ASCE7 & API Load Combinations PDF

 

Load combinations and calculations A. ASCE 7 strength-design load combinations  1. 1.4(DL + F) 2. 1.2(DL + F + T) + 1.6(L + H) + 0.5(L r or S or R) 3. 1.2 DL + 1.6(Lr or S or R) + (0.5L or 0.8W) 4. 1.2 DL + 1.6W + 0.5L + 0.5(Lr or S or R) 5. 1.2 D + 1.0E + 0.5L + 0.2S 6. 0.9 DLL + 1.6 W + 1.6 H 7. 0.9 DL + 1.0E + 1.6 H

Long-term loads Live load Roof load Wind Seismic Overturning from wind Overturning from seismic

B. Revised ASCE 7 strength-design load combinations  1. 1.4(DL + F) 2. 1.2(DL + F) + 1.6P + 0.5(Lr or S) 3. 1.2 DL + 1.6(Lr or S) + (0.5P or 0.8W) 4. 1.2 (DL + F) + 1.6W + 0.5P + 0.5(L r or S) 5. 1.2 (DL + F) + 1.0E + 0.5P + 0.2S

Long-term loads Live loads Roof loads Wind loads Seismic loads

C. API load combinations when ASCE load factors are divided by 1.4  Allowable stress; API load combinations Strength design; ASCE load combinations 1. DL + F 1. 1.4(DL + F) 2. 0.9(DL + F) + 1.1P + 0.4(Lr or S) 2. 1.2(DL + F) + 1.6P + 0.5(Lr or S) 3. 0.9 DL + 1.1(Lr or S) + (0.4P or 0.6W) 3. 1.2 DL + 1.6(Lr or S) + (0.5P or 0.8W) 4. 0.9 DL + 0.9 F + 1.1W + 0.4P + 0.4(L r or S) 4. 1.2 (DL + F) + 1.6W + 0.5P + 0.5(L r or S) 5. 0.9 DL + 0.9 F + 0.7E + 0.4P + 0.1S 5. 1.2 (DL + F) + 1.0E + 0.5P + 0.2S D. Pressure substitutions in load combinations  1. DL + F 2a. 0.9(DL + F) + 1.1Pi + 0.4(Lr or S) 2b. 0.9(DL + F) + 1.1Pe + 0.4(Lr or S) 3a. 0.9 DL + 1.1(Lr or S) + (0.4Pi or 0.6W) 3b. 0.9 DL + 1.1(Lr or S) + (0.4Pe or 0.6W) 4a. 0.9 DL + 0.9 F + 1.1W + 0.4Pi + 0.4(Lr or S) 4b. 0.9 DL + 0.9 F + 1.1W + 0.4Pe + 0.4(Lr or S) 5a. 0.9 DL + 0.9 F + 0.7E + 0.4Pi + 0.1S 5b. 0.9 DL + 0.9 F + 0.7E + 0.4Pe + 0.1S E. Discarding load combinations that counteract  1. DL + F 2a. 0.9(DL + F) + 1.1Pi + 0.4(Lr or S) 2b. 0.9(DL + F) + 1.1Pe + 0.4(Lr or S)

Roof gravity loads counteract internal pressure. Fluid counteracts external pressure and roof loads.

 

3a. 3b. 4a. 4b.

0.9DL + 1.1(Lr or S) + (0.4Pi or 0. 0.6W) 0.9DL + 1.1(Lr or S) + (0.4Pe or 0. 0.6W 6W)) 0.9(DL + F) + 1.1W + 0.4Pi + 0.4(Lr or S) 0.9(DL + F) + 1.1W + 0.4Pe + 0.4(Lr or S) 0.9 DL + 1.1W + 0.4Pe + 0.4(Lr or S) 0.9 DL + 1.1W + 0.4Pe + 0.4(Lr or S) 5a. 0.9 DL + 0.9 F + 0.7E + 0.4Pi + 0.1S 5b. 0.9 DL + 0.9 F + 0.7E + 0.4Pe + 0.1 0.1S S

Intern rnal al pressure an and wi win nd co counteract ro roof lo loads. Win ind d co coun unte tera ract cts s ro roo of lo load ads s an and d ext xte ern rnal al pr pres essu sure re.. Roof Ro of gr grav avity ity loa loads ds co coun unte tera ract ct win wind d and and pr pres essu sure re up uplif lift. t. Becomes two cases: Roof loads don’t affect shell compression. Wind uplift counteracts Pe and roof loads. Internal pressure and seismic add on anchors. Exte Ex tern rnal al pr pres essu sure re is no nott a fa fact ctor or fo forr ve vert rtic ical al sh shel elll com compr pres essi sion on..

F. Resulting combinations  1. DL + F 2a. 0.9 DL + 0.9F + 1.1Pi 2b. 0.9 DL + 1.1Pe + 0.4(Lr or S) 3a. 0.9 DL + 1.1(Lr or S) 3b. 0.9 DL + 1.1(Lr or S) + 0.4Pe 4a. 0.9 DL + 1.1W + 0.4Pi 4b1. 4b 1. 0. 0.9 9 DL + 1.1W + 0.4Pe 4b2. 4b 2. 0. 0.9 9 DL + 0.4Pe + 0.4(Lr or S) 5. 0.9 DL + 0.9 F + 0.7E + 0.4Pi + 0. 0.1S

Shell - hoop tension Shell - hoop tension Roof - downward load; Shell - vertical compression. Roof - downward load Roof - downward load Roof - uplift Shell - hoop compression Roof - downward load Shell - vertical co compression, An Anchors - tension

G. Grouping combinations according to affected tank component  1. DL + F Shell - hoop tension 2a. 0.9 DL + 0.9F + 1.1Pi Shell - hoop tension 5. 0.9 DL + 0.9 F + 0.7E + 0.4Pi + 0.1S Shell - vertical compression; anchor bolts 2b. 0.9 DL + 1.1Pe + 0.4(Lr or S) Shell - vertical compression 4b1. 4b 1. 0. 0.9 9 DL + 1.1W + 0.4Pe Shell - hoop compression 2b. 0.9 DL + 1.1Pe + 0.4(Lr or S) Roof - downward load 3a. 0.9 DL + 1.1(Lr or S) Roof - downward load 3b. 0.9 DL + 1.1(Lr or S) + 0.4Pe Roof - downward load 4b2. 4b 2. 0. 0.9 9 DL + 0.4Pe + 0.4(Lr or S) Roof - downward load 4a. 0.9 DL + 1.1W + 0.4Pi Roof – uplift H. Loads after adjustments, eliminating redundant combinations  Combination Component checked 2a. DL + F + Pi Shell - hoop tension 4a. DL + W + 0.4Pi Roof - compression ring 2a. DL + Pi Roof - compression ring (this is the same as the shell check but with fluid load F absent) 4b1. DL + W + 0.4Pe Shell - hoop compression 3b. DL +(Lr or S) + 0.4Pe Roof - downward load 2b. DL + Pe + 0.4(Lr or S) Roof - downward load 5. DL + F + 1.0E + 0.4Pi + 0.1S Shell - vertical compression; anchor bolts

API 650 Appendix letter (a) (c)

(d) (e)(1) (e)(2) (f)