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Anchorage of Ground Vertical Duct Connections for Precast Bent Caps

Brenes, Francisco, J.

2005

In the last decade, the need to reduce traffic disruption at construction sites has led to innovations in bridge prefabrication. In Texas, most of these recent innovations have involved prefabrication of bent cap elements. Bent cap-to-column connections currently being used incorporate either corrugated galvanized steel or plastic ducts that are precast in the bent cap element to serve as sleeves to house connectors. Designers and contractors prefer this type of precast connection over other types because the volume of grout that is required to complete the cap-to-column connection is minimized.

This research intends to reduce some of the uncertainties that currently surround the design of grouted vertical duct connections. The main test parameters that influence connection performance are identified. These parameters include bar coating, duct material, embedment depth, number of connectors, bar eccentricity, and transverse reinforcement.

The experimental program examines the behavior and failure modes of grouted vertical duct connections. Results from thirty-two large-scale pullout tests are reported, and the effects of the studied parameters on connection behavior are evaluated. A simple phenomenological bond-slip model is presented that can be used to estimate the observed behavior.

The development of the anchorage design provisions considers the stress in the connectors at service load levels. Design provisions are developed for connectors that experience: (1) compression or low tension, and (2) significant tension. Design provisions applicable to connectors that experience compression or low levels of tension are based on limiting serviceability stresses related to widespread splitting in the connection specimens. Connectors that experience significant tension and may be expected to yield are designed using anchorage provisions based on experimental average peak bond strengths. Observed pullout modes of failure are precluded by incorporating adequate levels of safety in the development of the design recommendations.

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