KR20240060816A - Composite RCC deck and prestressed parabolic deck current underslung open web steel bridge superstructure - Google Patents

Abstract

Composite decks increase the strength and rigidity of bridges. Prestressed composite open web steel girders have the added benefit of high-strength cable support. Results are provided for a typical 125 m span bridge with heights of 9.0 m, 10.0 m and 12.5 m, as well as a 50.0 m span and 2.5 m height bridge. During installation, member stresses and bridge displacements are safely maintained. For a 125 m bridge, the average steel off-take is 2.65 t/m, and for a 50 m span bridge, the Span/800, which limits live load displacement, is 1.77 t/m. Its reserve strength is 3.2 times the service condition live load. The girders are manufactured in a panel-type workshop, assembled on site, jacked up or lifted with a crane and fixed on bearings. The connection of the cross members and in-situ deck casting of the sections using graded bottom current compressive stresses are performed. Short to long span bridges for single or multiple lanes of road, rail, metro rail and coastal link projects are feasible.

Description

Composite RCC deck and prestressed parabolic deck current underslung open web steel bridge superstructure

The invented 'composite RCC deck and prestressed parabolic bottom chord underslung open web steel bridge superstructure' belongs to the bridge engineering branch of civil engineering. Short (10 m) to long (200 m) span superstructures can be used for infrastructure projects involving single or multi-lane roads, railways, subways, flyovers and marine connections.

In transportation systems such as road, rail and metro rail, bridges are often required to cross rivers, such as overpasses and sea connections. For bridges, high-tensile strength (HTS) steel cables are very economical and are used to build long-span suspension bridges, cable-stayed bridges and, more recently, stressed ribbon bridges. However, HTS cables are very flexible, which poses structural disadvantages for bridges.

Using shear connectors, composite RCC deck slabs with the upper chords of the underslung open web steel girder bridge superstructure prevent their buckling and increase the strength and rigidity of the bridge. This is greatly improved. Compressively stressing the floor chords, in addition to inducing a beneficial pre-compression in the deck slab, counteracts its tension due to the applied load, which exerts a counterbalance to the upward thrust. This type of bridge using HTS cables in the bottom chord is designed for its high strength. If the bottom chord profile of the bridge is made parabolic (polygonal), its uniform tension occurs under a uniformly distributed load due to its own weight or live load, making it easier for it to be subjected to compressive stress. Accordingly, 'composite RCC deck and prestressed parabolic bottom chord underslung open web steel girder bridge superstructure' (hereinafter referred to as 'prestressed composite bridge') was invented.

The goal was to develop a robust prestressed composite bridge superstructure with high strength, low structural steel consumption, low cost, high reserve strength and easy erection, enabling substructure and superstructure construction. Construction time and costs can be reduced by planning as parallel activities. The goal is also to provide bridge superstructure solutions of this type suitable for short span (10 m) as well as long span (200 m), fly over and projects such as single or multi-lane roads, railways, metros and coastal connections. It was.

A typical design and approximate installation phase analysis example of a 125 m span and 50 m span prestressed composite bridge is provided. Girder stresses at all stages of installation are low and safe, but member stresses under serviceability limit state (SLS) conditions are also very safe as they are dominated by the limiting displacements of the SLS conditions.

The maximum deflection under SLS conditions for a two-lane Class-A IRC load is 155.6 mm with an average steel off-take of 2.65 t/m for a 125 m span bridge and 1.77 t/m for a 50 m span bridge. It is 57.6mm in m.

Due to the low SLS condition stress, the conservative reserve strength of the bridge beyond SLS condition to yield condition is 3.2 times the SLS condition live load for a 125 m span bridge and 2.8 times the SLS condition live load. Therefore, a design and construction method for this type of bridge was invented, supported by design guidelines in accordance with existing codes of practice.

A summary of the design and installation phase analysis results for steel offtake, member stress, applied compressive stress and displacement under live load for the 125 m and 50 m span bridges is provided in Table 1.

Table 1 Analysis results of design and installation stages

[Table 1]

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

These and additional features and advantages of embodiments of the invention will become apparent upon consideration of the following detailed description of embodiments of the invention thereof, particularly when considered in conjunction with the accompanying drawings.
Figure 1 shows a line diagram of a girder with top chords (1), bottom chords (2) and web members (3) indicated. Cable anchorage details at 'A' are shown in Figure 2. The 27T15 standard cable (4) and anchorage (5) are aligned within and along the bottom chord. The composite RCC deck is cast on top chords supporting the cross girder and stringer beam, using shear connectors (6). The end cross girder (7) connects the two main girders. The girders at the ends are supported on bearings (8), and the RCC deck slab beyond the girders is supported on earth walls (9). Figure 3 shows the FEM model of the bridge. Figure 4 shows the service load stresses of a prestressed composite 125mx9m bridge. Figures 5 to 10 show member stresses during corresponding construction stages 1 to 6. Line diagram (Figure 11), 3-d FEM model view (Figure 12) and live load axial stress (Figure 13) are shown for a 50 mx2.5 m bridge. A line sketch of the 50mx23m superstructure layout is provided in Figure 14.
To aid understanding, drawing titles and brief explanatory drawings are provided in Table 2.
Table 2 Drawing titles and brief descriptions
[Table 2]

The headings used herein are for organizational purposes only and are not intended to limit the scope of the description or claims. As used throughout this application, the word "may" is used in a permissive sense (i.e., meaning that it is possible) rather than in a mandatory sense (i.e., that it is necessary to do so). Likewise, the words “comprise,” “including,” and “includes” mean including but not limited to. To aid understanding, where possible, like reference numbers have been used to designate similar elements that are common to the drawings. Optional portions of the drawings may be illustrated using dashed or dotted lines, unless the context of use indicates otherwise.

A typical 125 m span and 9 m depth composite prestressed two-lane open web steel girder bridge was designed for which a two-dimensional line sketch is provided in Figure 1. The top chord consists of a 500mm

A typical anchorage system in the supports of an under-slung bridge superstructure is shown in Figure 2. E410 grade steel with a yield stress of 410 N/mm ² is used in end panels for high strength in anchorages, supports and transition areas. Two 27T15 cables for each girder's 125 m span case are used. Excluding the top and bottom plates, the load from the cable anchors is transmitted through two extended E410 grade bottom chord side plates and one central reinforcement plate (10). Anchorage systems must be designed with high fos, manufactured at the factory and tested prior to assembly.

analyze:

Using FEM software, the superstructure is analyzed as a space frame with a composite deck modeled as plate elements, the model for which is shown in Figure 3. The low member axial stress diagram in service and analyzed for two lanes of Class A (IRC:6-2017) loading is shown in Figure 4.

The maximum displacement of the bridge under live load is 155.6 mm, which is within the predefined limit of Span/800. The average steel off-take of the bridge superstructure is 2.65 t/m, which is significantly lower than the steel off-take of similar open web steel girder superstructures. The parallel 125m span depth 10m and 12.5m depth girder models are also analyzed to compare the results of 9m, 10m, and 12.5m depth girders.

Installation of bridge superstructure:

Bridge girder panels can be fabricated in the workshop using welded or HSFG bolted connections. The panels are transported to site where they are assembled and connected, and the individual girders are lifted into position safely on bearings using jacks, cranes or any other suitable device. The cross members for the top and bottom chords can then be connected. The superstructural deck slabs are cast in symmetrical sections using bonding agents and stage compressive stresses.

HTS prestressed cables are deployed in parabolic bottom currents. Compressive stressing of the strands is carried out in stages according to the design. The results of various construction stages for member stresses and maximum displacements are shown in Figures 4 to 10 for the 125 m x 9 m bridge case.

A typical example of step compressive stress for two No. 27T15 cables in each bottom chord is given below.

Step 1: Launch the girders including cross members, cross girders, and stringer beams and apply a compressive stress of 2000 kN appropriately (Figure 5). At this stage, the displacement at the mid-span of the girder is 17.8 mm (downward).

Step 2: Apply an additional 2000 kN compressive stress (Figure 6). At this stage, the displacement at the mid-span of the girder is 151.7 mm (upwards).

Step 3: Cast the deck slab at 1/5 span from both ends. These steps include a construction load of 5 kN/m ² . At this stage, the displacement of the girder mid-span is 3.5 mm (upwards).

Step 4: 10 days after pouring the concrete in Step 3, an additional 1000 kN compressive stress is applied and the next 1/5th span (11) is cast. At this stage, the displacement of the middle span of the girder is 121.7mm (downward).

Step 5: 10 days after pouring the concrete in Step 4, an additional 1000 kN compressive stress is applied and the central 1/5th span (11) is cast. At this stage, the displacement of the mid-span of the girder is 7.6 mm (downward).

Step 6: 28 days after application of SIDL on deck 11, compressively stress by additional 3100 kN force. At this stage, the displacement at the mid-span of the girder is 75.5 mm (upwards).

Alternatively, a two-stage compressive stress, the first before deck casting and the second after its curing, may be better.

Live loads are now applied to the bridge. At this stage, the displacement of the middle span of the girder is 80.5mm (downward). Additional compressive stresses may be applied after an appropriate period of time to compensate for losses due to tines, etc., reflected in terms of sagging displacement.

Another typical 50 m span and 2.5 m deep composite prestressed two-lane open web steel girder bridge is designed (Figure 11). The top chord consists of a 300mm

The FEM model and axial stress diagram in service conditions are provided in Figures 12 and 13, respectively.

Compressive stress calculation using load balance:

After application of compressive stress, the girder is horizontal and the cables are assumed to carry the total permanent load and half of the live load due to impact. Fine adjustments of compressive stress for losses, etc. can be made as required for the final deck profile.

Taking the parabolic bottom current center as the origin, the equation for this is as follows;

y = ax ² , or a= 2.5/(25x25) = 0.004

(dy/dx) _end = 2ax = 0.008 x 25 = 0.2 rad

Balance load = SW- 750 + deck - 2660 + WC - 610 + CB - 750 + (LL with impact)/2 - 604 = 5374 kN

Required condensation pressure per girder = 5374/(2x2x0.2) = 6797 kN

2 Supplied with cable number 19T15 (3870 kN).

Pre-compression in deck slabs:

Taking the stressed 19T15 cable after deck slab curing, compression condensation is applied along two bottom chords.

= 2x3870 = 7740 kN

The vertical component moves to the support and the horizontal force = 7740 cos11.4 = 7587 kN

Area (Cm ² ) ; Top Chord = 192, Equal Deck = 1770, Bottom Chord = 330

Force per bottom current shard = (330/2292) x 7740x.98 = 1093 kN

Force experienced by RCC deck = (7740-1093)x 1770/1962 = 5996 kN

Therefore, axial stress in the deck = 5996000/ 2125000 = 2.8 N/mm ²

By adding 1.4 N/mm ² to the tensile strength of concrete and maintaining appropriate cross girder spacing, it is possible to design a deck slab on a crack-free basis, which is highly desirable for composite decks.

Typical examples of 125 m span, 9 m deep and 50 m span, 2.5 m deep two-lane highway superstructure girders are optimized to produce steel offtake of 331.0 t and 88.5 t, respectively. The maximum displacement due to live load at intermediate spans is 151.3 mm and 57.6 mm for 125 m and 50 m spans, respectively, which are within the allowable displacement of Span/800.

In the case of a 125m span bridge, safety is ensured by checking the stress of the axial member during deck installation and concrete pouring by applying compressive stress step by step according to the design. The limiting live load for elastic conditions was 3.2 times the SLS live load at a 125 m span and 2.8 times at a 50 m span, confirming their robustness. For a 125 m span, for parallel 10 m and 12.5 m deep girders, the steel offtake is 310 t and 299 t, and the corresponding live load displacements are 135.5 mm and 140.1 mm, respectively.

Concrete Grouting: Expanded concrete grouting of box sections is preferred as the dead weight of the superstructure is fully supported by compressive stress alone with favorable pre-compression of the RCC deck. Concrete filled steel tubes (CFST) are now composites, providing additional strength and rigidity to the bridge superstructure.

Claims (12)

A method for constructing a prestressed open web steel girder composite bridge superstructure, comprising:
connecting the composite top chord (1) to a prestressed parabolic (polygonal) bottom chord (2) using a plurality of open web members (3);
aligning cables (4) and anchorages (5) within and along the prestressed parabolic bottom chord;
Supporting the cross girder (7), stringer beam, and composite deck slab using a plurality of shear connectors (6);
connecting at least two main girders with end cross girders (7), wherein the girders at the ends are supported on bearings (8);
For underslung bridges, a prestressed parabolic (polygonal) bottom chord (2) is obtained and connected to the top chord (1) for nearly uniform tension under a uniformly distributed load, which helps in compressive stressing. Obtaining an underslung bridge, wherein the composite prestressed underslung bridge is up to a predefined span of 10 m to 200 m;
Fabricating a plurality of superstructure panels in a workshop, assembling and connecting them on site, launching them in a girder manner, and then using designed stepped compressive stresses to make in-situ composite RCC deck slab concrete in symmetrical sections - of the superstructure. Deck slabs are cast in symmetrical sections using adhesive -; and
A method comprising staged compressive stressing of the bottom chords, from the girder lifting stage to the bridge commissioning stage, to facilitate management of member stresses and bridge displacements within threshold limits during bridge construction and service life. 2. The method of claim 1, wherein the stiffness of the composite deck slab connected to the upper chord and the strength of the high tensile cable provided in the composite prestressed underslung bridge, having its low displacement, high strength and stiffness, are about three times the elastic limit. How to indicate reserve strength. 3. The method of claim 2 including prestressing a high tensile strength cable lying within the parabolic bottom chord. 2. Method according to claim 1, wherein the compressive stress in the bottom chord (2) corresponds to the tension due to the applied load, and the compressive stress in the bottom chord balances the upward thrust. 2. A method according to claim 1, wherein the compressive stress in the floor chord (2) causes longitudinal pre-compression of the deck slab, which allows crack-free design and is highly desirable for better fatigue performance. 2. A method according to claim 1, wherein the effect of curvature and girder bending stress due to live load in the deck slab is reduced by half by applying compressive stress to counteract half of the live load due to impact. 2. Method according to claim 1, wherein if the profile of the bottom chord (2) of the bridge is made parabolic, its uniform tension develops under a uniformly distributed load due to dead weight or live load, thereby facilitating the bottom chord compressive stress. 2. Method according to claim 1, wherein the predefined span is between 10 m and 200 m of composite prestressed underslung bridge for projects such as single or multi-lane road, railway, metro rail and flyover and marine connections. The method of claim 1, wherein the axial member stress is low and safely confirmed by applying compressive stress at different stages as necessary when installing the composite RCC deck slab and pouring concrete. The method of claim 1, wherein the RCC deck slab is made of a composite material as the upper chord of a bridge by using the plurality of shear connectors to prevent premature buckling failure and increase its strength and rigidity. 2. The method of claim 1, wherein expanded concrete grouting converting box sections to CFST composites increases the strength and rigidity of the superstructure in addition to preventing corrosion. a top chord (1) connected to a prestressed parabolic (polygonal) 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) received and aligned along the prestressed parabolic bottom chord (2);
A plurality of shear connections (6) adapted to support the cross girders and stringer beams;
a plurality of bearings (8) configured to connect the end cross girders with at least two main girders; and
Composite RCC deck slabs (7) cast on top chords (1), cross cudders and stringer beams and longitudinally pre-compressed due to compressive stresses enabling crack-free design for better fatigue performance - the superstructure The deck slabs of a prestressed open web steel girder composite bridge comprising - are cast into symmetrical sections using adhesives.