JP7428170B2 - bridge - Google Patents

Description

The present invention relates to bridges.

BACKGROUND ART Bridges have traditionally been constructed as prestressed concrete structures (Patent Document 1).

Japanese Patent Application Publication No. 2006-348656

Japan Society of Civil Engineers, Concrete Committee, Super High Strength Fiber Reinforced Concrete Research Subcommittee, ed., "Design and Construction Guidelines for Ultra High Strength Fiber Reinforced Concrete (Draft)", Japan Society of Civil Engineers, published September 28, 2004.

In the prior art, the compressive stress applied to the concrete may be reduced by an unsteady force (also referred to as a secondary force) accompanying the introduction of prestress. As a result, sufficient compressive stress may not be applied to the concrete, and there is a possibility that the required performance may not be obtained.

In order to solve the above problems, one aspect of the present invention is a girder of a precast concrete structure that extends in the axial direction of a bridge and has a concrete cross section, the primary steel material applying compressive stress to the concrete cross section in a pre-tensioning manner. and a secondary steel material that increases the compressive stress in a post-tensioning manner with respect to the concrete cross section.

Another aspect of the present invention is a method for constructing a girder of a precast concrete structure that extends in the axial direction of a bridge and has a concrete cross section, wherein compressive stress is applied to the concrete cross section using a pretension method using a primary steel material. and a step of increasing the compressive stress on the concrete cross section using a secondary steel material in a post-tensioning manner.

According to the present invention, a bridge with high performance can be provided.

They are a perspective view and a partially enlarged view of a bridge in an embodiment. 1 is a top view of a bridge according to an embodiment, showing the girder segment arrangement; FIG. It is a sectional view of the bridge in an embodiment. Note that the reinforcement arrangement is shown in the cross section at the center of the span. It is a flow of a widening part construction process according to an embodiment. It is a figure showing the construction state of the precast member in an embodiment, and shows (a) a center segment, (b) an end segment, and (c) a floor slab. Note that a side view is shown on the left, and a cross-sectional view is shown on the right. It is a figure which shows the construction situation of the widening part in embodiment, (a) end segment installation, (b) central part segment installation, (c) floor slab fixing, and (d) enlarged view of d frame in figure c. shows. It is a figure which compares the compressive stress applied to the girder cross section in (a) embodiment and (b) prior literature. It is a sectional view of a girder in a modification, and shows the shape of the sheath and secondary steel material installed in the girder.

<Summary>
A bridge 1 that is an embodiment of the present invention will be described below. The bridge 1 has a prestressed concrete structure at least in part. In addition, in the following description, the direction in which the bridge 1 extends is assumed to be the bridge axis direction, and the direction orthogonal to this is assumed to be the bridge axis perpendicular direction.

The bridge 1 mainly includes an existing section 2 that was constructed the oldest, an existing section 3 that was constructed next, and a widened section 4 constructed between the existing section 2 and the existing section 3. The existing portion 2, the existing portion 3, and the widened portion 4 all extend in the bridge axis direction.

The existing part 2 includes a girder 21, a flat slab 22 formed on the upper surface of the girder 21, and a pier 23 that supports the girder 21.

Like the existing part 2, the existing part 3 includes a girder 31, a flat slab 32 formed on the upper surface of the girder 31, and a pier 33 that supports the girder 31.

The widening part 4 is joined to the existing part 2 and the existing part 3, and functions as a bridge that widens the existing part 2 and the existing part 3. The widening section 4 is a bridge having a hollow cross section as shown in FIGS. 1 to 4, FIGS. It also includes a pier 45 that supports the girder 41.

The girder 41 is formed by joining a plurality of segments having the same cross-sectional shape and a precast concrete structure in the bridge axis direction. The girder 41 includes a segment 41A located between the piers 45, that is, at the center of the span, and a segment 41B located near the fulcrum. Segment 41B is a segment supported by pier 45, and segment 41A is fixed between two segments 41B (FIGS. 2, 3, and 6). The cross section of the girder 41 (ie, segments 41A, 41B) defines a centroid line 41C.

The segments 41A and 41B each include a concrete portion 411, a sheath 412, a primary steel material 413, a secondary steel material 414, and an anchor 415 (FIGS. 3 and 5). The concrete part 411 is provided with reinforcement such as main reinforcement and safety reinforcement.

The sheath 412 is a pipe extending substantially in the axial direction of the bridge, through which the secondary steel material 414 passes, and is buried in the concrete portion 411 (FIGS. 3 and 5). The sheath 412 is installed in a cross section of the segments 41A and 41B in a direction perpendicular to the bridge axis so as to substantially coincide with the centroid position of the cross section. In this embodiment, the sheath 412 is installed at multiple locations, but in this case, the centroid of the entire sheath 412 is located on the centroid line 41C in the cross section of the girder 41 (that is, the segments 41A, 41B).

The lower part of the anchor 415 is fixed to the upper part of the concrete part 411 (FIG. 3). Various members are used for the anchor 415. For example, a headed anchor bolt may be employed as the anchor 415. The upper part of the anchor 415 is fixed to the floor slab 42. In this way, the floor slab 42 and the girder 41 are joined via the anchors 415.

The primary steel material 413 is a steel material that extends approximately in the axial direction of the bridge and applies prestress using a pretension method to a cross section of the concrete portion 411 (hereinafter referred to as a concrete cross section). In addition, in FIG. 3, the primary steel material 413 is indicated by a black circle. Tension is applied to the primary steel material 413, and the primary steel material 413 applies compressive stress to the concrete portion 411 through its adhesion to the concrete portion 411.

The primary steel material 413 is placed at the bottom of the segment 41A, and at the top of the member in the segment 41B (FIGS. 2, 3, and 6). By changing the arrangement position of the segment 41A to which a positive bending moment (bending moment that produces tensile stress on the lower side of the member) is applied and the segment 41B to which a negative bending moment is applied, the primary steel material 413 is Compressive stress is applied to the concrete portion 411 at an appropriate position. In addition, in FIG. 5, the primary steel material 413 is partially omitted.

The secondary steel materials 414 are inserted into the sheath 412 one by one and fixed to the girder 41 under tension. Each secondary steel material 414 is installed continuously across two piers 45, that is, over one span. Both ends of the secondary steel material 414 are fixed to the ends of the segment 41B. The arrangement of the secondary steel material 414 is almost the same as that of the sheath 412. In other words, the secondary steel materials 414 are arranged linearly so as to extend substantially in the bridge axis direction. Furthermore, when viewed in cross section, the centroid of the entire secondary steel material 414 is located on the centroid line 41C of the segments 41A and 41B (FIGS. 3 and 5). In other words, the secondary steel material 414 is arranged so as to be substantially symmetrical with respect to the cross-sectional center line 41C of the segments 41A and 41B. Therefore, the center of tension in the entire secondary steel material 414 is generally located on the centroid line 41C.

In addition, a joining key 416 is provided at each end of segments 41A, 41B (FIG. 5). Joining key 416 joins segment 41A and segment 41B, and transmits shear force and bridge axial direction compressive force between both segments. The structure of the joining key 416 is appropriately selected depending on design conditions. Therefore, the joint key 416 may be made of steel, but in this embodiment, a concrete joint key is used. The space between the segments 41A and 41B (that is, between the opposing joint keys 416) is filled with non-shrinkage mortar as necessary.

The floor slab 42 is a precast concrete member formed into a flat plate shape, and is fixed to the upper surface of the girder 41 via anchors 415 (FIGS. 3, 5, and 6). The floor slab 42 has a prestressed concrete structure using a pretension method. A compressive stress is applied to the cross section of the floor slab 42 by a steel material 421 that is a prestressing steel material. The steel material 421 is arranged so as to be able to apply substantially uniform compressive stress to the cross section of the deck slab 42. In addition, in FIG. 5, the position, number, etc. of the primary steel materials 413 are simply shown.

The vertical joint portion 43 is formed between the floor slab 22 and the floor slab 42 and between the floor slab 32 and the floor slab 42 so as to extend in the bridge axis direction. As shown in FIGS. 1 and 2, the vertical joint portion 43 joins the ends of the deck slab 22 and the deck slab 42 in the direction perpendicular to the bridge axis, and also connects the ends of the deck slab 32 and the deck slab 42 in the direction perpendicular to the bridge axis. join the parts. The vertical joint portion 43 is a reinforced concrete member formed by reinforcement 431 and a concrete portion 432.

The reinforcement arrangement 431 includes a plurality of reinforcing bars that protrude from at least the ends of the deck slab 22 and the ends of the deck slab 42 in the direction perpendicular to the bridge axis to provide anchorage (FIG. 3).

The concrete portion 432 is preferably made of fiber-reinforced concrete, particularly ultra-high strength fiber-reinforced concrete (UFC). Although UFC is a material with various properties, Non-Patent Document 1 specifies that the tensile strength of UFC is 5 N/mm ² or more.

Because it is a material with such high tensile strength, when UFC is used for the concrete portion 432, it is possible to shorten the anchorage length of the reinforcement 431 compared to other concrete materials. By shortening the anchoring length, the width of the vertical joint portion 43 can be shortened, and the construction range of the construction work can be reduced.

By reducing the construction area, it will be easier to suspend and restore the construction work, and to open it to traffic. For example, in cases where the construction period spans multiple days, traffic may be allowed during the suspension of construction. In this case, it is common to temporarily pave the construction area or cover the construction area with iron plates to allow vehicles and the like to pass during the suspension of construction. If the construction area is small, the area for temporary paving or laying of iron plates can be made smaller, and the work required for preparation for construction suspension and construction restoration can also be reduced. Therefore, it is possible to shorten the construction period and reduce costs.

The lateral joint portion 44 is formed between the deck slabs 42 so as to extend approximately in a direction perpendicular to the bridge axis. As shown in FIG. 1, the lateral joint portion 44 has a function of joining the deck slabs 42 together in the bridge axis direction. The horizontal joint portion 44 is a reinforced concrete member formed by reinforcement 441 and a concrete portion 442 (FIG. 6(d)).

As shown in FIGS. 1 and 6(c), the horizontal joint portion 44 is provided at a position different from the joint position of the segments 41A and 41B. By shifting the position of the lateral joint 44 in the bridge axis direction from the joining position of the segments 41A, 41B, excessive strain can be avoided from occurring in the lateral joint 44. This prevents problems such as cracks occurring in the lateral joints 44 and contributes to maintaining the quality of the bridge 1.

The reinforcing bars 441 include at least a plurality of reinforcing bars or anchors that protrude from the deck slab 42 in the bridge axis direction to take anchor.

The concrete portion 442 is preferably made of fiber-reinforced concrete, particularly UFC construction. By using UFC, the anchoring length of the reinforcement 441 can be shortened, and the width and construction range of the horizontal joint 44 can be reduced, similarly to the vertical joint 43. As a result, as described above for the vertical joint portion 43, various effects such as shortening the construction period can be obtained.

The pier 45 is a member that supports the girder 41. As shown in FIG. 2, the piers 45 are installed independently of the piers 23 and 33, and do not necessarily match the piers 23 and 33 both in installation position and distance between the piers. The method of supporting the girder 41 by the pier 45 and the shape of the fulcrum are appropriately selected depending on the conditions, such as rigid connection, pin, roller, or hinge support via a support, for example.

<Process>
The construction procedure for the widened portion 4 configured as described above will be explained below. The construction procedure is comprised of steps S1 to S7, as shown in FIG.

[Girder, floor slab production]
First, the segments 41A, 41B and the floor slab 42 are manufactured (S1). Fabrication is carried out in a factory equipped with manufacturing equipment or in a yard with equivalent construction conditions. As shown in FIG. 5, the segments 41A, 41B and the floor slab 42 are all manufactured as precast concrete members using a pretension method.

In manufacturing the segments 41A and 41B, the primary steel material 413 and sheath 412 are placed at the designed positions, and concrete is poured while the primary steel material 413 is kept under tension using a device such as a jack. (Fig. 5(a), Fig. 5(b)). Similarly, in manufacturing the floor slab 42, concrete is poured while tension is applied to the steel material 421 (FIG. 5(c)).

After the concrete develops strength, the tension applied to the primary steel material 413 is released, but a curing period of approximately 3 to 6 months is provided thereafter (S2). By providing a curing period, the development of strain due to concrete creep or drying shrinkage is brought to an end.

[Construction on site]
After or in parallel with the fabrication of the segments 41A, 41B and the floor slab 42, the construction of the widened portion 4 is proceeded on-site.

First, the segments 41B are installed on the pier 45 (S3, FIG. 6(a)), and then the segments 41A are installed between the segments 41B (S4, FIG. 6(b)).

Next, tensioning of the secondary steel material is performed (S5). After the segment 41A is placed in a designed position by supporting it with a support or the like, the secondary steel material 414 is inserted into the sheath 412. The secondary steel material 414 is arranged so as to span the plurality of segments 41A and 41B and to be continuous in one span (FIG. 6(b)). After the insertion is completed, tension is applied to the secondary steel material 414 by a device such as a jack, and the end of the secondary steel material 414 is fixed to the segment 41B and grout is injected into the sheath 412. Furthermore, if necessary, spacing is performed between the segments 41A and 41B. When the installation of the segment 41A is completed, the shoring that supported the segment 41A is removed.

Next, the floor slab 42 is joined to the girder 41 (S6). The floor slab 42 is fixed to the upper part of the girder 41 via anchors 415. Further, by placing UFC between the floor slabs 42, a lateral joint 44 is formed (FIGS. 6(c) and 6(d)). The horizontal joints 44 join the deck slabs 42 adjacent in the bridge axis direction to each other.

Further, a UFC is placed between the end of the deck slab 42 in the direction perpendicular to the bridge axis and the deck slabs 22, 32, and a vertical joint 43 is formed (S7). The vertical joint portion 43 rigidly connects the floor slab 42 and the floor slab 22, and the floor slab 42 and the floor slab 32, respectively.

By executing the above steps S1 to S7 for each span, the construction of the widened portion 4 progresses.

<Effect>
The girder 41 in the above embodiment is a girder of a precast concrete structure with a concrete cross section, and includes a primary steel member 413 that applies compressive stress to the concrete cross section by a pre-tension method, and a compressive stress to the concrete cross section by a post-tension method. It has a secondary steel material 414 that increases.

By adopting such a construction method and structure, compressive stress is increased in two stages in the concrete cross section of the girder 41 by the primary steel material 413 and the secondary steel material 414, as shown in FIG. 7(a). Ru.

The widened portion 4 is constrained around its periphery, and a large tensile force is generated (reactively) due to the constraint of shrinkage strain caused by creep and drying shrinkage of the widened portion 4 itself. Therefore, the compressive stress applied to the girder 41 and the deck slab 42 is greatly reduced by the above-mentioned tensile force.

In this embodiment, even if a decrease in compressive stress occurs in the girder 41, the compressive stress is applied by the secondary steel material 414. Therefore, a girder 41 that compensates for the decrease in compressive stress and satisfies the designed performance can be obtained.

Further, since a part of the compressive stress is applied by the primary steel material 413 before construction, the tension applied to the secondary steel material 414 is less than that of a general bridge. In addition, the stress applied by the primary steel material 413 is based on the pre-tension method, and by providing a sufficient curing period, the development of strain due to creep and drying shrinkage can be brought to a certain level before delivery to the site. . Therefore, the tensile force generated by restraining the existing portions 2 and 3 can be suppressed.

On the other hand, in the conventional technology (Patent Document 1), compressive stress is applied to the girder cross section in only one operation, and the compressive stress of the deck does not contribute to the girder member (FIG. 7(b)). In this construction method and structure, it is necessary to introduce all the necessary compressive stress in just one tensioning operation, so it is necessary to increase the tension introduced into the steel material. For this reason, the introduction of prestress also generates a large unsteady force on the girder. In addition, the reduction in compressive stress due to relaxation of the steel and creep of concrete is also significant, so it is not easy to provide the girder with the compressive stress required in the design.

In addition, if a method is adopted in which the girder cross section is enlarged to increase the amount of prestress in order to cope with unsteady force and restraint of the existing section, the difference in flexural rigidity between the existing section and the expanded section increases, causing torsion in the existing section. Such effects will occur. In order to avoid this problem, it is necessary to make the girder height similar to the existing girder (small cross section), but if this is done, there will be no degree of freedom in the arrangement of the PC steel materials, and the structure will not be able to be established. This embodiment solves these problems.

In addition, with conventional technology, bridge widening work is often carried out while using the existing section and implementing traffic regulations (lane regulations, etc.). In conventional bridge widening, the widening section is cast in place, which requires a curing period of about 3 to 6 months at the construction site, and traffic control must continue during this curing period. By adopting a precast concrete structure in this embodiment, it becomes possible to carry out curing in a temporary storage yard other than the site, which has the effect of shortening the traffic regulation period. In addition, the curing period is not limited to 3 to 6 months, but longer curing can be carried out without traffic restrictions, and the effects of creep and drying shrinkage are reduced more than usual by simply adopting a precast concrete structure. You can expect the effect of

In the embodiment described above, the bridge 1 includes piers 45 (corresponding to the support section of the present invention) that support the girders 41. In the vicinity of the pier 45, the primary steel material 413 is placed on top of the girder 41.

By having the above configuration, the primary steel members can be effectively arranged in accordance with the direction and magnitude of the bending moment generated in the girder 41, and compressive stress with an appropriate amount and distribution can be applied to the concrete cross section. becomes possible. In the embodiment, the secondary steel material 414 is arranged symmetrically with respect to the cross-sectional center line 41C of the girder 41.

In the above configuration, the center of tension of the secondary steel material 414 is located on or near the centroid line 41C of the concrete cross section. The secondary steel material 414 can apply uniform compressive stress to the concrete cross section and reduce the influence of unsteady force due to prestress.

In the embodiment, the vertical joint part 43 (corresponding to the first joint part) connects the end of the deck slab 42 in the direction perpendicular to the bridge axis to the deck slabs 22, 32 (corresponding to surrounding structures) using ultra-high strength fiber reinforced concrete. ) to join.

By joining the ends of the floor slabs 42 using UFC as described above, the strength or durability can be improved even in the vertical joints 43 where prestress cannot be introduced. Further, as described above, the width of the vertical joint portion 43 and the construction range can be reduced, thereby achieving effects such as shortening the construction period.

In the embodiment, the horizontal joint portion 44 (corresponding to the second joint portion) joins the deck slabs adjacent in the bridge axis direction using ultra-high strength fiber reinforced concrete.

By joining the floor slabs 42 together using UFC as described above, the strength or durability can be improved even in the lateral joint parts 44 where prestress cannot be introduced. Further, as described above, the width of the horizontal joint portion 44 and the construction range can be reduced, thereby achieving effects such as shortening the construction period.

In the embodiment, the lateral joint 44 is provided at a position shifted in the bridge axis direction with respect to the joint between the segments 41A and 41B.

Such a configuration prevents excessive displacement or strain from occurring in the lateral joint portion 44. It is possible to prevent defects such as the occurrence of cracks in the lateral joints 44, and improve the quality of the bridge 1, such as its durability.

<Modified example>
In the above configuration, the secondary steel material 414 was installed linearly along the centroid line 41C of the concrete cross section. The present invention is not limited to this configuration, and as shown in FIG. 8, the secondary steel materials 414 may be arranged in a curved shape corresponding to the magnitude and direction of the bending moment generated in the girder 41.

Although the girder 41 had a U-shaped cross section in the embodiment, the present invention does not limit the cross-sectional shape and structure of the girder. The structure of the girder can be appropriately set according to the design conditions, such as a T-girder, a box girder, or a composite girder. Further, in the embodiment, the case where the digits 41 are continuous digits has been described, but the digits 41 may be simple digits. In this case, the shape and position of the primary steel material 413 and the secondary steel material 414 are appropriately designed to match the direction and magnitude of the bending moment, such as by arranging the primary steel material 413 at the bottom of the girder 41 over the entire span length. be done. The centroid line is also set according to the shape of the girder.

In the embodiment, the girder 41 was constructed by joining segments 41A, 41B. Alternatively to this construction method, the girder 41 may be manufactured as a single precast member.

In the embodiment, the bridge 1 includes an existing portion 2, an existing portion 3, and an expanded portion 4, but the existing portion 3 is not an essential configuration. That is, the bridge 1 may not include the existing portion 3 but may be configured by the existing portion 2 and the widening portion 4 that widens the existing portion 2.

Bridge 1
Existing part 2
Existing part 3
Widened part 4
Digit 41
Segments 41A, 41B
Floor slab 42
Vertical joint 43
Lateral joint 44
Pier 45

Claims (8)

A girder of precast concrete structure with a concrete cross section extending in the axial direction of the bridge,
a primary steel material that applies compressive stress to the concrete cross section in a pretensioning manner;
a girder having a secondary steel material that increases the compressive stress in a post-tensioning manner with respect to the concrete cross section,
The said secondary steel material is a bridge arrange|positioned symmetrically with respect to the cross-sectional center line of the said girder . further comprising a support part that supports the girder,
The bridge according to claim 1, wherein the primary steel material is arranged above the girder near the support portion. The bridge according to claim 1 or 2 , further comprising a precast deck slab of prestressed concrete structure fixed to the girder. The bridge according to claim 3 , further comprising a first joint part that joins an end of the deck in a direction perpendicular to the bridge axis direction to a surrounding structure using ultra-high strength fiber-reinforced concrete. The bridge according to claim 3 or 4 , further comprising a second joint portion that joins the deck slabs adjacent in the bridge axis direction using ultra-high strength fiber reinforced concrete. A girder of precast concrete structure with a concrete cross section extending in the axial direction of the bridge,
a primary steel material that applies compressive stress to the concrete cross section in a pretensioning manner;
a girder having a secondary steel material that increases the compressive stress with respect to the concrete cross section in a post-tensioning manner;
a precast deck slab of prestressed concrete structure fixed to the girder;
a second joint part that joins the deck slabs adjacent in the bridge axis direction,
the girder has a plurality of segments;
The second joint portion is a bridge provided at a position shifted in the bridge axis direction with respect to a joint position of the plurality of segments. 7. The bridge according to claim 6, wherein the deck slabs adjacent in the bridge axis direction are joined at the second joint using ultra-high strength fiber-reinforced concrete. A method of constructing a bridge having a girder of precast concrete structure with a concrete cross section extending in the direction of the bridge axis, the method comprising:
applying compressive stress to the concrete cross section using a pretension method using primary steel;
A construction method comprising the step of increasing the compressive stress in the concrete cross section using a post-tension method using secondary steel materials arranged symmetrically with respect to the cross-sectional center line of the girder .

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