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Inside the $170M Tian’e Longtan Bridge: How China Built the World’s Longest-Span Concrete Arch — Transcript

by Engineering Revealed · 1,256 words · 278 segments · language en · Watch on YouTube

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0:00Above Longtan Reservoir, every movement
0:02begins with exposure, precision, and
0:05disciplined control.
0:17The first challenge was aligning a 600 m
0:20crossing between two steep mountain
0:22walls. At this height, tiny connection
0:25errors could multiply across the
0:27unfinished arch.
0:30Before closure, both advancing halves
0:32had to meet at one exact crown position.
0:35To understand the bridge, return to the
0:37untouched reservoir corridor before
0:40construction began.
0:51Engineers first mapped fractures and
0:53weathered rock where the arch would
0:55enter the mountains.
0:56>> [music]
1:04>> Core samples revealed whether each
1:06springing zone could carry immense
1:07compressive forces.
1:14Survey teams on opposite shores fixed
1:17one shared access across the water.
1:25The selected solution used twin deck
1:27type steel reinforced concrete arch
1:29ribs. Inside each stiff skeleton, four
1:32steel cord tubes formed the temporary
1:35load-carrying frame. A cable crane moved
1:38segments while buckle stays restrained
1:40each growing cantilever.
1:45Wind testing defined safe lifting
1:47windows for large exposed steel
1:50segments.
2:02>> Construction could not start until
2:04machines carved controlled access into
2:07the mountain. The hall road became the
2:09supply artery linking workshops,
2:11foundations, and both work fronts.
2:28Purpose-built jigs kept every fabricated
2:31segment within the geometry [music]
2:32required for closure.
2:34Parallel work fronts allowed both shores
2:36to advance toward the reservoir
2:38together.
2:46Controlled blasting prepared strong rock
2:49without turning excavation into an
2:51uncontrolled event.
2:58Deep anchors tied the springing
3:00foundations directly into competent
3:02bedrock. Reinforcement and embedded
3:04steel would transfer arch compression
3:06safely into each foundation block.
3:19Cooling and curing controlled heat
3:20inside the newly placed mass concrete.
3:23The opposite springing repeated the
3:25sequence while preserving its own
3:27mountain geometry.
3:34>> [music]
3:36>> With both springings formed, the
3:38permanent arch still had not risen above
3:41them.
3:42Approach foundations were built
3:43separately to carry the roadway toward
3:45the main arch.
3:54Different pier heights showed genuine
3:56progress, not an instant jump to
3:58completion.
3:59Temporary tower foundations carried the
4:01cable crane system that would span the
4:03reservoir.
4:20Main carrying cables created an aerial
4:23transport path between the two mountain
4:25work fronts.
4:31A no-load test check travel, alignment,
4:34braking, and control before lifting
4:36steel.
4:43Only after towers, anchors, hoists, and
4:47buckle stays were ready could erection
4:49begin.
4:52>> [music]
4:57>> Node plates and diagonal braces turned
5:00individual tubes into a rigid arch truss
5:03segment.
5:09Trial assembly exposed fit-up errors
5:11while [music] corrections were still
5:12possible on the ground.
5:14Protective coating shielded inaccessible
5:17steel surfaces before they entered the
5:19permanent structure.
5:28The mast crane rotated each segment into
5:31the orientation required for transport.
5:36>> [music]
5:43>> Barges carried finished segments through
5:45the reservoir to the cable crane pickup
5:47zone.
5:54Multi-point rigging controlled the
5:56segment without placing workers beneath
5:58the suspended load. The first lift
6:01transformed months of preparation into
6:04the beginning of the arch.
6:13Hydraulic tools seated the first segment
6:16precisely into its embedded springing
6:18connection.
6:37Load transferred gradually from the
6:39crane into the springing [music] and
6:40temporary stays. The second arrival
6:43began a repeatable cycle of transport,
6:45lift, connection, and restraint.
6:49Each added segment required another stay
6:51level to control the longer cantilever.
6:55Three connected segments formed a short
6:57cantilever, still far from the reservoir
7:00center. Balanced erection began when the
7:03opposite shore received its first
7:04segment.
7:16Alternating cycles limited imbalance
7:18while both cantilevers advanced toward
7:20mid-span.
7:22>> [music]
7:27>> After every connection, surveyors
7:29checked vertical and lateral movement at
7:31the cantilever tip.
7:34>> [music]
7:36>> Dawn measurements corrected for thermal
7:37movement before the next critical lift.
7:43A controlled aerial rotation matched the
7:45segment to the changing arch curvature.
7:48Temporary guides brought four cord ends
7:50into alignment high above the water. New
7:53buckle stays accepted the segment load
7:55before the crane was released.
7:58>> [music]
7:59>> The twin skeletons remained separate,
8:01parallel ribs joined by transverse
8:03stability members.
8:14>> [music]
8:16>> Near quarter span, the growing
8:18cantilevers still depended on cables and
8:21temporary stays.
8:32When wind exceeded the operating window,
8:34lifting stopped and the load returned to
8:36safety.
8:40At mid-erection, the intended arch curve
8:42finally became visible across the
8:44reservoir.
8:50Near the crown, every joint demanded
8:53tighter alignment and controlled bolt
8:55sequencing.
8:57The two arch tips approached one
8:58another, but the final gap remained
9:01deliberately open. Engineers [music]
9:03tuned stay forces until both tips
9:05reached the required elevation and
9:07position.
9:13The closure segment entered the center
9:14gap with only a narrow controlled
9:16clearance.
9:18Hydraulic adjustment reduced the
9:19remaining error to the millimeter scale.
9:23Locking the final connection converted
9:25two cantilevers into one continuous arch
9:28skeleton.
9:30Stay forces were then redistributed
9:32gradually into the newly continuous
9:35structural system.
9:43Ports, vents, and pipelines prepared the
9:45hollow steel cords for concrete filling.
9:55Pressure and vent response tracked the
9:56rising concrete [music] inside each
9:58concealed cord tube.
10:03Concrete reaching the crown vent
10:05confirmed a complete fill path before
10:06sealing. Filling progressed between the
10:09twin ribs in a sequence designed to
10:11maintain balance.
10:13External reinforcement prepared the
10:15steel skeleton to become a composite
10:17concrete arch.
10:24The encasement advanced through three
10:26rings, six segments, and coordinated
10:28work fronts. Before each upper pour,
10:31inspectors verified cover,
10:33reinforcement, and embedded components.
10:36Symmetrical pours controlled stress
10:38while the concrete shell developed
10:40around the skeleton.
10:44Curing protected strength development
10:46and limited temperature gradients
10:48through the new concrete.
10:54Repeated formwork cycles extended the
10:56concrete encasement without skipping
10:58intermediate stages. The twin concrete
11:01arch ribs were complete, but the roadway
11:03still did not exist.
11:09Crosslinks appeared progressively,
11:11stabilizing the two ribs at the future
11:14column lines. Pre-stressing compressed
11:17each cured crosslink and strengthened
11:19transverse continuity.
11:29Column heights varied because the curved
11:31arch rose and fell beneath a level
11:33roadway.
11:35The uneven construction heights
11:37reflected the real geometry of the
11:39completed bridge.
11:41All 20 column lines now define the
11:43support [music] pattern above the arch.
11:45Near the springings, rigid frame
11:47structures avoided impractically tall
11:50conventional columns.
12:00Pre-stressed T-beams were cast in
12:02batches before delivery to the erection
12:04front.
12:05Tension strands gave each beam the
12:07capacity to span between its supports.
12:13Bearing checks confirmed that every beam
12:15seated correctly before rigging was
12:18released.
12:23Cross diaphragms tied adjacent T-beams
12:26together and improved lateral
12:28continuity. Reinforcement and drainage
12:31details were installed before the
12:33structural deck slab was poured.
12:40Closing the final slab bay created one
12:42continuous traffic deck across the
12:44structure. Expansion joints preserved
12:47controlled movement where the roadway
12:49crossed structural interfaces.
12:51Waterproofing protected the deck while
12:54leaving every drainage opening
12:55functional.
13:01The final wearing course produced an
13:03even roadway without burying movement
13:05joints.
13:09Drains and down pipes moved water away
13:12without uncontrolled discharge from the
13:14deck.
13:18Protected conduits carried power to
13:21lighting and operational systems without
13:24obstructing traffic.
13:30Reflectors and restrained safety
13:32hardware completed the roadway's visual
13:34guidance system. The bridge only became
13:37usable after both approaches were tied
13:39into the completed deck.
13:45Temporary sensors measured how the deck,
13:48columns, and arch responded under
13:51controlled loading.
13:57>> [music]
13:59>> During the static hold, engineers
14:01compared measured response with expected
14:04structural behavior.
14:09Controlled braking tested the roadway
14:11response without creating a dangerous
14:13skid.
14:15Post-test surveys checked the arch ribs
14:17and all 20 varied height column lines.
14:27Commissioning reviewed barriers,
14:29drainage, lighting, joints, and roadway
14:32as one complete system. Operations crews
14:35rehearsed maintenance access without
14:37inventing an accident or emergency.
14:44Technical handover transferred the
14:46completed structure from construction to
14:49future operations.
14:52The first controlled release introduced
14:54ordinary vehicles gradually, lane by
14:56lane.
14:58Light two-way traffic marked [music] the
15:00transition from controlled opening to
15:02stable daily operation. For the first
15:05time, the completed bridge visibly
15:07connected both mountainous shores.
15:10Passenger and freight movement revealed
15:11the practical value of the new regional
15:14connection.
15:16The final view reveals the full arch, a
15:19mountain barrier transformed into
15:21connection.

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