<PAGE>
 
===============================================================================
                                 UNITED STATES
                       SECURITIES AND EXCHANGE COMMISSION
                            WASHINGTON, D.C.  20549
                                        
                                   FORM 10-K
   (Mark One)
     [X]    ANNUAL REPORT PURSUANT TO SECTION 13 OR 15(D) OF THE
            SECURITIES EXCHANGE ACT OF 1934
            FOR THE FISCAL YEAR ENDED DECEMBER 31, 1998

                                       OR

     [ ]    TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(D) OF THE
            SECURITIES EXCHANGE ACT OF 1934
            FOR THE TRANSITION PERIOD FROM      TO

                         Commission file number 1-5259
                                        
                             PITT-DES MOINES, INC.
             (Exact name of registrant as specified in its charter)
                                        
             PENNSYLVANIA                                    25-0729430
  (STATE OR OTHER JURISDICTION OF                         (I.R.S. EMPLOYER
   INCORPORATION OR ORGANIZATION)                         IDENTIFICATION NO.)

1450 LAKE ROBBINS DRIVE, SUITE 400, THE WOODLANDS, TEXAS            77380
    (ADDRESS OF PRINCIPAL EXECUTIVE OFFICES)                     (ZIP CODE)

                                 281-765-4600
             (REGISTRANT'S TELEPHONE NUMBER, INCLUDING AREA CODE)

          SECURITIES REGISTERED PURSUANT TO SECTION 12(B) OF THE ACT:

        TITLE OF EACH CLASS       NAME OF EACH EXCHANGE ON WHICH REGISTERED
        -------------------       -----------------------------------------
    COMMON STOCK, NO PAR VALUE            AMERICAN STOCK EXCHANGE

       SECURITIES REGISTERED PURSUANT TO SECTION 12(G) OF THE ACT:  NONE
                                        
INDICATE BY CHECK MARK WHETHER THE REGISTRANT (1) HAS FILED ALL REPORTS REQUIRED
TO BE FILED BY SECTION 13 OR 15(D) OF THE SECURITIES EXCHANGE ACT OF 1934 DURING
THE PRECEDING 12 MONTHS (OR FOR SUCH SHORTER PERIOD THAT THE REGISTRANT WAS
REQUIRED TO FILE SUCH REPORTS), AND (2) HAS BEEN SUBJECT TO SUCH FILING
REQUIREMENTS FOR THE PAST 90 DAYS.
YES  X       NO  
    ---        ---         

INDICATE BY CHECK MARK IF DISCLOSURE OF DELINQUENT FILERS PURSUANT TO ITEM 405
OF REGULATION S-K IS NOT CONTAINED HEREIN, AND WILL NOT BE CONTAINED, TO THE
BEST OF REGISTRANT'S KNOWLEDGE, IN DEFINITIVE PROXY OR INFORMATION STATEMENTS
INCORPORATED BY REFERENCE IN PART III OF THIS FORM 10-K OR ANY AMENDMENT TO THIS
FORM 10-K [  ].

THE AGGREGATE MARKET VALUE OF THE REGISTRANT'S VOTING STOCK HELD BY NON-
AFFILIATES WAS AT LEAST $87,666,729 ON FEBRUARY 26, 1999, BASED UPON THE AVERAGE
BETWEEN THE HIGHEST AND LOWEST SALES PRICES OF THE REGISTRANT'S COMMON STOCK AS
REPORTED IN THE CONSOLIDATED TRANSACTIONS REPORTING SYSTEM.

     COMMON STOCK OUTSTANDING AS OF FEBRUARY 26, 1999.......7,245,916 SHARES.

DOCUMENTS INCORPORATED BY REFERENCE:

     CERTAIN PORTIONS OF THE DOCUMENTS OF THE REGISTRANT LISTED BELOW HAVE BEEN
INCORPORATED BY REFERENCE INTO THE INDICATED PARTS OF THIS ANNUAL REPORT ON FORM
10-K:

     PROXY STATEMENT ANTICIPATED TO BE DATED MARCH 31, 1999...................
        PART III, ITEMS 10-13

     ANNUAL REPORT TO STOCKHOLDERS FOR FISCAL YEAR ENDED DECEMBER 31, 1998.... 
        PART I AND PART II

-------------------------------------------------------------------------------
<PAGE>
 
                                     PART I

ITEM 1.  BUSINESS

GENERAL

Pitt-Des Moines, Inc. and its subsidiaries ("PDM" or the "Company") began
conducting business in 1892 and was incorporated in Pennsylvania on February 14,
1916.  The Company's principal executive offices are located at 1450 Lake
Robbins Drive, Suite 400, The Woodlands, Texas  77380, telephone number (281)
765-4600.

PDM is a diversified engineering and construction company, and a distributor of
a broad range of carbon steel products.  The Company currently operates in two
business segments:  Engineering and Construction, and Steel Distribution.  The
Engineering and Construction segment specializes in the engineering and design,
procurement, fabrication, erection and rehabilitation of steel products
including liquid and cryogenic storage and processing systems, water storage
systems, bridges and buildings.  The Steel Distribution segment processes and
distributes a full line of heavy carbon steel products and manufactures and
markets corrugated metal culvert pipe and accessories.

A summary of the Company's products and services by business segment is set
forth below.

ENGINEERING AND CONSTRUCTION

In March of 1998, we opened a new steel fabricating facility in Eloy, Arizona.
This new facility doubles our capacity and increases our capabilities in the
California, Arizona and Nevada construction markets.

  We acquired the remaining interest in Tecnologia de Almacenamiento Industrial,
TAI, S.A. (TAISA) an engineering and construction company located in Caracas,
Venezuela.

  We also expanded our Palatka, Florida fabrication facility, enhancing our
ability to respond to opportunities in the East Coast bridge market.

The Engineering and Construction business provides:

  a) The capability to design, fabricate and erect oil and chemical storage
     tanks used for storing crude oil, petroleum, gasoline and other petroleum
     derivatives and chemicals.  We have developed and patented certain systems,
     parts and sealing devices which help to reduce the hazards of fire and
     explosion from the stored products, as well as to decrease air pollution
     and vapor loss.  Additionally, we fabricate and erect various vessels used
     in the processing of a variety of oil and chemical products.  The oil and
     chemical tanks, sealing devices and process vessels are produced
     principally for the petroleum, petrochemical, chemical and food processing
     industries as well as government agencies.

                                       2
<PAGE>
 
  ITEM 1.  BUSINESS (CONT'D)

  b) The capability to design, fabricate and erect elevated and flat bottom
     water storage tanks for water service and fire protection requirements and
     treatment tanks for the purification, filtration and softening of water.
     The principal purchasers of the Company's water storage tanks and
     wastewater treatment facilities are government agencies and private
     industry.

  c) The capability to design, fabricate and erect many types of facilities and
     structures; services offered include research and design, material
     selection, preparation of detailed drawings, shop fabrication, field
     erection and subcontract management.

  d) The capability to fabricate and erect miscellaneous plate work which
     includes penstocks and breechings, stacks and stack liners, scrubbers,
     absorbers, flow conductors and heat exchangers for utilities and private
     industry.

  e) The capability to design, fabricate and erect high speed wind tunnels,
     altitude test chambers, hydrospace test facilities and high vacuum and
     thermal test facilities for use in connection with energy, aerospace and
     defense research.

  f) The capability to design and build supercritical fluid extraction
     facilities for the food processing industry.

  g) The capability to design and build anaerobic digesters for the wastewater
     treatment industry.

  h) The capability to fabricate and erect structural steel for commercial,
     institutional and public sector buildings for government agencies, private
     developers and general contractors.

  i) The capability to fabricate structural steel for new bridges and fabricate
     and erect structural steel for bridge rehabilitation for government
     agencies and general contractors.

STEEL DISTRIBUTION

The Company's Steel Distribution segment operates eight steel service centers
and three culvert facilities located in the West and Midwest regions of the
United States.  During 1998, the Company completed the conversion of an existing
PDM facility in Des Moines, Iowa into a steel distribution center to serve a
growing Midwest market.  The Company also broke ground on a new steel service
center in Woodland, Washington.  This new facility will open in April of 1999
and will serve Portland, Seattle and the entire Pacific Northwest.

  In early 1999, the Company acquired the remaining interest in Oregon Culvert
Company, Inc., which operated facilities in Washington and Oregon.

                                       3
<PAGE>
 
ITEM 1.  BUSINESS (CONT'D)

  The steel service centers process and distribute to end users a general line
of carbon steel products including plates, sheets, structural shapes, bars,
tubes, pipe and other miscellaneous metal products.  This segment also
manufactures and markets to end users corrugated metal culvert pipe and
accessories.  Steel Distribution's primary markets include steel fabricators,
original equipment manufacturers, mining, logging, agricultural and road
construction industries.

  The Company and the industry as a whole deem the maintenance of adequate
levels of inventory to be integral to the Steel Distribution business.  The
Company believes that it has adequate levels of inventory on hand to meet
current and anticipated customer demand.

OTHER

Several large companies compete nationally in some product lines with the
Company and there are several local and regional companies that compete in
certain product lines in specific geographic areas.  The majority of the
Company's business is secured through open competitive bidding or through direct
negotiations with industry or government agencies.  Competition is based
primarily on performance including the ability to provide design, engineering
and on-site field construction services in a cost-effective and timely manner.
The Steel Distribution Segment's volume of business is based on the price,
delivery, credit terms, and first stage preprocessing of products, offered to
its customers as well as its reputation.

  The Company's earned revenue was $567 million in 1998, compared with $475
million in 1997 and $468 million in 1996.  For further financial information
refer to Consolidated Financial Statements contained in PDM's 1998 Annual Report
to Stockholders and incorporated herein by reference.

  The principal raw materials essential to the Company's business are steel,
alloys and other metal plates and structural sections.  The Company procures
these raw materials from various domestic and foreign sources including, the
mills of USX Corporation, Bethlehem Steel Corporation, Northwestern Steel and
Wire Company, Nucor Steel, British Steel and Mitsubishi International
Corporation.

  The Company has a license and technical assistance agreement with Roediger, a
German corporation, which gives the Company exclusive rights in North America
and other selected countries worldwide to use the Roediger technology, a process
which utilizes anaerobic digestion in the treatment of wastewater.  Revenues to
date from this technology have not been material to the Company.

  Some components of the other products made and erection techniques used by the
Company are covered by patents owned or licensed by the Company.  None of these
are deemed to be material to the Company from an overall financial viewpoint.

                                       4
<PAGE>
 
ITEM 1.  BUSINESS (CONT'D)

  The Company had a backlog of uncompleted contracts of $346 million on December
31, 1998 compared to $252 million on December 31, 1997.  Substantially all
backlog is expected to be completed during 1999.

  Factors such as the type and scope of operations in progress at any given
time, including weather conditions at field sites, create fluctuations in the
employment level at PDM.  On December 31, 1998, the Company employed 2,479
persons, of which 821 were salaried personnel and 1,658 were hourly personnel.

  Financial information for the Company's two business segments is included in
the Business Segment Information Section of PDM's 1998 Annual Report to
Stockholders, which section is incorporated herein by reference.

ITEM 2.  PROPERTIES

Operations of the Company are conducted at both owned and leased properties.  In
addition, certain owned properties of the Company are leased to third party
tenants.  The following table indicates each of the Company's facilities by:
segment, location, type of facility, year operations began, and square footage
of property owned or leased on December 31, 1998:
<TABLE>
<CAPTION>
 
                                                                  YEAR
                                            TYPE OF            OPERATIONS  SQUARE
LOCATION                                    FACILITY             BEGAN     FOOTAGE
 
ENGINEERING AND CONSTRUCTION
-------------------------------
<S>                                   <C>                         <C>      <C> 
Harpersville, Alabama                 Warehouse and office         1996    11,500
Eloy, Arizona                          Fabrication plant           1998   108,450
Fresno, California                         Toolhouse               1963    52,140
Stockton, California              Fabrication plant and office     1987   143,000
Tustin, California                           Office                1996       185
Palatka, Florida                  Fabrication plant and office     1997   148,564
Clive, Iowa                       Fabrication plant and office     1955   176,540
Des Moines, Iowa                           Toolhouse               1900    29,000
Pittsburgh, Pennsylvania              Office and toolhouse         1927    98,780
Warren, Pennsylvania                   Fabrication plant           1959   125,960
Franklin, Tennessee                        Toolhouse               1977    28,220
Conroe, Texas (1)                            Office                1996     1,600
Hitchcock, Texas (2)                       Toolhouse               1994     5,000
The Woodlands, Texas (3)                     Office                1996    32,600
Provo, Utah                            Fabrication plant           1959   154,950
Eau Claire, Wisconsin             Fabrication plant and office     1994   309,500
Wausau, Wisconsin                 Fabrication plant and office     1991   157,000
</TABLE>

                                       5
<PAGE>
 
ITEM 2.  PROPERTIES (CONT'D)
 
<TABLE> 
<CAPTION> 
                                                                      YEAR
                                                TYPE OF            OPERATIONS   SQUARE
LOCATION                                        FACILITY             BEGAN      FOOTAGE
 
ENGINEERING AND CONSTRUCTION (Cont'd)
-------------------------------------
<S>                                      <C>                         <C>          <C> 
Port Coquitlam, B.C. Canada (4)                   Office              1997      12,300
Trenton, Ontario, Canada (5)                      Office              1997         800
                                                                            
STEEL DISTRIBUTION                                                          
------------------                                                          
                                                                            
Fresno, California                       Warehouse and office         1955     112,800
Santa Clara, California                  Warehouse and office         1947     108,530
Stockton, California                     Warehouse and office         1967     191,500
Cedar Rapids, Iowa                       Warehouse and office         1976      66,800
Des Moines, Iowa                         Warehouse and office         1900     109,100
Sparks, Nevada                           Warehouse and office         1974      78,940
Tualatin, Oregon                         Warehouse and office         1973      31,620
Spanish Fork, Utah                       Warehouse and office         1977      74,280
Arlington, Washington (6)                Warehouse and office         1993      13,970
Vancouver, Washington (7)                Warehouse and office         1997     138,600
 
IDLE HOLDINGS, INCLUDING PLANT AND PROPERTY (8)
-----------------------------------------------
 
Chicago, Illinois                                 Office              1987      20,800
Des Moines, Iowa                      Fabrication plant and office    1900     230,000
Hilliard, Ohio                        Fabrication plant and office    1971     179,000
Pittsburgh, Pennsylvania                          Office              1927      10,234
Provo, Utah (9)                                   Office              1959      15,731
----------                                                              
</TABLE>                                                                
                                                                       
  (1) Company leases building from outside third party. Lease is month-to-month.
  (2) Company leases land and building from outside third party. Lease will
      expire July 1, 1999.                                             
  (3) Company leases building from outside third party. Lease will expire August
      31, 2006.                                                         
  (4) Company leases building from outside third party. Lease will expire
      November 30, 2002.                                                
  (5) Company leases building from outside third party. Lease is month-to-month.
  (6) Company leases land from outside third party. Lease will expire January
      31, 2003.                                                         
  (7) Company leases land and building from outside third party. Lease will
      expire September 1, 1999.                                         
  (8) Company pursues the sale or development of all idle facilities and
      regularly evaluates similar opportunities for facilities not fully
      utilized.
  (9) Company is leasing facility to outside third party.

  The properties listed above are utilized by the Company's business segments as
indicated.  The Company's production capacity is adequate for its present needs.
The Company believes that its properties have been adequately maintained, are
generally in good condition and are suitable for the Company's business as now
conducted.

                                       6
<PAGE>
 
ITEM 3.  LEGAL PROCEEDINGS

See Contingencies note accompanying the consolidated financial statements
contained in PDM's 1998 Annual Report to Stockholders, which note is
incorporated herein by reference.

ITEM 4.  SUBMISSION OF MATTERS TO A VOTE OF SECURITY HOLDERS

  Not applicable.

EXECUTIVE OFFICERS OF THE REGISTRANT

  Information regarding executive officers of the Registrant is presented in
Part III of this report and is incorporated herein by reference.

                                       7
<PAGE>
 
                                    PART II

Information for Items 5, 6 and 7 is included in PDM's 1998 Annual Report to
Stockholders and is incorporated herein by reference (and except for these
sections, and sections incorporated herein by reference in Items 1 and 8 of this
report, PDM's Annual Report to Stockholders is not deemed to be filed as part of
this report):

<TABLE>
<CAPTION>
 
                                                                        ANNUAL REPORT
                                                                       TO STOCKHOLDERS
ITEM NO.                TITLE                                           SECTION/TITLE
---------------------------------------------------------------------------------------------
<S>                     <C>                                          <C> 
ITEM 5.                 Market for Registrant's Common Equity        Common Stock Information
                        and Related Stockholder Matters              included in Stockholders'
                                                                     Reference section
 
ITEM 6.                 Selected Financial Data                      Five-Year Selected
                                                                     Financial Data
 
ITEM 7.                 Management's Discussion and Analysis         Management's Discussion
                        of Financial Condition and Results of        and Analysis
                        Operations

ITEM 8.                 Financial Statements and Supplemental Data

</TABLE> 

The financial statements consisting of Consolidated Statements of Income,
Consolidated Statements of Financial Condition, Consolidated Statements of Cash
Flows, Consolidated Statements of Stockholders' Equity, Notes to Consolidated
Financial Statements, and Business Segment Information are included in the
Consolidated Financial Statements section of PDM's 1998 Annual Report to
Stockholders, which is incorporated herein by reference.  The report of
independent auditors on PDM's consolidated financial statements is contained in
the Report of Independent Auditors and Management section of PDM's 1998 Annual
Report to Stockholders, which is incorporated herein by reference.

  The unaudited Two Year Quarterly Results of Operations contained in PDM's 1998
Annual Report to Stockholders is incorporated herein by reference.

ITEM 9.   CHANGES IN AND DISAGREEMENTS WITH ACCOUNTANTS ON ACCOUNTING AND
          FINANCIAL DISCLOSURE

  Not applicable.

                                       8
<PAGE>
 
                                    PART III

ITEM 10.  DIRECTORS AND EXECUTIVE OFFICERS OF THE REGISTRANT (1)

  Regarding the directors of the Registrant, reference is made to the
information set forth under the caption "Election of Directors" in the Company's
definitive Proxy Statement anticipated to be dated March 31, 1999 (the "Proxy
Statement") which information is incorporated herein by reference.

  The principal executive officers of the Company and their recent business
experience are as follows:

W. R. Jackson, age 90

 Director since 1940;
 Chairman Emeritus since 1988; formerly Chairman of the Board since 1971.
 Mr. Jackson has been with the Company since 1936 and is the father of Mr.
 Jackson, Jr. and Mrs. Townsend.

P. O. Elbert, age 68

  Director since 1988;

  Chairman of the Board of the Company since 1990; formerly President of the
  Company since 1988 and President, PDM Structural Group since 1987.  Mr. Elbert
  joined the Company in 1987.  Prior to 1987, Mr. Elbert was Vice Chairman of
  Chicago Steel Corporation since 1986; formerly a partner of Elbert and McKee
  Company since 1984; formerly President and Chief Executive Officer of Flint
  Steel Corporation since 1979; and formerly Group Vice President of Inryco,
  Inc., a subsidiary of Inland Steel Company since 1969.

Wm. W. McKee, age 60 (2)

  Director since 1988;

  President and Chief Executive Officer of the Company since 1990; formerly
  President, PDM Plate Group since May 1987 and formerly Executive Vice
  President, PDM Structural Group since April 1987.  Mr. McKee joined the
  Company in 1987.  Prior to 1987, Mr. McKee was Secretary of Chicago Steel
  Corporation since 1986; formerly a partner of Elbert and McKee Company since
  1984; formerly a consultant with McKee and Associates since 1983; formerly
  President of Hogan Manufacturing since 1980; and formerly President of Herrick
  Corporation since 1973.
 
R. A. Byers, age 51 (2)

  Treasurer since 1988 and Vice President, Finance and Administration since
  1987; formerly Vice President, Finance since 1984; formerly Controller since
  1982; formerly Assistant Controller since 1981; formerly Manager of Financial
  Reporting since 1979; and formerly with Ernst & Young LLP for ten years.

                                       9
<PAGE>
 
ITEM 10.  DIRECTORS AND EXECUTIVE OFFICERS OF THE REGISTRANT (CONT'D)

T. R. Lloyd, age 50 (2)

  Secretary and General Counsel since 1990; formerly Senior Attorney of Buchanan
  Ingersoll Professional Corporation, since 1989; formerly Vice President,
  Secretary and General Counsel for Arch Mineral Corporation since 1984; and
  formerly Director and Secretary of U.S. Steel Mining Co., Inc. since 1979.

____________________
(1)   Except where otherwise indicated, all references are to positions held
      with Pitt-Des Moines, Inc.  Each executive officer of the Company is
      elected annually by the Board of Directors until his successor is elected
      and qualified, and each has served continually as an officer since first
      elected.

(2)   The Company has agreements with each of Messrs. McKee, Byers and Lloyd
      covering, among other things, their positions as executive officers of the
      Company after a change of control.

ITEM 11.  EXECUTIVE COMPENSATION

  Reference is made to the information set forth under the captions "Board of
Directors and Committees of the Board," "Executive Compensation and Other
Information," and "Compensation Committee Interlocks and Insider Participation"
appearing in the Company's Proxy Statement, which information is incorporated
herein by reference; provided, however, that the information set forth under the
captions "Compensation Committee Report on Executive Compensation" and
"Performance Graph" in the Proxy Statement shall not be deemed to be soliciting
material or to be "filed" with the Commission or subject to Regulation 14A or
14C (other than as provided in Item 402 of Regulation S-K) or to the liabilities
of Section 18 of the Securities Exchange Act of 1934, as amended.

ITEM 12.  SECURITY OWNERSHIP OF CERTAIN BENEFICIAL OWNERS AND MANAGEMENT

  Reference is made to the information contained under the captions
"Stockholdings of Management" and "Principal Holders of Common Stock" in the
Company's Proxy Statement, which information is incorporated herein by
reference.

ITEM 13.  CERTAIN RELATIONSHIPS AND RELATED TRANSACTIONS

  Reference is made to the information contained under the caption "Compensation
Committee Interlocks and Insider Participation" in the Company's Proxy
Statement, which information is incorporated herein by reference.

                                       10
<PAGE>
 
                                    PART IV

ITEM 14. EXHIBITS, FINANCIAL STATEMENT SCHEDULES AND REPORTS ON FORM 8-K

(a) 1.   Financial Statements

         The following consolidated financial statements and Report of
         Independent Auditors previously incorporated by reference in Part II,
         Item 8 of this report are incorporated herein by reference:
 
         Report of Independent Auditors

         Consolidated Statements of Income -- Years Ended December 31, 1998,
         1997 and 1996

         Consolidated Statements of Financial Condition as of December 31, 1998
         and 1997

         Consolidated Statements of Cash Flows -- Years Ended December 31, 1998,
         1997 and 1996

         Consolidated Statements of Stockholders' Equity -- Years Ended December
         31, 1998, 1997 and 1996

         Notes To Consolidated Financial Statements

  2.     Financial Statement Schedules

         The following consolidated financial statement schedule of Pitt-Des
         Moines, Inc. and subsidiaries is included in Item 14(d):

         Schedule II. Valuation and Qualifying Accounts for years ended December
         31, 1998, 1997 and 1996

         All other schedules are omitted because they are not applicable or the
         required information is shown in the consolidated financial statements
         or notes thereto.

  3.     Exhibits:

  3.1    Articles of Incorporation, as amended to date (filed as Exhibit 3.1 to
         the Company's quarterly report on Form 10-Q for the quarter ended
         September 30, 1989 and incorporated herein by reference)

  3.2    Bylaws, as amended to date (filed herewith)

                                       11
<PAGE>
 
ITEM 14. EXHIBITS, FINANCIAL STATEMENT SCHEDULES AND REPORTS ON FORM 8-K
         (CONT'D)

  4.1    Revolving Credit and Letter of Credit Issuance Agreement dated as of
         February 16, 1999 by and among Pitt-Des Moines, Inc. and PNC Bank,
         National Association, Wells Fargo Bank, N.A., American National Bank
         and LaSalle National Bank (filed herewith)

  10.1*  Agreement executed by and between the Company and Wm. W. McKee (filed
         as Exhibit 10.1 to the Company's annual report on Form 10-K for the
         year ended December 31, 1990 and incorporated herein by reference)

  10.2*  Amendment to agreement executed by and between the Company and Wm. W.
         McKee filed as Exhibit 10.1 hereto (filed as Exhibit 10.2 to the
         Company's annual report on Form 10-K for the year ended December 31,
         1997 and incorporated by reference)

  10.3*  Agreement executed by and between the Company and R. A. Byers (filed as
         Exhibit 10.1 to the Company's quarterly report on Form 10-Q for the
         quarter ended June 30, 1991 and incorporated herein by reference)

  10.4*  Amendment to agreement executed by and between the Company and R. A.
         Byers filed as Exhibit 10.3 hereto (filed as Exhibit 10.4 to the
         Company's annual report on Form 10-K for the year ended December 31,
         1997 and incorporated herein by reference)

  10.5*  Agreement executed by and between the Company and T. R. Lloyd (filed as
         Exhibit 10.2 to the Company's quarterly report on Form 10-Q for the
         quarter ended June 30, 1991 and incorporated herein by reference)

  10.6*  Amendment to agreement executed by and between the Company and T. R.
         Lloyd filed as Exhibit 10.5 hereto (filed as Exhibit 10.6 to the
         Company's annual report on Form 10-K for the year ended December 31,
         1997 and incorporated herein by reference)

  10.7*  Management Incentive Plan (filed as Exhibit 10.5 to the Company's
         annual report on Form 10-K for the year ended December 31, 1992 and
         incorporated herein by reference)

  10.8*  Summary of Company 1998 Management Incentive Plan (MIP) (filed
         herewith)

  10.9*  Retirement Plan for PDM Outside Directors as amended, effective May 26,
         1994 (filed as Exhibit 10.7 to the Company's annual report on Form 10-K
         for the year ended December 31, 1994 and incorporated herein by
         reference)

                                       12
<PAGE>
 
ITEM 14. EXHIBITS, FINANCIAL STATEMENT SCHEDULES AND REPORTS ON FORM 8-K
         (CONT'D)
 
  10.10* Retirement Plan for PDM Outside Directors, effective May 26, 1994, as
         amended on September 14, 1995 (filed as Exhibit 10.7 to the Company's
         annual report on Form 10-K for the year ended December 31, 1995 and
         incorporated herein by reference)

  10.11* Stock Option Plan of 1990 (filed as Exhibit 4.01 to the Company's
         Registration Statement No. 333-34787 on Form S-8 filed May 7, 1990 and
         incorporated herein by reference)

  10.12* Investment Letter and Registration Rights Agreement dated September 21,
         1993 by and between Pitt-Des Moines, Inc. and William W. McKee, Jr.
         (filed as Exhibit 10.1 to the Company's quarterly report on Form 10-Q
         for the quarter ended September 30, 1993 and incorporated herein by
         reference)

  10.13* Amendment to Investment Letter and Registration Rights Agreement dated
         September 21, 1993 by and between Pitt-Des Moines, Inc. and William W.
         McKee, Jr. filed as Exhibit 10.12 hereto (filed as Exhibit 10.13 to the
         Company's annual report on Form 10-K for the year ended December 31,
         1997 and incorporated herein by reference)

  10.14* Investment Letter and Registration Rights Agreement dated September 21,
         1993 by and between Pitt-Des Moines, Inc. and Phillip O. Elbert (filed
         as Exhibit 10.2 to the Company's quarterly report on Form 10-Q for the
         quarter ended September 30, 1993 and incorporated herein by reference)

  10.15* Amendment to Investment Letter and Registration Rights Agreement dated
         September 21, 1993 by and between Pitt-Des Moines, Inc. and P. O.
         Elbert filed as Exhibit 10.14 hereto (filed as Exhibit 10.15 to the
         Company's annual report on Form 10-K for the year ended December 31,
         1997 and incorporated herein by reference)

  10.16* Directors Stock Plan (filed under the Company's Registration Statement
         No. 333-13043 on Form S-8 dated September 30, 1996 and incorporated
         herein by reference)

  10.17* Stock Option Agreement executed by and between the Company and P. O.
         Elbert (filed as Exhibit 10.12 to the Company's annual report on Form
         10-K for the year ended December 31, 1996 and incorporated herein by
         reference)

  10.18* Amendment to Stock Option Agreement executed by and between the Company
         and P. O. Elbert filed as Exhibit 10.17 hereto (filed as Exhibit 10.15
         to the Company's annual report on Form 10-K for the year ended December
         31, 1997 and incorporated herein by reference)

                                       13
<PAGE>
 
ITEM 14. EXHIBITS, FINANCIAL STATEMENT SCHEDULES AND REPORTS ON FORM 8-K
         (CONT'D)

  10.19* Supplemental Benefit and Supplemental Salaried Retirement Plan (filed
         as Exhibit 10.15 to the Company's annual report on Form 10-K for the
         year ended December 31, 1997 and incorporated herein by reference)

  10.20* Long Term Incentive Stock Plan of 1997 (filed under the Company's
         Registration Statement No. 333-68853 on Form S-8 dated December 14,
         1998 and incorporated herein by reference)

  13     Those portions of the Annual Report to Stockholders for fiscal year
         ended December 31, 1998, which are incorporated herein by reference
         (filed herewith)

  21     Subsidiaries of Pitt-Des Moines, Inc. (filed herewith)

  23     Consent of Independent Auditors, Ernst & Young LLP (filed herewith)

  27     Financial Data Schedule

(b)      Reports on Form 8-K:

         None.
------------------------
* Denotes management contract or compensatory plan or arrangement.

                                       14
<PAGE>
 
                                   SIGNATURES

  Pursuant to the requirements of Section 13 or 15(d) of the Securities Exchange
Act of 1934, the registrant has duly caused this report to be signed on its
behalf by the undersigned, thereunto duly authorized.

                                     PITT-DES MOINES, INC.

March 29, 1999                             By: /s/ Wm. W. McKee
                                              -----------------------------
                                              Wm. W. McKee
                                              President and
                                              Chief Executive Officer

   Pursuant to the requirements of the Securities Exchange Act of 1934, this
report has been signed below by the following persons on behalf of the
Registrant and in the capacities and on the dates indicated.

 SIGNATURES                             TITLE                   DATE

PRINCIPAL EXECUTIVE OFFICER:


/s/ Wm. W. McKee                President, Chief            March 29, 1999
----------------------          Executive Officer and
    Wm. W. McKee                Director
 

PRINCIPAL FINANCIAL AND ACCOUNTING OFFICER:


/s/  R.A. Byers                Chief Financial Officer      March 29, 1999
----------------------         and Chief Accounting
     R. A. Byers               Officer


OTHER DIRECTORS:

/s/  J. C. Bates               Director                     March 29, 1999
----------------------    
     J. C. Bates


/s/  V. G. Beghini             Director                     March 29, 1999
----------------------    
     V. G. Beghini

                                       15
<PAGE>
 
                              SIGNATURES (CONT'D)

 SIGNATURES                             TITLE                   DATE


/s/ R. W. Dean                 Director                     March 29, 1999
----------------------
    R. W. Dean



/s/ P. O. Elbert               Director                     March 29, 1999
----------------------
    P. O. Elbert


/s/ W. R. Jackson              Director                     March 29, 1999
----------------------
    W. R. Jackson


/s/ W. R. Jackson, Jr.         Director                     March 29, 1999
---------------------- 
    W. R. Jackson, Jr.


/s/ W. E. Lewellen             Director                     March 29, 1999
----------------------
    W. E. Lewellen


/s/ A. J. Paddock              Director                     March 29, 1999
----------------------
    A. J. Paddock


/s/ J. W. Robinson             Director                     March 29, 1999
----------------------
    J. W. Robinson


/s/ P. J. Townsend             Director                     March 29, 1999
----------------------
    P. J. Townsend

                                       16
<PAGE>
 
                SCHEDULE II - VALUATION AND QUALIFYING ACCOUNTS
                             Pitt-Des Moines, Inc.
                                        
<TABLE>
<CAPTION>
                                                                    ADDITIONS         DEDUCTIONS (1)                 
                                                               -----------------     ------------------
                                               BALANCE AT           CHARGED TO                                               
                                              BEGINNING OF          COSTS AND                                 BALANCE AT    
             DESCRIPTION                         PERIOD              EXPENSES        CREDITED TO ASSET       END OF PERIOD 
--------------------------------------    -----------------    -----------------    -------------------     ----------------
<S>                                       <C>                  <C>                  <C>                     <C>
Deducted from accounts receivable as
 allowance for doubtful accounts:

Year ended December 31, 1998                     $1,058,724             $599,298               $865,022           $  793,000
 
Year ended December 31, 1997                     $  868,000             $363,233               $172,509           $1,058,724
 
Year ended December 31, 1996                     $  868,000             $ 90,000               $ 90,000           $  868,000
</TABLE>

---------------------
(1)  Write-off of accounts deemed to be uncollectible and adjustment of
     accruals.
<PAGE>
 
                                 EXHIBIT INDEX
                                        

  3.1    Articles of Incorporation, as amended to date (filed as Exhibit 3.1 to
         the Company's quarterly report on Form 10-Q for the quarter ended
         September 30, 1989 and incorporated herein by reference)

  3.2    Bylaws, as amended to date (filed herewith)

  4.1    Revolving Credit and Letter of Credit Issuance Agreement dated as of
         February 16, 1999 by and among Pitt-Des Moines, Inc. and PNC Bank,
         National Association, Wells Fargo Bank, N.A., American National Bank
         and LaSalle National Bank (filed herewith)

  10.1*  Agreement executed by and between the Company and Wm. W. McKee (filed
         as Exhibit 10.1 to the Company's annual report on Form 10-K for the
         year ended December 31, 1990 and incorporated herein by reference)

  10.2*  Amendment to agreement executed by and between the Company and Wm. W.
         McKee filed as Exhibit 10.1 hereto (filed as Exhibit 10.2 to the
         Company's annual report on Form 10-K for the year ended December 31,
         1997 and incorporated by reference)

  10.3*  Agreement executed by and between the Company and R. A. Byers (filed as
         Exhibit 10.1 to the Company's quarterly report on Form 10-Q for the
         quarter ended June 30, 1991 and incorporated herein by reference)

  10.4*  Amendment to agreement executed by and between the Company and R. A.
         Byers filed as Exhibit 10.3 hereto (filed as Exhibit 10.4 to the
         Company's annual report on Form 10-K for the year ended December 31,
         1997 and incorporated herein by reference)

  10.5*  Agreement executed by and between the Company and T. R. Lloyd (filed as
         Exhibit 10.2 to the Company's quarterly report on Form 10-Q for the
         quarter ended June 30, 1991 and incorporated herein by reference)

  10.6*  Amendment to agreement executed by and between the Company and T. R.
         Lloyd filed as Exhibit 10.5 hereto (filed as Exhibit 10.6 to the
         Company's annual report on Form 10-K for the year ended December 31,
         1997 and incorporated herein by reference)

  10.7*  Management Incentive Plan (filed as Exhibit 10.5 to the Company's
         annual report on Form 10-K for the year ended December 31, 1992 and
         incorporated herein by reference)
<PAGE>
 
                            EXHIBIT INDEX  (CONT'D)
                                        
  10.8*  Summary of Company 1998 Management Incentive Plan (MIP) (filed
         herewith)

  10.9*  Retirement Plan for PDM Outside Directors as amended, effective May 26,
         1994 (filed as Exhibit 10.7 to the Company's annual report on Form 10-K
         for the year ended December 31, 1994 and incorporated herein by
         reference)

  10.10* Retirement Plan for PDM Outside Directors, effective May 26, 1994, as
         amended on September 14, 1995 (filed as Exhibit 10.7 to the Company's
         annual report on Form 10-K for the year ended December 31, 1995 and
         incorporated herein by reference)

  10.11* Stock Option Plan of 1990 (filed as Exhibit 4.01 to the Company's
         Registration Statement No. 333-34787 on Form S-8 filed May 7, 1990 and
         incorporated herein by reference)

  10.12* Investment Letter and Registration Rights Agreement dated September 21,
         1993 by and between Pitt-Des Moines, Inc. and William W. McKee, Jr.
         (filed as Exhibit 10.1 to the Company's quarterly report on Form 10-Q
         for the quarter ended September 30, 1993 and incorporated herein by
         reference)

  10.13* Amendment to Investment Letter and Registration Rights Agreement dated
         September 21, 1993 by and between Pitt-Des Moines, Inc. and William W.
         McKee, Jr. filed as Exhibit 10.12 hereto (filed as Exhibit 10.13 to the
         Company's annual report on Form 10-K for the year ended December 31,
         1997 and incorporated herein by reference)

  10.14* Investment Letter and Registration Rights Agreement dated September 21,
         1993 by and between Pitt-Des Moines, Inc. and Phillip O. Elbert (filed
         as Exhibit 10.2 to the Company's quarterly report on Form 10-Q for the
         quarter ended September 30, 1993 and incorporated herein by reference)

  10.15* Amendment to Investment Letter and Registration Rights Agreement dated
         September 21, 1993 by and between Pitt-Des Moines, Inc. and P. O.
         Elbert filed as Exhibit 10.14 hereto (filed as Exhibit 10.15 to the
         Company's annual report on Form 10-K for the year ended December 31,
         1997 and incorporated herein by reference)

  10.16* Directors Stock Plan (filed under the Company's Registration Statement
         No. 333-13043 on Form S-8 dated September 30, 1996 and incorporated
         herein by reference)

  10.17* Stock Option Agreement executed by and between the Company and P. O.
         Elbert (filed as Exhibit 10.12 to the Company's annual report on Form
         10-K for the year ended December 31, 1996 and incorporated herein by
         reference)
<PAGE>
 
                            EXHIBIT INDEX  (CONT'D)
                                        
  10.18* Amendment to Stock Option Agreement executed by and between the Company
         and P. O. Elbert filed as Exhibit 10.17 hereto (filed as Exhibit 10.15
         to the Company's annual report on Form 10-K for the year ended December
         31, 1997 and incorporated herein by reference)

  10.19* Supplemental Benefit and Supplemental Salaried Retirement Plan (filed
         as Exhibit 10.15 to the Company's annual report on Form 10-K for the
         year ended December 31, 1997 and incorporated herein by reference)

  10.20* Long Term Incentive Stock Plan of 1997 (filed under the Company's
         Registration Statement No. 333-68853 on Form S-8 dated December 14,
         1998 and incorporated herein by reference)

  13     Those portions of the Annual Report to Stockholders for fiscal year
         ended December 31, 1998, which are incorporated herein by reference
         (filed herewith)

  21     Subsidiaries of Pitt-Des Moines, Inc. (filed herewith)

  23     Consent of Independent Auditors, Ernst & Young LLP (filed herewith)

  27     Financial Data Schedule

(b)      Reports on Form 8-K:

         None.
------------------------
* Denotes management contract or compensatory plan or arrangement.