# Temperature Effects on the Natural Frequencies of Composite Girders
## 3 Experiments on Temperature Effects  
### Test Specimen and Measurement Setup  
A composite steel plate girder (Figure 1) was constructed for modal tests to investigate the effects of temperature on its natural frequencies. The girder consisted of an SM355 steel I-beam and a concrete deck. An H150 \(\times\) 100 \(\times\) 6 \(\times\) 9 rolled section was used for the beam, and shear stiffeners were installed every 375 mm. The stiffeners were 6 mm thick and welded to the web and flange of the beam. The beam span length was 3000 mm. The width and the thickness of the deck were 500 mm and 55 mm, respectively. The concrete compressive strength was 27.8 MPa as evaluated through six cylindrical compressive tests conducted at 28 days. Thirty-six welded headed studs were used to attach the steel beam and the concrete deck for composite action.  
A bearing device was designed to provide simply supported boundary conditions for the composite girder. The bearing device consisted of lug plates and cylindrical bars, as shown in Figure 2. Two types of lug plates were machined to simulate hinge and roller conditions. Circular holes were created in the lug plates for the hinge, and slotted holes were created for the roller.  
To control the temperature at the top of the deck, a positive temperature coefficient (PTC) film was attached as shown in Figure 3. A PTC film was a planar element that generated heat using electrodes; it was formed by fixing a copper foil on a film coated with a carbon heating element. A temperature controller was attached to the PTC film, and the PTC film was covered with a curing cloth to maintain a constant temperature. The temperature of the top deck could be increased up to 50 \({}^{\circ}\)C using the PTC film.  
Figure 1: Dimensions of the specimen.  
Figure 2: Bearing devices: (**a**) hinge support; and (**b**) roller support.  
In this study, accelerations and static displacements were measured in addition to temperature changes. Eight (T1 to T8) adhesive-type thermocouples (RKC ST-50 (RKC Instrument Inc., South Bend, IN, USA)) were used to measure the temperature distribution of the specimen. Three thermocouples were attached at the midspan, and one thermocouple was attached at one-sixth and one-third of the span on the top deck. Along the depth direction, three thermocouples were attached underneath the top flange, midweb, and above the bottom flange separately. The thermocouples were connected to a data logger (Hioki Memory Hillogger LR8431, (Hioki, Seoul, Republic of Korea)). Additionally, a thermometer was installed near the specimen to measure the room temperature. Two displacement transducers (CDP-25 (TML, Tokyo, Japan)) were installed to measure the static responses of the specimen with temperature variations. For the vertical response, one displacement transducer was installed under the steel beam at the midspan. The other transducer was installed horizontally at the end of the roller support to measure its movement. Five (A1 to A5) accelerometers (PCB 393 B12 (PCB Piezotronics, Depew, NY, USA)) with a sensitivity of 10 V/g, a resolution of 8 \(\times\) 10\({}^{-6}\) g rms, and a frequency range of 0.15-1000 Hz were installed under the bottom flange using magnets to measure the vertical acceleration of the specimen. The accelerometers were positioned at uniform intervals of 0.56 m with the first accelerometer (A1) and the final accelerometer (A5) located 0.38 m away from the supports, as shown in Figure 4a,b.  
Figure 4: Schematic views of the measurement setup: (**a**) top view of the concrete; and (**b**) side view of the specimen.  
Figure 3: PTC film on the top deck of the concrete.