A pile cap in concrete refers to the pile cap of a concrete foundation structure. The foundation works of a concrete structure involve various key elements such as the foundation wall, grade beams, slabs on grade, pile caps, pilings, and more. The pile cap is the concrete element that sits upon the piles of a building.
A pile cap is a concrete element designed by a structural engineer with dimensions to suit the requirements of the building footprint, its weight, and the soil conditions. For instance, the dimensions (width, height, and length) of the pile cap have to be appropriately selected for use with the piling design of a building, which coincides with the diameter of the concrete pile and top of pile elevation.
Pile Cap Schedule
The typical concrete schedule on a structural project will include for pile cap dimension requirements, reinforcement specifications, and elevation requirements.
Typical dimensions provided include for depth, width, and length.
The reinforcing schedule coincides with the mark for each pile cap, and includes generally speaking for bottom and top rebar schedules.
(T.O. PC) Top of Pile Cap elevation coincides with the determinations for structural foundation layouts. For instance, pile cap elevation can be provided within a structural concrete schedule, but also throughout concrete structural plans. Frequently, the role of a general contractor or a concrete contractor involves ensuring that the top of pile cap elevation per the structural schedules aligns with the structural plans and architectural plans. This review allows for the coordinated concrete construction of building foundations to commence!
Geodetic Elevation
A geodetic elevation for a project will be provided to coincide with the main level top of slab (MF) elevation. From the main slab elevation (ELEV 100′ -0″) for instance in (foot-in) then the corresponding top of pile cap elevation is typically provided from this elevation. Geodetic elevation is the vertical distance from a point on the Earth’s surface, but to make reading top of pile elevations easier, project structural drawings note typically main floor elevation for other elevations to be read from.
Top of pile / caisson or pile cap elevation is critical to get right for a project, as it is literally the basis or foundation of the remaining structure.
Pile Cap Rebar Cage
From a trade or contractor perspective, the pile cap for the reinforcement involved with the component is easiest tied/fabricated on the ground. Tying rebar on the ground rather than trying to install the rebar within the formwork of the pile cap is effective for ensuring that the structural engineer’s design instructions are being followed.
In addition, fabricating a pile cap rebar on the ground ensures that the necessary structural reinforcement of the pile cap is produced expediently and cost-effectively. This is typically known as a rebar cage.
Rebar can extend through a pile cap for utilization with foundation walls, pilasters, footings and more…
Position of Pile Cap
Furthermore, the pile cap needs to sit on top of a pile. For example, a pile will have a set embedded depth within the pile cap. This top-of-pile embed depth provides the necessary tie-in of the vertical rebar components of the concrete pile into the pile cap. The bottom of the pile cap sits below top of pile elevation as the detailed excavation exposes part of the top of the pile.
From a concrete contractor’s perspective, the pile cap pour is done to satisfy the conditions of connecting the above slab structures with the piles supporting the building. When you think about piles, the key is to ensure that the pile cap (top of pile cap elevation) properly sits to support the slab above. This could be with pour-through of the slab or crushed gravel.
Rebar from a top of pile also may extend into the pile cap. This helps to ensure the pile cap and pile are adjoined properly.
Photo Above: A pile cap is essentially a concrete square/cube or rectangle that may look akin to the photo above. Commonly vertical rebar projects can be provided from pile caps to tie into other concrete elements.
Detailed Excavation
The installation of the pile cap involves detailed excavation of the surrounding footprint of the pile cap, usually 1’ to 2’ feet, so that both the formwork and reinforcement can be installed properly. Formwork and reinforcement have to be installed around the pile existing, to facilitate the proper adjoinment of the two structures.
A qualified engineer of record can properly inspect the structural reinforcement and formwork. Further to the pile cap top elevation, coinciding with the depth of the pile cap, the top of pile elevation has to be checked. If the top of pile elevation is too low, the corresponding pile cap has to be increased in depth to accommodate or an engineer might provide separate instructions. We work to accommodate foundation and piling plans when pouring and constructing concrete pile caps.
Concrete Pour for Concrete Pile Caps / Pile
Further, pile caps are provided with high-strength concrete. This is not to say that they should not have air entrainment, with such accommodation for a reduction in MPA compensating for the necessary drop in strength that happens with a move to air-entrained concrete.
A pour-through from a slab is where the backfill surrounding the pile cap is brought around the pile cap, and the slab is effectively poured through from the elevation distance from the pile cap (top) to the U/S of the slab elevation. This provides a thickening in the slab, but most crucially, it ensures that the pile cap is supporting the slab, which supports the building. Alternatively, the sub-grade structure can be carried over the top of the pile cap which is then also supporting the U/S of the slab as the slab-on-grade is poured over it.
The piles themselves are typically poured first and then the pile cap formwork and reinforcement can be built around the pile.
Photo Above: Concrete columns can be positioned directly on top of a slab/pile-cap structure. Structures may be poured separately or monolithically, depending on the structural design intent and the design of the building.
Purpose of Pile Cap
Pile caps can also be positioned directly under columns, pilasters or other supporting structural elements like walls and masonry, further supporting building structures. In that sense, pile caps, and piles, work closely together to ensure a strong foundation for your building. The quality and utilization of sound concrete practices throughout the pile cap placement, formwork, and reinforcement installation process are essential to overall building quality. They are key to utilizing the strength and stability the piles in a concrete structural provide.
Together, the systems avoid issues like settlement, cracking, sinking, serious foundation cracks, and potential architectural diminishment of the above structure.
Conclusion
A surveyor’s services are needed to facilitate the proper installation of a pile cap and pile foundation, though. A professional surveyor’s layout is provided either by a concrete trade or a general contractor. The surveyor needs to ensure not only proper alignment with structural gridlines but match those in addition with architectural gridlines. Inconsistencies with pile cap, piling, or structural building foundation layout can have impacts on the finishing of the building as the structure is completed. Therefor, it is generally critical for all parties involved to not only assess the pile and structural foundation drawings, but ensure uniformity with the other disciplines like architectural and mechanical. This way errors can be caught.
So, a concrete pile cap is a structure used with concrete piles to support elements like foundation walls. To create a cohesive structure, foundation walls can tie in with concrete pilasters and pile caps. The role of the pile cap can vary from project to project, but it is essentially a base foundation component of a building structure.
At Deluxe Concrete Services we provide professional Calgary foundation concrete service for residential and commercial projects. If you have any questions about our services, please contact us. If you found this post helpful, please share it!
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