This page is not a record of named projects. It is three engineering scenarios: three environments we are asked about constantly, and the pultruded GRP sections we would specify if the enquiry landed on the desk today. Pultruded GRP profiles — written as FRP in a great many specifications — earn their place in exactly these conditions, so it is worth walking through the reasoning rather than the result.
How to read the three scenarios: every section code and dimension below comes from our standard range, and every sentence is written in the conditional, because that is what these are. Nothing here describes work already carried out. Your own span, load, guarding specification and fire clause will move the choices, and that conversation is where a real section gets settled.
Screening channels, aeration lanes, sludge thickeners. The air above them carries moisture almost permanently, and where anaerobic conditions develop it carries hydrogen sulphide with it. Washdown is routine. Cleaning chemicals reach the steelwork whether they were aimed at it or not. Nothing about this environment is dramatic; it is simply relentless, and it never dries out for long enough for a protective system to recover.
Galvanised steel does not fail here quickly. It fails slowly and in the places nobody inspects: the underside of a bearer, the cut face of a beam that was trimmed on site, the shim stack behind a bracket. A hot-dip coating is a sacrificial system, and once the coating has been consumed the base metal is exposed to the same humid, sulphide-bearing air that consumed it. Stainless steel handles the chemistry better and costs considerably more, and in a plant where dissimilar metals meet at every bracket it brings a galvanic pairing of its own. The honest summary is that metal here is not a material problem but a maintenance programme: recoating, isolation washers, and access for both.
A walkway over a channel is a deflection problem before it is a strength problem. GRP has high tensile strength along the length of the profile and a low to medium modulus of elasticity, so in almost every case the serviceability limit is reached before the strength limit. That single fact drives the whole table below: we go deeper rather than thicker.
| Role | Code | Size (mm) | Wall (mm) | Why this one |
|---|---|---|---|---|
| Main beam | I-05 | 150 × 75 | 8 | Carries the grating panels across the channel |
| Main beam, deeper option | I-07 | 200 × 100 | 10 | Where the clear span is longer |
| Cross bearer | C-100 | 50 × 100 (w × h) | 6 | Intermediate support under the grating |
| Edge angle | L-05 | 50 × 50 | 6 | Grating edge trim and kerb fixing |
| Guarding post | K-07 | 75 × 75 | 6 | Post at the platform edge |
Sizes are quoted height × width except for the C-series row, which follows the channel convention of width × height and is marked as such.
The choice between I-05 and I-07 is settled by deflection, not by strength. Both will be well inside their strength limit at the loads a maintenance walkway sees; what separates them is how much the beam moves underfoot at mid-span, and deflection responds to load and to span together. Send both numbers and the answer falls out quickly — the method is set out on mechanical properties and load capacity, and the sections themselves on GRP I-beam and GRP channel.
A polyester system with a surface veil is the normal specification here. The veil is what stands between the structural laminate and the environment: it holds a resin-rich layer at the surface so that the glass fibres are not the first thing the atmosphere meets. Where the plant’s fire clause is the governing document, a flame-retardant resin is the conversation to have — and to have before ordering, because it changes the make-up of the profile. What that clause requires and whether a given system satisfies it is a question for your specification, not something we assert on your behalf. The background is on resin systems and surface veil, UV and fire.
The distinctive change in this scenario is what happens to the maintenance programme. There is no recoating cycle to schedule over a live channel, which is the part of the plant that is hardest and most expensive to get access to. Cut ends made on site are sealed rather than re-galvanised, and the isolation detailing that a mixed-metal assembly demands is not part of the drawing at all. Fixing practice is different from steel and worth reading before the first delivery arrives: installation and fastening, and maintenance and service life.
Open ground, full sun, wind, and a design life measured in decades rather than years. The structure is repeated thousands of times, so every decision is multiplied. Two conditions dominate: ultraviolet exposure that never lets up, and a site that is frequently remote, which makes anything requiring a return visit disproportionately expensive.
Metal is not weak here; it is simply committed. A galvanised table in a coastal or agricultural atmosphere carries a coating with a finite life, and the plant operator inherits an inspection and touch-up obligation across the whole array. Aluminium avoids the rust question and brings its own: it is the lighter of the two metals, but at the fixing points and where it meets steel components it needs the galvanic detail thought through. And on any metal frame, the structure itself is part of the electrical picture and has to be treated as such.
A mounting table is a frame with a clear hierarchy: something spans between the legs, something crosses that, and something small carries the modules. The sections follow that hierarchy directly, which is why the deepest member is not the heaviest one.
| Role | Code | Size (mm) | Wall (mm) | Why this one |
|---|---|---|---|---|
| Rafter | I-04 | 150 × 75 | 6 | The deepest member, spanning between the legs |
| Leg | K-11 | 100 × 100 | 6 | Closed section, equal stiffness about both axes |
| Purlin | C-80 | 50 × 80 (w × h) | 5 | Cross member between rafters |
| Module rail | K-05 | 75 × 40 | 3 | Light rail under the module clamps |
| Brace | L-02 | 40 × 40 | 4 | Diagonal bracing in the plane of the frame |
Sizes are quoted height × width except for the C-series row, which follows the channel convention of width × height and is marked as such.
The rafter is an I-04 at 150 mm deep rather than a square tube, and the reason is where the material sits. An I section concentrates its glass in the flanges, at the greatest distance from the neutral axis, which is exactly where bending stiffness comes from. A closed section of the same depth would put a great deal of material in the webs, where it contributes far less to bending and a great deal to weight. The legs are the opposite case: a K-11 square tube is chosen precisely because it is closed and behaves the same way whichever direction the wind arrives from. Compare the two families on GRP square tube and GRP I-beam, or see the whole standard range on FRP structural shapes.
This is the scenario where the surface veil does the most work, because ultraviolet exposure is continuous and the structure is expected to stand for decades. The pigment is in the resin, through the section, rather than applied as a coating. What UV produces over the years is a gradual change in surface tone, not a loss of section: there is no film to lift, blister or peel, and the load-carrying laminate underneath is unchanged. Specify the veil deliberately rather than accepting whatever comes.
The change that matters most in this scenario is what happens at grade, in a field, thousands of times. The GRP frame itself has no coating to touch up, so the recurring work on the structure is inspection rather than remediation; foundations, piles and fixings keep whatever maintenance their own materials call for. The frame is non-conductive in itself, which removes the bonding a metal frame requires for its own structure; module frame earthing, DC equipment and any lightning protection are unaffected by that and remain entirely with the plant’s electrical design. And the profiles arrive light — GRP is roughly a quarter the density of steel — which changes who can carry a member across soft ground and what plant is needed to place it.
Salt spray, wetting and drying twice a day, sunlight off the water, and a structure the public puts its hands on. A marina handrail is also, unusually for an industrial product, something people look at. Rust staining down a white pontoon is a complaint before it is a structural matter.
Chloride is the difficulty. Galvanised steel in a splash zone is on a short clock, and the first sign is usually a stain on the deck rather than a defect in the rail. Marine-grade stainless performs well and is the honest benchmark to beat here — it is strong, stiff, and looks the part for a long time. What it brings is cost, a sensitivity to crevice conditions where fittings trap salt water, and a galvanic relationship with every other metal on a pontoon. Aluminium is lighter and needs its own protective treatment maintained. None of these are failures; they are commitments, made at the point of specification and paid for over the life of the marina.
A handrail is the one assembly on this page where geometry is not ours to choose. Post centres, rail heights, infill and loading come out of the guarding specification that applies to your site, and the sections have to serve that geometry. What we can settle is which member does what.
| Role | Code | Size (mm) | Wall (mm) | Why this one |
|---|---|---|---|---|
| Post | K-04 | 50 × 50 | 6 | Heavier wall for the moment at the base connection |
| Top rail | K-02 | 40 × 40 | 4 | Small enough across to be held comfortably |
| Mid rail | K-01 | 25 × 25 | 3 | Infill member, not load-critical |
| Base cleat | L-04 | 50 × 50 | 5 | Connection of post to deck structure |
| Toe channel | U-01 | 75 × 32 | 5 | Edge upstand at the deck line |
The top rail is deliberately the smaller of the two square sections. A hand closes comfortably around something in the region of a K-02 at 40 mm across; a broader section may be perfectly adequate structurally and still be the wrong thing to hold. Whether 40 mm satisfies the graspability requirement written into your guarding specification is a check to make against that document, not an assurance we can give from here. Complete assemblies, including grating decking, are covered on GRP handrail and platform systems, and the individual sections on GRP square tube and GRP angle.
Same principle as the solar scenario, applied to a surface people touch. The colour is in the resin, right through the section, rather than sitting on it as a coating. A mooring line or a trolley wheel that scuffs the rail does not strip a finish and expose bare material underneath — though a rail that has stood in full sun for years will differ in tone from the material below the weathered surface, which is the same gradual change described above. The practical consequence is that a scratch is a scratch and not the start of a corrosion path.
The change specific to this scenario is visual and public. There is no rust staining running down the pontoon or the concrete, which for a marina operator is a large part of why the question was asked in the first place. The profile itself is not conductive, so the rail is not an electrical path in the way a metal rail is; the fixings, base plates and the marina’s own electrical design remain the responsibility of the installation’s electrical engineer, and nothing on this page changes that. Handling matters too: a rail run that two people can carry along a floating pontoon, without a crane and without a hot works permit for cutting, is a genuinely different job to programme.
Read together, the three point at the same short list. Each one is a place where the environment attacks the protective system rather than the structure, where access for maintenance is difficult or expensive, and where weight at the point of installation is a real constraint. In all three, deflection rather than strength is what sizes the member, so the design conversation starts with span and serviceability limit rather than with an allowable stress. And in all three the properties that matter are inherent to the material rather than applied to it: GRP and FRP profiles do not rust or rot, are non-conductive, are poor conductors of heat, and carry their pigment through the section.
The commercial thread is the same as well. There is no recoating cycle to budget, no galvanic isolation detail to design at every mixed-metal junction, and no hot works when a member has to be shortened. Fiberglass structural shapes are handled and cut with ordinary site tools, with the dust and edge-sealing precautions set out on installation and fastening.
Three scenarios chosen to favour a material would not be worth writing. There are conditions in which we would tell you to stay with metal. Above the service temperature range of a polyester system, the profile is the wrong tool and no section choice rescues it. Where the fire requirement in your specification cannot be met by a flame-retardant resin, the same applies — and a flame-retardant additive changes the behaviour of the profile, so whether it satisfies the clause you are working to is a question to settle before an order is placed, with the document in front of you. Where stiffness is the governing criterion and depth is unavailable, steel’s much higher modulus wins on the merits. And where a structure is repeatedly bolted, unbolted and re-drilled through its life, a material that is strong along its length and weaker across it needs more thought at every connection than a metal one does. What we hold to is set out plainly on quality, standards and testing: we describe what pultrusion controls, and we do not claim scope we cannot evidence.
The three scenarios above are the shape of the conversation, not the answer to it. What actually moves a section is your span, your load, the guarding or fire document you are working to, and what the atmosphere does to steel on that particular site. NA-ME Composite has been pultruding sections in Ankara since 1982 and can cut a die where the standard range does not fit, so the discussion is not limited to what is already in the tables above. Deliveries reach Europe by road in a matter of days rather than the weeks a container takes from the Far East.
Send the span, the load and a sentence about the environment. If it is easier, send the metal section you are replacing and we will work back from it.
Send your dimensions, get a quote
Related reading: applications by industry, what is a GRP profile, GRP vs FRP, the pultrusion process.