A 3.5 m full-metal acoustic screen on 150×150 H-steel posts for a Guangzhou bridge retrofit — the choice logic versus transparent panels, lightweighting for an existing structure, and corrosion protection to EN ISO 1461 / ASTM A123 (70–85 µm).
For a historic bridge retrofit, full metal won on durability and maintenance, not just cost. The 1,800 m screen used full-metal absorptive panels on 150×150 H-steel posts, was lightweighted for the existing deck, and was protected by hot-dip galvanizing to EN ISO 1461 / ASTM A123 (70–85 µm). Transparent modules were reserved for specific sightline windows only.
The retrofit targeted a historic bridge crossing in an urban setting, where a noise screen was needed to protect the adjacent community but the structure itself — and its heritage status — constrained what could be added. The brief favored a robust, low-maintenance solution that would age gracefully and add a controlled, predictable dead load the existing deck could accept. Zhaobang Metal supplied the full-metal barrier material package: full-metal absorptive panels and 150×150 H-section steel posts with fixing accessories, plus shop drawings and acoustic data. On-site construction was performed by the contractor and EPC, not by Zhaobang.
| Parameter | Supplied specification |
|---|---|
| Location | Historic bridge retrofit, Guangzhou (Panyu, Shiqiao) |
| Total barrier length | 1,800 m |
| Barrier height | 3.5 m |
| Post system | 150×150 H-section steel columns |
| Panel system | Full-metal absorptive panel |
| Acoustic target | Panels specified to JT/T 646-2025: Rw ≥ 26 dB (non-transparent), NRC ≥ 0.60 (absorptive), generally aligned with the bridge's insert-loss expectation |
| Corrosion protection | Hot-dip galvanized posts & frames to EN ISO 1461 / ASTM A123, coating 70–85 µm typical, generally with powder-coat (RAL) over galvanizing |
| Project role | Material supply (panels, posts, accessories), shop drawings, acoustic data; erection by local contractor |
Durability and maintenance. A full-metal absorptive panel resists impact, vandalism and weathering better than a transparent module, and avoids the UV-yellowing and regular cleaning regime that acrylic or polycarbonate demands. On a heritage bridge with limited access for maintenance, that robustness was decisive.
Acoustic performance. A full-metal absorptive panel still delivers the NRC the project needs — our standard absorptive panels reach NRC 0.80–0.95, above the NRC ≥ 0.60 baseline in JT/T 646-2025 — so going full-metal did not compromise the acoustic target.
Where transparent would earn its place. Transparent panels are the right call where residents must keep daylight and views, or where a heritage streetscape demands openness. For this bridge, transparent modules were reserved only for the specific sightline windows the design called out. See transparent vs absorptive barriers for the full comparison.
Thin-sheet panel construction. The full-metal absorptive panel uses thin galvanized or aluminium sheet (0.8–1.5 mm typical) over a lightweight mineral-wool or fibre core. That gives real sound reduction without the mass of a solid section, so the screen adds a predictable, bounded dead load.
Right-sized posts. The 150×150 H-post section was chosen to carry the bridge wind load at the required spacing without over-building the foundation. Post spacing was finalized with the structural engineer from the site wind zone, generally in the 2.0–2.5 m band for an exposed bridge deck.
Move with the structure. The barrier was segmented at the bridge expansion joints so it expands and contracts with the deck under temperature and traffic movement, avoiding the racking you get from a rigid wall built across a moving joint.
Hot-dip galvanizing. The posts and frames were hot-dip galvanized, generally to EN ISO 1461 or ASTM A123, with a coating thickness in the 70–85 µm range. Galvanizing forms a metallurgically bonded zinc layer that protects even at small scratches — exactly what you want in a damp, salt-laden bridge atmosphere where paint nicks would otherwise start rust.
Powder coat over galvanizing. Where the specification called for a colour or extra service life, a powder-coat (RAL) finish was applied over the galvanizing. This duplex system combines the barrier protection of zinc with the appearance and additional life of the coating.
Fasteners. In aggressive environments the fixing hardware is generally upgraded to 304/316 stainless so the whole assembly ages at a similar rate. The full material and finish envelope is on the noise barrier specifications page; supply options are on the noise barrier product page.
The supplied package delivered a continuous 1,800 m full-metal acoustic screen along the bridge. Panels were accepted against the project's acoustic and structural requirements: non-transparent and absorptive panels specified to meet or exceed JT/T 646-2025 (Rw ≥ 26 dB for non-transparent panels, NRC ≥ 0.60 for absorptive panels), with the 150×150 H-post system verified for the bridge wind load under GB/T 51335-2018.
The hot-dip galvanized (EN ISO 1461 / ASTM A123, 70–85 µm typical) structure gives the screen a long, low-maintenance service life suited to a heritage bridge with limited access. Acceptance generally followed visual and dimensional inspection plus acoustic spot checks against the HJ/T 90-2004 design insert-loss target. Comparable delivered work is listed on the projects page.
Choose full-metal when the priority is durability, lowest maintenance and a robust absorptive face rather than sightlines. On a bridge retrofit, a full-metal absorptive panel resists impact, vandalism and weathering better than a transparent module and avoids the UV and cleaning regime that acrylic or polycarbonate needs. Transparent panels earn their place where residents must keep daylight and views, or where a heritage streetscape demands openness. For this historic bridge the acoustic and maintenance case favored full metal, with transparent modules reserved only for the specific sightline windows the design called out.
The structural steel is hot-dip galvanized, typically to EN ISO 1461 or ASTM A123, with a coating thickness in the 70–85 µm range for the posts and frames. Galvanizing gives a metallurgically bonded zinc layer that protects even at small scratches, which is ideal for a damp, salt-laden bridge atmosphere. Where the specification calls for extra life or a colour, a powder-coat (RAL) finish is applied over the galvanizing. Fasteners are generally upgraded to 304/316 stainless in aggressive environments so the whole assembly ages at a similar rate.
Lightweighting starts with the panel: a full-metal absorptive panel uses thin galvanized or aluminium sheet (0.8–1.5 mm typical) over a lightweight mineral-wool or fibre core, so it delivers sound reduction without a heavy solid section. The 150×150 H-post size was chosen to carry the wind load at the required spacing without over-building the foundation, and the barrier was segmented at the bridge expansion joints so it moves with the deck. The result is a continuous screen that adds controlled, predictable dead load the existing structure can accept.