CONTAINMENT LEVEL H4b RESTRAINT SYSTEM ON THE HUGE GERMAN SIEGTAL-BRIDGE - A PROJECT REPORT -

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25 Νοε 2013 (πριν από 3 χρόνια και 8 μήνες)

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CONTAINMENT LEVEL H4b RESTRAINT SYSTEM

ON THE HUGE GERMAN SIEGTAL
-
BRIDGE

-

A PROJECT REPORT
-

Bmst. Dipl.
-
Ing. Thomas Edl

DELTA BLOC EUROPA

GmbH
, Precast Concrete Barrier Systems

www.deltabloc.com


Key words:

precast concrete barrier system, containment l
evel, H4b, EN 1317, dilatation,
Siegtal bridge

Abstract:
After some heavy accidents on bridges in the past where heavy vehicles broke
through the insufficient safety barrier and fell onto residential areas located underneath,
experts throughout Europe dema
nd the highest containment level for bridges where third
parties are endangered. Therefore the decision was made to apply a H4b restraint system
on the 1050m German Siegtal
-
bridge as part of the reconstruction of the bridges edge
beam. The challenge was t
o deal with the requirement for minimum stress in the bridge
structure even due to a heavy impact and to handle a dilatation in two axis by keeping all
the features of the restraint system.

1. THE GERMAN SIEGTAL
-

BRIDGE

The bridge was designed by Hans Wi
ttfoht and was opened in 1969. In the run of the A45
motorway it crosses the Siegtal valley on a length of more than one kilometre in a height of
up to 100 metres above the bottom of the valley. Parts of the area underneath the bridge are
densely populated
, partly railway tracks and streets cross the valley.

The bridge consists of two separate structures, each 1.050 metres long. It is supported by 12
pillars with a span of 63 to 105 metres in between. The main construction is a concrete box
girder with a he
ight of 5,80 metres and a total width of 30.5 metres including the cantilever
slabs on each side of the box girder. The bridge follows a curve with a main radius of 1.400
metres.

On each side of the bridge a dilatation of 90 centimetres in lateral directio
n as well as 16
centimetres in radial direction due to the curved line routeing is possible.



Figure
1
: Bridge over the Siegtal


length 1.050m, height 96m

After a main examination of the more than 30 years old concrete bridge i
t was decided to
reconstruct some parts of the box girder, the bearings, the bridge deck, the bridge edge
beams and also the restraint system.

For the decision what containment level is needed for securing the bridge experts consulted
the following criteri
a:



How big is the share of trucks/day?



What speed is allowed ?



Are there higher ranking streets underneath?



Are there residential areas underneath?



Are there railway tracks underneath?



Are there industrial or chemical plants or sensible
-
environmentally pro
tected areas
in this endangered region?

Bearing these aspects and having the responsibility to eliminate the endangerment of third
parties underneath the bridge the authorities and engineers decided to use a precast concrete
restraint system


containment
level H4b.



Figure 2: Precast concrete barrier system DB 100 AS
-
R


containment level H4b

2. THE CHOSEN RESTRAINT SYSTEM

Actually there are only a few restraint systems available on the market that could probably
meet the special requirements of this pro
ject. A very important feature of the chosen precast
concrete barrier was the behaviour of the barrier at a heavy impact and its positive effects
for the bridge structure.


An impact of a vehicle might be the most hazardous load for the edge beam. So the
engineers wanted to know more about impact forces to be sure that the 30 year old bridge
structure is able to handle an H4b crash. With the results of recent research projects carried
out in Austria and Germany they were aware of the necessity for a restra
int system that is
able to manage both: avoiding a breakthrough of vehicles and providing minimum stress for
the bridge structure at an impact.


Therefore the chosen precast concrete barrier system was perfectly suitable for these special
requirements. Whe
n the full scale crash tests were carried out at accredited test houses the
chronological run of the forces generated in the bridge edge beam and the bridge structure
were measured. Now these data can be used for designing new bridges on one hand and of
co
urse to evaluate the sufficiency of existing bridge structures when upgrading existing
restraint systems on the other hand. Hence it is possible to design a bridge by taking into
consideration the real characteristic forces that will occur due to an heavy
impact.

For dimensioning the bridges edge beam and the shear rails only a horizontal force of
h=75[kN/m] has to be considered when using Delta Bloc 100 AS
-
R. There is no bending
moment to calculate with because there is no anchoring of the barrier within t
he tension
area (see also Figure 11, 12). Actually the chosen type of barrier only needs one M16 bolt
every 6 metres for position fixing


therefore the flow of impact loads into the bridge
structure is “soft”. For calculating the resistance of the cantile
ver slab the load case would
be as shown in Figure 3.


h=70[kN/m], v=100[kN/m], m=100[kNm/m]

Figure 3: Accidental load case “Impact”

Another essential part of this precast concrete system is the continuous tension bar. A
patented coupling links the indiv
idual elements thus building a sort of tensioned link chain.
A steel band runs longitudinally through the precast elements, thus providing a continuous
steel tension bar with a precisely defined tensile force that absorbs the impact energy and
prevents bre
aking through.


Figure 4: Continuous steel tension bar with special couplings inside the concrete elements

3. THE CRASH TESTS

In Europe the restraint systems ha
ve to be tested according to the European standard
EN

1317. This means that a H4b system has to withstand an impact of a 38 ton truck. The
barrier also has to fulfil some other aspects like redirecting the vehicle back onto the
carriage way or providing a
“soft” impact behaviour to prevent heavy injuries for car
passengers.

The crash tests were performed on a true to original built bridge deck construction on the
testing ground of the TÜV in Munich under the supervision of the Federal office for Road
Admini
stration („Bundesanstalt für Straßenwesen
-
BASt).

The system was successfully tested for containment level H4b (TB 11 and TB 81).
The ASI
value (Acceleration Severity Index) was within the boundaries according to the EN

1317
and classified as level B. The
deflection of 88 cm makes up a working width of 146 cm
(=

level W5: width of the system plus its maximum deflection during the impact.)
A
handrail mounted at a distance of 112 cm from the backside of the restraint system
remained totally unaffected.



Figure 5, 6: H4b/TB81 test with a 38 ton truck at 65 km/h

TB 11



car impact test
: At a speed of 100 km/h a 900 kg vehicle was driven into the
restraint system at an impact angle of 20°, from which it was guided back to the driving
lane conforming to the
standards.

TB 81


truck impact test
: The crash test with a 38 ton truck at 65 km/h and 20° of impact
angle was also passed positively. The M16 anchor was shorn off as expected, deflection
was only 88 cm. A number of sensors thereby recorded all substantia
l forces acting upon
the bridge.

If this accident had happened on a real bridge only a few elements would have had to be
exchanged thereafter which would have taken only 90 minutes to be done.


Figure 7, 8: Restraint system before and after the H4b test

3. THE INSTALLATION

Both sides of the bridge were equipped with the Delta Bloc precast concrete elements
within 4 days. The barrier was transported to the construction site by lorry, installation took
place by means of a mobile crane. The asymmetric eleme
nts were connected to each other
with the patented couplings. To secure their position the elements were fixed to the bridge
deck only every 6 metres with one M16 anchoring bolt as mentioned above.



Figure 9, 10: Reconstruction of the edge beam and inst
allation of the precast barrier system



Figure 11, 12: The stiffening plate at the bottom is anchored with one M16 bolt which is
positioned on the opposite side of the impact
-

therefore no bending moment can be induced
into the bridge edge beam


A
special challenge was to implement the expansion joints at both ends of the bridge with a
longitudinal movement of 90 centimetres and a radial movement of 16 centimetres without
losing the features of a continuous tension bar. Therefore a special dilatatio
n element was
built with a hydraulic damper and Teflon bearings to prevent constraint forces within the
chain of elements.




Figure 13, 14: D
ilatation elements on a steel sledge and Teflon bearings


ready installed
with a steel cover



Figure 15: Dilatation of the bridge in neutral position


possible movements are indicated

SUMMARY

The safety barriers were installed on both sides of
the bridge within four days to the full
satisfaction of the customer
-

the dilatation elements work as well as expected. The Siegtal
-
bridge is now safe at the containment level H4b, secured by Delta Bloc DB 100 AS
-
R
precast concrete barriers. The next step

in the process of reconstruction is now the exchange
of the old steel central reserve restraint system. Therefore the DB 80 AS
-
R with
containment level H2 will be installed
by the end of

2006.

More information at:


www.deltabloc.com
.

Bmst. Dipl.
-
Ing Thomas Edl


DELTA BLOC EUROPA GMBH


A
-
2700 Wiener Neustadt, Postfach 153

Tel.: 0043 (0) 2622 / 400
-

144

Fax: 0043 (0) 2622 / 400
-

130

Mobil: 0043 (0) 664 / 819 65 23

thomas.edl@
deltabloc
.
com

www.deltabloc.com




B
or
n
on the
05.03.1975


Graduate in civil engineering at the Technical University of Vienna 01/2001


Several years of experience
as

constructional engineer (focused on concrete and
timber

structures
)


Division manager

at

DELTA BLOC EUROPA
GMBH
since 2005
and
in charge of
technical development and license contracting


Active member of the “Working Group for Road Restraint Systems”

of the
European Road Federation

ERF


DELTA BLOC EUROPA GMBH is developer of the precast concrete barrier system
“DELTA BLOC
®


and li
censor in 20 countries in Europe.