New Overhead Self-launching Launching Gantry Systems

TECHNICAL FIELD

Construction Engineering

BACKGROUND ART

Bridge construction can be made by different kind of equipment such as Movable Scaffolding System (MSS) for cast in-situ concrete bridges and Launching Gantries (LG) for precast segments^ as well as Formtravellers for free cantilever and cable-stayed bridges.

Segmental, launching gantries was developed, and brought to market by NRS Consulting Co. Ltd. in the early 1990's and has since grown rapidly in reputation as one of the most recognized suppliers of launching gantries for "span by span" and "balanced cantilever" methods of construction. NRS has continued to introduce several new innovations in the equipment which h ve' been used with remarkable success in many challenging bridge projects worldwide.

The new concepts introduced in NRS launching gantries include:

Special "hinge" solution for curved bridges

- Glue-as-you-go" for reducing double handling of segments

"Turnaround" of last segment within, span for overhead type gantries to reduce stacking

Unique gantry crane structure to enable smooth' movement around hinge

Fail-proof hydraulic launching system.

Type of LG

The LG can be divided into two types, namely, (i) underlane (or underslung) and (ii) overlane (or overhead). The underlane type of LG has two parallel girders which supports the bridge segments. The overlane or overhead type of LG has one or two main girders from which the bridge segments are suspended under the girder(s).

"Hinged LG" - A solution for curved bridges ,

In the past when the segments had to be installed along the horizontal curve bridge, the conventional straight gantries had a lot of difficulties for the operations. Either it needed the extra steps and external supports for launching and lifting operations or the external cranes for lifting and moving the straight LG. These extra operations affect very much on the extra time and the whole construction budget. To overcome the difficulties of erecting spans for curve with the conventional straight LG, NRS has developed in the early 90s' the innovative "hinged" concept which allows the articulation of the LG to handle segment erection and launching operation. The hinge concept enables span erection on horizontal radius as small as 75m (40m span) previously never thought possible without the need of additional external temporary supports. As many as 6 hinges, each regulated by hydraulic cylinders, have been used on a single LG. A specially designed gantry crane is also used to travel smoothly through the kinked hinges along the LG during lifting and placing of segments.

The hinge concept remains today a unique feature well known in the industry for erection of precast segmental bridges oh tight curves. This solution has been proven successful in many major projects particularly in Metro or Light Rail Transit projects where tight curves are qiiite common along the alignment. The hinged LG offers significant advantages over the conventional straight gantries in terms of erection speed and cost of construction.

BRIEF DESCRIPTION OF DRAWING

Figure 1 shows LG Type 1 General Arrangement: Elevation (Fig. 1 -A) and Plan (Fig. 1 -

B)

Figure 2 shows LG Type 1 Sections: at Rear Support (Fig. 2- A) and Front Support (Fig.

2- B)

Figure 3 shows LG Type 1 Sections: at Suspension Beam (Fig. 3-A), Front Leg and

Front Nose (Fig. 3-B) and Middle Launching Support (Fig.

3- C)

Figure 4 shows LG Type" 2 General Arrangement: Elevation (Fig. 4-A) and Plan (Fig. 4- B)

Figure 5 shows LG Type 2 Sections: at Rear Support (Fig. 5- A) and Front Support (Fig.

5- B)

Figure 6 shows LG Type 2 Hanger's positions during segment installation (Fig. 6-A), typical launching (Fig. 6-B), launching pass portal area (Fig.

6- C): ^;

Figure 7 shows LG Type 2 Sections: at Front Leg and Front Nose (Fig. 7-A) and Middle

Launching Support (Fig. 7-B) DISCLOSURE OF THE INVENTION

The new overhead self-launching launching gantry systems according to this invention comprises of

Main Girder (100) is made up of several plates to become box section and being the principle bearing components which transfer the segment loads to the supports. The segment loads are transferred from the stressing bars (140) to the Suspension Beams (130) which run on top of the main girder (100) for LG Type 1 or transferred from bottom slabs of the Hangers (200) which are bolted to top of main girder (100) for — LG Type 2.-At-the end- of main girder, there is a hinge (120) connected between main girder (100) and' the front hose (1 10) to 'facilitate the operation of LG while going' to the curve bridge.

Front Nose (1 10) is connected to front end 'of the main girder ( 100) arid is designed' to transfer loads to the support during launching. The shape of me ^' front nose (HO) is the upright triangle for LG Type 1 and the rectangular shape for LG Type 2 ^' .

Suspension beam (130) is specially ^equipped ^' on top of main girde (100) for 'LG Type 1. The 'Crane (700) picks up ^' segment and ^' moves along' bottom rail of main girder (100) to bring the segment into correct position. Pfestressing' bars (140) ^: a're connected ^' to 'segrhent at the bottom and suspension ^' beam (130) at the top ^' ; then, segment can ^{1 '} be released from the crane (700). The suspension beam ( 130) is transferring' segment loads into the main girder (100) after the ^' segments have been released ^' from the ^' crane (700). Segment can be adjusted transversely by hydraulic cylinder connected between suspension beam (130) and main "girder (100); and vertically' adjuster! by adjusting the length of prestressing bars ( 140)'.

Hanger with bottom 'beam ¹ (200) for LG Type 2. The hanger 'is transferring segment loads' from the bottom beam ^' into the main girder (100) ^' ' during segriierits' installation. There is the second folding function by two opening joints (210) on the upper part of the said hahger (200) which ^' creates the wider opening and the' higher ^' position as show' in Figure ^' 6-C. This will allow the LG to pass the portar pier area' or other Obstructions. When all bottom beams are connected at the middle', they will support the Trolley (800) Tor carrying the segments and the screw jacks for supporting the segments. There are no any stressing bars or any bstructi0ris ⁺ 'i ^' n between hangers (200); therefore," after the segments have been delivered by ^' th'e 'trolley (800)',' ^' the workers ^' can easily work oh'the segments installation process - Rear Support (400) which provides support to the LG, during launching and segments installation. The said rear support _. (400) is opened in the center for bridge segment to pass through as shown in Figures 2- A and 5-A. There are two rear support side , shifting cylinders (500) equipped at top of the rear support (400) on top of main girder, (100). They are used for transverse adjusting of main girder (100) while launching pass through curve spans. Rear support's position is adjustable; therefore, it is most suitable for segments installation of bridge with various span lengths.

Front Support (410) which provides support to the LG during segments installation. Uhlike' tfie bthe'r previous systems ' that? require the bldck- uts ih ^' bridge- stri!icture; ^: there ^; fs¾b½n ^: part ^; '0f ^' the fro¼ ¾u pbrt'(4l S) pa¾s ^, th Ugh 'the bridge' ^

support' main front suppbrt 16) ^' pro vide' ^' έ tra ^! hsfer' ^l of'Toad ^: 'm^ column 'fbbtifig There^'are ^* ' froht ^' ¾ip drt ^t: 'si8e ^" ' ^L s¾iffiiig

height and much stronger than previous system making the system more stable during launching.

Crane (700) provides segment delivery into the correct position. The crane (700) can lift up the segments either from the rear or front of the being installed bridge span. After picking up the segment, the crane (700) can move along bottom rail of main girder (100) to bring the segment into the correct position. Segments are hung by the prestressing bars (140) to the suspension beam (130) for LG Type 1 or sit on the trolley (800) for LG Type 2.

Trolley (800) ^' is specially designed and equipped on bottom slab of the hanger (200) for LG Type 2. The trolley (800) will move back and forth to bring the segments into the correct ^' position. After segment is in the correct position, ^' it will be released from the trolley (800) and supported by the adjustable jack supports. ·' ^{' ' '}

In order to operate the said SL-LG, the assembling and erecting sequence of the said SL-LG can be described as the following;

1. Install the temporary tower at the front pier of the span being erected.

2. Install and secure the middle launching support (430) over the temporary concrete foundation behind the bridge abutment. .

3. Assembly the main girder (100) on ground. ,

4. Install the said main girder (100) on to the temporary tower and the said middle launching support (430).

5. ^{' '} install the front support (410) and rear support (400) to the said main girder ( 100).

Activate both supports to take load.

6. Remove the temporary tower and the said middle launching support (430).

7. install the Suspension beams (130) on top of ^' the said main girder (100). ^' This operation is ^' for LG Type 1 only.

8. Install the' hanger with bottom beams (200) to the said main girder (100). This operation is for LG Type 2 only. ' '

9. Assembly the front nose (1 10) on ground. Install the said front nose (1 10) to the said main girder (100).

10. Install the crane (700) and lifting systems to the said main girder (100).

1 1. Install other ' miscellaneous parts i.e. hydraulic equipments, pumps, working platform to complete. The launching sequence of the said SL-LG comprises of the segment installation and launching stages as the following;

Stage 1

1.1 LG is set at the segment installing position.

1.2 Front support (410) and rear support (400) are activated.

1.3 Middle launching support (430) is suspended to the front nose ( 1 10).

1.4 Front leg (420) is ready set on top of the next pier.

1.5 Install the bridge segments and prestressing the span.

Stage 2

2.1 Move back and install the middle launching support (430) on the already finished bridge deck.

2.2 Release the main jacks at front support (410) and rear support (400) respectively.

Rear support (400) is now on the steel wheels.

2.3 LG is supported by middle launching support (430) and rear support (400).

2.4 Release the prestressing bars (140) from the suspension beams (130) for LG Type 1 or open the hanger with bottom beams (200) for LG Type 2,

2·.-5 · ^■ Prepare for launching forward to the next span.

Stage 3

3.1 Launch forward the LG to the new span until the front support (410) is in same line with the front leg (420). During launching the LG is supported by front leg (420), middle launching support (430) and rear support (400).

3.2 Activate the main jacks at front and rear supports (410 and 400) to take load of the LG. Middle launching support (430) and front leg (420) are now free.

Stage 4 .

4.1 Release the front leg (420) to set on the next pier.

4.2 Release the middle launching support (430) to suspend to the front nose (1 10).

4.3 Close up the hanger with bottom beams (200) for LG Type 2 or prepare prestressing bars for LG Type 1. Prepare the LG for segments installation.

4.4 Repeat the stage 1-4 to complete the cycle for the next span.

The dismantling process of the said SL-LG can be described as the following; Process of this operation is depended on the actual condition at site and varied from job to job. A careful planning and drawings should be done before actual dismantling begins.

The general steps to dismantle the LG after the last span has been completed are as follows:

1. Install temporary tower at rear of main girder ( 100) to take load of LG.

2. LG is supported by temporary tower at the rear and the middle launching support (430) at the front.

3. Dismantle the front nose (1 0) and front leg (420).

4. Fold down the bottom beanis of the hangers (200) for'LG Type 2 & start dismantling the bottom beams and the hangers.

5. Dismantle the suspension beams (130) for LG Type Γ.

6. Dismantle the front support (410).

7. Dismantle the rear support '(400).

8. Bring down the main girder (100) and dismantle each module.

9. Dismantle the middle launching support (430) and the temporary tower.

The advantages of the new launching gantry are as following:

Fast and efficient span erection - fastest erection cycle 3 days/span (40m span) Lightweight

Easy to assemble

Reduced manpower

Very efficient for spans on tight horizontal curves as small as 75 m (cannot be achieved using conventional gantries)

Self launching option (no crane required for supports relocation).