    <SEC-DOCUMENT>0000352825-21-000054-index.html : 20210816
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    <ACCEPTANCE-DATETIME>20210816080353
    ACCESSION NUMBER:		0000352825-21-000054
    CONFORMED SUBMISSION TYPE:	8-K
    PUBLIC DOCUMENT COUNT:		15
    CONFORMED PERIOD OF REPORT:	20210816
    ITEM INFORMATION:		Entry into a Material Definitive Agreement
    ITEM INFORMATION:		Creation of a Direct Financial Obligation or an Obligation under an Off-Balance Sheet Arrangement of a Registrant
    ITEM INFORMATION:		Regulation FD Disclosure
    ITEM INFORMATION:		Financial Statements and Exhibits
    FILED AS OF DATE:		20210816
    DATE AS OF CHANGE:		20210816

    FILER:

    	COMPANY DATA:
    		COMPANY CONFORMED NAME:			FOSTER L B CO
    		CENTRAL INDEX KEY:			0000352825
    		STANDARD INDUSTRIAL CLASSIFICATION:	WHOLESALE-METALS SERVICE CENTERS & OFFICES [5051]
    		IRS NUMBER:				251324733
    		STATE OF INCORPORATION:			PA
    		FISCAL YEAR END:			1231

    	FILING VALUES:
    		FORM TYPE:		8-K
    		SEC ACT:		1934 Act
    		SEC FILE NUMBER:	000-10436
    		FILM NUMBER:		211174614

    	BUSINESS ADDRESS:
    		STREET 1:		415 HOLIDAY DR
    		CITY:			PITTSBURGH
    		STATE:			PA
    		ZIP:			15220
    		BUSINESS PHONE:		4129283431

    	MAIL ADDRESS:
    		STREET 1:		415 HOLIDAY DR
    		CITY:			PITTSBURGH
    		STATE:			PA
    		ZIP:			15220
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    <FILENAME>fstr-20210816.htm
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    <TEXT>
    Document 1 - file: fstr-20210816.htm

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    <FILENAME>ex-10182021creditfacility.htm
    <DESCRIPTION>EX-10.1
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    Document 2 - file: ex-10182021creditfacility.htm

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    <FILENAME>ex-99182021creditfacility.htm
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    <FILENAME>fstr-20210816.xsd
    <DESCRIPTION>XBRL TAXONOMY EXTENSION SCHEMA DOCUMENT
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    <FILENAME>fstr-20210816_pre.xml
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    <TEXT>
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