Everything about Podium Slab that you should know

A unique type of floor system known as a podium slab shifts the weight of a steel or wood frame structure above it to the walls and columns below the slab. Occasionally, load-bearing elements in the upper structure—such as columns and walls—do not align with those in the lower structure. Typically, structural steel, metal studs, or wood are used to make the upper structure. This kind of slab is frequently found in parking lots at ground level, with three or four stories of typical residential buildings above it. The reason this slab is named a "podium" is because it divides these two areas of the structure.

The purposes of a podium slab

Transfer Slab and Structural Floor: 

It supports the weight of the walls and columns below by acting as a bridge between the upper portions of the building.

Horizontal Separation: 

The podium slab also serves as a barrier to stop fire from spreading from one area of the building to another.

Thickness of a Slab

The National Building Code of India states that a podium with a ramp may have more than one level, but the total height above the ground cannot exceed thirty metres. The podium may still have several levels if it has a car lift in place of ramps, but the overall height must not exceed nine metres above the floor.

When a fire engine cannot reach the podium directly, there are special regulations that apply. In these situations, the portion that is accessible to fire engines should not protrude farther than 11 metres from the building's footprint. 

Design of Podium Slabs

Building codes also impose height restrictions on all structures. So, you can have a two-story podium with a mezzanine level if you want, but make sure you do not exceed the maximum allowed height for both the building and the podium.

Podium slabs are typically designed as a two-way system. They are made to withstand weight from the structure's lower as well as upper levels. Typically, different engineering groups collaborate on the design of the main building and the concrete podium.

Engineers recommend using post-tensioned slabs 12 to 14 inches thick to make enough room for parking. This is useful when you need three or more stories of parking above. It is critical to balance the weight of the podium slabs when designing the post-tensioning. To ensure that the slabs are strong enough, they usually have strong steel on top at the columns and a mat of reinforcement bars on the bottom.

Podium Slab Waterproofing

The top layer of podium slabs faces constant stress from the elements and the weight of vehicles driving over it. To ensure longevity, it's essential to apply waterproofing.

Because podiums have a larger surface area, they are more exposed to weather changes and experience greater vibrations from vehicles. To protect against this, it's crucial to use a high-quality waterproofing solution. Additionally, since the load from vehicles can vary, a flexible waterproof coating is necessary.

The pressure on the podium's surface affects the supporting structure beneath it, causing stress on the concrete surface. In such cases, applying an elastic waterproof coating can serve as an effective shield against the structural strain caused by vehicle traffic and temperature fluctuations.

Things to understand while constructing a Podium

Tie-down System

A continuous tie-down system is a structure that uses a connected network of cables to collect and transfer the upward forces experienced on multiple levels down to the base or foundation. In multi-story buildings, these tie-down systems offer benefits such as straightforward installation and impressive capacity to counter uplift forces. Conversely, an in-wall system poses more significant challenges when it comes to handling these forces.

Two-Stage Designing

The two-stage design process involves a distinct approach to the upper wooden frame of the building compared to the concrete lower section. This approach is implemented to guarantee that the entire building doesn't exhibit the same seismic response and that forces are distributed optimally throughout the structure.

Grade and Species

Having a clear grasp of the type and quality of wood used in construction streamlines the process by addressing cost and availability considerations in advance.

Various types of podium slab construction

Precast Podium Slab:

This is a prefabricated podium slab, which is a time-saving and user-friendly construction approach. Key structural elements are manufactured and cast at a central facility, then transported and assembled on-site. The primary benefits of the precast method include:

Cost-Efficiency and Accelerated Construction: Reduced construction expenses and minimal formwork requirements result in quicker project completion.

Ideal for Space-Constrained Projects: Suited for projects with restricted space where post-tensioning may not be feasible.

Post-Tensioning Podium Slabs: 

These podium slabs have a higher load-bearing capacity and can cover more extensive areas compared to precast alternatives. In this approach, the slabs and beams are constructed together on-site to minimise the number of joints, which demand ongoing maintenance. 

The benefits of choosing post-tensioning podium slabs include:

Enhanced Shape Control and Footprint Consideration: 

Onsite construction facilitates better control over the shape of the structure and allows for careful consideration of the building's footprint.

Improved Weight Distribution: 

Post-tensioning results in more even weight distribution over a broader area, with beams typically spaced about 20 to 24 feet apart, rather than the five to six feet spacing seen in precast methods.

Advantages of a Podium Slab

Structural Balance Zone: 

This designated space between living and parking areas provides structural load balance.

Fire Resistance and Noise Isolation: It offers fire protection and minimizes sound transmission to upper living spaces.

Generous Open Space: 

Ensures ample open space below or at ground level for retail or parking purposes.

Efficient Parking Design: 

Utilizing post-tensioned podium slabs reduces frame thickness and excavation, making underground parking more practical.

Budget-Friendly Vibration Control: 

A cost-effective solution for mitigating floor vibrations in multi-family residences.

Considerations for a podium slab

Gentle Handling and Transport: 

Precautionary measures are necessary during the transportation of precast hollow units to avoid potential damage in transit.

Accident Risks with Post-Tensioning: 

The post-tensioned podium slab carries a risk of accidents, particularly if the construction workmanship is subpar and tendon corrosion occurs.

National Building Code for Podium Construction

Parking Facilities Requirements:

For podiums used for parking, each floor must have two washbasins and two urinals for every 500 vehicles.

At least one restroom should be conveniently located near accessible parking spaces.

Non-residential building podiums must include provisions for drivers' restrooms.

Recreational Use:

The topmost portion, open to the sky, can be repurposed as a recreational area.

It can also be transformed into a landscaped space for leisure and enjoyment.

Front Open Space Restriction:

Podium construction is prohibited in the minimum mandatory front open space.

Fire Tender Accessibility:

If the podium is accessible to fire tenders, it must possess the strength to support a fire tender with a weight of up to 45 tonnes.

Conclusion

In conclusion, podium slabs play a pivotal role in modern construction, offering versatility, structural support, and space optimization. Whether precast or post-tensioned, these innovative systems enable architects and engineers to create efficient, multi-functional spaces while addressing various design and structural challenges in the ever-evolving world of urban development.