Hydraulic and earth engineering – Earth treatment or control – Rock or earth bolt or anchor
Patent
1984-09-04
1986-09-23
Taylor, Dennis L.
Hydraulic and earth engineering
Earth treatment or control
Rock or earth bolt or anchor
411 8, 411 9, E21D 2102
Patent
active
046132546
DESCRIPTION:
BRIEF SUMMARY
The invention relates to an expanding bolt anchor which can be inserted into a hole in a ground and which has an expanding sleeve divided by longitudinal slits into segments. The sleeve can be expanded by at least one conical expander engaging the bore-internal end of the sleeve, preferably by two conical expanders pointing toward one another with their tapered ends and engaging the opposite ends of the sleeve, by tightening a bolt whose bore-internal end engages the bore-internal expander and which passes in a longitudinally displaceable manner through the expander that may be provided at the bore-orifice end of the sleeve. A nut or bolt head is provided on the bore-external end of the bolt and through a spacer bushing thrusts against the expanding sleeve, or against the expander provided at the bore-orifice end of the sleeve as the case may be. At the bottom of the bolt head or nut facing the ground, a washer is provided which clamps the workpiece against the surface of the ground, and a sleeve-like tube section of a soft steel with a pronounced plastic flow limit (compression yield point) is provided between the bolt head or nut and the expanding sleeve or the expander provided at the bore-orifice end of the sleeve as the case may be. The wall thickness of the tube section is so dimensioned that, upon the application of a setting force specific for the bolt anchor, compression stresses will prevail in this tube section which just equal the stresses prevailing in the material of the tube section when the plastic flow limit (compression yield point) is reached.
When workpieces are to be fastened to a ground by means of anchors, the maximum holding power that can be achieved by each anchor, and thus also the maximum strength and life of the fastening, is generally reached when the setting force characteristic for a particular anchor is maintained in the bolt, i.e., the tension force or forces are maintained in the bolt, which are allowable for the particular stress involved and the cross-sectional area of the bolt. It is important, however, for a slippage-free setting of the expanding sleeve, that, in the setting process, a maximum allowable setting force specific for the anchor is introduced into the anchor, which on the other hand may not be exceeded if the bolt is not to be overstrained. Since the force or tensions prevailing in the bolt are not directly measurable, the anchor manufacturers prescribe the tightening torques to be applied to the nut threaded on the bolt or to the bolt head, as the case may be, which are calculated on the basis of the tension allowable in the cross section of the particular bolt in consideration of the strength of its material, and which can easily be established by means of torque wrenches. In practice, however, the calculated (and prescribed) torque does not correspond to the setting force that is allowable in view of the load that can be applied to the bolt. As a result of friction occurring between the anchor components during the setting process, only a portion of the applied torque is converted to tension in the bolt. If the friction loss in anchors of the same constructional design were in any way equal, allowance could be made for it simply by means of correspondingly higher prescribed torques, i.e., a tightening efficiency could be introduced. Unfortunately, however, the setting force achieved in similar anchors by the same tightening force varies so greatly that they cannot be correctly determined by mathematical correction of the torque. Therefore an anchor has already been developed (DE-OS No. 30 22 011) in which the attainment of the prescribed setting force, regardless of the different friction resistances occurring when the anchor is tightened, is indicated by a spherically cupped washer. If its material is properly selected and if it is properly dimensioned, this washer will have a resistance to deformation such that, when it is axially deformed from the original cupped shape to a flattened disk, it will correspond precisely to the magnitude of the setting
REFERENCES:
patent: 1852297 (1932-04-01), Gelpcke
patent: 4019420 (1977-04-01), Fischer
patent: 4289061 (1981-09-01), Emmett
patent: 4312613 (1982-01-01), Binns
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