This belt looks similor to those normal to adventuring.
It is imbued with very powerful magic, of course, and when
worn it increases the physical prowess of its wearer as follows:

<+>

The wearer of the girdle is able to otherwise hurl rocks && bend bars as if
he or she had imbibed a potion of giant strength. These abilities are:
 

Dice Roll	Type of Giant Strength	Rating	To Hit	Damage	Open Doors	<>	Weight Allowance	Range	Base Damage	Rock Wt. **	Bend Bars/  Lift Gates
01-30	Hill ()	19	+ 3	+ 7	7 in 8 (3)	Hill	+ 450	8"	1-6	14	50%
31-50	Stone ()	20	+ 3	+ 8	7 in 8 (3)	Stone	+ 500	16"	1-12	19.8	60%
51-70	Frost ()	21	+ 4	+ 9	9 in 10 (4)	Frost	+ 600	10"	1-8	15.6	70%
71-85	Fire ()	22	+ 4	+ 10	11 in 12 (4)	Fire	+ 750	12"	1-8	17	80%
86-95	Cloud	23	+ 5	+ 11	11 in 12 (5)	Cloud	+ 900	14"	1-10	18.4	90%
96-00	Storm	24	+ 6	+ 12	19 in 20 (7 in 8)	Storm	+ 1200	16"	1-12	21.2	100%

* The number in parentheses is the number of chances out of 6 (8 for storm
giant strength) for the character to be able to force open a locked,
barred, magically held, or wizard locked door, but only one attempt ever
(per door) may be made, and if it fails, no further attempts can succeed.

** Approximate average missile weight.

The strength gained is not cumulative with normal or magical strength
bonuses except with regard to use in combination with gauntlets of ogre power and magic war hammers (q.v.).
 

Question: How much experience are the various Girdles of
Giant Strength worth? I seriously doubt 200, when Gauntlets
of Ogre Power are worth 1,000.

Answer: The Girdles are only worth 200 points for several reasons.
First, while they do add to the strength of an individual, they do little to add to the intelligence or cautiousness of that being.
Secondly, while the strength of a giant is given, the giant’s innate toughness is not conferred upon the wearer.
This means that while a giant could smash its fist through a wooden door, a human would break bones when doing it.
While a giant could hurl bars apart, a human would rip flesh in the attempt.
The gauntlets, on the other hand, offer a great deal of protection for the hands and arms and thus are worth more. — JW

Q: I understand that strength bonuses
from gauntlets of ogre power
and the various girdles of giant
strength are cumulative under certain
conditions. What are these conditions?
A: These items are cumulative only when
the wearer is wielding a magical war
hammer, either held or hurled. (See the
DMG, page 145, girdle of giant strength;
the reference to ?hurled weapon? in the
text for the gauntlets of ogre power on the
same page should be taken to mean a
magical war hammer. See also pages 168
169, hammer +3, dwarven thrower and
hammer of thunderbolts.) The gauntlets?
and girdle?s powers may not be combined
for any other purpose.
(147.12)

Q: If a character wearing gauntlets of
ogre power or a girdle of giant
strength is struck by a shadow or
other attack that drains strength,
what happens?
A: Temporary strength losses are taken
from the character?s augmented strength
score, and results are taken accordingly.
Such losses are always a full point, so that
a hit from a shadow will reduce a character
wearing gauntlets of ogre power to a
17 strength. Permanent strength losses,
such as those due to aging, are taken from
the character?s base strength score. In
these cases, the magically augmented
score is unchanged.
(147.12)

Q: In the DMG, page 123, the sale
price of a girdle of giant strength is
listed as 2,500 gp. Isn?t this a bit
low? Gauntlets of ogre power,
which bestow less strength, sell for
10,000 gp.
A: This was a misprint. The sale price for
such a girdle is 25,000 gp. The experience
value was also misprinted; it should be
2,000 xp, not 200 xp. Note that a girdle
imbues the wearer?s entire body with
extra strength, while the gauntlets enhance
only the wearer?s chest and arms.
(147.12)


Belt of giant strength

Q: Will gauntlets of ogre power or a
girdle of giant strength allow a
demi-human fighter an increased
level-advancement limit?
A: Strength bestowed by magical items
such as girdles or gauntlets is temporary;
it lasts only as long as a character wears
such an item. Thus, these items do not
allow extra advancement in level. Only a
permanent increase in an ability score will
allow extra advancement.
(147.12)