# Effects of Flexural Stiffness on Deformation Behaviour of Steel and FRP Stress-Ribbon Bridges
## 3 Experimental Program
### Loading Procedure  
Three loading layouts are considered: one symmetrical and two asymmetrical (with different ratio between the live load, \(q\), and the dead load, \(g\))--_Model-1_ and _Model-2_ were subjected to the same loading schemes. The prototypes were loaded incrementally using iron weights. Figures 3 and 4 show the loading schemes and typical arrangements of the weights corresponding to symmetrical and asymmetrical loading scenarios. The load held constant for two minutes after each loading step to stabilise the vertical displacement of the bridge systems. The increments of the symmetrical load are the following. A timber bridge deck was constructed over the steel ribbons inducing the 0.077 kN/m load at the first step. At the further increments, the iron weights (\(\approx\)24 kg each) were distributed uniformly over the timber deck resulting in approximately 0.31 kN/m load. The final (seventh) increment induced a 2.22 kN/m load.  
Figure 4: Typical loading layouts: (**a**) symmetrical load situation; (**b**) asymmetrical load situation.  
Figure 3: The bridge prototypes’ loading schemes: (**a**) symmetrical load; (**b**) asymmetrical load (\(q/g=0.49\)); (**c**) asymmetrical load (\(q/g=1.17\)).  
Figure 2: Geometry characteristics of the prototypes with different flexural stiffness of stress-ribbons: (**a**) the bridge with flexible bands; (**b**) the bridge with flexural-stiff ribbon-profiles.  
The asymmetrical loads were applied with the ratio \(q/g\) equal to 0.49 and 1.17. In all scenarios, the dead load, \(g\), was distributed over the bridge span in the same manner as in the symmetrical loading case (Figure 3). For the ratio \(q/g=0.49\), the first five loading increments induced the dead load \(g=1.49\) kN/m. The additional live load (\(q\)) applied in two steps has induced 0.73 kN/m distributed over the bridge half span. Analogously, the ratio \(q/g=1.17\) generated in three loading steps to achieve the target load \(g\) and three successive increments to reach the necessary magnitude of the load \(q\). The corresponding load components are the following: \(g=0.93\) kN/m and \(q=1.09\) kN/m.  
Deformations of the stress-ribbons were measured using the 20 mm strain gauges. Vertical displacements of the ribbons and horizontal movements of the supports were monitored using linear variable displacement transducers (LVDT) with a 0.01 mm accuracy. Figure 5 shows the monitoring scheme. In _Model-1_ (Figure 5a), vertical displacements were recorded at the mid-span (LVDT \(I_{3}\), \(I_{4}\), \(I_{9}\), and \(I_{10}\)) and quarters of the span (LVDT \(I_{2}\), \(I_{8}\), \(I_{5}\), and \(I_{11}\)), whereas the LVDT \(I_{12\text{h}}\), \(I_{16\text{h}}\), \(I_{17\text{h}}\), and \(I_{19\text{h}}\) monitored the horizontal movements of the supports. Deformations of the top and bottom surfaces of the steel bands were estimated at the location of the LVDT devices using the strain gauges \(T_{7}\), \(T_{8}\), \(T_{13}\), and \(T_{14}\) (located at the mid-span) and two sets of the indicators (\(T_{3}\), \(T_{4}\), \(T_{5}\), \(T_{6}\) and \(T_{9}\), \(T_{10}\), \(T_{15}\), \(T_{16}\)) placed at quarters of the span. _Model-2_ had a similar monitoring devices' distribution scheme (Figure 5b): the LVDT \(I_{3}\) and \(I_{8}\) were put at the mid-span; two sets of LVDT (\(I_{2}\), \(I_{7}\) and \(I_{4}\), \(I_{9}\)) were located at the span quarters. Four LVDT (\(I_{11\text{h}}\), \(I_{12\text{h}}\); \(I_{16\text{h}}\), and \(I_{17\text{h}}\)) monitored the supports' horizontal movements. Deformations of the top and bottom surfaces of the ribbons were measured at the mid-span (using the gauges \(T_{17}\), \(T_{18}\), \(T_{10}\), and \(T_{12}\)) and the span quarters (strain gauges \(T_{3}\), \(T_{4}\), \(T_{7}\), \(T_{9}\) and \(T_{19}\), \(T_{20}\), \(T_{13}\), \(T_{14}\)).