Natural hazards (optimisation of protection, interaction with structures)

Temperature gradients in a composite steel-concrete road bridge

J. Římal, V. Křístek, V. Kuráž, V. Jelínek, A. Kovářová & J. Zaoralová Faculty of Civil Engineering, Czech Technical University in

1 DESCRIPTION OF THE BRIDGE The composite steel and concrete bridge structure over the Vltava River in Prague, the Barikadniku Bridge, carries six lanes of car traffic of one of the principal arterial roads in the capital of Prague, Fig.1. Each traffic direction is carried by a separate bridge. The structure of the bridge, consisting of two box girders connected by a slab, is continuous, of four spans, viz. 46.4 + 51.1 + 51.75 + 46.1 m; the structure is supported by six piers. The diaphragms are lattice work, sufficiently rigid in their own planes to prevent the deformation of the cross-sectional shape, but entirely flexible perpendicu- larly to this plane; they are not connected to the cantilevers of the cross sections (Fig. 2) and they are placed in the end cross sections of the bridge and above the interior sup- ports (intermediate cross sections are not braced). The structure is composite: the road- way slab is made of concrete, the webs and the lower flanges are made of steel and they are longitudinally and transversely stiffened.

Fig. 1 - The Barikadniku Bridge (foto Dhípa Dás)

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2 MEASUREMENT OF TEMPERATURE GRADIENTS IN THE BRIDGE STRUCTURE The measurement method applied involved the measurement of temperature gradi- ents applying platinum sensors. This method was selected because platinum sensors possess long-term stability of their electrical parameters achieving relatively high meas- urement accuracy. Because of their application on the composite steel and concrete structure, two types of temperature sensors were developed for the measurement pur- poses. Based on commercially available resistance sensors, the following modifications were constructed: • contact sensors for temperature measurement of steel structures • probes for temperature measurement inside concrete. The principal demand for the development of contact sensors was to achieve the op- timum heat transfer between the sensor and the measured structure (steel), while providing maximum thermal insulation of the sensor in relation to the outside environment. The developed sensor had a large contact area of 1260 mm2. The probes for temperature measurements inside concrete were mounted inside the concrete slab to measure the temperature gradient along the height of the slab. In order to reach the highest possible measurement precision, all the sensors were individually calibrated. The whole measurement system was verified in the laboratory. The placement of resistance temperature sensors is shown in Fig.3.

Fig. 2 - The Barikadniku Bridge (foto Dhípa Dás) – arrangement of cross-sections

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Fig. 3 The Barikadniku Bridge - Scheme of Placing of Temperature Sensors

3 MEASUREMENT RESULTS The results of the measurements are graphically presented in the following page.

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BARIKÁDNÍKŮ BRIDGE - Temperature Gradients 11 th July 1981 240 3ĜtURGQtNDWDVWURI\ RSWLPDOL]DFHRFKUDQ\LQWHUDNFHVHVWDYHEQtPLNRQVWUXNFHPL 

No. 3 TIMEMEASUREMENTOF SENSOR -STEEL STRUCTURE SENSOR STRUCTURE -CONCRETE No. 2 No. 1

150 No. 0 Natural hazards(optimisationofprotection,interactionwithstructures) 20:00 16:00 230 4 6 No.4 5 21:00 17:00 760 2000

No.6 22:00 18:00 21:00 17:00 18:00 22:00 16:00 760 20:00 19:00 19:00

No.5

100 TEMPERATURE [°C]

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4 CONCLUSIONS In designing composite steel and concrete bridge structures, the potential non-uniform warming of the load-bearing bridge cross section due to different thermal conductivity and different thickness of both materials constituting the cross section must be consid- ered. This is given by different insulation characteristics of both structure parts and dif- ferent conditions during the bridge structure cooling by airflow. Furthermore, we must consider some specific circumstances such as geographical altitude at which the bridge was built, the climate conditions, bridge north-south orientation, the road pavement thickness etc. The results of the measurements on the Barikadniku Bridge may be summed up as follows: • the temperature distribution along the thickness of the concrete slab may be considered as linear • the highest temperature difference between concrete and steel in summer is -6.30C or +8.50C respectively. The minus sign indicates that the plate is colder than the girder while plus indicates that the plate is warmer than the girder.

ACKNOWLEDGEMENTS

This research has been supported by the Grant Agency of the Czech Republic – grants No. 103/09/1149 and 103/08/1677 and the Research Project MSM 6840770005.

REFERENCES

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