I tried a lot but I couldn't solve this poroblem. My aim write a variable in single quote to set dynamic active but when I want to do it I get syntax errors.
$('#tabs a[href="#vtab" + result.step_next + ]').tab('show');
Moving my comment to an answer
You aren't concatenating the string properly. Try:
$('#tabs a[href="#vtab' + result.step_next + '"]').tab('show');
It appears to work here.