Geotechnical Engineering Circular No. 9 Design, Analysis, and Testing of Laterally Loaded Deep Foundations that Support Transportation Facilities
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Soldier Rev B
| 8.4.1 Ice Loads AASHTO (2014) includes consideration for ice loads on bridge piers in freshwater lakes and rivers saltwater ice loading conditions requiring specialized analysis, are beyond the scope of the AASHTO specifications and this manual. The expected ice forces are assumed to act directly on the bridge piers and are expected to include the following modes of action Dynamic pressure resulting from moving sheets of ice or ice flows carried by stream, wind, or currents. Static pressure due to thermal movement of ice sheets Pressure resulting from hanging dams or jams of ice Static uplift or vertical loads resulting from adhering ice in fluctuating water levels. AASHTO (2014) Section 3.9 provides a detailed discussion of the development of both lateral and vertical ice loads. Lateral ice loads maybe dependent on the thickness of the ice flow, the crushing strength of the ice and the potential failure mechanism of the ice flow, the width of the pier, the inclination of the pier nose, the size of the stream, and the angle of the pier relative to the ice flow, among other factors. The forces from ice maybe treated as dynamic forces or static forces according to the list above. Dynamic forces for impacts of ice sheets or ice flows should be considered in a dynamic analysis of the bridge model. Such an analysis should consider the potential for resonance between the bridge pier and the ice forces, and should consider the damping coefficient that is applicable to the piers. AASHTO (2014) indicates that Montgomery et al. (1980) found that flexible piers and foundations may cause considerable amplification of dynamic ice forces due to resonance between the ice and the structure at low levels of structural damping. Brown et al. (2010) indicate that drilled shafts may offer an advantage in such a situation compared to driven piles due to relatively high structural rigidity and higher damping than piles. Static loads due to static pressure from thermal ice sheet movement or hanging dams or jams are treated as static loads acting directly on the bridge piers. These loads are incorporated into static structural analyses to determine the applicable force effects acting on the foundation group and elements. Once the loads on the foundation are determined, the analysis for lateral loads proceeds as a conventional lateral load analysis according to the procedure in Chapter 5 and the analysis methods in Chapters 6 and 7. Vertical and uplift forces due to ice must also be considered, but are beyond the scope of this manual. These are discussed in more detail in Brown et al. (2010) for drilled shaft and Hannigan et al. (2016) for driven piles, with detailed procedures for determining structural loads presented in AASHTO (2014). |