I am designing a pile foundation for a new building based on information provided by the geotechnical engineer for the project. The pile foundation is required due to the high probability of liquefaction of the underlying soil during a seismic event. The pile system proposed consists of 8" dia. hollow steel pipes that will resist both vertical and lateral loads from the structure. Many questions have been raised by the city plan reviewer in which I cannot find direct code answers or answers from the common engineering practice for similar systems.
The three questions are:
1. Is the table from IBC 1810.3.2.6 commonly used that requires the allowable pile stress to be limited to 0.35Fy? None of the calculations I have from other foundation designs in the area include this reduction but it seems like this should apply according the the IBC code language.
2. Does the R value used in the base shear equation for lateral loading to the individual piles need to be reduced to 2.5 (special cantilevered steel column resisting system) instead of the value used for the lateral system for the building above the pile system (R=5 for special reinforced masonry shear walls). Again, the designs I have seen in the area do not appear to change the R value for the foundation design but the plan reviewer thinks that should be done for this system.
3. Does the ASCE 7-10 requirement in section 12.2.5.2 for cantilevered column systems that limits the axial strength in the column to 15 percent of the available axial strength apply for pile foundation systems? I cannot find any references to using this reduction in any pile foundation literature or design examples. The plan reviewer thinks this reduction should be applied on top of the 35% reduction for allowable stress which would effectively only allow for 5.3% of the steel stress to be used for design.
I cannot find any design examples or literature that addresses the above questions. Has anybody run into this before and is there any literature available that addresses any of these questions?
Thanks in advance for any help or direction.
The three questions are:
1. Is the table from IBC 1810.3.2.6 commonly used that requires the allowable pile stress to be limited to 0.35Fy? None of the calculations I have from other foundation designs in the area include this reduction but it seems like this should apply according the the IBC code language.
2. Does the R value used in the base shear equation for lateral loading to the individual piles need to be reduced to 2.5 (special cantilevered steel column resisting system) instead of the value used for the lateral system for the building above the pile system (R=5 for special reinforced masonry shear walls). Again, the designs I have seen in the area do not appear to change the R value for the foundation design but the plan reviewer thinks that should be done for this system.
3. Does the ASCE 7-10 requirement in section 12.2.5.2 for cantilevered column systems that limits the axial strength in the column to 15 percent of the available axial strength apply for pile foundation systems? I cannot find any references to using this reduction in any pile foundation literature or design examples. The plan reviewer thinks this reduction should be applied on top of the 35% reduction for allowable stress which would effectively only allow for 5.3% of the steel stress to be used for design.
I cannot find any design examples or literature that addresses the above questions. Has anybody run into this before and is there any literature available that addresses any of these questions?
Thanks in advance for any help or direction.
