Elevated Water Tank Anchorage Design - Load Factors 2

[djvan]

I am designing post-installed adhesive anchorage into a concrete slab-on-grade for an elevated tank, supported on 4 legs and grout pads. I have calculated all the forces per the proper guidelines in API-650, API-620, and ASCE 7-10. However, I am a little stumped when it comes to the LRFD load factors for 2 of the force components, convective (sloshing) force and impulsive forces both due to seismic accelerations. Maybe I am just missing it in the codes somewhere, but what load factors should be used on those forces to design the concrete anchorage? Ive been told 1.0 because its seismic derived and 1.6 because its "Live" load and "impulse"

 

[GC_Hopi]

Wouldn't those forces be considered seismic load effects? And ASCE 7 - 10 has load factors for seismic load effects.

 

[JStephen]

Those ARE the seismic loads. (Also, vertical seismic.)
Also refer to AWWA D100-21, which covers leg-type elevated water tanks.
If this is a small tank (little horizontal fuel tank on 4 legs or something), details are not as critical. For a municipal water tank or something of similar size, more detail is warranted.
I don't think convective forces are normally figured for elevated tanks, but would have to peruse the standards again.
Also note the overstrength requirements, addressed in AWWA D100 by requiring the structure to be adequate for yielding of the sway rods.
Note that seismic loads as generated by API-650 and AWWA D100 are service level loads, and need to have appropriate load factors applied for concrete design. If you're working from ASCE 7-10, you should be generating ultimate-level loads.

 

[HTURKAK]

This expression 'post-installed adhesive anchorage into a concrete slab-on-grade for an elevated tank' implies this is small elevated tank , If so , my points are ;

- The scope of API-650 and API-620 are ground supported storage tanks and are not relevant standards in this case..

- You may look AWWA D100-21 as Mr JStephen (Mechanical) as pointed out,

- The relevant clause at ASCE 7-10 is ( 15.7.10 Elevated Tanks and Vessels for Liquids and Granular Materials )

Clause 15.7.10.2 Effective Mass The design of the supporting tower or pedestal, anchorage, and foundation for seismic overturning shall assume the material stored is a rigid mass acting at the volumetric center of gravity. The effects of fl uid–structure interaction are permitted to be considered
in determining the forces, effective period, and
mass centroids of the system if the following requirements
are met:
a. The sloshing period, Tc is greater than 3T where T = natural period of the tank with confined liquid (rigid mass) and
supporting structure.

- You may provide more details to get better responds


Most Probably the impulsive mode will govern ..

My opinion..






Not to know is bad;
not to wish to know is worse.

NIGERIAN PROVERB

 

[djvan]

This was super helpful. The AWWA D100 code laid the forces/accelerations out similar to API with the exception that convective forces need not be applied for elevated pedestal type water tanks and to treat the tank + contents as a singular rigid mass upon the appropriate period checks. Also, after further discussions and in agreeance with JStephen and GC Hopi the appropriate load factors should reflect that they are seismic ultimate level load factors.

Thanks Everyone! This cleared everything up for me.