Application of Endurance Time Analysis in Seismic Evaluation of an Unreinforced Masonry Monument

In this article, seismic behavior of the main dome of a well-known middle-eastern historical- monument, “Imam Reza Shrine” (Mashhad, Iran) which is located in a high seismic area in Iran is evaluated. This study focuses on the response history analysis using intensifying dynamic excitations in the framework of Endurance Time Method. Endurance Time Analysis gives acceptable results for a wide range of earthquake intensities and considerably reduces the computational demand in comparison to the conventional Time History Analysis and Incremental Dynamic Analysis. The aim of this study is to investigate the applicability and efficiency of Endurance Time Analysis for masonry monuments and to suggest modifications and interpretations to improve compatibility of the results with Time History Analysis. In addition, to facilitate evaluation of the structural behavior, a dimensionless index, Cumulative Plastic Strain Index, is proposed as a criterion to compare structural performance in terms of the severity and the extent of damage as a function of earthquake intensity.     

Dynamic Analysis and Seismic Response of Planar Circular Arches with Variable Cross-Section

The aim of this paper is to investigate the dynamic response of planar circular arches with variable cross-section subjected to seismic ground motions. Arches have a wide range of application (e.g. bridges, roofs) thanks to their capacity to span large areas by resolving vertical actions into compressive stresses and confining tensile stresses. The full understanding of their dynamic response is a challenging technical and computational problem, especially when seismic loading is considered. For example, the assumption of axial inextensibility simplifies the differential equations but overestimates the vibration frequencies, especially those of shallow arches since axial forces are of paramount importance (as opposed to beams). In lieu of the above, our formulation incorporates the effect of axial extension, and the arches are modeled using a new generic curved beam model that includes both axial (tangential) and transverse (normal) to the arch centerline deformations, and is able to account for variable mass and stiffness properties, as well as elastic support or restraint. The resulting dynamic governing equations of the circular arch are formulated in terms of the displacements, and solved using an efficient integral equation method. Three circular arches with variable rectangular cross-section are analyzed in order to investigate their dynamic properties and seismic performance. Using both time history and modal analysis useful conclusions are drawn with regard to the contribution of each mode on the calculation of different response quantities.     

An Assessment of the Influence of the Inter-Tropical Discontinuity on Inter-Annual Rainfall Characteristics in Nigeria

This study assessed the influence of the Inter-Tropical Discontinuity (ITD) on inter-annual rainfall characteristics in Nigeria between 1970 and 2000. This involved determining the strength and direction of the relationships between the total annual rainfalls in the extreme southern and northern parts of the country and the total annual rainfalls during the period of the Little Dry Season in southwestern Nigeria, and the surface locations of the ITD over Nigeria and some other factors that may impact ITD characteristics (such as the pressure differences between Azores, Libyan and St. Helena anticyclones and the sea surface temperature of the Gulf of Guinea). Results indicate that although the surface location of the ITD significantly accounts for rainfall inter-annual variability in Nigeria, it does so in the northern part of the country only. Pressure differences between the various anticyclones were observed to be another significant factor influencing inter-annual rainfall variability in the north. However, the influence of the sea surface temperature of the Gulf of Guinea on the rainfall characteristics in the northern region is ill-defined. It was also noted that the only factor influencing inter-annual variability in the Little Dry Season rainfall in the southwest and the total annual rainfalls in the south is the sea surface temperature of the Gulf of Guinea. The results obtained indicate that the total annual rainfalls in the north have significant positive relationships with the surface location of the ITD but significant negative relationships with the pressure differences between the Azores, Libyan and St. Helena anticyclones. The Little Dry Season rainfalls and total annual rainfalls in the south have significant positive relationships with the sea surface temperature of the Gulf of Guinea.     

Shock Response from Pseudodynamic Test Using Momentum Equations of Motion

The feasibility of using pseudodynamic techniques to yield shock responses from impulses is studied herein. A direct integration method is often used to solve the force equation of motion in performing a conventional pseudodynamic test. However, this technique might not be applicable to obtain an accurate shock response from an impulse as a load discontinuity occurs at the end of the impulse. This is because this discontinuity will lead to an extra amplitude distortion and the amount of this amplitude distortion is increased with the increase of time step. Hence, a small time step is needed to reduce the extra amplitude distortion and thus the displacement increment for each time step might be smaller than or as small as the resolution of the displacement transducer. As a result, the displacement increment cannot be accurately imposed upon the specimen and the responses will be contaminated by the noise. In addition, the test duration is drastically increased. Alternatively, this difficulty might be overcome if the momentum equation of motion instead of the force equation of motion is solved pseudodynamically. Hence, an external momentum is used in the solution of the momentum equation of motion. Since the external momentum is a resultant of the time integration of the external force the discontinuity problem will automatically disappear. Consequently, reliable shock responses can be obtained from pseudodynamic tests.     

Nonlinear Structural Response to Low-Cut Filtered Ground Acceleration Records

Ground acceleration records obtained from instruments in the field are often filtered to reduce noise in both low and high frequency bands before being used for structural response analyses. The structural analysis using a filtered acceleration record may elongate the fundamental period of a structure which will potentially lead to an underestimation of the nonlinear response.

The nonlinear response of single-degree-of-freedom systems to low-cut filtered ground acceleration records is investigated. Based on the results of this study, a simple criterion for selecting ground acceleration records for seismic response analyses is proposed to avoid underestimating the nonlinear structural response.     

The nature of the times deceas'd

The essay reflects on the nature of time as a cultural function, especially in the light of the ‘heritage industry’ of the 1980s. In trying to identify the nature of some changes in relationships between pasts and present in the 1990s, the author suggests the concept of ‘post‐heritage’, defines it, and glances at its applicability to 1994.     

The representation of time at two shaker village sites

Abstract

Historical restorations spatialise time, thus sometimes being criticised for their static representation of a dynamic reality. Yet restorations, like the groups they represent, themselves have complex histories. This paper explores how forms of representation relate to intended content historically, through discussion of two American sites: Hancock and Pleasant Hill Shaker Villages. Founded in the early 1960s, both saw demands for change by the 1990s. With the passing of the founders, these museum villages began to reevaluate their interpretive practices and plan for the future. The paper focuses on earlier decisions which have affected the representation of time.     

Seismic Analysis of Non Proportionally Damped Two-Way Asymmetric Elastic Buildings Under Bi-Directional Seismic Ground Motions

This study investigates the effectiveness of the modal analysis using three-degree-of freedom (3DOF) modal equations of motion to deal with the seismic analysis of two-way asymmetric elastic systems with supplemental damping. The 3DOF modal equations of motion possessing the non proportional damping property enable the two modal translations and one modal rotation to be non proportional in an elastic state. The simple approximation method is to use the single degree-of-freedom (SDOF) modal equations of motion, which are obtained by neglecting the off-diagonal elements of the transformed damping matrix. One, one-story and one, three-story non proportionally damped two-way asymmetric buildings under the excitation of bi-directional seismic ground motions are analyzed. The analytical results are obtained by using the proposed method, noted simple approximation method, and direct integration of the equation of motion. It is seen that the proposed method can significantly improve the accuracy of the analytical results compared with those obtained by using the simple approximation method. Moreover, the proposed method does not substantially increase the computational efforts.     

Seismic Performance and Modeling of a Half-Scale Base-Isolated Wood Frame Building

The concept of base isolation is a century old, but application to civil engineering structures has only occurred over the last several decades. Application to light-frame wood buildings in North America has been virtually non existent with one notable exception. This article quantitatively examines issues associated with application of base isolation in light-frame wood building systems including: (1) constructability issues related to ensuring sufficient in-plane floor diaphragm stiffness to transfer shear from the superstructure to the isolation system; (2) evaluation of experimental seismic performance of a half-scale base-isolated light-frame wood building; and (3) development of a displacement–based seismic design method and numerical model and their comparison with experimental results. The results of the study demonstrate that friction pendulum system (FPS) bearings offer a technically viable passive seismic protection system for light-frame wood buildings in high seismic zones. Specifically, the amount and method of stiffening the floor diaphragm is not unreasonable, given that the inter-story drift and accelerations at the upper level of the tested building were very low, thus resulting in the expectation of virtually no structural, non structural, or contents damage in low-rise wood frame buildings. The nonlinear dynamic model was able to replicate both the isolation layer and superstructure movement with good accuracy. The displacement-based design method was proven to be a viable tool to estimate the inter-story drift of the superstructure. These tools further underscore the potential of applying base isolation systems for application to North America's largest building type.     

Unusual Overshooting in Steady-state Response for Structure-dependent Integration Methods

It is numerically illustrated that an unusual overshooting phenomenon might occur in the solution of a forced vibration response if a structure-dependent integration method is applied to conduct the analysis, such as Chang explicit method [2002] and CR explicit method [2008]. This overshooting may occur in the steady-state response of a high frequency mode and it becomes significant as the natural frequency of the mode increases. This unusual overshooting behavior can be successfully detected by using a local truncation error derived from a forced vibration response rather than a free vibration response. A missing loading term in the difference equation for displacement increment is responsible for this unusual overshoot. It is analytically and numerically verified that the unusual overshooting behavior will automatically disappear after introducing the missing loading term into the difference equation for displacement increment.     

Effects of Vertical Load,Strain Rate and Cycling on the Response of Lead-Rubber Seismic Isolators

Lead-rubber isolators represent a valid and economic solution for the seismic isolation of bridge structures and modern manufacturing techniques make available large devices. Velocity effects on small to medium-scale isolators have been discussed by several authors (e.g., Clark et al., 1997 Clark, P. W., Aiken, I. D. and Kelly, J. M. 1997. Experimental studies of the ultimate behavior of seismically isolated structures, Berkeley, CA: Earthquake Engineering Research Center, University of California. Report No. UCB/EERC-97/18 [Google Scholar]; Thompson et al., 2000 Thomson, A. C., Whittaker, A. S., Fenves, G. L. and Mahin, S. A. 2000. “Property modification factors for elastomeric seismic isolation bearings”. In Proceedings of the 12th World Conference on Earthquake Engineering, New Zealand: Auckand. January [Google Scholar]) as well as included in reports of experimental programs (e.g., CERF, 1999 CERF. Civil Engineering Research Foundation, Summary of evaluation findings for the testing of seismic isolation and energy dissipation devices. CERF Report No. 40404. 1999.  [Google Scholar]). Only recently, however, the behavior of large devices was validated under full-scale displacements, loads, and velocities.

In this article, results obtained from an experimental investigation on the effects of axial load and strain rate on the performance of a full-scale lead-core elastomeric bearing for bridge applications, are reported. The bearing response was analyzed with particular attention to the variation of critical performance characteristics in order to produce a set of information that could be implemented in a physically motivated numerical model.

The results, in line with additional tests performed on similar full-scale bearings at the Caltrans SRMD Testing Facility at the University of California San Diego, indicate a moderate effect of the applied vertical load but a significant effect of the strain rate and cycling on all the significant response parameters. This information should be taken into account by designers, particularly when high component of velocities are associated with the expected seismic motion. A simplified numerical model is proposed for the assessment of lead-rubber bearing performance.     

Multi-Component Seismic Response Analysis – A Critical Review

Issues related to multi-components seismic response analysis are critically reviewed and their implications with respect to the current codified approaches are studied. The issues specifically addressed are: (1) the directions of earthquake forces to excite a structure when the direction of the potential epicenter is known; (2) different commonly used combination rules to obtain the critical response when responses are available in different directions; and (3) the applicability of the combination rules for elastic and inelastic analyses. Based on an extensive parametric study consisting of three-dimensional 1-, 3-, 8-, and 15- story buildings made of moment-resisting steel frames and 20 recorded earthquakes, it is observed that the principal components produce larger responses than the normal components. The 30% and SSRS rules generally underestimate the axial loads in columns. The 30% combination rule is slightly better than the SSRS rule. For both rules, the uncertainty in the estimation of the axial loads in terms of COV is very large (about 25%). The statistics obtained for axial loads and total base shear indicate that the combination rules are applicable for both elastic and inelastic cases. The critical response could be obtained for an orientation different from that of the principal components. The differences are found to be slightly greater for the scaled earthquakes producing a considerable inelastic behavior. Considering the enormous amount of efforts needed to address the directionality effect, it is believed that the responses obtained by the principal components will be acceptable in most cases; however, for critical structures the components should be rotated to obtain the critical responses.     

Seismic Evaluation of Tall Buildings Using a Simplified but Accurate Analysis Procedure

A simplified analysis procedure for evaluating the nonlinear seismic responses of tall reinforced concrete (RC) buildings is examined in this study. It is called the Uncoupled Modal Response History Analysis (UMRHA) procedure. It can be viewed as an extended version of the classical modal analysis procedure, where the nonlinear response of each vibration mode is first computed, and they are later on combined into the total response of the structure. The procedure requires the knowledge of the modal hysteretic behavior, which can be obtained from a cyclic modal pushover analysis. The responses of four tall buildings in Bangkok to distant large earthquakes are computed by this procedure and compared with those obtained from the Nonlinear Response History Analysis (NLRHA) procedure. These four buildings have different heights—varying from 20 to 44 stories, different configurations of floor plan, and different arrangement of RC walls. The comparison shows that the UMRHA procedure is able to accurately compute the story shears and story overturning moments, floor accelerations, and inter-story drifts of all these tall buildings. The required computational effort is also extremely low compared to that of the NLRHA procedure. Moreover, since the UMRHA procedure computes the response of each individual vibration mode, it provides more understanding and insight into the complex nonlinear seismic responses of these tall buildings.     

Influence of Time Step of Ground Motions on Site Effect and Structural Response Analyses for Long-Duration Earthquakes

Long-duration ground motions may be down-sampled to speed up the computational process. However, using ground motions with large time step (Δt) would inevitably bring in numerical errors. The influence of Δt on the site effect and structural response analyses was quantitatively examined in this study. The results show that the nonlinear site response method is more sensitive to a change of Δt than the equivalent-linear method. For the structural analysis, the impact of Δt is highly dependent on the magnitude of damage parameters. Thus, using input motions with Δt as 0.005 s is recommended for structures subjected to strong shakings.     

A Method for Selecting Ground Motions that Considers Target Response Spectrum Mean and Variance as Well as Correlation Structure

This study proposes a method for selecting ground motions from a ground motion library with response spectra that match the target response spectrum mean, variance, and correlation structures. The proposed method is conceptually simple and straightforward. In this method, a desired number of ground motions are sequentially selected from first to last. The accuracy and consistency of the proposed method are verified through comparisons of the ground motions selected using the proposed method with those selected using conventional methods. This study shows that the seismic responses of the frames vary according to ground motion selection and correlation structures.     

历史逻辑进程中的存在意蕴

从历史逻辑进程中存在意蕴的内在张力去理解历史和阐释存在,以其发现历史和历史存在的运行规律,多维度的探求未来视野中的存在。     

Synthesizing Broadband Time-Histories at Near Source Sites; Case Study, 2003 Bam Mw6.5 Earthquake

The main objective of this article is to synthesize the 2003 Bam earthquake. A hybrid method is proposed for synthesizing the near-fault broadband timehistories; a theoretical green's function method and a stochastic finite-fault approach for generating time histories at low and high frequencies, respectively. A genetic algorithm is developed to optimize the differences between synthesized and recorded ground motions.

The proposed technique can be used for dynamic nonlinear analysis of structures and site specific hazard analysis of the regions with lack of sufficient data and also for retrofitting the damaged structures during Bam earthquake, particularly the well-known adobe buildings of Arg-e-Bam.     

Passive Control of Steel Storage Racks for Parmigiano Reggiano Cheese under Seismic Accelerations

Recent earthquakes in Italy resulted in the collapse of steel storage racks for aging Parmigiano Reggiano cheese, damaging a huge number of cheese wheels. In order to improve the seismic performance of surviving racks with low-budget solutions, when replacement cannot be considered, we investigate the possibility of using viscous dampers that connect the racks to a surrounding structure. Time-history analyses with natural and spectrum-compatible artificial accelerograms allow one to determine the optimal damping factor that reduces both the stress in the rack and the actions transmitted to the constraining structure. Results confirm the noteworthy benefits of the proposed retrofitting system.     

陈垣在近代史学领域的开拓

2 0世纪中国实证史学家中 ,陈垣先生是当之无愧的泰山北斗。他不但以扎实的考据成果解决了大量历史疑难问题 ,而且以开创性的研究 ,拓展了宗教史、历史文献学和其他历史辅助学科等多学科领域 ,为中国史学的科学化和中国史学走向世界 ,做出了他人无可替代的贡献。