Study On Calculation Of Internal Forces For Anchor Cable Frame Considering Friction

Prestressed anchor cable frame beam is a new technique about slope reinforcing and defending .It safe and steady ,light and beautiful ,and the economic benefit is superior to the traditional heavy-duty supporting structures obviously , and popularly applied in railway,highway and water conservancy project .At present ,there is no unified standard to provide the calculating method of the internal forces of the frame beam ,and the existing methods ignore the change of the internal force of the beam caused by the huge friction between the frame and the slope frequently .So ,it is necessarily to discuss the influence of friction under the frame to the internal forces of the anchor cable frame beam .The main contents of this thesis are :(1)The influence of the selection of the optimal anchor cable-angle to the action form of the friction under the frame is discussed .The calculating method of the optimal anchor cable–angle is confirmed by considering Mohr-Coulomb rule ,the computing formula of the anchor power and the request of the use and construction of the anchor cable frame .The anchor cable–angle should be the angle of depression between 15°and30°generally ,relate to the slope angle and the inclination of failure face .It shows that the friction under the frame is the breakout friction ,and points to the bottom of the slope.(2)Winkler elastic foundation model is selected to calculate the internal force about the frame beam ,and on the basis of it ,estimate the afresh distributing of the beam stress caused by the friction . Split the frame as transverse beam and upright beam when calculating the influence of the friction ,then establish the mechanical model respectively ,and use the elasticity's technology to deduce a formula about the effect of the friction to anchor frame beam.(3)Using the formula about the effect of the friction to anchor frame beam which has deduced to analyze the influence rule of the friction :for the transverse beam ,the internal force increases in some direction ;for the upright beam , the internal force increased and reduced segments appear beside the anchor alternately .And the biggest increase is on the point where having the anchor cable of the cantilever beam at the direction of the bottom of the slope ,and increases as the elongation of the cantilever beam ;the increase of the internal force of the transverse beam is bigger than the upright beam's ;when the height of the section of the beam is stated ,the influence of the friction reduces as the increasing of the width of the beam ,and the range of the change of the transverse beam is bigger than the upright beam's;(4) For analyzing the influence of the torque produced by the friction to the design of the steel bar ,whether calculating the load of tweaking and shearing resistance must be judged by the formula which is Q/(bh₀)+T/W_t≤0.7f_t.Then selecting the design mode of the stirrup and torsion longitudinal reinforcement.