The 5 Best Technical Advantagess of Cellular PEB Structures for Economy, Strength and Serviceability are listed below. Before we come to technical advantages that the cellular beams enjoys over solid web I sections, remember that cellular beams are usually desirable in places where there are services below the ceiling and the openings in cellular beam allow services to pass through without increasing the floor height or building height. Architects also prefer this type of members due to their aesthetic look.
What is Cellular Beam?
Cellular beam is an improved version of the castellated beam prepared from rolled steel I-beam/built up I beam (prefabricated in PEB frames with high tensile steel grades) with circular perforations in the web. Comparing the cutting pattern of castellated members, cellular members have more flexibility in their finished depth, perforation diameter and spacing. In addition, cellular members need less infill plates and easier infill cut parts compared to castellated members. Moreover, cellular members can be fabricated as asymmetric sections while castellated members can be constructed only as symmetric sections. Shown are some pictures where cellular beams are used as PEB (pre-engineered building) structures.
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Cellular Beam Fabrication Process |
As shown in the figure above, Cellular Beams are produced by a range of steel manufacturers, using their own patented processes. The process generally applied is to fabricate the whole girder by welding profiled steel plates to form the flanges and the web of the Built Up I section. Prior to the weldin process, openings are cut in the web plate, shifted to match in web creating holes and then welded together to form a cellular bram. Generally, the Cellbeam is 50% more in depth than the solid I section.
Now let us discuss about the top 5 advantages of cellular beam applications in PEB structures.
#1 Aesthetics:
Cellular beams are one of the most sought after steel sections that architects prefer in steel framed structures (e.g. industrial and commercial buildings) since it has a unique shape and lighter (slender) appearance that attracts the user’s sight and make the internal and external look of the building more aesthetically appealing. It allows more natural lights into the space below structure.
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Curved Cellbeam Roof Structure |
#2. Geometric Properties to enhance strength and serviceability:
When a built up I beam or a rolled I beam of height h is expanded into a cellular beam with perforation dia d = h the enhanced geometric properties in major axis are as below because it is 50% deeper and has more than 40% stronger bending strength with no added steel.
Section Modulas ; Zcellular ~ 1.4 x Zsolidweb in floor beams & 1.5 x Zsolidweb for lightly loaded Roof Beams. Therefore bending strength gain is minimum 40% or more, In other words, increase in span of building is possible by 20% more without additional frame weight. Suppose, you designed a PEB structure with solid web rafter to spam 30m, the same span can be enhanced to 36m by converting the same rafter section into cellular beam section
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Cellular Long Span Roof |
Second Moment of Inertia: Icellular ~ 1.8 x Isolid for only steel section & 3 x Isolid of composite secton. This gives enormous advantage for cellular beams used as long span floor beams with column free areas that encounters floor vibrations and meet serviceability requirements easyly. (example: Car park structure). However caution needs to be exercised for heavy point loads by reinforcing web holes.
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Cellular Car Park |
#3. Long span flooring system with assymetric cellular sections:
Cellular beams may be used as assymetric cellular composite long span floor beams where more column free space is needed for example commercial floors, parking structures etc.
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Commercial Building with cellbeams |
#4. Improved Service Integration within the web: There is no increase in construction depth of any structural cross section due to services being passed through the openings with the web.So cellular beamd used in multistorey buildings often reduce the floor zone height because the services are passed within the cellular perforations.
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Service Integration Through Cellbeams |
#5. Reduction in overall building height and cost:
Lighter framing yet spans more resulting more free space, less columns and footing cost for the covered area. No additional height required below the beam because service ducts can pass through perforations/web cells resulting reduced building height.
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Cellbeam PEB Structure |
Disadvantages:
- Slightly more additional cost in cutting and welding of cellular beams
- No local standard design code available for Cellular Beams
- Rigorous calculations necessary (softwares are now available to aisc and eurocode)
Usage of Cellular Beams:
The use of cellular beams has been gradually increased through the past decade. It is widely used in almost all types of buildings due to its structural and architectural advantages. They are mainly used as secondary beams. Moreover, cellular members can be used as roof beams, floor beams, tapered and cantilevers beams, normal and tapered columns and beams. One of the most important advantage is that the curved beams can be obtained through the manufacturing process without extra costs.
Cellular beams are widely used in:
- Multi storey car parking structures,
- Stadium Roof Truss, Sports flooring
- Transportation facilities such as metro stations and bus stop sheds,
- Hospitals, Factories, Warehouse
- Bridges and high rise buildings,
- Industrial buildings, residential and commercial buildings
- Arches, Gymnasium
- Art galleries, Libraries, Museums
Food for Thought:
Suppose as a PEB building supplier, you have completed 500 projects with average built up solid web frame weight of 100 MT for each project. So Total supplied Frame wieght = 50000 MT. If you have had used Cellular Beam framing instead with 40% savings, you would have needed only 500 x 60 = 30000MT. So switching to cellular beam approach, you would have saves national resources in steel by 20000MT. And possibly, there are hundreds of PEB suppliers like you. Just think over the loss of national resource in steel!!
Readymade Suppliers:
Macsteel, Westok, Arceloarmittal, Graitec, Fabsec and New Millennium are some of the main manufacturers of cellular beams and they have their own design manuals, which are based on Eurocodes and other design standards. These manuals enable the designers to understand the design procedures of cellular beam sections.
Valuable Resources/Publications on Cellular Beam Design
1. AISC Design Guide 31 2. SCI P355
Recommendation
The above writing is meant to inspire upcoming PEB structural engineers who are fearless to explore the opportunities of designing PEB structures with Cellular Beam Design. Hope this information would serve as an aid to structural engineers and decision makers to explore feasibility of Cellular PEB Structures with more zeal and confidence. The author has no conflict of interest and the opinions are of his own.
Disclaimer
The contents of this article is for informational purpose only and proper professional guidence must be sought before implementation of design and construction of Cellular PEB Structures.
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