Dear sirs,
According to the Seismic report of the Tank v.3.20 the value of the Ac (convective spectral accel parameter) is exactly the same with the value of Ai (impulsive spectral accel parameter).Why is that? Shall I consider it correct? Thanks in advance

SEISMIC EVALUATION RESULTS - Appendix E
API-650 11th Edition, Addendum 1, Nov. 2008
Site-Specific Ground Motion

Design Fluid Weight (N. ) 0.41141E+07
Sp -design level peak accel for nonASCE 0.24000
Ss -MCE at period of 0.2 seconds 0.60000
S0 -MCE at period of 0.0 seconds 0.24000
S1 -MCD at period of 1.0 seconds 0.30000
SDS-design spectral accel parameter 1.1700
FA -acceleration based site coefficient 1.3200
FV -velocity based site coefficient 1.8000
TS - FvS1 / FaSs 0.68182
TC -convective sloshing period (sec) 2.8863
Ac -convective spectral accel parameter 0.22286
Ai -impulsive spectral accel parameter 0.22286

Note how equation E.4.6.2-3 is written in the Code:

Ac = QK(I/Rwc)SaX < Ai

It is this " < Ai" that is important to your question. If the computation results in a value of Ac larger than Ai, then Ac is reset to be equal to Ai.

At that specific tank the value of Ac is larger than the value of Ai so it is correct to proceed with Ac=Ai but i have noticed with other tanks calculations, that even if the Ac value is smaller than Ai the seismic results are always Ac=Ai.

Send me one of "those" and I'll look at it.

API Design Code ( 650 or 653 )...... 650
Design Method (V, O, or A) ........ O
(V=variable, O=one foot, A=Appendix A)
Run Objective (D=design, A=analyze). A

Design Temperature ...........(C ) 70.000
Design Pressure at Top ..(KPa ) 1.5000
Shell Material .................. S 355
Shell Design Stress [Sd] .(KPa ) 0.19581E+06
Shell Hydro Test Stress [St] ..(KPa) 0.20994E+06
Tank Nominal Diameter [D] ....(m. ) 49.200
Tank Shell Height [HTK] .....(m. ) 20.000
Design Liquid Level [H] .......(m. ) 19.600
Liquid Specific Gravity [G] ..... 1.0100
Weight of Attachments/Structures.(N. ) 0.15000E+06
Distance down to Top Wind Girder (m ) 0.00000
Joint Efficiency (App A or 653) [E] 0.85000
Wind Velocity ......(M./sec. ) 53.000
Insulation Thickness .......(mm.) 0.00000
Insulation Density ....(kg./cu.cm.) 0.00000
Include Annular Base Plate Details . Yes
Include Wind Moment in Appendix F_4_2 Calculations Yes

Number of Shell Courses ........... 8
Shell Course # 1 Height ....(m. ) 2.5000
Shell Course # 1 Thickness ...mm.) 28.000
Shell Course # 1 Corrosion Allowance [CA] (mm.) 2.0000
Shell Course # 2 Height ...(m. ) 2.5000
Shell Course # 2 Thickness mm.) 24.000
Shell Course # 2 Corrosion Allowance [CA] mm.) 1.5000
Shell Course # 3 Height m. ) 2.5000
Shell Course # 3 Thickness mm.) 22.000
Shell Course # 3 Corrosion Allowance [CA] mm.) 1.5000
Shell Course # 4 Height m. ) 2.5000
Shell Course # 4 Thickness mm.) 18.000
Shell Course # 4 Corrosion Allowance [CA] mm.) 1.5000
Shell Course # 5 Height m. ) 2.5000
Shell Course # 5 Thickness mm.) 16.000
Shell Course # 5 Corrosion Allowance [CA] mm.) 1.5000
Shell Course # 6 Height m. ) 2.5000
Shell Course # 6 Thickness mm.) 14.000
Shell Course # 6 Corrosion Allowance [CA] mm.) 1.5000
Shell Course # 7 Height m. ) 2.5000
Shell Course # 7 Thickness mm.) 10.000
Shell Course # 7 Corrosion Allowance [CA] mm.) 1.5000
Shell Course # 8 Height m. ) 2.5000
Shell Course # 8 Thickness mm.) 8.0000
Shell Course # 8 Corrosion Allowance [CA] mm.) 1.5000
ANCHOR BOLT DETAILS
Anchor Bolt Diameter (optional) ...(mm.) 0.00000
Threads per Unit Length (1/mm.) 0.27000
Bolt Allowable Stress ...(KPa ) 0.00000
Number of Anchor Bolts (optional) 0.00000
Bolt Yield Stress .....(KPa ) 0.30000E+06
Bolt Offset from Mean Tank Diameter .(m. )0.10000
Anchor Bolt Corrosion Allowance (optional) .(mm.) 0.00000

Wind Data
Kz parameter 1.0400
Kzt parameter 1.0000
Kd parameter 0.95000
Importance Factor (I) 1.0000
Gust Factor (G) 0.85000


API-650 SEISMIC DATA (AppE.)
Minimum Yield Strength of Bottom Plate .....(KPa 0.34500E+06
Minimum Yield Strength of Weld Material ....(KPa 0.34500E+06
Nominal Thickness of Bottom Plate (tb) ..........(mm. ) 8.0000
Seismic Use Group (SUG1.0000
Friction Factor 0.40000
Importance Factor 1.0000
Initial Anchorage Type S
Earthquake Type S
Site Class 4.0000
Spectral Acceleration Adjustment Coefficient (K) 1.5000
Scaling Factor (Q) 1.0000
Transtiional Period (TL) 4.0000
Mapped maximum earthquake for short periods (Ss) 0.00000
Mapped maximum earthquake for 1 sec periods (S1) 0.00000
Mapped maximum earthquake for 0 sec period (S0) 0.00000
Non-ASCE peak ground acceleration (Sp) 0.36000
ASCE short period design acceleration parameter (SDS) 1.5000
--- Site Specific Data ---
Spectral acceleation parameter at 0 period (Sa0*) ..... 0.40320
Spectral acceleation parameter at any period (Sa*) .... 1.0080

SEISMIC EVALUATION RESULTS - Appendix E
API-650 11th Edition, Addendum 1, Nov. 2008

Site-Specific Ground Motion

Design Fluid Weight (N. ) 0.36863E+09

Sp -design level peak accel for nonASCE 0.36000
Ss -MCE at period of 0.2 seconds 0.90000
S0 -MCE at period of 0.0 seconds 0.36000
S1 -MCD at period of 1.0 seconds 0.45000
SDS-design spectral accel parameter 1.5000

FA -acceleration based site coefficient 1.1400
FV -velocity based site coefficient 1.5500
TS - FvS1 / FaSs 0.67982
TC -convective sloshing period (sec) 7.7458

Ac -convective spectral accel parameter 0.28800
Ai -impulsive spectral accel parameter 0.28800
Wc -effective convective fluid weight(N. ) 0.19113E+09
Wi -effective impulsive fluid weight (N. ) 0.16524E+09
Vc -convective liquid base shear (N. ) 0.55045E+08
Vi -impulsive liquid base shear (N. ) 0.49187E+08
V -total design base shear (N. ) 0.73819E+08
VS -shear resistance (N. ) 0.13710E+09

Xc -ring wall convective moment arm (m. ) 11.239
Xi -ring wall impulsive moment arm (m. ) 7.3500
XCS-slab convective moment arm (m. ) 17.392
XIS-slab impulsive moment arm (m. ) 19.409
WS -shell+appurtenances weight (N. ) 0.42900E+07
Wrs-roof, framing 10% snow weight (N. ) 0.00000
Mrw-ringwall overturning moment (N.m. ) 0.71553E+09
Ms -slab overturning moment (N.m. ) 0.13371E+10

AV -vertical acceleration parameter 0.21000
Ge -effective specific gravity 0.92516

wa -resisting annulus force (N./cm. ) 683.77
wt -tank + roof weight at shell base (N./cm. ) 277.55
J -the anchorage ratio 3.1514
L -reqd min annular plate projection (m. ) 0.65635

Anchorage ratio too large, anchors needed

Wab-Minimum anchorage resistance (N./cm. ) 8912.1
N -number of anchor bolts required 52
Pab-anchor seismic design load (N. ) 0.10429E+07
Sc -shell compressive stress (KPa ) 14514.
Sa -shell allowable stress (KPa ) 47085.

Height of sloshing wave (m. ) 1.7159
Required Freeboard (m. ) 1.2011

Just e-mail the TKI file to techsupport@coade.com

Ok i have sent an e-mail.I will look forward for your reply