Field Prototype Experimental Study On The Concrete Frame Structure With Prestressed Anchor Cable

With the construction of the high level road between Yuanjiang and Mohei (YuanMo Highway), an international highway from KunMing to Bangkok, Ministry of Communications has awarded China Academy of Railway Sciences a research project on western traffic, "side slope defect preventive treatment technique research on high level road construction" (project serial number G2001GG20). Based on three typical sites in terms of engineering geologies and failure/deformation modes along YuanMo Highway, this research performed prototype experiments to study the behavior of prestressed anchor-cable frame structures.First, a literature review of prestressed anchor-cable frame structures was carried out in this research with respect to design methods, frame-slope interaction, and experimental studies. Second, this study systemically demonstrated working mechanism and design methods of prestressed anchor-cable frame structures and proposed further study on prestressed anchor-cable frame structures.By embedding apparatus and instruments including anchor-cable force gauge, steel bar gauge, earth pressure boxes and concrete strain gauge in anchor-cable frame structures, this research collected parameters such as anchor-cable stresses, frame moments, contacting stresses between frame beams and soil, axial compressive stresses of anchorage segment within anchor cable and frame joint displacements. After more than two years of field tests, more than 400,000 effective data were recorded. Based on the analysis and study on the field recorded data, the primary research achievements are as below:1. The values and distribution of axial compressive stresses in the anchorage segment of the pressure-type cable depend on the anchor-cable inter forces. The axial compressive stresses mainly occur near bearing plates and reduce significantly when aparting from the bearing plates, with a nonlinear relationship of exponentialσ=αe^bx between the stresses and distances. For the pressure-type cable embedded within moderately weathered sandy slate, the axial compressive stresses mainly appears around 7.0 times aperture in bearing plate if cable tensions is less than 300kN.2. The change of anchor cable stresses is composed instant loss at-lock and long term changes. The total stress loss is approximate 16% of the total dragging force, with 10% caused by the loss at-lock and 6% loss due to the long term effects. Therefore, incremental loading is an effective method to reduce the stress losses during the dragging stage. The dragging interaction between different anchor-cables is insignificant.3. Beam on Winkler Foundation theory can be applied to calculate the momentum distribution of frame beams due to the anchor loads and therefore can be employed for the design of anchor-cable frame structures. Specifically, this study suggests that calculated results from Beam on Winkler Foundation theory can be used directly for the positive moment design at the mid-span of frame beams, while 0.8 times of the calculated values are used for the bending moment design at frame joints.4. The joint moments depend on the ratio between perpendicular beam spans and crossbeam spans. The bigger the ratio is, the greater moment the perpendicular beam experiences. The smaller the ratio is, the greater moment the crossbeam has.5. The in-plane displacements of frame structures are insignificant, in the level of millimeters, due to the anchor cable loads, and could be ignored when compared with the elongation of anchor-cables .6. Recorded data are accurate and reliable if concrete strain gauges, anchor cable force gauges and reinforce bar gauges are used in the data collection. However, the contacting forces between frame beams and rock-soil of side slope recorded by earth pressure boxes can not be used with confidence. The general trend and sequences of the contacting stresses can be displayed, but the recorded values differs significantly from the actual contacting stresses. Therefore, the test method needs to be further discussed, especially in terms of embedding technologies.7. A few suggestions are presented in this research for the design of pressure-type anchor cable and the stress analysis methods of prestresses anchor-cable frame structures, and can be applied to its structure design and construction.