuation relationships for horizontal and vertical components of peak ground acceleration, peak ground velocity, and pseudo-absolute acceleration response spectra. Seismological Ressearch Letters, 68: 154–179. [Crossref] , [Google Scholar]; Huo, 1989 Huo, J. R. Ph.D. 1989. Study on the attenuation laws of strong earthquake ground motion near the source, Dissertation, Institute of Engineering Mechanics, China Earthquake Administration. (In Chinese) [Google Scholar]] commonly used in America and China; comparison between the average response spectra at three distance bins and the Chinese seismic design spectra under major earthquake (with the recurrent interval of over 2,000 years);, the vertical-to-horizontal ratio of response spectra and its dependence on the rupture distance, period, and local site condition; and comparison between the fault-normal and fault-parallel component spectral accelerations within the rupture distance of 60 km. Based on these analyses, we finally drew some conclusions regarding the engineering characteristics of spectral accelerations from large earthquakes, such as Wenchuan of M _w 7.9.     

Development and Performance Evaluation of Disk-Type Piezoelectric Transducer for Measurement of Shear and Compression Wave Velocities in Soil

A piezoelectric transducer capable of measuring both shear and compression wave velocities in soil simultaneously in triaxial testing conditions is presented. Performance evaluation of disk transducer system showed that the use of low-noise coaxial cables, proper grounding, and high resolution wave recorder can significantly enhance signal quality and eliminates crosstalk deterioration. Distortions due to near-field effects were found to diminish by increasing input frequency and by using sinusoidal input waveform, compared to square input. Disk-type piezoelectric transducers show significant future potential for laboratory determination of shear, and compression modulus of soil because of their robustness and noninvasive nature.     

Effective Stiffness of Non-Rectangular Reinforced Concrete Structural Walls

The effective stiffness of a structural wall is an important property in design, which many design codes estimate by the moment inertia of the wall section with a reduction factor. The reduction factor is typically estimated by empirical equations based on configurations of the wall. The existing methods for the reduction factor were proposed based on investigations on rectangular reinforced concrete (RC) walls. The effective stiffness of non-rectangular RC walls can be more complex than that of rectangular RC walls. As such, more research investigations are required. Based on finite element models, the effective stiffness of U-shaped and T-shaped RC walls was investigated in this paper. The numerical results were further adopted to develop methods for calculating the effective stiffness of non-rectangular wall in different loading directions. The proposed method was afterward compared with the experimental data.     

DOES HISTORY MATTER? CHARLES TAYLOR ON THE TRANSCENDENTAL VALIDITY OF SOCIAL IMAGINARIES

Since its appearance in 2007, Charles Taylor's monumental book A Secular Age has received much attention. One of the central issues in the discussions around Taylor's book is the role of history in philosophical argumentation, in particular with regard to normative positions on ultimate affairs. Many critics observe a methodological flaw in using history in philosophical argumentation in that there is an alleged discrepancy between Taylor's historical approach, on the one hand, and his defense of fullness in terms of openness to transcendence, on the other. Since his “faith‐based history” is unwittingly apologetic, it is not only “hard to judge in strictly historical terms,” but it also proves that “when it comes to the most ultimate affairs history may not matter at all.” This paper challenges this verdict by exposing the misunderstanding underlying this interpretation of the role of history in Taylor's narrative. In order to disambiguate the relation between history and philosophy in Taylor's approach, I will raise three questions. First, what is the precise relation between history and ontology, taking into account the ontological validity of what Taylor calls social imaginaries? Second, why does “fullness” get a universal status in his historical narrative? Third, is Taylor's position tenable that the contemporary experience of living within “an immanent frame” allows for an openness to transcendence? In order to answer these questions, I will first compare Peter Gordon's interpretation of the status of social imaginaries with Taylor's position and, on the basis of that comparison, distinguish two definitions of ontology (sections I and II). Subsequently, I try to make it clear that precisely Taylor's emphasis on the historical character of social imaginaries and on their “relaxed” ontological anchorage allows for his claim that “fullness” might have a trans‐historical character (section III). Finally, I would like to show that Taylor's defense of the possibility of an “openness to transcendence”—as a specific mode of fullness—is not couched in “onto‐theological” terms, as suggested by his critics, but that it is the very outcome of taking into account the current historical situation (section IV).     

Axial Force Estimation in Historical Metal Tie-Rods: Methods,Influencing Parameters,and Laboratory Tests

This research focuses on estimating the axial force of historical metal tie-rods by means of non-destructive testing (NDT) which provides useful information for calibrating structural models. The first part of this work describes the behavior of tie-rods, emphasizing the key role played by cross-section stiffness, which is usually neglected in the case of cables. Particular attention is then given to common effective parameters and dynamic aspects in terms of acquiring the set-up and which modal parameters to examine.

For new insights into methods for assessing historical tie-rods and evaluating the reliability of analytical and numerical predictions, laboratory tests on four samples with typical cross-sections were carried out on historical metal tie-rods. A set of 224 configurations, including various methods of excitation, boundary conditions, and stress states, were analyzed. In addition to laboratory parameters, this analysis also includes details of sensor positions and number of modes to be examined, and proposes a simplification for less time-consuming tests on-site.