Capacity Design of Coupled RC Walls

Capacity design aims to ensure controlled ductile response of structures when subjected to earthquakes. This article investigates the performance of existing capacity design equations for reinforced concrete coupled walls and then proposes a new simplified capacity design method based on state-of-the-art knowledge. The new method is verified through a case study in which a set of 15 coupled walls are subject to nonlinear time-history analyses. The article includes examination of the maximum shear force in individual walls in relation to the total maximum shear force in the coupled wall system, and subsequently provides recommendations for design.     

Predicting the Seismic Response of Capacity-Designed Structures by Equivalent Linearization

An equivalent linearization procedure is developed for predicting the inelastic deformations and internal forces of capacity-designed structures under earthquake excitations. The procedure employs response spectrum analysis, and mainly consists of the construction of an equivalent linear system by reducing the stiffness of structural members that are expected to respond in the inelastic range. These members are well defined in structures designed with capacity principles. Maximum modal displacement demands of the equivalent linear system are determined either from the equal displacement rule, or from independent nonlinear response history analysis of SDOF systems representing inelastic modes.

Predictions obtained from the proposed equivalent linearization procedure are evaluated comparatively by using the results of nonlinear response history analysis as benchmark, linear elastic response spectrum analysis and conventional pushover analysis. The deformations and capacity controlled actions of a 12-story symmetrical plan concrete frame and a 6-story unsymmetrical plan concrete frame are obtained by each method under 96 strong ground motions. It is observed that the proposed procedure results in better accuracy in estimating the inelastic seismic displacement response parameters and capacity controlled forces than the other two approximate methods.     

SOIL DAMPING FORMULATION IN NONLINEAR TIME DOMAIN SITE RESPONSE ANALYSIS

Nonlinear time domain site response analysis is used to capture the soil hysteretic response and nonlinearity due to medium and large ground motions. Soil damping is captured primarily through the hysteretic energy dissipating response. Viscous damp-ing, using the Rayleigh damping formulation, is often added to represent damping at very small strains where many soil models are primarily linear. The Rayleigh damping formulation results in frequency dependent damping, in contrast to experiments that show that the damping of soil is mostly frequency independent. Artificially high damp-ing is introduced outside a limited frequency range that filters high frequency ground motion. The extended Rayleigh damping formulation is introduced to reduce the over-damping at high frequencies. The formulation reduces the filtering of high frequency motion content when examining the motion Fourier spectrum. With appropriate choice of frequency range, both formulations provide a similar response when represented by the 5% damped elastic response spectrum.

The proposed formulations used in non-linear site response analysis show that the equivalent linear frequency domain solution commonly used to approximate non-linear site response underestimates surface ground motion within a period range relevant to engineering applications. A new guideline is provided for the use of the proposed formulations in non-linear site response analysis.     

Modulation of the solar daily geomagnetic variation

A least squares spectral analysis is used to investigate cyclic and seasonal changes of the harmonic coefficients of the solar daily and semi-diurnal variation over the 24 year interval from 1 January 1960 to 31 December 1983 at a single magnetic observatory (Dourbes, Belgium). As a preparation for the treatment of other long runs of observations a statistical method is presented to combine the output of the spectral and harmonic analyses of a group of stations. The annual means of the Fourier coefficients are significantly correlated with the solar cycle. The spectra show peaks at periods of 11 years, 1 year, 6 months and 27 days, which entails an important amplitude and phase modulation of the daily and semi-diurnal variation. No simple relationship between the peaks in the broad solar rotation band can be proposed.     

Soil-Structure Interaction on a Shallow Rigid Circular Foundation: SH Wave Source from Near-Field Excitations

A closed-form wave function analytic solution is presented in this article regarding the two-dimensional scattering and diffraction of a flexible wall sitting on a rigid shallow circular foundation embedded in an elastic half-space that is activated by a nearby anti-plane line source such as a blast caused by underground construction or mineral exploration or a near-field fault rupture, using similar methodology as the other paper in a series [Lee and Luo, 2013]. These wave propagation influences, although often treated as a transient process, may be simulated as linear combinations of steady-simple harmonic responses as studied in this article. Ground surface displacements spectra for wide-band of incident wave frequencies are calculated. Based on the spectra obtained, the dependence of near-field ground displacements are shown with respect to the rise-to-span ratio of foundation profile, frequency of incident waves, distance of source from the foundation, and mass ratios of various media (foundation-structure-soil). The screening effect of rigid foundation upon ground motions behind grazing incident waves is also presented.     

Inelastic Displacement Demand of Strength-Degraded Structures

This article presents findings from parametric studies involving nonlinear time-history analyses of inelastic systems with and without strength degradation. Results showed that estimates based on the equal-displacement and equal-energy propositions can be exceeded significantly by the inelastic displacement demands in the acceleration and velocity-sensitive regions of the response spectrum. The displacement demand behaviour is sensitive to the strength degradation and the frequency properties of the ground shaking. With a modest strength reduction factor of 2, the inelastic displacement demand would typically be constrained by the Peak Displacement Demand as indicated on the elastic displacement response spectrum for 5% damping.     

Influence of Frequency Content and Peak Intensities in the Rocking Seismic Response of Rigid Bodies

The rocking response of a family of bodies given by its width and height due to synthetic and recorded strong ground motions is presented; this allow us to identify the main parameters that govern their response: peak acceleration and velocity, dominant frequency, and acceleration time-history. Recorded strong ground motions were scaled to the same peak acceleration and also to the same peak velocity to analyze the effect of both parameters in the response of rigid bodies. These three parameters were used to build an equation to obtain the height/width overturning plots. The proposed equation was tested for many well-known strong ground motions and the results were compared to other methods shown to be more accurate. This parametric equation does not need iterations or numerical approximations to be solved and can provide engineers, in a very practical way, minimum design requirements or particular specifications to protect non structural elements.     

Observational technique and parameter estimation in plasma line spectrum observations of the ionosphere by chirped incoherent scatter radar

With the 430 MHz incoherent scatter radar facility at the Arecibo Observatory, the plasma line spectrum has been measured with a linearly frequency modulated or ‘chirped’ pulse. On reception the signal is demodulated (‘dechirped’). The paper describes the experimental set-up and the parameter estimation for day-time ionosphere observations. Using a non-linear least squares fit it is possible to determine the linear and quadratic coefficients of a locally parabolic plasma line frequency versus height profile. The strength of the plasma line and the point of tangency of the locally parabolic plasma line frequency profile can be determined very accurately. In measurements of the day-time ionosphere the plasma line was found to be enhanced by about 70 times over the thermal equilibrium level.     

Displacement-Based Seismic Design Approach for Prestressed Precast Concrete Shear Walls and its Application

ABSTRACT

Prestressed precast concrete shear wall (PPCW) is a new kind of shear wall utilizing a combination of unbonded post-tensioning steel and mild steel for flexural resistance across horizontal joints. A simple procedure of direct displacement-based design approach for PPCW based on concept of inelastic design spectra is proposed. Section design is then carried out according to base overturning moment. A detailed design example demonstrating a step-by-step application of the design procedure is also provided. Nonlinear time-history analysis verified that this approach is applicable to control the target displacement to the performance acceptable limit.     

SLIDING MODE CONTROL OF BUILDING FRAMES UNDER RANDOM GROUND MOTION

A sliding mode control theory is presented to control the response of building frames to predominant frequency components of the random ground motions. The control algorithm is derived based on a sliding surface which is a function of a state vector containing the structural displacements and velocities and variables that dictate the predominant frequency components of the excitation. Three control mechanisms are employed to control the response of the building frame namely, (1) active mass damper (AMD) placed at the top storey of the building, (2) an actuator placed at a storey level and, (3) an actuator placed at a storey level along with a tuned mass damper (TMD) situated at the top storey level. Responses obtained by the proposed control strategy are compared with those obtained by the linear feedback and feedforward-feedback control strategies (conventional control strategies). Also, they are compared with those obtained by the sliding mode control strategy that considers in its state vector only structural displacements and velocities. It is shown that the proposed control strategy generally performs better than other control strategies in the higher range of control forces. For the lower range of control forces, conventional control strategies are more effective.     

A Data-based Probabilistic Approach for the Generation of Spectra-Compatible Time-History Records

A data-based procedure is presented to develop spectra-compatible time-history records that are based on the dominant probabilistic features of an ensemble of records corresponding to the non-stationary stochastic phenomena of interest (e.g., earthquakes, wind loads, etc). The method requires a statistically significant collection of time-history records that are used to construct the associated covariance kernel of the random process. Subsequently, orthogonal decomposition approaches are used to determine the dominant eigenvectors of the covariance matrix, and these vectors are then linearly combined, with an adjustable amplitude-scale and phase-shift, to determine, via a nonlinear optimization scheme (employing a combination of stochastic and deterministic approaches), a time-history record that matches the target spectrum within a specified error bound. The utility of this approach is demonstrated with several collections of earthquake records from different regions of the world (Japan, Los Angeles, and San Francisco) that are then used to match various spectra widely used in seismic design applications. Issues that impact the selection of the bases vectors to construct the optimum spectra-matching record are discussed, and guidelines are provided for successful implementation of the proposed methodology.     

Rule of Law: A Comparison between Ancient Persia and Ancient Greece

The ancient Persian empires are denoted as despotic, practicing arbitrary rule while Greece, Persia's archrival during the sixth to fourth century BC, exercised rule of law. This paper uses a contract theory framework to analyze some of the geographical and environmental underpinnings of the existence of rule of law in the city-states of ancient Greece and its absence in Persia. I discuss the role of geographical conditions of land (open plains versus mountains), population pressure, proximity to the sea and form of trade (overland versus overseas) as factors conducive to rule of law in the city-states of ancient Greece and to despotism in ancient Persia. Specifically, the role of trade via land in Persia prior to the fifth century BC is compared to the role of sea trade (alongside with piracy) in ancient Greece. I argue that in ancient Persia monarchs could tax or expropriate much of the gains from overland trade, preventing the accumulation of an independent form of wealth by merchants. In Greece, sea trade alongside the practice of piracy led to gains from trade that could not be easily expropriated by the monarchs and acted as a balancing force vis-à-vis the power of the monarchs, creating a basis for rule of law in the Greek city-states.     

Optimal Control of Structures under Earthquakes Including Soil-Structure Interaction

It is well known that the soil-structure interaction (SSI) changes the dynamic response of a structure supported on flexible soil. The analysis of optimally controlled SSI systems has certain difficulties due to the nature of the SSI and the optimal control problem. In this paper, a two-step iteration-based numerical algorithm is proposed to handle optimally controlled SSI systems under earthquakes. First, the optimal control forces are obtained by using a fixed-base system. Then, the optimal control forces are converted to the frequency domain by the Fourier transform technique to be used in the equations of the SSI system. The lateral displacement and the rocking of the foundation are obtained from the equations of the SSI system containing the optimal control forces in the frequency domain. The lateral displacement and rocking of the foundation are then converted to the time domain by the inverse Fourier transform technique, and the lateral accelerations and the rocking accelerations of the foundation are obtained by the forward finite difference method. During the second step, the optimal control forces are calculated again by using the lateral acceleration and the rocking acceleration of the foundation along with the earthquake ground motion. Using the method explained above, the optimal control forces obtained in the time domain are used in the equations of the soil-structure system from which the behavior of foundation and structure is obtained. In the final section of the paper, a numerical study is conducted for a controlled structure supported on flexible soil.     

Rational Choice Theory and the Evaluation of Public Policy

The dominance of rational choice-inspired models of policy development, implementation, and evaluation has grown dramatically over the years as a challenge to traditional, pluralist politics. In this article, we analyze the theoretical foundations of the rational choice perspective and its criticism of pluralist politics. We explore the values inherent in the rational choice perspective and suggest that they feed into growing public cynicism about government and lead to a conservative policy agenda of less government. We then develop an unusual argument that the very tools of rational choice analysis and its values actually produce far more government involvement than expected. by examining school voucher programs. We conclude by making a case for pluralist politics as a more appropriate means for addressing the concerns of classical liberals and others about excessive government intrusion.     

An Assessment of the Space-Time Differential Model for Aggregate Trip Behavior to Planned Suburban Shopping Centers

Aggregate trip behavior to planned suburban shopping centers is studied in terms of changes in trip distance and shopping time within a framework of trip frequency, center scale, and consumer mobility. Such changes are expressed by a second-order differential equation. The assumed shopping strategy is that consumers accelerate the shopping trip cycle by minimizing trip distances. This can be solved to provide theoretical norms to assess against an exploratory data set compiled from 2,810 surveys undertaken in 1980/82 and 1988/89 over a range of centers. The analysis shows a significant relationship between the gravity coefficient and trip frequency. The samples are tested for periodicity using Fourier analysis. The results show that “small” centers are more likely to exhibit periodic behavior. “Large” centers do not follow this hypothesis. Both the gravity coefficient and trip frequency are shown to be quadratic functions of center size. The nonlinearity may be introduced by the agglomeration of shopping opportunities at larger centers. A critical value for “small-” and “large-”center behavior is determined from the minimum points of these distributions. A second equation from classical diffusion analysis is tested for “large” center behavior, where consumers accelerate spatial choice through a time minimization strategy. The results suggest that this strategy occurs at the midrange specialty center during the afternoon of the pre-Christmas rush rather than at large regional centers. The empirical characteristics of the three types of trip behavior are summarized.     

Congress and Back Seat Driving

Few pieces of legislation in the realm of foreign policy decisionmaking have greater potential effect or are more controversial than the War Powers Resolution. The Resolution was intended originally to create greater leverage for Congress over executive use of military force. In this effort, it is widely believed that the Resolution has been ineffective. This paper uses an information theoretic model to examine the War Powers Resolution. Results of the modeling process allow for two general assertions. First, the model suggests that the Resolution is an optimal choice of procedure by the legislature. In other words, the War Powers Resolution is better for Congress than its alternatives. Second, the information theoretic approach used here seems to coincide with an anecdotal history of the war powers debate better than do alternative explanations. Indeed, the analysis helps to explain why war powers legislation was not considered seriously sooner. Though criticism of the War Powers Resolution has its merits, claims for a variety of alternative procedural systems may be open to challenge. Those wishing to establish mechanisms for curtailing executive adventurism abroad may find it more rewarding to focus efforts on the budgeting process or on the reduction of military force structures.     

Site Classification System and Site Coefficients for Shallow Bedrock Sites in Korea

Recent studies have shown that the site coefficients obtained from site response analyses of Korean soil sites are significantly different from those specified in the current Korean seismic code, especially in the short-period portion of site response. This difference is mainly attributed to the shallow bedrock conditions (bedrock depth usually less than 30 m) in Korea. This study proposes a new site classification system and site coefficients for shallow bedrock sites based on site response analyses of more than 300 sites. The proposed site classification scheme and site coefficients proposed in this study are an improvement over the current seismic code and previous studies.     

Testing for the Law of One Price and Identifying Price-Leading Markets: An Application to Corn Markets in Benin

A data-determined method is proposed to test for the law of one price as a long-run equilibrium condition and to identify which markets in a network of spatially dispersed commodity markets quote the reference price. The method consists of supplementing Johansen's FIML cointegration procedure with a permanent-transitory decomposition and rules of inference in linear time-series models with unit roots. As an example, we apply our method to prices of six corn markets in Benin. We find that the law of one price holds in the long-run. It appears that two rural markets quote the reference price: their prices adjust fastest towards the permanent change induced by the common stochastic trend.     

Effect of Nonlinearity of Frame Buildings on Peak Horizontal Floor Acceleration

Using representative numerical models of eight code-designed steel moment-resisting frame buildings and several ground motions, time-history analyses are performed and a critical evaluation of Peak Horizontal Floor Acceleration (PHFA) demands is conducted. The frames are modeled alternatively as linear and nonlinear systems to isolate the effect of building nonlinearity on PHFA. In most cases, PHFA is reduced when nonlinear behavior of a building is considered; however, in some cases, significant amplification of PHFA is observed. Results from the numerical study provide insight into the trend of modal response modification factors presented taking ground motion spectral shape into account.     

SEISMIC DESIGN REGULATION CODES: CONTRIBUTION OF K-NET DATA TO SITE EFFECT EVALUATION

The purpose of this study is to compare the site effect section of building codes (EC8 and UBC97) with the set of data provided by the Kyoshin network. In order to obtain a set of site coefficients and spectral shapes, we have first deduced an attenuation law for both horizontal and vertical motion. Site conditions are represented by the shear velocity averaged over the upper 30 m (V _s ³⁰). Our site classification (4 categories similar to those proposed in the new ECS and the UBC97) is based on borehole investigations at every station. This classification has permitted to distinguish clearly four response spectra which demonstrates the efficiency of V _s ³⁰ as characterising site conditions. Our law is then used to test site coefficients and spectral shapes of building codes ECS and UBC97. Concerning spectral shapes and site coefficients, our results are found to be in good agreement with EC8 and UBC97 only if category B (400<V _s ³⁰<800 m/s) is taken as reference. We also conclude that a site which is characterised as “rock” on geological criteria can not generally be classified in category A (V _s ³⁰>800 m/s). This suggests that classification in category A should be based only on field measurements. Concerning vertical motion, our analysis of the K-NET data shows that the ratio av/ah (vertical peak ground acceleration over horizontal peak ground acceleration) is between 0.50 and 0.68.