Application of ConSteel© in design of UTE Stadium

F. Papp Department of Structural Engineering, BUTE, Budapest, Hungary

Keywords: steel structures, computer aided design

ABSTRACT: As the first step of the Hungarian ’Stadium Program’ the old buildings as well as the arena of UTE Stadium were rebuilt. The eighty percent of the arena has been covered by new steel structure. The structural solution rightly acknowledged in both of aesthetic and engineering points of view. This paper de-scribes the theoretical and practical background of design using the ConSteel integrated structural design program in the Steel Structural Design Office of the KÉSZ Ltd. The structure was fabricated in the new CNC workshop, which was implemented by the company in 2000.

1 INTRODUCTION

The old concrete stand was build decades ago (see Figure 1.). The new geodesic measurement showed that the ground of the stand is not regular: one side is shorter with 2 meters than the opposite side. This fact and some financial conditions leaded to the building strategy, where firstly the four sides, later the four – at first sight uniform - corner structures were designed and built as independent structures. The dramatically short design time as well as the geometrically different corners required “automatic” structural design technology. The designers applied the ConSteel© (2002) integrated steel structure de-sign program. This paper introduces this design sys-tem by means of the new steel structure of the UTE Stadium (see Figure 2).

Figure 1. The old structure (concrete stand).

Figure 2. The new structure (steel roof). 2 MAIN FRAME The governing members in the uniform side struc-tures are the main frames (see Figure 3).

Figure 3. The main frame.

In the first step of the design the governing form of the main frame was determined. Many solutions (truss structure, welded section frame, and so on…) were examined and compared in cost. The solution of light truss and internal column locate in the stand seemed to be the cheapest solution, but it had to be rejected: the fans of the team did not wanted see any column within the stand. However, the evolution of the structural form is illustrated in Figure 4.

Figure 4. Evolution of the form of the main frame. The starting model was the simply fix and prismatic column with tapered cantilever. This version had to be rejected because the moment at the ground re-sulted too expensive base. To avoid the large base structure, in the next version the column was sup-ported by a sloped bar. By this solution the column got the required stiffness, but the beam showed ex-cessive deflection. To avoid the large beam defor-mation, it had to be “hanged” up by “tension” sys-tem (see the green bars in Figure 4). This was the evaluation of the format of the frame. The detailed analyses showed that the “tension” system should be a tension-compression beam-column system, be-cause of the considerable wind up effect.

2.1 Structural details After the architectural design of the main frame, the next step was the “optimal” structural design. The governing conditions were the following: • the distances between main frames are 8,3 me-

ters, • the covering system is a Hösch-donga system, • the second ground point should be located within

4,5 meters band. However, the beam was designed as tapered mono-symmetric member, where the upper flange is a cold-formed profile, which can accept covering donga plates (see Figure 5).

Figure 5. Special beam shape with closely located stiffeners to support the donga system.

The thin web of the beam should be stiffened rela-tively closely to keep the cross-section shape, which is deformed by the local effect of the donga. How-ever, the design of tapered member with Class 4 cross-sections required advanced design tool. The column was also designed as tapered member with no stiffened Class 4 web plate. This type of member should have considerable end-stiffeners as it is shown in Figure 6.

Figure 6. Column end with considerable end-stiffener to encourage the thin web plate.

The back cantilever had considerable effects; there-fore it was designed as tapered member starting with the height of the beam. The special beam flange was reduced gradually as far as the end plate connection between the beam and the cantilever. The tension-compression member system consists of sloped bars and it was designed from hot-rolled HEA shapes with shear bolted connections. To reduce the effect of the self-weight of the slender sloped members, tension bars were applied around the minor axis (see Figure 7.).

Figure 7. Sheared-bolt connection of the upper “ten-sioned” stiffener member.

Both the column and the base points of the stiffener system were connected to the ground by encourage bolts fixed in the head of the concrete base. The base head are fixed to the drilled concrete piles. 2.2 Modelling The main frame was modelled by the ConSteel© structural design program. The 3D model was com-posed of thin-walled beam-column finite elements. The model was supported laterally in the points where the members of the wind-bracing system con-nect to the frame. At these points of the beam the ro-tations about the member axis are also restricted since the bottom flange are stiffened by sloped bars. In the ConSteel© system the tapered members are modelled approximately by a set of prismatic beam-column elements with eccentricity, as it is illustrated in Figure 8.

Figure 8. Modelling tapered member by a set of ec-centric prismatic finite elements.

2.3 Analysis of tapered beam To verify the ConSteel approach of tapered mem-bers, let us consider the test beam published by Andrade & Camotim (2002) and illustrated in Figure 9.

Figure 9. Andrade & Camotim (2002) tapered beam The exact theoretical solution for the elastic critical moment (Mcr) was compared to the result of the ConSteel solution (see Figure 10).

Figure 10. Simulation of LTB in the ConSteel system using n=32 finite elements.

The conclusion of the above test was that the n=8 finite elements gave reasonable result for the lateral-torsional buckling of the tapered beam. At n=16 the “error” of the solution was less than 1%.

eccentricity

top-steel

8000

200-10

200-10

400(200)-6 E=210 GPa ν=0.3

M

k N mk N mk N mk N m 1 8 4 . 41 8 4 . 41 8 4 . 41 8 4 . 4MMMMc r . e x a c tc r . e x a c tc r . e x a c tc r . e x a c t =

4 8 16 32 n

ConSteel.cr

exact.cr

M

M

1.05

1.0

2.4 Analysis Using the above tapered member modelling, the 3D model of the main frame was built up in the Con-Steel system (see Figure 11.).

Figure 11. 3D model of the main frame by ConSteel User Interface.

The ConSteel program is an integrated system with the following main components: • CAD modelling • Analysis (first order, second order, elastic stabil-

ity, dynamic) • Structural design following Eurocode 3 The 3D stability analysis allows the standard struc-tural design being fully automatic (Papp & Iványi 2002), because the procedure does not need the in-teraction of the user defining the member restraints for the resistance of member stability. Figure 12. shows the result (3D buckling modes) of the stability analysis of the main frame to wind up effect. Mode 1 indicates the buckling of the upper stiffener member about its minor axis. Mode 2 shows the buckling of the same member, but about its major axis and with parallel buckling of other stiffener members. Mode 3 indicates the buckling of the other stiffener mem-bers. Mode 4 shows the buckling of these members but about their major axes and with the slight tor-sional buckling of the tapered column. It is impor-tant to mention that the first three buckling modes had almost the same eigenvalue (critical load factor). Mode 4 was larger by 70%. The study of the buck-ling modes leaded to the conclusion that the member slenderness specified by Eurocode 3 might be evalu-ated with the first eigenvalue. This concept is “con-

servative” but allows automatic structural design procedure.

Figure 12. 3D Buckling modes of the main frame. 2.5 Structural design The full analysis provided a complex database for the standard structural design according to Eurocode 3. The main points of the design were the following:

• cross-section resistances, • member stabilities, • connection resistances.

Figure 13 shows the colour-mapped resistances of the main frame to the relevant load combinations. The automatically generated data table showed by

Figure 13. Colour-mapped resistances by Eurocode 3. Figure 14 allowed the designers to analyse the rea-sons of the given resistances. The left hand side data-block shows the design effects on the relevant cross-sections, the right hand side data-block gives the parameters of the design equations relating to the

Mode 1 Mode 2

Mode 3 Mode 4

Figure 14. Diagnostic data table for cross-section and member resistances according to Eurocode 3.

relevant resistances. Details of design within the relevant cross-section can be examined by the user: Figure 15 shows the diagnostic table with the col-umn cross-section located just below the point where the sloped member supports the column (Papp, Iványi & Jármai 2001).

Figure 15. Design data table for cross-section accord-ing to Eurocode 3.

The 2D graphics indicates the effective cross-section model of the Class 4 column shape (the middle part of the web is a non-effective zone). However, using the automatically generated design diagnostic tables, user may find the optimal configuration of the struc-ture in some minutes. We have to emphasis, that the program does not replace the engineering back-ground but urges the engineer to understand the be-haviour of the structure much deeper than those de-sign tools, which follows the conservative design techniques.

The final step of the structural design was the design of connections. The ConSteel system has a powerful JOINT module, which was developed in a coopera-tion with the Czech FINE software firm. The JOINT follows the component method established by the Eurocode 3 (see Figure 16). The JOINT is integrated into the ConSteel analysis, where a complex joint object can be generated as an • individual joint object, which is generated within

the JOINT tool, • structural joint object, which is automatically

generated from the actual structural model.

Figure 16. The integrated ConSteel/JOINT module – design of column base.

3 THE CORNERS The four corners were designed and built in the sec-ond building phase, when the four sides were have been ready (see Figure 17).

Figure 17. One of the four “independent” corner struc-tures.

Since the sides followed the old concrete structure (stand), they formed irregular rectangular. However, the four corner grounds were unique, respectively.

The architectural concept of the corners was based on the idea illustrated in Figure 18.

Figure 18. Concept of the four “independent” corner. The distances between the last frames of the sides and the corner frame are changeable, because the sides and the corners are not connected to each other except the flat covering plates. By this concept the corners can be really independent structures. How-ever, a corner structure is composed of four main frames, where two of them is turned about its verti-cal axis by 90 degree. The four beams – connected to each other at their ends – compose a rectangular area without any internal columns (it was a pre-condition for the design). The roof structure was built up with one double and four single light trusses. The roof creases in the line of the double truss giving the needed slope for the two triangular roof areas. 3.1 Modelling and analysis The corner structures were modelled in the ConSteel system (see Figure 19). The two main points of the columns had to be connected by a tension bar to provide stiffness for the structure against crushing. The light trusses were modelled by tension-compression bars, which distribute the roof load be-tween the main beams. The beams had to be loaded in the shear centre to avoid the excessive torsion of the “soft” open shape. This condition was achieved by a special truss-beam joint, which is illustrated in Figure 20. The truss ends in hot-rolled HEA profile,

Figure 19. 3D beam-column model of the corner.

Figure 20. Truss-beam joint close to shear centre.

which is put into a CHS profile that is welded cen-trically into the web closely to the shear centre. In-side the profile special rectangular bars fix the truss ends against the axial displacements but allow the rotations. The effect of the covering to the stiffness was neglected in the model. The global elastic stability analysis showed the rele-vant buckling modes of the model. Figure 21 shows the first buckling mode, which indicates the tor-sional rotation of the columns with the lateral tor-sional buckling of the beams.

Figure 21. First global buckling mode of the model.

Side A

Side B

last main frame corner frame flat roof connection tension bar base

400 m2 free area

Because the higher eigenvalues were close to this value, the first critical load factor was accepted as the generalised value for the critical forces. The automatic design provided a sufficient tool for the designers to find the optimal configurations of the four different corners, respectively. 4 CONCLUSIONS The design of the new steel structural roof system of the UTE Stadium had more irregular conditions, which would made the design too difficult using the traditional design technologies. The ConSteel inte-grated steel structural design system provided an adequate tool for the designers to satisfy the irregu-lar conditions in the prescribed building time and cost. The main advantages of the design tool are the following: • Easy beam-column modelling on the advanced

CAD User Interface. • Advanced analysis for global 3D stability analy-

sis including the warping effects. • Application of the unified object-oriented cross-

section definitions. • Automatic and standard design procedure sup-

porting by advanced diagnostics of the design equations.

REFERENCES ConSteel 2002, “ConSteel concurrent steel struc-tural design program”, User Manual, KÉSZ Ltd. 2002, Budapest, Hungary

Andrade & Camotim 2002, “Lateral-Torsional sta-bility behaviour of arbitrary singly symmetric ta-pered steel beams: a Variational formulation”, Eu-roSteel 2002, Proceedings, pp. 107-118, Coimbra, Portugal

Papp & Iványi 1998, “Steel CAD. Computer aided design of steel structures”, textbook in Hungarian, ISBN 963 420 590 9, Mőegyetemi Kiadó, Budapest

Papp & Iványi 2002, “Developments in structural design of beam-columns: a review from CAD point of view”, SDSS 2002 Proceedings, pp. 13-22, Buda-pest, Hungary

Papp, Iványi & Jármai 2001, “Unified object-oriented definition of thin-walled steel beam-column cross-sections”, Computers & Structures 79 (2001), pp. 839-852

The rebuilt UTE Stadium at sunshine and at night…(KÉSZ Ltd.)