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  • ASCE 7 Update and the Impact on Bolted Tanks

    Tuesday, October 31, 2017

    The latest edition of the American Society of Civil Engineering (ASCE) 7-16 Standard for Minimum Design Loads and Associated Criteria for Building and Other Structures published in August 2017, includes an exception to the AWWA D103.  Section 15.7.7.2 relating to bolted steel tanks, includes new requirements regarding bolted tanks with an embedded steel base setting ring:

     

    • “b. For Type 6 tanks, the overturning ratio, J, as determined using AWWA D103, Eq. (14-32) shall not exceed 0.785.” This new verbiage has significance to bolted tank design as it impacts where a bolted tank with a Type 6 foundation can be used.

     

    A Type 6 bolted steel tank utilizes a steel base ring shell embedded into the concrete foundation which also serves as the tank bottom.  The J ratio relates to the seismic loading and is a criteria used to determine if the storage tank requires anchorage.  A value of less than 0.785 indicates the tank wall will not experience uplift and does not need anchorage. Conversely, a J ratio greater than 1.54 requires the bolted tank to be mechanically anchored. Ratios between the two values may or may not require mechanical anchorage depending on other factors.

     

    Essentially, the ASCE is requiring embedded shell bolted steel tanks not to be used in areas where uplift occurs due to seismic activity. The concern is there are no specific design requirements for  the anchorage of the shell to foundation and the concrete bottom included in the AWWA D103 therefore it is difficult to ensure ductility of the tank to foundation connection. There is a risk of the shell separating from concrete tank bottom during a seismic event as a design criteria does not exist to ensure the connection is properly designed. ASCE 7-16 does not restrict bolted tanks with other foundation types; only tanks with an embedded shell.

     

    For most applications, Superior Tank Co., Inc. will design our bolted tanks to use foundation types 1 through 5. With foundation types 1 through 5, the storage tank will include a steel bottom which structurally ties into the bolted tank shell creating one uniform structure.

     

    This new terminology is another example of how bolted tank standards are continuously evolving resulting in more resilient bolted steel tanks.




  • NSF International Certification for Bolted Tanks

    Wednesday, August 23, 2017

    NSF Storage Tanks

    Superior Tank Company is proud to announce we have recently earned NSF International Certification for our bolted steel tanks over 14,309 gallons. NSF/ANSI 61 and 372 Certification of our bolted tanks demonstrates compliance to the internationally recognized health effects standard for drinking water system components. NSF International led the development of the American National Standards for all materials and products coming into contact with drinking water and NSF/ANSI 61 & 372 sets health effects criteria for many water system products, components and materials. For example, NSF International standards are used to verify the safety and performance of water treatment and plumbing components and to ensure these products do not leach harmful levels of contaminants into drinking water.

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  • How Much Does A Bolted Steel Tank Cost?

    Tuesday, August 8, 2017

    33 Years of Bolted Tanks

    One of the first questions we are asked is “how much does a bolted steel tank cost”? Unfortunately, the answer is a little complex as the price of a bolted tank is impacted by a variety of factors. Elements include storage tank design specification, relevant local building codes, quality of raw materials, scope of work included in the contract, manufacturer experience and tank installation team skills/training.

    The various design specifications such as AWWA D103, NFPA 22 and API 12B determine tank appurtenances, shell design, steel thickness and even tank size in some cases. For example, the American Water Works Association (AWWA) D103 standard applies to all bolted tanks used for potable water storage and mandates the interior epoxy coating is NSF 61 certified. Bolted tanks for fire protection need to comply with the National Fire Protection Association (NFPA) 22 standards which requires specific tank components such as tank heating systems when needed and reinforced concrete ringwall foundation. When a bolted tank is used for oil storage, the American Petroleum Institute (API) 12B standard is commonly used as a reference but tanks do not have to comply. However, for customers desiring a guaranteed level of quality, the API 12B monogram program ensures the tank meets very specific design criteria and the bolted tank manufacturer is API Spec Q1 / ISO 9001:2008 certified.

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