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                                                                    Exhibit 3.21


                               STATE OF DELAWARE
                                        
                                  [STATE SEAL]
                                        
                          OFFICE OF SECRETARY OF STATE
                                        

        I, MICHAEL HARKINS, SECRETARY OF STATE OF THE STATE OF DELAWARE DO
HEREBY CERTIFY THE ATTACHED IS A TRUE AND CORRECT COPY OF THE CERTIFICATE OF
INCORPORATION OF ARDEE INVESTMENT CO., INC. FILED IN THIS OFFICE ON THE
THIRTY-FIRST DAY OF AUGUST, A.D. 1988 AT 9 0'CLOCK A.M.


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[STATE SEAL]
DEPARTMENT OF STATE
OFFICE OF THE SECRETARY OF STATE        /s/ Michael Harkins
1835   1793   1970                      ---------------------------------------
DELAWARE                                    Michael Harkins, Secretary of State

882440099
                                        AUTHENTICATION:  |844918

                                                  DATE:  08/31/1988
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                         CERTIFICATE OF INCORPORATION

                                      OF

                          ARDEE INVESTMENT CO., INC.


        THE UNDERSIGNED, in order to form a corporation for the purposes
hereinafter stated, under and pursuant to the provisions of the General
Corporation Law of the State of Delaware, does hereby certify as follows:

                                  ARTICLE I
                                  ---------

        The name of the Corporation is Ardee Investment Co., Inc.

                                  ARTICLE II
                                  ----------

        The registered office of the Corporation in the State of Delaware is
located at 229 South State Street, in the City of Dover, County of Kent. The
name of the Corporation's registered agent in the State of Delaware at such
address is The Prentice-Hall Corporation System, Inc.

                                 ARTICLE III
                                 -----------

        The purpose of the Corporation is to engage in any lawful act or
activity for which corporations may be organized under the General Corporation
Law of Delaware.

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                                  ARTICLE IV
                                  ----------


        The total number of shares of stock which the Corporation shall have
authority to issue is three thousand (3,000) shares of Common Stock, with a par
value of $.01 per share.

                                  ARTICLE V
                                  ---------

        Election of directors need not be by ballot unless the By-Laws of the
Corporation shall so provide.

                                  ARTICLE VI
                                  ----------

        In furtherance and not in limitation of the power conferred upon the
Board of Directors by law, the Board of Directors shall have power to make,
adopt, alter, amend and repeal, from time to time, the By-Laws of the
Corporation, subject to the right of the stockholders entitled to vote with
respect thereto to alter and repeal By-Laws made by the Directors.

                                 ARTICLE VII
                                 -----------

        The incorporator of the Corporation is Frank T. Guadagnino, whose
mailing address is Box 2009, Pittsburgh, Pennsylvania 15230.


                                 ARTICLE VIII
                                 ------------

                       Personal Liability of Directors
                       -------------------------------

        1.  To the fullest extent that the laws of the State of Delaware, as
the same exist or may hereafter be amended, permit

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elimination of the personal liability of directors, no director of this
Corporation shall be personally liable to this Corporation or its stockholders
for monetary damages for breach of fiduciary duty as a director.

        2.  The provisions of this Article VIII shall be deemed to be a
contract with each director of this Corporation who serves as such at any time
while this Article VIII is in effect, and each such director shall be deemed to
be serving as such in reliance on the provisions of this Article VIII.  Any
amendment or repeal of this Article VIII or adoption of any By-Law of this
Corporation or other provision of the Certificate of Incorporation of this
Corporation which has the effect of increasing director liability shall operate
prospectively only and shall not affect any action taken, or any failure to
act, by a director of this Corporation prior to such amendment, repeal, By-Law
or other provision becoming effective.

                                   ARTICLE IX
                                   ----------

                    Indemnification of, and Advancement of
                 Expenses to, Directors, Officers and Others.
                 --------------------------------------------

        1.  RIGHT TO INDEMNIFICATION.  Except as prohibited by law, every
director and officer of the Corporation shall be entitled as of right to be
indemnified by the Corporation against all expenses and liability (as those
terms are defined below in this Paragraph 1) incurred by such person in
connection with any actual or threatened claim, action, suit or proceeding,
whether

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civil, criminal, administrative, investigative or other, or whether brought by
or against such person or by or in the right of the Corporation or otherwise, in
which such person may be involved, as a party or otherwise, by reason of such
person being or having been a director or officer of the Corporation or a
subsidiary of the Corporation or by reason of the fact that such person is or
was serving at the request of the Corporation as a director, officer, employee,
fiduciary or other representative of another corporation, partnership, joint
venture, trust, employee benefit plan or other entity (such claim, action, suit
or proceeding hereinafter being referred to as "Action"); provided, however,
that no such right to indemnification shall exist with respect to an Action
brought by an indemnitee (as defined below) against the Corporation (an
"Indemnitee Action") except as provided in the last sentence of this Paragraph
1. Persons who are not directors or officers of the corporation may be similarly
indemnified in respect of service to the Corporation or a subsidiary of the
Corporation or to another such entity at the request of the Corporation to the
extent the Board of Directors of the Corporation at any time designates any of
such persons as entitled to the benefits of this Article IX. As used in this
Article IX, "indemnitee" includes each director and officer of the Corporation
and each other person designated by the Board of Directors of the Corporation as
entitled to the benefits of this Article IX; "expenses" means all expenses
actually and reasonably incurred, including fees and expenses of counsel
selected by an indemnitee; and "liability" means all liability incurred,


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including the amounts of any judgments, excise taxes, fines or penalties and
any amounts paid in settlement. An indemnitee shall be entitled to be
indemnified pursuant to this Article against expenses incurred in connection
with an Indemnitee Action if (i) the Indemnitee Action is instituted under
paragraph 3 of this Article IX and the indemnitee is successful in whole or in
part in such Indemnitee Action, (ii) the indemnitee is successful in whole or
in part in another Indemnitee Action for which expenses are claimed or (iii) the
indemnification for expenses is included in a settlement of, or is awarded by
a court in, such other Indemnitee Action.

        2.  RIGHT TO ADVANCEMENT OF EXPENSES.  Every indemnitee shall be
entitled as of right to have the expenses of the indemnitee in defending any
Action or in bringing and pursuing any Indemnitee Action under Paragraph 3 of
this Article IX paid in advance by the Corporation prior to final disposition
of the Action or Indemnitee Action, provided that the Corporation receives a
written undertaking by or on behalf of the indemnitee to repay the amount
advanced if it should ultimately be determined that the indemnitee is not
entitled to be indemnified for the expenses.

        3. RIGHT OF INDEMNITEE TO BRING ACTION. If a written claim for
indemnification under Paragraph 1 of this Article IX or for advancement of
expenses under Paragraph 2 of this Article IX is not paid in full by the
Corporation within 30 days after the

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claim has been received by the Corporation, the indemnitee may at any time
thereafter bring an Indemnitee Action to recover the unpaid amount of the claim
and, if successful in whole or in part, the indemnitee shall also be entitled to
be paid the expense of bringing and pursuing such Indemnitee Action. The only
defense to an Indemnitee Action to recover on a claim for indemnification under
Paragraph 1 of this Article IX shall be that the conduct of the indemnitee was
such that under Delaware law the Corporation is prohibited from indemnifying the
indemnitee for the amount claimed, but the burden of proving such defense shall
be on the Corporation.  Neither the failure of the Corporation (including its
Board of Directors, independent legal counsel and stockholders) to have made a
determination prior to the commencement of such Indemnitee Action that
indemnification of the indemnitee is proper in the circumstances, nor an actual
determination by the Corporation (including its Board of Directors, independent
legal counsel or stockholders) that the conduct of the indemnitee was such that
indemnification is prohibited by Delaware law, shall be a defense to such
Indemnitee Action or create a presumption that the conduct of the indemnitee was
such that indemnification is prohibited by Delaware law. The only defense to an
Indemnitee Action to recover on a claim for advancement of expenses under
Paragraph 2 of this Article IX shall be failure by the indemnitee to provide the
undertaking required by Paragraph 2 of this Article IX.

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        4.  FUNDING AND INSURANCE.  The Corporation may create a trust fund,
grant a security interest, cause a letter of credit to be issued or use other
means (whether or not similar to the foregoing) to ensure the payment of all
sums required to be paid by the Corporation to effect indemnification as
provided in this Article IX. The Corporation may purchase and maintain
insurance to protect itself and any indemnitee against any expenses or
liability incurred by the indemnitee in connection with any Action, whether or
not the Corporation would have the power to indemnify the indemnitee against the
expenses or liability by law or under the provisions of this Article IX.

        5. NON-EXCLUSIVITY; NATURE AND EXTENT OF RIGHTS. The rights to
indemnification and advancement of expenses provided for in this Article IX 
shall (i) not be deemed exclusive of any other rights, whether now
existing or hereafter created to which any indemnitee may be entitled under any
agreement, provision in the Certificate of Incorporation or By-Laws of the
Corporation, vote of stockholders or disinterested directors or otherwise, (ii)
be deemed to create contractual rights in favor of each indemnitee who serves
at any time while this Article IX is in effect (and each such indemnitee shall
be deemed to be serving in reliance on the provisions of this Article IX),
(iii) continue as to each indemnitee who has ceased to have the status
pursuant to which the indemnitee was entitled or was designated as entitled to
indemnification under this Article IX and insure to the benefit of the heirs
and legal representatives of each indemnitee and (iv) be

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applicable to Actions commenced after this Article IX becomes effective, whether
arising from acts or omissions occurring before or after this Article IX becomes
effective. Any amendment or repeal of this Article IX or adoption of any By-Law
of this Corporation or other provision of the Certificate of Incorporation of
this Corporation which has the effect of limiting in any way the rights to
indemnification or advancement of expenses provided for in this Article IX shall
operate prospectively only and shall not affect any action taken, or any failure
to act, by an indemnitee prior to such amendment, repeal, By-Law or other
provision effective.

        6. PARTIAL INDEMNITY.  If an indemnitee is entitled under any provision
of this Article IX to indemnification by the Corporation for some or a portion
of the expenses or liability incurred by the indemnitee in the preparation
investigation, defense, appeal or settlement of any Action or Indemnitee
Action but not, however, for the total amount thereof, the Corporation shall
indemnify the indemnitee for the portion of such expenses or liability to which
the indemnitee is entitled.

        IN WITNESS WHEREOF, I have hereunto set my hand and seal this 30th day
of August, 1988.


                                        /s/ Frank T. Guadagnino
                                        ---------------------------------------
                                        Frank T. Guadagnino, Incorporator

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