Tension pile reinforcement anchorage in pile cap and shear link anchorage using headed bars 1

[Jeysha]

I want to enquire about the requirements of using headed bars for anchoring reinforcement of tension pile in pile cap. The tension force is in the order of about 4.3MN in ULS and 6B40+4B32 pile bars are anchored in the pile cap to take up this force. Though not ideal, the headed bars are placed below the top mat of pile cap to avoid clashes. To check the detailing arrangement, a local STM is developed and additional transverse links is provided around the pile reinforcement within the pile cap depth.



Additionally, the shear links (12 or 16mm dia) within the pile cap is anchored at bottom (B1 layer) using headed bars. This was done for easy placement of the links at site. Are there any additional requirements for the shear anchorage of headed bars apart from the ones stated in 25.4.4.1 & 25.4.4.2 of ACI 318-19.

I am curious to know whether the approach followed for detailing is reasonable and as to what others have done in similar situations. Thank you very much!

 

[HTURKAK]

The tension force is in the order of about 4.3MN in ULS and 6B40+4B32 pile bars are anchored in the pile cap to take up this force.

Tension force developing at each pile 4.3 MN but apparently the pile cap reinf. is for compression piles . Will you post a sketch showing the dimensions , forces ?

 

[Jeysha]

The tension force of 4.3MN is the maximum value for a corner pile from a envelope of forces and to standardize this value was adopted for a group of pile caps. The piles are mainly subjected to compression with a maximum compression in the order of about 10MN and co-existing tension of about 3MN at the other end for the pile cap shown in sketch below (depth is 2m). The top reinforcement provided over the width of pilecap was okay for the co-existing cases under tension. There are cases where all the piles are in compression in the range of about 3 to 7.5MN. The pile cap plan is as below.

 

[KootK]

@Jeysha: so the thing that the pile cap supports is in a state of overturning which produces the local tensions, correct?

 

[HTURKAK]

The tension force is in the order of about 4.3MN in ULS and 6B40+4B32 pile bars are anchored in the pile cap to take up this force. Though not ideal, the headed bars are placed below the top mat of pile cap to avoid clashes.

JEYSHA , You did not provide a lot of info. here. Tension force 4.3MN develop at a corner pile in some combinations but apparently you did not provide necessary tension reinf. at the top of pile cap. If tension force develop at corner piles , the pier would be subject to bending effects and you should have similar anchorage problem for the pier tension reinf .

You did not provide the full dimensions and apparently the cap thick. should be in the range of 2000 mm . In this case , the shear span/ depth ratio is less than 1.5 , and you are expected to use STM method , ( truss action is dominant )

Is this a bridge pier ? Have a look to the following doc. free of charge at web.

 

[Jeysha]

@Jeysha: so the thing that the pile cap supports is in a state of overturning which produces the local tensions, correct?

Yes, it is subjected to biaxial moments with large moments along the longer length of pile cap.

JEYSHA , You did not provide a lot of info. here. Tension force 4.3MN develop at a corner pile in some combinations but apparently you did not provide necessary tension reinf. at the top of pile cap. If tension force develop at corner piles , the pier would be subject to bending effects and you should have similar anchorage problem for the pier tension reinf .

You did not provide the full dimensions and apparently the cap thick. should be in the range of 2000 mm . In this case , the shear span/ depth ratio is less than 1.5 , and you are expected to use STM method , ( truss action is dominant )

Is this a bridge pier ? Have a look to the following doc. free of charge at web.

Thank you for sharing the document. We had referred this document when developing the STM for pile cap. It is a bridge pier pile cap and the depth is 2000mm. STM was utilized for analysis of pile cap and reinforcement provided accordingly. 4.3MN was under seismic action for another pile cap. The pile cap reinforcement at top shown in the first sketch has pile tension of about 3MN & the top reinforcement provided was okay. At top of pile cap for tension, the reinforcement over the full width of pile cap is considered to be effective. At bottom, the reinforcement over pile strip (1.5x pile diameter) is considered to be effective for the ties.

The pier reinforcement was anchored at bottom of pile mat with a 90 Deg hook. Anchorage for pier reinforcement was considered from center of pile cap as it is difficult to predict the depth of nodal region (reference from TXDOT report Strut-and-Tie Model Design Examples for Bridges below). Additionally the outer links of pier (12 or 16mm dia at 150mm spacing) was extended into the pile cap.

For the headed bars of tension piles & shear links, was curious to understand the requirements and local reinforcement requirement if any.