Metal Construction News, May 2018

KNOW YOUR PRODUCTS Effi cient Design Utilizing Decorative Guardrails By Dan Stachel Providing fall protection and facilitating safe movement with beautiful aesthetics A guardrail is typically required wherever an individual could fall 30 inches or more within 36 inches of an edge This includes all open sided surfaces such as mezzanines platforms aisles stairs ramps and landings In addition a guardrail must be constructed in a manner to prevent a 4 inch sphere from passing through it at any point Structural considerations are driven by national and local building codes i e IBC OSHA ADA For railing systems to achieve these safety requirements careful attention must be paid to material selection the sizes and shapes used in the construction of the railing and the method by which the railing is affi xed to the structure When selecting a railing system there are fi ve key considerations loading requirements safety factors material selection defl ection and style Loading Requirements Guardrails must be engineered to endure specifi ed loads without failure typically defi ned as permanent deformation Loads are driven by environment wind loads location seismic loads and use live loads from human activity Loading requirements vary by municipality so it is important that each project be assessed individually Safety Factors A safety factor is the ratio of a materials strength to an expected stress level In railing systems these ratios can vary from 1 1 2 to 4 times based on the material The factor of safety for metals such as aluminum and steel is dictated by material specifi c codes typically 1 1 2 to 2 times Material Selection Another important aspect of effi cient design is the use of appropriate materials and sizes Typically railing systems have posts spaced approximately 4 feet apart Should a designer choose to increase the span between posts additional material will be required on the horizontal members as well as the vertical posts Conversely shorter spans may allow for a reduction in materials However loading requirements at the vertical post may limit the possible savings in short space designs Defl ection An additional consideration with slightly more ambiguity is the amount of defl ection within a system Defl ection is the degree to which a structural element is displaced under an applied load In glass design for instance the glass may not defl ect more than the thickness of the glass between panels This can be an issue with 1 2 inch glass at elevations in excess of 42 inches and often requires the use of a top cap and or a handrail The allowable defl ection within any railing system should be addressed by the designer during the specifi cation process Style In light of the countless requirements todays designers face a considerable challenge how to design unobstructed railing systems that enhance a view while also providing enough protection to meet structural and safety requisites Fortunately there are a number of stylish ways to accomplish this goal with infi ll options ranging from cable and glass to mesh and grid designs all offering their own distinct advantages Heightened Function and Design A handrails primary purpose is to assist with movement Handrail height should be uniformly consistent between 34 and 38 inches from the ground Among a handrails most important features is its graspability the ability for people to quickly cling to the handrail for support when they lose balance or suffer from muscle weakness With this in mind a handrails diameter is critical The IBC requires that circular handrails have an outside diameter between 1 1 4 and 2 inches Square or rectangular handrails should have a perimeter dimension between 4 and 6 1 4 inches and a cross sectional dimension between 1 and 2 1 4 inches Keeping codes proper installation and material selection in mind is critical for designing effi cient railing systems that will withstand the test of traffi c and time Fortunately todays railing systems offer an abundance of options that are not only compliant but also creatively inspiring and aesthetically designed to complement and elevate the vision of any space Dan Stachel is vice president of Trex Commercial Products Minneapolis To learn more visit www trexcommercial com 52 METAL CONSTRUCTION NEWS May 2018