JP5105016B2 - I-girder structure near the continuous I-girder bridge and its intermediate fulcrum - Google Patents

Description

  The present invention relates to a civil engineering structure such as a bridge, and more particularly to a continuous I-girder bridge and a structure of an I-girder near its intermediate fulcrum.

  As shown in FIG. 17, a large negative bending moment is generated in the vicinity of the intermediate fulcrum 12 of the continuous I girder bridge 10. Due to this negative bending moment, a large compressive force acts on the cross-section of the spar from the lower part of the web 136 of the I-spar 130 shown in FIGS. 18 to 20 to the lower flange 134. Therefore, as shown in FIG. The lower part of the web 136 may be buckled locally, as shown in FIG. 19, or the entire I-girder 130 may be laterally buckled or laterally buckled, as shown in FIG. In particular, when a high-strength steel or the like is applied to the I-girder 130 when the span of the continuous I-girder bridge 10 is relatively long, such a problem becomes significant. 18 to 20, 132 is an upper flange, and 180 is a floor slab installed on the I-girder 130.

As prior art 1 for this, in the vicinity of the intermediate fulcrum 12,
(1) The plate thickness of the lower flange 134 is increased.
(2) Increase the thickness of the web 136.
(3) The gaps such as the horizontal beams and the horizontal grooves are made smaller and densely arranged.
There are measures such as.

  Moreover, as the prior art 2, the continuous girder for bridges described in Patent Document 1 can be cited. This bridge continuous girder has a steel girder body having upper and lower flanges and a web, extending in the bridge axis direction and supported by one or a plurality of intermediate fulcrums, and the periphery of the intermediate fulcrum of the girder body In this case, reinforced concrete with all or part of vertical and horizontal reinforcing bars embedded is placed so as to follow the web, and the vertical reinforcing bars extend vertically and have upper and lower ends on the upper and lower flanges, respectively. The horizontal rebar is connected and extends in the bridge axis direction and is orthogonal to the vertical rebar, and the supported region around the intermediate fulcrum is reinforced with reinforced concrete.

  Further, Patent Literature 2 and Patent Literature 3 can be cited as the prior art 3, and Patent Literature 2 and Patent Literature 3 include a support for a continuous girder bridge in which at least a pair of I girders are arranged in the direction of the bridge axis. It is described that a reinforcing plate (Patent Document 2) or a concrete plate (Patent Document 3) is installed and fixed between the lower flanges of the pair of I girders in the vicinity of the supported portion by reinforced as a box-shaped cross section.

  Furthermore, Patent Document 4 can be cited as the prior art 4, and in Patent Document 4, in the box girder bridge, the entire internal space of the steel box girder in the area around the intermediate fulcrum is filled with concrete and reinforced. Are listed.

  Further, Patent Document 5 can be cited as the prior art 5. In Patent Document 5, a precast plate is disposed on the upper surface of the lower flange of the I-girder to prevent local buckling of the lower flange, and in the vicinity of the intermediate fulcrum. The I-digit structure is described.

JP 2002-266317 A JP-A-11-81240 Japanese Patent Laid-Open No. 11-148110 JP 2004-176344 A JP 2006-299554 A

However, the prior art 1 has the following problems.
(A) When the plate thickness of the lower flange and web is increased, the steel weight increases significantly, and the work by welding and bolting for each cross section becomes difficult, so the number of man-hours increases and the construction cost increases. It will be.
(B) In the case where the gaps such as the cross beams and the horizontal grooves are made small and densely arranged, the number of the cross beams and the horizontal grooves increases, so that the steel weight and the man-hour increase, and the work cost increases.

  Further, the conventional technique 2 described in Patent Document 1 has the following problems.

  In the prior art 2, it is necessary to connect the upper and lower ends of the vertical reinforcing bar to the upper and lower flanges directly or by welding or the like via a short reinforcing bar and a coupler. In general, since the gap between the upper and lower flanges of the girder bridge is about 2 to 3 m, the vertical rebar also has a length of about 2 to 3 m. The operation of directly welding long reinforcing bars of 2 to 3 m to the upper and lower flanges is complicated and difficult, and it is difficult to ensure accuracy. In addition, when connecting short rebars via couplers, it is necessary to first weld the short rebars and connect longer rebars via the couplers. High accuracy is required. Further, FIG. 6 of Patent Document 1 describes an embodiment in which only the lower side portion of the vertical reinforcing bar is embedded in concrete so that the girder body does not buckle due to compressive stress in the non-supporting region. The upper part of the reinforcing bar is exposed to the atmosphere, and there is concern about corrosion.

  In addition, the technique described in Patent Documents 2 and 3 (Prior Art 3) reinforces the I-girder by forming a box-shaped cross section by fixing a reinforcing plate or a concrete plate between the lower flanges of adjacent I-girder. However, since it has a box-shaped cross section, in order to improve the effect of preventing local buckling of the I-girder web, increasing the thickness of the reinforcing plate and concrete plate to be installed and fixed increases the weight of the superstructure. It will increase significantly.

  The technique described in Patent Document 4 (Prior Art 4) is a technique in which the entire interior space of the steel box girder in the region around the intermediate fulcrum is filled with concrete to reinforce the web. It is not restrained and the effect of preventing local buckling of the box girder web is not sufficient.

  In the technique described in Patent Document 5 (Prior Art 5), a precast plate is disposed on the lower flange of the I-girder and the I-girder web is sandwiched from both sides. Unlike the technology that has been made, the box-shaped cross section is not formed, and even if the thickness of the precast plate is increased in order to widen the range in which the I-digit web is sandwiched, the technology described in Patent Document 3 The weight of the superstructure does not increase. However, since the precast board is used, it is difficult to sandwich the I-girder web from both sides without play, and it is difficult to sufficiently restrain the I-girder web. Moreover, since the precast board is used, there exists a limit in improving the synthetic effect of steel and concrete in each cross section orthogonal to the longitudinal direction of I digit.

  The present invention has been made to solve the above-mentioned conventional problems, and considers the ease of construction and the prevention of corrosion of steel members to be installed while reducing the weight of steel, superstructure, man-hour and cost. Then, in the vicinity of the intermediate fulcrum where the negative bending moment acts on the continuous I-girder bridge supported by one or more intermediate fulcrums, local buckling of the lower flange of the I-girder and the lower part of the web, and the lateral seating of the entire I-girder The problem is to improve the load carrying capacity of the I-girder near the intermediate fulcrum of the continuous I-girder bridge while preventing the occurrence of bending and enhancing the composite effect of steel and concrete in each cross section orthogonal to the longitudinal direction of the I-girder. To do.

The first aspect of the structure of the I-girder near the intermediate fulcrum in the continuous I-girder bridge according to the present invention is constituted by an I-girder having an upper flange, a lower flange, a web, a vertical stiffener, and a floor slab. In the vicinity of the intermediate fulcrum where the negative bending moment acts on the continuous I-girder bridge supported by the end fulcrum and one or more intermediate fulcrums, a plurality of detents are arranged on the upper surface of the lower flange. In the space surrounded by the upper surface of the lower flange, the lower portion of the web, and the lower portion of the vertical stiffener, the fresh concrete is placed in a compression zone where the concrete formed by hardening the fresh concrete is below the plastic neutral axis. Placing all of the stoppers, the upper surface of the lower flange, the lower part of the web, the lower part of the vertical stiffener together with the concrete made by hardening the fresh concrete. The interval between the vertical stiffeners directly above the intermediate fulcrum among the vertical stiffeners is greater than the interval between the vertical stiffeners not directly above the intermediate fulcrum among the vertical stiffeners. On the other hand, a reinforcing bar whose length is longer than the interval between the vertical stiffeners that are not directly above the intermediate fulcrum among the vertical stiffeners is above the lower flange at a portion that is not directly above the intermediate fulcrum. In the longitudinal direction of the I-girder, the vertical stiffener not directly above the intermediate fulcrum is disposed so as not to be buffered. With the above configuration, the local buckling of the lower flange and the lower part of the web and the lateral seating of the entire I-girder It is characterized by preventing bending and improving the load carrying capacity of the I girder.

  Here, the plastic neutral axis is a neutral axis of a section in a plastic stress state caused by a bending moment.

  The continuous I girder bridge consists of an upper work and a lower work, but in this specification, “the upper work of the continuous I girder bridge” is described as “continuous I girder bridge”.

A lower part of the vertical stiffener directly above the intermediate fulcrum among the vertical stiffeners may be stiffened by a steel member .
The second aspect of the I-girder structure in the vicinity of the intermediate fulcrum in the continuous I-girder bridge according to the present invention is constituted by an I-girder having a top flange, a bottom flange, a web, a vertical stiffener, and a floor slab. In the vicinity of the intermediate fulcrum where the negative bending moment acts on the continuous I-girder bridge supported by the end fulcrum and one or more intermediate fulcrums, a plurality of detents are arranged on the upper surface of the lower flange. In the space surrounded by the upper surface of the lower flange, the lower portion of the web, and the lower portion of the vertical stiffener, the fresh concrete is placed in a compression zone where the concrete formed by hardening the fresh concrete is below the plastic neutral axis. Placing all of the stoppers, the upper surface of the lower flange, the lower part of the web, the lower part of the vertical stiffener together with the concrete made by hardening the fresh concrete. The interval between the vertical stiffeners directly above the intermediate fulcrum among the vertical stiffeners is greater than the interval between the vertical stiffeners not directly above the intermediate fulcrum among the vertical stiffeners. The lower part of the vertical stiffener that is narrow and is directly above the intermediate fulcrum of the vertical stiffener is stiffened by a steel member. It is characterized by preventing the buckling and the lateral buckling of the entire I-girder and improving the load bearing capacity of the I-girder.

  Moreover, it may not be necessary to place concrete in the gap between the vertical stiffeners directly above the intermediate fulcrum among the vertical stiffeners.

  On the other hand, concrete may be placed in the gap between the vertical stiffeners directly above the intermediate fulcrum among the vertical stiffeners.

  Further, in the continuous I-girder bridge, the structure of the I-girder is arranged only in the region where the negative bending moment acts, thereby suppressing an increase in the weight of the entire continuous I-girder bridge, and the local seat on the lower flange and the lower part of the web. Bending and lateral buckling of the entire I-girder can be effectively prevented.

In the first aspect of the present invention , the entire stopper, the upper surface of the lower flange, the lower portion of the web, and the lower portion of the vertical stiffener are integrated with concrete to form a composite structure. In particular, the lower part of the web is restrained by concrete from both sides, and local buckling of the lower part of the web is prevented. Furthermore, since a plurality of slip stoppers are arranged on the upper surface of the lower flange, the lower flange is also integrated with concrete, and local buckling of the lower flange is prevented. Furthermore, the interval between the vertical stiffeners directly above the intermediate fulcrum among the vertical stiffeners is narrower than the interval between the vertical stiffeners not directly above the intermediate fulcrum among the vertical stiffeners. We have been,
On the other hand, a reinforcing bar whose length is longer than the interval between the vertical stiffeners not directly above the intermediate fulcrum among the vertical stiffeners is above the lower flange in a portion not directly above the intermediate fulcrum. In the longitudinal direction, it is arranged so as not to be buffered with a vertical stiffener not directly above the intermediate fulcrum .
In the second aspect of the present invention, the entire stopper, the upper surface of the lower flange, the lower portion of the web, and the lower portion of the vertical stiffener are integrated with concrete to form a composite structure. In particular, the lower part of the web is restrained by concrete from both sides, and local buckling of the lower part of the web is prevented. Furthermore, since a plurality of slip stoppers are arranged on the upper surface of the lower flange, the lower flange is also integrated with concrete, and local buckling of the lower flange is prevented. Furthermore, the interval between the vertical stiffeners directly above the intermediate fulcrum among the vertical stiffeners is narrower than the interval between the vertical stiffeners not directly above the intermediate fulcrum among the vertical stiffeners. The lower part of the vertical stiffener directly above the intermediate fulcrum is stiffened by a steel member.

  For this reason, in the present invention, the load resistance against local buckling of the lower flange and the lower part of the web and lateral buckling of the entire I-girder is remarkably enhanced.

  Therefore, even when a large negative bending moment is generated in the vicinity of the intermediate fulcrum of the continuous I-girder and a large compressive force acts on the lower flange, the I-girder structure in the vicinity of the intermediate fulcrum according to the present invention has the lower flange and the web. The local buckling of the lower part and the lateral buckling of the entire I-girder are effectively prevented, and the performance in the plastic region of the steel material can be utilized.

  Further, as described above, the I-girder structure in the vicinity of the intermediate fulcrum according to the present invention has a composite structure of steel and concrete, and the cross section perpendicular to the longitudinal direction of the I-girder is resistant to bending moment as a composite cross section. can do.

  Therefore, in the I-girder structure in the vicinity of the intermediate fulcrum according to the present invention, the load bearing capacity is greatly improved, and as in the prior art 1, the plate thickness of the lower flange or web is increased, or the cross-girder and the lateral groove are increased. Therefore, it is not necessary to arrange them closely and to arrange them densely, so that it is possible to reduce the steel weight, the number of man-hours, and the construction cost as compared with the prior art 1.

  Further, in the structure of the I-girder near the intermediate fulcrum according to the present invention, a detent is used, and the reinforcing bars do not have to be disposed in the concrete. Like the prior art 2 described in Patent Document 1, Construction is easy because there is no need to connect vertical reinforcing bars to the upper and lower flanges. In the prior art 2 described in Patent Document 1, since it is necessary to connect the vertical reinforcing bars to the upper and lower flanges, it is necessary to perform a complicated and difficult work management such as welding the reinforcing bars. High accuracy is required for angle and angle. Further, in the I-girder structure in the vicinity of the intermediate fulcrum according to the present invention, even when reinforcing bars are installed, the assembly and installation work can be performed on the upper surface of the lower flange which is generally flat and stable. Construction management is easy.

  For this reason, in the structure of the I girder near the intermediate fulcrum according to the present invention, the construction work is reduced, and the construction cost and the construction period can be reduced.

  In addition, since the concrete is disposed so as to be in the compression region, which is a region below the plastic neutral axis, even in the plastic stress state, cracking does not occur in the concrete, and until the total plastic bending moment is reached, It is possible to make full use of the performance of concrete and to suppress weight increase. On the other hand, Patent Document 1 describes that fresh concrete may be partially placed in the height direction of the web, but there is no specific description about the height of the concrete to be disposed. . For this reason, in the technique described in Patent Document 1, when the height of the concrete to be arranged is high, there is a possibility that the concrete portion may be cracked or broken. Conversely, if the height of the concrete to be disposed is low, the web may be locally buckled.

  Furthermore, in the structure of the I girder near the intermediate fulcrum according to the present invention, unlike the technique described in FIG. 6 of Patent Document 1, the steel member is entirely contained in the concrete and is not exposed to the atmosphere. Moreover, corrosion of the steel member to be installed is also suppressed. Further, in the technique shown in FIG. 6 of Patent Document 1, there is a concern about fatigue failure at the connecting portion between the vertical reinforcing bar and the lower surface of the upper flange, but in the I-girder structure in the vicinity of the intermediate fulcrum according to the present invention, There is no serious concern.

  Further, in the present invention, unlike the techniques described in Patent Documents 2 and 3, since a box-shaped cross section is not formed, in order to improve the effect of preventing local buckling of the I-digit web, the concrete to be disposed Even if the height is increased, an increase in weight can be suppressed as compared with the case where a box-shaped cross section is formed.

  Moreover, in the present invention, unlike the technique described in Patent Document 4, the lower part of the web is restrained by concrete from both sides, so that the effect of preventing local buckling of the web can be sufficiently exhibited.

  Also, in the present invention, unlike the technique described in Patent Document 5, since a precast plate is not used, the I-digit web can be sandwiched without play from both sides, and the I-digit web can be sufficiently restrained. it can. Moreover, since the concrete and the I-girder are integrated by placing fresh concrete, it is possible to enhance the combined effect of steel and concrete in each cross section orthogonal to the longitudinal direction of the I-girder.

  Further, in the continuous I-girder bridge, when the I-girder structure is disposed only in the region where the negative bending moment acts, local buckling of the lower flange and the lower part of the web is suppressed while suppressing an increase in the weight of the entire continuous I-girder bridge. In addition, the lateral buckling of the entire I-girder can be effectively prevented.

The perspective view which shows the structure of the I girder near the intermediate fulcrum according to the first embodiment of the present invention. Same side view The perspective view which shows the construction stage which has arrange | positioned the plate member which is a slip stopper on the upper surface of the lower flange of I girder near an intermediate fulcrum Same side view A perspective view showing an example of a plate member Side view showing an example of a notch in a plate member Side view showing an example where the bridge reinforcement in the axial direction of the bridge and the band reinforcement is installed on the upper surface of the lower flange with predetermined reinforcement The perspective view which shows the condition which drops a bridge axial direction reinforcing bar in the notch of a board member, and arranges it in a predetermined position Side view showing the situation where the formwork is installed Conceptual diagram of stress distribution in the cross section in the state of plastic stress in the I-digit structure near the intermediate fulcrum subjected to negative bending moment Side view showing the situation where the middle fulcrum vertical stiffener is stiffened with steel members Side view showing the situation where fresh concrete is filled in the space directly above the intermediate fulcrum and the concrete is placed up to the height of hc Side view showing the structure of the I-girder near the intermediate fulcrum according to the second embodiment of the present invention Side view schematically showing an example of the arrangement position of the concrete in the bridge axis direction arranged on the upper surface of the lower flange Side view schematically showing another example The perspective view which looked at the cross section which cut | disconnected the intermediate | middle fulcrum vicinity by the surface of the orthogonal direction of a bridge axis from the diagonal upper direction at the time of applying embodiment of this invention to a continuous I girder bridge (2 main I girder bridge). Side view schematically showing an example of bending moment distribution in continuous I girder bridge Front view showing local buckling of the lower flange near the intermediate fulcrum of a continuous I-girder bridge Front view showing local buckling at the bottom of the web near the intermediate fulcrum of the continuous I-girder bridge Front view showing lateral buckling near intermediate fulcrum of continuous I-girder bridge

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 (perspective view) and FIG. 2 (side view) are views showing a first embodiment of the present invention. This embodiment is applied to the I girder 30 near the intermediate fulcrum 12 among the I girder 30 in the continuous I girder bridge 10 (see FIG. 17). The I girder 30 includes an upper flange 32, a lower flange 34, a web 36, and a vertical stiffener 38. The vertical stiffener 38 includes an intermediate fulcrum portion vertical stiffener 38A and a general portion vertical stiffener 38B. The upper surface of the lower flange 34 includes a plate member 40 serving as a slip stopper and predetermined reinforcing bars (bridge axial rebars 42 and strips 44), and the upper surface of the lower flange 34, the lower portion of the web 36, and vertical stiffening. Concrete 46 integrated with the lower part of the material 38 is disposed. The region where the concrete 46 is disposed is in the compression region, which is a region below the plastic neutral axis.

  In FIG. 1 and FIG. 2 showing the state after the fresh concrete is placed and the fresh concrete is hardened to become the concrete 46, the plate member 40 and the plate member 40, which are the features of this embodiment, are utilized. Since the arrangement of the reinforcing bars 42 and 44 is difficult to understand, the structure and construction method of the present embodiment will be described below with reference to the drawings during construction.

  FIG. 3 is a perspective view showing a construction stage in which a plate member 40 as a stopper is disposed on the upper surface of the lower flange 34 of the I girder 30 in the vicinity of the intermediate fulcrum 12, and FIG. 4 is also a side view.

  The I girder 30 is manufactured at a predetermined length (up to about 12 m) at a factory or the like, and is sequentially connected and installed at the site. The plate member 40, which is a displacement preventing member, is generally disposed by welding or the like at a factory or the like, but may be disposed at the site.

  As shown in FIG. 5, the plate member 40 is a steel plate having a thickness of, for example, about 19 mm, and is provided with a notch 40 </ b> A having such a shape that a reinforcing bar can be arranged at a predetermined position. The shape of the cutout 40A is not particularly limited as long as the reinforcing bar can be arranged at a predetermined position, and can be, for example, a keyhole shape shown in FIGS.

  FIG. 6A shows an example of a shape in which two rows of reinforcing bars are arranged in one stage and two reinforcing bar doors are provided. FIG. 6B shows two rows of reinforcing bars arranged in two stages. FIG. 6C shows an example of a shape in which two rows of reinforcing bars are arranged in two stages, and one reinforcing door is provided. FIGS. 6D and 6E show a shape in which a key is attached to the notch 40 </ b> A where the reinforcing bar is arranged so that the position of the arranged reinforcing bar is not shifted. FIG. 6D is an example of a shape in which three rows of reinforcing bars are arranged in one stage and three entrances and exits are provided. FIG. 6E shows three rows of reinforcing bars arranged in two stages. This is an example of a shape with three doorways.

  Further, as shown in FIGS. 3 and 4, the plate member 40 is disposed on the upper surface of the lower flange 34 between the vertical stiffeners, thereby preventing local buckling of the lower flange when the I-girder 30 is installed. Therefore, it can also contribute as a stiffener.

  Next, the assembly and installation work of the reinforcing bars 42 and 44 and the fresh concrete placing work will be described.

  FIG. 7 is a side view showing an example in which predetermined reinforcement is arranged on the upper surface of the lower flange 34 with respect to the bridge axis direction reinforcing bars 42 and the band bars 44. In this example, a total of four bridge axis direction reinforcing bars 42 in two rows are arranged in two stages, and the band bars 44 are arranged so as to surround the four bridge axis direction reinforcing bars 42 from the outside at a predetermined interval. Yes.

  In this embodiment, since the notch 40A is provided in the plate member 40, as shown in FIG. 8, the bridge axis direction reinforcing bar 42 is dropped into the notch 40A of the plate member 40 and is arranged at a predetermined position. Can do. Note that the notch 40A of the plate member 40 in FIG. 8 is drawn in a shape (shape of FIG. 6A) in which two reinforcing bars can be arranged for convenience of illustration, but the notch in the present embodiment. The actual shape of 40A is the shape shown in FIG. 6B, and a total of four bridge-axial reinforcing bars 42 in two rows can be arranged in two stages.

  In the concrete bar arrangement work on site, first, the four bridge axis direction reinforcing bars 42 are dropped into the notches 40A of the plate member 40, and are arranged at predetermined positions. Thereafter, the reinforcing bars 44 are arranged at predetermined intervals so as to surround the four bridge axis direction reinforcing bars 42 from the outside, and the reinforcing bars are arranged as shown in FIG. Thus, in this embodiment, even if it does not assemble a reinforcing bar beforehand and assembles a reinforcing bar on-site, on-site work and construction management are very easy. In the present embodiment, the bridge axial direction reinforcing bars 42 may be dropped into the notches 40A of the plate member 40 and arranged at predetermined positions using rebars assembled in advance. In either case, it is only necessary to install a reinforcing bar on the substantially flat and stable lower flange 34, and the plate member 40 provided with the notch 40A is disposed. It becomes easy.

  Further, when using a pre-assembled reinforcing bar, for example, the notch 40A in FIG. 5 is formed into a long and long long hole having a width corresponding to the diameter of the bridge axial direction reinforcing bar 42 to be installed, and the reinforcing bar assembled in the long hole is used. May be installed.

  In addition, since the area | region of the concrete which casts and arrange | positions fresh concrete is an area | region below a plastic neutral axis, the area | region which arrange | positions the reinforcing bars 42 and 44 and the board member 40 also considers cover thickness. It is necessary to decide.

  After completion of the bar arrangement work, as shown in FIG. 9, the formwork 48 is installed to a predetermined height, and the space surrounded by the upper surface of the lower flange 34, the lower portion of the web 36, and the lower portion of the intermediate fulcrum vertical stiffener 38A. Place fresh concrete. The fresh concrete is placed so that the concrete 46 formed by hardening the fresh concrete is entirely included in the compression region, which is a region below the plastic neutral axis.

  For example, as shown in FIG. 9, the mold 48 can be installed by temporarily fixing the intermediate fulcrum vertical stiffener 38A, the lower flange 34, and the like at a temporary fixing point 48A. The height of the concrete 46 to be arranged varies depending on the thickness of the lower flange 34 and the web 36 and the expected bending strength, but in the case of an I-girder bridge with a girder height of 3 m, for example, it may be about 300 to 700 mm. it can.

  When the formwork 48 is removed after the hardening of the fresh concrete, as shown in FIGS. 1 and 2, the upper surface of the lower flange 34, the lower portion of the web 36, the lower portion of the intermediate fulcrum vertical stiffener 38A, and the entire plate member 40 The entire rebars 42 and 44 and the concrete 46 are integrated. As a result, a large negative bending moment is generated in the vicinity of the intermediate fulcrum 12 of the continuous I girder bridge 10, so that even when a large compressive force acts on the cross section of the girder from the bottom of the web 36 to the lower flange 34, the lower flange 34 and the web. The possibility that the lower portion of 36 is locally buckled or the entire I-girder 30 is laterally buckled is extremely small.

  For this reason, in this embodiment, while being able to effectively utilize the performance of the plastic region of the steel material constituting the I girder 30 near the intermediate fulcrum 12, it is possible to resist bending moment as a composite cross section of steel and concrete. Thus, the load bearing capacity of the I girder 30 near the intermediate fulcrum 12 can be dramatically improved.

  Moreover, in this embodiment, the plate member 40 and the reinforcing bars 42 and 44 that are steel members are all embedded in the concrete 46, and unlike the case of FIG. 6 of Patent Document 1, the plate member 40 that is a steel member, Since the reinforcing bars 42 and 44 are not exposed to the atmosphere, corrosion of the steel member to be installed is suppressed.

Here, FIG. 10 shows a conceptual diagram of the stress distribution of the cross section in the plastic stress state in the structure of the I girder 30 near the intermediate fulcrum 12 that receives a negative bending moment. Here, the balance of forces in the plastic stress state is considered in consideration of the bridge axis direction reinforcing bars 60A, the I girders 30, and the concrete 46 in the floor slab 60, and the plastic neutral axis is calculated. In addition, since the concrete of the floor slab 60 becomes a tension | pulling region and a crack is produced, it is not considered here. A region above the plastic neutral axis is a tensile region where tensile stress is generated, and a region below the plastic neutral axis is a compression region where compressive stress is generated. In FIG. 10, hc represents the height of the concrete 46, and Dcp represents the distance from the lower surface of the concrete 46 to the plastic neutral axis.

As in the present embodiment, in consideration of the stress distribution of the cross section in the plastic stress state, the height of the concrete 46 to be disposed is limited within the compression region below the plastic neutral axis (hc ≦ Dcp), whereby the concrete 46 The stress acting on can always be a compressive stress. For this reason, cracks do not occur in the concrete 46, and the performance of the concrete 46 can be fully utilized until the total plastic bending moment is reached. In addition, by limiting the height of the concrete 46 to be disposed within a compression region below the plastic neutral axis (hc ≦ Dcp), the amount of fresh concrete to be placed is reduced, and an increase in weight is suppressed.

  When the performance of the concrete 46 is fully utilized up to the total plastic bending moment, the intermediate fulcrum vertical stiffener 38A is stiffened with the steel member 50 as shown in FIG. It is preferable to improve the bending strength. In addition, as shown in FIG. 12, fresh concrete is filled in a space immediately above the intermediate fulcrum 12 formed from the lower part of the intermediate fulcrum vertical stiffener 38A, the upper surface of the lower flange 34, and the lower part of the web 36. 52 may be provided up to a height approximately equal to the height hc of the concrete 46 to improve the bending strength in the vicinity of the intermediate fulcrum 12.

  In the first embodiment described above, the plate member 40 is used as the displacement preventing member. However, the displacement preventing member is not limited to the plate member 40. For example, the headed stud 54 (see FIG. 13) is replaced with the plate member 40. May be used. Also in this case, the reinforcing bars may be assembled in advance and installed on the lower flange 34, or may be assembled directly on the lower flange 34 at the site. In either case, it is only necessary to install a reinforcing bar on the lower flange 34 that is generally flat and stable. However, when the headed stud 54 is used, assembling the reinforcing bar directly on the lower flange 34 takes more time in positioning the reinforcing bar than when the plate member 40 is used. Further, the headed stud 54 cannot contribute as a stiffener for preventing local buckling of the lower flange when the I-girder is installed.

  A second embodiment of the present invention is shown in FIG. 13 (side view). The second embodiment is an embodiment in which a headed stud 54 is installed on the lower flange 34 by welding or the like in addition to the plate member 40 as a slip stopper. By installing the headed stud 54 on the lower flange 34 in addition to the plate member 40, the effect of combining steel and concrete can be further enhanced, and the load bearing capacity of the I girder 30 near the intermediate fulcrum 12 can be further improved. Can do. In FIG. 13, for convenience of illustration, the plate member 40 and the headed stud 54 included in the concrete 46 are drawn with solid lines.

  In the embodiment described above, the plate member 40 and the headed stud 54 are used as the slip stopper. However, the slip stopper applicable to the present invention is not limited to these, and, for example, a shape steel may be used for the slip stopper. However, it is also possible to use a truss-shaped displacement stopper formed of a shape steel or a reinforcing bar. However, it is necessary to select an appropriate type in consideration of the shear strength, toughness, and the synthetic effect of the cross section.

  In the embodiment described above, the bridge axial rebar 42 and the strip 44 are used. However, if a sufficient detent is provided, the bridge axial rebar 42 and the strip 44 are not essential and are omitted. May be. However, if the bridge axis direction reinforcing bars 42 and the strip bars 44 are omitted, the load bearing capacity is reduced as compared with the case where the bridge axis direction reinforcing bars 42 and the band bars 44 are provided.

  Next, the case where 1st Embodiment or 2nd Embodiment is applied to a continuous I girder bridge is demonstrated. FIGS. 14 and 15 schematically show the arrangement position of the concrete 46 arranged on the upper surface of the lower flange 34 in the bridge axis direction when the first embodiment or the second embodiment is applied to the continuous I girder bridge 10. FIG. 14 and 15, reference numeral 14 indicates an end fulcrum.

  In the embodiment of the present invention, the concrete 46 is disposed in a region where a negative bending moment acts (hereinafter referred to as a negative bending region). As shown in FIG. 14, the concrete 46 may be disposed over the entire negative bending region, or may be disposed only in a region where the negative bending moment is particularly large as shown in FIG. The arrangement position of the concrete 46 in the bridge axis direction may be determined in consideration of the magnitude of the negative bending moment acting on the cross section, the magnitude of the bending moment when buckling occurs in the I-girder, and the like. In this way, by restricting the position where the concrete 46 is disposed to a predetermined negative bending region, the local buckling of the lower flange 34 and the web 36 and the lateral buckling of the entire I-girder 30 are effective while suppressing an increase in weight. Can be prevented.

  FIG. 16 shows the case where the first embodiment or the second embodiment is applied to a continuous I girder bridge (two main I girder bridges) 20, and a cross section obtained by cutting the vicinity of the intermediate fulcrum 12 with a plane perpendicular to the bridge axis is obliquely upward. It is the perspective view seen from. Concrete 46 is disposed on the upper surface of the lower flange 34 on both sides of the lower portion of the web 36 of the I girder 30, and the lower portion of the web 36 of the I girder 30 is constrained by the concrete 46 from both sides. A floor slab 80 is disposed on the two I-beams 30 arranged in parallel.

  In the embodiment described above, the construction of the floor slab 80 installed on the I girder 30 is not described, but it is necessary to perform the construction appropriately in consideration of the erection step and the construction order. As a device for the construction order of the floor slab 80, a device for the order of the block construction (such as post-implantation of the intermediate fulcrum block) or fresh concrete is placed on the lower flange 34 of the I-girder 30 and arranged. It may be possible to devise a construction order with the concrete 46 to be performed.

10 ... Continuous I girder bridge 12 ... Intermediate fulcrum 14 ... End fulcrum 20 ... Continuous I girder bridge (2 main I girder bridge)
30 ... I Girder 32 ... Upper flange 34 ... Lower flange 36 ... Web 38 ... Vertical stiffener 38A ... Intermediate fulcrum vertical stiffener 38B ... General part vertical stiffener 40 ... Plate member 40A ... Notch 42 ... Bridge shaft Directional reinforcing bar 44 ... Strip reinforcement 46, 52 ... Concrete 48 ... Formwork 50 ... Steel member 54 ... Stud with head 60, 80 ... Floor slab 60A ... Bridge axial direction reinforcement in the floor slab 60

Claims (6)

Negative bending moment of continuous I-girder bridge composed of I-girder and floor slab with upper flange, lower flange, web, vertical stiffener and supported by end fulcrum at both ends and one or more intermediate fulcrum In the vicinity of the intermediate fulcrum at which the The concrete is placed so that the concrete formed by hardening the fresh concrete is all included in the compression region, which is the region below the plastic neutral axis, and the entire displacement prevention, the upper surface of the lower flange, the lower part of the web, the vertical The lower part of the stiffener is integrated with the concrete obtained by curing the fresh concrete,
Among the vertical stiffeners, the interval between the vertical stiffeners directly above the intermediate fulcrum is narrower than the interval between the vertical stiffeners not directly above the intermediate fulcrum among the vertical stiffeners. On the other hand, a reinforcing bar whose length is longer than the interval between the vertical stiffeners that are not directly above the intermediate fulcrum among the vertical stiffeners is above the lower flange in a portion that is not directly above the intermediate fulcrum. In the longitudinal direction, the vertical stiffener not directly above the intermediate fulcrum is arranged so as not to buffer,
With the above configuration, local buckling of the lower flange and the lower part of the web and lateral buckling of the entire I-girder are prevented, and the load carrying capacity of the I-girder is improved, so that the I-girder near the intermediate fulcrum in the continuous I-girder bridge Structure. The lower portion of the vertical stiffener directly above the intermediate fulcrum among the vertical stiffeners is stiffened by a steel member , wherein I in the vicinity of the intermediate fulcrum in the continuous I-girder bridge according to claim 1. Digit structure. Negative bending moment of continuous I-girder bridge composed of I-girder and floor slab with upper flange, lower flange, web, vertical stiffener and supported by end fulcrum at both ends and one or more intermediate fulcrum In the vicinity of the intermediate fulcrum where the sway acts, a plurality of stoppers are arranged on the upper surface of the lower flange, and the fresher is installed in a space including the stoppers and surrounded by the upper surface of the lower flange, the lower part of the web, and the lower part of the vertical stiffener. The concrete is placed so that the concrete formed by hardening the fresh concrete is all included in the compression region, which is the region below the plastic neutral axis, and the entire displacement prevention, the upper surface of the lower flange, the lower part of the web, the vertical The lower part of the stiffener is integrated with the concrete obtained by curing the fresh concrete,
Among the vertical stiffeners, the interval between the vertical stiffeners directly above the intermediate fulcrum is narrower than the interval between the vertical stiffeners not directly above the intermediate fulcrum among the vertical stiffeners. And the lower part of the vertical stiffener directly above the intermediate fulcrum of the vertical stiffener is stiffened by a steel member,
With the above configuration, local buckling of the lower flange and the lower part of the web and lateral buckling of the entire I-girder are prevented, and the load carrying capacity of the I-girder is improved, so that the I-girder near the intermediate fulcrum in the continuous I-girder bridge Structure. The continuous I girder bridge according to any one of claims 1 to 3, wherein no concrete is placed in a gap between the vertical stiffeners directly above the intermediate fulcrum among the vertical stiffeners. Structure of I-girder near the intermediate fulcrum. The continuous I girder bridge according to any one of claims 1 to 3 , wherein concrete is placed in a gap between vertical stiffeners directly above the intermediate fulcrum among the vertical stiffeners. I-digit structure near the intermediate fulcrum.   A continuous I-girder bridge, wherein the I-girder structure according to any one of claims 1 to 5 is disposed only in a region where a negative bending moment acts.

Images