Equipment World Digital Magazine
Issue link: http://read.dmtmag.com/i/506694
geosynthetics to reinforce the soil beneath the sleeper slab, thereby increasing the soil's bearing capac- ity, helping redistribute the load to wider area, and thus reducing the sleeper slab's settlement, they researchers say. To validate this approach, several research projects were initiated by LaDOTD. Field performance – in- cluding deformation and internal stresses of the concrete slabs, contact stresses between slab and embank- ment, stress distributions within the reinforced soil foundation, and strain distributions along the geogrid – was monitored for two years. The authors concluded: s 4HE WEST APPROACH SLAB OF THE Bayou Courtableau Bridge, with the new design method, retained its contacts and supports from the embankment soil during the first static load test (at the time when the bridge was ready for traffic). However, during the second static load test, after about a year and half, the west approach slab lost most of its support from the em- bankment soil. s /N THE OTHER HAND THE EAST AP- proach slab, with the traditional design method, showed slightly gradual loss of its contacts from the embankment soil starting from bridge abutment side towards the pavement side. s 4HE ROUGHNESS PROlLES DEMON- strated better performance of the new approach slab system (west approach slab) compared to the traditional design method (east approach slab) with much lower International Roughness Index values. Connections, grout influence prefab deck panel success Accelerated bridge construction depends on the use of precast, pre- stressed and otherwise prefabricated bridge elements and systems, but their success depends on how well they are implemented. New research from TRB 2 indicates that connections and grouts used are the weakest links in the process, but application guidance is available that will ensure long-life performance. Noting that prefab deck panels have gained popularity, the authors of the paper point out the primary challenge for deck systems is the connectors, typically made using interlaced connector elements and field-cast grout. "Poor detailing and design considerations have been shown to pose problems with deck durability, serviceability and ultimate capacity," the authors say. For this research, a series of precast deck panel connection tests were car- ried out at Federal Highway Admin- istration's Turner-Fairbank Highway Research Center to further understand deck-level connections under realistic performance demands. Several de- sign variations – including shear key shape, reinforcement type, joint mate- rial type, and precast surface prepara- tion – were investigated. "Seventy two large-scale, deck-level connection assemblies were tested in four-point bending and subjected to cyclic crack loading, fatigue loading, and monotonic loading until failure," the authors say. The three loading protocols allowed researchers to as- sess the durability, serviceability and ultimate strength of the connections. Their conclusion: the performance of these connections "is heavily influ- enced by the grout and the precast component interface surface prepara- tion." They also determined: s 4HE SELECTION OF GROUT MATERIALS IS a critical design consideration for deck-level prefabricated bridge elements and systems connec- tions. This assumes that lap splice lengths have been selected such that bond failure does not occur. s $EPENDING ON THE GROUT MATERIAL selected, surface preparation of precast concrete deck panels can have a significant impact on tensile bond resistance of the panel-to- grout interface. s !LTHOUGH EPOXY GROUT AND ULTRA high performance concrete grout systems have higher initial cost, they could provide better value when long-term performance and required maintenance are considered. s .ONSHRINK CEMENTITIOUS GROUT AND magnesium phosphate grout may lead to durability issues as a result of poor bond to precast concrete regardless of surface preparation, and poor performance under repeated loading. s !N EXPOSED AGGREGATE SURFACE preparation preformed the best for promoting bond between precast concrete components and cementi- tious grout connection materials. s 4HE EPOXY GROUT EXHIBITED GOOD bond with precast concrete regard- less of the surface preparation. Hybrid jackets for quake- damaged bridge columns Hybrid jacketing – made up of a thin cold-formed steel sheet wrapped around an earthquake damaged reinforced concrete column – of- fers a fast solution to getting bridges reopened following a seismic event, says one research team. 3 Such a jacket, which is also sup- ported on the outside by prestress- ing strands, was tested using a large-scale RC column with a defi- cient lap splice (where two pieces of rebar are overlapped to create continuous reinforcement), typical road science | continued May 2015 | EquipmentWorld.com 42 2 Experimental Evaluation of Prefabricated Deck Panel Connections, by Zachary B. Haber, Ph.D., Professional Service Industries, Inc., and Benjamin A. Graybeal, Ph.D., P.E., Team Leader, Bridge and Foundation Engineering, at FHWA's Turner-Fairbank Highway Research Center, McLean, Va. 3 Hybrid Jacketing for Rapid Repair of Seismically Damaged Reinforced Concrete Columns, by Mostafa Fakharifar, Genda Chen, Ph.D., P.E., Mahdi Arezoumandi, Ph.D., and Mohamed ElGawady, Ph.D., Missouri University of Science and Technology, Rolla.