Hazard Mitigation of Civil Infrastructure

Design of Thick Pile Caps

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Alkali Barry

What is a Pile cap?• Reinforced concrete structural slab which

distributes column load to a group of individual piles.

• Loads from columns transferring to pile cap induce tensile forces at the bottom of the cap.

• Generally have a thickness ≥ distance from center line of pile to the face of support column.

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What Happens ?

• The rigid pile caps usually defined as 𝑐𝑜𝑙𝑢𝑚𝑛 𝑡𝑜 𝑝𝑖𝑙𝑒 𝑑𝑖𝑠𝑡𝑎𝑛𝑐𝑒 ≤ 2 ∗𝑡ℎ𝑖𝑐𝑘𝑛𝑒𝑠𝑠

• Linear redistribution of pile reactions.

• In the case of flexible pile caps the distribution of pile reactions is non-linear.

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B- Regions

• Well understood

– St Venant’s Principle: The effects of a localized force on a body will dissipate at a sufficiently large distance from the load.

– Bernoulli Hypothesis: Plain sections remain plain after bending

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D-Region

– Caused by a geometric discontinuity or

– A load acting at a point on a member.

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D-regions as described by Schlaich (1987), drawing adopted from (ACI 318-08)

Why considered D-Region?

• The small distance between the piles and the column.

• The dimension of the cap is such than beam theory in not valid

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Method Used

• 3D strut and Tie Model

• Recommended my most standards

– American Concrete Institute

– Spanish Structural Concrete Code

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Spanish Structural Concrete Code (EHE-08)Figs. 58.4.1.2.2.1.a,b

Limitations of the STM• In 3D

- Main vertex position.

- 3D struts section for verification.

- Splitting of struts.

- 3D nodes geometrical definition.

• In 2D

- Easy to determine the and locate the above geometric points.

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ACI 318-008 fig. RA 1.3a ACI 318-008 fig. RA 1.4 (b)

Reinforcement configurations

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STM ACI

Research project BIA 2012-32300. Spanish RD National PlanResearch project BIA 2012-32300. Spanish RD National Plan

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Research project BIA 2012-32300. Spanish RD National Plan

Research project BIA 2012-32300. Spanish RD National Plan

Spanish Code recommendation

Reinforcement based on STM

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Research project BIA 2012-32300. Spanish RD National Plan

ACI Recommendation

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Research project BIA 2012-32300. Spanish RD National Plan

Spanish Code

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Research project BIA 2012-32300. Spanish RD National Plan

Strain Gage.Measures the strain using a the change in electrical resistance.

. A gage factor of 2 will change in electrical resistance of 0.1% therefore the

120 Ω gage will measure is a change of 0.12 Ω.

Strain Gage Strain gage fixed to the rebar

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Research project BIA 2012-32300. Spanish RD National Plan Research project BIA 2012-32300. Spanish RD National Plan

Procedure for attaching gage

• Make sure all selected gages have the same Gage-Factor

• The rebar should be lightly grounded to provide a flat surface.

• The surface should be cleaned with Acetone

• The gage is then bonded to the rebar

• After the bond dries, cover the sensor area with and elastic plaster

• And secure the rest of the wire to the rebar

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Plastered strain gages

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Research project BIA 2012-32300. Spanish RD National Plan

Formwork for four-pile cap

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Research project BIA 2012-32300. Spanish RD National Plan

Rebar cage on spacer wheels

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Research project BIA 2012-32300. Spanish RD National Plan

Pre-Cast set up

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Research project BIA 2012-32300. Spanish RD National Plan

Pile cap and concrete cylinders casted from the same batch.

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Research project BIA 2012-32300. Spanish RD National Plan Research project BIA 2012-32300. Spanish RD National Plan

References• http://best.umd.edu/publications/stm.pdf

• http://www.engineeringcivil.com/which-type-of-pile-cap-transfers-loads-equally-to-piles-flexible-pile-cap-or-rigid-pile-cap.html

• McCormac, Jack C., and Russell H. Brown. Design of Reinforced Concrete. Ninth Edition, ACI 318-14 Code ed. 187-398. Print.

• Hormigon Estructural Normas UNE E Instruccion EHE. 2a ed. Madrid: AENOR, 2009. Print.

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Thanks……..

• Questions?

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