There are traditionally three important fields of application for heavy steel plates in civil engineering: heavy steel buildings made of welded constructions (e.g., multi-story buildings, shipbuilding halls, or power plant buildings), bridges with spans between 4 and 1000 m, and offshore platforms for the production and processing of oil and gas at sea. Nowadays, a wide range of heavy steel plates is available for these fields of application. Heavy steel plates offer technical designers a nearly unlimited range of dimensions, strength, and toughness levels. Due to optimized properties, heavy steel plates enable very economical and durable constructions.
User-Oriented Development of Heavy Steel Plates
At present, heavy steel plates are widely used in constructional steelwork. Among these, the steel grades between S235 and S355 are particularly popular. The development of heavy steel plates for steel structures during the past few decades was first aimed at increasing the strength level while at the same time maintaining an acceptable weldability. In this way, the volume of steel used in the construction could be reduced.
At the beginning of the ’70s, high-strength steel levels such as S460 and S690 were developed. These require a relatively difficult welding procedure along with higher fabrication costs, and therefore limit their widespread use.
The demand to reduce weight (i.e., the reduction of the dead weight of the structure and the reduction of the total volume of steel required) was the starting point for the development of longitudinally profiled plates (LP-plates). Through a special control of the roll gaps during the rolling process a longitudinal profile with a continuously varying thickness along the length of the plate can be given to a heavy plate. Thus, various types of LP-plates with different geometries can be produced (Figure 1). Such plates allow an optimized adaptation of the plate thickness to the actual stress in the structure. (Examples for the application of these plates are presented in Figures 2–6.)
Today, LP-plates are applied in bridge-building all over Europe (Figure 7). Besides reducing weight, the application of LP-plates also saves fabrication costs and time due to the possibility of avoiding complicated weldings.
Aspects of fabrication and manufacturing costs savings gained more and more importance during the ’80s and led to the development of the modern generation of thermomecanically (TM or TMCP)-rolled heavy steel plates. TM-rolled heavy steel plates in steel grades S355, S420, and S460, which have been available since the end of the ’80s, offer not only high strength, but also excellent weldability. Thus, the possibility of designing even more economical steel constructions is established.
The recent heavy steel plates for offshore applications were derived from fine-grained structural steels and standard grades as the normalized S355 steels. They are designed to give a reasonable toughness in the heat-affected zone after welding. Since the end of the ’80s, TMCP-heavy steel plates of the yield levels 355, 420, 450, and 500 have been developed for this field of application too. These grades are characterized by excellent toughness levels after welding—even with these high strength properties.
As far as building construction is concerned, two different fields of application may be distinguished. On the one hand, simple and standardized multi-story and hall buildings; and on the other hand, heavy welded constructions for industrial halls, power plants, and special, tall, multi-story buildings. Regarding the standardized constructions, which hold the biggest share of the total steel consumption in the construction market, heavy steel plates are only used for head plates or stiffeners for framework constructions predominantly composed of rolled beams. Mostly steel grades S235 and S275 are applied here.
In cases in which high loads or large spans have to be designed, columns, piles, and girders are normally welded and made from heavy steel plates. This design and construction method shows an economical advantage for girders up to a height of about 600 mm because the cross sections of the supporting structure can be adapted individually to the constructional task by using a minimum of steel. Steel grade S355 is predominantly applied for these applications, but sometimes heavy steel plates of the higher steel grade S460 are used. Common dimensions for heavy steel plates in the heavy building construction area are:
– Thicknesses from 8 to 100 mm;
– Widths up to 1.5 m; and
– Lengths up to 18 m.
The following examples give an idea of the typical application range of heavy steel plates:
- Power plant buildings, e.g., the thermal power station Schwarze Pumpe, Germany, (Figures 8 and 9) with an overall height of 161 m. The columns and beams were mainly fabricated with TM-rolled heavy steel plates S355M/ML and the standard structural steel S355 J2 G3 mod. in plate thicknesses up to 65 mm. Additionally, S690QL grade was used in some high tension loaded areas.
- Commerzbank Tower, Frankfurt, Germany (Figures 10–12)
Due to the very strict requirements of architects in regards to the aesthetics of multi-story buildings, heavy steel skeleton constructions have been used more and more over the past 10 years. A typical example for this is the Commerzbank Tower in Frankfurt, with a height of more than 298 m. Its steel-framed structure contains about 18000 t of heavy steel plates. S355M steel was used for plate thicknesses exceeding 30 mm, whereas in highly loaded girders and columns S460M was applied. Fabrication costs were reduced through this optimal selection of heavy steel plates.
- Sony Center Berlin, Building F, Germany (Figure 13)
In this example the architectural requirements were also decisive for the application of high-strength heavy steel plates. The supporting structure consists of three heavy columns on which two welded truss girders made of heavy steel plates form the load-bearing structure. On the latter the individual stories are hung up. The truss girders were made of plates with thicknesses up to 100 mm, in grades of S460M/ML and S690QL1.
- High-speed train (ICE) station, Frankfurt Airport, Germany
The 700-m-long and 50-m-broad reception hall of the high ICE station near the Frankfurt airport rests on heavy welded columns. More than 18000 t of steel grade S355M/ML and 2000 t of S355K2G3 were used for this building. Each upper supporting framework has a weight of about 320 t and is supported by columns with an individual carrying force of 7500 t.
In bridge construction in recent years more and more heavy steel plates have been applied due to the progress in the construction of composite bridges (steel supporting structure with a concrete deck). In particular, bridges with a medium span between 30 and 150 m are utilize these plates. Typical examples for cross-sections of these composite bridges are presented in Figures 3, 4, and 14. These constructions can exploit the whole range of feasibility in regards to both dimensions and steel grades. Very thick plates (girders with a thickness of up to 150 mm) are used, as are very wide plates (width up to 4300 mm, and in special cases more than 5000 mm) and long plates for segment lengths between 18 and 36 m or steel grades up to S690QL1. These dimensions enable cost-effective bridge constructions.
Bridges with very small spans between 3 and 6 m can be built with a single heavy plate. Plate thicknesses up to 250 mm may be reached depending on the loading and deflexion criteria used. Typical plate bridges are shown in Figures 15 and 16 (La Moyaz and Creux de Mas in Switzerland). These plate bridges consist of heavy steel plates of the steel grade S275NL lying side by side. The dimensions used in these plate bridges are thicknesses between 160 mm and 220 mm, widths of about 2300 mm, and a length of about 4400 mm. The main advantage of this bridge type is the small traffic interruption period while the bridge is being erected. The entire process of erecting the bridge (from pulling down the old bridge structure to the passage of the first train on the new bridge) takes no more than eight hours.
Due to construction techniques, bridges with big spans (more than 150 m) belong to the field of pure steel structures. Constructions made of welded heavy steel plates are almost generally applied for such types of bridges.
Mainly heavy steel plates of the steel grade S355 are used in European bridge-building. However, high strength plates of S420 and S460 are being employed more and more for big-span bridges. Sometimes even the higher-strength steel grade S690 is used (e.g., in the water-quenched and tempered condition). Normally the plate thicknesses are less than 50 mm, but occasionally even plates of thicknesses up to 150 mm can be found in the load-bearing sections.
Typical examples for modern bridge-building are given by the following figures:
- Railroad Bridge Nantenbachtal, Germany
The double-track composite bridge has an overall length of 695 m and a maximum overall height (at the posts) of 15.5 m (Figure 17). The main span is 208 m. This three-span, concrete-haunched composite building consists of an upper concrete deck plate and a concrete compression plate in the region of negative bending moments above the posts (double composite). The steel grade S355J2G3 mod. is used in plate thicknesses up to 65 mm.
- TGV-Méditerranée, France
Among the 23 bridge constructions, 15 were established as composite bridges with twin girders. The most important composite bridges are the bridge of Cavaillon (5200 t), the bridge of Orgon (3600 t), and the bridge Cheval Blanc (3500 t). In addition, five smaller bridges and three big truss-arched bridges were built in steel: Viaduc de Donzere, Viaducs de Mondragon, and Mornas (Figures 18 and 19). Besides the classical steel grade S355K2G3 (plate thickness up to 30 mm), heavy steel plates of the steel grades S355N and S355NL (plate thicknesses more than 80 mm) were also applied, partly in the form of LP-plates.
- Erasmus Bridge Rotterdam, The Netherlands
The Erasmus bridge connects the inner city of Rotterdam with the North Bank of the Nieuwe Maas, Kop Van Zuid, where a new quarter will be established in a former harbor area (Figure 20). The steel structure has an overall length of 499 m with a 410-m-long cable-stayed bridge composed of a 139-m-tall pylon and an 89-m-long flap bridge. In total, 6000 t of heavy steel plates of steel grades S355M (thickness less than 100 mm, 4200 t), S460L (thickness less than 80 mm, 2000 t), and S460QL (thickness less than 125 mm) were used for this bridge.
- Øresund Bridge, Danmark-Sweden
The Øresund fixed link (Figure 21) consists of a 7500-m-long framework composite bridge, a 4000-m-long artificial island and a 3500-m-long tunnel. The approach bridges and the cable-stayed main bridge were built as a truss bridge with an upper concrete deck and a lower steel deck (railroad deck). Heavy steel plates of the steel grades S460M/ML in thicknesses up to 80 mm (60000 t) were used for the shore spans, whereas the main bridge was constructed of S420M/ML in thicknesses up to 50 mm (16000 t).
- Normandy Bridge, France
In 1995 the Normandy Bridge was opened to traffic. At that time it was the biggest cable-stayed bridge of the world (Figure 22). altogether, 624 m of the total length of the main opening (856 m) were constructed with heavy steel plates for weight reasons. The aerodynamically optimized cross-section was designed and built using plates in steel grades S355K2G3, S355N, and S420M in thicknesses up to 30 mm (single pieces up to 125 mm).
In the ’60s and ’70s the construction of offshore platforms for the production of oil and gas in the North Sea required heavy plate properties that significantly exceeded the requirements of conventional constructional steels. Due to stringent requirements on the safety and reliability of the platforms under very extreme external conditions (low temperatures, severe storms, high waves, and corrosion by sea water), as well as the necessity of partial assembly on-site at sea, heavy steel plates with especially high ductility, high resistance against crack growth, and good fabrication properties had to be developed. These steels involved substantial developments from fine-grained steels to special offshore grades.
The supporting framework of platforms standing on the ocean floor usually consists of a framework made of relatively thick-walled constructional pipes. In order to produce these pipes in an economical way, the heavy steel plates have to be as wide as possible. That way, the number of pipe segments necessary for the welded framework structure can be reduced. Typical plate widths for such structures are between 3500 and 4500 mm with thicknesses between 20 and 90 mm. Today, heavy plates of the steel grade S355-Offshore are applied as a standard. These plates can be delivered in either a normalized or TM/TMCP-rolled condition with thicknesses of up to 250 mm and 120 mm respectively. In particular, the TM-rolled heavy steel plates show very good toughness properties after welding and can be processed in a cost-effective manner.
Recent platform constructions are characterized by the necessity of a higher overall height due to deeper sea levels or the development of swimming platforms. When applying the classical S355-Offshore steel grade in these constructions, the necessity of big carrying cross-sections considerably increases the total weight of the structure. Therefore, higher-strength heavy steel plates of the steel grade S420-Offshore have gained recognition in the North Sea platform applications. These plates are delivered in thicknesses of up to 120 mm in a TM/TMCP-rolled condition. Plates with greater thicknesses are normally used in the quenched and tempered condition.
The following figures show typical examples of modern offshore platforms:
- Ekofisk IIa (Figure 23)
The Ekofisk field, a very old oil and gas field near the Norwegian coast, had to be reconceived because of the lowering of the central storage tank. Therefore, two new platforms were built. About 45,000 t of plates predominately of the steel grade S420M-Offshore were used for these two platforms. The six-legged platform 2/4X weighs 7900 t, the jacket alone weighing 5800 t (not including the ram piles for the foundation into the sea bottom). The new central platform 2/4J consists of an 11400 t jacket tied to the sea bottom by 16 ram piles with a total weight of 5500 t and carries the deck with a weight of 23000 t. The two platforms are standing about 90 m above the sea bottom and are connected to each other and the total complex by several bridges.
- Petronius Tower (Figure 24)
Today, the Petronius Tower with its overall height of 564 m is the highest (or, more accurately, deepest) offshore platform in the world. It is situated in the Gulf of Mexico, around 200 km from New Orleans. This project was only possible due to the application of high-strength steels of the grade S460M-Offshore (about 2200 t used) in the area of specially constructed elastic flexible joints. These flexible joints permit the tower to adapt to the movement of fluxes and waves. The plate thickness used for this construction was 90 mm.
- Siri (Figure 25)
Siri is situated in the northwestern part of the Danish sector of the North Sea, around 220 km from the coast. The 104-m-long legs have an outer diameter of 3.5 m and a single weight of 800 t. The jacking system is characterized by a special locking mechanism, which enables the platform to be a temporarily fixed structure. The steel grade S690Q-Offshore, for which improved fracture toughness properties had to be approved, was used for the first time in this construction.
At present, the offshore grade S500TMCP, which requires the same toughness properties as lower-strength steels, is being prepared for application (e.g., the Grane project in Norway). In addition, the yield strength grade S690Q-Offshore is being used more and more frequently. However, many questions concerning crack resistance and corrosion fatigue have to be answered prior to the wide-spread use of this very high-strength steel.
Today, the designers of constructional steelworks and offshore structures can choose from a nearly unlimited selection of heavy steel plates (with regard to dimensions and steel grades).
- Thickness — between 8 mm and 250 mm
- Width — between 300 mm and 5200 mm
- Length — between 6000 mm and 36000 mm
- Weight of single piece up to 60 t
- General structural steels — S235N – S355N incl. offshore grades and LP-plates
- Fine-grained steels N — S275N – S460N incl. offshore grades and LP-plates
- Structural steels with improved atmospheric corrosion resistance
S235W – S355W incl. LP-plates
- Fine-grained steels TM/TMCP — S355M – S460M incl. offshore grades
- Water quenched and tempered structural steels — S460Q – S690Q incl. offshore grades
Through this wide selection of steel grades, nearly unlimited opportunities are available to designers for the dimensioning and design of buildings, as well as efficient fabrication properties with for an economical and competitive construction process. The current delivery programs of the plate products will meet the demands and desires of the next few decades.
Future developments in heavy plate technology for steelwork and offshore constructions will be characterized by the user’s desire for further reductions in fabrication costs using further improved heavy steel plates. Additional requirements in the homogeneity of the mechanical and chemical characteristics, as well as dimensional tolerances and flatness, pose a great challenge for the processing and rolling technologies of heavy steel plates.
This article originally appeared at Dillinger Hütte and is reproduced with permission.