JPS59217830A - Removable anchoring work - Google Patents

Abstract

PURPOSE:To lessen the lowering of the tensile strength of anchors by a method in which the cross section of the end of PC steel material is reduced by drawing work, a compression grip is welded to the position of the end, a bearing plate is provided, and PC steel material is tensed and fractured. CONSTITUTION:The end of PC steel material, whether unbond or not or whether having grease 5 or sheath 6 as a covering material, is subjected to a swaging work, a bearing plate 3 for dispersing tensing load is inserted into the swaged portion 2, and a compression grip 4 is attached. Primary cement mortar for fixation is poured to fix the fitting portion and hardened, and then secondary cement mortar 8 is poured to integrate the steel materials with anchor 9. Only a specific position can thus be broken and one or plural steel materials can be removed concurrently.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a removable anchor construction method, which is a construction method in which a PC steel material is anchored under tension to the ground, rock, etc., and removed after it has been stabilized.

Conventionally, in construction work in urban areas, the removable anchor method is often applied when constructing underground structures that are foundation work. However, P, which is a steel material for anchors,
The tip of the C-steel will be inserted into a neighboring underground site that is owned by someone else, so it will need to be removed. This removal is extremely time consuming as it is necessary to pull out the steel material, and if it becomes impossible to remove the steel material, it will have to be removed by excavation or the like, resulting in a waste of time and effort.

The present invention reduces the tensile strength by reducing the diameter of the PC steel material in the anchoring part of the steel material for anchors, crimping a compression grip to the steel material part, and transmitting the introduced load to the anchoring part mortar via the bearing plate, This involves a removable anchor construction method in which a load higher than the introduced load is applied to the steel material near the compression grip to cause it to break and be removed.

Steel anchors can be broken by applying a tension greater than the tensile strength of the steel material; however, with this method, the location at which the anchor breaks is unspecified and often breaks at the anchorage on the tension side. Therefore, it is not suitable for the purpose of removing the anchor steel material as a tension system.

Previously, research had been conducted to reduce the tensile strength by annealing a portion of the anchor in advance, but the heating temperature and heating time differed slightly depending on the chemical composition, structural shape, dimensions, etc. of the steel material, making it difficult to control the process. It was practically impossible for mass production. Also, the connection of dissimilar steel materials is less practical because the 'If becomes large.

Ki-nii@14 is PC! f1 Phrase material In particular, this was done on the unbonded PC value system where the PC steel strand wire is coated with grease and coated with polyethylene, etc. or the PC steel surface is coated with Teflon, and corresponds to the purpose of the steel material. 9F
It is also characterized in that the effective cross-sectional area is reduced by cutting out at appropriate locations and subjecting it to a process such as peeling swaging, thereby reducing the tensile strength at break and causing only the erect parts Qi to break.

The specific structure related to the present invention is shown in FIG.
PC! After inserting the bearing plate 3 into the processed part 2 where the end of the copper TT 1 is swaged, the compression grip 4 is attached. The PC steel may be an unbonded product, or the PC steel may be coated with grease 5 and a sheath 6 made of -+s Su.

The same pressure plate 3 is used to distribute the tension load.

After that, a secondary mortar 7 for fixing is injected to fix the fixing part, and after hardening, a secondary mortar 8 is injected and the steel material and the anchor part 9 are injected.
to integrate.

FIG. 2 shows the relationship between the tensile strength and elongation of the steel material during removal in the present invention. Since the length of the swaging portion is extremely small compared to the total length of the steel material, even if the elongation rate for a given tension load is large, the elongation value is very small. In the steel part, the load-elongation curve of the non-swaging part is A, that of the swaging part is B, and A
, C shows curves in which only the elongation amounts of B are added. The breaking load of the steel material is determined only by the tensile strength of the swaging portion, and the amount of elongation is the sum of the amount of elongation of the entire unprocessed portion of the steel material and the amount of elongation of the swaging portion. Therefore, the fracture position is limited to the swaging part where the cross-sectional area and elongation are the smallest, and when removing the steel material, the swaged part can be left behind.

An embodiment according to the present invention will be described below.

P from 7 pieces specified in Steel Material 1dJ Engineering S G 3536
Using a steel material made by unbonding 15.21 After insertion, compression processing was performed.

To prevent rust, the processed area was protected with black tape after being coated with a rust preventive agent.

After completing these operations, insert the anchor into the pre-drilled anchor, inject mortar, and after the mortar hardens, PC is installed by jacking.
Tension fixing was carried out under a tensile load of 80 degrees from the steel legs, but no abnormality such as breakage or slipping occurred. In the removal operation, tension was applied by breaking and freezing using jacks in the same manner as tension fixing, and the wire broke at a maximum load of 22,500 Kp, allowing seven strands to be removed from the swaging section. The impact of breakage is 1 with grease.
? There were no significant impingements due to friction resistance. Similarly, in this example, the area reduction rate was set to 1()chi, but there are other large reductions Ir1i.
When processing at a high temperature, it is preferable to perform strain removal heat treatment by heating at a low temperature in a tubular heating furnace.

As described above, the present invention provides f′ in the removable anchor construction method.
As a means of reliably removing l1iil material, a part of the brass material is subjected to a reduction process such as swaging to reduce the strength of the steel material, which causes it to break under tension, making it possible to remove not only one but multiple steel materials at the same time. It is. Furthermore, fixation can be done not only with a compression grip, but also with a wedge-type fixing device using a spring.

[Brief explanation of drawings]

FIG. 1 is a schematic explanatory diagram of the steel inserted into the anchor. Second
The figure is a comparison diagram of tensile load and elongation line of PC steel stranded wire. 1: PC steel material, 2 varnished part, 3: bearing plate, 4
: Compression grip, 5 Nigelise, 6: Cover [
D material, 7 secondary mortar, 9: One hole for anchor.

Claims (1)

[Claims] Removal characterized by reducing the cross section of the end of the PC steel material by reduction processing such as swaging processing, crimping a compression grip at the position, providing a bearing plate, and pulling the PC TFI material at the position to cause it to break. Type anchor construction method.