US3778947A

US3778947A - Fire-rated grid member with controlled expansion means

Info

Publication number: US3778947A
Application number: US00195237A
Authority: US
Inventors: G Sauer
Original assignee: Flangeklamp Corp
Current assignee: Donn Inc; Flangeklamp Corp
Priority date: 1971-11-03
Filing date: 1971-11-03
Publication date: 1973-12-18
Anticipated expiration: 1990-12-18

Abstract

A fire-rated grid member having a plurality of cut-out sections in the web thereof defining connecting portions for controlling deformation of the grid member to predetermined areas upon expansion. The bead surmounting the web is deformed to create a weakened portion deformable upon grid member expansion. The opposite ends of the grid member are provided with a slot and tongue arrangement for splicing adjacent grid members together.

Description

Sauer FIRE-RATED GRID MEMBER WITH CONTROLLED EXPANSION MEANS [75] Inventor: Gale E. Sauer, Williamsville, NY.

[73] Assignee: Flangeklamp Corporation, Buffalo,

22 Filed: Nov. 3, 1971 211 Appl. No.: 195,237

[52] U.S. C1 52/232, 52/484, 52/573, 52/664, 52/D1G. 5, 287/189.36 A [51] Int. Cl. E04c 2/52, E04c 2/42, 1504b 5/52 [58} Field of Search 52/232, 664, 665, 52/667, 573, 484, 475, DIG. 5; 287/189.36 A

[56] References Cited UNITED STATES PATENTS 3,388,519 6/1968 Downing 52/573 3,589,089 6/1971 Kedel 52/232 3,305,256 2/1967 Znamirowski 52/664 3,565,474 2/1971 Stumbo et al 52/667 3,189,139 6/1965 Znamirowski et a1. 52/232 3,093,221 6/1963 Purdy 52/665 3,457,688 7/1969 Znamirowski 52/DlG. 5 3,606,417 Rousey 52/667 Dec. 18, 1973 3,239,035 3/1966 Znamirowski 52/667 3,175,655 3/1965 Brown et a1. 52/667 3,390,503 7/1968 Emerith et a1 52/484 3,397,501 8/1968 Jahn 52/573 3,677,589 7/1972 Roles 52/665 3,675,957 7/1972 Lockhter et a1. 52/667 FOREIGN PATENTS OR APPLICATIONS 848,115 8/1970 Canada SZ/DIG. 5

Primary Examiner-Frank L. Abbott Assistant Examiner-Leslie A. Braun Attorney-Conrad Christel et a1.

[5 7] ABSTRACT A fire-rated grid member having a plurality of cut-out sections in the web thereof defining connecting portions for controlling deformation of the grid member to predetermined areas upon expansion. The bead surmounting the web is deformed to create a weakened portion deformable upon grid member expansion. The opposite ends of the grid member are provided with a slot and tongue arrangement for splicing adjacent grid members together.

14C1aims, 12 Drawing Figures F'MENIEDUEE 18 ms 3.778.947

SHE 1 BF 3 INVENTOR.

Gale E Sauer @M ww ATTORNEYS.

PMENTEU DEC 1 8 I975 SHEET 2 OF 3 M fiww Q w NE INVENTOR.

Gale E Sauer lp s a vv l I l l I I l ILIIIIIIIII -I I WI I LUP llllllll'llll PATENTEUOEC 18 m5 SHEET 30F 3 INVENTOR.

Gale E. Sauer ATTORNEYS.

FIRE-RATED GRID MEMBER WITH CONTROLLED EXPANSION MEANS BACKGROUND OF THE INVENTION This invention relates generally to fire-resistant tile supporting grid systems and the like and, more particularly, to tile supporting members capable of absorbing expansion without substantial buckling of the ceiling tiles during abnormally elevated temperatures, thereby preserving the integrity of the ceiling as a barrier under such conditions.

The present invention is particularly adapted for use in ceiling tile supporting grid systems of the type comprising a plurality of parallel spaced main grid members and cross grid members extending transversely between the main grid members and having end portions interlocking therewith. These interconnected grid members generally are suspended from a conventional ceiling or an overhead support structure.

One of the critical problems encountered in these ceiling tile supporting grid structures is to maintain the integrity thereof under abnormally elevated temperatures, such as accompany a fire. Under these high temperature conditions, the metallic grid members, which generally are fixed at opposite ends, expand and buckle whereby the supported ceiling tiles are displaced and sometimes tilted to such an extent that they drop through the openings formed by the intersecting grid members. As a result, the effectiveness of the suspended ceiling as a barrier is destroyed and the overhead ceiling and related support structure is exposed to the tire whereby the latter can spread more easily and rapidly through the entire structure.

SUMMARY OF THE INVENTION Accordingly, a primary object of this invention is to provide an improved fire-rated grid member which accommodates expansion resulting from extreme heat and controls deformation of the grid member upon expansion to predetermined areas to preserve the integrity of the ceiling under elevated ambient temperature conditions.

Another object of the present invention is to provide an improved fire-rated grid member having especially configurated cut-out sections in the web thereof providing weakened connecting portions adapted to influence deformation of the grid member at predetermined areas.

A further object of this invention is to provide the foregoing grid member with a deformed bead surmounting the web and having weakened portions to control deflection thereof upon expansion.

Still another object of the present invention is to provide splice means at the opposite ends of the foregoing grid member for interlocking adjacent grid members in an abutting end-to-end relation and thereby extending the effective length of the main grid support member.

The foregoing and other objects, advantages and characterizing features of the present invention will become clearly apparent from the ensuing detailed description of an illustrative embodiment thereof, taken together with the accompanying drawings wherein like reference characters denote like parts throughout the various views.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a fragmentary, perspective view of intersecting grid members incorporating a fire-rated main grid member of this invention;

FIG. 2 is a fragmentary, perspective view of two main grid members, shown in an interconnected, abutting, end-to-end relation;

FIG. 3 is a fragmentary, perspective view of one end of a main grid member constructed in accordance with this invention;

FIG. 4 is a fragmentary, perspective view of the other end of the main grid member shown in FIG. 3;

FIG. 5 is a side elevational view of a fire-rated main grid member of this invention, being broken away for ease of illustration;

FIG. 6 is a top plan view, of the fire-rated grid member shown in FIG. 5, being broken away for ease of illustration;

FIG. 7 is a vertical, cross-sectional view, on an enlarged scale, taken about on line 77 of FIG. 5;

FIG. 8 is a fragmentary, side elevational view, on an enlarged scale, showing the cut-out sections in the grid member web and the deformation of the grid member bead for controlling expansion of the grid member;

FIG. 9 is a vertical, cross-sectional view, on an enlarged scale, taken about on line 9-9 of FIG. 5;

FIG. 10 is a fragmentary, horizontal sectional-view, on an enlarged scale, taken about on line 10-10 of FIG. 2;

FIG. 11 is a fragmentary, side elevational view, on an enlarged scale, illustrating the actual deformation of the grid member of this invention upon the application of heat; and

FIG. 12 is a fragmentary top plan view of the deformed grid member of FIG. 11.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT Referring now in detail to the illustrative embodiment depicted in the accompanying drawings, there is shown in FIG. 1 a ceiling tile supporting grid system incorporating a main T support member, generally designated l0, detachably connected to a pair of cross T support members, generally designated 12. Main T member 10 can be conveniently fabricated from a single piece of any suitable material, preferably an inexpensive, lightweight metal such as soft steel for example, and is formed to provide a generally vertical web portion 14 upstanding from laterally projecting, tile supporting flanges 16 on opposite sides thereof and surmounted by a generally boxshaped, longitudinally extending, reinforcing member or bead 18.

Web portion 14 is provided at spaced intervals with rectangular, normally vertical slots 20 (FIG. 5) for the reception of the end portions of cross T members 12. Slots 20 are generally H-shaped, being formed with downwardly and upwardly projecting

center tabs

22 and 24, respectively, at the top and bottom of the slot which serve as partitions or separators between the two cross T members 12 in the assembled joint. While slots 20 are shown as being I- I-shaped in the illustrative embodiment, it should be understood that slots 20 may take any shape compatible with the end portions of cross T support members 12 so that such end portions will be snugly received in the associated slots.

Cross T members 12 can be similarly fabricated from a single piece of any suitable material, such as soft steel by way of example, and formed to provide a normally vertical web portion 26 upstanding from laterally projecting, tile supporting flanges 28 and surmounted by a generally box-shaped, longitudinally extending, reinforcing member or bead 30. lt should be appreciated that reinforcing members or

beads

18 and 30 can take various shapes in cross-section, such as a rounded or bulbous shape, as desired.

Cross T support members are provided at their opposite ends with tongue portions generally designated 32, extending axially outwardly from said opposite ends of said cross T member 12 and slightly offset from web portion 26 in opposite lateral directions. Any suitable locking means can be provided on tongue portions 32 for interlocking engagement behind web portion, 14 of main T support member 10.-As shown in FIG. 1, two cross T support members 12 extend perpendicularly to main T support member on opposite sides thereof with their respective tongue portions 32 inserted into slot for passage therethrough and for interlocking engagement with web portion 14. It will be understood that main T support member 10 includes throughout its length at predetermined spaced intervals a plurality of slots 20 with corresponding pairs of cross T members insertable therethrough in the assembled relation. Various interlocking cross T tongue arrangements can be utilized, as will be readily understood by those skilled in the art. For additional details of the illustrated arrangement, reference is made to pending application Ser. No. 178,893, filed Sept. 9, 1971 and assigned to the same assignee as the present application.

In accordance with the present invention, main T support member 10 is formed in such a manner as to confine expansion thereof .under abnormally elevated temperatures to predetermined areas of such member ,10 in an effort to preserve the integrity of the suspended ceiling. To this end, a series of cut-out sections, generally designated 36, are provided in web portion 14 of main T support member 10. As seen in'FIG. 8, each cut-out section 36 comprises a horizontally elongated slot 38 of trapezoidal shape in outline defined by an upper, horizontally extending wall 40 generally parallel to the longitudinal axis of web portion 14, a lower horizontally extending wall 42 in substantial parallelism with upper wall 40 and a pair of side walls 44 joining lower wall 42 to upper wall 401and inclined upwardly ina converging relation. A generally V-shaped notch 46 is cut into web portion 14 extending downwardly from each slot 38 intermediate the opposite ends thereof and terminating in an apex 48 disposed slightly above flanges 16. While three such slots 38 are shown in the illustrative embodiment, it should be understood that more or less than three slots can be utilized in the present invention.

A series of elongated, vertically extending slots 50 are cut into web portion 14, the slots 50 being disposed adjacent opposite ends of horizontally extending slots 38 and spaced therefrom at the narrowest dimension therebetween approximately one-sixteenth of an inch.

Slots 50 terminate at their lower ends in V-shaped portions 52 having apices 54 disposed in substantially the same horizontal plane as apices 48 of V-shaped notches 46. It will be seen that a plurality of narrow, connecting portions 56 of web portion 14 (FIG. 8) remain between

slots

38 and 50 and between

apices

48, 54 and flanges 16 and serve to influence or concentrate deformation at these weakened connecting portions 56 upon expansion or elongation of mairt'l' support member 10. While the removal of material to provide

slots

38 and 50 somewhat weakens web portion 14, they are so arranged and proportioned to only negligibly weaken web portion 14 whereby main 1 support member 10 possesses the requisite rigidity and strength to withstand the stresses imparted thereto under normal conditions of handling, installation and usage. A plurality of ribs 58, constituting remaining parts of web portion 14 after

slots

38 and 50 are cut-out, disposed below slots 38 between V-

shaped notches

46 and 52 and joined by web portions 56, aid in reinforcing web portion 14 under normal conditions.

In order to provide for the expansion of the upper portion of main T support member 10, a portion of web 14 is cut out to form an opening 60 which extends into the lower edge of bead 18. Also, head 18 is deformed above opening 60 to form an embossment 62 in one side of bead 18. In the fabrication of main T support member 10, as by a roll forming operation for example, head 18 is initially formed into a box-shaped configuration (FIG. 9) comprising a top wall 64, a bottom wall 66, and a pair of

side walls

68 and 70. In forming embossment 62, a portion of side wall '70 is pressed against side wall 48, as shown in FIGS. 7 and 8, to form a wall portion 72 of double thickness having opposite ends which serve as longitudinally spaced, vertically extending

fold lines

74 and 76 to influence relative movement between the portions of head 18 adjacent embossment 62 upon expansion of main T support member 10. Opening 60 and embossment 62 are formed by a single punching operation, together with an opening 61 through top wall 64, the opening 61 being of the same length, and depth into bead 18, as opening 60. As a result, side wall of bead I8 is deformed slightly inwardly at spaced points toward

fold lines

74 and 76 defining curved surfaces 78 and 80 (FIG. 6).

While the deformation of head 18 to form embossment 62 somewhat weakens bead 18 to permit deformation thereof during thermal expansion, the double thickness wall portion 72 possesses the requisite strength and rigidity to provide the necessary resistance against bending under normal conditions of handling, installation and usage. Embossment 62 serves as a connecting link between the box-shaped portions of head 18 to provide a continuous bead 18 throughout the length of support member 10 to provide a strong and rigid compression member under normal conditions.

Means are provided for releasably securing a pair of main T support members 10 in an abutting, end-to-end relation to form a splice therebetween. Such means comprise a tongue 84 extending axially outwardly from one end of main T support member 10 and formed integral therewith as shown in FIG. 4. Tongue 84 is slightly offset from web portion 14 (FIG. 10) but lies in a plane parallel to the plane of web portion 14. A tab 86 extends laterally inwardly from the end of tongue 84 at an angle of approximately 45 to the plane of tongue 84 and is joined thereto along a vertical fold line 88. Tab 86 is trapezoidal in configuration having a progressively decreasing width from tongue 84 to the free end of tab 86 for facilitating insertion of tab 86 into its associated opening 100. A finger 90 is struck out from web portion 14 adjacent the end thereof, in spaced relation to tongue 84, and is bent laterally outwardly for a purpose hereinafter explained.

The other end of main T support member 10 is provided with an extension 92 (FIG. 3) projecting axially outwardly from'said other end and slightly offset in the opposite direction from the plane of web portion 14. Extension 92 is provided with a forked end having two axially extending

projections

94 and 96 defining an abutment shoulder 98 therebetween adapted to engage with finger 90 of the adjacent main T support member 10. An axially elongated opening 100 is provide in web portion 14 of main T support member provided adjacent the end having extension 92, in spaced relation thereto, for receiving tab 86 of the adjacent main T support member in assembled relation.

In assembling a pair of main T support members 10 in an end-to-end relation, the end edges of web por tions 14, flanges l6, and beads 18 of adjacent main T support members 10 which are coplanar, are brought into abutting relation with tongue 84 overlying extension 92. In these relative positions of tongue 84 and extension 92, tab 86 is in registry with opening 100 and can be inserted therein. Finger 90 of one member 10 engages abutment shoulder 98 of the other member 10 preventing further axial inward movement of tongue 84 relative to extension 92. The upper and lower edges of finger 90 fit snugly between

projections

94 and 96 to prevent relative vertical movement therebetween. Tab 86 can then be reversely bent about fold line 88 to extend along web portion 14 of the adjoining main T support member 10 in order to firmly secure members 10 together, as shown in FIGS. 2 and 10. In this secured position, tab 86 is oriented generally parallel to tongue 84 and spaced therefrom a distance approximating the thickness of web portion 14 of the adjacent main T support member 10 for sandwiching the latter therebetween.

In use, with the ends of main T support member fixed or restricted with respect to movement in axial directions and upon the application of heat to the ceiling structure, such as might be caused by fire, main T support'member l0 seeks to expand and elongate and will buckle unless such expansion can be absorbed by member 10. In the present invention, any such expansion or elongation is accommodated, and controlled deformation of member 10 is achieved as follows:

The compressive reaction forces acting axially against the opposite ends of main T support member 10 caused by expansion thereof are transmitted through the body of member 10 including the narrow, connecting portions 56. It should be realized that the lower surfaces of flanges 16 are directly exposed to the heat and these flanges tend to initially expand to a greater degree than the web portion 14 thereabove which is somewhat insulated by flanges 16 and the ceiling tiles. The narrow, connecting portions 56 of web portion 14 offer less resistance to deformation than any other portion of web 14 and influences the deflection of flanges 16 to occur adjacent these connecting portions 56. Accordingly, flanges 16 will bend downwardly carrying ribs 58 therewith, the latter deflecting about connecting portions 56. At full expansion of main T support member 10, ribs 58 shear at these connecting portions 56 and, together with those portions of flanges 16 connected to ribs 58, assume a V-shaped contour, as shown in FIG. ll. FIGS. 11 and 12 illustrate the actual deformation imparted to a fire-rated grid member of this invention which was exposed to fire. While FIG. 11 shows maximum deformation adjacent the right hand cut-out section 36, partial deformation adjacent the central cut-out section 36, and substantially no deformation adjacent the left hand cut-out section 36, it

should be understood that any one or all of these sections can experience this deformation depending on the direction of movement of the fire and the duration of the exposure of these areas to the fire.

As the upper portion of main T support member 10 expands, bending of head 18 occurs about the spaced

fold lines

74 and 76 to cause the spaced deformed end portions of bead 18 at opposite sides of embossment 62 to by-pass each other as shown in FIG. 12.

Curved surfaces

78 and 80 on bead l8 facilitate the bending of wall portion 72 of bead 18 into a generally S-shaped bend, as shown in FIG. 12. The relatively narrow portion of web 14 disposed between slot 38 and opening 60 is bent in a similar S-shaped pattern along with bead 18.

The main T support member 10 of this invention satisfactorily passed the two-hour A S T M Fire Endurance Test conducted in accordance with the Standard Methods of Fire Tests on Floor and Ceiling Constructions. In this test, a section of a ceiling construction, including main and cross T support members and ceiling tiles supported thereon, was exposed to fire at temperatures ranging from l0O0 1900F. The main T support member 10 of the present invention readily met the fire-rated requirements consistent with the tire endurance time of two hours. Flanges 16 of main T support member 10 did not deform sufficiently, even at its maximum deflection during this two hour period, to disrupt the continuity of the ceiling system, thus maintaining the overall integrity of the ceiling structure. Moreover, the specimen tested serves as a tire retarding and heat transmission barrier to prevent the fire from spreading to other superstructure. The specimen not only effectively withstood the 2-hour fire-rated test, but remained exposed to the fire for yet another hour. While more pronounced deformation of the support members took place during this third hour, flanges 16 were still capable of supporting the ceiling tiles so that none were displaced or dislodged to the extent that they fell through the openings defined by the intersecting tile supporting members. FIGS. 11 and 12 depict actual deformation of the main T support member of this invention after having been exposed to fire for three hours at temperatures ranging from 1000-1900F.

From the foregoing, it is apparent that the objects of the present invention have been fully accomplished. As a result of this invention, an improved fire-rated grid member is provided for maintaining the integrity of a ceiling structure upon the application of heat thereto and preserving the fire retarding qualities thereof to prevent the escape of heat therethrough to the superstructure. By the provision of a plurality of specially configurated cut-out sections in the web portion of the grid member, deflection of the flanges can be influenced in predetermined directions to prevent buckling of the grid system upon expansion. These cut-out sections tend to concentrate the heat to certain predetermined areas to achieve the above action and also interrupt the transmission of heat through the web portion. Also, by providing an embossment in the bead of the grid member, deflection of the upper portion of the grid member is effectively controlled to absorb expansion. At the same time, the support member possesses the strength and stability required in use for this pur pose.

been disclosed in detail, it is to be understood that this has been done by way of illustration only.

1 claim: 7

LA grid member for supporting grid systems and the like comprising: a support member having a web and flanges extending laterally outwardly on opposite sides of said web, said web being formed with at least one generally horizontally extending cut-out section having a portion terminating in close proximity to said flanges and at least a pair of vertically extending slots adjacent opposite sides of said cut-out section in closely spaced relation thereto and terminating at ends in close proximity to said flanges, relatively narrow connecting portions of said web remaining between said slot ends and said flanges and between said cut-out section and said slots for strengthening said web under normal conditions of usage and severable upon expansion for permitting controlled deformation of said flanges and certain portions of said web.

2. A grid member as defined in claim 1 wherein said cut-out section comprises an elongated slot extending generally parallel to the longitudinal axis of said web and a V-shaped notch extending from said slot intermediate the opposite ends thereof and terminating in an apex in close proximity to said flanges.

' 4. A grid member as defined in claim 1 including a bead surmounting said web, said bead having a deformed portion forming a continuation thereof to provide a pair of longitudinally spaced weakened portions for controlling deflection of said bead upon expansion of said support member.

5. A grid member as defined in claim 4 wherein said web is provided with an opening below said deformed portion of said bead and extending partially thereinto.

6. A grid member as defined in claim 4-wherein said deformed portion has a double wall thickness of lesser width than the major portion of said bead.

7. A grid member as defined in claim 1 wherein said cut-out section comprises an elongated slot extending generally parallel to the longitudinal axis of said web and a V-shaped notch extending from said slot intermediate the opposite ends thereof and terminating in an apex in close proximity to said flanges, said adjacent slots extending in a direction normal to the longitudinal axis of said web and having V-shaped portions terminating in apices in close proximity to said flanges, a bead surmounting said web and having a deformed por tion controlling deflection of said bead upon expansion of said support member, and said web being provided with an opening below said deformed portion of said bead for controlling deflection of said web upon expansion.

8. A grid member as defined in claim 1 together with means on opposite ends of said web for interlocking engagement with adjacent grid members.

9. A grid member as defined in claim 8 wherein said interlocking means comprises a tab extending laterally outwardly at an angle of approximately 45 from one end of said grid member web and insertable into an adjacent grid member slot.

10. A grid member as defined in claim 9 wherein said interlocking means comprises a slot in said web adjacent the other end thereof for receiving an adjacent grid member tab.

11. A grid member as defined in claim 10 including an extension projecting longitudinally outwardly from said other end of said grid member web in a plane laterally offset therefrom and parallel thereto, said extension having an abutment shoulder engageable with an adjacent grid member stop.

12. A grid member assembly comprising: at least two coaxially aligned grid members each having a web, connecting means on adjacent ends of said webs for splicing said grid members in an abutting end-to-end relation, said connecting means comprising a tongue extending longitudinally outwardly from the abutting end of one web in a plane laterally offset'from said one web and parallel thereto, a tab projecting laterally outwardly from the end of said tongue remote from said web at an angle of approximately 45", said web having stop means projecting outwardly therefrom and disposed longitudinally inwardly from the abutting end thereof, a slot provided in said other web adjacent the abutting end thereof for receiving said tab, an extension projecting longitudinally outwardly from the abutting end of said other web in a plane laterally offset from said other web and parallel thereto, said extension having means adjacent the free end thereof engageable with said stop means in the assembled relation of said grid members.

13. A grid member assembly as defined in claim 12 wherein said stop means comprises a laterally projecting finger struck out of said other web.

14. A grid member assembly as defined in claim 13 wherein said extension is provided with a pair of axially extending, vertically spaced projections defining an abutment shoulder therebetween engageable with said finger in the assembled relation of said grid members whereby said projections prevent vertical displacement of said grid members relative to each other.

I 5 i i

Claims

1. A grid member for supporting grid systems and the like comprising: a support member having a web and flanges extending laterally outwardly on opposite sides of said web, said web being formed with at least one generally horizontally extending cut-out section having a portion terminating in close proximity to said flanges and at least a pair of vertically extending slots adjacent opposite sides of said cut-out section in closely spaced relation thereto and terminating at ends in close proximity to said flanges, relatively narrow connecting portions of said web remaining between said slot ends and said flanges and between said cut-out section and said slots for strengthening said web under normal conditions of usage and severable upon expansion for permitting controlled deformation of said flanges and certain portions of said web.

3. A grid member as defined in claim 1 wherein said adjacent slots extend in a direction normal to the longitudinal axis of said web and have V-shaped portions each terminating in an apex in close proximity to said flanges.

4. A grid member as defined in claim 1 including a bead surmounting said web, said bead having a deformed portion forming a continuation thereof to provide a pair of longitudinally spaced weakened portions for controlling deflection of said bead upon expansion of said support member.

6. A grid member as defined in claim 4 wherein said deformed portion has a double wall thickness of lesser width than the major Portion of said bead.

7. A grid member as defined in claim 1 wherein said cut-out section comprises an elongated slot extending generally parallel to the longitudinal axis of said web and a V-shaped notch extending from said slot intermediate the opposite ends thereof and terminating in an apex in close proximity to said flanges, said adjacent slots extending in a direction normal to the longitudinal axis of said web and having V-shaped portions terminating in apices in close proximity to said flanges, a bead surmounting said web and having a deformed portion controlling deflection of said bead upon expansion of said support member, and said web being provided with an opening below said deformed portion of said bead for controlling deflection of said web upon expansion.

9. A grid member as defined in claim 8 wherein said interlocking means comprises a tab extending laterally outwardly at an angle of approximately 45* from one end of said grid member web and insertable into an adjacent grid member slot.

12. A grid member assembly comprising: at least two coaxially aligned grid members each having a web, connecting means on adjacent ends of said webs for splicing said grid members in an abutting end-to-end relation, said connecting means comprising a tongue extending longitudinally outwardly from the abutting end of one web in a plane laterally offset from said one web and parallel thereto, a tab projecting laterally outwardly from the end of said tongue remote from said web at an angle of approximately 45*, said web having stop means projecting outwardly therefrom and disposed longitudinally inwardly from the abutting end thereof, a slot provided in said other web adjacent the abutting end thereof for receiving said tab, an extension projecting longitudinally outwardly from the abutting end of said other web in a plane laterally offset from said other web and parallel thereto, said extension having means adjacent the free end thereof engageable with said stop means in the assembled relation of said grid members.