This paper introduces a novel type of buckling restrained braces (BRBs) called core-separated assembled BRBs (CSA-BRBs). These braces are comprised of two single BRBs that are confined by lightweight ...concrete-infilled tubes, which are longitudinally connected by two continuous webs. The CSA-BRBs utilize materials more efficiently by increasing the height of the webs to create a large inner cavity, leading to an economical design. This paper predicts the threshold of the restraint ratio of CSA-BRBs approximately. This is achieved by assuming that the maximum moment resulting from applied loads at mid-height is less than the moment-bearing resistance that is conducted according to the outermost fiber of the external restraining section reading yielding. Elastic-plastic numerical analysis is conducted using FEM with beam elements for CSA-BRBs that are subjected to both monotonic and cyclic axial loads. The load resistance, hysteretic performance, and failure mechanism of CSA-BRBs are investigated by varying their restraining ratios. It is recommended that the restraint ratio threshold of CSA-BRBs under monotonic axial compression is used as a bearing type and the restraint ratio threshold of CSA-BRBs under axially compressive-tensile cyclic loads as an energy-dissipation type. This method provides a complete design for CSA-BRBs.
The simulation abilities of the Coupled Model Inter-comparison Project Phase 5 (CMIP5) models to the arid basin (the Tarim River Basin, TRB) and humid basin (the Yangtze River Basin, YRB) were ...evaluated, determining the response of precipitation to external changes over typical basins. Our study shows that the future temporal and spatial variation characteristics of precipitation are different in different regions with the CMIP5. The annual and seasonal changes in precipitation were analyzed for the RCP2.6, RCP4.5 and RCP8.5 during 2021~2100 compared to those during 1961~2005. Precipitation shows an increasing trend in the TRB, but which decreases and then increases in the YRB, with a turning point in the middle of twenty-first Century. The ranges in annual precipitation increase with the increase in the scenario emissions in the future. Note that the Tarim River Basin is more vulnerable to the impact of emissions, especially for annual or spring and winter precipitation. Based on the uncertainty of CMIP5 data, the links between future precipitation changes and the elevation and relief amplitude were evaluated. The change of precipitation decreases with elevation, relief amplitude in the TRB, while it increases with elevation but decreases with relief amplitude in the YRB.
Unstiffened steel plate walls (SPWs) are prone to buckling in practical engineering and will invariably be subjected to vertical loads. The use of stiffeners can improve the buckling behavior of thin ...plates. Considering the effect of the torsional stiffness of C-shaped stiffeners, the elastic buckling of the diagonally stiffened steel plate wall (DS-SPW) under combined shear and non-uniform compression is investigated. The interaction curves for the DS-SPW under combined action are presented, as well as a proposed equation for the elastic buckling coefficient. In addition, the effects of the stiffener’s flexural and torsional stiffness on the elastic buckling stress were investigated, and the threshold stiffness formulae were proposed. The results show that the interaction curve of the DS-SPW under combined shear and non-uniform compression is approximately parabolic. The critical buckling stress of the DS-SPW can be increased by increasing the stiffener’s torsional-to-flexure stiffness ratio and the non-uniform compression distribution factor, while the buckling stress can be decreased by increasing the non-uniform compression-to-shear ratio. Simultaneous action of shear and axial compression will increase the threshold stiffness by approximately 40% when compared to the plate under pure shear action. Therefore, the safety threshold stiffness formula is suggested, considering the combined action of shear and non-uniform compression.
The paper proposes partially connected steel plate shear walls, in which the infill plates and frames are connected by discretely distributed fish plates at the corners and at the centers. The high ...lateral resistance of a steel plate shear wall has led to its widespread use in the design of structural shear resistance. In this paper, finite element models of the partially connected steel plate shear walls are established by the finite element method, and the effect of the different partial connections on the shear strength is firstly investigated. Moreover, the variation of the shear strength with the plate-to-frame connectivity ratio is analyzed numerically, and the effect of the connectivity ratio on the development of the tensile field is studied. Based on the numerical analysis results, the effect of the connectivity ratio on shear strength is evident at low levels. When the connectivity ratio is over 80%, the shear strength of the partially connected steel plate shear wall can reach 95% of that of the fully connected steel plate shear wall. When the connection ratio is at a low level, the advantages of the central connection on the shear strength of the structures are higher than those with corner connections. Furthermore, the fitting formula for the partially connected steel plate shear wall is obtained by changing the connectivity ratio and width-to-height ratio of the examples, which can predict the shear capacity of the partially connected steel plate shear wall with different partial connections.
The Tarim River Basin (TRB) is an extremely arid area in China, suffering from dry climate and intense human activities, which have brought about significant changes in ecological processes and then, ...led to serious ecological vulnerability (EV). This study proposes an assessment framework to evaluate EV and analyze its dynamic change in the TRB during 2005–2015. An integrated method is developed with the Fuzzy Analytic Hierarchy Process (FAHP) and the Pressure-State-Response (PSR) framework, which highlights impacts of nature and anthropogenic interference on the ecology. Specific management strategies are put forward based on the spatial recognition of ecologically vulnerable areas in the TRB. The EV is divided into four vulnerability levels including Light I, Medium II, Heavy III and Very heavy IV. Results show that the average EV is at Heavy III vulnerability level in the TRB in the last 2005–2015, and there has been an increasing trend in EV, which even has come up to the Very heavy IV vulnerability level in the year 2013–2015. As a whole, the EV displays a high-to-low gradient from east to west during the study period. Heavy III and Very heavy IV vulnerability levels, distributed in the East, mainly in the mainstream areas with characterization of frequent human interferences, tend to increase persistently. In contrast, Light I vulnerability level, mainly in the west source areas, shows a significant decline after 2010. Based on the results, some suggestions targeted at different vulnerable areas were proposed to help restore ecological environments by integrating legal managements with public efforts. The proposed methodology, reflecting the nature and human interaction on the EV is of practical use for the ecological restorations in the TRB.
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•An integrated indicator system for specially assessment of ecological vulnerability (EV) is established.•The EV was largely aggravated in the Tarim River Basin (TRB) during 2005–2015.•The Heavy III level dominates throughout the TRB with a low-to-high spatial distribution from west to east.•Ecological restorations with different use control for different partitions are proposed.
With large-scale developments, the Manas River Basin (MRB) is in an extreme imbalance especially in land use, thus causing a series of ecological problems. A reliable dynamic ecological risk ...assessment is expected to provide useful information for the economic development. Through coupling spatial Cellular Automaton-Markov (CA-Markov) model and Landsat satellite images in 2000, 2008 and 2016, we forecasted the land use maps in 2024 and 2032. Based on the ecological risk model, we evaluated the ecological risk at landscape level from 2000 to 2032. More importantly, an improved evaluation of ecological risk was proposed based on terrain gradients and the correlation between terrain niche index (TNI) and future ecological risk was analyzed. The results showed that the artificial oases and urban are expanding, while the natural grassland is shrinking. Corresponding to the rapid development stage and stable consolidation stage, farmland will be followed by a slower increase (2016–2032) after a rapid increase (2000–2016), and water decreases first but then is projected to recover. As the overall spatial diversity increasing, the ecological risk in the whole basin is growing, especially in grassland. Compared with the stable critical state in artificial landscape, the future ecological risks in natural landscape tend to increase due to the cumulative effects of human activities. Also, we found that the great ecological risk mainly happens in “high altitude and complex terrain” or “low altitude and flat terrain” areas. The future ecological risk in medium terrain niche index (TNI) gradient will increase, while it will decrease in the lowest. Above all, the proposed framework can do well in forecasting ecological risk at landscape level, and can help simply infer the changes of ecological risk based on terrain.
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•Land use evaluation and projection with CA-Markov•Artificial oases and urban are expanding, the natural grassland is shrinking.•Overall ecological risk has risen with increasing spatial diversity.•Future ecological risk will increase in the medium terrains, but decrease in the low.
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•The lag time of cumulative ecohydrological response and the growth rates of cumulative effects were determined.•Curves of cumulative ecological response were plotted to make the ...cumulative response quantifiable.•A cumulative ecological water conveyance volume (CEWCV) model was established via the Four-Parameter Logistic Model.•The cumulative ecohydrological response laws were revealed by spatiotemporal variations of groundwater and vegetation.
As a main anthropogenic hydrological process in arid areas, an ecological water conveyance project usually shows profound effects on the hydro- and bio-systems in the region. In order to explore novel methods and theories to assess cumulative effects of human activities on an ecological system, this study presents a method of cumulative ecohydrological response curves to quantitatively evaluate the effects of an ecological water conveyance project which the lag time of the cumulative response and growth rates of the cumulative effects can also be identified. With the lower Tarim River, Northwest China as a case study, we analyzed the spatiotemporal variations of the cumulative ecohydrological response in terms of two indicators, groundwater depth and vegetation coverage, based on the eighteen phases of the ecological water conveyance project. The cumulative ecohydrological response to the ecological water conveyance project was evaluated with an integrated methodology of combining the Spearman empirical statistical model, the dimidiate pixel model and the Kriging Interpolation. A cumulative ecological water conveyance volume model was further built using the Four-Parameter Logistic Model to make the cumulative response quantifiable. The cumulative quantified scheme can give a keen insight into the cumulative effects of hydrological processes under the influence of human activities.
The cumulative ecohydrological response shows that: 1) the cumulative effects reflected by the positive correlation among the cumulative ecological water conveyance volume, the groundwater depth and the vegetation coverage, 2) there existed time lags in the cumulative time response, 80-day lag for groundwater and 4–7 years lag for vegetation, 3) and the cumulative spatial response of groundwater depth and vegetation was deduced. Our results suggest that the ecological water conveyance volume can be lowered to 0.5 × 108–1.5 × 108 m3 at each period. With a reasonable water conveyance strategy, the cumulative effects can reach the groundwater depth at 3.6885 m–3.7651 m and the vegetation coverage at 0.1339–0.1374 after the 5 phases of water infusion in consecutive years.
Saltwater intrusion is an essential problem in estuaries that can threaten the ecological environment, especially in high-salinity situations. Therefore in this paper, traditional multiple linear ...regression (MLR) and artificial neural network (ANN) modeling are applied to forecast overall and high salinity in the Lower Scheldt Estuary, Belgium. Mutual information (MI) and conditional mutual information (CMI) are used to select optimal driving forces (DFs), with the daily discharge (Q), daily water temperature (WT), and daily sea level (SL) selected as the main DFs. Next, we analyze whether applying a discrete wavelet transform (DWT) to remove the noise from the original time series improves the results. Here, the DWT is applied in Signal-hybrid (SH) and Within-hybrid (WH) frameworks. Both the MLR and ANN models demonstrate satisfactory performance in daily overall salinity simulation over the Scheldt Estuary. The relatively complex ANN models outperform MLR because of their capabilities of capturing complex interactions. Because the nonlinear relationship between salinity and DFs is variable at different locations, the performance of the MLR models in the midstream region is far inferior to that in the downstream region during spring and winter. The results reveal that the application of DWT enhances simulation of both overall and high salinity in this region, especially for the ANN model with the WH framework. With the effect of Q decline or SL rise, the salinity in the middle Scheldt Estuary increases more significantly, and the ANN models are more sensitive to these perturbations.
Future changes projected in surface temperature and precipitation behave differently in different regions or watersheds and vary greatly in space and time, even within the same region under climate ...change. This study aims to detect and compare differences in the climatological characteristics in response to climate change in arid and humid areas. Based on the CN05.1 reanalysis gridded dataset (high-resolution climate model validation launched by China Meteorological Administration) and output from the Coupled Model Inter-comparison Project Phase 5 (CMIP5), the projected responses of temperature and precipitation to climate change under three representative concentration pathways (RCP2.6, RCP4.5, and RCP8.5) in the arid basin (the Tarim River Basin, the TRB) and the humid basin (the Yangtze River Basin, the YRB) were characterized. Our results show that the swings of annual temperature and precipitation will extend with the rising emission scenarios in the future, while those are more vulnerable in the TRB. The topography-related changes of temperature and precipitation were further evaluated to explore the uncertainty. The elevation-dependent warming (EDW) may be weakened but still hold in the future at the watershed scale. Change in precipitation will decrease with increase in elevation in the TRB, while it will increase in the YRB. Compared with the general growth in seasonal temperature, precipitation shows more striking changes during spring and winter under climate change. Further researches to improve our understanding of the projected changes in temperature and precipitation are needed for better prediction of extreme weather conditions, such as drought and floods.
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