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KR-102961885-B1 - Bi-prestressed PSC girder

KR102961885B1KR 102961885 B1KR102961885 B1KR 102961885B1KR-102961885-B1

Abstract

The present invention relates to a bi-prestressing PSC girder in which a PS steel strand for introducing compression prestress is embedded in the lower tension side of a girder body that is a PC member, and a PC steel rod for introducing tension prestress is embedded in the upper compression side divided into two or more in the longitudinal direction, thereby increasing the critical buckling load of the PC steel rod placed on the upper part of the girder for introducing bi-stressing in the PSC girder, and furthermore, reducing the stress deviation when the PC steel rods arranged in multiple rows are pressed, thereby minimizing the occurrence of transverse bending of the PSC girder. The bi-prestressing PSC girder of the present invention is characterized by being composed of: a girder body which is a precast concrete member; a PS steel strand embedded in the lower tension side inside the girder body in the longitudinal direction to introduce compressive prestress; and a PC steel rod divided into at least two in the longitudinal direction to embedded in the upper compression side inside the girder body to introduce tensile prestress.

Inventors

  • 김철호
  • 양태선
  • 김흥균
  • 김경수
  • 김길상
  • 이동건

Assignees

  • 에이스이건설(주)

Dates

Publication Date
20260507
Application Date
20251020

Claims (7)

  1. girder body (2) which is a precast concrete member; PS steel strands (3) embedded longitudinally in the lower tension side inside the girder body (2) to introduce compressive prestress; A PC steel rod (4) divided into at least two or more in the longitudinal direction, which is embedded in the upper compression side inside the girder body (2) to introduce tensile prestress; and An open upper surface is exposed to the upper surface of the girder body (2) so as to accommodate a pressure device (6) that presses the end of the PC steel rod (4) inside, and is provided between the divided PC steel rods (4) so as to be connected to the inner ends of the divided PC steel rods (4) inside. A first through hole (511) through which the end of the PC steel rod (4) passes is formed in each of the two end walls (51), and a second through hole (541) through which the end of the PC steel rod (4) passes is formed inside at a position corresponding to the first through hole (511), and a support partition wall (54) is provided so as to be spaced apart from the end wall (51). A first receiving space (501) for accommodating the pressure device (6) is formed between the two support partition walls (54), and a first fixing nut ( N1) that is screw-coupled to the PC steel rod (4) is formed between the end wall (51) and the support partition wall (54). A bi-prestressing PSC girder characterized by being composed of a pressure box (5) in which a second receiving space (502) is formed to accommodate )
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  4. In paragraph 1, The bi-prestressing PSC girder is characterized in that the above PC steel rods (4) are provided in multiple rows, and a pressure plate (55) that simultaneously presses the multiple PC steel rods (4) by driving the pressure device (6) is provided in the first receiving space (501) of the pressure box (5) so as to be slidably movable at the front and rear of the pressure device (6).
  5. In Paragraph 4, A bi-prestressing PSC girder characterized by having a head nut (41) fastened to the end of the PC steel rod (4) in the first receiving space (501) and configured so that the pressure plate (55) presses the head nut (41).
  6. In Paragraph 4, A bi-prestressing PSC girder characterized by having a guide means (56) that guides the longitudinal sliding of the pressure plate (55) inside the pressure box (5).
  7. In paragraph 1, A bi-prestressing PSC girder characterized in that a pocket portion (21) with an open top is formed in the girder body (2) at the fixed end position of the PC steel rod (4), and a fixing member (7) is provided in the pocket portion (21), which includes a front wall (71) formed with a fourth through hole (711) through which the end of the PC steel rod (4) passes, spaced apart from the front of the pocket portion (21) at a certain distance, and a second fixing nut ( N2 ) that is screw-coupled to the PC steel rod (4) is provided between the front wall (71) and the front of the pocket portion (21).

Description

Bi-prestressed PSC girder The present invention relates to a bi-prestressing PSC girder in which a PS steel strand for introducing compression prestress is embedded in the lower tension side of a girder body that is a PC member, and a PC steel rod for introducing tension prestress is embedded in the upper compression side divided into two or more in the longitudinal direction, thereby increasing the critical buckling load of the PC steel rod placed on the upper part of the girder for introducing bi-stressing in the PSC girder, and furthermore, reducing the stress deviation when the PC steel rods arranged in multiple rows are pressed, thereby minimizing the occurrence of transverse bending of the PSC girder. Prestressed Concrete (PSC) girders are girders that introduce compressive force into concrete by tensioning tensioning members, offering excellent crack resistance and durability. These PSC girders are widely used in the construction of small to medium-span bridges due to their economic efficiency and structural performance. Meanwhile, for river-crossing bridges, low-profile bridges are required to secure clearance in consideration of flood levels, and for road-crossing bridges, there is an increasing demand for extended spans as the number of lanes must increase due to increased traffic volume. Therefore, various technologies are being developed to achieve low profiles and long spans in the case of PSC girders as well. Accordingly, the phased tensioning method is often applied to lower the height of PSC girders and increase the span. In the staged tensioning method, a primary tension force is introduced to the PS steel strands placed on the tension side during girder fabrication, and after installing the girder with the primary tension force introduced, a deck slab is installed and a secondary tension is performed while the deck slab load is applied. By increasing the efficiency of prestress introduction through this, the girder height can be reduced and the span length can be extended to more than 50m. However, even when applying the staged tensioning method, if the height of the PSC girder is low, introducing tensioning force to the PS steel strands increases the influence of axial force relative to bending moment, resulting in excessive compressive stress at the upper edge of the girder. In addition, there is a problem where additional secondary dead loads and live loads are applied, causing the allowable compressive stress at the upper edge of the girder cross-section to be exceeded. In response to this, to relieve excessive compressive stress on the upper edge, the upper cross-section can be enlarged or reinforced by inserting steel. However, in this case, additional prestressing is required due to the increase in self-weight, and a decrease in constructability due to steel composite is inevitable. Furthermore, when the upper flange is enlarged, the center of gravity rises, posing a risk of overturning, and construction safety is compromised because secondary tensioning work is performed at a height. Accordingly, a bi-prestressing method was developed in which PC steel is placed at the bottom and top of the girder cross-section, and then the lower PC steel is tensioned to introduce compressive force to the lower edge of the girder, and the upper PC steel is compressed to introduce tensile force to the upper edge of the girder (Registered Patent No. 10-1356675, etc.). The bi-prestressing method enables economical design without expanding the cross-section or increasing the girder height by compressing and anchoring PC steel placed on the upper edge of the girder to introduce tensile stress into the upper edge through repulsive force, thereby offsetting the compressive stress in the upper edge, and simultaneously introducing compressive stress into the lower edge through couple force. However, when PC steel is arranged vertically to introduce double prestressing, it provides high stiffness along the strong axis, but there is a problem in that the lateral stiffness becomes relatively weak as the axial stiffness increases. In particular, in the case of bi-prestressing girders that apply compressive force to PC steel, the risk of lateral bending may increase further due to buckling of the PC steel and asymmetric compressive force introduced into the concrete in the form of reactions, especially when multiple PC steels are arranged symmetrically around the vertical neutral axis. FIG. 1 is a perspective view illustrating the PSC girder of the present invention. FIG. 2 is a side view illustrating the PSC girder of the present invention. FIG. 3 is a perspective view illustrating a pressure box. FIG. 4 is a perspective view illustrating a girder body with a pressure box embedded therein. FIG. 5 is a perspective view illustrating the connection relationship between a pressure box and a PC steel rod. FIG. 6 is a side cross-sectional view illustrating the anchoring process of PC steel rods in a pressure box. FI