What are the types of anchors?

Clamp-type (single-hole and multi-hole clamp anchors): Support-type (upset head anchors, nut anchors, etc.): Upset head anchors, screw-end rod anchors, strip anchors. Cone plug type: Steel cone anchors. Grip-type (extrusion anchors, embossed anchors, etc.): Cone screw anchors, embossed anchors. The engineering design unit shall select the anchorages based on structural requirements, product technical performance, and tensioning construction methods.

Types of anchorages There are many types of anchorages, and different types of prestressed tendons require different anchorages. The common types of anchorages include the following: 1. Screw-end rod anchorage, which consists of a screw-end rod, a nut, and a washer. The models range from LM18 to LM36, and they are suitable for grade II and III prestressed steel bars with a diameter of 18–36 mm, as shown in Figure 4-19. The length of the anchor is generally 320 mm; when tensioning is applied at one end or the length of the prestressed tendon is large, the length of the screw should be increased by 30–50 mm. The screw end rod and the prestressed tendon are connected by butt welding, and the welding should be carried out before the prestressed tendon is cold-drawn. When cold-drawing the prestressed tendons, the nut is placed at the top of the end rod, and the pulling force should be transmitted from the nut to the screw end rod and the prestressed tendons. http://www.scutde.net/t14courses/1412-efmdljiaif/yuyingli/4.3/IMAGE/4-19.GIF Figure 4-19 Screw-end rod anchor a) Screw-end rod anchor ； b) Screw end rod ； c) Nut ； d) Shims 2. Strip anchors A strip anchor consists of a strip and a backing plate. The reinforcement bars used for the tie bars are of the same grade as those used for prestressed tendons, while the backing plates are made of ordinary low-carbon steel sheets. The three straps of the anchor shall be evenly arranged at 120º angles to each other, and welded firmly to the backing plate and the prestressed tendons, as shown in Figure 4-20. Strand welding should also be carried out before cold drawing of the rebar; during welding, care must be taken to prevent damage to the prestressed strands. http://www.scutde.net/t14courses/1412-efmdljiaif/yuyingli/4.3/IMAGE/4-20.GIF Figure 4-20 Strip anchor 1—Strip ； 2—Liner plate ； 3. Prestressed tendons 3. Headed anchors: Anchors used for individual large-diameter steel bars are generally formed by hot heading, cold heading, or forging at the end of the prestressed tendon. Upset anchorages are also suitable for anchoring any number of Φ5 and Φ7 wire bundles. The form and specifications of head-driven anchorages can be designed as needed; the commonly used wire rope head-driven anchorages are divided into Type A and Type B. Type A consists of an anchor ring and a nut, and can be used at the tensioning end ； Type B is an anchor plate used for fixing the end, and its structure is shown in Figure 4-21. For head forging, the slip value of the anchor should not exceed 1 mm. The upsetting strength of the upset anchor shall not be less than 98% of the specified tensile strength of the steel wire. Both the inner and outer walls of the anchor ring have threads; the inner threads are used to connect the tensioning screw rod, while the outer threads are used to tighten the nut in order to secure the wire bundle. Holes are drilled around the anchor ring and anchor plate to secure the steel wires with heads forged up; the number and spacing of these holes depend on the number of wires. The steel wire is headed using an LD-10 type hydraulic cold heading machine. One end of the wire bundle can have its end forged during bundling, while the other end is forged after the wires are inserted; therefore, hole ends in the components need to be enlarged. During tensioning, one end of the tensioning screw rod is connected to the internal threads of the anchor ring, while the other end is connected to the pull head of the rod-type jack. When the controlled stress is reached, the anchor ring is pulled out; at this point, the nut on the external threads of the anchor ring is tightened to secure it in place. Upset anchorages are tensioned using YC-60 jacks (through-type jacks) or tie-rod jacks. http://www.scutde.net/t14courses/1412-efmdljiaif/yuyingli/4.3/IMAGE/4-21.GIF Figure 4-21 Wire bundle upset anchor a) Type A ； b) Type B 1-anchor ring ； 2—Nut ； 3—Anchorage plate ； 4—Wire rope bundles: http://www.scutde.net/t14courses/1412-efmdljiaif/yuyingli/4.3/PIC/4.3.1.JPG. Anchor devices: 4. Cone-shaped screw anchors, used for anchoring 14–28 wire rope bundles with a diameter of 5 mm each. It consists of a tapered screw, sleeve, nut, etc. (Figure 4-22). The conical screw anchor is used in conjunction with YL-60 and YL-90 rod-type jacks; YC-60 and YC-90 through-type jacks can also be employed. http://www.scutde.net/t14courses/1412-efmdljiaif/yuyingli/4.3/IMAGE/4-22.GIF Figure 4-22 Cone-shaped screw anchor 1—Hub ； 2—Tapered screw ； 3 – Shimming plate ； 4—Nut ； 5—Wire bundle 5. Steel conical anchor: Composed of an anchor ring and an anchor plug (Figure 4-23), it is used to anchor the wire bundle tensioned by a conical double-acting jack. The taper of the inner hole of the anchor ring should be consistent with that of the anchor plug. The anchor plug is fitted with fine toothed grooves to clamp the steel wire and prevent slippage. The main drawback of conical anchors is that when there is a large variation in the diameter of the steel wires, individual wires are prone to slipping, and it is difficult to remedy this issue after slipping occurs. Attempting to prevent slipping by increasing the anchoring force can cause the steel wires to be damaged. Furthermore, the steel wires are arranged in a radial pattern during anchoring, resulting in greater stress at the bends. Steel conical anchors are tensioned using conical double-acting jacks. http://www.scutde.net/t14courses/1412-efmdljiaif/yuyingli/4.3/IMAGE/4-23.GIF Figure 4–23 Steel conical anchor: 1 – Anchor ring ； 2—Anchorage plugs. 6. JMl2 type anchors: The JMl2 type anchors come in ten varieties, namely optical types JM12-3～JM12-6, screw types JMl2-3～JM12-6, and twisted types JMl2-5～JM12-6; these are used to anchor 3～6 steel bars of grade IV with a diameter of 12 mm, as well as 5～6 bundles of steel strands with a diameter of 12 mm. The JMl2 type anchor consists of an anchor ring and clamps. The structure of the JMl2 type anchor is shown in Figure 4-24. http://www.scutde.net/t14courses/1412-efmdljiaif/yuyingli/4.3/IMAGE/4-24.GIF Figure 4-24 JM12 type anchor a) JM12 type anchor ； b) Clamping plates of JM12 type anchorages ； c) Anchor ring of JM12 type anchor 1—Anchor ring ； 2—Clamp piece ； 3—Reinforcement bars and steel strand bundles ； 4—Circular plier ring ； 5—Square anchor ring: The JMl2 type anchor has excellent performance; during anchoring, the rebar strands or steel strand bundles are clamped individually, so diameter variations have no impact. Moreover, the prestressed strands are tensioned and anchored in a straight position, resulting in good mechanical properties. To this end, in order to accommodate the anchoring of low-tonnage high-strength wire bundles, JM5-6 and JM5-7 types of anchors capable of anchoring 6–7 Φ5 carbon steel wires have also been developed in recent years; their principle is exactly the same. To reduce the cost of anchors, there is also the precision-cast JM12 type anchor. The JMl2 type anchor is an anchor that utilizes the wedge principle to secure multiple prestressed tendons; it can be used as an anchor at the tensioning end, as an anchor at the fixing end, or as a reusable tool anchor. For JM12 type anchors, the corresponding YC-60 type through-type jack should be used to tension the prestressed tendons. 7. KT-Z type anchor: This is a forged cast iron conical anchor, whose structure is shown in Figure 4-25. It can be used to anchor steel reinforcement bundles and steel strand bundles. Such as anchoring 3 to 6 grade III steel bars with a diameter of 12 mm and grade IV steel bar bundles with a diameter of 12 mm, as well as anchoring 3 to 6 Φj12(7Φ4) steel strand bundles. The KT-Z type anchor consists of an anchor plug and an anchor ring. All are formed from malleable cast iron. This anchor is semi-buried; during use, the smaller end of the anchor ring is first inserted into the load-bearing steel plate and secured there with intermittent welds, after which they are both embedded together at the end of the component. When this anchor is used, the prestressed tendons bend at the small opening of the anchor ring, resulting in friction losses; the magnitude of these losses is approximately 4% of the control stress σcon for the steel tendon bundle ； For the steel strand bundle, it is approximately 2% of the control stress σcon. When the KT-Z type anchor is used with threaded rebar bundles, it is advisable to use a conical-anchor type double-acting jack for tensioning (see Figure 4-35) ； For steel strand bundles, it is advisable to use a YC-60 type double-acting jack for tensioning. http://www.scutde.net/t14courses/1412-efmdljiaif/yuyingli/4.3/IMAGE/4-25.GIF Figure 4-25 KY-Z type anchor 1—anchor ring ； 2—Anchorage plug 8. Porous plate anchor: This is a wedge-type anchor in which a set of clamps is used, placed in each conical hole on a porous anchor plate, to clamp a steel strand. The advantage of this type of anchor is that the failure of the anchorage of any single steel strand will not result in the failure of the entire bundle, and there is no limit to the number of strands in each bundle; however, the ends of the components need to be enlarged. This anchor is widely used in modern prestressed concrete projects. The main products include: (1) XM-type anchor. This is a new type of anchor that consists of an anchor plate and three clamping plates, as shown in Figure 4-26. It is suitable for anchoring both steel strand bundles and wire strand bundles ； It can anchor either a single prestressed tendon or multiple prestressed tendons, and is suitable for anchoring bundles of 3 to 37 Φ15 steel strands or 3 to 12 Φ5 steel wires. When used to anchor multiple prestressed tendons, it is possible to tension and anchor them individually, or to tension and anchor them in groups. Additionally, it can be used as both a working anchor and a tool anchor. In recent years, with the development of prestressed concrete structures and unbonded prestressed structures, XM-type anchors have been widely used. Practice has shown that the XM-type anchorages feature strong versatility, reliable performance, ease of installation, and convenience for work at heights. http://www.scutde.net/t14courses/1412-efmdljiaif/yuyingli/4.3/IMAGE/4-26.GIF Figure 4-26 XM-type anchor a) Assembly diagram ； b) Anchor plate ； c) Clip 1—Anchorage plate ； 2—Clips (three pieces) ； 3—Steel strands: http://www.scutde.net/t14courses/1412-efmdljiaif/yuyingli/4.3/PIC/4.3.2.jpg. The anchor holes on the anchor plate of the YX anchor and XM type anchors are arranged in a circular pattern, with a spacing of not less than 36 mm; the inclination of the centerlines of these anchor holes is 1:20. The top surface of the anchor plate should be perpendicular to the drilling centerline to facilitate even insertion of the clamps. The clamping pieces are of a three-piece design, with seams spaced 120° apart from each other; they have an axial tilt angle, and the direction of this tilt angle is opposite to that of the twist angle of the steel strands, so as to ensure that the clamping pieces can grip each individual wire in the steel strand or wire bundle, thereby providing a reliable anchor. Under conditions that fully satisfy the self-anchoring requirement, the XM anchor uses a larger cone angle for its clamping plates, enabling it to be used as both a working anchor and a tool anchor. When used as a tool anchor, a layer of solid lubricant that can maintain its lubricating properties under extreme pressures (such as graphite, paraffin, etc.) can be applied between the clamping piece and the anchor plate; when the jack retracts, a gentle strike with a hammer is sufficient to release it. When used as a working anchor, it has the function of continuous repeated tensioning; jacks with a limited stroke can be used to tension steel strands of any length. (2) The QM type anchor is suitable for anchoring 4–31 Φj12.7 steel strands or 3–19 Φj15 steel strands. This anchor consists of an anchor plate and clamps, as shown in Figure 4-27. The QM-type anchoring system is equipped with specialized tool anchors to ensure easy withdrawal of the wedges after each tensioning process, and to reduce the time required for installing these tool anchors. http://www.scutde.net/t14courses/1412-efmdljiaif/yuyingli/4.3/IMAGE/4-27.GIF Figure 4-27 QM-type anchor and its accessories 1—Anchor plate ； 2—Clamp piece ； 3—Steel strand ； 4—Trumpet-shaped cast iron gasket ； 5—Bourdon tube ； 6—Spiral tube for reserved ducts ； 7—Grouting hole: The OVM type anchor is based on the QM type anchor; its clamping plates are changed to a two-piece design, and an elastic groove is cut into the upper part of the back of these clamping plates in order to improve the anchoring performance. The OVM13 type anchor is suitable for steel strands shown in http://www.scutde.net/t14courses/1412-efmdljiaif/yuyingli/4.3/IMAGE/6%C4%DA%8Co.gif, while the OVM15 type anchor is suitable for steel strands shown in http://www.scutde.net/t14courses/1412-efmdljiaif/yuyingli/4.3/IMAGE/6%C4%DA%8Cp.gif. (3) The BS-type anchor is suitable for anchoring 3–55 Φj15 steel strands; a steel backing plate, a welded flared tube, and spiral reinforcement are used beneath the anchor. The grouting holes are located on the flared tube and lead out through plastic pipes, as shown in Figure 4-28. http://www.scutde.net/t14courses/1412-efmdljiaif/yuyingli/4.3/IMAGE/4-28.GIF Figure 4-28 BS-type anchorage system