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UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 SCHEDULE 13G Under the Securities Exchange Act of 1934 (Amendment No. _________ )* Gibraltar Steel Corporation - ------------------------------------------------------------------------------- (Name of Issuer) Common Stock - ------------------------------------------------------------------------------- (Title of Class of Securities) 37476F103 - ------------------------------------------------------------------------------- (CUSIP Number) *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). SEC 1745(2/92) Page 1 of 7 pages - ----------------------- --------------------- CUSIP NO. 37476F103 13G PAGE 2 OF 7 PAGES - ----------------------- --------------------- - ------------------------------------------------------------------------------ NAME OF REPORTING PERSON 1 S.S. or I.R.S. IDENTIFICATION NO. OF ABOVE PERSON 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 6 796,000 OWNED BY ----------------------------------------------------------- EACH SOLE DISPOSITIVE POWER 7 REPORTING None PERSON ----------------------------------------------------------- SHARED DISPOSITIVE POWER WITH 8 796,000 - ------------------------------------------------------------------------------ AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON 9 796,000 - ------------------------------------------------------------------------------ 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 6.42% - ------------------------------------------------------------------------------ TYPE OF REPORTING PERSON* 12 IA - ------------------------------------------------------------------------------ *SEE INSTRUCTIONS BEFORE FILLING OUT! - ----------------------- --------------------- CUSIP NO. 37476F103 13G PAGE 3 OF 7 PAGES - ----------------------- --------------------- - ------------------------------------------------------------------------------ NAME OF REPORTING PERSON 1 S.S. or I.R.S. IDENTIFICATION NO. OF ABOVE PERSON Wanger Asset Management, Ltd. - ------------------------------------------------------------------------------ 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 6 796,000 OWNED BY ----------------------------------------------------------- EACH SOLE DISPOSITIVE POWER 7 REPORTING None PERSON ----------------------------------------------------------- SHARED DISPOSITIVE POWER WITH 8 796,000 - ------------------------------------------------------------------------------ AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON 9 796,000 - ------------------------------------------------------------------------------ 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 6.42% - ------------------------------------------------------------------------------ TYPE OF REPORTING PERSON* 12 CO - ------------------------------------------------------------------------------ *SEE INSTRUCTIONS BEFORE FILLING OUT! 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: Wanger Asset Management, L.P. ("WAM") Wanger Asset Management Ltd., the general partner of WAM ("WAM LTD.") Item 2(b) Address of Principal Business Office: WAM and WAM LTD. are located at: 227 West Monroe Street, Suite 3000 Chicago, Illinois 60606 Item 2(c) Citizenship: WAM is a Delaware limited partnership. WAM LTD. is a Delaware corporation. Item 2(d) Title of Class of Securities: Common Stock Item 2(e) CUSIP Number: 37476F103 Item 3 Type of Person: (e) WAM is an Investment Adviser registered under section 203 of the Investment Advisers Act of 1940; WAM LTD. is the General Partner of the Investment Adviser. Page 4 of 7 pages Item 4 Ownership (at December 31, 1997): -- (a) Amount owned "beneficially" within the meaning of rule 13d-3: 796,000 shares (b) Percent of class: 6.42% (based on 12,401,869 shares outstanding on September 30, 1997) (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: 796,000 (iii) sole power to dispose or to direct the disposition of: none (iv) shared power to dispose or to direct disposition of: 796,000 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. Persons other than WAM and WAM LTD. are entitled to receive all dividends from, and proceeds from the sale of, those shares. 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 5 of 7 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 in the ordinary course of business and were not acquired for the purpose of and do not have the effect of changing or influencing the control of the issuer of such securities and were not acquired in connection with or as a participant in any transaction having such purpose or effect. Page 6 of 7 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 5, 1998 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. WANGER ASSET MANAGEMENT, LTD. for itself and as general partner of WANGER ASSET MANAGEMENT, L.P. By: /s/ Bruce H. Lauer --------------------------------- Bruce H. Lauer Vice President Page 7 of 7 pages