Patent Application
20120124937
This application claims the benefit of Chinese Patent Application No. 201010180716.6 filed on May 24, 2010, the entire content of which is hereby incorporated by reference.
The invention relates to loaded members in bridge and construction structures, and particularly, relates to hybrid FRP-concrete-steel double-skin tubular beams (DSTBs) and hybrid DSTB/slab units using the hybrid beams.
Popular beam forms that are currently widely employed in bridge and construction structures include reinforced concrete (RC) beams and steel beams. Undesirably, both beam forms are prone to deteriorating and corrosion in harsh environments, such as in the wild, at the seaside or in a humid environment. In other words, these beam forms suffer from poor corrosion resistance.
Recently, fibre-reinforced polymer (FRP) composites have been increasingly widely employed for the purpose of solving deterioration and endurance issues that would otherwise occur in bridge and construction structures worldwide. FRP is a novel nonmetal material that is composed by mixing fibers of high performance, such as carbon fibers, glass fibers and Basalt fibers, with resin matrix and then compounding the mixture through a certain process. As a material with high corrosion resistance, FRP possesses additional advantages of lightweight, high strength, and easiness for moulding.
Prior art beam forms that employ FRP include: (a) all-FRP beams (referred to as type I beams hereinafter) which commonly resume forms resembling those of steel beams (such as I-shaped or box-shaped beams), (b) hybrid beams incorporating FRP and concrete, such as FRP bar-reinforced concrete beams, hybrid beams composed of an FRP profile that functions to bear tension and a concrete layer cast thereon that functions to bear compression, and concrete-filled FRP tubes (hereafter referred to as type II beams, type III beams and type IV beams, respectively). The above-mentioned beam forms suffer from high costs due to the use of a large amount of FRP material as the main longitudinal reinforcement. In addition, these beam forms suffer from a low stiffness which renders its deformation, instead of its load capacity, the critical concern in design, and poor ductility due to the brittle nature of FRP materials.
The purpose of the invention is to provide a novel hybrid FRP-concrete-steel double-skin tubular beam and a hybrid beam/slab unit which employs the hybrid tubular beam to address the aforementioned drawbacks in the prior art.
The technical solution that the invention proposes is a hybrid double-skin tubular beam, wherein the hybrid double-skin tubular beam consists of an outer FRP tube, an inner steel tube, and concrete filled between the outer FRP tube and the inner steel tube, and the inner steel tube is provided with a plurality of shear connectors on its side engaged with concrete so as to ensure the inner steel tube and the concrete to work together.
In an embodiment according to the invention, the plurality of shear connectors are distributed along the circumferential and longitudinal directions of the inner steel tube.
In an embodiment according to the invention, the inner steel tube is located eccentrically relative to the outer FRP tube towards the side of the hybrid tubular beam to be tensed.
In an embodiment according to the invention, the cross sectional shape of the hybrid double-skin tubular beam is an arbitrary combination of an outer FRP tube of circular, square, rectangular or any other suitable shapes and an inner steel tube of circular, square, rectangular or any other suitable shapes. In an embodiment, the cross sectional shape of the hybrid double-skin tubular beam is identical along the longitudinal direction. Alternatively, the inner steel tube is located inclinedly relative to the outer FRP tube along the longitudinal direction in such a way that the inner steel tube is closer to the lower portion of the cross section in the region of positive bending moments and is closer to the upper portion of the cross section in the region of negative bending moments.
In an embodiment according to the invention, the outer FRP tube may be manufactured by means of a winding moulding process. The orientation of the fibers of the outer FRP tube may be customized according to structural requirements. In most applications, fibers are mainly wound along the circumferential direction or substantially along the circumferential direction.
The invention additionally proposes a hybrid DSTB/slab unit which is comprised of a beam and a slab provided thereon, wherein the beam is a hybrid double-skin tubular beam, including an outer FRP tube, an inner steel tube and concrete filled therebetween; and the inner steel tube is provided with a plurality of shear connectors on its side engaged with concrete to ensure the inner steel tube to work together with the concrete.
The invention further proposes a hybrid DSTB/slab unit which consists of a hybrid double-skin tubular beam and an FRP-rib reinforced concrete slab, wherein the upper portion of the hybrid double-skin tubular beam is engaged with the bottom of the FRP-rib reinforced concrete slab thereinside so as to form an integrated body; the hybrid double-skin tubular beam is comprised of an outer FRP tube, an inner steel tube and concrete filled therebetween; and the inner steel tube is provided with a plurality of shear connectors on its side engaged with concrete to ensure the inner steel tube to work together with the concrete.
In the embodiment according to the invention, the hybrid double-skin tubular beam is embedded with a reinforcement rib in the upper portion thereof; the reinforcement rib penetrates through the outer FRP tube, and is connected with the bottom FRP ribs of the FRP-rib reinforced concrete slab so as to integrate the hybrid double-skin tubular beam and the FRP-rib reinforced concrete slab.
Compared with RC beams and steel beams, the hybrid FRP-concrete steel double-skin tubular beams (DSTBs) according to the invention have a main advantage of excellent corrosion resistance. Compared with types I to IV beams, the advantages of hybrid DSTBs lie in: (1) cost effectiveness because of the use of less FRP material (only a thin outer FRP tube is needed); (2) excellent ductile behavior as the inner steel tube acts as the ductile longitudinal reinforcement. Besides the above two advantages, hybrid DSTBs allow for easier connection to other members than type I beams due to the presence of the inner steel tube and concrete. In addition, the outer FRP tube of the hybrid double-skin tubular beam provides good confinement to the compressive concrete, which is not provided by type II and III beams. Furthermore, the hybrid double-skin tubular beam is lighter than type II and IV beams due to the elimination of redundant tensile concrete.
Hereinafter the invention will be further described with reference to the embodiments and the accompanying figures, wherein,
To clarify the purpose, the technical solutions and the advantages of the invention, the invention will be further described with reference to the accompanying figures and embodiments. It should be appreciated that the embodiments illustrated herein are intended to explain the invention, and will not limit the scope of the invention by any means.
Even though various embodiments of the hybrid double-skin tubular beam that have different cross sectional shapes are hereinbefore described with reference to
In the hybrid double-skin tubular beam according to the invention, the outer FRP tube offers mechanical resistance primarily in the circumferential direction, and mainly functions to confine the concrete and to enhance the shear resistance of the beam. Only a low level of mechanical resistance of the outer FRP tube is needed in the longitudinal direction to support wet concrete when in-situ casting is used and to avoid undesirable tensile cracking under service loading. This characteristic of the hybrid double-skin tubular beam features two advantages. Firstly the FRP tube may be very thin such that the material cost may be reduced; and secondly, the concrete is confined and the ductility of the beam is enhanced. Such outer FRP tube may be manufactured by means of fiber-winding moulding process in which fibers are wound substantially along the circumferential direction (e.g. ±80°). In such a way the shear resistance of the hybrid tubular beam is enhanced and the confinement imposed on the concrete is ensured.
The predominant advantage of the hybrid double-skin tubular beam according to the invention is excellent corrosion resistance since the outer FRP per se features an excellent corrosion resistance and the inner steel tube is protected by the outer FRP tube and the concrete from corrosion. If necessary, the both ends of the inner steel tube may be welded with steel plate so as to seal the hybrid tubular beam. Among others, the hybrid double-skin tubular beam according to the invention possesses the following advantages. Its ductility is excellent since the inner steel tube with good ductility is employed as the material to bear longitudinal tension and the concrete is appropriately confined by the inner and outer tubes. The hybrid tubular beam is lightweight since a large amount of concrete under tension may be dispensed with due to the hollow configuration of the cross section. The inner tube and the outer tube may function as the permanent dies for casting concrete such that the hybrid tubular beam is easy for construction. The hybrid tubular beam allows for easier connection to other members due to the presence of the inner steel tube and the concrete. In addition, employment of the inner steel tube ensures that the hybrid tubular beam features a high resistance against bending, such that the main drawback associated with the prior art glass fiber FRP bar-reinforced concrete beams that the excessive flexibility (instead of strength) becomes the critical design consideration due to relatively low elastic modulus is overcome.
The hybrid double-skin tubular beam according to the invention is cost-effective even considered for initial constructions. The fibers in the outer FRP tube mainly take tension due to the fact that the outer FRP tube primarily serves as the protective layer against corrosion, the permanent die for concrete casting and the outer shell for enhancing shear resistance and ductility. Therefore relatively thin FRP tube may fulfill these purposes. In this way, the cost of the thin outer FRP tube and the inner steel tube can be entirely compensated by labor and/or material costs saved by dispensing with excessive concrete under tension, temporary dies and steel bars. Therefore, the initial construction cost of the hybrid double-skin tubular beam according to the invention is comparable to that of the prior art reinforced concrete. In addition, since the former is lighter, the cost of the supports will be further reduced. Finally the maintenance cost will be greatly reduced due to excellence corrosion resistance of the hybrid double-skin tubular beam according to the invention.
Hereinbefore, the hybrid double-skin tubular beams with identical cross sections along the longitudinal direction are described with reference to the embodiments as illustrated in
The hybrid double-skin tubular beams according to the invention can be employed as bridge girders, bridge girder/slab components, and flexural members (e.g. beams and slabs) in other structures in a corrosive/harsh environment. Hereinafter, the applications of the hybrid double-skin tubular beams according to the invention in hybrid beam/slab units will be described with reference to
The hybrid DSTBs and hybrid DSTB/slab units employing the DSTBs according to the invention are competitive alternatives to existing beam forms and bridge deck/floor systems. The invention provides a durable, ductile and cost-effective solution to help overcome the worldwide infrastructure deterioration problem.
Although preferred embodiments of the invention have been described and illustrated herein, it is recognized that modifications, alternatives and variations may readily occur to those skilled in the art and, consequently, it is intended that the claims be interpreted to cover such modifications and equivalents.
| Number | Date | Country | Kind |
|---|---|---|---|
| 201010180716.6 | May 2010 | CN | national |
