What Does Depressed Slab Mean In Construction?

What Does Depressed Slab Mean In Construction?

In construction, a depressed slab is an area of concrete or other rigid material that has been lowered from the level of surrounding areas into a depression.

This allows for the construction of features such as drainage channels, utilities, wiring runs, or even stairways.

Depressed slabs can be cast integral to the floor or constructed separately. They are often used in areas like parking lots and sidewalks that are prone to flooding due to their level design.

Depressed slabs can be created using a variety of methods. One method is to use a depression rail which impedes the flow of concrete when it is poured, creating an exterior depressed slab portion.

Another method is to use separate slab edge commands when creating the slab edges for the large primary slab and the depressed floor slab.

In addition to their use in construction, depressions can also refer to localized pavement surface areas having elevations slightly lower than those of the surrounding pavement.

These depressions can be observed or located by water ponding or stained area due to ponding and may cause hydroplaning potential on runways.

How Is A Depressed Slab Designed?

A depressed slab is a concrete slab that has been reduced in depth or thickness. This can be achieved by using beam components of different thicknesses around the depression, such as 12″x16″ beams for a 12″ thick slab with a 4″ depression.

In Revit, this can be modeled by creating separate floors and drawing closed outlines for interior areas to create void spaces in the floor.

In SAFE, the depressed portion of a slab can be modeled by adjusting the vertical offset relative to the top of the slab.

The length of fold should be more than twice the slab depth to ensure proper moment connection.

What Are The Advantages Of Depressed Slab?

Depressed slab design offers several advantages in construction, such as allowing direct connection to walls and columns, reducing cutting and vibrating costs, providing insulation, and creating features such as drainage channels, utilities, wiring runs, or stairways.

It is also often used in areas prone to flooding due to its level design.

Depressed slabs can be used in various parts of a building such as bathrooms, toilets, and laundry areas, where pipes or drainage systems are laid.

The advantages of underslung plumbing include easy maintenance of drainage systems without affecting the structure and eliminating the cost of filler material required in the sunken slab.

Post-tensioned slabs are also commonly used in construction due to their ability to produce buildings and structures with clear open spaces allowing more architectural freedom.

This method also reduces the amount of concrete needed for a given span by transferring loads through tension rather than compression.

What Are The Disadvantages Of Depressed Slab Design?

Disadvantages of depressed slab design include decreased height of the slab, increased time and cost for construction due to the need for waterproofing and brick bat, and difficulty in maintaining drainage systems.

Additionally, depressed slabs are prone to cracking due to overloading or inadequate moisture content during finishing.

To reduce these risks, designers should use low-shrinkage concrete mixes, provide joints in the design, use thickened slab edges, and employ vacuum dewatering or post-tensioning techniques.

What Is The Structural Analysis Of Depressed Slab Design?

Structural analysis of depressed slabs involves calculating the dead load of the slab, which is determined by the thickness and weight of the materials used in its construction.

This includes the thickness of the reinforced concrete slab, light-weight concrete, floor finish, and ceiling plaster.

The depressed portion of a slab can be modeled by adjusting its vertical offset relative to the top of the slab.

This can be done in v16 and below by right-clicking on the slab and adjusting its vertical offset within the Assignments tab.

In v20 and above, this can be done by selecting the slab and using Assign>Shell >Insertion point.

It is important to uncheck Ignore Vertical Offsets when manually adjusting slab elevation.

What Are The Types Of Depressed Slab?

There are several types of depressed slab designs used in construction, including one-way joist slabs, flat slabs, flat plates, waffle slabs, hollow core slabs, precast slabs, and slabs on grade.

A depressed slab is a term used to describe an area of concrete or other rigid material that has been lowered from the level of surrounding areas into a depression.

This allows for the construction of features such as drainage channels, utilities, wiring runs, or even stairways.

Depressed slabs can be cast integral to the floor or constructed separately.

Slab continuity is based on edge conditions which are automatically determined by the program and can be manually changed to a cutout, raised slab, or depressed slab.