JP2024507436A - Composite RCC deck and prestressed parabolic lower chord suspended open web steel girder bridge superstructure - Google Patents

Abstract

Composite decks increase the strength and stiffness of bridges. Prestressed composite open web steel girders have the added benefit of high strength cable supports. Results are shown for a typical 125 m span height 9.0 m, 10.0 m and 12.5 m bridge, and another 50.0 m span height 2.5 m bridge. Member stresses and bridge deflections during construction remained safe. For the critical live load deflection of the span /800, the average steel offtake for a 125m bridge is 2.65t/m and for a 50m span bridge is 1.77t/m. The reserve strength is 3.2 times the live load of operating conditions. The girders are manufactured in a factory as panels, assembled on site, jacked up or craned, and secured above the bearings. The joining of the cross members and the forming of the deck slab components on site and the stepwise prestressing of the bottom chord are carried out. Short to long span bridges for single lane or multiple lanes in road, rail, subway, and coastal road projects are possible.

Description

The "Synthetic RCC Deck and Prestressed Parabolic Lower Chord Suspended Open Web Steel Girder Bridge Superstructure" of the present invention belongs to the field of bridge engineering in civil engineering. Short (10 m) to long (200 m) span superstructures can be used for infrastructure projects related to single or multi-lane roads, railways, subways, flyovers and maritime highways.

In transportation systems such as roads, railways and subways, bridges are often required to cross rivers, such as elevated roads and maritime highways. For bridges, high tensile strength (HTS) steel cables are very economical and are used to construct long span suspension bridges, cable-stayed bridges, and more recently stressed ribbon bridges. However, HTS cables are very flexible, which poses a structural disadvantage in bridges.

The use of cleats when combining the RCC deck with the top chord of a suspended open web steel girder bridge superstructure prevents buckling and significantly increases the strength and stiffness of the bridge. The prestressing of the lower chord, in addition to creating an appropriate preload in the deck, creates an upward thrust that counteracts and balances the tension due to the applied load. This type of bridge using HTS cables in the lower chord is an invention for high strength. The lower chord profile of this bridge, when made parabolic (polygonal shape), produces uniform tension under uniformly distributed loads due to dead weight or live loads, which promotes prestressing. Thus, the "Synthetic RCC Deck and Prestressed Parabolic Lower Chord Suspended Open Web Steel Girder Bridge" (hereinafter referred to as the "Prestressed Composite Bridge") was invented.

(Purpose of the invention)
The objective was to invent a robust prestressed composite bridge superstructure with high strength, low consumption of structural steel, low cost, high reserve strength, and easy construction; , construction of the substructure and superstructure may be planned as parallel operations reducing construction time and costs. Also suitable for short spans (10m) as well as long spans (200m), this kind of bridge superstructure for projects like single or multi-lane roads, railways, subways, flyovers and coastal roads. The aim was also to provide solutions.

Examples of typical design and approximate construction stage analysis of prestressed composite bridges for 125 m and 50 m spans are shown. Although the stress in the girder is small and safe under all construction stages, the stress in the member at the service life limit (SLS) condition is also very safe as it is determined by the critical deflection at the SLS condition.

The maximum deflection under SLS conditions for IRC Class-A loads for two lanes is 155.6 mm for a 125 m span bridge, and the average steel offtake is 2.65 t/m for a 50 m span bridge. , 57.6 mm, and the average steel offtake at this time is 1.77 t/m.

Due to the lower stress in the SLS condition, for a bridge with a 125 m span, the conservative reserve strength of the bridge beyond the SLS condition to the yield condition is 3.2 times the live load in the SLS condition, and for a bridge with a 50 m span. , it is 2.8 times. Therefore, a method for designing and constructing bridges of this type is invented, supported by design guidelines according to existing codes of practice.

Table 1 summarizes the results of the design and construction phase analysis for steel offtake, member stresses, applied prestresses and deflections under live loads for the 125 m span bridge and the 50 m span bridge.

These results show that the prestressed composite bridge superstructure is economical, strong, and has high reserve strength.

The above and further characteristics and advantages of embodiments of the invention will become readily apparent upon consideration of the following detailed description of embodiments of the invention, particularly in conjunction with the accompanying drawings.

FIG. 1 shows a diagram of a girder, in which the top chord (1), bottom chord (2) and web material (3) are shown. Details of the cable fixing section in "A" are shown in FIG. A 27T15 standard cable (4) and anchorage (5) are shown aligned in and along the lower chord. The composite RCC deck is molded using cleats (6) above the top chord, supporting cross beams and stringers. The terminal crossbeam (7) joins the two main beams. The end girder is supported above the bearings (8) and the RCC deck is supported beyond the girder and above the dirt wall (9). Figure 3 shows the FEM model of the bridge. Figure 4 shows the operational load stress for a prestressed composite 125m x 9m bridge. FIG. 5 shows the stresses in the members during construction phase 1. FIG. 6 shows the stresses in the member during construction phase 2. FIG. 7 shows the stresses in the member during construction stage 3. FIG. 8 shows the stresses in the member during construction stage 4. FIG. 9 shows the stresses in the member during construction stage 5. FIG. 10 shows the stresses in the member during construction stage 6. A diagram for a 50m x 2.5m bridge is shown. A three-dimensional FEM model diagram of a 50m x 2.5m bridge is shown. The live load axial stress for a 50m x 2.5m bridge is shown. Figure 3 shows a diagram for the arrangement of a 50m x 23m superstructure.

For a better understanding, the drawing titles and brief descriptions are provided in Table 2.

(Detailed description of the invention)
The headings used herein are for organizational purposes only and are not intended to be used to limit the scope of this description or the claims. As used throughout this application, the phrase "may" has a permissive meaning (i.e., meaning that (meaning "possible"). Similarly, the words "include,""including," and "includes" mean including, but not limited to. For ease of understanding, similar reference numerals have been used, where possible, to refer to similar elements common to multiple figures. Any portion of the drawings may be illustrated using dashed or dotted lines unless the context in which they are used does not contradict the same.

A typical 125 m span, 9 m high composite prestressed two-lane open web steel girder bridge was designed, and its two-dimensional diagram is shown in Figure 1. The top chord consists of a 500 mm x 500 mm x 16 mm box section, the bottom chord consists of a 500 mm x 600 mm x 22 mm box section, and the web material has a 500 mm x 200 mm x 16 mm section.

A typical anchoring system in the support section of a suspended bridge superstructure is shown in FIG. In the end panels in the anchorage, support and transition areas, E410 grade steel with a yield stress of 410 N/mm ² is used for high strength. For the 125m span case, use two 27T15 cables for each digit. Loads from the cable anchorage are transferred through the top and bottom plates as well as two extending E410 grade bottom chord side plates and one central stiffener plate (10). Fusing systems must be designed with a high safety factor, manufactured at the factory, and tested before assembly.

analysis:
Using FEM software, the superstructure was analyzed as a space frame with composite decks modeled as plate elements, and the model is shown in Figure 3. This was analyzed for two-lane Class A (IRC: 6-2017) loads, and a diagram of the low member axial stress under operational conditions is shown in Figure 4.

The maximum deflection of the bridge under live load is 155.6 mm, which is within the given limit of span/800. The average steel offtake of the bridge superstructure is 2.65 t/m, which is significantly lower than the steel offtake of a similar open web steel girder superstructure. Similar 10 m or 12.5 m high girder models with 125 m spans are also analyzed and the results for 9 m, 10 m and 12.5 m high girders are compared.

Bridge Superstructure Construction Bridge girder panels may be manufactured in a factory using welded or bolted connections. The panels are transported to the site where they will be assembled and joined, and the individual girders are lifted and secured above the bearings using jacks or cranes or other suitable equipment. Next, the cross members for the top and bottom chords may be joined. The deck slabs for the superstructure are formed into symmetrical parts using bonding agents and graded prestressing.

The HTS prestressed cable is placed in the parabolic lower chord. The cable is prestressed in multiple stages according to the design. For the case of a 125 m x 9 m bridge, the results for different construction stages in terms of member stresses and maximum deflections are shown in Figures 4-10.

A typical example of graded prestressing for two 27T15 cables in each lower string is shown below.

Stage 1: Construct the girder including cross members, cross beams and longitudinal girders and apply appropriate prestress of 2000 kN (Figure 5). The mid-span deflection of the girder at this stage is 17.8 mm (downward).

Step 2: Add a further 2000 kN prestress (Figure 6). The mid-span deflection of the girder at this stage is 151.7 mm (upwards).

Step 3: Form the deck slab in 1/5 span from each end. The construction load at this stage is 5kN/ ^m2 . The mid-span deflection of the girder at this stage is 3.5 mm (upwards).

Stage 4: 10 days after concreting in Stage 3, a further 1000 kN prestress is applied to form the next 1/5 span (11). The mid-span deflection of the girder at this stage is 121.7 mm (downward).

Stage 5: 10 days after concreting in Stage 4, a further prestress of 1000 kN is applied to form the central 1/5 span (11). The mid-span deflection of the girder at this stage is 7.6 mm (downward).

Stage 6: 28 days after applying the SIDL to the slab (11), prestressing is further applied with a load of 3100 kN. The mid-span deflection of the girder at this stage is 75.5 mm (upwards).

As an alternative option, a two-stage prestressing, i.e. a first prestressing performed before slab formation and a second prestressing after slab curing, may be better. be.

A live load is then applied to this bridge. The mid-span deflection of the girder at this stage is 80.5 mm (downward). Additional prestress may be added at appropriate times to compensate for tine dependent losses, etc. reflected in droop deflection.

Another typical 50 m span, 2.5 m high composite prestressed two-lane open web steel girder bridge was designed (Fig. 11). The top chord consists of a 300 mm x 300 mm x 16 mm box section, the bottom chord consists of a 300 mm x 450 mm x 22 mm box section, and the web material is 300 mm wide, 16 mm thick and 250 mm high.

The FEM model and axial stress diagram under operating conditions are shown in FIGS. 12 and 13, respectively.

Prestress calculation using load balance After prestressing, the girder is assumed to be horizontal and the cables are assumed to carry all the permanent loads and half of the affected live loads. More precise prestress adjustments may be made, such as reduction, as needed for the final slab profile.

When the origin is the center of the lower chord of the parabola, the equation is as follows.
y=ax ² or=2.5/(25×25)=0.004
(dy/dx) end=2ax=0.008×25=0.2rad
Balancing load = SW-750 + floor slab -2660 + WC-610 + CB-750 + (LL affected) / 2-604 = 5374kN
Prestress required for each digit = 5374/(2 x 2 x 0.2) = 6797 kN
Two no. Prepare a 19T15 (3870kN) cable.
Preload on the deck:
Prestress applied along the two lower chords when stressing the 19T15 cable after deck curing;
=2×3870=7740kN
The vertical component is towards the support, horizontal force = 7740cos11.4 = 7587kN
Area (Cm ² ); Upper chord = 192, corresponding floor slab = 1770, lower chord = 330
Force shared by the lower chord = (330/2292) x 7740 x 0.98 = 1093kN
Force applied to RCC slab = (7740-1093) x 1770/1962 = 5996kN
Therefore, axial stress in the floor slab = 5996000/2125000 = 2.8N/mm ²

By applying tension to the concrete, e.g. 1.4 N/ ^mm2 , and maintaining proper spacing of the crossbeams, the slab can be designed on a crack-free basis, which is highly desirable for composite slabs. .

By optimizing two-lane highway superstructure girders of 9 m height with 125 m span and 2.5 m height with 50 m span, the steel offtake will be 331.0 t and 88.5 t, respectively. The maximum deflection due to live load at mid-span is 151.3 mm and 57.6 mm for the 125 m span and 50 m span, respectively, which is within the allowable deflection of the span/800.

For 125m span bridges, the stresses in the shaft members during the construction of the deck and concreting are safely matched with the prestresses applied at different stages according to the design. The critical live load for the elastic condition was found to be 3.2 times the SLS live load for the 125 m span and 2.8 times the SLS live load for the 50 m span, which confirms their robustness. . In the 125m span case, the steel offtakes are 310t and 299t and the corresponding live load deflections are 135.5mm and 140.1mm for similar 10m and 12.5m height girder examples, respectively.

Concrete grouting: The dead weight of the superstructure is fully supported by prestressing alone, providing a favorable prestress on the RCC deck. Therefore, box section expandable concrete grouting is preferred. Concrete-filled steel tubes (CFST) are thus composite, providing additional strength and stiffness to the bridge superstructure.

Claims (12)

A method for the construction of a prestressed open web steel girder composite bridge superstructure, the method comprising:
connecting the composite top chord (1) to the prestressed parabolic (polygonal) bottom chord (2) using a plurality of open web members (3);
aligning the cable (4) and the anchorage (5) within and along the lower chord of the prestressed parabola;
supporting the cross beams (7), stringers, and composite deck using a plurality of shears (6);
connecting a terminal cross beam (7) to at least two main beams, wherein said terminal cross beam is supported above a bearing (8);
For suspended bridges, we obtain a prestressed parabolic (polygonal) lower chord (2) joined to the upper chord (1) for nearly uniform tension under uniformly distributed loads, resulting in a prestress-facilitating synthesis To realize a prestressed suspension bridge,
Said composite prestressed suspension bridges up to predetermined spans of 10 m to 200 m, multiple superstructure panels are fabricated in a factory, assembled and bonded on site, constructed into girders, and then designed in stages. concreting a composite RCC deck slab into a symmetrical part in situ by stressing, wherein the deck slab for the superstructure is formed into a symmetrical part using a bonding agent; and Prestressing the lower chord in stages from the girder lifting stage to the bridge operation stage facilitates controlling member stresses and bridge deflections within acceptable thresholds during the construction and operational life of the bridge. A method including: The stiffness of the composite deck bonded to the upper chord and the strength of the high-tensile cables provided in the composite prestressed suspension bridge have low deflection, high strength and stiffness, and a reserve of approximately three times the elastic limit. 2. The method of claim 1, which provides strength. 3. The method of claim 2, comprising prestressing a high-tensile cable placed within the parabolic lower chord. 2. A method according to claim 1, wherein the prestressing of the lower chord (2) counteracts the tension due to the applied load, and the prestressing of the lower chord generates a balancing upwardly pushing load. The prestressing of the lower chord (2) creates a longitudinal prestress in the deck, which may enable design on a crack-free basis, which is due to better fatigue performance. A method according to claim 1, which is highly desirable for. 2. The method of claim 1, wherein a prestress is applied to counteract half of the live load affected, which reduces by half the live load bowing of the deck and the bending stress of the girder. A method according to claim 1, wherein the lower chord (2) profile of the bridge, when made parabolic, produces a uniform tension under uniformly distributed loads due to dead weight or live loads, which promotes lower chord prestressing. . 2. The predetermined span is between 10 m and 200 m of the composite prestressed suspension bridge for projects such as single or multi-lane roads, railways, subways, and elevated roads and maritime highways. the method of. 2. The stress of the shaft member during the construction and concreting of the composite RCC deck is, if necessary, matched with prestresses applied at different stages in a low and safe manner. Method. 2. The use of the plurality of cleats prevents premature buckling defects and increases strength and stiffness, whereby the RCC deck is composited with the upper chord of the bridge. the method of. 2. The method of claim 1, wherein expandable concrete grouting of box sections is converted to a CFST composite, increasing the strength and stiffness of the superstructure in addition to corrosion protection. a top chord (1) joined to a prestressed parabolic (polygon) bottom chord (2) using a plurality of open web boxes or CFST members (3);
a plurality of cables (4) and a plurality of anchorages (5) housed in and aligned along the prestressed parabolic lower chord (2);
a plurality of stanchions (6) adapted to support the transverse and longitudinal girders;
a plurality of bearings (8) configured to join the terminal transverse girders by at least two main girders, and formed above said upper chord (1), transverse girders and longitudinal girders, for better fatigue performance; Synthetic RCC deck slabs (7) which are longitudinally prestressed by prestressing to enable the design on a crack-free basis of Prestressed open web steel girder composite bridges, including molded into symmetrical parts.

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