Probabilistic analysis of exterior hanging scaffold strength under impact load

Abstract

Mega bridges require maintenance after long-term service. Exterior hanging scaffolds are widely employe to ensure that traffic is not disrupted during the construction. The working platform, composed of the light steel beam and wooden plane, is usually eccentrically hanged under the deck. Additional horizontal support fixed on the girder is needed to balance the huge moment, i.e. rubber pad or spring bearing. With the eccentric structure, the impact load is an important factor that affects scaffolding failure during the construction process. This study focused on the safety of typical exterior hanging scaffolds used in the rehabilitation of the Nanjing Yangtze River Bridge. First, on-site impact tests were carried out. The proposed regression model for the impact force history achieved satisfactory precision in comparison with the monitoring results. To carry out further probabilistic analysis, a numerical model of this scaffold was developed with the ABAQUS software, and was verified with the on-site monitored acceleration history under an impact load. Based on this model, the Latin hypercube sampling method was adopted to calculate the probability of the fall-induced impact stress in the scaffold. Additionally, a partial correlation coefficient was used to evaluate the sensitivity of the random parameters. In the random simulations, the location of the maximum stress was always close to the rubber pads regardless of the impact location. The variability in the maximum stress of the steel beams was smaller than that of the wooden plane. As the falling weight increased, the failure probability of the steel beams increased faster than that of the wooden plane. To this end, the key component in the exterior hanging scaffold moved from the wooden plane to the steel beams when the falling weight was larger than 200 kg.