<PAGE>
 
                                                                     EXHIBIT 3.2



                          AMENDED AND RESTATED BYLAWS

                                       of

                             PITT-DES MOINES, INC.

                                Amended through

                               February 11, 1999

                 (hereafter the "Corporation" or the "Company")


                                   ARTICLE I

                                 Shareholders



          Section 1.1 Annual Meeting.  An annual meeting of the shareholders
shall be held in each calendar year on such date as may be fixed by the board of
directors, for the purpose of electing directors and for the transaction of such
other business as may properly come before the meeting. If the day fixed for the
annual meeting shall be a legal holiday in the state where the meeting is to be
held, such meeting shall be held on the next succeeding business day.

          Section 1.2 Special Meetings. Special meetings of the shareholders may
be called at any time by the chief executive officer or the board of directors
or any person who is entitled to do so by law. Upon written request of any
person who has called a meeting the secretary shall fix the time of the meeting
which, if the meeting is called pursuant to a statutory right, shall be held not
more than sixty days after the receipt of the request. If the secretary neglects
or refuses to fix the time of the meeting, the person or persons calling the
meeting may do so.

          Section 1.3 Place of Meeting. All meetings of the shareholders shall
be held at the registered office of the Corporation or at such other place,
within or without the Commonwealth of Pennsylvania, as may be designated by the
board of directors from time to time.

          Section 1.4 Notice. Except as provided in Section 1.5 of these bylaws,
written notice of every meeting of the shareholders, specifying the place, day
and hour of the meeting and, in the case of a special meeting, the general
nature of the business to be transacted, shall be given by, or at the direction
of, the secretary or other person authorized by the chief executive officer or
if they neglect or refuse to do so, the person or persons calling the meeting,
to each shareholder of record entitled to vote at the meeting, at least ten days
prior to the day named for the meeting, unless a greater period of notice is
required by law in the particular case. Such notice may be given to each
shareholder either personally or by sending a copy thereof by first class or
express mail, postage prepaid, or by telegram (with messenger service
specified), telex or TWX (with answerback received) or courier service, charges
prepaid, or by telecopier, to the shareholder's address (or to the shareholder's
telex, TWX, telecopier or telephone number) appearing on the books of the
Corporation. Notice sent by mail, telegraph or by courier service shall be
deemed to have been given when deposited in the United States mail or with a
telegraph office or courier service for delivery or, in the case of telex, TWX
or telecopier, when dispatched.
<PAGE>
 
          Section 1.5 Adjournments. Adjournment or adjournments of any annual or
special meeting, including one at which directors are to be elected, may be
taken for such period or periods as the shareholders present in person or by
proxy and entitled to vote shall direct. When a meeting is adjourned, it shall
not be necessary to give any notice of the adjourned meeting or of the business
to be transacted at the adjourned meeting, other than by announcement at the
meeting at which the adjournment is taken, unless the board of directors fixes a
new record date for the adjourned meeting. Subject to quorum requirements, at
any such adjourned meeting, any business may be transacted which might have been
transacted at the meeting as originally noticed.

          Section 1.6 Quorum. Except as otherwise allowed by law, a shareholders
meeting duly called shall not be organized for the transaction of business
unless a quorum is present. The presence in person or by proxy of shareholders
entitled to cast at least a majority of the votes that all shareholders are
entitled to cast on a particular matter to be acted upon at the meeting shall
constitute a quorum for the purposes of consideration and action on the matter.
The shareholders present at a duly organized meeting can continue to do business
until adjournment, notwithstanding the withdrawal of enough shareholders to
leave less than a quorum. If a meeting cannot be organized because a quorum has
not attended, those present may adjourn the meeting to such time and place as
they may determine.

          Section 1.7 Action by Shareholders. Whenever any corporate action is
to be taken by vote of the shareholders, it shall be authorized by a majority of
the votes cast at a duly organized meeting of shareholders by the holders of
shares entitled to vote thereon, except where a greater percentage is required
by law or the articles of incorporation.

          Section 1.8 Shareholder Proposals. Any shareholder who desires to
submit any proposal for shareholder action at a shareholders meeting shall
submit such proposal and a reasonably detailed explanation of the proposal and
the reasons therefor to the chairman of the board of the Corporation in writing.
Such written submission must be received by the chairman of the board not less
than sixty days nor more than ninety days prior to the meeting; provided,
however, that in the event that less than seventy days' notice or prior public
disclosure of the date of the meeting is given or made to shareholders, such
submission must be received by the chairman of the board not later than the
close of business on the tenth day following the date on which notice of the
meeting was mailed or public disclosure was made. Nothing in this bylaw shall be
construed to affect or otherwise empower the shareholders of the Corporation to
make any proposals that pursuant to these bylaws, the articles or law such
shareholders are not entitled to make. Any proposals not made in accordance
herewith may, in the discretion of the chairman of the meeting, be disregarded
by the chairman and ruled out of order.
<PAGE>
 
          Section 1.9 Redeemable Shares. Unless otherwise provided in the
articles of incorporation, redeemable shares that have been called for
redemption shall not be entitled to vote on any matter and shall not be deemed
outstanding shares after written notice has been mailed to holders thereof that
the shares have been called for redemption and that a sum sufficient to redeem
the shares has been deposited with a specified financial institution with
irrevocable instruction and authority to pay the redemption price to the holders
of the shares on the redemption date upon surrender of certificates therefor,
and the sum has been so deposited.

          Section 1.10 Proxies. Every shareholder entitled to vote at a meeting
of shareholders or to express consent or dissent to corporate action in writing
without a meeting may authorize another person or persons to act for such
shareholder  by proxy. Every proxy shall be executed in writing by the
shareholder or by the shareholder's  duly authorized attorney-in-fact and filed
with the secretary of the Corporation. Notwithstanding any other agreement or
any provision in the proxy to the contrary, a proxy shall be revocable at will
unless coupled with an interest, but the revocation shall not be effective until
written notice of the revocation has been given to the secretary of the
Corporation. An unrevoked proxy shall not be valid after three years from the
date of its execution unless a longer time is expressly provided therein. A
proxy shall not be revoked by the death or incapacity of the maker unless,
before the vote is counted or the authority is exercised, written notice of such
death or incapacity is given to the secretary of the Corporation.

          Section 1.11 Voting List. The officer or agent having charge of the
transfer books for shares of the Corporation shall make a complete list of the
shareholders entitled to vote at the meeting, arranged in alphabetical order,
with the address of and the number of shares held by each. The list shall be
produced and kept open at the time and place of the meeting and shall be subject
to the inspection of any shareholder during the whole time of the meeting for
the purposes thereof. Failure to comply with the requirements of this bylaw
shall not affect the validity of any action taken at a meeting prior to a demand
at the meeting by any shareholder entitled to vote thereat to examine the list.

          Section 1.12 Determination of Shareholders of Record. The board of
directors may fix a time prior to the date of any meeting of shareholders as a
record date for the determination of the shareholders entitled to notice of, or
to vote at, the meeting, which time, except in the case of an adjourned meeting,
shall be not more than 90 days prior to the date of the meeting of shareholders.
In such case, only such shareholders as shall be shareholders of record on the
date so fixed shall be entitled to notice of, or to vote at, such meeting,
notwithstanding any transfer of shares on the books of the Corporation after the
record date so fixed. The board of directors may similarly fix a record date for
the determination of shareholders of record for any other purpose. When a
determination of shareholders of record has been made as provided in this bylaw
for purposes of a meeting, the determination shall apply to any adjournment
thereof unless the board fixes a new record date for the adjourned meeting. The
board of directors may from time to time adopt a procedure whereby a shareholder
of the Corporation may certify in writing to the Corporation that all or a
portion of the shares registered in the name of the shareholder are held for the
account of a specified person or persons.
<PAGE>
 
          Section 1.13 Presiding Officer. All meetings of the shareholders shall
be called to order and presided over by the chairman of the board or, in the
chairman's absence, by the president, or, in the absence of the president, by an
officer or director of the Corporation appointed by the chief executive officer,
or, if none of those persons are present, by a chairman of the meeting elected
by the shareholders.

          Section 1.14 Voting by Fiduciaries and Pledgees. Shares standing in
the name of a trustee or other fiduciary and shares held by an assignee for the
benefit of creditors or by a receiver may be voted either in person or by proxy
by the trustee, fiduciary, assignee or receiver. A shareholder whose shares are
pledged shall be entitled to vote the shares, in person or by proxy, until the
shares have been transferred into the name of the pledgee or a nominee of the
pledgee.

          Section 1.15 Voting by Joint Holders of Shares. Where shares are held
jointly or as tenants in common by two or more persons, as fiduciaries or
otherwise, if only one or more of such persons is present in person or by proxy,
all of the shares standing in the names of such persons shall be deemed to be
represented for the purpose of determining a quorum and the Corporation shall
accept as the vote of all such shares the vote cast by such person or a majority
of such persons who are present; and if the persons present are equally divided
upon whether the shares held by them shall be voted or upon the manner of voting
the shares, the voting of such shares shall be divided equally among the persons
present without prejudice to the rights of the joint owners or the beneficial
owners thereof among themselves, except that, if there has been filed with the
secretary of the Corporation a copy, certified by an attorney-at-law to be
correct, of the relevant portions of the agreement under which such shares are
held or the instrument by which the trust or estate was created or the order of
court appointing them or of an order of court directing the voting of such
shares, the persons specified as having such voting power in the latest document
so filed, and only those persons, shall be entitled to vote such shares but only
in accordance therewith.

          Section 1.16 Voting by Corporations. Any other domestic or foreign
corporation for profit or not-for-profit that is a shareholder of this
Corporation may vote by any of its officers or agents, or by proxy appointed by
any such officer or agent, unless some other person, by resolution of its board
of directors or pursuant to a provision of its articles or bylaws, a copy of
which resolution or provision certified to be correct by one of its officers has
been filed with the secretary of this Corporation, is appointed its general or
special proxy, in which case such person shall be entitled to vote the shares.
Shares of this Corporation owned, directly or indirectly, by this Corporation
and controlled, directly or indirectly, by the board of directors of this
Corporation, as such, shall not be voted at any meeting and shall not be counted
in determining the total number of outstanding shares for voting purposes at any
given time.
<PAGE>
 
          Section 1.17 Judges of Election. In advance of any meeting of
shareholders, the board of directors may appoint judges of election, who need
not be shareholders, to act at such meeting or any adjournment thereof. If
judges of election are not so appointed, the presiding officer of any such
meeting may, and on the request of any shareholder or his proxy shall, make such
appointment at the meeting. The number of judges shall be one or three. No
person who is a candidate for office to be filled at the meeting shall act as a
judge. In case any person appointed as a judge fails to appear or fails or
refuses to act, the vacancy may be filled by appointment made by the board of
directors in advance of the convening of the meeting or at the meeting by the
presiding officer thereof. The judges of election shall determine the number of
shares outstanding and the voting power of each, the shares represented at the
meeting, the existence of a quorum, the authenticity, validity and effect of
proxies, receive votes or ballots, hear and determine all challenges and
questions in any way arising in connection with the right to vote, count and
tabulate all votes, determine the result and do such acts as may be proper to
conduct the election or vote with fairness to all shareholders. The judges of
election shall perform their duties impartially, in good faith, to the best of
their ability, and as expeditiously as is practical. If there are three judges
of election, the decision, act or certificate of a majority shall be effective
in all respects as the decision, act or certificate of all. On request of the
presiding officer of the meeting, or of any shareholder or his proxy, the judges
shall make a report in writing of any challenge or question or matter determined
by them, and execute a certificate of any fact found by them. Any report or
certificate made by them shall be prima facie evidence of the facts stated
therein.


                                  ARTICLE II

                              Board of Directors
                                        
                                        
          Section 2.1 General. The general powers, number, tenure and
qualifications of the board of directors and the manner in which directors shall
be elected and take action shall be as set forth in the articles of
incorporation.

          Section 2.2 Nominations. Nominations for election to the board of
directors may be made by the board of directors or by any shareholder of the
Corporation entitled to notice of, and to vote at, any meeting called for the
election of directors. Nominations, other than those made by or on behalf of the
board of directors of the Corporation, shall be made in writing and shall be
received by the chairman of the board of the Corporation not later than (i) with
respect to an election of directors to be held at an annual meeting of
shareholders, sixty days prior to the anniversary date of the immediately
preceding annual meeting, and (ii) with respect to an election of directors to
be held at a special meeting of shareholders, the close of business on the tenth
day following the date on which notice of such meeting is first given to
shareholders or public disclosure of the meeting is made. Such notification
shall contain the following information to the extent known to the notifying
shareholder:(a) the name and residence address of each proposed nominee and of
the notifying shareholder; (b) the principal occupation of each proposed
nominee; (c) a representation that the notifying shareholder intends to appear
in person or by proxy at the meeting to nominate the person or persons specified
in the notice; 
<PAGE>
 
(d) the total number of shares of the Corporation that will be voted for each
proposed nominee; (e) the total number of shares of the Corporation owned by the
notifying shareholder; (f) a description of all arrangements or understandings
between the notifying shareholder and each nominee and any other person or
persons (naming such person or persons) pursuant to which the nomination or
nominations are to be made by the notifying shareholder; (g) such other
information regarding each nominee proposed by such shareholder as would be
required to be included in a proxy statement filed with the Securities and
Exchange Commission; and (h) the consent of each nominee to serve as a director
of the Corporation if so elected. Nominations not made in accordance herewith
may, in the discretion of the chairman of the meeting, be disregarded by him,
and upon his instructions the judges of election may disregard all votes cast
for each such nominee.

          Section 2.3 Removal and Resignation. (a) Removal by action of the
shareholders. The entire board of directors, or a class of the board or any
individual director may be removed from office by the shareholders only as set
forth in the articles of incorporation.

          (b) Removal by action of the directors.  The board of directors may
declare vacant the office of a director (i) if the director  is judicially
declared of unsound mind, (ii) if the director is convicted of an offense
punishable by imprisonment for a term of more than one year, (iii) if within 60
days after notice of  election the director does not accept such office either
in writing or by attending a meeting of the board of directors or (iv) for any
other proper cause.

          (c) Other removal.  The provisions of this section shall not be deemed
exclusive of any provision of law authorizing the removal of any director or
directors.

          (d) Resignation.  Any director may resign at any time from the
position as a director of the Corporation upon written notice to the
Corporation.  The resignation shall be effective upon receipt thereof by the
Corporation or at such subsequent time as may be specified in the notice of
resignation.

          Section 2.4 Regular Meetings.  The board of directors shall hold an
annual meeting for the election of officers and the transaction of other proper
business as soon as practical after, and at the same place as, the annual
meeting of shareholders or at such other time and place as may be fixed by the
board.  The board of directors may designate by resolution the time and place,
within or without the Commonwealth of Pennsylvania, of other regular meetings.

          Section 2.5 Special Meetings.  Special meetings of the board may be
called by the chairman of the board, the president, or any two directors.  The
person or persons calling the special meeting may fix the time and place, within
or without the Commonwealth of Pennsylvania, of the meeting, provided that the
place shall be within 500 miles of the registered office of the Corporation
unless all of the directors agree that the meeting can be held at a place more
than 500 miles from the registered office.

          Section 2.6 Notice of Meetings.  Written  notice of the annual or any
regular meeting of the board of directors shall  be given to each director not
<PAGE>
 
less than five days prior to any such meeting, specifying the time and place of
the meeting.  Written  notice of each special meeting of the board of directors,
specifying the time and place of the meeting, shall be given to each director at
least 24 hours before the time set for the meeting either personally or by
sending a copy thereof by first class or express mail postage prepaid or by
telegram (with messenger service specified), telex or TWX (with answerback
received) or carrier service, charges prepaid, or by telecopier, to his address
(or to his telex, TWX, telecopier or telephone number) supplied by him to the
Corporation for the purposes of notice.  Notice sent by express mail, telegraph
or courier service shall be deemed to have been given when deposited in the
United States mail or with a telegraph office or courier service for delivery
or, in the case of telex, TWX or telecopier, when dispatched. Notice sent by
regular mail shall be deemed to have been given forty-eight hours after
deposited in the United States mail. When a meeting of directors is adjourned,
notice need not be given at the adjourned meeting other than by announcement at
the meeting at which the adjournment is made.

          Section 2.7 Interested Directors or Officers; Quorum.  So long as any
one of the following three requirements are met, no contract or transaction
between the Corporation and one or more of its directors or officers, or between
the Corporation and any other corporation or enterprise in which one or more of
this Corporation's directors or officers are directors or officers, or in which
such officers or directors have a financial or other interest, shall be void or
voidable solely for that reason, or solely because the director or officer is
present at or participates in the meeting of the board that authorizes the
contract or transaction, or solely because the interested director's or
officer's vote is counted for such purposes.  Any such contract or transaction
must meet the requirement that either: (1) the material facts as to the
interested director's or officer's relationship or interest and as to the
contract or transaction are disclosed or are known to the board of directors and
the board authorizes the contract or transaction by the affirmative votes of a
majority of the disinterested directors even though the disinterested directors
are less than a quorum; or (2) the material facts as to the interested
director's or officer's relationship or interest and as to the contract or
transaction are disclosed or known to the shareholders entitled to vote thereon,
and the contract or transaction is specifically approved in good faith by vote
of those shareholders; or (3) the contract or transaction is fair as to this
Corporation as of the time it is authorized, approved or ratified by the board
of directors or the shareholders. Interested directors may be counted in
determining the presence of a quorum at a meeting of the board of directors
which authorizes such a contract or transaction.

          Section 2.8 Compensation. By resolution of the board of directors,
each director may be paid the expenses, if any, of attendance at each meeting of
the board of directors or committee thereof, and may be paid a  salary or
retainer as director, in cash or other compensation as determined by the board,
or a fixed sum for attendance at each meeting of the board of directors or
committee thereof or both. Subject to the limitations in Section 4.12 of these
bylaws no such compensation  shall preclude any director from serving the
Corporation in any other capacity and receiving further compensation therefor.

          Section 2.9 Presumption of Assent. A director of the Corporation who
is present at a meeting of the board of directors at which action on any
<PAGE>
 
corporate matter is taken shall be presumed to have assented to the action taken
unless  such director's dissent is entered in the minutes of the meeting or
unless  such director files written dissent to such action with the secretary of
the meeting before the adjournment thereof or transmits the dissent to the
secretary of the Corporation immediately after the adjournment of the meeting.
Such right to dissent shall not apply to a director who voted in favor of such
action.

          Section 2.10 Presiding Officer. All meetings of the board of directors
shall be called to order and presided over by the chairman of the board of
directors or, in the chairman's absence, by the president or, in the absence of
the president, by a director appointed by the chief executive officer, or, if
none of those persons is present, by a chairman of the meeting elected by the
board of directors.

          Section 2.11 Directors Liability. A director of the Company shall not
be personally liable to the Company or any of its shareholders for monetary
damages for breach of fiduciary duty as a director for any act or failure to act
occurring on or after the effective date of the Directors' Liability Act, unless
such breach or failure to perform constitutes self-dealing, willful misconduct
or recklessness; provided, however, that the foregoing provision shall not
eliminate or limit the liability of a director (i) for any responsibility or
liability of such director pursuant to any criminal statute, or (ii) for any
liability of a director for the payment of taxes pursuant to local, State or
Federal law. Any repeal or modification of this bylaw by the shareholders of the
Company shall be prospective only, and shall not adversely affect any limitation
on the personal liability of a director of the Company existing at the time of
such repeal or modification. [Restatement of bylaw contained in Article III,
Section 11 of Corporation's prior bylaws as adopted by the shareholders on April
21, 1987.]


                                  ARTICLE III

                            Committees of the Board

          Section 3.1 Committees of the Board. The board of directors may, by
resolution adopted by a majority of the directors in office, establish one or
more committees, each committee to consist of one or more of the directors of
the Corporation. The board may designate one or more directors as alternate
members of any committee, who may replace any absent or disqualified member at
any meeting of the committee or for purposes of any written action of the
committee. In the absence or disqualification of any member or alternate member
of a committee, the member or members thereof present at any meeting and not
disqualified from voting, though less than a quorum, may unanimously appoint
another director to act at the meeting in the place of the absent or
disqualified member. A committee, to the extent provided in the resolution of
the board of directors creating it, shall have and exercise all of the powers
and authority of the board of directors except that a committee shall not have
any power or authority as to (i) the submission to shareholders of any action
requiring by law the approval of shareholders, (ii) the creation or filling of
vacancies in the board of directors, (iii) the adoption, amendment or repeal of
the bylaws, (iv) the amendment, adoption or repeal of any resolution of the
board that by its terms is amendable or repealable only by the full board, or
(v) action on matters committed by the bylaws or resolution of the board to
another committee of the board.
<PAGE>
 
          Section 3.2 Committee Rules. Unless the board of directors provides
otherwise, each committee established by the board may adopt and amend rules for
the conduct of its business. In the absence of a resolution of the board or a
provision in the rules of such committee to the contrary, a majority of the
entire authorized number of members of such committee shall constitute a quorum
for the transaction of business, the vote of a majority of the members present
at a meeting if a quorum is then present shall be the act of such committee, and
in other respects each committee shall conduct its business and take action in
the same manner as the board conducts its business pursuant to the articles of
incorporation or these bylaws.


                                  ARTICLE IV

                                   Officers


          Section 4.1 Officers and Qualifications. The Corporation shall have a
chairman of the board, a president, a chief executive officer (who shall also be
the chairman or the president), a secretary, and a treasurer, each of whom shall
be elected by the board of directors. The board may also elect one or more group
presidents or vice presidents, one or more vice presidents, a controller, and
such other officers and assistant officers as the board deems necessary or
advisable. The officers shall be natural  persons of full age. Any two or more
offices may be held by the same person. It shall not be necessary for officers
to be directors. Officers of the Corporation as between themselves and the
Corporation shall have such authority and perform such duties in the management
of the Corporation as is provided by or pursuant to these bylaws, or as is
determined by or pursuant to resolutions or orders of the board of directors
which shall take precedence over the bylaw provisions set forth in this Article
IV.

          Section 4.2 Election, Term, and Vacancies. The officers of the
Corporation shall be elected by the board of directors at the annual meeting of
the board or from time to time as they determine. Each officer shall hold office
until such officer's successor has been duly elected and qualified or until
such officer's earlier death, resignation or removal. A vacancy in any office
occurring in any manner may be filled by the board of directors.

          Section 4.3 Removal; Resignation. (a) Removal. Any officer or agent
elected or appointed by the board of directors may be removed by the board of
directors with or without cause, but such removal shall be without prejudice to
the contract rights, if any, of the person so removed. Election or appointment
of an officer or agent shall not of itself create contract rights.

          (b) Resignation. Any officer may resign at any time upon written
notice to the Corporation. The resignation shall be effective upon receipt
thereof by the Corporation or at such subsequent time as may be specified in the
notice of resignation.

          Section 4.4 Chairman of the Board. The chairman of the board of
directors shall preside at all meetings of the shareholders and of the directors
at which the chairman  is present, and shall have such authority and perform
such duties as the board of directors may designate.
<PAGE>
 
          Section 4.5 Chairman Emeritus. The chairman emeritus of the board of
directors shall have such authority and perform such duties as the board of
directors may designate.

          Section 4.6 President. The president shall, in the absence of the
chairman of the board, preside at all meetings of the shareholders and of the
board of directors at which the president is present, and shall have such
authority and perform such duties as the board of directors may designate.

          Section 4.7 Chief Executive Officer. The president or the chairman of
the board, as the board determines, shall be the chief executive officer.
Subject to the control of the board of directors, the chief executive officer
shall (a) have general and active management of all the business, property and
affairs of the Corporation, (b) see that all orders and resolutions of the board
of directors are carried into effect, (c) appoint and remove subordinate
officers and agents, other than those appointed or elected by the board of
directors, as the business of the Corporation may require, (d) have custody of
the corporate seal, or entrust the same to the secretary, and (e) in general
perform all the usual duties incident to the office of chief executive officer
and such other duties as may be assigned to the chief executive officer by the
board of directors. In the absence or disability of the chief executive officer,
the chairman or the president, whoever is not also the chief executive officer,
shall perform the duties of the chief executive officer.

          Section 4.8 Vice Presidents. Each vice president, if any, shall
perform such duties as may be assigned to such vice president by the board of
directors or the chief executive officer.

          Section 4.9 Secretary. The secretary shall (a) keep the minutes of all
meetings of the shareholders, the board of directors, and any committees of the
board of directors in one or more books kept for that purpose, (b) have custody
of the corporate records, stock books and stock ledgers of the Corporation, (c)
keep a register of the address of each shareholder, which address has been
furnished to the secretary by such shareholder, (d) see that all notices are
duly given in accordance with law, the articles, and these bylaws, and (e) in
general perform all the usual duties incident to the office of secretary and
such other duties as may be assigned to the secretary by the board of directors
or the chief executive officer.

          Section 4.10 Treasurer.  The treasurer shall (a) have custody of all
funds and securities of the Corporation, (b) keep, or cause to be kept, complete
and accurate accounts of receipts and disbursements in books kept for that
purpose, (c) deposit in the name and to the credit of the Corporation, in such
depositories as the board of directors shall designate, all monies and other
valuable effects of the Corporation not otherwise employed, (d) as directed by
the board of directors or the president, disburse monies of the Corporation,
taking proper vouchers for such disbursements, and render to the chief executive
officer and directors an account of all of the treasurer's transactions   and of
the financial condition of the Corporation, and (e) in general perform all the
usual duties incident to the office of treasurer and such other duties as may be
assigned to  the treasurer by the board of directors or the chief executive
officer.  The treasurer shall be ex-officio an assistant secretary.
<PAGE>
 
          Section 4.11 Controller.  The controller, if any, shall (a) have
general charge of the accounting of the Corporation, and (b) in general perform
all the usual duties incident to the office of controller and such other duties
as may be assigned to the controller by the board of directors, the chief
executive officer or the vice president, finance.

          Section 4.12 Salaries.  The salaries of the officers shall be fixed
from time to time by the board of directors, and no officer shall be prevented
from receiving such salary by reason of the fact that such officer is also a
director of the Corporation, provided however, that no officer of the
Corporation who is receiving a salary from the Corporation, and who is also a
director, shall receive any additional compensation by reason of the fact that
such officer is also a director.


                                   ARTICLE V

                       Share Certificates and Transfers

          Section 5.1 Certificates.  Share certificates shall state (i) that the
Corporation is incorporated under the laws of the Commonwealth of Pennsylvania,
(ii) the name of the registered holder of the shares represented thereby and
(iii) the number and class of shares and the designation of the series, if any,
which the share certificate represents.  Every share certificate shall be signed
by facsimile or otherwise, by the chairman, president or any vice president and
countersigned by the treasurer or an assistant treasurer or by the secretary or
an assistant secretary.

          Section 5.2 Transfer of Shares.  Transfer of shares of the Corporation
shall be made only on the stock transfer books of the Corporation by the holder
of record of the shares to be transferred or by the holder's legal
representative, who shall furnish proper evidence of authority to transfer, or
by the holder's attorney thereunto authorized by power of attorney duly executed
and filed with the secretary of the Corporation, and on surrender for
cancellation of the certificate representing such shares. The person in whose
name shares stand on the books of the Corporation shall be deemed by the
Corporation to be the owner thereof for all purposes.

          Section 5.3 Lost or Destroyed Certificates. In case of loss or
destruction of a share certificate, another may be issued in lieu thereof in
such manner and upon such terms as the board of directors may authorize in the
particular case.


                                  ARTICLE VI

             Waiver of Notice, Action Without Meeting and Meetings

                            By Conference Telephone
                                        

          Section 6.1 Waiver of Notice. Whenever any written notice is required
to be given by law, the articles, or these bylaws, a waiver thereof in writing,
signed by the person or persons entitled to the notice, whether before or after
the time stated therein, shall be deemed equivalent to the giving of the notice.
<PAGE>
 
Except in the case of a special meeting of shareholders, the general nature of
the business to be transacted at the meeting need not be specified in the waiver
of notice of such meeting. The attendance of a person, either in person or by
proxy, at any meeting shall constitute a waiver of notice of the meeting, except
where the person attends the meeting for the express purpose of objecting, at
the beginning of the meeting, to the transaction of any business because the
meeting was not lawfully called or convened.

          Section 6.2 Action by Consent. Any action which may be taken at a
meeting of the shareholders, of the directors, or of any committee of directors
may be taken without a meeting if, prior or subsequent to the action, a consent
or consents thereto in writing setting forth the action so taken is signed by
all the shareholders who would be entitled to vote at a meeting for such
purposes, or by all of the directors in office, or by all of the members of such
committee, as the case may be, and is filed with the secretary of the
Corporation.

          Section 6.3 Meetings by Means of Conference Telephone. One or more
persons may participate in a meeting of the shareholders, of the directors, or
of any committee of directors by means of conference telephone or similar
communications equipment by means of which all persons participating in the
meeting can hear each other. Such participation shall constitute presence in
person at the meeting.

                                  ARTICLE VII

                          Certain Shareholder Rights
                                        

          Section 7.1 Inspection of Corporate Records. Every shareholder shall,
upon written verified demand stating the purpose thereof, have a right to
examine, in person or by agent or attorney, during the usual hours for business
for any proper purpose, the share register, books or records of account, and
records of the proceedings of the incorporators, shareholders and directors, and
to make copies or extracts therefrom. A proper purpose shall mean a purpose
reasonably related to the interest of the person as a shareholder. In every
instance where an attorney or the agent is the person who seeks the right of
inspection, the demand shall be accompanied by a power of attorney or other
writing that authorizes the attorney or other agent to so act on behalf of the
shareholder. The demand shall be directed to the Corporation at its registered
office or at its principal place of business.


                                 ARTICLE VIII

                   Indemnification of Directors and Officers

                                        
          Section 8.1 Indemnification. The Corporation shall indemnify to the
full extent authorized or permitted by law any person made, or threatened to be
made, a party to or otherwise involved in (as a witness or otherwise) an action,
suit or proceeding (whether civil, criminal, administrative or investigative,
and whether by or in the right of the Corporation or otherwise) by reason of the
fact that the person is or was a director or officer of the Corporation or while
a director or officer of the Corporation either serves or served as a director,
officer, trustee, employee or agent of any other related enterprise or in
connection with a related employee benefit plan at the request of the
Corporation 
<PAGE>
 
or serves or served as a director, officer, trustee, employee or agent of any
other unrelated enterprise at the specific written request of the Corporation
against any expenses and liability actually incurred including without
limitation judgments and amounts paid or to be paid in settlement of and in
actions brought by or in the right of the Corporation. Expenses incurred by such
a person in defending a civil or criminal action, suit or proceeding or in
enforcing any right under this Article shall be paid by the Corporation in
advance of the final disposition of the action, suit or proceeding upon receipt
of an undertaking by or on behalf of such person to repay such amount to the
extent it shall ultimately be determined that such person is not entitled to be
indemnified by the Corporation or, in the case of a criminal action, the
majority of the Board of Directors so determines. The right to indemnification
and advancement of expenses conferred in this bylaw shall not be deemed
exclusive of any other rights to which any person indemnified may be entitled
under any agreement, vote of stockholders or directors or otherwise, the
Corporation having the express authority to enter such agreements as the Board
of Directors deems appropriate for the indemnification of and advancement of
expenses, including the creation of a fund therefor or equivalent guarantee, to
present or future directors and officers of the Corporation in connection with
their service as director or officer of the Corporation or their service as
director, officer, trustee, employee or agent of any other enterprise or in
connection with an employee benefit plan at the request of the Corporation. The
right to indemnification and the advancement of expenses provided in this bylaw
shall be a contract right, shall continue as to a person who has ceased to serve
in the capacities described herein, and shall inure to the benefit of the heirs,
executors and administrators of such person.

          Section 8.2 Repeal; Alteration. No amendment, alteration or repeal of
this Article VIII, nor the adoption of any provision inconsistent with this
Article VIII, shall adversely affect the rights of a director or officer to
indemnification and advancement of expenses, existing at the time of such
amendment, modification or repeal, or the adoption of such an inconsistent
provision.


                                  ARTICLE IX

                              General Provisions


          Section 9.1 Registered Office. The registered office of the
Corporation, required by law to be maintained in the Commonwealth of
Pennsylvania, shall be 3400 Grand Avenue, Neville Island, Pittsburgh,
Pennsylvania 15225. The principal place of business of the Corporation may be,
but need not be, the same as the registered office. The address of the
registered office may be changed from time to time by the board of directors.

          Section 9.2 Other Offices. The Corporation may have additional offices
and places of business in such places, within or without the Commonwealth of
Pennsylvania, as the board of directors may designate or as the business of the
Corporation may require.

          Section 9.3 Corporate Seal. The Corporation shall have a corporate
seal which shall have inscribed thereon the name of the Corporation, the year of
<PAGE>
 
organization, and the words "Corporate Seal - Pennsylvania" or such inscription
as the board of directors may determine. The seal may be used by causing it or a
facsimile thereof to be impressed or affixed, or in any manner reproduced.

          Section 9.4 Amendment of Bylaws. These bylaws may be amended or
repealed, and new bylaws may be adopted, by the board of directors, except where
the power to repeal, adopt or amend a bylaw on any subject is expressly
committed to the shareholders by law, and subject always to the power of the
shareholders to change any action taken by the board.

          I hereby certify that the foregoing are the Bylaws of Pitt-Des Moines,
Inc., adopted by its Board of Directors on February 11, 1999. I also certify
that Section 2.11 of these Bylaws was approved by the shareholders of the
Corporation on April 27, 1987.


Date:  February 11, 1999

                                  /s/ Thomas R. Lloyd 
                                  -------------------------------
                                  Thomas R. Lloyd, Secretary