Peikko Frame: The Best Alternative to Post-Tensioned Structures

Post-tensioned concrete structures offer many benefits in multi-story buildings such as long spans, thin floor depths and of course fire resistance. Although this type of structure can be labor intensive and require specialized labor, it remains an excellent design choice. However, when this workforce is  unavailable in a certain area or if a project is over budget, the Peikko Frame is the best alternative to post-tensioned concrete.

Peikko Frame / Source: Peikko

Peikko Frame Video / Source: Peikko

The Traditional Alternatives:

Reinforced concrete or Cast-in-place Structures

A cast-in-place concrete structure is in some regards similar to a post-tensioned structure, yet in order to achieve the same spans, the reinforced concrete slabs need to be thicker and therefore heavier. Not only does this additional thickness add to the cost of the concrete but it also increases the weight of the entire structure which will lead to bigger and more expensive foundations.

Just like a post-tensioned structure, cast-in-place is inherently non-combustible.

Cast-in-place structure / Source: Peikko

Steel Structures

Since it is to a large extent prefabricated, a steel structures has the ability to be erected quickly with a comparatively small crew of installers. Nevertheless, the thickness of the traditional assembly of the beams supporting the joists and deck will inevitably increase the floor-to-floor height when compared to a post-tensioned structure. With steel structures, to maintain the same number of floors the building height will have to be increased. If the overall height cannot be increased than there is a possible lost of one or more floor levels. 

Conventional steel decking / Source:weldersuniverse.com

Additionally this increased floor-to-floor height will have a direct impact on the cost especially on the more expensive vertical components such as exterior cladding.

Since unprotected steel members do not resist fire, the fireproofing of steel structures adds another trade that will lead to additional costs.

Fireproofing a steel structure / Source: Wikipedia

Precast Structures

Precast structures composed of hollowcore slabs, precast columns and precast beams are not very common in the United States. Even though hollowcore slabs are a very competitive product, making precast columns and beams at low cost remains a challenge in most regions.

The prestressed hollowcore slabs offer an unmatched span to depth ratio, but the bottom flange of the precast beams protruding under the hollowcore slabs will inevitably increase the floor to floor height.

Precast beam supporting hollowcore slabs / Source:Peikko

Precast beam supporting hollowcore slabs / Source:Peikko

Just like post-tensioned and cast-in-place, precast structures are non-combustible

The Peikko Frame:

The Peikko Frame was developed to encompass all the major benefits of the traditional types of structures in one simple system.

Speed of construction with minimal workforce

By utilizing long span prefabricated components such as 36 feet hollowcore slabs combined to 25 feet Deltabeam®, Peikko frames allow for exceptionally fast construction without an extended workforce. 

Peikko Frame Time LapseVideo / Source: Peikko

Another great advantage is that precast slabs do not require shoring allowing for sub-trades to access the job site faster.

Shoring of a conventional concrete slab  / Source:Peikko

Shoring of Deltabeam®  / Source:Peikko

The Peikko Frames are typically shored only for torsion when loading the precast slabs on one side of the beam. The few shoring posts are typically removed only a few days after the hollowcore slabs have been installed.

Superior span to depth ratio without protruding beams

It is well known that hollowcore slabs offer an excellent span to depth ratio since they are prestressed and light weight due to their longitudinal voids. However, when combined with traditional beams, the overall floor assembly can sometimes be increased by the full height of the beam profile.

Hollowcore slabs on wide flange steel beams / Source:Peikko

Additional floor depth when using wide flange beam vs. Deltabeam® / Source:Peikko

Deltabeam® is designed to only have its bottom flange protruding under the hollowcore slabs. Typically the flange will be less than 1” thick and will not interfere with HVAC or other systems.

Deltabeam® bottom flange supporting hollowcore slabs / Source:Peikko

Non-combustible structures

Peikko frames will result in exposed steel columns and Deltabeam (bottom flange) that do not require any fireproofing material applied on site.

Deltabeam® has been tested by Underwriters laboratories (UL) and is now listed for 1, 2, 3 & 4 hours without requiring any kind of fireproofing material. The reinforcement inside the concreted beam will assure the beam capacity remains sufficient in case of fire.

Interior of Deltabeam®  / Source:Peikko

Click to play the video:

Deltabeam® Fire test at UL  / Source:Peikko

The composite columns act in a similar fashion by relying on its reinforced concrete core to ensure the load bearing capacity in under fire.

Cost effective solution

Direct Costs

By using big prefabricated components major savings can be made. Less components means less time to erect a floor and large floor-plates can be installed with a handful of installers.  

Hollowcore slab installed on a Deltabeam® / Source:Peikko

One of the major components of the Peikko Frame is the hollowcore slab. Hollowcore slabs have been used in millions of square feet of buildings in America and have a proven record of being economical and highly capable.

Indirect Costs

In addition to having a competitive direct cost, the Peikko Frame leads to other significant savings.

When compared to post-tensioned structures, Peikko Frames allow for immediate access to the lower floors to other sub-trades (partition walls, plumbing, HVAC, etc.) since it requires minimal shoring.

The reduced weight of the hollowcore slabs also leads to savings for the foundations.

Having very minimal formwork reduces the cost of waste collection.

Compared to steel structures, the Peikko Frame will greatly reduce the floor-to-floor height. Also, hollowcore slabs are usually faster to install than traditional metal deck and requires less steps to be completed.

Extra Costs

Perhaps the most important cost reduction factor with the Peikko Frame is the most intangible: Predictability. Since the entire frame is prefabricated and modeled in 3D and it leaves limited probabilities for errors and omissions. Also, large prefabricated component are less impacted by weather during construction and erection can proceed even with relatively high winds, rain or snowfall.

Peikko Frames are also very easily enclosed during construction which leads to saving on heating when the construction site runs during winter time.

The Alternative to Post-Tensioned Structures
When a multi-story building requires long spans, a non-combustible structure and low floor-to-floor height, the Peikko Frame should be a system to consider. With it's prefabricated components, the Peikko frame will likely reduce the construction time and budget when compared to a conventional post-tensioned building. 

For more information:
www.peikkousa.com
1-888-PEIKKO-1 
1-888-734-5567