Geotechnical Engineering Circular No. 9 Design, Analysis, and Testing of Laterally Loaded Deep Foundations that Support Transportation Facilities
Download 6.03 Mb. View original pdf
|
Soldier Rev B
| 7.5.2 Loads in Batter Piles The lateral load response of a foundation group with batter piles differs from that of a foundation group with only vertical piles. Fora pile group consisting of only vertical piles, the response to an applied lateral load and overturning moment results in the pile group translating horizontally and deflecting downward as shown in Figure a. Fora pile group with battered piles (outwardly battered piles in the direction of the lateral load and moment, the response to the same lateral load and overturning moment results in the pile group translating horizontally and displacing vertically upward as shown in Figure b. Therefore, the inclusion of battered piles will influence the overall design of the foundation group and the loads and reactions for each pile (Wilson et al. 2006). (a) (b) Figure 7-8: Variation of foundation response for vertical and batter piles (modified from Wilson et al. 2006). 114 The additional lateral load resistance from a batter pile, compared to a vertical pile, comes from the horizontal component of the axial load in the batter pile. The horizontal component of the axial compression load contributes to the overall lateral load resistance of the group when the piles are battered outward, away from the load. In cases where the piles are battered inward, towards the load, the horizontal component of the axial load will reduce or subtract from the lateral load resistance of the group. The analysis fora pile group with battered piles is similar to that fora group of vertical piles as described previously, but with the following modifications as described by Wilson et al. (2006): 1. Assuming the cap is rigid, the axial load for each pile is determined from the vertical load at each pile and the batter angle. The horizontal component of the axial batter pile load is then determined for each batter pile. This resistance to this horizontal load component (for outwardly battered piles) will provide resistance to applied lateral loads. 2. The sum of all the horizontal batter pile loads is determined. If this sum is less than the applied lateral load, then the remaining lateral load component must be resisted by the piles through bending as determined from a p-y analysis. If the sum of horizontal load components is greater than and in the opposite direction to the applied load, then the net horizontal load in the piles will result in displacement and bending towards the applied load. It is important to carefully assess the applied horizontal loads and vertical load distribution within the pile group when determining the location and orientation of batter piles to ensure that the batter piles are used efficiently (i.e., contribute to lateral load resistance through horizontal axial components as well as bending. Considering this and the concerns indicated previously for batter piles, when designing a pile group, it is recommended to design the group first using vertical piles only. If the lateral load resistance cannot be fully addressed with only vertical piles, or if this approach requires a significant increase in the number of piles then batter piles can be incorporated into the design, with careful consideration of the pile arrangement to maximize the efficiency of the batter piles through axial loads and bending. Download 6.03 Mb. Share with your friends:
|