Experimental Identification of Waves Generated by Ribbon-Type Pontoon Bridge and Their Effect on Its Maximum Draught

The paper presents the model, methodology and results of experimental research focused on identification of the wave form generated during the crossing of 30-ton and 60-ton vehicles on a ribbon-type pontoon bridge and the analysis of its influence on the characteristics of the maximum draught. A review of the literature revealed that ribbon-type pontoon bridges are subject to significant vertical deflection. This results from the need to generate sufficient buoyant force to balance the weight of crossing vehicles. The area of maximum draught occurs directly beneath the vehicle and moves along with it, generating a front wave—referred to as a bow wave—which propagates along the crossing and alters the local draught of individual pontoons. Due to the fact that pontoon bridges transfer loads through buoyancy force, a key issue in the process of their design is the precise knowledge of the formation of the volume of the droughted part. No information was found in any publication about the influence of the front wave on the draught form of a ribbon-type pontoon bridge. Their authors do not indicate that the analytical or simulation models they use reflect this phenomenon. Equally, the analysis of the methodologies and results of experimental studies in this area did not show that any attempts were made to identify the form of the front wave. The paper presents the results of measurements of vertical displacements of individual pontoon blocks of the crossing and the characteristics of the front wave occurring during the passing of 30- and 60-ton vehicles with speeds ranging from 7.4 to 30 km/h. Based on the obtained data, an attempt was made to identify the phenomenon of undulation of the surface of the water obstacle and its impact on the loads on the bridge structure. The results allow for identifying a significant front wave with a wavelength of 30–50 m, appearing clearly at speeds above 21 km/h. This wave substantially affects the draught measurement—at a speed of 25 km/h, the maximum draught increased by approximately 30%. Statistical analysis confirmed the significance of this effect (p < 0.05), indicating that wave formation must be considered for accurate determination of pontoon block draught. Furthermore, the mass of the vehicle had a strong influence on the wave and draught parameters—the 60-ton vehicle produced wave troughs and draught depths 55–65% greater than those of the 30-ton vehicle.