Issue link: https://cp.revolio.com/i/288390
24 | THE DATA CENTER JOURNAL www.datacenterjournal.com fabricated from fewer pieces, each of which is more substantial, it may be easier and less expensive to increase their capacity, since doing so involves "beefing up" fewer components than is the case for joists. New Buildings Because rolled sections can be designed to carry moderate to very high loads, they are typically the steel system of choice for the more highly loaded data center structures and particularly multi- story buildings. CONCRETE STRUCTURE—CAST- IN-PLACE Perhaps the most resilient system is cast-in-place reinforced concrete. e high "dead weight" of the beams and slab put some limitations on the column bay spacing, but the structure is a monolithic whole when complete and can be designed to carry very high loads. e dead weight naturally resists wind upli forces, and reinforcing placed in the top and bottom of the beams can be added for more capacity. Structural depths can be reduced through the use of post-tensioning cables in beams and slabs, but the use of post ten- sioning severely limits the ability to cut or modify openings in the slab in the future. Existing Buildings ese structures are more oen used when specific loads must be accommodat- ed. Modifications can be made by adding steel members to the existing concrete members if required. New Buildings Although highly resilient, and having high load carrying capacity, cast-in-place concrete is not widely used owing to cost and slower speed of construction. CONCRETE STRUCTURE—PRE- CAST A common structure for large single- story data centers is pre-cast concrete. Significant spans are achievable resulting in very long column-bay spacing in at least one direction. Long spans use pre-cast double Ts, which bear on "inverted T" beams supported by pre-cast columns. is system is very good for gravity loads, but since the bottom ends of the vertical legs of the double T's are completely unbraced, the system cannot be subjected to upli that significantly exceeds the dead weight of the structure without risking failure. To increase the wind resistance, the topping slab, which is poured directly on top of the double Ts, can be increased in depth and weight. Alternatively (or ad- ditionally for higher wind resistance), a ballast slab can be installed on top of the roof membrane and insulation. Existing Buildings Existing pre-cast double T struc- tures are not easily modifiable to increase capacity. New Buildings Pre-cast structures are cost effective, quickly erected, long-span structures that are suitable for single-story data centers. REPRESENTATIVE ROOFING OPTIONS Code Minimum—Approximately 90mph wind resistance in most locations • Steel joist structure • Metal roof deck • Insulation • Overlayment board • Single roof membrane Enhanced Wind Resistance— Approximately 125mph wind resistance • Steel or concrete structure • Concrete or concrete topped steel roof deck • Insulation • Overlayment board • Single roof membrane Enhanced Wind and Projectile Resistance—Approximately 125mph wind resistance • Steel or concrete structure • Concrete or concrete topped steel roof deck • "Vapor barrier" applied to roof deck to serve as a secondary roof membrane • Insulation • Overlayment board • Top roof membrane Optimized High Wind and Projectile Resistance—150mph wind resistance • Steel or concrete structure • Concrete or concrete-topped steel roof deck • First roof membrane applied to roof deck (which also serves as a vapor barrier) • Drainage board • Insulation • Overlayment board • Concrete ballast slab • Top roof membrane • Dual-drain system to drain top and bot- tom roof membranes • 150mph "Dade County–rated" compo- nents for all openings • 150mph "Dade County–rated" me- chanical equipment Maximized High Wind and Projectile Resistance—175+ mph wind resistance • Steel or concrete structure • Concrete or concrete topped steel roof deck • First roof membrane applied to roof deck (which also serves as a vapor barrier) • Drainage board • Insulation • Overlayment board • Concrete ballast slab • Top roof membrane • Dual-drain system to drain top and bot- tom roof membranes • 150mph "Dade County–rated" components for non-critical building components • Specialized high wind resistance protec- tion for critical building area openings • Concrete cooling towers n About the Author: Brian George is a principal with Corgan, which has deep expertise and experience designing mission-critical facilities such as data centers. 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