Conditional Statement in QGIS Field Calculator

I'm using QGIS to calculate total loss in an earthquack attack. I wrote this expression in Field Calculator.

CASE 

WHEN  "build_type"  = 1 AND  "MMI"  < 5  THEN  "perc_loss"  = 0
WHEN  "build_type"  = 1 AND  (5 >= "MMI" AND "MMI" < 6) THEN  "perc_loss"  = 20
WHEN  "build_type"  = 1 AND  (6 >=  "MMI" AND "MMI" < 7) THEN  "perc_loss"  = 28
WHEN  "build_type"  = 1 AND  (7 >=  "MMI" AND "MMI" < 8) THEN  "perc_loss"  = 33
WHEN  "build_type"  = 1 AND  (8 >=  "MMI" AND "MMI" < 9) THEN  "perc_loss"  = 35
WHEN  "build_type"  = 1 AND  (9 >=  "MMI" AND "MMI" < 10) THEN  "perc_loss"  = 71
WHEN  "build_type"  = 1 AND   "MMI"  >= 10 THEN  "perc_loss"  = 95 END

There's no error/invalid warning, but no value resulted. Is there any wrong syntax I used? Anyone can help please? :)

Answer

I think it should be

CASE 
WHEN  "build_type"  = 1 AND  "MMI"  < 5  THEN   0
...

without the "perc_loss" = part