UNITED STATES
                       SECURITIES AND EXCHANGE COMMISSION
                             Washington, D.C. 20549


                                  SCHEDULE 13G

                    Under the Securities Exchange Act of 1934

                               (Amendment No.      5     )*
                                              -----------

                           Gibraltar Steel Corporation
--------------------------------------------------------------------------------
                                (Name of Issuer)

                                  Common Stock
--------------------------------------------------------------------------------
                         (Title of Class of Securities)


                                    37476F103
                  ---------------------------------------------
                                 (CUSIP Number)



                                December 31, 2001
         --------------------------------------------------------------
             (Date of Event Which Requires Filing of this Statement)


     Check the appropriate box to designate the rule pursuant to which this
     Schedule is filed:

                                [X]  Rule 13d-1(b)
                                [_]  Rule 13d-1(c)
                                [_]  Rule 13d-1(d)



*The remainder of this cover page shall be filled out for a reporting person's
initial filing on this form with respect to the subject class of securities, and
for any subsequent amendment containing information which would alter the
disclosures provided in a prior cover page.

The information required in the remainder of this cover page shall not be deemed
to be "filed" for the purpose of Section 18 of the Securities Exchange Act of
1934 ("Act") or otherwise subject to the liabilities of that section of the Act
but shall be subject to all other provisions of the Act (however, see the
Notes).

                               Page 1 of 10 pages




-------------------------                               ----------------------
  CUSIP No. 37476F103                   13G              Page 2 of 10 Pages
           ----------                                   ----------------------
-------------------------

------------------------------------------------------------------------------
      NAME OF REPORTING PERSON
 1    S.S. or I.R.S. IDENTIFICATION NO. OF ABOVE PERSON

      Liberty Wanger Asset Management, L.P. 36-3820584
------------------------------------------------------------------------------
      CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*
 2                                                              (a) [_]
      Not Applicable                                            (b) [_]
------------------------------------------------------------------------------
      SEC USE ONLY
 3
------------------------------------------------------------------------------
      CITIZENSHIP OR PLACE OF ORGANIZATION
 4
      Delaware
------------------------------------------------------------------------------
                          SOLE VOTING POWER
                     5
     NUMBER OF            None
      SHARES       -----------------------------------------------------------
                          SHARED VOTING POWER
   BENEFICIALLY      6
     OWNED BY             1,065,600
                   -----------------------------------------------------------
       EACH               SOLE DISPOSITIVE POWER
                     7
    REPORTING             None
      PERSON       -----------------------------------------------------------
                          SHARED DISPOSITIVE POWER
       WITH          8
                          1,065,600
------------------------------------------------------------------------------
      AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
 9
      1,065,600
------------------------------------------------------------------------------
      CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES*
10
      Not Applicable                                                [_]
------------------------------------------------------------------------------
      PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9
11
      8.5%
------------------------------------------------------------------------------
      TYPE OF REPORTING PERSON*
12
      IA
------------------------------------------------------------------------------
                      *SEE INSTRUCTION BEFORE FILLING OUT!



-------------------------                               ----------------------
  CUSIP No. 37476F103                   13G              Page 3 of 10 Pages
            ------------                                ----------------------
-------------------------

------------------------------------------------------------------------------
      NAME OF REPORTING PERSON
 1    S.S. or I.R.S. IDENTIFICATION NO. OF ABOVE PERSON

      WAM Acquisition GP, Inc.
------------------------------------------------------------------------------
      CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*
 2                                                              (a) [_]
      Not Applicable                                            (b) [_]
------------------------------------------------------------------------------
      SEC USE ONLY
 3
------------------------------------------------------------------------------
      CITIZENSHIP OR PLACE OF ORGANIZATION
 4
      Delaware
------------------------------------------------------------------------------
                          SOLE VOTING POWER
                     5
     NUMBER OF            None
      SHARES       -----------------------------------------------------------
                          SHARED VOTING POWER
   BENEFICIALLY      6
     OWNED BY             1,065,600
                   -----------------------------------------------------------
       EACH               SOLE DISPOSITIVE POWER
                     7
    REPORTING             None
      PERSON       -----------------------------------------------------------
                          SHARED DISPOSITIVE POWER
       WITH          8
                          1,065,600
------------------------------------------------------------------------------
      AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
 9
      1,065,600
------------------------------------------------------------------------------
      CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES*
10
      Not Applicable                                                [_]
------------------------------------------------------------------------------
      PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9
11
      8.5%
------------------------------------------------------------------------------
      TYPE OF REPORTING PERSON*
12
      CO
------------------------------------------------------------------------------
                      *SEE INSTRUCTION BEFORE FILLING OUT!



------------------------                               -----------------------
  CUSIP No. 37476F103                 13G                Page 4 of 10 Pages
            ---------
------------------------                               -----------------------
------------------------------------------------------------------------------
      NAME OF REPORTING PERSON
 1    S.S. or I.R.S. IDENTIFICATION NO. OF ABOVE PERSON

      Liberty Acorn Trust
------------------------------------------------------------------------------
      CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*
 2                                                              (a) [_]
      Not Applicable                                            (b) [_]
------------------------------------------------------------------------------
      SEC USE ONLY
 3
------------------------------------------------------------------------------
      CITIZENSHIP OR PLACE OF ORGANIZATION
 4
      Massachusetts
------------------------------------------------------------------------------
                          SOLE VOTING POWER
                     5
     NUMBER OF            None
      SHARES       -----------------------------------------------------------
                          SHARED VOTING POWER
   BENEFICIALLY      6
     OWNED BY             840,000
                   -----------------------------------------------------------
       EACH               SOLE DISPOSITIVE POWER
                     7
    REPORTING             None
      PERSON       -----------------------------------------------------------
                          SHARED DISPOSITIVE POWER
       WITH          8
                          840,000
------------------------------------------------------------------------------
      AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
 9
      840,000
------------------------------------------------------------------------------
      CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES*
10
      Not Applicable                                                [_]
------------------------------------------------------------------------------
      PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9
11
      6.7%
------------------------------------------------------------------------------
      TYPE OF REPORTING PERSON*
12
      IV
------------------------------------------------------------------------------



Item 1(a)       Name of Issuer:

                      Gibraltar Steel Corporation


Item 1(b)       Address of Issuer's Principal Executive Offices:

                      3556 Lake Shore Road
                      P.O. Box 2028
                      Buffalo, New York  14219-0228


Item 2(a)       Name of Person Filing:

                      Liberty Wanger Asset Management, L.P. ("WAM")
                      WAM Acquisition GP, Inc., the general partner of WAM
                       ("WAM GP")
                      Liberty Acorn Trust ("Acorn")


Item 2(b)       Address of Principal Business Office:

                      WAM, WAM GP, and Acorn are all located at:

                      227 West Monroe Street, Suite 3000
                      Chicago, Illinois  60606


Item 2(c)       Citizenship:

                      WAM is a Delaware limited partnership; WAM GP is a
                      Delaware corporation; Acorn is a Massachusetts business
                      trust.

Item 2(d)       Title of Class of Securities:

                      Common Stock

Item 2(e)       CUSIP Number:

                      37476F103

Item 3          Type of Person:

                      (d)     Acorn is an Investment Company under section 8 of
                              the Investment Company Act.

                      (e)     WAM is an Investment Adviser registered under
                              section 203 of the Investment Advisers Act of
                              1940; WAM GP is the General Partner of the
                              Investment Adviser.

                               Page 5 of 10 pages



Item 4          Ownership (at December 31, 2000):

                      (a)   Amount owned "beneficially" within the meaning of
                            rule 13d-3:

                            1,065,600

                      (b)   Percent of class:

                            8.5 % (based on 12,598,499 shares outstanding as of
                            September 30, 2001)

                      (c)   Number of shares as to which such person has:

                               (i)   sole power to vote or to direct the vote:
                                     none
                              (ii)   shared power to vote or to direct the vote:
                                     1,065,600
                             (iii)   sole power to dispose or to direct the
                                     disposition of:  none
                              (iv)   shared power to dispose or to direct
                                     disposition of:  1,065,600


Item 5          Ownership of Five Percent or Less of a Class:

                      Not Applicable

Item 6          Ownership of More than Five Percent on Behalf of Another Person:

                      The shares reported herein have been acquired on behalf of
                      discretionary clients of WAM, including Acorn. Persons
                      other than  WAM and WAM GP are entitled to receive all
                      dividends from, and proceeds from the sale of, those
                      shares. Acorn is the only such person known to be entitled
                      to all dividends from, and all proceeds from the sale of,
                      shares reported herein to the extent of more than 5% of
                      the class.

Item 7          Identification and Classification of the Subsidiary Which
                Acquired the Security Being Reported on by the Parent Holding
                Company:

                      Not Applicable

Item 8          Identification and Classification of Members of the Group:

                      Not Applicable

Item 9          Notice of Dissolution of Group:

                      Not Applicable

                               Page 6 of 10 pages



Item 10   Certification:

               By signing below I certify that, to the best of my knowledge and
          belief, the securities referred to above were acquired and are held in
          the ordinary course of business and were not acquired and are not held
          for the purpose of or with the effect of changing or influencing the
          control of the issuer of the securities and were not acquired and are
          not held in connection with or as a participant in any transaction
          having that purpose or effect.

                               Page 7 of 10 Pages



                                    Signature
                                    ---------

         After reasonable inquiry and to the best of my knowledge and belief, I
certify that the information set forth in this statement is true, complete and
correct.

Date:  February 12, 2002


               The undersigned corporation, on the date above written, agrees
               and consents to the joint filing on its behalf of this Schedule
               13G in connection with its beneficial ownership of the security
               reported herein.

                                  WAM Acquisition GP, Inc.
                                      for itself and as general partner of
                                      LIBERTY WANGER ASSET MANAGEMENT, L.P.



                                  By:  /s/ Bruce H. Lauer
                                       -----------------------------------------
                                           Bruce H. Lauer

                                           Senior Vice President and Secretary

               The undersigned corporation, on the date above written, agrees
               and consents to the joint filing on its behalf of this Schedule
               13G in connection with its beneficial ownership of the security
               reported herein.

                                  LIBERTY ACORN TRUST



                                  By:  /s/ Bruce H. Lauer
                                       -----------------------------------------
                                           Bruce H. Lauer
                                           Vice President, Treasurer and
                                           Secretary


                               Page 8 of 10 Pages



                                  Exhibit Index
                                  -------------

Exhibit 1      Joint Filing Agreement dated as of February 12, 2002 by and among
               Liberty Wanger Asset Management, L.P., WAM Acquisition GP, Inc.
               and Liberty Acorn Trust



                               Page 9 of 10 Pages



                                                                       EXHIBIT 1

                             JOINT FILING AGREEMENT

         The undersigned hereby agree to the joint filing of the Schedule 13G to
which this Agreement is attached.

             Dated:  February 12, 2002


                                  WAM Acquisition GP, Inc.
                                      for itself and as general partner of
                                      LIBERTY WANGER ASSET MANAGEMENT, L.P.



                                  By:  /s/ Bruce H. Lauer
                                       -----------------------------------------
                                           Bruce H. Lauer
                                           Senior Vice President and Secretary

                                  LIBERTY ACORN TRUST



                                  By:  /s/ Bruce H. Lauer
                                       -----------------------------------------
                                           Bruce H. Lauer
                                           Vice President, Treasurer and
                                           Secretary

                              Page 10 of 10 Pages