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Abstract
FAQs
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Introduction
Brief Description of Reviewed Codes and Standards
Provisions on Design Seismic Force
Provisions on Analysis of Tanks
References
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Engineering
Civil Engineering

Review of Seismic Codes on Liquid-Containing Tanks

Profile image of O R JaiswalO R Jaiswal

2007, Earthquake Spectra

https://doi.org/10.1193/1.2428341
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22 pages

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Abstract

Liquid storage tanks generally possess lower energy-dissipating capacity than conventional buildings. During lateral seismic excitation, tanks are subjected to hydrodynamic forces. These two aspects are recognized by most seismic codes on liquid storage tanks and, accordingly, provisions specify higher seismic forces than buildings and require modeling of hydrodynamic forces in analysis. In this paper, provisions of ten seismic codes on tanks are reviewed and compared. This review has revealed that there are significant differences among these codes on design seismic forces for various types of tanks. Reasons for these differences are critically examined and the need for a unified approach for seismic design of tanks is highlighted.

FAQs

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What key differences exist between seismic codes for liquid-containing tanks?add

The study reveals significant variations in design seismic forces across ten different codes, with discrepancies in provisions for impulsive and convective base shear coefficients notably affecting safety. For instance, API 650 specifies a constant convective base shear coefficient for short period tanks, unlike ASCE 7's variable approach.

How are response modification factors defined across different codes?add

Codes differ in classifying tanks based on ductility and redundancy, which affects response modification factors. Notably, ACI 350.3 and D-115 have factors approximately 1.4 times higher than ASCE 7, indicating diverse approaches in seismic force reduction.

What are the implications of varied damping specifications in seismic analysis?add

Different codes prescribe specific damping percentages for impulsive and convective modes; for instance, ASCE 7 uses 5% for impulsive but only 0.5% for convective modes. This results in varying design response spectra, which significantly impacts the analysis and safety of tank designs.

How does the hydrodynamic modeling differ across codes?add

Most codes utilize a rigid tank model for impulsive and convective analyses, though NZSEE allows for flexibility in its modeling of steel tanks. This distinction is crucial as it influences the evaluation of dynamic behavior under seismic loading.

What role does the importance factor play in seismic tank design?add

Codes classify tanks based on utility and potential consequences, with ASCE 7 categorizing importance factors as high as 1.5 for critical tanks. In contrast, NZSEE's risk factor ranges from 0.5 to 1.6, which can radically alter seismic force regulations.

Figures (14)
Table 1. Details of reviewed codes and standards 1=Ground-supported RC/PSC tanks; 2=ground-supported steel tanks; 3=elevate: tanks on shaft-type tower 4=elevated tanks on frame-type tower ’ SD=strength design level; ASD=allowable stress design level ’ Provisions on convective mode are given for ground-supported tanks only.
Table 1. Details of reviewed codes and standards 1=Ground-supported RC/PSC tanks; 2=ground-supported steel tanks; 3=elevate: tanks on shaft-type tower 4=elevated tanks on frame-type tower ’ SD=strength design level; ASD=allowable stress design level ’ Provisions on convective mode are given for ground-supported tanks only.
Table 2. Base shear coefficient from 2006 IBC/ASCE 7, Eurocode 8, and NZSEE
Table 2. Base shear coefficient from 2006 IBC/ASCE 7, Eurocode 8, and NZSEE
Note: Z is zone factor; S is soil factor; / is importance factor; R, R;, R,, and R,,; are response modification factor; Sps and Sp, are design spectra response coefficients; S, is mapped maximum considered earthquake spectral response acceleration at a period of 1 s; C, and C,, are seismic acceleration coefficients; 7; is natural period of impulsive mode; 7,=0.2Sps5/Sp,; T,=Sp1/Sps; and 7; is transition period for long-period range. Table 3. Impulsive mode base shear coefficient from American industry standards
Note: Z is zone factor; S is soil factor; / is importance factor; R, R;, R,, and R,,; are response modification factor; Sps and Sp, are design spectra response coefficients; S, is mapped maximum considered earthquake spectral response acceleration at a period of 1 s; C, and C,, are seismic acceleration coefficients; 7; is natural period of impulsive mode; 7,=0.2Sps5/Sp,; T,=Sp1/Sps; and 7; is transition period for long-period range. Table 3. Impulsive mode base shear coefficient from American industry standards
Note: Z is zone factor; S is soil factor; / is importance factor; R,, R,, and R,, are response modification factor; Sps and Sp; are design spectra response coefficients; T,=Sp,/Sps; T, is natural period of convective mode; and T,, is transition period for long-period range. Table 4. Convective mode base shear coefficient from American industry standards
Note: Z is zone factor; S is soil factor; / is importance factor; R,, R,, and R,, are response modification factor; Sps and Sp; are design spectra response coefficients; T,=Sp,/Sps; T, is natural period of convective mode; and T,, is transition period for long-period range. Table 4. Convective mode base shear coefficient from American industry standards
Table 5. Basic seismic hazard coefficient, C,(7,1), for flexible soil (NZS 4203)
Table 5. Basic seismic hazard coefficient, C,(7,1), for flexible soil (NZS 4203)
Table 6. Type of tanks and response modification factors from American standards
Table 6. Type of tanks and response modification factors from American standards
Table 7. Types of tanks, ductility factor u, damping ratio € and correction factor Cy, from NZ- SEE (Whittaker and Jury 2000) * Check that elastic buckling does not occur before elephant foot. > Capacity design check required to protect against other forms of failure. "As appropriate for support structure. Capacity design approach shall be used to protect elevated tanks against failure while yielding occurs in the chosen support system ™ Damping ratio € depends on soil type and aspect ratio of tank. Values given here are for soil with shear-wave velocity of 500 m/s and height to radius ratio of 2.0.
Table 7. Types of tanks, ductility factor u, damping ratio € and correction factor Cy, from NZ- SEE (Whittaker and Jury 2000) * Check that elastic buckling does not occur before elephant foot. > Capacity design check required to protect against other forms of failure. "As appropriate for support structure. Capacity design approach shall be used to protect elevated tanks against failure while yielding occurs in the chosen support system ™ Damping ratio € depends on soil type and aspect ratio of tank. Values given here are for soil with shear-wave velocity of 500 m/s and height to radius ratio of 2.0.
Figure 1. Base shear coefficient for RC/PSC tanks.
Figure 1. Base shear coefficient for RC/PSC tanks.
Figure 2. Base shear coefficient for ground-supported steel tanks.
Figure 2. Base shear coefficient for ground-supported steel tanks.
Figure 3. Base shear coefficient for elevated tanks.
Figure 3. Base shear coefficient for elevated tanks.
Table 8. Parameters from various codes and standards
Table 8. Parameters from various codes and standards
In ASCE 7, the value of 7; is taken as 4 s. * common for ACI 350.3, D-110, and D-115 Table 9. Comparison of base shear coefficient obtained from original expressions of various American industry standards with their modified expressions given in ASCE 7!
In ASCE 7, the value of 7; is taken as 4 s. * common for ACI 350.3, D-110, and D-115 Table 9. Comparison of base shear coefficient obtained from original expressions of various American industry standards with their modified expressions given in ASCE 7!
'RC tanks and unanchored steel tanks ? PSC tanks 3 Anchored steel tanks with ductile bolts Table 10. Comparison of sloshing wave height from various codes and standards
'RC tanks and unanchored steel tanks ? PSC tanks 3 Anchored steel tanks with ductile bolts Table 10. Comparison of sloshing wave height from various codes and standards

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  23. 260 O. R. JAISWAL, D. C. RAI, AND S. K. JAIN

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