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                                                                     EXHIBIT 3.1

                              AMENDED AND RESTATED
                           ARTICLES OF INCORPORATION
                                       OF
                             PITT-DES MOINES, INC.


          FIRST. The name of the Corporation is Pitt-Des Moines, Inc.

          SECOND. The location and post office address of its registered office
in this Commonwealth is Neville Island, 3400 Grand Avenue, Pittsburgh,
Pennsylvania 15225.

          THIRD. The purpose or purposes of the Corporation are to have
unlimited power to engage in and to do any lawful act concerning any or all
lawful business for which corporations may be incorporated under the Business
Corporation Law, approved the 5th day of May, A.D. 1933, P.L. 364, as amended,
including but not limited to, manufacturing, processing, research or
development, and the business of engineering, fabricating and erecting steel and
other metal structures of all types.

          FOURTH. The term of its existence is perpetual.

          FIFTH. (a) The Corporation shall have the power to create and issue a
total of eighteen million shares, divided into a class of fifteen million shares
of Common Stock, no par value, and a class of three million shares of Preferred
Stock, par value $.01 per share.  The Preferred Stock shall be divided into one
or more series as the Board of Directors may determine as hereinafter provided.

     (b) The holders of Common Stock shall have one vote per share.  The Common
Stock shall be subject to the prior rights of holders of any series of Preferred
Stock outstanding, according to the preferences, if any, of such series.

     (c) Each series of Preferred Stock may have full, limited, multiple or
fractional, or no voting rights, and such designations, preferences,
qualifications, privileges, limitations, restrictions, options, conversion
rights and other special or relative rights as determined by the Board of
Directors as hereinafter provided.  The division of the Preferred Stock into
series, the determination of the designation and the number of shares of any
such series and the determination of the voting rights, preferences,
qualifications, privileges, limitations, restrictions, options, conversion
rights and other special or relative rights of the shares of any such series may
be accomplished by an amendment to this Article FIFTH which amendment may be
made solely by action of the Board of Directors which shall have the full
authority permitted by law to make such division and determinations.

     (d) Unless otherwise provided by law or in a resolution or resolutions
establishing any particular series of Preferred Stock, the aggregate number of
authorized shares of Preferred Stock may be increased by an amendment to the
Articles of Incorporation approved solely by the 
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holders of the Common Stock and of any Preferred Stock which is entitled
pursuant to its voting rights designated by the Board to vote thereon, if at
all, voting together as a class.

     (e) Shares may be issued at a price determined by the Board of Directors or
the Board may set a minimum price or establish a formula or method by which the
price may be determined.  Consideration for shares may consist of money,
obligations (including an obligation of a shareholder), services performed
whether or not contracted for, contracts for services to be performed or any
other tangible or intangible property.  If shares are issued for other than
money, the value of the consideration shall be determined by or in a manner
provided by the Board of Directors. Consideration for shares shall be paid to
the Corporation or as ordered by the Board of Directors.

     (f) Upon authorization by the Board of Directors, the Corporation may issue
or distribute its own shares pro rata to its shareholders or the shareholders of
one or more classes or series, if the relative rights of the holders of any
class or series are not adversely affected thereby, to effectuate stock
dividends or splits and any such transaction shall not require payment of
consideration.  The Board of Directors may authorize and the Corporation may
make distributions to the fullest extent now or hereafter permitted by the laws
of the Commonwealth of Pennsylvania.

     (g) Notwithstanding any other provision of this Article FIFTH, shareholders
shall not be entitled to cumulate their votes in the election of Directors.

          SIXTH. (a) All powers vested by law in the Corporation shall be
exercised by or under the authority of, and the business and affairs of the
Corporation shall be managed under the direction of, the Board of Directors.

     (b) The Board of Directors of the Corporation shall consist of at least six
(6) and not more than fifteen (15) Directors, the exact number to be set from
time to time by resolution of the Board of Directors of the Corporation.
Directors shall be natural persons of full age, but need not be residents of the
Commonwealth of Pennsylvania or shareholders of the Corporation.

     (c) Directors of the Corporation shall be elected by the shareholders,
except as provided in this subparagraph (c).  Vacancies in the Board of
Directors, including vacancies resulting from an increase in the number of
Directors, may be filled by a majority vote of the remaining members of the
Board though less than a quorum, or by a sole remaining Director, and each
person so selected shall hold office until the next selection of the class for
which such Director has been chosen and until his successor has been selected
and qualified or until his earlier death, resignation or removal.

     (d) The Board of Directors shall be classified in respect of the time for
which they shall severally hold office by dividing them into three classes which
shall be as nearly equal in number as possible.  Each member of each class shall
be elected for a term until the third annual shareholders meeting following his
taking office and until his successor has been selected and qualified or until
his earlier death, resignation or removal.  The term of office of one class
shall expire at the annual meeting of shareholders in each year.  At each annual
meeting of 
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shareholders, the successors to the Directors of the class whose terms expire
that year shall be elected to hold office.

     (e) Only candidates for Director who have been duly nominated in accordance
with the bylaws of the Corporation shall be eligible for election.  In elections
for Directors, voting need not be by ballot, except upon demand made by a
shareholder entitled to vote at the election and before the voting begins.  The
candidates receiving the highest number of votes from each class or group of
classes, if any, entitled to elect Directors separately up to the number of
Directors to be elected by the class or group of classes shall be elected.  If
at any meeting of shareholders Directors of more than one class are to be
elected, each class of Directors shall be elected in a separate election.

     (f) The entire Board of Directors, or a class of the Board, or any
individual Director may be removed from office only for cause by the vote of
shareholders, or of the holders of a class or series of shares entitled to elect
Directors, or the class of Directors, except that the entire Board of Directors
may be removed without cause by the unanimous vote or consent of shareholders
entitled to vote thereon.  In case the Board or such a class of the Board or any
one or more Directors be so removed, new Directors may be elected at the same
meeting.  The amendment or repeal of this provision shall not apply to any
incumbent Director during the balance of the term for which he was elected.

     (g) No reclassification of the Board of Directors or decrease in its size
shall have the effect of shortening the term of any incumbent Director.

     (h) A majority of the Directors in office shall be necessary to constitute
a quorum for the transaction of business at a meeting of the full Board, and the
acts of a majority of the Directors present and voting at a meeting at which a
quorum is present shall be the acts of the Board of Directors.  If any meeting
of Directors cannot be organized because a quorum is not present, a majority of
the Directors present may adjourn the meeting to such time and place as they may
determine, subject to the Bylaws of the Corporation.  Every Director shall be
entitled to one vote.

          SEVENTH. (a) In addition to any affirmative vote required by law, the
Articles of Incorporation, or the Bylaws of the Corporation, any Business
Combination with an Interested Shareholder shall require the affirmative vote of
at least a majority of the votes entitled to be cast by the holders of all then
outstanding shares of Voting Stock other than the Interested Shareholder, voting
together as a single class; provided, however, that such affirmative vote shall
not be required and such Business Combinations shall require only the
affirmative vote, if any, required by law, the Articles of Incorporation, or the
Bylaws of the Corporation if:

          (i) The Business Combination shall have been approved by a majority of
     Disinterested Directors; or

          (ii) All of the following six conditions shall have been met:
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              (A) The transaction constituting the Business Combination shall
          provide for a consideration to be received by holders of Common Stock
          in exchange for their stock, and the aggregate amount of the cash
          consideration and the Fair Market Value as of the date of the
          consummation of the Business Combination of consideration other than
          cash to be received per share by holders of Common Stock in such
          Business Combination shall be at least equal to the highest of the
          following:

                  (I) (if applicable) the highest per share price (including any
              brokerage commissions, transfer taxes, and soliciting dealers'
              fees) paid by the Interested Shareholder in order to acquire any
              shares of Common Stock beneficially owned by the Interested
              Shareholder which were acquired (x) within the five year period
              immediately prior to the first public announcement of the proposed
              Business Combination (the "Announcement Date") or (y) in the
              transaction in which the Interested Shareholder became an
              Interested Shareholder, whichever is higher;

                  (II) the Fair Market Value per share of Common Stock on the
              Announcement Date or on the date on which the Interested
              Shareholder became an Interested Shareholder (the "Determination
              Date"), whichever is higher;

                  (III) the highest Fair Market Value per share of Common Stock
              for the two years immediately preceding the Announcement Date,
              where the closing sale price is determined for each trading day
              without reference to the immediately preceding 30-day period; and

                  (IV) (if applicable) the price per share equal to the Fair
              Market Value per share of Common Stock determined pursuant to
              clause (II) preceding, multiplied by the ratio of (x) the highest
              per share price (including any brokerage commissions, transfer
              taxes, and soliciting dealers' fees) paid in order to acquire any
              shares of Common Stock beneficially owned by the Interested
              Shareholder which were acquired within the five year period
              immediately prior to the Announcement Date to (y) the Fair Market
              Value per share of Common Stock on the first day in such five year
              period on which the Interested Shareholder beneficially owned any
              shares of Common Stock.

     All per share prices shall be adjusted to reflect any intervening stock
splits, stock dividends and reverse stock splits.

              (B) If the transaction constituting the Business Combination shall
          provide for a consideration to be received by holders of any class or
          series of outstanding Voting Stock other than Common Stock, the
          aggregate amount of the cash and the Fair Market Value as of the date
          of the consummation of the Business Combination of consideration other
          than cash to be received per share by 
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          holders of shares of such Voting Stock shall be at least equal to the
          highest of the following (it being intended that the requirements of
          this clause (ii)(B) shall be required to be met with respect to every
          such class or series of outstanding Voting Stock whether or not the
          Interested Shareholder beneficially owns any shares of a particular
          class or series of such Voting Stock);

                    (I) (if applicable) the highest per share price (including
               any brokerage commissions, transfer taxes, and soliciting
               dealers' fees) paid by the Interested Shareholder in order to
               acquire any shares of such class or series of Voting Stock
               beneficially owned by the Interested Shareholder which were
               acquired (x) within the five year period immediately prior to the
               Announcement Date or (y) in the transaction in which the
               Interested Shareholder became an Interested Shareholder,
               whichever is higher;

                    (II) (if applicable) the highest preferential amount per
               share to which the holders of shares of such class or series of
               Voting Stock are entitled in the event of any liquidation,
               dissolution, or winding up of the Corporation;

                    (III) the highest Fair Market Value per share of such class
               or series of Voting Stock for the two years immediately preceding
               the Announcement Date, where the closing sale price is determined
               for each trading day without reference to the immediately
               preceding 30-day period;

                    (IV) the Fair Market Value per share of such class or series
               of Voting Stock on the Announcement Date or on the Determination
               Date, whichever is higher; and

                    (V) (if applicable) the price per share equal to the Fair
               Market Value per share of such class or series of Voting Stock
               determined pursuant to clause (IV) immediately preceding,
               multiplied by the ratio of (x) the highest per share price
               (including any brokerage commissions, transfer taxes, and
               soliciting dealers' fees) paid in order to acquire any shares of
               such class or series of Voting Stock beneficially owned by the
               Interested Shareholder which were acquired within the five year
               period immediately prior to the Announcement Date to (y) the Fair
               Market Value per share of such class or series of Voting Stock on
               the first day in such five period on which the Interested
               Shareholder beneficially owned any share of such class or series
               of Voting Stock.

All per share prices shall be adjusted to reflect any intervening stock splits,
stock dividends, and reverse stock splits.

               (C) The consideration to be received by holders of a particular
          class or series of outstanding Voting Stock (including Common Stock)
          shall be in cash or in the same form as was previously paid in order
          to acquire shares of such class or 
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          series of Voting Stock which are beneficially owned by the Interested
          Shareholder. If the Interested Shareholder beneficially owns shares of
          any class or series of Voting Stock which were acquired with varying
          forms of consideration, the form of consideration to be received by
          holders of such class or series of Voting Stock shall be either cash
          or the form used to acquire the largest number of shares of such class
          or series of Voting Stock beneficially owned by the Interested
          Shareholder.

               (D) After such Interested Shareholder has become an Interested
          Shareholder and prior to the consummation of such Business
          Combination:

                  (I) except as approved by a majority of the Disinterested
               Directors, there shall have been no failure to declare and pay at
               the regular date therefor any periodic or regular dividends
               (whether or not cumulative) on any outstanding preferred stock;

                  (II) there shall have been (x) no reduction in the periodic or
               regular rate of dividends paid on the Common Stock (except as
               necessary to reflect any subdivision of the Common Stock), except
               as approved by a majority of the Disinterested Directors, and (y)
               an increase in such periodic or regular rate of dividends (as
               necessary to prevent any such reduction) in the event of any
               reclassification (including any reverse stock split),
               recapitalization, reorganization, or any similar transaction
               which has the effect of reducing the number of outstanding shares
               of the Common Stock, unless the failure so to increase such
               periodic or regular rate is approved by a majority of the
               Disinterested Directors; and

                  (III)  such Interested Shareholder shall not have become the
               beneficial owner of any additional shares of Voting Stock except
               as part of the transaction in which such Interested Shareholder
               became an Interested Shareholder.

               (E) After such Interested Shareholder has become an Interested
          Shareholder, such Interested Shareholder shall not have received the
          benefit, directly or indirectly (except proportionately as a
          shareholder), of any loans, advances, guarantees, pledges, or other
          financial assistance or any tax credits or other tax advantages
          provided by the Corporation, whether in anticipation of or in
          connection with a Business Combination or otherwise.

               (F) A proxy or information statement describing the proposed
          Business Combination and complying with the requirements of the
          Securities Exchange Act of 1934, as amended, and the rules and
          regulations thereunder (or any subsequent provisions replacing such
          Act, rules, or regulations) shall be mailed to public shareholders of
          the Corporation at least 30 days prior to the consummation of such
          Business Combination (whether or not such proxy or 
<PAGE>
 
          information statement is required to be mailed pursuant to such Act or
          subsequent provisions).

     (b) For the purposes of this Article SEVENTH:

          (i) The term "Business Combination" shall mean:

              (A) any merger or consolidation of the Corporation or any
          Subsidiary with (I) any Interested Shareholder or with (II) any other
          corporation (whether or not itself an Interested Shareholder) which
          is, or after such merger or consolidation would be, an Affiliate or
          Associate of an Interested Shareholder;

              (B) any sale, lease, exchange, mortgage, pledge, transfer, or
          other disposition (in one transaction or a series of transactions) to
          or with any Interested Shareholder and/or any Affiliate or Associate
          of any Interested Shareholder of any assets of the Corporation or any
          Subsidiary thereof having an aggregate Fair Market Value of, equal to
          or in excess of a Substantial Part of the assets of the Corporation;

              (C) the issuance, exchange, sale, or transfer by the Corporation
          or any Subsidiary (in one transaction or a series of transactions) of
          any securities of the Corporation or any Subsidiary to any Interested
          Shareholder and/or any Affiliate or Associate of any Interested
          Shareholder in exchange for cash, securities, or other consideration
          (or a combination thereof) having an aggregate Fair Market Value of,
          equal to or in excess of a Substantial Part of the assets of the
          Corporation;

              (D) the adoption of any plan or proposal for the liquidation or
          dissolution or division of the Corporation proposed by or on behalf of
          any Interested Shareholder or any Affiliate or Associate of any
          Interested Shareholder; or

              (E) any reclassification of securities (including any reverse
          stock split), or recapitalization or division of the Corporation, or
          any merger or consolidation of the Corporation with any of its
          Subsidiaries which involves or is proposed by or on behalf of any
          Interested Shareholder or any Affiliate or Associate of any Interested
          Shareholder and has the effect, directly or indirectly, of increasing
          the proportionate share of the outstanding shares of any class of
          equity securities or securities convertible into equity securities of
          the Corporation or any Subsidiary which is directly or indirectly
          owned by an Interested Shareholder or any Affiliate or Associate of
          any Interested Shareholder.

          (ii) The term "person" shall mean any individual, firm, corporation,
     partnership, trust or other entity.
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          (iii)  The term "Interested Shareholder" at any particular time shall
     mean any person (other than the Corporation or any Subsidiary and other
     than any profit sharing, employee stock ownership, or other employee
     benefit plan of the Corporation or any Subsidiary or any trustee of or
     fiduciary with respect to any such plan when acting in such capacity) who
     or which:

              (A) is at such time the beneficial owner, directly or indirectly,
          of more than twelve percent (12%) of the voting power of the
          outstanding Voting Stock;

              (B) was at any time within the two year period immediately prior
          to such time the beneficial owner, directly or indirectly, of more
          than twelve percent (12%) of the voting power of the then outstanding
          Voting Stock; or

              (C) is at such time an assignee of or has otherwise succeeded to
          the beneficial ownership of any shares of Voting Stock which were at
          any time within two years prior to such time beneficially owned by any
          Interested Shareholder, if such assignment or succession shall have
          occurred in the course of a transaction or series of transactions not
          involving a public offering within the meaning of the Securities Act
          of 1933, as amended.

          (iv) A person shall be a "beneficial owner" of any Voting Stock:

              (A) which such person or any of its Affiliates or Associates
          beneficially owns, directly or indirectly, within the meaning of Rule
          13d-3 of the General Rules and Regulations under the Securities
          Exchange Act of 1934, as amended, as in effect on October 1, 1989;

              (B) which such person or any of its Affiliates or Associates has
          (I) the right to acquire (whether or not such right is exercisable
          immediately or only after the passage of time) pursuant to any
          agreement, arrangement, or understanding or upon the exercise of
          conversion rights, exchange rights, warrants or options, or otherwise,
          or (II) the right to vote pursuant to any agreement, arrangement, or
          understanding; or

              (C) which is beneficially owned, directly or indirectly, by any
          other person with which such person or any of its Affiliates or
          Associates has any agreement, arrangement, or understanding for the
          purpose of acquiring, holding, voting, or disposing of any shares of
          Voting Stock.

          (v) For the purposes of determining whether a person is an Interested
     Shareholder pursuant to Section (b) (iii) of this Article SEVENTH, the
     number of shares of Voting Stock deemed to be outstanding shall include
     shares deemed owned by an Interested Shareholder through application of
     Section (b) (iv) of this Article SEVENTH but shall not include any other
     shares of Voting Stock which may be issuable pursuant to 
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     any agreement, arrangement, or understanding, or upon the exercise of
     conversion rights, warrants or options, or otherwise.

          (vi) "Affiliate" or "Associate" shall have the respective meanings
     ascribed to such terms in Rule 12b-2 of the General Rules and Regulations
     under the Securities Exchange Act of 1934, as amended, as in effect on
     October 1, 1989 (the term "registrant" in said Rule 12b-2 meaning in this
     case the Corporation).

          (vii)  "Subsidiary" means any corporation of which a majority of any
     class of equity security is owned, directly or indirectly, by the
     Corporation; provided, however, that for the purposes of the definition of
     Interested Shareholder set forth in Section (b)(iii) of this Article
     SEVENTH the term "Subsidiary" shall mean only a corporation of which a
     majority of each class of equity security is owned, directly or indirectly,
     by the Corporation.

          (viii)  "Disinterested Director" means any member of the Board of
     Directors of the Corporation (the "Board") who is unaffiliated with, and
     not a representative of, an Interested Shareholder and who was a member of
     the Board prior to the time that the Interested Shareholder became an
     Interested Shareholder and any successor of a Disinterested Director who is
     unaffiliated with, and not a representative of, the Interested Shareholder
     and is recommended or elected to succeed a Disinterested Director by a
     majority of the Disinterested Directors then on the Board.

          (ix) "Fair Market Value" means:  (a) in the case of stock, the highest
     closing sale price during the 30-day period immediately preceding the date
     in question of a share of such stock on the American Stock Exchange, or, if
     such stock is not listed on such exchange, on the principal United States
     securities exchange registered under the Securities Exchange Act of 1934,
     as amended, on which such stock is listed, or, if such stock is not listed
     on any such exchange, the highest closing bid quotation with respect to a
     share of such stock during the 30-day period preceding the date in question
     on the National Association of Securities Dealers, Inc., Automated
     Quotations System or any system then in use, or if no such quotations are
     available, the fair market value on the date in question of a share of such
     stock as determined by the Board of Directors in good faith with the
     approval of at least a majority of the Disinterested Directors in the
     determination made; and (b) in the case of property other than cash or
     stock, the fair market value of such property on the date in question as
     determined by the Board of Directors in good faith with the approval of at
     least a majority of the Disinterested Directors in the determination made.

          (x) In the event of any Business Combination in which the Corporation
     survives, the phrase "consideration other than cash to be received" as used
     in Section (a) (ii) of this Article SEVENTH shall include the shares of
     Common Stock and/or the shares of any class of outstanding Voting Stock
     retained by the holders of such shares.

          (xi) A "Substantial Part of the assets of the Corporation" shall mean
     more than ten percent (10%) (for purposes of subparagraph (b)(i)(B) of this
     Article SEVENTH) or 
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     five percent (5%) (for purposes of subparagraph (b)(i)(C) of this Article
     SEVENTH) of the fair market value of the total assets of the Corporation as
     of the end of its most recent fiscal quarter ending prior to the time the
     determination is made.

          (xii)  The term "Voting Stock" shall mean the outstanding shares of
     all classes or series of authorized capital stock of the Corporation
     entitled to vote generally in the election of Directors.

          (xiii)  The term "Common Stock" shall mean the outstanding shares of
     the Common Stock and shall also mean any class of common stock which may be
     authorized under the Articles of Incorporation.

     (c) A majority of the Disinterested Directors shall have the power and duty
to determine for the purposes of this Article SEVENTH on the basis of
information known to them after reasonable inquiry, all questions arising in
connection with the operation of or compliance with this Article SEVENTH,
including without limitation (i) whether a person is an Interested Shareholder,
(ii) the number of shares of Voting Stock beneficially owned by any person,
(iii) whether a person is an Affiliate or Associate of another, (iv) whether the
applicable conditions set forth in Section (a)(ii) of this Article SEVENTH have
been met with respect to any Business Combination, and (v) whether the assets
which are the subject of any Business Combination equal or exceed, or whether
the consideration to be received from the issuance or transfer of securities by
the Corporation or any Subsidiary in any Business Combination equals or exceeds,
a Substantial Part of the assets of the Corporation.  Any such determination
made in good faith shall be binding and conclusive on all parties.

     (d) Nothing contained in this Article SEVENTH shall be construed to relieve
any Interested Shareholder from any fiduciary obligation imposed by law.

     (e) Unless otherwise clear from the context, all terms used in this Article
SEVENTH shall have the meanings given to them in this Article SEVENTH.  The
masculine gender shall include the feminine and neuter genders, and vice versa;
and the singular shall include the plural, and vice versa.