Proceedings of the 30th Annual Conference on Deep Foundations, 2005, Chicago, Illinois, USA, (DFI)
Tension Testing of the Grouted Anchorage Assembly for Multistrand Anchors
Lucian I. Bogdan P.E.
Active loaded strand anchors are often used for slope stabilization, retaining walls or tiedown anchors. Normally, strands are tensioned against the structure and wedges are locked inside the anchorages at a certain lock-off load. During the life of the structure, anchors can receive additional loading during a surcharge, seismic event or other activity on the structure. In order to have a reliable ground anchor system, the strand must not slip through the anchorage wedges during its service life. Strand slippage has been reported during lock-off, when dirty wedge plates and wedges have been used. Low lock-off loads are believed to contribute to stand slippage too. Since the initial lock-off load for a ground anchor is usually lower than the lock-load for an equivalent capacity tendon in order types of post-tensioning construction, there is a concern that strand slippage may occur if the load on the anchor increases above the initial lock-off load. Corrosion protection grout, placed after the anchor is locked off, fills the pocket and surrounds the strand wedges. Some anchor installers believe that the grout will prevent the anchorage from developing additional capacity if the load increases above the initial lock-off load. The load-carrying capacity of an anchorage depends on several factors. Most important are: initial applied load, anchorage geometry, friction between wedge-anchorage-strand and condition of the contact surfaces. The ADSC Anchored Earth Retention Committee considers that the industry should know how wedges behave once the permanent strand anchors are stressed and grouted inside the transition pipe, between wedges and inside the grout cap. The committee recommended testing of strand anchors using wedge plates and wedges provided by the three ADSC associate member suppliers: *DSI, CON-TECH Systems and *LANG Tendons. Testing was conducted at DSIís Long Beach facility and was supervised by an independent inspector. *At the present time two of the ADSC associate members, DSI geotechnical division and LANG Tendons merged forming a new company: DSI-LANG Geotech, LLC. This paper presents the results of a test program to document wedge behavior after grouting.
|article #1293; publication #72 (AM-2005)|