Try this code :
REPORT YTEST.
data gt_tab type table of string.
data gs_tab type string.
data result type string.
data length type i.
gs_tab = 'Hello'. append gs_tab to gt_tab.
gs_tab = 'Hello How'. append gs_tab to gt_tab.
gs_tab = 'Hello How Are'. append gs_tab to gt_tab.
gs_tab = 'Hello How Are You'. append gs_tab to gt_tab.
loop at gt_tab into gs_tab.
if result is INITIAL.
result = gs_tab.
else.
length = strlen( result ).
CONCATENATE result gs_tab+length into result.
endif.
clear gs_tab.
endloop.
write : / result.
Regards,
Gagan