ALV Summ Issue

hellow Expertes,

please see the below structuer.

TYPES: BEGIN OF i_alv,                                    
  PERNR TYPE PA0001-PERNR,
  ENAME TYPE PA0001-ENAME,
  BET01 TYPE PA0008-BET01,
 BET02 TYPE PA0008-BET02,
 BET03 TYPE PA0008-BET03,
  BET04 TYPE PA0008-BET04,
   LSW1(10),
 END OF i_alv.

DATA: it_alv TYPE STANDARD TABLE OF i_alv INITIAL SIZE 0,
      wa_alv TYPE i_alv.

i want to disply LSW1 = bet01 + bet02 + bet03 + bet04

i made one loop like below

loop at it_alv into wa_alv.
WA_alv-LSW1 = wa_alv-bet01 + wa_alv-bet02 + wa_alv-bet03 + wa_alv-bet04.
endloop.

but nothing is showing , i already tried with Append and collect statment please help me out to resolve this issue.

Thanks.