Research on the Working Principle and Failure Mechanism of a Temporary Cable System Based on External Steel Anchor Boxs

The effectiveness of the temporary anchorage system is crucial for the safe application of the external steel anchor box cable replacement process. Taking the cable replacement project of a long-span concrete cable-stayed bridge as the background， a cable replacement system that uses pull-bolts as the anchoring system for the external steel anchor box is proposed. A full-scale model and a main beam segment model were designed and manufactured. The working principle and failure mechanism of this cable replacement system were explored through pull-bolt pretension tests and uniaxial static tensile tests under four contact conditions， and validated by numerical simulation. The results indicated that the anchoring performance of the system was determined by the interface friction between the external steel anchor box and the plain concrete pad as well as the bending-shear strength of the pull-bolts. The diagonal pre-tightening process ensured more uniform force distribution among the pull-bolts， and the design should consider the impact of individual bolt failure. The equivalent friction coefficient of dry contact between steel and plain concrete pads was relatively large. Before and after the failure of the plain concrete pad， the pull-bolts transitioned from being primarily in shear to being primarily in bending. Ultra-high performance concrete （UHPC） could be used in this type of cable replacement system.