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Creating and Renewing Urban Structures 1
Upgrading of a 70 year old Grandstand
István BÓDI
Assoc. Professor
Budapest University of
Technology and
Economics (BUTE)
Budapest, Hungary
bodi@vbt.bme.hu
István Bódi, born 1954, received
his civil engineering degree in
1978 and his PhD degree in
1997, both from the BUTE.
Kálmán KORIS
Assist. Professor
Budapest University of
Technology and
Economics (BUTE)
Budapest, Hungary
koris@vbt.bme.hu
Kálmán Koris, born 1970,
received his civil engineering
degree from the Univ. of .
Technology, Budapest in 1993
József ALMÁSI
Honorary Assoc. Professor
Director
CAEC Almási Engineering
Consulting Kft.
Budapest, Hungary
caec@t-online.hu
József Almási, born 1940,
received his civil engineering
degree in 1964 and his Dr. Univ.
degree in 1972, from the BUTE.
Summary
The Kerepesi Ügető (racecourse) in Budapest included several reinforced concrete grandstands of
different classes for use by the audience. The racecourse was closed in year 2000 and most of its
buildings were demolished except the Class II. Grandstand which was declared as a national
monument. Our task was on one hand to perform a complete statical investigation for this Grandstand,
on the other hand the methodology of the strengthening and renovation had to be developed. Statical
investigations of the Grandstand included in-situ measurements, material tests in the laboratory and
finite element analysis of the structure. Results of statical investigation showed that the requirements
of the European Standard (EC) are satisfied for most of the controlled cross-sections and structural
members, however the load carrying capacity was insufficient in some places therefore strengthening
was necessary. Strengthening methods included injection of cracks, integration of new structural
elements (anchoring beam, suspending column), application of new concrete shell on some of the
columns and application of CFRP (carbon fiber reinforced polymer) sheets on roof beams. The
strengthening extended the life-span of this Grandstand by 50 years.
Keywords: grandstand; reinforced concrete; strengthening; CFRP sheets; concrete jacketing.
1. Introduction
The building-complex of Kerepesi Ügető
(racecourse) in Budapest (Hungary) included
several reinforced concrete grandstands of
different classes for use by the audience. The
racecourse was closed in year 2000 and the land
was sold for investors who utilized the ground
for the construction of the second largest
shopping centre and amusing complex in Europe.
Most of the buildings of the racecourse were
demolished except the Class II. Grandstand
(Fig. 1) which was declared as a national
monument. Our task was on one hand to perform
a complete statical investigation for this
Grandstand, on the other hand the methodology
of the strengthening and renovation had to be
developed considering the seamless integration
of the old Grandstand and the surrounding urban
environment including the complex of the new
shopping centre [1]. Other important aspects of
the strengthening were to renew the function of
the structure and to extend the life-span of this
Grandstand by 50 years.
F
ig. 1: View of the Grandstand before renovation
2 17TH CONGRESS OF IABSE, CHICAGO, 2008
2. Historical and structural overview of the Grandstand
The building-complex of the racecourse was built between 1935 and 1941 according to the plans
(Fig. 2) of Ferenc Paulheim Jr. architect [2]. Structural plans and statical calculations were
performed by Vilmos Obrist civil engineer [3], in 1936. The Class II. Grandstand was built on the
basis of original plans with minimum changes in the construction. No other modifications or
strengthening were performed on the structure during the next 66 years. The structure remained
intact even during the II. World War.
The superstructure of the Grandstand is a monolithic reinforced concrete frame with crossway
beams supporting the concrete slabs that are directly carrying the loads [3]. The roof is a ripped
concrete slab structure supported by cantilever beams of the frame. Equilibrium of the cantilever
beams are ensured by tensioned columns. The reinforced concrete frames have pillar foundations.
The two-storey Grandstand has curved concrete stairs leading to the second floor.
Fig. 2: Original plan of the Class II. Grandstand (1935)
3. Investigations of the Grandstand
3.1 Investigations on site
The Grandstand was investigated six times in 2002. Physical conditions of the building were recorded
by visual checking and the amount and types of structural damages were also registered during these
investigations. Concrete core samples were bored at 7 different locations. Core samples were later
used for destructive laboratory tests. Structural uncovering was performed at several locations to
identify the size and location of the steel bars. A Proceq Scanlog profometer was also used for the
same purpose at different locations of the building. The profometer is a device using non-destructive
pulse-induction technology to the detection and analysis of rebar systems in concrete. The strength of
reinforcing steel was examined by Poldihammer. The Poldihammer is handy equipment for hardness
test. It consists of a firing pin led in a case, which carries down a hardened steel ball of 10 mm in
Creating and Renewing Urban Structures 3
diameter. By the impact with one about 1 kg heavy
hand hammer is pressed at the same time the ball
into the test sample and into a laterally introduced
piece of comparison made of metal. From the
relationship of the two diameters of impression with
a simple formula, the hardness of the test specimen
is computed. Some results of the investigations by
Poldihammer are presented in Table 1. Non-
destructive concrete quality testing was performed
by N-type Schmidt hammer in 49 different points of
the structure. A Schmidt hammer (also known as a
Swiss hammer) is a device to measure the strength
of concrete. It measures the rebound of a spring
loaded mass impacting against the surface of the
sample. Results of non-destructive concrete quality
tests were corrected by the laboratory test results.
During our investigations on the site, no visible sign
of major damage or overloading of reinforced
concrete structures could be detected [1]. However
cracks were spotted at the connections of outside
columns and cantilever beams. These cracks were
mainly caused by tensile forces in the columns.
Some cracks caused by shrinkage of the concrete were also detected in the secondary structures such
as concrete barriers and banisters. Higher grade of corrosion of reinforcing steel bars and the lack of
concrete cover were observed on the columns of the roof floor (Fig. 3). These problems were mainly
caused by water isolation problems. No sign of surface corrosion or decrease of bond between steel
bars and concrete was detected in case of uncovered beams and columns. Nevertheless of the
recorded damages, no major deterioration of the load carrying structures could be observed.
Table 1: Results of in-situ investigations by Poldihammer
Rebar Comparison
metal
Measured
values Mean value
1 3,70 3,00 22,2
2 4,00 3,20 21,5
3 4,05 3,25 21,6
4 2,95 2,50 25,7
5 3,25 2,60 21,1
6 3,25 2,55 20,05
Beam 22,3 230 Ø = 16 mm
(plain)
Column 21,8 225 Ø = 24 mm
(plain)
Number
Place of
investigation
Impression
[mm]
Strength
[Mp/in
2
]Design value
of strength
[N/mm
2
]
Remarks
3.2 Laboratory tests
Cylinder shaped concrete specimens were prepared from the core samples bored on site for
destructive testing. The diameter of the specimens was 63 or 73 mm (according to the inner
diameter of the drill head used on site) and the height of the cylinders was between 98 and
141 mm. Uniaxial compression tests were carried out on the concrete specimens in the
Structural Laboratory of Budapest University of Technology and Economics (Fig. 4). Test
results were evaluated according to the Standard MSZ 4720 for different structural groups
(beams, columns, slabs, balustrades) so we got the characteristic values of concrete strength for
F
i
g
. 3: Deterioration o
f
a column on the roo
f
4 17TH CONGRESS OF IABSE, CHICAGO, 2008
each group [1]. Deviation of the concrete
strength in case of some columns was
significantly higher than expected. It turned out
that there were originally chimneys inside of
these columns. The impact of the high
temperature gases streaming inside these
chimneys resulted in significant decrease of the
local concrete strength. Concrete strength was
also evaluated by in-situ non-destructive tests
based on the hardness of the concrete surface.
Results of the compression tests were used for
the calibration of the non-destructive test results.
Strength of the plain reinforcing steel bars was
determined by in-situ investigation using
Poldihammer [1]. The value of steel strength
was around 210 N/mm2. Tensile test was
performed in the laboratory on some steel bars
taken from the Grandstand during the
investigation on site. Results of the tensile tests
were used for the refinement of the in-situ test
results.
3.3 Statical analysis of the structure
The design values of internal forces were derived by computer analysis [1]. The finite element
model (Fig. 5) of the Grandstand was prepared using the Axis VM 6.0 software package.
Geometrical sizes measured on site and material properties derived from in-situ and laboratory tests
were used during the calculations. The possible action groups as well as local effects – such as
increased snow load and concentrated service load – were considered during the analysis. The
actions were calculated according to the European Standard “MSZ ENV 1991 Eurocode 1: Basis of
design and Actions on Structures”. A simplified calculation method was also used to control the
results of the finite element simulation.
Fig. 5: Finite element mesh and rendered view of the computer model for the Grandstand
F
ig. 4: Testing of a concrete specimen
Creating and Renewing Urban Structures 5
The typical cross sections were controlled by the Standard MSZ ENV 1992-1-1 Eurocode 2:
“Design of Concrete Structures. General rules and rules for buildings”. Statical investigations were
performed in 26 different cross sections. Beam sections were examined for bending and shear with
or without simultaneous axial force (depending on the location of the beam). Column sections were
examined for eccentric compression or tension. Deflection of the structure was also evaluated and
checked. Local values of concrete and reinforcing steel strengths derived from in-situ and
laboratory tests were used for the calculation. Material characteristics beyond strength were taken
from Eurocode 2 Standard. The geometrical data (including the amount of reinforcing steel) of
different cross sections were taken from structural investigations on the site as well as from original
plans. Most of the controlled cross section fully satisfied the requirements of the Eurocode Standard,
however the load carrying capacity was insufficient in some places. The tensioned columns outside
the roof that provide anchorage to the cantilever beams were in ultimate limit state. The load
carrying capacity of the 6 cm thick stepped concrete slab is satisfactory in case of distributed loads
but it is insufficient in case of concentrated live load (Q = 1.5 kN according to the Eurocode 1
Standard). Load carrying capacity of the longitudinal beams on the first floor as well as the
resistance of the front column under the first floor was insufficient. Due to these problems
strengthening of the Grandstand had to be performed as follows.
4. Strengthening of the Grandstand
Results of the complete statical investigation were used to plan the necessary construction works
that could extend the life-span of the Grandstand with additional 50 years. No major damage of the
reinforced concrete structure was found, however the resistance of some cross-sections did not
fulfill the requirements of the Eurocode Standards (EC1 and EC2), therefore the following
structural strengthening was implemented [4].
To provide appropriate anchorage for the cantilever structure, new suspending columns were
manufactured (Fig. 7). A new anchorage beam was also applied above the second level to withstand
the additional tension forces. Cantilever beams on the roof were strengthened by CFRP sheets
(Fig. 6) to provide the necessary load bearing capacity [5]. Cracks in the concrete structure were
cleaned and injected with MAPEI Epojet resin before strengthening (Fig. 6).
The concrete strength in the upper section of middle columns was insufficient therefore these
columns were also strengthened by 5 cm concrete jacketing (Fig. 7). Former chimneys were cleaned
with water jet and the holes were filled with concrete C20-8/K.
Fig. 6: Strengthening of the cantilever structure: a) New suspension column; b) Injection of cracks;
c) CFRP sheets
a
b
c
6 17TH CONGRESS OF IABSE, CHICAGO, 2008
Fig. 7. Strengthening plan of cantilever structure (2003)
The stepped concrete slab of the Grandstand was built with a thickness of 6 cm and the applied
reinforcing steel inside the slab was only Ø5/120 mm. Due to this reasons the resistance of the slab
is insufficient against concentrated live load. A force distribution layer was applied on the slab to
provide the necessary resistance against concentrated loads.
Shrinkage cracks were observed in the secondary concrete structures such as curved stairs, concrete
barriers and banisters. These cracks were cleaned and injected with MAPEI Epojet resin to avoid
further corrosion problems.
Strengthening of the reinforced concrete structural parts was followed by complete restoration of
the Grandstand including isolation of the roof, facing of walls and columns and tiling of floors and
stairs, decorative lighting, etc. (Fig. 8).
Creating and Renewing Urban Structures 7
5. Conclusions
Most of the buildings of the former racecourse in Budapest were demolished to permit the
construction of a new shopping centre. The building of class II. Grandstand was declared as a national
monument so it was preserved and integrated into the new building complex. A complete statical
investigation of the Grandstand was carried out including measurements on site, laboratory tests and
computer analysis. The strengthening of the building was designed and performed in view of the
results of the statical investigations. The strengthening and complete renovation (Fig. 8) extended the
life-span of the structure by 50 years and ensured the seamless integration of the 70 years old
Grandstand and the complex new of shopping centre.
6. References
[1] BÓDI I., KORIS K. and ERDŐDI L., “Statical condition of load bearing structures of II. and
III. class Kerepesi Grandstands, Budapest”, Final Report, BUTE Department of Structural
Engineering, Budapest, 2002.
[2] PAULHEIM F. JR., “Plans of the II. class Kerepesi Grandstand”, Budapest, 1935.
[3] OBRIST V., “Statical calculations of the reinforced concrete structures and the foundations of
II. class Kerepesi Grandstand”, Budapest 1936.
[4] ALMÁSI J., VARVASOVSZKY P. and JUHÁSZ S., “Strengthening plan of cantilever
structure of II. class Kerepesi Grandstand”, CAEC Kft., Budapest 2003.
[5] Sika Hungária Kft., “Technical Guide for the Sika CarboDur Composite Strengthening
Systems”, Budapest 1999.
F
ig. 8: View of the Grandstand after renovation