The traditional bolt-type anchoring system [2] recommended rubber dam bolt plate anchoring type, calculated: when the dam height is 5m, the theoretical diameter of the bolt is 3323mm, the actual bolt. The reaction force of the bolt's anchoring force is provided by the slinging force of the rubber dam floor concrete to the anchor bolt, so the anchor bolt must have sufficient anchoring length. Bolt anchor length L is 25d<3>, which is 900mm.
Theoretical analysis of high-strength bolt-type anchoring system The new high-strength bolting plate anchoring type divides the traditional bolting plate anchoring structure into two parts according to the force transmission condition: the connection between the anchor plate and the dam bag; the connection between the anchor plate and the concrete floor of the rubber dam. The first part uses high-strength bolts to connect the anchor plate to the dam bag. The connection between the anchor plate and the dam bag is usually frictional. The principle is to tighten the nut and apply a strong and controlled pre-tension to the screw. The pre-tension will pass through the anchor plate and the pressure plate. The rubber dam bag is clamped and relies on the frictional resistance between the dam bag and the anchor plate to withstand the radial tension of the dam bag. The second part uses two symmetrically arranged anchor ribs to connect the anchor plate to the reinforced concrete of the rubber dam floor, and the anchoring force of the anchor rib is provided by the reinforced concrete of the rubber dam floor.
To withstand the radial pulling force of the dam bag, the pre-tensioning force of the bolt needs to be large. If ordinary bolts are used, because of the low strength, the required bolt diameter is large, and it is uneconomical, and high-strength bolts can be used. After a lot of experimental research and engineering practice, the pre-tension of the high-strength bolt will not relax under the repeated load, and the screw will not break due to fatigue. Due to its fatigue resistance, safe and reliable work, high-strength bolts have been widely used in steel structure connections, especially in structures that are subjected to dynamic loads.
The force characteristics of the new bolt-type anchorage type anchorage ribs are: the anchor ribs only bear the radial tension of the dam bag, that is, the external force of the anchor, and the high-strength bolt provides the squeezing force of the anchor plate to the dam bag to withstand the dam. The anchoring force of the bag (the frictional resistance between the anchor plate and the dam bag), that is, the internal force of the anchor. The tensile force of the anchor rib is greatly reduced, and therefore, the diameter of the anchor rib can be greatly reduced. In addition, it is anchored in the bottom plate by two anchor ribs, which can better withstand the bending moment generated by the dam bag tension.
Actual engineering calculation of the diameter of the anchorage of the 2221 anchorage (1) When =0, the embedded part is the directly embedded ribbed embedded part <3>, the cross-sectional area of ​​the anchor rib As is calculated as follows: As=Vrvfy(3) Schematic diagram of bolted plate anchoring member v=(4-008d)fcfyV=T0n where V is the shear force design value, kN;r is the influence coefficient of the number of layers of the steel bar. When the anchor bars are arranged at equal intervals, the two layers take 10; The shear capacity coefficient of the steel bar; d is the diameter of the steel bar, mm; fy is the design value of the tensile strength of the anchor bar, N/mm2; fc is the design value of the compressive strength of the component concrete, N/mm2; T0 is the calculation of the bolt length per unit length Load, kN/m; n is the number of bolts in the length of 1 m.
The anchor rib is Q235, the fy is 210N/mm2; the bottom concrete is C25, and the fc is 125N/mm2. The calculation result: when the dam height is 5m, the theoretical cross-sectional area of ​​the anchor rib is 3253mm2.
(2) When =90, the embedded part is drawn and bent, and the cross-sectional area of ​​the anchor is as follows: AsN08bfy+M04rbfyz(4)b=06+025td where b is the reduction factor of the bending deformation of the anchor plate ;r is the influence coefficient of the number of layers of the steel bar. When the anchor bars are arranged at equal intervals, the two layers are taken as 10; fy is the design value of the tensile strength of the anchor bars, N/mm2; t is the thickness of the anchor plate, taking 20 mm; d is the anchor The diameter of the rib; z is the distance between the center line of the outer anchor rib, take 180mm; N is the normal tensile force, N; M is the bending moment of the anchor plate, the torque is 110mm, kNm. Comprehensive two kinds of working conditions, anchor rib Choose 220, the actual cross-sectional area is 628mm2. According to the requirements <3>, the length of the anchor is 25d, which is 50mm.
Calculation of high-strength bolts Under the shearing condition, the bearing capacity design value of each high-strength bolt is calculated by the following formula: <4>: NbV=09nfp (5) where nf is the force-transmitting friction surface coefficient, take 10; The anti-slip coefficient, the anti-slip coefficient of steel plate and rubber, generally takes the value 0204; p is the pre-tension of a high-strength bolt, as used.
The components of the stressed embedded parts are set, and the concrete strength grade is C25 grade. The connection design between the anchor plate and the rubber dam bag and the connection design between the anchor plate and the reinforced concrete floor, the structural requirements, the bolt connection in the literature <4>, the literature <5>, the design and construction of the embedded part are required to be implemented. The high-strength bolt hole is drilled into a hole, and the aperture diameter is 1520 mm<4> than the nominal diameter d of the bolt.
Comparative analysis of new and traditional anchoring types (1) The design anchors recommended in the literature <2> are single-layer anchors, and the single-layer anchors have the problem of poor load bearing capacity. The new type uses double anchors in the structure. It is superior to traditional bolt platen anchoring. (2) Compared with the traditional anchoring type, the single anchor type saves 4444% of the anchorage length and saves the weight of the reinforcement 6565%. (3) Since the diameter and length of the new anchorage type buried rib are smaller than the traditional anchoring type, the thickness of the bottom plate can be correspondingly Reduce and reduce floor investment.
According to the calculation of the construction headquarters of Liuhang Rubber Dam Project in Linyi City, this part saves about 200,000 yuan. The anchoring system method is appropriate, and the engineering application has broad prospects and can be promoted in similar projects. The problems existing in the practical application of the existing problems and improvement measures are mainly: the welded joint between the anchor plate and the anchor bar, the pad has slight deformation, and the welding has hidden troubles in processing. The improvement measures are mainly: the hot-melt integrated production and processing method of the pad and the anchor rib, reducing the deformation of the pad and reducing the unreliable factors of the manual welding. The anchor product is formed into a complete set and finalized factory product.
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