URS Corporation

Numerical modeling of civil infrastructure often involves assumptions about boundary conditions between adjacent structural components. For steel frame structures, such connections tend to be semi-rigid and often exhibit nonlinear mechanical behavior, making it difficult to determine the rotational stiffness when the connection is evaluated in an isolated manner. This article adapts a partitioned analysis approach using the Block Gauss-Seidel coupling technique to account for the semi-rigid, nonlinear nature of connections in steel frame structures. A case study of a steel frame with bolted connections is presented in which a constituent model is developed for the steel frame with rotational springs to represent the connections. Next, high fidelity, three-dimensional constituent models are developed for three different connection types present in the frame. At the cut-off points of the connection models the internal forces and displacements, calculated by the frame model under a predefined external load, are transferred to the constituent connection models as boundary conditions. Subsequently with the connection models, the rotational stiffness is calculated and transferred back to the frame model through the Block Gauss-Seidel iterations. Coupling iterations are repeated until the connection stiffness calculated by two successive iterations converges, at which point load applied to the frame is increased to develop a full moment-rotation curve. Comparison of the coupled model predictions against experiments show that coupled treatment of the constituent frame and connection models significantly increase the predictive capability of the overall model.

Mine explosions are caused by the ignition of excessive accumulations of combustible dust and/or flammable gas mixed with air in the presence of an ignition source. Rock dusting (limestone dust) is a primary measure to prevent propagating coal dust explosions in underground coal mines in the United States. Although rock dust is considered a nuisance dust, Continuous Personal Dust Monitors (CPDMs) do not distinguish between the coal dust and rock dust and assess the total dust exposure. During application, the < 10 mu m limestone particles and coal dust particles can become suspended and carried by the ventilating air for long distances and can be measured by the CPDMs. There is a concern in the mining industry that rock dust can be included in the CPDM measurements and make the samples noncompliant. Research conducted by the National Institute for Occupational Safety and Health (NIOSH) has found that all rock dust (RD) cakes after being wetted and then dried. To prevent rock dust from caking, several rock dust manufacturers have developed anti-caking rock dusts. The anti-caking additives used are typically fatty acids that make the rock dust hydrophobic and are added in very low quantities (< 1%). While this development will add to the rock dust fluidity, an inevitable problem may be the increased airborne re-entrainment of rock dust due to vehicle movement and foot traffic in the area. Thus, one consideration to reduce such exposure from rock dust is to remove the respirable size fraction (< 10 mu m) of the applied rock dust. This paper presents the results of experiments that were conducted to determine if a rock dust can still inert a coal dust explosion when the respirable (< 10 mu m) or inhalable (< 20 mu m) component of the particle size distribution is removed. Three different untreated rock dusts (untreated A, B, and C) with their treated counterparts (treated A, B, and C) were classified using mechanical sieves into several different-sized fractions, including < 10, 10-20, 20-38, 38-53 and > 75 mu m. The relative inerting effectiveness of these size fractions were determined using the United States Bureau of Mines (USBM) 20-L explosion chamber.

Regenerative stormwater conveyance (RSC) is an open-channel, sand-filtering system composed of a series of shallow aquatic pools, riffles and weirs, native vegetation, and underlying media beds. Surface runoff entering a RSC is conveyed as nonerosive surface flow or subsurface seepage through the media, and exits the system as surface flow, seepage out, exfiltration into the parent soil, or evapotranspiration (ET). While RSCs are expected to perform similarly to other sand-media-based low-impact development (LID) stormwater control measures (SCMs), little field research on this emerging technology have been published to date in peer-reviewed literature. Hydrologic and water quality of a RSC in the Piedmont (Alamance County) ecoregion of North Carolina was monitored from July 2013-June 2014. The Alamance RSC reduced volume and peak flow by a median 78 and 76%, respectively, while mimicking both predevelopment hydrograph shape and hydrologic flow pathways. RSC outflow matches the modeled predevelopment hydrograph shape and pathway components, including both pre-event and event water, as determined by deuterium isotope concentrations. Optimal storm mitigation performance is expected when RSCs include (1)a minimum of three pool/riffle cells, (2)established vegetation, and (3)exfiltration trenches to promote exfiltration into parent soils through extended subsurface ponding. By combining seep out water with surface flow from the RSC, the practice reduced incoming total suspended solids (TSS), total phosphorus (TP), and total nitrogen (TN) loads by a median of 70, 20, and 26%, respectively, likely due to filtration. The potential exists for further nutrient reduction if vegetated, wetlandlike conditions are present. Moreover, locating the RSC over more permeable soils would likely improve hydrologic performance.

Refuge alternatives provide shelter to miners trapped underground during a disaster. Manufacturers must demonstrate that their refuge alternatives meet the U.S. Mine Safety and Health Administration (MSHA) requirements for oxygen supply, carbon dioxide removal, and management of heat from the occupants and mechanical/chemical systems. In this study, miner size and activity level were used to determine the metabolic heat rate, oxygen requirements and carbon dioxide generation that are representative of miners in a refuge situation. A convenience sample of 198 male miners was used for the distribution of current U.S. coal miners, and the composite 95th percentile height and weight were determined to be 193 cm (76 in.) and 133 kg (293 lb). The resting metabolic rate (RMR) was determined to be representative of activity level in a refuge alternative. The highest likely metabolic heat generation ranged from 113 to 134 W, depending on occupancy. The highest required oxygen supply and carbon dioxide removal were estimated to be 23 L (0.81 cu ft) of oxygen per hour per person and 20 L (0.71 cu ft) of carbon dioxide per hour per person, which means the margin of safety is 50 percent or more compared with the MSHA requirements. The information on metabolic heat generation can be used to assess refuge alternative thermal environments by testing or simulation. The required oxygen supply and carbon dioxide removal can be used to assess refuge alternative requirements.