What is the difference between free-head pile group and fixed-head pile group?
Dear Hasan,
As I understand a pile is called fixed headed, if its deflection at the head is restricted by integrating the head of the pile into a pile cap. However, a pile whose deflection is not contained at the head by a pile cap is considered as a free head pile. So, group of piles which are connected by a pile cap can be called as a fixed head pile group and which are not connected are called a free head pile group.
Regards
Sravan MV
Thank you Sravan
but I believe pile group without cap is not named group...
Sravan is correct. Put another way, the pile head is fixed if there is no rotation of the top of the pile shafts relative to the pile cap (but the whole cap can rotate as the group sways). This requires sufficient reinforcement in the case of concrete piles to guarantee this is actually the case. It is theoretically possible to have free headed behaviour with a pile group, where the pile heads are "pinned" at the top. In reality there will be finite rotational stiffness at the head as full fixity is difficult (and expensive) to achieve.
Hi, It is always quite interesting to know whether the pile is fixed or free. I agree with John, Cameron & sravan. In a simple way, I can define whether fixed head or pile is free rotation at the head of group. For a group of 2 piles with pile cap, can act as a fixed head and free head depending on the loading direction. For a group of piles placed triangular or square or rectangular with pile cap with sufficient reinforcement will be considered as Fixed Head. As I said earlier, for two piles with pile cap can be considered as fixed head if, the governing load is acting parallel to piles i.e. along the length of pile cap. In this condition, the piles can not deflect neither independently nor as group. If the loading is normal to pile cap then it can be consider as FREE HEAD.
Hi, From the above answers, I am guessing a retaining wall with a small pile cap with a single pile would be considered as a free headed pile?
Fixed headed pile and free headed pile are not different types of piles. It depends on detailing at interface of pile and pile cap. In case of fixed head piles, interface need to be designed for fixed head moment as well.
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