Static structures (e.g. – buildings) – With component having discrete prestressing means
Reexamination Certificate
1999-11-01
2001-06-26
Kent, Christopher T. (Department: 3635)
Static structures (e.g., buildings)
With component having discrete prestressing means
Reexamination Certificate
active
06250030
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a prestressed concrete structure. More specifically, the invention relates to a prestressed concrete structure which, when PC steel members tightening a concrete molded article or tightening a plurality of concrete molded articles are broken, prevents the broken PC steel members from protruding or projecting outward beyond the side portions of the prestressed concrete structure.
2. Description of the Related Art
Prestressed concrete has heretofore been widely known. Prestressed concrete is a technology for enhancing the tensile load characteristics of the concrete by imparting a compressive load prior to the use, and is generally used for large concrete structures such as bridge structures. The compressive load can be imparted to the prestressed concrete in various ways. In a large concrete structure, the compressive load is often imparted relying on a pre-tension method, a post-tension method or a combination of the pre-tension method and the post-tension method.
In a large concrete structure and, particularly, the one adapted to the bridge structures, a plurality of tension members constituted by PC steel rods or PC steel wires that extend in a horizontally transverse direction perpendicular to the longitudinal direction of the bridges, are arranged in parallel in the horizontally longitudinal direction, so that a plurality of neighboring concrete molded articles are fastened together by these tension members, and a large tension is given to the tension members to tighten the concrete molded articles, in order to impart compressive load in the transverse direction to each of the concrete molded articles. In the thus formed concrete structure, in case a tension member to which a large tensile force is imparted breaks due to some cause, the broken tensile member protrudes or projects outward beyond the side portion of the concrete structure.
In order to solve this problem according to, for example, Japanese Patent No. 2742675, a reinforcing sheet of carbon fibers, aramid fibers or a combination thereof is adhered onto the axes of the PC steel members on the side surface of the prestressed concrete structure. In this reinforcing sheet, the warps and wefts are composed of fibers of the same material. When hit by the broken PC steel member, therefore, the reinforcing sheet peels roughly uniformly off the side surface of the prestressed concrete structure. When the reinforcing sheet is peeled up to the edges of the prestressed concrete structure, therefore, there results a conspicuous decrease in the adhesion strength of the reinforcing sheet on the side surface of the prestressed concrete structure. As described above, the reinforcing sheet is roughly uniformly peeled off the side surface of the prestressed concrete structure. When the prestressed concrete structure is a long one such as a bridge structure and has a side surface of an elongated shape, i.e., when the aspect ratio is relatively great, the peeling, which proceeds in a direction in parallel with the short side, quickly arrives at the edge of the prestressed concrete structure resulting in a remarkable drop in the adhesion strength of the reinforcing sheet.
The present invention was accomplished in order to solve this problem, and its object is to provide a prestressed concrete structure which, when the PC steel members used in the prestressed concrete structure are broken, prevents the broken PC steel members from protruding or projecting outward beyond the side portions of the prestressed concrete structure.
Another object of the present invention is to provide a fiber-reinforced resin composite material used for preventing the broken PC steel members from protruding or projecting outward beyond the side portions of the prestressed concrete structure.
A further object of the present invention is to provide a sheet member used for preventing the broken PC steel materials from protruding or projecting outward beyond the side portions of the prestressed concrete structure.
SUMMARY OF THE INVENTION
According to the present invention, there is provided a prestressed concrete structure comprising:
a long concrete molded article having a pair of side surfaces opposed to each other;
a plurality of tensile members penetrating and stretching inside the concrete molded article from one of the pair of the surfaces toward the other the surface in a transverse direction, secured at their both ends to the the surfaces of the concrete molded article in a tensioned state, and are imparting a compressive load to the concrete molded article;
a pair of side guards arranged along both side surfaces of the concrete molded article so as to cover the ends of the tensile members; and
reinforcing members arranged on the side surfaces of the pair of the guards in order to prevent the broken tensile members from protruding beyond the side surfaces thereof breaking through the side guards when the tensile members in the tensioned state are broken; wherein
the reinforcing members stretch little in the longitudinal direction of the side surfaces of the side guards but easily stretch in the transverse direction on the the surfaces of the side guards and, when pushed from the inside by the ends of the tensile members that protrude as a result of breakage, the peeling of the reinforcing members easily spreads out in the longitudinal direction of the side surfaces of the side guards but spreads out little in the transverse direction on the the surfaces of the side guides.
The tensile member that is broken no longer imparts a tensile force. Therefore, a large thrust acts upon the broken tensile member in the axial direction thereof. Due to the thrust, the broken tensile member moves in the axial direction. The magnitude of thrust acting on the tensile member at breakage varies depending upon the conditions such as the length of the tensile member that is broken, magnitude of tension acting on the tensile member at breakage, rate of progress leading to breakage, material of the tensile member, and the like. When the tensile member is a PC steel rod, in particular, it has been known that a large thrust acts. When the thrust is great, the broken tensile members often protrude beyond the side surfaces of the side guards.
According to the present invention, the tensile members that protrude penetrating through the side guard come into collision with the reinforcing member provided on the side surface of the side guard. The reinforcing member is peeled off the side surface of the side guard while being stretched, thereby to effectively absorb the kinetic energy of the tensile members that are broken.
In general, as the peeling of the reinforcing member spreads out and reaches the upper and lower edges on the side surface of the side guard, the bonding force of the reinforcing member on the side surface of the side guard greatly drops at that portion resulting in a sharp decrease in the ability for absorbing the kinetic energy of the tensile members that are broken. According to the present invention, the reinforcing member stretches little in the longitudinal direction but easily stretches in the transverse direction on the side surface of the side guard. Therefore, peeling of the reinforcing member spreads out in the longitudinal direction on the surface of the side guard but hardly spreads out in the transverse direction to alleviate the above-mentioned problem.
Preferably, furthermore, the reinforcing member includes warps that extend in the longitudinal direction on the side surfaces of said side guards, wefts that extend in the transverse direction, and a resin material for bonding said warps and said wefts, said warps having a tensile modulus of from 5000 to 18000 kgf/mm
2
and said wefts having a tensile modulus of from 300 to 4500 kgf/mm
2
.
The warps having a large tensile modulus stretch little. Therefore, the reinforcing members stretch little in the longitudinal direction on the side surfaces of the side guards and are easily peeled off the side surfaces of t
Kidera Akira
Sugimoto Morihiko
Yanagi Youji
Kent Christopher T.
McDermott Kevin
Sughrue Mion Zinn Macpeak & Seas, PLLC
Teijin Limited
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