Seismic structural control using a novel high‐performance active mass driver system

To resolve difficulties encountered by current technology in structural control against earthquakes, this study proposes a novel high‐performance active mass driver (HP‐AMD) system. Based on an active mass driver system, the device is integrated with a mechanical pulley system for stroke amplification to enhance simultaneously efficiency and save power. Meanwhile, an instantaneous optimal direct output feedback control algorithm is derived alongside the hardware development. Numerical simulation is performed using a five‐storey steel frame as the object structure under the 1940 El Centro earthquake. To gain further insight into the HP‐AMD system, the effects of stroke amplification as well as damper weight on system performance are explored. Analysis results demonstrate that the proposed HP‐AMD system is a promising means to improving current active structural control techniques. Copyright © 2000 John Wiley & Sons, Ltd.     

A study on using pre‐bent steel strips as seismic energy‐dissipative devices

Buckling is usually conceived as an unstable structural behavior leading to lateral instability of axially loaded members, if not properly supported. However, a pre‐bent strip would become an excellent seismic energy‐dissipative device if it is deformed in a guided direction and range. Geometrically large lateral deformation of the steel strips in buckling leads to inelastic behavior of the material and dissipates energy as a consequence. The purpose of this study is to propose a new type of seismic damper in the form of braces based on pre‐bent steel strips. The nonlinear elastic stiffness of monotonously loaded pre‐bent strips in both compression and tension is derived. The energy‐dissipative characteristics of the proposed damping device are investigated via component tests under cyclic loads. Experimental results indicate that the force–displacement relationship of pre‐bent strips in cyclic loads exhibits mechanical characteristics of displacement‐dependent dampers. A series of seismic performance tests has been conducted further to verify the feasibility and effectiveness of using the proposed device as seismic dampers. Encouraging test results have been obtained, suggesting feasibility of the proposed device for earthquake‐resistant design. Copyright © 2008 John Wiley & Sons, Ltd.     

Surface Deformation and Seismic Rebound: Implications and Applications

An earthquake process includes pre-seismic stress accumulation, co-seismic rock rupture and post-seismic elastic and/or viscoelastic rebound. Although co-seismic and post-seismic deformations have been readily observed using the global positioning system (GPS), detecting pre-seismic stress accumulation hidden in time-series data remains challenging. This study applies the Hilbert–Huang transform to extract non-linear and non-stationary pre-earthquake deformation data from GPS records for central Taiwan. By converting the derived surface deformation into horizontal azimuths, the randomly oriented GPS-azimuths are reoriented in a similar direction several days before and after earthquakes due to loading and rebound stress, respectively. Analytical results demonstrate that the stress accumulation and release along the entire course of an earthquake process provide significant evidence supporting the seismic rebound theory. This finding would be applicable to areas with dense GPS networks and active plate interactions. Surface deformations detected by the proposed analytical technique have encouraging potential for mitigating future seismic hazards.     

Estimation of ecological high flow

Floods can destroy fish habitat. During a flood a fish has to seek shelters (refuges) to survive. It is necessary to know the maximum discharge that the fish can sustain against the strong current. Ecological and hydraulic engineers can simulate the flow condition of high flow for designing the refuge when restoring and enhancing the rivers are needed. Based on the average ratio of the mean and maximum velocities invariant with time, discharge and water level, this paper tries to introduce the concept of ecological high flow. The mean‐maximum velocity ratio can be used to estimate the mean velocity of the river. If the maximum velocity of the cross section is replaced by the maximum sustained swimming speeds of fish, the mean velocity of ecological high flow can be calculated with the constant ratio. The cross‐sectional area can be estimated by the gage height. Then the ecological high flow can be estimated as the product of mean velocity of ecological high flow multiplied by the cross‐sectional area. The available data of the upstream of the Dacha River where is the habitat of the Formosan landlocked salmon were used to illustrate the estimation of the ecological high flow. Any restoration project at Sonmou that try to improve the stream habitat can use the ecological high flow to design the hydraulic structure at suitable location to offer refuges for the Formosan landlocked salmon that is an endangered species in Taiwan Copyright © 2005 John Wiley & Sons, Ltd.     

Semi‐analytical solution for a slug test in partially penetrating wells including the effect of finite‐thickness skin

This paper presents a new semi‐analytical solution for a slug test in a well partially penetrating a confined aquifer, accounting for the skin effect. This solution is developed based on the solution for a constant‐flux pumping test and a formula given by Peres and co‐workers in 1989. The solution agrees with that of Cooper and co‐workers and the KGS model when the well is fully penetrating. The present solution can be applied to simulate the temporal and spatial head distributions in both the skin and formation zones. It can also be used to demonstrate the influences of skin type or skin thickness on the well water level and to estimate the hydraulic parameters of the skin and formation zones using a least‐squares approach. The results of this study indicate that the determination of hydraulic conductivity using a conventional slug‐test data analysis that neglects the presence of a skin zone will give an incorrect result if the aquifer has a skin zone. Copyright © 2008 John Wiley & Sons, Ltd.     

Investigating the impact of the Chi‐Chi earthquake on the occurrence of debris flows using artificial neural networks

Debris flows have caused enormous losses of property and human life in Taiwan during the last two decades. An efficient and reliable method for predicting the occurrence of debris flows is required. The major goal of this study is to explore the impact of the Chi‐Chi earthquake on the occurrence of debris flows by applying the artificial neural network (ANN) that takes both hydrological and geomorphologic influences into account. The Chen‐Yu‐Lan River watershed, which is located in central Taiwan, is chosen for evaluating the critical rainfall triggering debris flows. A total of 1151 data sets were collected for calibrating model parameters with two training strategies. Significant differences before and after the earthquake have been found: (1) The size of landslide area is proportioned to the occurrence of debris flows; (2) the amount of critical rainfall required for triggering debris flows has reduced significantly, about half of the original critical rainfall in the study case; and (3) the frequency of the occurrence of debris flows is largely increased. The overall accuracy of model prediction in testing phase has reached 96·5%; moreover, the accuracy of occurrence prediction is largely increased from 24 to 80% as the network trained with data from before the Chi‐Chi earthquake sets and with data from the lumped before and after the earthquake sets. The results demonstrated that the ANN is capable of learning the complex mechanism of debris flows and producing satisfactory predictions. Copyright © 2009 John Wiley & Sons, Ltd.     

Lessons in bridge damage learned from the Wenchuan earthquake

A strong earthquake occurred in Wenchuan County, Sichuan Province, China, on May 12, 2008. Shortly after the earthquake, the Turner-Fairbank Highway Research Center of the Federal Highway Administration, in partnership with the Research Institute of Highways, the Ministry of Communication of China, led a reconnaissance team to conduct a post-earthquake bridge performance investigation of the transportation system in the earthquake affected areas. The U.S.transportation system reconnaissance team visited the area during July 20-24, 2008. This paper presents the findings and lessons learned by the team.     

Genetic differentiation of the soft shore barnacle Fistulobalanus albicostatus (Cirripedia: Thoracica: Balanomorpha) in the West Pacific

This study examined the phylogeography of the barnacle Fistulobalanus albicostatus, which inhabits mangroves and estuarine shores in the West Pacific. Differentiation in the mitochondrial cytochrome c oxidase subunit I (COI) and 12S ribosomal RNA (12S) genes of 401 specimens of F. albicostatus was examined in samples from 16 locations in the West Pacific, ranging from Honshu to Southern China. Our results revealed that F. albicostatus comprises two major clades exhibiting a COI divergence ranging from 1.25% to 2.8%. Clade A demonstrated the widest distribution, ranging from Japan to China, and was divided into three subclades occurring in the South China Sea (A1), Okinawa (A2), and Honshu, Korea and Qingdao (A3). Clade B was determined to be endemic to Okinawa; i.e. two endemic lineages occur in this island. Thus, F. albicostatus resembles several inter‐tidal species in having clades that are endemic to Okinawan waters. Nevertheless, in contrast to the rocky inter‐tidal barnacles Tetraclita spp. and Chthamalus malayensis, F. albicostatus was not found to be separated into continental and oceanic populations, but instead is divided into northern and southern clades, probably because of the Yangtze River discharge, which limits gene flow between the northern and southern populations.     

Blast simulation of explosives buried in saturated sand

Shallow buried explosives pose a significant threat to lightweight vehicles and their onboard personnel. To date, designers of lightweight vehicles are limited in their knowledge of what occurs during the blast. The high intensity, short term loading imparted by the explosion is enormously complex and can be significantly affected by a number of parameters including the size, shape, type, detonation point and depth of burial (DOB) of the explosive and the type, density and water content of the soil. Recent advancements in numerical simulations have enabled the complex blast event to be accurately modelled by coupling Eulerian and Lagrangian analyses: the former is well suited to modelling the blast and while the latter, the structural response. Further validation of the modelling technique is considered in the current paper, which details simulations performed utilising the coupled Eulerian-Lagrangian analysis to study the blast output of explosives buried in saturated sand. These experiments varied explosive charge size, its depth of burial, the target stand-off (SO) distance and the dimensions of the target plate. The investigation concludes with a discussion of the accuracy of the numerical simulations when compared with the experimental observations.     

Parameter identification for leaky aquifers using global optimization methods

In the past, graphical or computer methods were usually employed to determine the aquifer parameters of the observed data obtained from field pumping tests. Since we employed the computer methods to determine the aquifer parameters, an analytical aquifer model was required to estimate the predicted drawdown. Following this, the gradient‐type approach was used to solve the nonlinear least‐squares equations to obtain the aquifer parameters. This paper proposes a novel approach based on a drawdown model and a global optimization method of simulated annealing (SA) or a genetic algorithm (GA) to determine the best‐fit aquifer parameters for leaky aquifer systems. The aquifer parameters obtained from SA and the GA almost agree with those obtained from the extended Kalman filter and gradient‐type method. Moreover, all results indicate that the SA and GA are robust and yield consistent results when dealing with the parameter identification problems. Copyright © 2006 John Wiley & Sons, Ltd.