How to append an element to a row inside a 2-dim. array?

Hi,

Question regarding arrays: How can I append an element to a row inside
a 2-dim. array?
See example below.
And:
Does anybody have experiences how arrays perform if data grows (it's
"read-mostly")?

Yours, Stefan

--
-- Arrays Test
--

CREATE TABLE ourarrtable (id int primary key, arr int[]);

INSERT INTO ourarrtable VALUES (1, '{1,2,3}');
INSERT INTO ourarrtable VALUES (2, '{{11,12,13},{21,22,23},{31,32,33}}');

SELECT * FROM ourarrtable ORDER BY id;
/*
1;"{1,2,3}"
2;"{{11,12,13},{21,22,23},{31,32,33}}"
*/
SELECT arr[1:1] FROM ourarrtable WHERE id=2;
-- "{{11,12,13}}"

-- Works for 1-dim. array in row 1:
UPDATE ourarrtable SET arr = array_append(arr, 4) WHERE id = 1;

-- How to append say number 14 to '{11,12,13}' inside 2-dim. array?
UPDATE ourarrtable SET arr[1:1] = array_cat(arr[1:1], 14) WHERE id = 1;
/*
ERROR:  Function array_cat(integer[], integer) does not exist
LINE 1: UPDATE ourarrtable SET arr[1:1] = array_cat(arr[1:1], 14) WH...
*/