Self‐centering steel connections with steel bars and a discontinuous composite slab

Six cyclic tests were conducted on three full‐scale subassemblies to investigate the behavior of interior beam‐to‐column post‐tensioned (PT) connections. Strands were placed along each side of the steel beam web, passing through the steel column to provide precompression between the beams and a column. Top and bottom energy‐dissipating (ED) bars, passing through the column and welded to the beam, were used to increase the moment capacity and ED capacity of the connection. One of the subassemblies also had a composite concrete slab with discontinuity at the column centerline to eliminate restraint from the metal deck, reinforcement, and welded wire mesh. The objectives of this paper were to investigate the following: the durability of the connection by loading each specimen twice, the ED capacity of the ED bar, and the effects that the type of ED bar and type of composite slab have on the self‐centering behavior of the connection. The experimental results showed that: (1) the connection could sustain severe inelastic cyclic loading at least twice without strength degradation, (2) the ED capacity of the bar was much larger than that dissipated by a single AISC loading protocol, and (3) a specimen with a discontinuous composite slab, which opened freely at the centerline of the column, ensured the same self‐centering hysteretic behavior as the bare steel specimen. However, the decompression moment of the PT connection decreased significantly at each interstory drift, resulting in an early opening of a gap at the beam–column interface. Copyright © 2008 John Wiley & Sons, Ltd.     

Intrinsic and attenuative dispersion characteristics of direct P-waves in and near the source area of the 1999 MW7.6 Chi-Chi,Taiwan,earth-quake before and after the mainshock

Based on the measurement of the arrival time of maxima magnitude from band-pass filtering signals which were determined using a new Morlet wavelet multiple-filter method,we develop a method for measuring intrinsic and attenuative dispersion of the first cycle direct P-wave.We determine relative group delays of spectral components of direct P-waves for 984 ray paths from SML and ALS stations of the Taiwan Central Weather Bureau Seismic Network(CWBSN).Using continuous relaxation model,we deduce a new transfer...     

In situ experiment on retrofit of school buildings by adding sandwich columns to partition brick walls

Many significantly strong earthquakes have occurred over the years in Taiwan, which have caused tremendous damage to primary and middle school buildings; the 921 Chi‐Chi earthquake was particularly devastating. According to statistics, 786 schools (1,958 classrooms) were damaged on September 21, 1999 during this earthquake event. The devastation showed that a lack of seismic performance is a common problem for existing school buildings in Taiwan. Therefore, the retrofit of existing school buildings has become an urgent issue in the prevention of possible damage in the future. The retrofit technique of adding sandwich columns to partition brick walls is proposed in this paper, and the feasibility of the proposed method was verified by in situ pushover tests of two real school buildings, one without and one with retrofit. The experimental and analytical results show that the sandwich column itself contributes significantly to the seismic capacity of the examined school building. Moreover, the analytical results yielded conservative capacity curves when compared with the experimental results. Copyright © 2013 John Wiley & Sons, Ltd.     

The relationship among meteorological,agricultural, and in situ news-generated big data on droughts

Natural Hazards - The purpose of this study is to evaluate the effectiveness of agricultural drought risk management using news media data (NMD) by elucidating the relationships among the...     

Column restraint in post‐tensioned self‐centering moment frames

Gaps between beam‐to‐column interfaces in a post‐tensioned (PT) self‐centering frame with more than one column are constrained by columns, which causes beam compression force different from the applied PT force. This study proposes an analytical method for evaluating column bending stiffness and beam compression force by modeling column deformation according to gap‐openings at all stories. The predicted compression forces in the beams are validated by a cyclic analysis of a three‐story PT frame and by cyclic tests of a full‐scale, two‐bay by first‐story PT frame, which represents a substructure of the three‐story PT frame. The proposed method shows that compared with the strand tensile force, the beam compression force is increased at the 1st story but is decreased at the 2nd and 3rd stories due to column deformation compatibility. The PT frame tests show that the proposed method reasonably predicts beam compression force and strand force and that the beam compression force is 2 and 60% larger than the strand force with respect to a minor restraint and a pin‐supported boundary condition, respectively, at the tops of the columns. Therefore, the earlier method using a pin‐supported boundary condition at upper story columns represents an upper bound of the effect and is shown to be overly conservative for cases where a structure responds primarily in its first mode. The proposed method allows for more accurate prediction of the column restraint effects for structures that respond in a pre‐determined mode shape which is more typical of low and mid‐rise structures. Copyright © 2009 John Wiley & Sons, Ltd.     

Seasonal and spatial characteristics of seawater and sediment at Youngil Bay, southeast coast of Korea

The seasonal geochemical characteristics of the seawater and sediments and the major factors causing heavy metal contamination were investigated at the Youngil bay and the Hyungsan river estuary in the Southeast Coast of Korea, where a world-scale steel-industry complex (Pohang iron and steel industrial complex, POSCO) is located. The seasonal and spatial distribution characteristics of temperature, dissolved oxygen (DO), pH, and nutrients of the seawater were studied at 45 fixed stations, especially focusing on the river mouth area. Sediments at 27 stations were examined during winter and summer to determine the major controlling factors for the distribution of metals, using correlation matrix and R-mode factor analyses, and to evaluate the pollution status, using the modified geoaccumulation (I(geo)(')) index. Temperatures for the effluent from the POSCO located at the Hyungsan river mouth were 2-3 degrees C higher compared to other sampling areas, due to the thermal discharge from the POSCO. The DO concentration of the surface water at the Pohang old port was as low as 2-4 mg/L. In spring, the DO value at the Hyungsan river mouth was higher than 12 mg/L, by the mass multiplication of phytoplanktons at the river mouth where seawater temperature and nutrients concentrations were relatively high, resulting in the pH value of higher than 8.3. The nitrogen to phosphorus (N/P) ratios at the river mouth were 20-150 times higher compared to other areas, implying that the nitrogen loading into this semi-enclosed bay is significantly higher than phosphorus and the major nitrogen sources are not only the domestic sewage from the city but the industrial wastewater from the POSCO and other steel factories nearby. The phosphorus concentrations at the Pohang old port were shown 3-10 times higher than those at other stations, due to the inflow of pollutants generated from the nearby ships anchoring and the release of phosphate from the bottom sediment. Results from the sediment analysis showed that the major controlling factors for the distribution pattern of each metal are grain size and organic carbon (C(org)) content. Based on the factor analysis, Al, Fe, Cr, Li, and Pb were shown strongly correlated with the mean grain size (Mz), whereas Cd, Cu, Zn, and Sn with the C(org) content. Results from the fractionation of the sedimentary metals into lattice and labile fractions to characterize the mobility of sediment metals showed that the mineral lattice fraction was high in the order of Al=K>Cr>Li>Sr>Fe, while the labile fraction, which might be released to the overlying water, was in the order of Pb>Zn>Cd>Cu>Ca>Sn. Evaluation of the sediment pollution status by applying (I(geo)(')) of 13 metals showed Cd, Cu, and Zn as high as 1-3 range at the old port. Even though the overall marine pollution mainly by the world-class steel industrial complex in this semi-enclosed bay area studied does not currently pose a serious threat, due to the seawater circulation and the large influx of river discharge, the countermeasures to implement the sediments concentrated with heavy metals, especially at the old port with no seawater circulation, are still warranted for this coastal water environment.     

Viscosity-excluded formulations of 2-D river flow with a new wetting and drying algorithm

An efficient method for simulating 2-D river flow is developed in which horizontal turbulent shears are omitted from the 2-D depth-averaged momentum equations. It is shown that a pseudo-viscosity can be reproduced to take into account the lost shear action, by incorporating the vertically integrated continuity equation to the momentum equations and transforming the latter into a discrete integral form. To simulate river flows with wet and dry areas, negative water depths are allowed when solving the continuity equation. The concept of negative water depth enables us to track flow boundaries with about the same accuracy but much less effort as compared with traditional numerical methods. An optimal threshold value defining dry areas is first obtained by one-dimensional theoretical analysis and then sought by trial-and-error for two-dimensional flow simulation with tolerable node-to-node spurious oscillations, while mass is best conserved. Numerical solutions using the new procedure are compared with the one-dimensional benchmark solution of the Saint Venant equations and the experimental data from a two-stage channel. Robustness of the present approach is also tested through the study of water flow in a natural river and a hypothetical channel with several bumps.     

南黄海营养盐的平面分布及横向输运

黄海对我国是颇为重要的陆架海区,也是世界上最典型的半封闭性陆架浅海之一。它和所有陆架海区一样,是人类活动、经济开发最为集中的地带,也是陆地、海洋、大气各种过程相互作用较为激烈的地带。     

On Climate Variations and Changes Observed in South Korea

This study describes observations on possible climate changes occurring on the Korean Peninsula. We found that in large urban and industrial areas in Korea, there has been a significant increase in the annual mean temperatures according to data of the past 29 years. The increase in January temperatures was in the order of 0.8 ～ 2.4 ° C. However, in rural and marine stations, the increase in annual mean temperature was 0.6 ° C; the level of the global average. There was also an increase in precipitation: 259 mm over the recent 97 years. Observation has revealed that a month-long steady rainfall in late June and July with a quasi-stationary polar front has not occurred in recent years and has been replaced with scattered convective heavy-showers on a local scale in July and August. It is observed that the behaviour of this rainy front, `the Changma front' has brought changes to rainfall characteristics. Our results highlight the importance of the shortened rainy season. However, the amount of rainfall and the number of heavy rainfall days have increased.     

Evaluation of ACCMIP simulated fine-mode AOD and its implication for aerosol direct forcing

This study examines and evaluates simulated aerosol optical depth (AOD) and fine-mode AOD (fAOD) from the ACCMIP and CMIP5 global model archives. Satellite data nudged to AERONET data are used to construct reliable global observations of AOD and fAOD for validating the simulations. The difference in simulated global average AOD among models is of the order of a factor of 2, and the difference is even larger (～factor of 3) for fAOD. Compared to the observations, the models tend to underestimate AOD and fAOD significantly over eastern China. Another important discrepancy is that the models show larger fAOD over the Indus-Ganga Plain in summer than in winter, whereas the observations display an opposite feature. The models also overestimate the fAOD over the biomass burning regions of central Africa in DJF and underestimate the fAOD over the biomass burning regions of southern Africa in JJA. To evaluate the effect of the discrepancy between modeled and observed fAOD on aerosol direct radiative forcing, an offline radiation model is utilized. Comparing the model-fAODderived fine-mode forcing with the fine-mode forcing derived from the fAOD observation, the models tend to give too large (negative) value. This result implies that the calculated anthropogenic aerosol forcing in ACCMIP and CMIP5 models has a negative bias.