Tributary Area Research Articles

Trends in developed land cover adjacent to habitat for threatened salmon in Puget Sound, Washington, USA.

For widely distributed species at risk, such as Pacific salmon (Oncorhynchus spp.), habitat monitoring is both essential and challenging. Only recently have widespread monitoring programs been implemented for salmon habitat in the Pacific Northwest. Remote sensing data, such as Landsat images, are therefore a useful way to evaluate trends prior to the advent of species-specific habitat monitoring programs. We used annual (1986-2008) land cover maps created from Landsat images via automated algorithms (LandTrendr) to evaluate trends in developed (50-100% impervious) land cover in areas adjacent to five types of habitat utilized by Chinook salmon (O. tshawytscha) in the Puget Sound region of Washington State, U.S.A. For the region as a whole, we found significant increases in developed land cover adjacent to each of the habitat types evaluated (nearshore, estuary, mainstem channel, tributary channel, and floodplain), but the increases were small (<1% total increase from 1986 to 2008). For each habitat type, the increasing trend changed during the time series. In nearshore, mainstem, and floodplain areas, the rate of increase in developed land cover slowed in the latter portion of the time series, while the opposite occurred in estuary and tributary areas. Watersheds that were already highly developed in 1986 tended to have higher rates of development than initially less developed watersheds. Overall, our results suggest that developed land cover in areas adjacent to Puget Sound salmon habitat has increased only slightly since 1986 and that the rate of change has slowed near some key habitat types, although this has occurred within the context of a degraded baseline condition.

Estimation of internal forces in cladding support components due to wind-induced overall behaviors of long-span roof structure

Wind-induced internal forces in cladding support components of a long-span roof structure depend on local behaviors caused by local wind loads and wind-induced overall behaviors of the main structural frame. Based on the pioneering work of Ding and Tamura (2013); Ding et al. (2012), a new method is proposed to estimate internal forces in cladding support components due to wind-induced overall behaviors directly. A detailed investigation on the contributions of wind-induced overall and local behaviors for internal forces in cladding support components of a space truss structure is performed. The results demonstrate that the bending moments and shear forces in cladding support components are dominated by local wind loads acting on the corresponding tributary areas, and the axial forces are caused by the overall displacements of the main structural frame. Considering only the local behavior will underestimate the axial forces in cladding support components significantly, which may lead to buckling failure.

Efficiency of an emissions payment system for nitrogen in sewage treatment plants – A case study

An emissions payment system for nitrogen in Swedish sewage treatment plants (STPs) was evaluated using a semi-empirical approach. The system was based on a tariff levied on each unit of nitrogen emitted by STPs, and profitable measures to reduce nitrogen emissions were identified for twenty municipal STPs. This was done through direct involvement with the plant personnel and the results were scaled up to cover all treatment plants larger than 2000 person equivalents in the Swedish tributary areas of the Kattegat and the Baltic Proper. The sum of costs and nitrogen reductions were compared with an assumed command-and-control regulation requiring all STPs to obtain 80% total nitrogen reduction in their effluents. Costs for the latter case were estimated using a database containing standard estimates for reduction costs by six specified measures. For both cases a total reduction target of 3000 tonnes of nitrogen was set. We did not find that the emissions payment system was more efficient in terms of total reduction costs, although some practical and administrative advantages could be identified. Our results emphasize the need to evaluate the performance of policy instruments on a case-by-case basis since the theoretical efficiency is not always reflected in practice.

PARAMETRIC STABILITY ANALYSIS OF ROOM AND PILLAR METHOD IN DEEP COAL MINES

The goal of this paper is, to examine the validity of tributary area method, which is used as an empirical mean to estimate pillar dimensions, in room and pillar mines, taking into consideration a safety factor. A two-dimensional, linear elastic, finite element model (Phase 2D) is created for a simple case of a uniform pattern of room and pillar mine layout, that is lying flat 1200 m below ground surface. Sensitivity analysis has been done to study the effect of horizontal-to-vertical stress ratio, K, on the maximum stress that pillar can sustain without failure. Four cases have been presented in this investigation (K = 0.5, 1, 1.5 and 2). The results reveal that, the maximum stress on the pillar increases as K increases. Alternatively, factor of safety deteriorates as mining depth (i.e., increase of K-value) increases. The results also show that displacements/convergence expand as mining depth goes down.

Finite-element modeling of a light-framed wood roof structure

Past high speed wind events have exposed the vulnerability of the roof systems of existing light-framed wood structures to uplift loading, contributing greatly to economic and human loss. This paper further investigates the behaviour of light-framed wood structures under the uplift loading of a realistic pressure distribution. A three-dimensional finite-element model is first developed to capture the behaviour of a recently completed full-scale experiment. After describing the components used to develop the numerical model, a comparison between the numerical prediction and experimental results in terms of the deflected shape at the roof-to-wall connections is presented to gain confidence in the numerical model. The model is then used to analyze the behaviour of the truss system under realistic and equivalent uniform pressure distributions and to perform an assessment of the use of the tributary area method to calculate the withdrawal force acting on the roof-to-wall connections.

A new empirical model for estimating calanchi Erosion in Sicily, Italy

Calanchi (plural of calanco) are typical badland landforms of the Italian landscape. They consist of dense networks of V-shaped valleys, with a sparse or absent vegetation cover, which frequently develop on unconsolidated or poorly consolidated clayey deposits. In this paper, the dimensional analysis and the incomplete self-similarity theory were used to deduce a model relating the volume of sediments eroded from the calanchi area to a set of geometric attributes of their tributary areas. The morphometric characteristics of 209 calanchi basins were used to calibrate and validate the model. The predictive skill of the model was assessed by calculating the mean square error and the Nash–Sutcliffe model efficiency coefficient. The model was found to provide a reliable prediction of eroded volume from basins entirely covered by calanchi landforms as well as from basins only partially affected by badland erosion processes. Furthermore, as the residuals between the calculated and the measured volume of the eroded material are normally distributed, the deterministic model may be considered complete, meaning that no other variables are necessary to explain the studied physical process. In other words, the model is able to predict erosion volume in calanchi landforms from a deterministic point of view.

Calculation of Axial Loads on Columns by Tributary Area Method and Finite Element Method

Basic concept of structural design is to transmit the loading from superstructure to substructure. This idea normally required sound knowledge of structural design and rational engineering judgments. Recently, there have several techniques that can be utilized to determine the superstructure loading, such as finite element method and tributary area method. However, the compatibility of both methods in order to determine the loading from superstructure is prime important and has been investigated in this research framework. Axial loading, represented as products from dead load and service load, which are imposed on the top of slab is directly transmit to the column nearby and modelled through computer simulation. Models of slab were then varies and studies through comparison with broad dimensions of slab thickness, ranging in 100 mm to 600 mm. Results has shown the increasing of slab thickness will indirectly increases the rigidity characteristic of slab and potential to distribute the axial load equally for all column members. Axial load against slab thickness on corner, edge, center, outer and inner column demonstrated the incompatibility for both methods, finite element method and tributary area method in determining the axial loading from superstructure.

Aerodynamic devices to mitigate rooftop suctions on a gable roof building

A recent field survey provided eight typical soffits used in the residential houses within the typhoon-prone coastal region of southeastern China. Their aerodynamic effects in alleviating rooftop extreme wind pressures were evaluated via wind tunnel testing on a series of 1/20 gable roof house models. Local pressures, area-averaged pressures and uplift forces acting on roofs were examined. Results showed that in contrast to the model without soffits, the presence of these gutters or eaves gives a rise to a significant reduction of negative peak wind pressures at edges and corners near them. However, they hardly impact wind loads on the other roof surface. Some minor simple architectural elements attached to eaves, such as cantilevered spoiler and semicircular gutter, were observed to facilitate the reduction of extreme wind pressure at edges and corners. Additionally, the reduction rate of spatially averaged wind pressures with area was found to be dependent on the size of tributary area, rather than the shape of tributary area.

Wind loads on fasteners used to attach flexible porous siding on multi-layer wall systems

Recent full-scale studies of wind loads on components of multi-layer wall systems have shown that maximum instantaneous pressure differences across individual layers can be a large fraction of the net load across the wall system, as noted in Cope et al. (2012) The results of these studies are considerably different from results obtained using dynamic pressure chambers where the entire section of the wall is exposed to the same quasi-steady pressure difference or time varying pressures. The largest differences in results between the full-scale wind tests at the Insurance Institute for Business & Home Safety (IBHS) Research Center and the pressure chamber tests occurred for the exterior flexible multi-part siding layer. In the pressure chamber tests, the pressures tend to equalize rapidly between the exterior and interior surfaces of the flexible siding resulting in very low net loads on the siding. In the full-scale wind tests, the response of the flexible siding to the temporal and spatial variations in wind loads imposed by the flow around the building could be observed as a wave moving along the wall surface.The study reported in this paper investigates the loads on the fasteners used to attach the siding to the wall. Specifically, the relationship between the instantaneous pressure differences across the siding and the loads on the fasteners is presented; with the goal of determining whether any systematic reduction or amplification of loads on the fasteners resulted from the very short duration peak instantaneous pressure differences applied to the siding. Specialty instrumentation was developed that allowed measurement of outward acting loads applied to the siding fasteners. This paper describes that specialty instrumentation and presents comparisons of pressure differences multiplied by the tributary area assigned to a fastener against the withdrawal loads measured using the instrumented fasteners.While there is significant scatter in the results, probably due to friction in the fastener load system among other things, results show a strong overall one to one correlation between the net outward loads calculated by applying the pressure load to the tributary area and the measured loads on the fasteners.

Use of vibration characteristics to predict the axial deformation of columns

Vibration characteristics of columns are influenced by their axial loads. Numerous methods have been developed to quantify axial load and deformation in individual columns based on their natural frequencies. However, these methods cannot be applied to columns in a structural framing system as the natural frequency is a global parameter of the entire framing system. This paper presents an innovative method to quantify axial deformations of columns in a structural framing system using its vibration characteristics, incorporating the influence of load tributary areas, boundary conditions and load migration among the columns.

The Effect of Number of Storey's and Columns Dimensions on the Accuracy of Tributary Area Method

The Effect of Number of Storey's and Columns Dimensions on the Accuracy of Tributary Area Method

Surface emission determination of volatile organic compounds (VOC) from a closed industrial waste landfill using a self-designed static flux chamber

Closed landfills can be a source of VOC and odorous nuisances to their atmospheric surroundings. A self-designed cylindrical air flux chamber was used to measure VOC surface emissions in a closed industrial landfill located in Cerdanyola del Vallès, Catalonia, Spain. The two main objectives of the study were the evaluation of the performance of the chamber setup in typical measurement conditions and the determination of the emission rates of 60 different VOC from that industrial landfill, generating a valuable database that can be useful in future studies related to industrial landfill management. Triplicate samples were taken in five selected sampling points. VOC were sampled dynamically using multi-sorbent bed tubes (Carbotrap, Carbopack X, Carboxen 569) connected to SKC AirCheck 2000 pumps. The analysis was performed by automatic thermal desorption coupled with a capillary gas chromatograph/mass spectrometry detector. The emission rates of sixty VOC were calculated for each sampling point in an effort to characterize surface emissions. To calculate average, minimum and maximum emission values for each VOC, the results were analyzed by three different methods: Global, Kriging and Tributary area. Global and Tributary area methodologies presented similar values, with total VOC emissions of 237±48 and 222±46gday−1, respectively; however, Kriging values were lower, 77±17gday−1. The main contributors to the total emission rate were aldehydes (nonanal and decanal), acetic acid, ketones (acetone), aromatic hydrocarbons and alcohols. Most aromatic hydrocarbon (except benzene, naphthalene and methylnaphthalenes) and aldehyde emission rates exhibited strong correlations with the rest of VOC of their family, indicating a possible common source of these compounds. B:T ratio obtained from the emission rates of the studied landfill suggested that the factors that regulate aromatic hydrocarbon distributions in the landfill emissions are different from the ones from urban areas. Environmental conditions (atmospheric pressure, temperature and relative humidity) did not alter the pollutant emission fluxes.

단면의 변의 수가 초고층 건물의 공력특성에 미치는 영향

A series of wind tunnel tests were conducted on 7 super-tall buildings with various polygon cross-sections, including triangle, square, pentagon, hexagon, octagon, dodecagon, and circular. The primary purpose of the present study is to investigate the effect of increasing number of sides on aerodynamic characteristics for super-tall buildings. Wind tunnel tests were conducted under the turbulent boundary layers whose power-law exponent is 0.27. Fluctuating wind pressures from more than 200 pressure taps were recorded simultaneously, and time series of overturning moments were calculated considering tributary area of each pressure tap. The results show that the overturning moment coefficients and the spectral values decrease with increasing number of sides, and the largest mean and fluctuating overturning moments were found for the triangular super-tall building, and the largest spectral values were found for the square super-tall building. The analysis should be conducted more in detail, but currently it can be roughly said that there seems to be a little differences in the aerodynamic characteristics for the super-tall buildings whose number of sides is larger than 5 or 6.

Response of toe-nailed, roof-to-wall connections to extreme wind loads in a full-scale, timber-framed, hip roof

A full-scale, timber-framed, truss, hip roof was subjected to simulated wind loads. Spatially and temporally varying pressures were applied using an array of 58 Pressure Loading Actuators, together with air-boxes covering all roof surfaces. Load cells were incorporated at the top of the wall frame, just below the top plate, to measure the reactions at the toe-nailed roof-to-wall connections. Changes in influence functions and load sharing between adjacent trusses were observed to occur during withdrawal (slip) of the toe-nail connections caused by large magnitude, short duration peak pressures. Even for relatively small displacements, it was observed that the effective tributary area is substantially increased by the incremental withdrawals. This acts to increase the resilience of the roof by allowing more limber and/or more highly loaded connections to transfer loads to stiffer and/or less highly loaded connections. Influence functions, measured both prior to and following damage, were able to predict this behaviour.

Proposed approach for determination of tributary areas for scattered pressure taps

In wind load calculations based on pressure measurements, the concept of 'tributary area' is usually used. The literature has less guidance for a systematic computational methodology for calculating tributary areas, in general, and for scattered pressure taps, in particular. To the best of the author's knowledge, there is no generic mathematical equation that helps calculate the tributary areas for irregular pressure taps. Traditionally, the drawing of tributary boundaries for scattered and intensively distributed taps may not be feasible (a time and resource consuming task). To alleviate this problem, this paper presents a proposed numerical approach for tributary area calculations on rectangular surfaces. The approach makes use of the available coordinates of the pressure taps and the dimensions of the surface. The proposed technique is illustrated by two application examples: first, quasi-regularly distributed pressure taps, and second, taps that have scattered distribution on a rectangular surface. The accuracy and the efficacy of the approach are assessed, and a comparison with a traditional method is presented.

Research on exploiting residual coal around final end-walls by highwall mining system in China

To improve the resources’ recovery ratio and the economic benefits of surface coal mines, we present a residual coal extraction technology from final end-walls with highwall mining system in China. Based on Mark–Bieniawski formula and tributary area theory, the evaluation methodology of highwall mining parameters under the thick cover was given. Furthermore, the pillar design chart in the highwall mining system under the thick cover was also concluded. In order to examine the rationality of the pillar design with the presented methodology, numerical simulation was also carried out. The outcome shows that it will require a larger pillar width with the thickening of the cover; hence, the recovery ratio will decrease correspondingly. To improve coal recovery ratio, the backfilling technology should be considered under the thick cover. According to two-dimension numerical simulation results, the calculated methodology for pillar stability of highwall mining system under the thick cover presented in this article is acceptable. It also found that keeping the pillar width-to-height ratio above 1 is a key measure to maintain the pillar stable and integral under the thick cover. Meanwhile, it can be concluded that the bigger safety factor is demanded for roof of openings under much thicker cover and higher stress ratio. In other words, the highwall mining system is feasible to extract the residual coal around end-walls in Chinese surface coal mines. Thus, not only coal recovery ratio can be improved but also can increase the production life of surface coal mines in China.

Contributions of wind-induced overall and local behaviors for internal forces in cladding support components of large-span roof structure

Internal forces in cladding support components of large-span roof structures under wind loads were usually estimated only based on the local wind loads imposed on tributary areas. However, internal forces on such members depend not only on local behaviors caused by local wind loads but also on wind-induced overall behaviors of main structural frames. By ignoring the contribution of overall behaviors of main structural frames, internal forces in cladding support components may be underestimated following current wind load codes or recommendations. It is necessary to investigate the contributions of local and overall behaviors to improve the wind-resistant design of the cladding support component members on large-span roof systems. In this paper, a method was proposed to separate the internal forces of cladding support components due to wind-induced local and overall behaviors and investigate the corresponding contributions for the largest internal forces. Wind loads used for loading effects estimation were obtained based on wind pressures measured from a 1:400 scaled roof model under a boundary layer wind flow configuration. Wind loading effects considering wind-induced total behaviors (overall behaviors and local behaviors together) for axial force, bending moment and shear force were calculated by time-history analysis using finite element (FE) models of the prototype structure. Meanwhile, internal forces in cladding support components only considering local behaviors were extracted by using local wind loads based on quasi-static assumption. Finally, based on the contributions to the largest wind-induced internal forces resulting from the proposed method, a procedure for remedying the current wind load codes for such members were discussed.

Spatial and temporal patterns of greenhouse gas emissions from Three Gorges Reservoir of China

Abstract. Anthropogenic activity has led to significant emissions of greenhouse gas (GHG), which is thought to play important roles in global climate changes. It remains unclear about the kinetics of GHG emissions, including carbon dioxide (CO2), methane (CH4) and nitrous Oxide (N2O) from the Three Gorges Reservoir (TGR) of China, which was formed after the construction of the famous Three Gorges Dam. Here we report monthly measurements for one year of the fluxes of these gases at multiple sites within the TGR region, including three major tributaries, six mainstream sites, two downstream sites and one upstream site. The tributary areas have lower CO2 fluxes than the main storage; CH4 fluxes in the tributaries and upper reach mainstream sites are relative higher. Overall, TGR showed significantly lower CH4 emission rates than most new reservoirs in temperate and tropical regions. We attribute this to the well-oxygenated deep water and high water velocities that may facilitate the consumption of CH4. TGR's CO2 fluxes were lower than most tropical reservoirs and higher than most temperate systems. This could be explained by the high load of labile soil carbon delivered through erosion to the Yangtze River. Compared to fossil-fuelled power plants of equivalent power output, TGR is a very small GHG emitter – annual CO2-equivalent emissions are approximately 1.7% of that of a coal-fired generating plant of comparable power output.

Failure mechanisms of roof sheathing under fluctuating wind loads

Roof sheathing on typical North American timber frame house construction is subjected to high uplift loads during severe windstorms resulting in commonly observed failures. To investigate such failures in detail, ramp and fluctuating wind loads were applied to oriented strand board and plywood panels fixed to rafters with twisted and ring-shank nail varieties, as well as staples. It was observed for panels fixed with twist-shank nails that the panels separate from the rafters in small increments associated with the large peak pressures. In contrast, the failure progression for ring-shank nails is much more sudden. With both types of failure progression, however, it is observed that it is the short duration peak gusts which damage and fail the panels, and always at the nails with the largest tributary areas in the interior of the panel. Tests were also conducted with different missing nail configurations and the capacities assessed. It was observed that fasteners with the incremental failure mechanism were able to more effectively distribute the load such that the effects of missing nails are reduced compared to the panels which fail by the sudden mechanism.

Probabilistic characterization of roof panel uplift capacity under wind loading

The integrity of the roof system is important to the safety of inhabitants and prevents excessive damage to light-frame wood structures. The uplift capacity of fastened roof panels has been investigated using experimental tests and numerical models. Monotonically increasing uniform static pressure is often employed in experimental investigations and numerical modeling is carried out by assuming that the tributary area method is adequate and the fasteners can be modeled as linear elastic springs, even though the force–deformation relationship for nail withdrawal is nonlinear and uncertain. This study is aimed at assessing the statistical characteristics and modeling the uplift capacity for the roof panel under stochastic wind pressure by incorporating the uncertainty in nail withdrawal behaviour. The results show that the nonlinear behaviour of nail withdrawal needs to be considered to improve the accuracy of the estimated uplift capacity; the statistics and the probability model of the uplift capacity are affected by the degree of correlation of the fastener behaviour within the panel; and that nail spacing and missing nails influence the uplift capacity significantly.