Geotechnical Engineering Circular No. 9 Design, Analysis, and Testing of Laterally Loaded Deep Foundations that Support Transportation Facilities
Recommendations Regarding Strain Wedge Model Method
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| 6.4.1 Recommendations Regarding Strain Wedge Model Method The SWM method is accepted by a handful of state agencies. The SWM method does not have the same history of use and familiarity within the transportation industry as the p-y method (refer to Appendix E for additional discussion. For long foundation elements that bend rather than rotate, this method can be used to supplement p-y analyses, especially for large or complex projects. If used as the primary method for design, lateral load testing for verification is recommended. 6.5 BROMS METHOD Broms ab) developed a method for estimating the nominal lateral capacity and corresponding moments and shear forces along a vertical foundation element subjected to lateral loads. The method, which is based on limit equilibrium principles, relies on the assumption that soil stresses around the deep foundation element have mobilized their nominal values (i.e., passive and/or active states. This method is therefore applicable to the Strength Limit States. The method is applicable to relatively short, stiff foundation elements, such as drilled shafts, subject to lateral shear and overturning moments applied at the top of the foundation element which is free to rotate. In this method, only uniform pile/shaft dimensions and homogeneous soil profiles and properties can be considered. The Broms method is widely accepted for preliminary analyses or initial estimates of foundation lengths, or for design of simple, noncritical structures, such assign post or noise wall foundations, in relatively uniform soil profiles. However, the p-y method enables a more complete modeling of problem conditions compared to the simplified Broms method. 79 Broms ab) also developed expressions to estimate lateral deformations for long piles that bend rather than rotate. However, these methods are based on a simplified subgrade reaction model for an elastic pile. This method is not considered reliable and is not widely used in practice. Broms also proposed a method for analysis of piles with a moment connection to a fixed cap that prevents rotation of the head of the deep foundation element. However, this method also has significant limitations, is not widely accepted in practice, and is not recommended for use. Therefore, the Broms method referred to herein is only the method developed by Broms for short, stiff foundation elements with a free head that rotates rather than bends. Other methods of analyses developed by Broms for long piles or piles with fixed heads are not recommended for use in practice. Foundations that are more significant than the simple cases indicated above for the Broms method, or foundations that require estimation of lateral deformations, or have more complex loading, head fixity, or variable subsurface conditions should be analyzed using the more sophisticated and widely accepted p-y method (discussed in Section 6.3). The Broms method for short piles has not been calibrated to the LRFD design framework. The Broms method is based on simple passive soil pressure diagrams and a limit equilibrium solution obtained through equations of static equilibrium of shear and moment in the shaft. Although the method is based on simplifications and has limited capabilities, it is still useful for simple structures, widely accepted by many agencies for such simple applications, and is useful for understanding the loads and resistances of laterally loaded foundations. Download 6.03 Mb. Share with your friends:
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