Effect of Overweight Vehicles on the Design of PC Girder Bridges

Overloading has become a major concern for engineers in recent years. The mentality of logistics service providers towards increasing their profit margins and higher transportation and fuel costs in middle-income countries like Bangladesh induce overloading of freight traffic. These result in an increase in the number of accidents due to braking system failure and infrastructure damage such as roads and bridges. Increased frequency of overloads may trigger shorter service life of critical components and perhaps catastrophic bridge failure. This study aims to assess the impact of overweight vehicle on the design of prestressed concrete girder bridges, which comprise the majority of highway bridges. For this purpose, an overweight vehicle has been selected investigating monthly overweight truck status report from a previous study. Bridges of four different spans (30 m, 35 m, 40 m and 45 m) have been modeled and designed in CSiBridge for strength and serviceability combination. To explore the effects of overloading, series of selected overweight vehicles were driven over those bridges. Parameters considered for studying the effect are maximum mid span moment, D/C ratio, maximum reactions at supports for Strength I combination and girder bottom tensile stress at Service III combination. It has been observed that maximum moment has been increased by 20.46% for 30 m bridge, 25.74% for 35 m bridge, 31.59% for 40 m bridge and 37.89% for 45 m bridge. D/C ratio has been increased by 19.76% for 30 m bridge, 35.33% for 35 m, 41.44% for 40 m bridge and 32.41% for 45 m bridge. Substantial changes have been noticed in girder bottom tensile stresses. Stress has been increased by 625.8% for 30 m bridge, 1995% for 35 m bridge, 884.5% for 40 m bridge and 763.8% for 45 m bridge. Maximum support reaction has been increased by 44.33% for 30 m bridge, 37.83% for 35 m bridge, 48.77% for 40 m bridge and 41.63% for 45 m bridge for interior girders and for exterior girders 32.55% for 30 m bridge, 32.48% for 35 m bridge, 37.20% for 40 m bridge and 35.79% for 45 m bridge. This study provides quantitative evidence of damages caused by overweight vehicles to highway bridges and represents the significance of overloading in the design of pc girder bridges.