Request for explanation for load combination for Anchor Bolt design

[maverick29]

Hi Friends,

I am designing Anchor Bolt for tank using strength design method (ASCE7-05). As I understand we need to use to Eq. 5 and 7 to get tension on AB, i.e.


(1.2+0.2Sds)*D+ Over strength Factor*QE Eq 5

(0.9-0.2Sds)*D+ Over strength factor*QE Eq 7

In Eq 5 :

1.2 and 0.2Sds will be in same direction as D and opposite to earthquake forces in horizontal direction to get tension on Anchor Bolt

In Eq 7:

(0.9-0.2Sds)*D will be opposite to Earthquake forces in horizontal direction to get
tension in Anchor Bolt


I am getting confused with different directions. I will appreciate if somebody can explain me the directions.

Thanks for the Help