Steel Castings In Architecture And Engineering

STEEL CASTINGS IN ARCHITECTURE 

AND ENGINEERING 

Hans Schober is born 1943 in Germany and sudied civil 

engineering at the University of Stuttgart. After the study he 

was a structural engineer with the contractor Ph. Holzmann 

and afterwards lecturer at the University of Stuttgart. 

From 1982 to 1992 he was a senior engineer and since 

1992 he is partner with Schlaich Bergermann und Partner. 

His wide spread practise includes design and detailing of 

various pedestrian bridges, railway bridges, multi-storey 

buildings and glass structures at home and abroad. 

ABSTRACT 

Steel castings are being applied in civil engineering not 

only for delicate designed and shaped small elements but 

also for highly stressed structural elements. Today’s low 

carbon cast steel meets all quality requirements imaginable 

such as strength, toughness, weldability and fatigue resistance. 

This paper describes extensive personal experiences with 

cast steel elements in the design of cable net structures, 

glass structures, buildings, pedestrian bridges, highway 

bridges and railway bridges. Finally test results with cast 

steel and welded casts steel on small specimen and full size 

specimen under static and dynamic loads are presented. 

2003 NASCC Proceedings Baltimore, MD – April 2-5 Sessions D4/C18 – Page 1

1. INTRODUCTION 

The second half of the 18 th century saw the advent of widespread use of cast iron as a building material. 

However, its brittle quality made it safe only for structural elements under compression. 

The world's first cast iron bridge built in Coalbrookdale, England (1777 – 1779) was reminiscent of stone arch 

bridges, but required a lot less material due to the high compression strength (Fig. 1). 

Fig. 1: The first cast iron bridge 

Coalbrookdale, England (1777 – 79) 

In New York City's Soho, there are still quite a number of 19 th century buildings with cast iron supports and the 

buildings' cast iron facades carrying the loads (Fig. 2). 

Fig. 2: Cast iron facade 

Haughwout House, New York 

The development of steel production technologies, the welding technique and the use of rolled steel sections 

diminished the importance of cast structural elements. 

Lately however, there is evidence of a reversal back to castings in structural engineering. 

The new, low-alloy and low-carbon materials used in casting today are a far cry from the traditional perception 

of cast steel as a brittle, porous material to be used only under compression and impossible to weld. In the 

following it will be demonstrated that this new material meets all quality requirements imaginable such as 

strength, viscosity, weldability, and corrosion resistance. 


Cast steel permits beautiful, free flowing forms as well as the manufacture of even the most complicated nodes 

with numerous tubes entering from any direction. It is possible to perfectly adapt the shape of the node and the 

wall thicknesses to the flow of forces from the entering tubes. Since the material characteristics of cast steel are 

not affected by the direction of stress, they are especially well suited for nodes stressed three-dimensionally. 

With cast steel it is possible to create flowing forms without any sharp edges or leaps in the cross-section, thus 

avoiding stress concentrations and notch effects. This favourably affects the fatigue behaviour. 

In cast steel nodes the welded seams between node and tube may be placed away from the node core to the less 

stressed tubes and arranged there perpendicular to the axis resulting in a simple, easily accessible welded seam. 

This also avoids secondary stresses in the node due to welding. 

Water rolls off rounded cast steel nodes and they are well ventilated, thus reducing corrosion as well as greatly 

improving accessibility for inspection and maintenance. 

Aside from allowing free forms, steel castings possess above all technical advantages with regard to the static 

and dynamic strength, the accessibility of the welded seams, the simplicity of dimensioning, the maintenance, 

the service life and, in addition, their appearance inspires trust. These facts become even more obvious as the 

number of tubes entering one node from different directions increases (Fig. 3). 

Fig. 3 Tubular cast steel nodes 

Because of these advantages cast steel nodes have been favoured by the author’s consultancy for quite some 

time. 

2.1 Cable-Net Structures 

2. PERSONAL EXPERIENCE WITH CAST STEEL NODES 

The cable-net roof for the 1972 Olympics in Munich caused a virtual renaissance for cast steel. A multitude of 

nodes had to be built as compact and as durable as possible for the coupling of locked coil cables, bundles of 

strands and tubular supports of various geometries. Even now, over 30 years later, these cast steel elements are in 

mint condition without any flaws (Fig. 4). 

Fig. 4: Roof for the 1972 Olympics in Munich, cast steel nodes for cable coupling 

a) Roof b) Foam model c) Final installation of cable coupling 

a) 

2003 NASCC Proceedings Baltimore, MD – April 2-5 Sessions D4/C18 – Page 3 

b) 

c)

The ice skating rink in Munich, completed in 1985, profited from this previous experience (Fig. 5). 

Fig. 5: Ice skating rink in Munich, 1985. Cable net roof 

a) roof from inside b) steel casting for cable saddle 

2.2 Glass Structures 

Glass structures usually require delicate, well designed elements and the design generally calls for cast stainless 

steel with different finishes. 

The pillow-type roof structure (courtyard roof) of the Deutsche Bank in Berlin vaults while the diagonal cable 

net swerves downwards. The vertical posts with the stainless steel balls at both ends rest in cast ladles, 

permitting random spatial angles to the grid shell and the cable net with a single element (Fig. 6). The milled ball 

has a polished finish and the cast ladle is blast with glass spheres. 

Fig. 6: Courtyard roof of Deutsche Bank, Berlin with cast stainless steel cable clamps 

The roof of the Zeughaus in Berlin (Architect I. M. Pei) is a filigree shell. Diagonal cables transform the glazed 

quadrangles into triangles required for shells. Due to the complicated shape, cast steel GS 20 Mn 5 V is used for 

the mullion node (Fig. 7). 


Fig. 7: Courtyard roof of Zeughaus, Berlin with cast steel nodes 

The platform roof of the Lehrter Bahnhof in Berlin is supported by cables following the bending moments. Cast 

steel GS 18 NiMoCr3 6 V was used for all cable saddles, clamps and movable supports (Fig. 8). 


Fig. 8: Platform roof of the Lehrter Bahnhof, Berlin with cast steel cable saddles, cable clamps and supports 

In 1992 a very light cable net wall was developed for the Hotel Kempinski in Munich. The facade consists 

merely of a single-layer, plane, prestressed cable net with the glass panes intermittently attached to its nodes 

(Fig. 9). 

Fig. 9: Cable net facade for the Hotel Kempinski in Munich with stainless cast steel corner patch plates and 

cable clamps 

The cast stainless steel mounting brackets are manufactured using ceramic moulds. They hold the glass panes at 

the four corners, requiring no drilling of the glass, and are clamped to the cables. 

Since then this utterly minimized type of facade has been used several times (Fig. 10), including the AOL Time 

Warner Building in NYC at the Columbus Circle (Fig. 11), though this application included different mounting 

brackets. 


Fig. 10 Cable net wall at Badenweiler with stainless cast steel glass clamps for the wall 

Fig. 11: Cable net wall for the AOL Time Warner Building in New York with stainless cast steel corner patch 

plates and cable clamps 


For the Foreign Office in Berlin the vertical cable runs directly behind the glass pane and the horizontal cable is 

recessed about 40 cm. The necessary spacers as well as the mounting brackets for the glass are diligently 

designed stainless steel castings (Fig. 12). 

Fig. 12: Cable net facade for the Foreign Ministry in Berlin 

with cast stainless steel corner path plate 

2.3 Buildings 

In many cases technical aspects rather than aesthetic ones prompt us to use steel casting. 

Cast steel nodes are particularly well suited for tubular structures with several tubes meeting in one point. 

In the design competition for the assembly-shop roof of the VW-Skoda plant in the Czech Republic forked 

supports with cast steel nodes prevailed due to their light appearance (Fig. 13). 

Fig. 13: Forked supports for the VW-Skoda plant in the Czech Republic 


Terminal 1 at the Stuttgart Airport also receives its unique structural appearance through the forked-supports 

with their diligently designed cast steel nodes (Fig. 14). The same design will be used for the extension of the 

airport currently under construction. 

Fig. 14: Forked supports for the Terminal roof at the Stuttgart Airport 

The roof of the fair hall 13 in Hanover is a traditional spatial truss spanning a rectangle of 225 x 120 m. Here at 

least 5, but sometimes as many as 9 bars of different diameters are combined in the nodes. Cast steel nodes are 

an excellent solution for this problem. In order to keep the expenses for the model to a minimum, a modular 

construction system was used to develop basic structures. Their various attachments for diagonals and strut joints 

permit any possible joining scenario (Fig. 15). 

Fig. 15: Castings at the space truss of fair hall 13 in Hannover, 1998 


The funnel-shaped office-tower of the Porsche customer-service center in Leipzig is supported by V-shaped 

tubular steel supports with their cast steel top and base points perfectly adjusted to the flow of forces (Fig. 16). 

Fig. 16: Tubular nodes for the Porsche Customer Service Center in Leipzig 

2.4 Pedestrian Bridges 

Cast steel nodes also find various applications in pedestrian bridges. They are used above all for the cable 

saddles on the masts and the cable clamps of the main cable. Examples to be mentioned here for this application 

are the Max Eyth See bridge in Stuttgart (Fig. 17) and the pedestrian bridge in Bayreuth (Fig. 18). 

Fig. 17: Max Eyth See bridge near Stuttgart with cast steel cable anchoring 


Fig. 18: Pedestrian bridge in Bayreuth with cast steel cable clamps 

The higher strength, cold-viscous cast steel GS 18 NiMoCr3 6 V is mostly used for cable clamps and anchorings 

having a yield strength of 600 – 700 N/mm² and a tensile strength of approximately 800 N/mm². 

Various types of cast steel nodes are also used in pedestrian bridges with reinforced concrete decks resting on 

tubular steel supports. Due to the punching of the reinforced concrete slabs, as many points of support as 

possible are advantageous. Therefore, it is preferable to fork the tubular steel supports towards the slab. Cast 

steel nodes are perfect for the branching points of the tubular steel supports as well as for connecting the 

supports to the foundations and to the deck. This can be seen at the bridge in Sindelfingen and the Pragsattel and 

Heilbronner Straße bridge in Stuttgart. (Figs. 19 and 20). 

Fig. 19: Forked supports for pedestrian bridges 

Bridge in Sindelfingen, 1989, top 

Pragsattel bridge in Stuttgart, 1992, bottom 


Fig. 20: Arch bridge Heilbronner Straße in Stuttgart, 1992 

In the case of these two bridges the castings were equipped with a groove at the weld between the tube and the 

casting. This groove, 30 mm wide and 5 mm deep, is designed to distinguish the rough casting from the smooth 

tube and to define a clear boundary for burnishing the seam. 

The Ripshorst bridge, curved in plan, is supported by a single steel arch. A hanging model was used to determine 

its geometry. Due to the spatial curved arch numerous V-shaped vertical struts of different geometries have to be 

connected with the arch using cast steel nodes (Fig. 21). 

With castings the welded seams can be placed away from the node care to a less stressed position. 

Fig. 21: Pedestrian arch bridge in Ripshorst, 1998, curved in plan 


The module-type Expo-bridges in Hannover, carried by closely situated supports, rest on heavily rounded and 

defined cast steel elements (Fig. 22). 

Fig. 22: Expo-bridge Hannover, 1999 

There should be no reluctance to use rounded cast steel elements with stiffeners and varying wall thicknesses 

because this, in addition to the structural and aesthetic benefits, also provides advantages for the casting process. 

2.5 Highway Bridges 

The Nesenbach highway bridge in Stuttgart rests on a tubular steel truss with a concrete slab and is supported by 

Y-supports. All nodes of the Y-supports and of the truss including the connections to the concrete slab are cast 

steel (Fig. 23). 


Fig. 23: Nesenbachtal bridge in Stuttgart, 1999 

The Schattenring bridge in Stuttgart has its steel arch enter the concrete superstructure to optimize the arch rise. 

All tubular steel nodes as well as the feet and heads are carefully designed cast steel elements (Fig. 24). 

Fig. 24: Highway bridge near Stuttgart, 2002, with cast steel nodes 


2.6 Railway Bridges 

In the heart of Berlin, near the government buildings, a new main station, the Lehrter Bahnhof, is under 

construction. 

At an elevation of approximately 10 m a total of 6 tracks have to cross a distance of almost 1.000 m, passing 

through the station and crossing the Humboldthafen basin attached to the river Spree (Fig. 25). 

Fig. 25: Railway bridges at the Lehrter Bahnhof in Berlin 


At the center of the station building all railway bridges are supported by forked-supports with an overall height 

of approximately 23 m. They consist of 4 steel tubes with a diameter of 508 mm each, dissolving into 4 threedimensional 

forks at the top (Fig. 26). 

Fig. 26: Forked supports in the station building 

At the Humboldthafen the concrete superstructure is supported by a steel arch spanning 60 m. The arch consists 

of thick-walled, seamless steel tubes with a wall-thickness of 100 mm (Fig. 27). 

Fig. 27: Railway bridge across the Humboldthafen 


With the advantages of cast steel tubular nodes – especially under dynamic load – in mind, a central idea in the 

design process of the bridges was to use cold-viscose cast steel with favourable weldability for all nodes. The 

following node-types are used (Fig. 28): 

a) For the forked-supports in the station building (Fig. 28a): 

• Fork head at the transition to the concrete superstructure, 2.5 tons, with a diameter of 120 cm and wallthicknesses 

of max t = 200 mm and min t = 90 mm. 

• Support fork, 11.5 tons and wall-thicknesses of max t = 300 mm and min t = 90 mm. 

• Support base, 11.7 tons with the dimensions of ∅ = 225 cm, h = 105 cm, max t = 300 mm, 

min t = 90 mm. 

b) For the bridge across the Humboldthafen (Fig. 28b): 

• Arch head with stiffeners (2.8 tons) 

• Top of the impost abutment (13.5 tons) 

• Arch node (3.2 tons) with a diameter of 660 mm and wall thicknesses of t = 100 mm 

• Bottom of the impost abutment (9.8 tons) 

• Nodes of the diagonals at the impost with a diameter of 267 mm and wall-thicknesses of max t = 45 – 

60 mm. 

Fig. 28 a): Cast steel elements for the railway bridges 

Cast steel elements of the forked supports in the station 

Top: Head of the forked support 

Center: Fork 

Bottom: Base of the forked support 


Fig. 28 b): Cast steel elements of the Humboldthafen bridge 

Top: Top of the arch 

Center: Arch node 

Center: Top of the impost abutment 

Bottom: Bottom of the impost abutment 

Bottom: Node for the diagonals 

The cast steel used was GS 20 Mn 5 V according to german standard DIN 17182 (cast steel with improved 

weldability and toughness for general use), material No. 1.1120. The characteristics of this type of cast steel are 

comparable to those of steel St. 52-3 (S 355 J2 G3) with respect to strength, weldability and viscosity (Fig. 34). 

After intensive preliminary inspection, ensuing heat treatment and a final inspection in the work shop, the 

welded ends of the castings were machined. Proper machining and grove weld backing is very important under 

dynamic load because the quality of the weld root is a major factor in determining the fatigue category, and 

minimizes tolerances, facilitates the assessment (for ultrasonic testing) and provides controlled conditions. 

For the Humboldthafen bridge, the weld ends were machined to compensate for the tolerances of the tube and 

the casting (Fig. 29). 


Fig. 29: Butt joint at tubes and machined weld ends 

The client, the Deutsche Bahn AG, made high demands as to the quality of the dynamically stressed castings. In 

addition to the limitation of carbon content, there was a strict limitation of the internal and external defects. 

Therefore, for all weld ends the requirment was defect acceptance level 1 and for any other area defect 

acceptance level 2 according to DIN 1690 applied, though reducing the largest possible single defect and the 

largest possible total defect area to half of the stipulation in the code. 

While there was no problem to meet defect acceptance level 1 for the weld ends, the foundry faced major 

problems meeting defect acceptance level 2 which could only be mastered with great efforts (if at all). 

In the future it would be reasonable to adjust the quality requirements for the stresses in the casting, to define 

areas with different quality requirements, and to adapt the casting process. 

For castings purely under static load defect acceptance level 3 is sufficient, except for the weld ends. 

All castings were submitted to a 100 % surface crack inspection and to an ultrasonic inspection. In addition the 

quality inspector stipulated an x-ray test for 10 % of the welded ends. 

After being presented with all test records of the contractor the quality inspector submitted the castings to 

another ultrasonic and surface crack inspection and also examined the x-ray-films of the contractor. 

Defects could only be repaired with so-called shop-welds after the consent of the client. For inadmissible defects 

requests for allowances had to be submitted which, after a lengthy procedure, were either granted or dismissed. 

In case of a dismissal new castings had to be manufactured. 

3. TESTS WITH CAST STEEL 

Since this was the first application of cast steel nodes in modern railway bridge construction the static and 

dynamic behaviour of the cast steel welded to rolled steel had to be tested extensively. The following tests were 

conducted at the University of Karlsruhe. 

• Small specimen tests: 

Steel welded to cast steel plates with wall thicknesses of 25 and 40 mm. 

• Fatigue tests with cast steel tubes welded with a butt joint to rolled tubes with an outside diameter of 267 

mm and wall thickness of 20 mm. 

• Tests with steel columns (full size testing): 

Tubes with an outside diameter of 508 mm and 60 mm wall thickness, welded to cast steel nodes. 

• Fatigue tests with contact- and butt joints (steel to cast steel) of the arch tubes: 

Thick-walled tubes with an outside diameters of 660 mm and 100 mm wall thickness. 

• Diagnosis by sawing off the castings: 

Column foot with an outside diameter of 508 mm, wall thickness 60 mm (Fig. 30). 

Arch node with an outside diameter of 660 mm, wall thickness 110 mm (Fig. 31). 

• Investigation of the mechanical properties of the castings in spatial directions (Fig. 32). 


Fig. 30: Column foot with indicated defects Right: Sawing of the node 

Fig. 31: Arch node with indicated defects Right: Sawing of the node defect 


Fig. 3: Machined samples from cutted castings 

Since the tests are published in [2] only the most relevant results will be given below. 

Fig. 34 shows that the properties of GS 20 Mn 5 V derived from the static test are definitely comparable to that 

of ST 52 (S 355). 

Both materials have a yield strength of around 360 N/mm², ultimate strength of about 550 N/mm² and elongation 

at fracture of just about 30 % and they completely meet the standards. 

The measurements of the absorbed energy also confirmed cast steel is a tough material. 

Further tests with specimens showed virtually no dependency of the material properties on the stress directions 

(isotropic material) which is particularly relevant for three-dimensionally stressed nodes. At up to 200 mm wall 

thickness there was no distinct dependency on the thickness. 

The results of the fatigue tests with small specimens (R = + 0,1, swelling, tension), with tubes ∅ 267 x 20 mm, 

with columns ∅ 508 x 50 mm and with arch tubes ∅ 660 x 100 mm are presented in Fig. 35. 

All the tests proved that welded connection between S 355 (St. 52-3) tubes and GS20Mn5V castings possess 

fatigue resistance corresponding to the welds. 

This corresponds to a fatigue category ∆σ c = 80 N/mm 2 in the format of Eurocode EC3, valid without any 

further reductions for welded seams up to 60 mm. 

The weak-point of the fatigue strength was never the node itself but always the welded joint between the cast 

steel and the normal steel. 

Fig. 33: Tested material properties for steel S355J2G3 

and cast steel GS 20 Mn5 V (small specimens) 


Butt joints 

R=σmin/ σmax = 

+0,1 

Plate thickness 

25 mm 

40 mm 

25 + 40 mm 

112,7 

96,9 

103,6 

87,5 

78,8 

80,3 

Fig. 34: Fatigue resistance for welded steel-cast steel-connections 

(picture and table) 

For 2 ⋅ 10 6 L.C. determined stress 

range 

With backing 

Pü = 

50% 97,5% 

Without backing 

Pü = 

50% 97,5% 

146,1 

154,0 

148,6 

123,5 

135,1 

127,9 


References 

[1] Schlaich, J., Schober, H.: Bahnbrücken am Lehrter Bahnhof in Berlin. Die Humboldthafenbrücke. 

Stahlbau 68 (1999; H. 6, S. 448-456) 

[2] Schlaich, J., Schober, H.: Rohrknoten aus Stahlguss 

Stahlbau 68 (1999), H. 8 und 9 

[3] Mang, S., Herion, S. : Guß im Bauwesen 

Stahlbau Kalender 2001; Ernst und Sohn

Steel Castings In Architecture And Engineering

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