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OCR for page 101
101 drains; (3) bedding layer reinforcement and its location Precast bent cap connection details are expected to be relative to the first hoop at the top of the column; (4) the constructible. elevations and geometry for positioning the bedding layer Precast bent cap connections incorporate certain details not collar for bent cap placement; and (5) the details of grout- found in CIP connections that require attention: ing or concreting equipment and mix design and the method Use of a reinforced bedding layer. of mixing, placing, and curing. Accurate placement and spacing of the hoop at the top The trial batch is a key step in achieving the required instal- of the column and within the bedding layer. lation and performance of connection material--grout for Minimum joint shear (transverse) reinforcement for all grouted duct and concrete fill for cap pocket--and should SDC levels. be specified to (1) determine the required amount of water Vertical stirrups inside the joint for all SDC levels. to be added to achieve acceptable flowability and pot life Cap pocket connections: stay-in-place, partial-depth under expected field conditions, (2) determine the associ- steel pipe serving as joint shear (transverse) reinforce- ated compressive strength, (3) examine the material for ment; concrete fill in cap pocket void and bedding layer; undesirable properties, (4) establish the adequacy of pro- 2-leg vertical stirrups without overlapping within the posed equipment, (5) provide jobsite personnel experi- joint; supplementary hoop for full ductility; column bar ence in mixing and handling the connection material anchorage nearly full depth; and optional U-bars for prior to actual operations (grouting or concreting), and full ductility. (6) help the contractor to make a judicious decision Grouted duct connections: stay-in-place, full-depth steel regarding selection of connection material (grout brand or corrugated ducts; grout in grouted ducts and bedding concrete mix). layer; and column bar anchorage nearly full depth. Placement of the grout and concrete fill is a critical step in construction of precast bent cap connections and should be 4.6 Implementation Plan conducted as detailed in the proposed specifications. Based on the development of an Implementation Plan, the following conclusions can be drawn: 4.5 Example Connection Details Based on the development of example connection details for The Implementation Plan provides an effective roadmap for precast bent cap connections in SDCs A through D, the follow- implementing NCHRP Project 12-74 research products. ing conclusions can be drawn: All steps of the Implementation Plan should be closely fol- lowed through the appropriate channels to ensure that the Example precast bent cap connection details provide clear NCHRP Project 12-74 research products are implemented illustrations and sufficient detail and notes for a thorough in a timely and comprehensive manner. understanding of key features of grouted duct and cap pocket The extent of Research Team participation depends on connections. future funding.