JP5029271B2 - Structure of a continuous I-girder bridge and its I-girder near its intermediate support - Google Patents

Description

The present invention relates to civil engineering structures such as bridges, and in particular to the structure of a continuous I-girder bridge and an I-girder in the vicinity of its intermediate support.

As shown in Figure 17, a large negative bending moment occurs near the intermediate support 12 of the continuous I-girder bridge 10. This negative bending moment causes a large compressive force to act on the girder cross section from the lower part of the web 136 to the lower flange 134 of the I-girder 130 shown in Figures 18 to 20, which may cause local buckling of the lower flange 134 as shown in Figure 18, local buckling of the lower part of the web 136 as shown in Figure 19, or lateral buckling such as lateral torsional buckling of the entire I-girder 130 as shown in Figure 20. This problem becomes particularly noticeable when the span of the continuous I-girder bridge 10 is relatively long and high-strength steel is used for the I-girder 130. In Figures 18 to 20, 132 is the upper flange, and 180 is a deck installed on the I-girder 130.

In contrast, in the prior art 1, in the vicinity of the intermediate support 12,
(1) Increase the thickness of the lower flange 134.
(2) Increasing the thickness of the web 136.
(3) Reduce the spacing between cross beams, grooves, etc. and place them closer together.
There are measures such as:

As an example of prior art 2, there is a continuous girder for bridges described in Patent Document 1. This continuous girder for bridges has upper and lower flanges and webs, extends in the bridge axis direction, and is equipped with a steel girder body supported at one or more intermediate supports. Around the intermediate supports of this girder body, reinforced concrete with all or part of vertical and horizontal reinforcing bars embedded therein is poured along the web, and the vertical reinforcing bars extend vertically and are connected at the upper and lower ends to the upper and lower flanges, respectively, and the horizontal reinforcing bars extend in the bridge axis direction and are perpendicular to the vertical reinforcing bars. The supported area around the intermediate supports is reinforced with reinforced concrete.

Furthermore, examples of prior art 3 include Patent Document 2 and Patent Document 3, which describe how, in a continuous girder bridge with at least a pair of I-girders arranged in the bridge axis direction, a reinforcing plate (Patent Document 2) or a concrete slab (Patent Document 3) is erected and fixed between the lower flanges of the pair of I-girders near the part supported by the bearing, reinforcing the box-shaped cross section.

Furthermore, as prior art 4, Patent Document 4 can be mentioned, which describes a method of reinforcing a box girder bridge by filling the entire internal space of the steel box girder in the area around the intermediate support with concrete.

Patent Document 5 can also be cited as prior art 5, which describes the structure of an I-girder near the intermediate support, in which a precast plate is placed on the upper surface of the lower flange of the I-girder to prevent local buckling of the lower flange.

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

However, prior art 1 has the following problems.
(A) Increasing the plate thickness of the lower flange and web results in a significant increase in the weight of the steel, and also in the increased labor required for welding and bolting each cross section, resulting in increased labor hours and higher construction costs.
(B) If the spacing between cross beams, cross grooves, etc. is reduced and they are arranged densely, the number of cross beams, cross grooves, etc. will increase, which will increase the weight of steel and the number of labor hours, resulting in increased construction costs.

Furthermore, the prior art 2 described in Patent Document 1 has the following problems:

In the prior art 2, the upper and lower ends of the vertical rebar must be connected to the upper and lower flanges directly, or by welding via a short rebar and a coupler. Generally, the distance between the upper and lower flanges of a girder bridge is about 2 to 3 m, so the vertical rebar is also about 2 to 3 m long. The work of directly welding long rebars 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 via a short rebar and a coupler, it is necessary to first weld the short rebar and then connect the longer rebar via a coupler, which not only increases the number of steps but also requires high accuracy in the installation position and angle of the short rebar. In addition, Figure 6 of Patent Document 1 describes an embodiment in which only the lower part of the vertical rebar is embedded in concrete to prevent the girder body from buckling due to compressive stress in the non-supporting area, but the upper part of the vertical rebar is exposed to the air, and corrosion is a concern.

In addition, the technology described in Patent Documents 2 and 3 (Prior Art 3) is a technology in which a reinforcing plate or concrete slab is erected and fixed between the lower flanges of adjacent I-girders to form a box-shaped cross section and reinforce the I-girders. However, because the cross section is box-shaped, if the thickness of the reinforcing plate or concrete slab is increased to improve the effect of preventing local buckling of the I-girder web, the weight of the superstructure will increase significantly.

The technology described in Patent Document 4 (Prior Art 4) is a technology that fills the entire internal space of the steel box girder in the area around the intermediate support with concrete to reinforce it, but it does not restrain the web of the box girder from the outside, and therefore is not sufficiently effective in preventing local buckling of the web of the box girder.

In addition, the technology described in Patent Document 5 (Prior Art 5) arranges precast plates on the bottom flange of the I-girder to sandwich the I-girder web from both sides, but unlike the technology described in Patent Document 3, it does not form a box-shaped cross section, and even if the thickness of the precast plates is increased to widen the area in which the I-girder web is sandwiched, the weight of the superstructure does not increase as much as with the technology described in Patent Document 3. However, because precast plates are 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. In addition, because precast plates are used, there is a limit to enhancing the composite effect of steel and concrete in each cross section perpendicular to the longitudinal direction of the I-girder.

The present invention has been made to solve the above-mentioned problems of the past, and aims to prevent local buckling of the lower flange and web bottom of the I-girder and lateral buckling of the entire I-girder in the vicinity of the intermediate supports where a negative bending moment acts in a continuous I-girder bridge supported by one or more intermediate supports, while reducing the weight of the steel and the weight of the superstructure, the labor hours, and construction costs, while also taking into consideration ease of construction and prevention of corrosion of the installed steel members. It also aims to improve the load-bearing capacity of the I-girder in the vicinity of the intermediate supports of a continuous I-girder bridge supported by one or more intermediate supports, by increasing the composite effect of steel and concrete in each cross section perpendicular to the longitudinal direction of the I-girder.

The structure of the I-girder in the vicinity of the intermediate support in a continuous I-girder bridge according to the present invention is composed of an I-girder and deck slab equipped with an upper flange, a lower flange, a web, and vertical stiffeners, and is supported by end supports at both ends and one or more intermediate supports. In the vicinity of the intermediate support on which a negative bending moment acts, a plurality of shear stoppers are disposed on the upper surface of the lower flange, and fresh concrete is poured into a space including the shear stoppers and surrounded by the upper surface of the lower flange, the lower portion of the web, and the lower portion of the vertical stiffener, and the fresh concrete is hardened to form a shear stopper. The concrete is poured so that it is entirely contained within the compression zone, which is the area below the plastic neutral axis, and the entire shear stopper, the upper surface of the lower flange, the lower part of the web, and the lower part of the vertical stiffener are integrated with the concrete that is formed as the fresh concrete hardens.The shear stopper is a plate member that serves as a stiffener to prevent local buckling of the lower flange when the I-girder is erected.The above configuration prevents local buckling of the lower flange and the lower part of the web, as well as lateral buckling of the entire I-girder, thereby improving the load-bearing capacity of the I-girder.

Here, the plastic neutral axis is the neutral axis of the cross section in a state of plastic stress due to a bending moment.

Although a continuous I-girder bridge is technically composed of a superstructure and a substructure, in this specification the "superstructure of a continuous I-girder bridge" is referred to as the "continuous I-girder bridge."

The I-girder structure may further include reinforcing bars. In this case, by providing a notch in the plate member for arranging the reinforcing bars in a predetermined position, the reinforcing bars can be arranged in the predetermined position simply by inserting the reinforcing bars into the notch from above or the side and dropping them in.

In addition, in a continuous I-girder bridge, by placing the I-girder structure only in the area where negative bending moment acts, it is possible to effectively prevent local buckling of the lower flange and lower part of the web, as well as lateral buckling of the entire I-girder, while suppressing the increase in weight of the entire continuous I-girder bridge.

In the present invention, the entire shear stop, the upper surface of the lower flange, the lower part of the web, and the lower part of the vertical stiffener are integrated with the concrete to form a composite structure. In particular, the lower part of the web is restrained from both sides with concrete to prevent local buckling of the lower part of the web. Furthermore, since multiple shear stoppers are arranged on the upper surface of the lower flange, the lower flange also forms an integrated structure with the concrete, and local buckling of the lower flange is also prevented. Furthermore, since the shear stopper is a plate member, it can be used as a stiffener to prevent local buckling of the lower flange when erecting the I-girder.

As a result, the present invention significantly improves the load-bearing capacity against local buckling of the lower flange and the lower part of the web, and against lateral buckling of the entire I-girder.

Therefore, even if a large negative bending moment occurs near the intermediate support of a continuous I-girder bridge and a large compressive force acts on the lower flange, the I-girder structure near the intermediate support according to the present invention effectively prevents local buckling of the lower flange and the lower part of the web, and lateral buckling of the entire I-girder, making it possible to utilize the performance of the plastic region of the steel.

Furthermore, as mentioned above, the I-girder structure near the intermediate support of the present invention is a composite structure of steel and concrete, and the cross section perpendicular to the longitudinal direction of the I-girder is a composite cross section that can resist bending moments.

Therefore, in the I-girder structure near the intermediate support of the present invention, the load-bearing capacity is greatly improved, and since there is no need to increase the plate thickness of the lower flange or web, or to reduce the spacing between cross beams and cross grooves and place them more closely, as in conventional technology 1, the weight of steel, labor hours, and construction costs can be reduced compared to conventional technology 1.

In addition, in the I-girder structure near the intermediate support of the present invention, a slip stopper is used, and reinforcing bars do not need to be placed in the concrete, and there is no need to connect vertical reinforcing bars to the upper and lower flanges as in conventional technique 2 described in Patent Document 1, making construction easy. In conventional technique 2 described in Patent Document 1, it is necessary to connect vertical reinforcing bars to the upper and lower flanges, which requires complicated work such as welding the reinforcing bars, and high precision is required for the attachment position and angle of the reinforcing bars. In addition, in the I-girder structure near the intermediate support of the present invention, even when reinforcing bars are placed, assembly and installation work can be performed on the generally flat and stable upper surface of the lower flange, making work and construction management easy.

As a result, in the I-girder structure near the intermediate support of the present invention, construction work is reduced, and construction costs and time can be reduced.

In addition, because the concrete is placed so that it is in the compression zone, which is the region below the plastic neutral axis, cracks do not occur in the concrete even in a plastic stress state, and the concrete's performance can be fully utilized until the full plastic bending moment is reached, while weight increase can be suppressed. In contrast, Patent Document 1 describes that fresh concrete may be poured partially in the height direction of the web, but does not specifically describe the height of the concrete to be placed. For this reason, with the technology described in Patent Document 1, if the height of the concrete placed is high, there is a risk of cracking or destruction of the concrete. Conversely, if the height of the concrete placed is low, there is a risk of local buckling of the web.

Furthermore, in the I-girder structure near the intermediate support of the present invention, unlike the technology described in Figure 6 of Patent Document 1, the steel members are entirely contained within the concrete and are not exposed to the atmosphere, so corrosion of the installed steel members is also suppressed. Also, in the technology described in Figure 6 of Patent Document 1, there is a concern about fatigue failure at the connection between the vertical reinforcing bars and the underside of the upper flange, but there is no such concern in the I-girder structure near the intermediate support of the present invention.

In addition, unlike the technologies described in Patent Documents 2 and 3, the present invention does not form a box-shaped cross section, so even if the height of the concrete placed is increased to improve the effect of preventing local buckling of the I-girder web, the increase in weight can be suppressed compared to when a box-shaped cross section is formed.

In addition, unlike the technology described in Patent Document 4, the present invention restrains the lower part of the web from both sides with concrete, which can fully demonstrate the effect of preventing local buckling of the web.

In addition, unlike the technology described in Patent Document 5, the present invention does not use precast plates, so the I-girder web can be sandwiched from both sides without play, and the I-girder web can be sufficiently restrained. In addition, fresh concrete is poured to integrate the concrete and the I-girder, which can enhance the composite effect of steel and concrete at each cross section perpendicular to the longitudinal direction of the I-girder.

In addition, by placing additional reinforcing bars inside the concrete, the composite effect of steel and concrete and the restraining effect on the concrete web can be further enhanced. In this case, by providing the plate member with a specified notch for placing the reinforcing bars in a specified position, the reinforcing bars can be placed in the specified position simply by inserting the reinforcing bars into the notch from above or the side and dropping them in, making installation easy. In contrast, reinforcing bars in the bridge axis direction are generally long, sometimes up to about 12 m in length, and the work of placing the reinforcing bars in the bridge axis direction and the management of the installation are labor-intensive.

In addition, in a continuous I-girder bridge, if the I-girder structure is placed only in the area where negative bending moment acts, it is possible to effectively prevent local buckling of the lower flange and lower part of the web, as well as lateral buckling of the entire I-girder, while minimizing the increase in weight of the entire continuous I-girder bridge.

The following describes an embodiment of the present invention in detail with reference to the drawings.

FIG. 1 (perspective view) and FIG. 2 (side view) are diagrams showing a first embodiment of the present invention (corresponding to claim 2 ). This embodiment is applied to an I-girder 30 in the vicinity of an intermediate support 12 among the I-girders 30 in a continuous I-girder bridge 10 (see FIG. 17). The I-girder 30 is composed of an upper flange 32, a lower flange 34, a web 36, and a vertical stiffener 38. The vertical stiffener 38 is composed of an intermediate support vertical stiffener 38A and a general vertical stiffener 38B. On the upper surface of the lower flange 34, concrete 46 is arranged, which includes a plate member 40 as a shear stopper and a predetermined reinforcement (bridge axial direction reinforcing bars 42 and ties 44), and is integrated with the upper surface of the lower flange 34, the lower part of the web 36, and the lower part of the vertical stiffener 38. The area in which the concrete 46 is arranged is within a compression region, which is an area below the plastic neutral axis.

In Figures 1 and 2, which show the state after the fresh concrete has been poured and hardened to become concrete 46, it is difficult to see the plate member 40, which is a feature of this embodiment, and the arrangement of reinforcing bars 42, 44 using the plate member 40. Therefore, below, the structure and construction method of this embodiment will be explained with reference to figures showing the construction process.

FIG. 3 is a perspective view showing a construction stage in which a plate member 40 acting 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 support 12, and FIG.

The I-girders 30 are manufactured in a factory or other facility to a specified length (up to about 12 m) and then joined together one by one at the site for erection. The plate members 40, which act as anti-slip members, are in principle installed by welding or other methods at the factory, but may also be installed at the site.

As shown in FIG. 5, the plate member 40 is, for example, a steel plate having a thickness of about 19 mm, with a notch 40A shaped to allow the reinforcing bar to be placed in a predetermined position. The shape of the notch 40A is not particularly limited as long as it allows the reinforcing bar to be placed in a predetermined position, and can be, for example, a keyhole shape as shown in FIGS. 6(A) to (E).

Figure 6(A) is an example of a shape where two rows of reinforcing bars are arranged in one tier with two entrances for the reinforcing bars, Figure 6(B) is an example of a shape where two rows of reinforcing bars are arranged in two tiers with two entrances for the reinforcing bars, and Figure 6(C) is an example of a shape where two rows of reinforcing bars are arranged in two tiers with one entrance for the reinforcing bars. Figures 6(D) and (E) are shapes where the notch 40A where the reinforcing bars are arranged has a hook attached to prevent the reinforcing bars from shifting position. Figure 6(D) is an example of a shape where three rows of reinforcing bars are arranged in one tier with three entrances for the reinforcing bars, and Figure 6(E) is an example of a shape where three rows of reinforcing bars are arranged in two tiers with three entrances for the reinforcing bars.

In addition, as shown in Figures 3 and 4, the plate member 40 can be disposed on the upper surface of the lower flange 34 between the vertical stiffeners, and can also serve as a stiffener to prevent local buckling of the lower flange when erecting the I-girder 30.

Next, we will explain the assembly and installation of the reinforcing bars 42 and 44, and the pouring of the fresh concrete.

Figure 7 is a side view showing an example in which the bridge axis direction reinforcing bars 42 and tie bars 44 are arranged in a specified manner and placed on the upper surface of the lower flange 34. In this example, two rows of bridge axis direction reinforcing bars 42 are arranged in two stages, totaling four bars, and tie bars 44 are arranged so as to surround these four bridge axis direction reinforcing bars 42 from the outside at a specified interval.

In this embodiment, the plate member 40 has a notch 40A, so that the bridge axis direction reinforcing bars 42 can be dropped into the notch 40A of the plate member 40 and positioned at a predetermined position, as shown in Figure 8. Note that the notch 40A of the plate member 40 in Figure 8 is drawn in a shape (the shape of Figure 6 (A)) that allows two reinforcing bars to be positioned therein for convenience of illustration, but the actual shape of the notch 40A in this embodiment is the shape of Figure 6 (B), allowing two rows of bridge axis direction reinforcing bars 42 to be positioned in two stages for a total of four reinforcing bars.

In the concrete reinforcing bar arrangement work at the site, first, the four bridge-axis direction reinforcing bars 42 are dropped into the notches 40A of the plate member 40 and placed in the specified position. Then, the tie bars 44 are placed at a specified interval 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. 7. In this way, in this embodiment, even if the reinforcing bars are not assembled in advance and are assembled on site, the work and construction management at the site are extremely easy. Note that, in this embodiment, the bridge-axis direction reinforcing bars 42 may be dropped into the notches 40A of the plate member 40 using reinforcing bars assembled in advance and placed in the specified position. In either case, the reinforcing bars only need to be installed on the generally flat and stable lower flange 34, and the plate member 40 with the notches 40A is arranged, so that the work and construction management at the site are extremely easy.

When using pre-assembled rebar, for example, the notch 40A in FIG. 5 may be a vertically long hole with a width that matches the diameter of the bridge axis direction rebar 42 to be installed, and the assembled rebar may be installed in the long hole.

The area where fresh concrete is poured and placed is below the plastic neutral axis, so the area where the reinforcing bars 42, 44 and plate member 40 are placed must be determined taking into account the cover thickness.

After the reinforcement work is completed, as shown in FIG. 9, formwork 48 is set up to a specified height, and fresh concrete is poured into the space surrounded by the upper surface of lower flange 34, the lower part of web 36, and the lower part of intermediate support vertical stiffener 38A. The fresh concrete is poured so that the concrete 46 that hardens from the fresh concrete is entirely contained within the compression zone, which is the area below the plastic neutral axis.

As shown in FIG. 9, for example, the formwork 48 can be installed by temporarily fixing it to the intermediate support vertical stiffener 38A, the lower flange 34, etc. at the temporary fixing point 48A. The height of the concrete 46 to be laid varies depending on the plate 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, it can be, for example, about 300 to 700 mm.

When the formwork 48 is removed after the fresh concrete has hardened, a composite structure is formed in which the upper surface of the lower flange 34, the lower part of the web 36, the lower part of the intermediate support vertical stiffener 38A, the entire plate member 40, the entire reinforcing bars 42, 44, and the concrete 46 are integrated, as shown in Figures 1 and 2. As a result, even if a large negative bending moment is generated near the intermediate support 12 of the continuous I-girder bridge 10 and a large compressive force acts on the girder cross section from the lower part of the web 36 to the lower flange 34, the risk of local buckling of the lower part of the lower flange 34 and the web 36, or of lateral buckling of the entire I- girder 30, is extremely low.

As a result, in this embodiment, it is possible to effectively utilize the performance of the plastic region of the steel material that constitutes the I-girder 30 near the intermediate support 12, and it is possible to resist bending moments as a composite cross section of steel and concrete, dramatically improving the load-bearing capacity of the I-girder 30 near the intermediate support 12.

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

Figure 10 shows a conceptual diagram of stress distribution in the cross section of the I-girder 30 structure near the intermediate support 12 receiving a negative bending moment in a state of plastic stress. Here, the balance of forces in a state of plastic stress is considered, taking into account the bridge axis direction reinforcing bars 60A in the deck 60, the I-girder 30, and the concrete 46, and the plastic neutral axis is calculated. Note that the concrete of the deck 60 is not taken into account here because it is in a tension zone and will cause cracks. The area above the plastic neutral axis is a tension zone where tensile stress occurs, and the area below the plastic neutral axis is a compression zone where compressive stress occurs. In Figure 10, hc indicates the height of the concrete 46, and Dcp indicates the distance from the bottom surface of the concrete 46 to the plastic neutral axis.

As in this embodiment, by considering the stress distribution in the cross section in the plastic stress state and limiting the height of the concrete 46 to within the compression region below the plastic neutral axis (hc≦Dcp), the stress acting on the concrete 46 can always be a compressive stress. Therefore, no cracks will occur in the concrete 46, and the performance of the concrete 46 can be fully utilized until the full plastic bending moment is reached. In addition, by limiting the height of the concrete 46 to within the compression region below the plastic neutral axis (hc≦Dcp), the amount of fresh concrete to be poured is reduced, and weight increase is suppressed.

When making full use of the performance of the concrete 46 up to the full plastic bending moment, it is preferable to stiffen the intermediate support vertical stiffener 38A with a steel member 50 as shown in FIG. 11 to improve the bending strength near the intermediate support 12. Also, as shown in FIG. 12, the space directly above the intermediate support 12 formed by the lower part of the intermediate support vertical stiffener 38A, the upper surface of the lower flange 34, and the lower part of the web 36 may be filled with fresh concrete, and concrete 52 may be provided up to a height approximately equal to the height hc of the concrete 46 to improve the bending strength near the intermediate support 12.

In the first embodiment described above, the plate member 40 is used as the anti-slip member, but the anti-slip member is not limited to the plate member 40. For example, the headed stud 54 (see FIG. 13) may be used instead of the plate member 40. In this case, the reinforcing bar 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, the reinforcing bar can be installed on the generally flat and stable lower flange 34, making on-site work and construction management easier. However, when the headed stud 54 is used, assembling the reinforcing bar directly on the lower flange 34 requires more effort in positioning the reinforcing bar than when the plate member 40 is used. In addition, the headed stud 54 cannot contribute as a stiffening material to prevent local buckling of the lower flange during the erection of the I-girder.

The second embodiment of the present invention is shown in FIG. 13 (side view). In the second embodiment, in addition to the plate member 40, headed studs 54 are installed on the lower flange 34 by welding or the like as a slip stopper. By installing the headed studs 54 on the lower flange 34 in addition to the plate member 40, the composite effect of steel and concrete can be further enhanced, and the load-bearing capacity of the I-girder 30 in the vicinity of the intermediate support 12 can be further improved. Note that in FIG. 13, for convenience of illustration, the plate member 40 and headed studs 54 contained inside the concrete 46 are drawn with solid lines.

In the embodiment described above, plate members 40 and headed studs 54 are used as shear stoppers, but the shear stoppers that can be applied to the present invention are not limited to these. For example, structural steel may be used as the shear stopper, or a truss-shaped shear stopper formed from structural steel or reinforcing bars may be used. However, it is necessary to select an appropriate type after taking into consideration the shear strength, toughness, cross-sectional composite effect, etc.

In addition, in the embodiment described above, the bridge axis direction reinforcing bars 42 and the tie bars 44 are used, but as long as sufficient shear stoppers are provided, the bridge axis direction reinforcing bars 42 and the tie bars 44 are not essential and may be omitted. However, if the bridge axis direction reinforcing bars 42 and the tie bars 44 are omitted, the load-bearing capacity will decrease compared to when the bridge axis direction reinforcing bars 42 and the tie bars 44 are provided.

Next, the case where the first or second embodiment is applied to a continuous I-girder bridge will be described. Figures 14 and 15 are side views that show the position of concrete 46 placed on the upper surface of the lower flange 34 in the bridge axis direction when the first or second embodiment is applied to a continuous I-girder bridge 10. In Figures 14 and 15, the reference numeral 14 indicates an end support.

In an embodiment of the present invention, the concrete 46 is placed in the area where the negative bending moment acts (hereinafter, referred to as the negative bending area). As shown in FIG. 14, the concrete 46 may be placed throughout the entire negative bending area, or as shown in FIG. 15, it may be placed only in the area where the negative bending moment is particularly large. The placement position of the concrete 46 in the bridge axis direction may be determined taking into consideration the magnitude of the negative bending moment acting on the cross section and the magnitude of the bending moment when buckling occurs in the I-girder. In this way, by limiting the placement position of the concrete 46 to a specified negative bending area, it is possible to effectively prevent local buckling of the lower flange 34 and the lower part of the web 36 and lateral buckling of the entire I-girder 30 while suppressing weight increase.

Figure 16 shows a perspective view of a cross section taken near the intermediate support 12 at a plane perpendicular to the bridge axis when the first or second embodiment is applied to a continuous I-girder bridge (two-main I-girder bridge) 20, viewed from diagonally above. Concrete 46 is placed on the upper surface of the lower flange 34 on both sides of the lower part of the web 36 of the I-girder 30, and the lower part of the web 36 of the I-girder 30 is restrained by the concrete 46 from both sides. A deck 80 is placed on top of the two I-girders 30 arranged in parallel.

In the above-described embodiment, the construction of the deck 80 to be installed on the I-girder 30 is not described, but it is necessary to perform the construction appropriately taking into consideration the erection steps and construction sequence. Possible ways to improve the construction sequence of the deck 80 include improving the order of block construction (such as pouring the intermediate support blocks after the construction sequence) and improving the construction sequence with the concrete 46, which is placed by pouring fresh concrete on the bottom flange 34 of the I-girder 30.

FIG. 1 is a perspective view showing a structure of an I-girder in the vicinity of an intermediate support according to a first embodiment of the present invention; Side view FIG. 13 is a perspective view showing a construction stage in which a plate member is provided as a stopper on the upper surface of the lower flange of the I-girder near the intermediate support point. Side view FIG. 1 is a perspective view showing an example of a plate member; FIG. 11 is a side view showing an example of a cutout in a plate member; A side view showing an example of the bridge axial reinforcing bars and tie bars arranged as specified and installed on the top surface of the lower flange. A perspective view showing the bridge axial reinforcing bars being dropped into the notches in the plate members and placed in the designated positions. Side view showing the formwork in place Schematic diagram of stress distribution in the cross section of an I-girder structure near an intermediate support subjected to negative bending moment under plastic stress A side view showing the state in which the intermediate support vertical stiffener is stiffened with a steel member. A side view showing the state in which fresh concrete is filled in the space directly above the intermediate support and the concrete is placed up to a height of hc. FIG. 11 is a side view showing the structure of an I-girder in the vicinity of an intermediate support according to a second embodiment of the present invention. FIG. 13 is a side view showing a schematic example of the position of the concrete placed on the upper surface of the lower flange in the bridge axis direction. FIG. 11 is a side view showing another example of the same. FIG. 1 is a perspective view of a cross section taken along a plane perpendicular to the bridge axis near an intermediate support when an embodiment of the present invention is applied to a continuous I-girder bridge (two main I-girder bridge), viewed from diagonally above A side view showing a schematic example of bending moment distribution in a continuous I-girder bridge. Front view showing local buckling of the bottom flange near the intermediate support of a continuous I-girder bridge Front view showing local buckling of the bottom of the web near the intermediate support of a continuous I-girder bridge Front view showing lateral buckling near the intermediate support of a continuous I-girder bridge

Explanation of symbols

10...Continuous I-girder bridge 12...Intermediate support 14...End support 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 support vertical stiffener 38B...General vertical stiffener 40...Plate member 40A...Notch 42...Bridge axial direction reinforcing bar 44...Hoop 46, 52...Concrete 48...Formwork 50...Steel member 54...Headed stud 60, 80...Deck 60A...Bridge axial direction reinforcing bar in deck 60

Claims (3)

In a continuous I-girder bridge composed of an I-girder and a deck slab equipped with an upper flange, a lower flange, a web, and vertical stiffeners, and supported by end supports at both ends and one or more intermediate supports, a plurality of shear stoppers are arranged on the upper surface of the lower flange near the intermediate supports on which a negative bending moment acts, and fresh concrete is poured into a space including the shear stoppers and surrounded by the upper surface of the lower flange, the lower part of the web, and the lower part of the vertical stiffeners so that the concrete obtained by hardening of the fresh concrete is entirely contained within the compression zone, which is the area below the plastic neutral axis, and the entire shear stopper, the upper surface of the lower flange, the lower part of the web, and the lower part of the vertical stiffeners are integrated with the concrete obtained by hardening of the fresh concrete,
The shear stopper is a plate member and serves as a stiffening material to prevent local buckling of the lower flange when erecting the I-girder.
The above configuration prevents local buckling of the lower flange and lower part of the web, as well as lateral buckling of the entire I-girder, thereby improving the load-bearing capacity of the I-girder. The structure of an I-girder near an intermediate support in a continuous I-girder bridge as described in claim 1, further comprising a reinforcing bar, and the plate member has a notch for arranging the reinforcing bar in a predetermined position, and the reinforcing bar is arranged in the predetermined position simply by inserting the reinforcing bar into the notch from above or the side and dropping it in. A continuous I-girder bridge, characterized in that the I-girder structure according to claim 1 or 2 is arranged only in an area where a negative bending moment acts.

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