THE CONCEPTION OF THE RESISTANCE STRUCTURE

OF THE CITY STADIUM OF CLUJ-NAPOCA UNDER

ACCIDENTAL LOADINGS

PETRINA MIRCEA

NICOLAE SOCACIU

BOGDAN PETRINA

RADU HULEA

RADU ZOICAS

CRISTIAN MOJOLIC

TUDOR PETRINA

ABSTRACT This study describes the accidental loadings on the structure of the City Stadium of

Cluj-Napoca. The structure is made of reinforced concrete frames with isolated foundations

under columns and continuous under the reinforced concrete walls, with a steel structure

for the roof.

The first part of this study contains the detailed description of the structural

solution, in the second chapter, legal issues according to SR EN 1991-1-7 General actions

Accidental actions. The third chapter contains the analyzing of the reinforced concrete

structure in the case of accidental loading. At this point, the displacements and the

deformed shape of the structure in the case of one structural element collapse were

observed in two cases. In the fourth chapter the influence of an accidental action on the

steel structure of the stadium roof due to a structures element collapse was studied. The

fifth chapter includes remarks and conclusions to this study.

Key words: Accidental actions, reinforced concrete structure, structure of the stadium roof

THE PRESENTATION OF THE CITY STADIUM OF CLUJ-

NAPOCA

The stadium is situated in Cluj-Napoca in the Central Park, on the

south side of the Somes River. The new stadium is under construction now,

it has international standards, will have an approximately 30000 capacity,

will follow all the standards imposed by FIFA and UEFA and also will

follow the codes that rules athletics tracks of A category figure 1, [1], [10].

The levels on the height will be: two underground levels, ground

level and two stories in the north and south parts and with five stories in the

main parts. The maximum height is 36.60m and at the cornice is 33.60m,

[1], [10].

Fig.1. City Stadium of Cluj-Napoca

Fig.2. Transversal section of the T2

The foundation solution chosen for all parts is isolated foundation

under the columns and continuous foundation under the reinforced concrete

walls.

The isolated foundations are made of a plain concrete part plus an

upper part made of reinforced concrete. The continuous foundations are also

with a part made of plain concrete plus an upper part made of reinforced

concrete. The isolated foundations go to a depth of -5.15m to -6.55m

(measured from the level 0.00) and at -8.05m in the area where the depth of

the underground is bigger. These foundations are connected by reinforced

concrete beams on both directions. The foundations will be placed for all

parts T1 and T2 in the layer of ground called diorite sand with a

conventional base pressure of Pconv = 750kPa and for the parts P1 and P2 in

the layer made of sand and grabble with a conventional base pressure of

Pconv = 450kPa , [1], [10].

The resistance structure of the stadium is made of frames with

reinforced concrete columns and beams (Fig.2.). The slabs are made of

reinforced concrete cast on site, with or without precast under plates (hp =

20cm) and are computed to have adequate horizontal rigidity to undertake

horizontal loading. The slabs contain beams (cast on site or precast). The

stepped slab where the seats are placed lay on oblique frame beams.

On the contours of the underground levels, reinforced concrete walls

are designed that have tie beams on their base and also upper side. These

walls are hydro-insulated with thermo-welded membranes protected with a

Tefond-type layer. In the joint zone special joint pieces are placed. Because

the water level is rather high, the slab on the ground will have a thickness of

25cm, to resist to water pressure. This slab is anchored to the isolated and

continuous foundations. The reinforcement is designed to undertake water

pressure. First, an equalizing layer of concrete will be placed and then the

hydro-insulation made of thermo-welded membranes is realized. At the

joints, special pieces and plastic taps will be placed. The insulation will be

protected with a thin layer of concrete on which the reinforcement of the

slab will be realized. In the columns and walls zones, rigid hydro-insulations

will be realized that will be connected to the membranes. The vertical

insulation will be connected with the horizontal one, developing a sealed

bowl of the underground levels , [1], [10].

The resistance structure of the roof is made of a plane cantilever

truss that covers the seats (Fig.3.). The steel structure for the roof will be

made of parts pre-assembled or assembled on site on the ground or directly

at the position. On the longitudinal direction plane trusses are designed with

the goal to create rigidity for the cantilevers on that direction. The final

cover will be a light one. At the roof level joints are created by placing

simply supported longitudinal elements. The steel structure of the roof is

divided into four parts and the cantilever trusses are placed on the reinforced

concrete frames. The expansion joints are placed in correspondence with the

joints created in the concrete structure. In these joints the longitudinal

elements are simply supported to the cantilevers.

Fig. 3. The steel structure of the roof. Opening from T2

These trusses are made of a column and a cantilever beam. The truss

is fixed in the reinforced concrete column having the section of 1.20m x

0.80m in four points. The joints where created screwed with base plates,

their dimensions where computed according to the corresponding efforts.

The truss is made of four sections in order to be transported and put

together. The longitudinal parts of the cantilever are made of steel plates

welded together in the form of H, the diagonals and the vertical elements of the truss are made of two U profiles placed face to face and connected with steel plates. The joints between the four sections are made of SIRP.

The joints between the elements of each section are welded, [1], [10].

The structure was made rigid by introducing diagonals in the roof

plane made of prestressed bars. These are of two types: longitudinal and

transversal diagonals. The longitudinal ones were placed at the end parts of

the truss and in the connection area between the column and the beam, in

the free part of the cantilever and on the lower side of the column. The

transversal diagonals are placed two pieces at each end of roof section,

parallel to the truss. The longitudinal diagonals that arent in the roof plane are made of pipe profiles for the longitudinal elements and vertical elements

and have prestressed bars as diagonals.

The longitudinal elements of the roof are pinned to the trusses in the

upper nodes and they are also trusses made of pipe-type profiles. Some of

these longitudinal trusses are linked with ties with the lower node of the

main truss, too. For transversal fixing the lower side of the longitudinal

trusses, transversals are used, [1], [10].

PRESCRIPTION ACCORDING TO SR EN 1991-1-7

This chapter contains legal issues for verifying the structure at

accidental loadings according to the code 1991-1-7, and the consequences of

a local collapse of the structure due to a not specified cause [2].

The strategies that need to be taken into consideration are divided in

two main categories: the first category refers to the identification of the

accidental actions (explosions, impact) and implies the design of the

structure for in insuring minimum properties, preventing or reducing the

accidental action (protection measures) and the design of the structure to

undertake the action [2].

The second category implies strategies based on the limitation of the

local collapse by introducing increased redundancy, by prescriptive rules

(integrity, ductility) and by designing the key-element to undertake the

accidental nominal action [2].

On the base of classifying into importance classes, the City Stadium

of Cluj-Napoca is placed in the class 3 that includes all types of buildings

that are in the class 2 of importance but exceeds the number of levels and

the surface limits; all the buildings that have significant admitted number of

participants; the stadiums with more than 5000 places and buildings that

contain dangerous substances and/or processes [2].

According to this analysis a local collapse due to accidental actions

may be accepted with the condition that it doesnt affect the possibility of emptying the stadium in case of emergency. The structure has to be

designed such as the stability of the entire or a local main structure will not

be affected by a local collapse. The minimum necessary time period for the

structure to survive in the case of an accident will be the one that insures in

safe conditions the evacuation and saving of the persons in the building and

in the nearby zones [2].

The following recommended strategies have to assure for the

building a resistance coefficient big enough to undertake local collapse

without having a disproportioned level of damage. For the buildings from

the class 3 of importance a risk evaluation needs to be made with taking into

consideration all known and not known dangers. According to the code, the

admitted limit of a local collapse is different from building to building, the

recommended value is of minimum 15% from the level surface or 100m2 for

each two adjacent stories figure 4 [2].

Fig. 4. Case of structural element failure

THE DESIGN OF THE REINFORCED CONCRETE STRUCTURE The accidental analysis described in chapter 2 was made in two

hypotheses, the first case by eliminating the reinforced concrete column

having a section of 90x90cm from axis C from the -1 level, and in the

second case the column from axis D from the ground level having the

section of 120x80cm was eliminated. In this case the displaced shape and

the maximum values from the columns, beams and slabs were studied. In

the first case a difference of 1.1cm in the displacement of the node situated

on the upper end of the column was noted. In the case of the column from

axis D a difference of 1.3cm between the displacements of the upper end of

the column was noticed figure 5, 6, 7.

The analysis of the structure under the influence of the accidental loading

was computed in the case of the special group by using the following coefficients: 1.00 for dead load and 0.40 for snow load.

Fig. 5. Initial frame deformed shape Fig. 6. The deformed shape after

column from axis C failure

Fig. 7. The deformed shape after column from axis D failure

THE DESIGN OF THE STEEL STRUCTURE For the steel structure two accidental actions were studied by failure of

one structural element in each case: an element from the lower part and then

an element from the upper side of the cantilever truss.

The analysis is made according to codes and the effect of the

accidental action has to respect the maximum percent given by the code for

the affected zone.

The effect of the accidental action on the adjacent trusses was

studied by comparing stresses and strains and internal forces in them. As

one may see in the figura 8, 9 and in table 1, the case in which the lower

part of the truss collapse is more dangerous.

a) b)

Fig. 8. The deformed shape of the steel structure a)of failure of an

element situated on the lower part of the truss, b) the case of an element

from the upper side of the truss

c)

Fig. 9. The initial deformed shape

Table 1: The displacements of the structure in the studied cases

UX (cm) UY (cm) UZ (cm)

Lower side element failure Maximum

displacement

from adjacent

trusses

-4.10 9.70 -11.80

Upper side element failure -3.10 9.50 -11.50

Initial structure -3.00 9.60 -8.90

After the verification on the adjacent trusses the fact that those dont collapse from a point of view of resistance and stability was seen. The

verification of the steel elements was made according to Eurocode 3. In

table 2 the values of the computing force (NE) divided by the portant

capacity (Nd) are given in some characteristic sections of the adjacent

trusses of the collapsed truss. Were taken into account the models with the

failure of lower part of the truss (a), the upper part of the truss (b) and they

were compared to the initial base moment (c).

In figures 10 and 11 the percentage of participation of all the

elements from the adjacent main trusses and one may observe an increasing

of those after the accidental loading from a maximum of 0.4 to a new

maximum of 0.7.

Table 2. The values of NE/ Nd in different sections of the adjacent

main trusses in the case of the considered models

Verified

Section

Model Structural Fraction

a) Failure of

element from

lower part of the

main truss

b) Failure of element

from upper part of

the main truss

c) Initial

structure a/c b/c

1. T inf 7 0,29 0,26 0,23 1,26 1,13

2. T sup 5 0,14 0,17 0,11 1,27 1,55

3. 2U 180 0,73 0,54 0,37 1,97 1,46

Fig.10. The analysis of stresse from the elements from the adjacent trusses

Fig.11. The analysis of stresses before the producing of the accidental

action.

CONCLUSIONS

The researches on the structure of the stadiumin the case of

accidental actions reflects the fact that when collapsing a key element of the

steel structure of the roof, only the failure of the truss containing that

element occurs. The adjacent trusses have an increase of stresses and strains,

but they dont collapse. For this, the issues presented in chapter 2 are

followed.

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