Browsing by Author "Liu, Z."

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    A new instrument to measure plot-scale runoff
    Stewart, Ryan D.; Liu, Z.; Rupp, David E.; Higgins, Chad W.; Selker, John S. (2015-03-02)
    Accurate measurement of the amount and timing of surface runoff at multiple scales is needed to understand fundamental hydrological processes. At the plot-scale (i.e., length scales on the order of 1 to 10 m) current methods for direct measurement of runoff either store the water in a collection vessel, which is unconducive to long-term monitoring studies, or utilize expensive installations such as large-scale tipping buckets or flume/weir systems. We developed an alternative low-cost, robust and reliable instrument to measure runoff that we call the "Upwelling Bernoulli Tube" (UBeTube). The UBeTube instrument is a pipe with a slot machined in its side that is installed vertically at the base of a runoff collection system. The flow rate through the slot is inferred by measuring the water height within the pipe. The geometry of the slot can be modified to suit the range of flow rates expected for a given site; we demonstrate a slot geometry which is capable of measuring flow rates across more than three orders of magnitude (up to 300 L min−1) while requiring only 30 cm of hydraulic head. System accuracy is dependent on both the geometry of the slot and the accuracy of the water level measurements. With an off-the-shelf pressure transducer sensor, the mean theoretical error for the demonstrated slot geometry was ~17% (ranging from errors of more than 50% at low flow rates to less than 2% at high flow rates), while the observed error during validation was 1–25%. A simple correction factor reduced this mean error to −14%, and further reductions in error could be achieved through the use of taller, narrower slot dimensions (which requires greater head gradients to drive flow) or through more accurate water level measurements. The UBeTube device has been successfully employed in a long-term rainfall-runoff study, demonstrating the ability of the instrument to measure surface runoff across a range of flows and conditions.
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    Rapid Replacement of Tangier Island Bridges Including Lightweight and Durable Fiber-Reinforced Polymer Deck Systems
    Cousins, Thomas E.; Lesko, John J.; Majumdar, P.K.; Liu, Z. (Virginia Center for Transportation Innovation and Research, 2009-09-01)
    Fiber-reinforced polymer (FRP) composite cellular deck systems were used as new bridge decks on two replacement bridges on Tangier Island, Virginia. The most important characteristics of this application were reduced self-weight and increased durability for an FRP deck system over a reinforced concrete bridge deck. Tangier Island is in the Chesapeake Bay and is accessible only by water or air; each bridge is over saltwater. The two bridge deck systems used were from different manufacturers: Strongwell Corp. and Zellcomp, Inc. The deck system from Strongwell was virtually identical to a previous application by the Virginia Department of Transportation (VDOT) in Covington, Virginia. Because of the extensive testing of this system conducted as part of a prior Innovative Bridge Research and Deployment project, further investigation of its behavior was not warranted. The objectives of the testing of the Zellcomp deck system were four-fold: (1) investigate connection behavior under simulated pseudo-static service load; (2) examine flexural strength and failure mode of connections and deck; (3) explore fatigue behavior during simulated cyclic wheel loading and residual strength after fatigue loading; and (4) investigate viability of transition connection. Two test sections were constructed in the Structures and Materials Laboratory at Virginia Tech. The test sections included sections of the Zellcomp deck attached to supporting steel stringers. The first was flat, 11 ft by 8 ft in plan, and subjected to static and simulated truck loadings. The second included a transition connection and was 17 ft by 8 ft in plan. Of special interest during this testing was the investigation of the static and cyclic behavior of all Zellcomp deck connections (top plate to supporting T-sections, T-section to T-section, and T-section to supporting stringers). The flat Zellcomp deck test specimen had a 1.4 safety factor against sustaining permanent damage and a 2.4 safety factor against failure when subjected to an HL-93 wheel load of 22 kips. There was no measured composite action between the top plate and supporting T-section. Generally, the specimen performed well during the fatigue test. However, there was some indication of deterioration of the lap joint connections at 1 million cycles of load and loss of stiffness at about 2.5 million cycles of load. The bent lap joint connection was difficult to construct. A permanent gap between the top plate and supporting T-sections resulted because of inherent construction tolerances. The slope Zellcomp deck specimen underwent significant deterioration during the first 600,000 cycles of load. Numerous top plate screw connections loosened, with several completely fracturing. The damage to the deck increased for the next 400,000 cycles. The study recommended that VDOT's Structure and Bridge Division (1) not use the sloped deck transition on any applications of the Zellcomp bridge deck system; (2) consider close inspection of all screw connections on the Zellcomp deck during regularly scheduled bridge inspections; and (3) consider additional more rigorous full-scale testing of the Zellcomp deck system before considering its use on any bridge structure that has truck traffic. The Tangier Island Bridge is subjected to very light truck traffic, and the Zellcomp system proved to be adequate for this specific application only