Mechanisms of Control in Emergent Interorganizational Networks

The delegation of decision‐making capacity from one actor to another—known variously as authority or control—is a central phenomenon of organizational sociology. Despite its theoretical and practical significance, however, the dynamics of control within disrupted settings (such as disasters) remain poorly understood. Here, we shed light on this question by a reexamination of historical data on multiorganizational disaster response networks, using recently developed statistical methods for robust inference from error‐prone informant reports. Specifically, we test competing hypotheses about the relationship of control during the response process to the structure of interorganizational communication. We find that both the realized and normative response hierarchies are likely shaped by coordination among both nonadjacent alters and along indirect channels. Our results suggested that the communication structure of these networks is consistent with a control at a distance model of command. This article makes a substantial contribution to understanding the role of network structure in the emergence of control between organizations in disrupted settings. Additionally, our innovative approach to network inference will guide researchers in dealing with error‐prone data in their own research on policy networks.     

ELASTIC AND INELASTIC RESPONSE OF TUNNELS UNDER LONGITUDINAL EARTHQUAKE EXCITATION

This paper addresses the problem of the behaviour of underground tunnels subjected to longitudinal earthquake excitation. State-of-the-art solutions, which are relative to infinite length tunnels in the stationary case, with linear models for both the ground and the structure, are first recalled. These models are either static or dynamic; results generally indicate large strains, often incompatible with reinforced concrete structures, and small crack widths.

For finite length tunnels, in this study the dynamic solution for the linear case is developed and it is shown that maximum strain is an increasing function of the tunnel length so that, in many situations, the behavior of the lining is satisfactory also under the aspect of crack formation. When the nonlinear behaviors of the tunnel and soil are taken into account, segments of reinforced concrete tunnels, after cracking, may undergo considerable relative displacement, undesired both for serviceability and ultimate limit states. After review of the constitutive relationship for the ground, a parametric study on the crack openings for an example tunnel is presented. It is shown that crack widths computed with linear static analyses underestimate the real value for tunnels embedded in stiff grounds and that the lining longitudinal reinforcement can reduce crack width so as to cope with serviceability and ultimate limit states.     

AN ANALYTICAL RESPONSE OF CHURCH BELLS TO EARTHQUAKE EXCITATION

Occasionally there is an earthquake in the UK during which church bells are reported to have been set ringing. The motion of a medium sized church bell has been simulated and the response to earthquake records from the Parkfield earthquake of 1966 has been calculated. The response of the bells is found to depend on the mechanical properties of the bell and the tower in which it is hung. The analyses do show that for a bell to ring in an earthquake the peak ground acceleration is in the range 0.97 to 29.4 m s^?2 considerably in excess of the range indicated by the MMI VI “church and school bells ring” of 0.4 to 1.5 m s^?2. The best correlation between recognised earthquake parameters and the ringing of the bell was obtained by combining the spectral values for clapper-bell angle, obtained from the linearised set of equations, at the bells natural frequencies using the SRSS method. The values of this parameter to set the bell ringing was in the range 0.25 and 0.38 rad, compared with the actual striking angle 0.54 rad.     

COMPLEX MODE SUPERPOSITION ALGORITHM FOR SEISMIC RESPONSES OF NON-CLASSICALLY DAMPED LINEAR MDOF SYSTEM

This paper deals with a complex mode superposition method for the seismic responses of general multiple degrees of freedom (MDOF) discrete system with complex eigenvectors and eigenvalues. A delicate general solution, completely in real value form, for calculat-ing seismic time history response of the MDOF system which cannot be uncoupled by normal modes, is deduced based on the algorithms of the complex superposition method. This solution comprises of two parts which are in relation to the Duhamel integration to sine and cosine function respectively. The related term of the Duhamel integration to sine function is actually the displacement response of the oscillator with corresponding modal frequency and the damping ratio. The other can be transferred into a combina-tion of the displacement and velocity responses of the same oscillator. In order to meet the practical needs of seismic design based on code design spectra for various kinds of structures equipped by viscous dampers, the complex complete quadratic combination (CCQC) method is deduced following similar procedures such as the well-known CQC method, in which a new modal velocity correlation coefficient, together with a new modal displacement-velocity correlation coefficient are involved besides the modal displacement correlation coefficient in normal CQC formula. The new algorithm of CCQC is not only as concise as that of the normal CQC but also has explicit physical meaning. The results obtained from complex mode superposition approaches are discussed and verified in some examples through step by step integration computation under a prescribed earth-quake motion input. From these examplary analyses, it may be pointed that the CCQC algorithm normally yields conservative outcome and that the forced mode uncoupling approach has good approximation even the discussed examplary structures are strongly non-proportional.     

EUROCODE 8 DESIGN RESPONSE SPECTRA EVALUATION USING THE K-NET JAPANESE DATABASE

The Eurocode 8 (EC8) currently proposes two standard shapes for the design response spectra. Type 1 spectra are enriched in long period and are suggested for high seismicity regions. Conversely, Type 2 spectra are proposed for low to moderate seismicity areas (like France), and exhibit both a larger amplification at short period, and a much smaller long period contents, with respect to Type 1 spectra. These propositions, however, were constrained using few events mostly recorded on analogical instruments. In the present study, we use the Japanese high quality digital K-net array in order to evaluate the proposed ECS response spectra. Furthermore, all K-net stations have geotechnical characterisation. We first constructed a database of shallow events, depth less than 25 km, to avoid subduction related records. The database spans six years of seismicity from 1996 until 2003. Thus, 591 events were selected with moment magnitude between 4 and 7.3, recorded at 691 stations, giving a total of 6812 two horizontal components accelerograms. Using these records, we computed spectral ground-motion prediction equations and we used them to review the shape of the proposed EC8 spectra. In particular, we studied the plateau-PGA ratio level, the period interval where this plateau is constant, and site amplification effects. The results show surprisingly that the Type 2 rock better envelope the Japanese data. Another interesting observation is that the K-net data corresponding to all soil classes are rich in short periods around 0.1 s. This characteristic has not been observed in other worldwide databases. Normalised empirical predictions show a widening of the plateau as the soil conditions degrade. This suggests that the Type 2 EC8 spectra do not cover enough the long periods for EC3-soil classes C, D and E. Finally, the computed ground-motion prediction equations show that the peak ground acceleration (PGA) is nearly invariant to the soil conditions. Soil effects are mainly seen in the shape and plateau level.     

VERTICAL EARTHQUAKE GROUND MOTION RECORDS: AN OVERVIEW

Recent research clearly shows the importance of including the vertical component of earthquake ground motion in seismic analysis and design. In addition, pioneering studies [e.g., Elnashai and Papazoglou (1997)] have explored and documented the characteristics of available near-field vertical ground motion records. As a follow-up, this paper complements earlier studies, and investigates additional far-field records and available downhole array vertical motion records. A total of 111 free-field strong motion records (from California) and available downhole array records are employed. Compared to near-field records, far-field records generally contain more energy at longer periods. Based on the available data, response spectra are presented for near-field and far-field records respectively. The currently scarce downhole-array vertical motion records show that significant amplification may occur within the top 10-20 m soil layers. A simple one-dimensional (ID) vertical wave propagation model did not appear adequate for modelling the observed downhole array response. In using such a simplified model, very high viscous damping in the range of 15-25% was needed to match the recorded downhole vertical response, even for small tremors. Additional data and research are required [Beresnev et al., 2002] towards the development of a rational vertical motion site response analysis procedure.     

GENERATION OF ARTIFICIAL EARTHQUAKE MOTION RECORDS USING WAVELETS AND PRINCIPAL COMPONENT ANALYSIS

In the last century alone two to three million people died in earthquakes; More than 240 000 perish in Tangshan earthquake in China, 20 000 in the Izmit [Ikeya, 2004] 50 000 in India Bhuj earthquake, 100000 in Sumatra and 90000 in Pakistan earthquakes. Earthquake engineering has progressed to the stage where it is now computationally practical and desirable to perform a dynamic analysis of most civil engineering structures. Such an analysis requires the engineer to create an accurate analytical model of the structures as well as prescribe an earthquake input excitation. The design earthquake input excitation for the site under consideration is usually prescribed in the form of response spectra or in the form of an ensemble of artificial earthquake acceleration time histories. There is every need for generating artificial accelerograms since recorded accelerograms are very limited at site. This paper proposes five neural network based models for the generation of artificial earthquake and response spectra using wavelet transforms (WT) and principal component analysis (PCA) where the recorded accelerograms are limited at site of interest. The proposed model is compared with Lee and Han's model. The data for 25 earthquakes are taken for training and 4 for testing. Just like response spectra, this is also a convenient way of obtaining the design solution to a structural dynamics problem and is certainly an important tool.     

EVALUATION OF CAPACITY SPECTRUM METHOD FOR ESTIMATING THE PEAK INELASTIC RESPONSES

The accuracy of the capacity spectrum method (CSM) depends on the precise estimation of equivalent period and damping ratio as well as the modification of the demand spectrum. In this paper, the CSM provided in ATC-40 for estimating the peak inelastic responses is evaluated. First, the effect of equivalent period and damping ratio estimation on the accuracy of the CSM is assessed. Analyses results indicate that the difference between estimation methods is large when the structural nonlinearity is large, but becomes negligible as the hardening ratio increases. Next, the reduction factors provided in ATC-40 and Eurocode are evaluated. It is found that the acceleration responses obtained using the factor of Eurocode is closer to the actual ones than those obtained using the factors of ATC-40. Finally, the demand spectrum is constructed using the peak absolute acceleration and pseudo-acceleration. The results obtained using the peak absolute acceleration is found to be generally larger than those obtained using the pseudo-ones. Since the original CSM generally underestimates the response, the use of peak absolute acceleration in the construction of demand spectrum produces the response relatively closer to the exact one. However, the use of peak absolute acceleration overestimates the response more when the original CSM overestimates the response.     

TORSIONAL EFFECTS IN THE PUSHOVER-BASED SEISMIC ANALYSIS OF BUILDINGS

The general trends of the inelastic behaviour of plan-asymmetric structures have been studied. Systems with structural elements in both orthogonal directions and bi-axial eccentricity were subjected to bi-directional excitation. Test examples include idealised single-storey and multi-storey models, and a three-storey building, for which test results are available. The response in terms of displacements was determined by nonlinear dynamic analyses. The main findings, limited to fairly regular and simple investigated buildings, are: (a) The amplification of displacements determined by elastic dynamic analysis can be used as a rough, and in the majority of cases conservative estimate in the inelastic range, (b) Any favourable torsional effect on the stiff side, which may arise from elastic analysis, may disappear in the inelastic range. These findings can be utilised in the approximate pushover-based seismic analysis of asymmetric buildings, e.g. in the N2 method. It is proposed that the results obtained by pushover analysis of a 3D structural model be combined with the results of a linear dynamic (spectral) analysis. The former results control the target displacements and the distribution of deformations along the height of the building, whereas the latter results define the torsional amplifications. The proposed approach is partly illustrated and evaluated by test examples.     

INSTANTANEOUS OPTIMAL CONTROL FOR SEISMIC ANALYSIS OF NON-LINEAR STRUCTURES

In this paper, an effective active control algorithm is developed for the vibration control of non-linear structural systems subjected to earthquake excitation. It is an attempt to include the non-linear characteristics of the structural behaviour throughout the entire analysis (design and validation), accounting for the eventual cumulative structural damage and energy dissipation. This is a very important factor since, in current design practice, structures are assumed to behave nonlinearly when subjected to strong ground motion. The proposed algorithm focusses on the instantaneous optimal control approach for the development of the control algorithm where the nonlinearities are brought into the analysis through a non-linear state vector and a non-linear open loop term. A performance index that is quadratic in the control force and in the non-linear states and is subjected to a non-linear constraint equation, is minimised at every time step. The effectiveness of the proposed non-linear instantaneous optimal control (NIOC) strategy is critically evaluated in comparison with currently available active control techniques. Numerical simulation results indicate that the proposed approach provides a significant reduction of the peak response quantities, such as maximum response deformation, maximum response acceleration, ductility of the system, associated with a reduced maximum control force.