As a truss with high strength, uniform material and easy installation, steel girder truss is often used as the main load-bearing structure for industrial engineering and civil buildings, such as roofs, bridges and pylons. Due to the long-term load, the deformation of the truss beam will directly affect its fatigue life and ultimately affect the stability of the civil structure. Therefore, under the load conditions, the study of the deformation law of steel girder truss is very important.
Figure 1 Fiber layout on the truss girder
The OFDR technique was used to measure the strain of the steel truss. The test steel girder truss is made up of two trusses and has a length of 4 m. Each truss is made up of equilateral angle steel. Polyimide fiber and ETFE tightly-packed fiber are laid on one of the trusses, as shown in Figure 1. Polyimide fibers were attached to the positions 1, 2, 3, 4, and 5, and ETFE tightly-packed fibers were attached to the 6th, 7th, and 8th positions for a total of 8 segments. Each segment of fiber is approximately 30 cm in length. The load is applied to the entire steel truss beam by the load-bearing beam. The strain of the steel truss beam is measured by OSI-S under each load and the spatial resolution is 1 cm.
Figure 2 Steel truss girder
The strain measurement results of the steel truss under each load are shown in Figure 3. Under different loads, the strain distribution on the truss is basically the same. The inclined truss beams (1, 5, 6) bear compressive stress, the transverse truss beams (2, 3, 4, 7, 8) bear tensile stress and the strain distribution of segment 1 and segment 5(or 6) is symmetrical.
Figure 3 Results of strain
As the load increases, the strain at each position increases. The measurement results of different optical fibers at the same position are basically the same, indicating that both of the polyimide fiber and the ETFE tightly-packed fiber can perform very good strain measurement.