US3457688A

US3457688A - Suspended ceiling

Info

Publication number: US3457688A
Application number: US452713A
Authority: US
Inventors: Henry Znamirowski; David J Roles
Original assignee: EASTERN PROD CORP
Current assignee: Eastern Products Corp; EASTERN PROD CORP
Priority date: 1965-05-03
Filing date: 1965-05-03
Publication date: 1969-07-29
Anticipated expiration: 1986-07-29

Description

July 29, 1969 H. ZNAMIROWSKI E AL 3,457,683

SUSPENDED CEILING 5 Sheets-Sheet 1 Filed May 5. 1965 y 9, 1969 H. ZNAMIROWSKI ET AL 3,457,688

SUSPENDED CEILING 5 Sheets-Sheet 2 Filed May 5, 1965 July 29, 1969 H. ZNAMIROWSKI E 3,457,558

SUSPENDED CEILING Filed May 5, 1965 5 Sheets-Sheet 5 FIGIO.

FIGS.

FIGQ.

y 1969 H. ZNAMIROWSKI ET AL 3,457,688

SUSPENDED CEILING Filed May 3, 1965 5 Sheets-Sheet 4 34 35 a 39 a s 35 34 July 29, 1969 H. znmmowsm ET 3,457,633

V SUSPENDED CEILING Filed May a. 1965 5 Sheets-sheaf 5 25 I2 I2 25 O 6 f 27 [9 g :I /9 2 7 1L6 20 up 26 I, as 26 as; 23 2s 2 20 Q l3 I 1 9 /a 9 United States Patent US. Cl. 52-573 9 Claims ABSTRACT OF THE DISCLOSURE A beam construction for use in a fire retarding structural ceiling system in which the beam ends are normally abutting but formed so as to collapse under application of excessive compressive loads with means for holding the abutting ends together While permitting the collapsing movement.

The present invention relates to ceiling constructions and more particularly to suspended ceiling constructions in which a metallic grid system is suspended from primary ceiling members and used to support acoustical tiles or other ceiling panels.

In recent years it has been common in the construction of new buildings and in the renovation of old buildings to employ suspended ceilings in which acoustical tiles or other types of panels are supported by flanged beams, usually made of steel or aluminum. In most such systems, the flanged beams are arranged in a rectangular grid system with long parallel beams, called main runners, being joined at suitable intervals by transverse parallel beams called cross Ts. In some systems the bottom flange 0f the metal beams form a part of the visible ceiling surface, while in others the metal beams are not visible after the ceiling panels are installed. An example of the former type in the ceiling system shown in US. Patent 2,963,130 to Rosenbaum which issued Dec. 9, 1960 While an example of the latter type is the ceiling system shown in U.S. Patent 2,866,233 to Lydard which issued Dec. 30, 1958.

When the metal beams of a ceiling suspension system are subjected to the high temperatures which accompany fires, the beams tends to twist and buckle and to break and drop the ceiling panels onto the floor beneath. Such buckling of the beams results from the restraint imposed on expansion of the individual beams by the grid construction and the contact thereof with the walls or other side members of the enclosure. Thus, even though ceiling panels which are highly resistant to fire conditions have been developed, such of the fire retarding advantage of such panels is lost when the panel suspension system buckles and causes some or all of the panels to break and fall.

Some grid constructions which will accommodate expansion forces resulting from high temperatures have been proposed. Two particularly desirable examples of such constructions are those described and claimed in the copending US. patent applications of Henry Znamirowski, Ser. Nos. 147,337 and 205,279 filed Oct. 24, 1961 and June 26, 1962, and now US. Patent No. 3,189,138 and US. Patent No. 3,189,139 respectively. The ceiling construction of said copending applications are highly eflicient and relatively simple in design. Nevertheless, for some classes of service an even simpler design which will be more economical to manufacture and install is desirable and the principal object of the present invention has been to provide such a simpler and more economical ceiling construction which will afford satisfactory fire retarding characteristics.

Another object of the invention has been to provide a novel and improved ceiling construction which will accommodate fire temperatures for prolonged periods of "ice time without buckling in such a way as to break or drop the ceiling panels.

A further object of the invention has been to provide a novel and improved beam which is especially adapted for use in fire retarding ceiling constructions.

A further object of the invention is to provide a novel splice for joining the ends of two beams.

Still another object of this invention is to provide an improved cross T which can easily be attached to a main beam or runner and which is especially adapted to accommodate expansion stresses arising from fire conditions.

Other and further objects, features and advantages of the invention will appear more fully from the following description taken in connection with the appended drawings in which:

FIG. 1 is a side elevation of a main runner or beam constructed in accordance with this invention;

FIG. 2 is a fragmentary plan view of a metal strip illustrating a pre-blanking operation in the formation of the main runner of FIG. 1;

FIG. 3 is a vertical cross-section taken along the line 33 of FIG. 1;

FIG. 4 is a side elevation of a main beam splice plate;

FIG. 5 is a left end elevation of the splice plate of FIG. 4;

FIG. 6 is a fragmentary perspective of a splice joining the ends of two main runners;

FIG. 7 is a perspective of the splice plate ready for application to the joint of FIG. 6;

FIG. 8 is a side elevation of an improved cross T constructed in accordance with this invention;

FIG. 9 is a left end elevation of the cross T of FIG. 8;

FIG. 10 is a right end elevation of the cross T of FIG. 8;

FIG. 11 is a fragmentary perspective illustrating assembly of two cross TS to a main runner in the ceiling construction of the invention;

FIG. 12 is a vertical cross-section taken along the line 12-12 of FIG. 11 and showing the cross Ts of FIG. 11 assembled;

FIG. 13 is a front elevation of the main runner joint of FIG. 6 under normal conditions;

FIG. 14 is a view similar to FIG. 13 but showing the distoration that has occurred shoftly after exposure to fire temperatures; and

FIG. 15 is a view similar to FIG. 14 but showing the distortion that has occurred following prolonged exposure to fire temperatures.

Referring to the drawings in detail, the ceiling suspension system embodying the invention includes a main beam or runner generally indicated 5 of an inverted T cross section and formed from cold rolled coil steel or other suitable temperature resistant metal (see FIGS. 1 and 3). Cross Ts having a different construction will be described below in connection with FIGS. 8-10.

The main runner 5 comprises an upstanding web 6 provided along its upper edge with a bulbous rib 7 and along its lower edge with a pair of oppositely extending

flanges

8, 8 which form ceiling panel supporting surfaces. A decorative cover 9 may be used to cap the flanges 8 in installations where the under surface of the beam forms a visible part of the ceiling.

Since both ends of the beam 5 are of identical but oppositely disposed configuration, a detailed description of only one end will be given in the interest of brevity; but like reference characters will be applied to the opposite end.

Referring particularly to FIG. 1 of the drawings it will be seen that at each end of the beam 5 the upper part of the web 6 and the rib 7 have been cut back to 3 define a right angled notch 10 having a width A.,The depth of the notch 10 is not critical; however, it should be deep enough to extend down into the web 6 below the bottom of the rib 7.

A similar right angled notch 11 is cut into the end of the web 6 in vertical alignment with the notch 10 and is spaced downwardly therefrom a distance suflicient to define, at the web end, a generally square longitudinally projecting ear or lug 12 which is laterally deformable by column action when the main beam is assembled into a ceiling suspension system and exposed to fire temperatures as will be hereinafter more fully described.

The lower portion of the end of the web 6 is cut back to define an angularly flared notch generally indicated 13 which includes an upper edge 14 extending from the vertical edge of the notch 11 to a terminus 15 of uniform radius. The edge 14 is positioned at a predetermined angle such as 45 from the horizontal. The arcuate terminus 15 is provided with a short straight edge portion 16 disposed at a lesser angle from the horizontal, say 30, than the edge 14. Thus the

edges

14 and 16 diverge from the arcuate terminus 15. The edge 16 joins with a horizontal edge 17 to define a short wall portion 18. The outer end of the wall portion 18 is bevelled inwardly at a suitable angle, say 30 from the vertical, starting from the plane of the top of the flanges 8.

A rectangular slot 19 is formed in the web 6 adjacent each end thereof. A plurality of cross T connecting slots 20, having oppositely extending upper and

lower notches

21, 21, are spaced at uniform intervals along the web 6.

As illustrated in FIGS. 4-7 of the drawings, an important feature of this invention is the provision of a novel splice for securely holding the main beams in end abutting relation when assembled in a ceiling suspension system, yet which permits relative motion to take place when portions of the beams expand during exposure to elevated temperatures.

A splice plate generally indicated 22 is formed from a single blank of sheet metal and is symmetrically constructed about its center vertical axis as viewed in FIG. 4.

The upper edge of the splice plate 22 is rolled or otherwise shaped into a clip or hanger 23 having a general hook or question mark cross section as viewed in FIG. 5. The upper arcuate part of the clip 23 is shaped to closely conform to the outer surface of the main runner rib 7 when attached thereto. The central part of the splice plate is substantially flat and terminates at its lower edge with a rearwardly and downwardly projecting flange 24. The height of the flat portion of the splice plate including the vertical component of the flange 24 is substantially equal to the height of the Webs 6 of the main beams so that the splice plate can fit snugly thereagainst.

An inner pair of symmetrically disposed oppositely extending securing

flaps

25, 25, each having a forwardly projecting embossed rib 26, are formed in the splice plate 22 and are so spaced and proportioned as to be insertable through the rectangular slots 19 of the main beam webs 6. A similar pair of outer securing flaps 27, 27, each having a forwardly projecting embossed rib 28, are formed at the ends of the splice plate 22 and are so spaced and proportioned as to be insertable through the first of the rectangular slots adjacent to the slots 19 of the main runner webs 6.

Other areas of the flat portion of the splice plate 22 may be cut out, as at the areas immediately above and below the

flaps

25 and 27. An embossed area 29 may be provided to afford rigidity.

The

flaps

25 and 27 of the splice plate 22 are bent forwardly at right angles to the general plane of the splice plate (see FIG. 7) during manufacture. When the ends of two main runners 5 are to be joined the clip 23 is engaged over the opposing ribs 7 and the flaps project hookingly through the

slots

19 and 20. Then the flaps 25 are bent toward each other Q that the embossed ribs 26 4 are brought into clamping contact with the front faces of the webs 6 and the front face of the flat central portion of the splice plate is brought into contact with the rear faces of the webs. Similarly the end flaps 27 are bent toward each other so that the embossed ribs 28 are also brought into clamping contact with the front faces of the webs 6 to further secure the splice plate in position.

In this manner the splice plate 22 ties the main runner 5 together in end abutting relation and the

flaps

25 and 27 prevent longitudinal separation from taking place, while the engagement of the clip 23 with the ribs 7 and the engagement of the flat central portion of the splice place with the full depth of the rear faces of the webs 6 prevents flexing about either the vertical or horizontal axes of the joint.

By reference to FIG. 13 of the drawings it will be seen that when a butt joint between the ends of two main runners 5 is formed the lugs 12 at the ends of the webs 6 are in abutting contact as are the flanges 8 and the decorative cover 9. In this relationship the opposing

upper notches

10, 10 together define a rectangular opening having a length 2A to accommodate expansion of the ribs 7 when the main beams are exposed to elevated temperatures such as those occurring during a fire. Similarly the opposed notches 11, 11 the

flaring notches

13, 13 and the

shallow wall portions

18, 18 together define a generally butterfly shaped opening in the

webs

6, 6 to accommodate expansion of the webs and beam flanges under such conditions.

It will be appreciated that the dimensions of the above described openings are determined from a study of several factors including the type of metal used, beam length, co-efficient of expansion and degree of temperature change to be withstood.

The butt joint as illustrated in FIG. 13 shows the beam ends as they would appear in a ceiling suspension system exposed to normal room temperature.

When a fire occurs the resultant rise in temperature causes a longitudinal expansion of the beams of the system which is resisted by the grid construction of the ceiling and contact thereof with the Walls or other side members of the enclosure. This resistance to expansion is relieved through the use of the above described butt joints.

In FIG. 14 the structure has been exposed to a substantial temperature rise as would occur shortly after the outbreak of a fire and a certain amount of longitudinal expansion of the ribs, webs and flanges of the main beams has taken place. Expansion of the

ribs

7, 7 is accommodated by the opening defined by the

notches

10, 10. The

webs

6, 6 can expand into the butterfly shaped opening therebelow, and in so doing the compression forces exerted against the abutting lugs 12, 12 cause them to be deflected laterally. Similarly the compression forces developed by expansion of the flanges 8 and covers 9 cause the abutting ends thereof to be deflected downwardly, thus accommodating that portion of the beam expansion.

As this expansion occurs relative motion is permitted between the splice plate clip 23 and the ribs 7 and between the securing flexes 25, 27 and the webs 6. Compare FIGS. 13 and 14.

A further substantial temperature rise produces the condition illustrated in FIG. 15, and although some buckling of the joint about its transverse (vertical) axis has taken place, there has been no lateral twisting or buckling of the main runner webs or flanges which would break ceiling panels and cause them to drop. By lateral twisting or buckling is meant twisting or buckling in a direction normal to the main runner longitudinal axes and parallel to the ceiling surface.

FIG. 15 demonstrates an important advantage of the construction of the invention. Thus with the main runner construction of the invention it is only necessary to provide for longitudinal expansion of the main runner up to a temperature at which the beam metal softens. At higher temperatures expansion is accommodated by deflection of the main runner beam between the supporting hangers and by upward distortion of the joints at the ends of the beam, as illustrated in FIG. 15. For the cold rolled coils steels commonly used in suspended ceiling constructions, longitudinal expansion of the main runner beams should be permitted to a temperature in the range of about 1000 to 12.00 F.

In grid ceiling suspension systems of this nature it is also necessary to employ cross Ts having expansion relief means in order that cross T expansion will not twist or buckle the main beams to which they are attached and in order to prevent lateral twisting or buckling of the cross Ts themselves under fire conditions.

Therefore, in accordance with a further aspect of this invention, expansion relief for cross and bridging Ts is achieved through improved design of the T ends.

Referring now to FIGS. 8-10 there is shown a cross T generally indicated 30 having an inverted T cross section and which is formed from cold rolled coil steel or other suitable temperature resistant metal. The cross T comprises a two-ply upstanding web 31 provided along its upper edge with a bulbous rib 32 and along its lower edge with a pair of oppositely extending

flanges

33, 33 which form ceiling panel supporting surfaces. A decorative cover 34 may be used to cap the flanges 33 in installations where the under surface of the cross T forms a visible part of the ceiling. The extreme ends of the flanges 33 and cap 34 are transversely bent into a step configuration to form an abutment shoulder 35.

The opposite ends of the cross T 30 are shaped difi'erently. Thus the left end (FIG. 8) is provided with a longitudinally projecting nose 36 formed as an integral extension of one of the plies of the web 31. The height of the nose 36 is aproximately equal to the combined height of the slots 20 and

notches

21, 21 in the main beam web 6 so that the nose 36 may be inserted and retained therein (see FIGS. 11 and 12). To facilitate entry of the nose 36 into the slot 20, its outer end is cha-mfered as at 37 and 38. A hook-like notch 39 is formed in the lower edge of the nose 36 adjacent its outer end and prevents accidental removal of the nose from the slot 20 during ceiling assembly.

In assembly the cross T 30 is positioned so that the nose 36 extends through the slot 20 and the shoulder 35 formed at the ends of the flanges 33 and cover 34 abuts against the decorative cover 9 along the outer edge of a flange 8 of the main runner 5.

A longitudinally projecting tongue 40 is disposed in spaced parallel relation to the upper edge of the nose 36 and abuts against the adjacent web 6 of the main runner 5.

An elongated slot 41 having a vertical left wedge 42 and a semi-circular right edge 43 is formed in the Web 31 just to the right of the nose 36.

The right end of the cross T 30 (FIG. 8) includes a longitudinally projecting nose 44 formed as an integral extension of the other ply of the web 31 and terminates in a relatively long tongue 45. A short tongue 46, corresponding to the tongue 40 at the opposite end, is disposed in spaced parallel relation to the upper edge of the nose 44. The tongue 45 is provided with a hole 47 to facilitate bending.

Since the nose and other elements at one end of the cross T are integral with one web ply, and those at the other end are integral with the other web ply, it is possible to axially align two cross Ts when positioned on opposite sides of a main runner at any selected attaching location.

As shown in FIG. 11, when the left end of one cross T is inserted into a main runner slot 20, the right end of another cross T is inserted into the same slot from the opposite side of the main runner. In order to receive the

noses

36 and 44 the width of the notches 21 should be slightly greater than the combined thickness of the noses, and their depth should be such as to allow a slight clearance over the height of the noses and which should be equal to or slightly greater than the depth of the abut ment shoulder 35.

When the cross Ts are positioned as shown in FIG. 12, the cross T shoulders 35 abut against the respective main beam flanges, and the

tongues

40 and 46 abut against respective faces of the main beam web 6. The cross Ts are then locked in place by bending the tongue 45 through the slot 41 until the forward part of the tongue lies against the face of the nose 36.

As mentioned above, when a fire occurs the resultant rise in temperature causes a longitudinal expansion of all of the beams of the system. In the case of the cross Ts, their expansion is normally resisted because of their abutting engagement between adjacent main runners. However, in accordance with this invention, the longitudinal expansion stresses are accommodated Without lateral twisting or buckling of the cross Ts by means of their end configurations.

Referring to FIG. 12, as the cross Ts 30 develop substantial expansion stresses, the

tongues

40 and 46 will crumple, and relative sliding motion between the

noses

36 and 44 will take place as the webs 31 expand. The slot 41 accommodates the bent tongue 45 as this occurs. Simultaneously, the flanges 33 and covers 34 have expanded to force the abutment shoulders 35 to ride up onto the tops of their associated main runner flanges and thus lift the ends of both cross Ts. As this takes place the

noses

36 and 44 move upwardly into the clearance space provided in the upper notch 21 in the main runner web 6. The top corners of the cross Ts have been cut back at an angle of say 15 to provide additional expansion clearance for the ribs 32 with respect to the main runner rib 7.

In effect, the cross Ts will ride up onto the main runner flanges to accommodate the expansion stresses, and this is accompanied by crumpling of and relative motion between cross T parts which will not produce overall lateral buckling of either the cross Ts or main runners and hence will not act to break or drop ceiling panels supported on the flanges thereof.

Some ceiling suspension systems may require the use of bridging Ts between certain cross Ts and preferably the bridging Ts will have end configurations like those of the cross TS in order to relieve expansion stresses in the same way. In such instances the cross Ts will be provided with rectangular fastening slots similar to the main runner slots 20.

While the invention has been described in connection with specific embodiments thereof and in specific uses, various modifications thereof will occur to those skilled in the art without departing from the spirit and scope of the invention.

What is claimed is:

1. A beam for use in a fire retarding structural ceiling system, said beam being formed as an inverted T including a vertical web provided along its upper edge with a bulbous rib and along its lower edge with a flange projecting laterally from each side thereof, each end of said rib and the adjacent upper portion of said web being cut back to define a first notch, each end of the central and lower portions of said web being cut back to define a relatively large second notch having generally divergent edges extending toward the web ends, that portion of the web remaining between said notches at each end thereof defining a longitudinally extending abutment ear of limited height to facilitate collapse upon being subjected to endwise pressure, said notches together at each end defining expansion relief spaces when two of said beams are assembled in end-to-end abutting relationship to accommodate endwise movement upon collapse of the abutment ear.

2. A beam for use in a fire retarding structural ceiling system, comprising a pair of elongated metal strips disposed in side by side relationship and forming an upstanding web, an elongated bulbous rib joining the tops of said strips, and an elongated flange extending laterally from each side of the base of said web whereby said beam has substantially an inverted T cross section, each end of said rib and the adjacent upper portion of said web being cut back to define a notch, each end of the central and lower portions of said web being cut back to define a relatively large notch having generally divergent edges extending toward the web ends, that portion of the web remaining between said notches at each end thereof being of limited extent to define a deformable longitudinally extending abutment ear, said notches together at each end defining expansion relief spaces when two of said beams are assembled in end-to-end abutting relationship.

3. In a butt joint for fire retarding structural ceiling systems using beams each having an inverted T cross section and including a vertical web provided along its upper edge with a bulbous rib and along its lower edge with a flange projecting laterally from each side thereof and in which the abutting portions of the opposed ends of pairs of beams are of limited extent capable of being deformed upon application of a compressive load and configured to define expansion relief spaces therebetween; a splice plate spanning one side of the abutting ends of a pair of said beams and provided along its upper edge with an elongated clip engaged over the opposing rib ends of said beams, and a flat central portion disposed in face-toface contact with the opposing web ends of said beams, the lower edge of said flat central portion being disposed in abutting relation to the upper faces of opposing flange ends of said beams, and means carried by the flat central portion of said splice plate and connected with the opposing web ends of said beams for preventing longitudinal separation of said beam ends under normal temperature conditions while permitting expansion of said beam ends toward each other when exposed to elevated temperatures.

4. In a butt joint for fire retarding structural ceiling systems using beams each having an inverted T cross section and including a vertical web provided along its upper edge with a bulbous rib and along its lower edge with a flange projecting laterally from each side thereof and in which the opposed abutting ends of pairs of beams are configured to define expansion relief spaces therebetween; a splice plate spanning one side of the abutting ends of a pair of said beams and provided along its upper edge with an elongated clip engaged over the opposing rib ends of said beams, and a flat central portion disposed in face-to-face contact with the opposing web ends of said beams, the lower edge of said flat central portion being disposed in abutting relation to the upper faces of opposing flange ends of said beams, a pair of securing flaps carried by the flat central portion of said splice plate and disposed on opposite sides of the plane of beam end abutment and engaged through slots formed in the web ends of the respective beams for bending about the edges of the slots to prevent longitudinal separation of said beam ends under normal temperatures and to clamp the flat central portion of said splice plate against its associated web faces, said web end slots having a width substantially greater than the thickness of said securing flaps whereby to permit expansion of said beam ends toward each other when exposed to elevated temperatures without causing buckling of said splice plate or misalignment of said butt joint.

5. A cross T for use in a fire retarding structural ceiling grid system including spaced parallel main beams each having a horizontal flange and a vertical web having a transverse slot therethrough, said cross T comprising a vertical web and a horizontal flange extending from each side of said web and having a transverse abutment shoulder at each end thereof and arranged to engage the edge of the horizontal flange of a corresponding main beam, a first nose projection extending from one end of said cross T web beyond said abutment shoulder and arranged to enter the transverse slot in the adjacent main beam web, a second nose projection extending from the other end of said cross T web beyond said abutment shoulder and arranged to enter the transverse slot in the adjacent main beam web, said cross T web having a longitudinally extending slot adjacent said one end thereof, a first tongue projecting from the end of said second nose and arranged to be bent through the longitudinally extending slot of a corresponding cross T for locking said cross Ts together and to the corresponding main beam, and a pair of deformable tongues projecting from opposite ends of said cross T beyond said abutment shoulders and each being arranged to contact the adjacent main beam web, the heights of said first and second noses being less than the height of the main beam web transverse slot whereby to permit the cross T ends to become lifted by the overriding of said abutment shoulders onto the flanges of said main beam as said cross Ts expand when exposed to elevated temperatures.

6. A fire retarding ceiling grid system, comprising a plurality of spaced, parallel main beams and a plurality of spaced, parallel cross Ts extending between said main beams at right angles thereto; each of said main beams being formed from two or more sections with the ends of adjacent sections being aligned in abutting relationship, each of said main beam sections being formed as an inverted T including a vertical web provided along its upper edge with a bulbous rib and along its lower edge with a flange projecting laterally from each side thereof, the opposing ends of said ribs and said webs being configured to provide cut out areas which together define expansion relief spaces at the abutting ends, a splice plate spanning the abutting ends of said main beam sections, means carried by said splice plate for preventing longitudinal separation of the abutting ends under normal temperatures and for permitting expansion of said beam ends toward each other when exposed to elevated temperatures, said expansion relief areas being effective to accommodate expansion of the beam web and rib portions while permitting downward buckling of the flanges only in the area of the joint, the main beam section webs being pro vided with a plurality of transverse slots corresponding in number at least to the number of cross T s; and said cross Ts each comprising a vertical web and a horizontal flange extending from each side of said web and having a transverse abutment shoulder at each end thereof and arranged to engage the edge of the horizontal flange of a corresponding main beam, a first nose projection extending from one end of said cross T web beyond said abutment shoulder and arranged to enter a respective transverse slot in the adjacent main beam web, a second nose projection extending from the other end of said cross T web beyond said abutment shoulder and arranged to enter a respective transverse slot in the adjacent main beam web, said cross T web having a longitudinally extending slot adjacent said one end thereof, a first tongue projecting from the end of said second nose and arranged to be bent through the longitudinally extending slot of a corresponding cross T for locking said cross T s together and to the corresponding main beam, and a pair of deformable tongues projecting from opposite ends of said cross T beyond said abutment shoulders and each being arranged to contact the adjacent main beam web, the heights of said first and second noses being less than the height of the main beam web transverse slot whereby to permit the cross T ends to become lifted by the overriding of said abutment shoulders onto the flanges of said main beam as said cross Ts expand when exposed to elevated temperatures.

7. A fire retarding ceiling grid system, comprising a plurality of spaced, parallel main beams and a plurality of spaced, parallel cross Ts extending between said main beams at right angles thereto; each of said main beams being formed from two or more sections with the ends of adjacent sections being aligned in abutting relationship, each of said main beam sections being formed as an inverted T including a vertical web provided along its upper edge with a bulbous rib and along its lower edge with a flange projecting laterally from each side thereof, the opposing ends of said ribs and said webs being configured to provide cut out areas which together define expansion relief spaces at the abutting ends, a splice plate spanning one side of the abutting ends of a pair of said beams and provided along its upper edge with an elongated clip engaged over the opposing rib ends of said beams, and a flat central portion disposed in face-to-face contact with the opposing web ends of said beams, the lower edge of said flat central portion being disposed in abutting relation to the upper faces of opposing flange ends of said beams, a pair of securing flaps carried by said flat central portion and disposed on opposite sides of the plane of beam end abutment and engaged through slots formed in the web ends of said beams to prevent longitudinal separation of said beam ends under normal temperatures and to clamp the flat central portion of said splice plate against its associated web faces, said web end slots having a width substantially greater than the thickness of said securing flaps whereby to permit expansion of said beam ends toward each other when exposed to elevated temperatures without causing buckling of said splice plate or misalignment of said butt joint, said expansion relief areas being eifective to accommodate eX- pansion of the beam web and rib portions while permitting downward buckling of the flanges only in the area of the joint, the main beam section webs being provided with a plurality of transverse slots corresponding in number to the number of cross TS; and said cross Ts each comprising a vertical web and a horizontal flange extending from each side of said web and having a transverse abutment shoulder at each end thereof and arranged to engage the edge of the horizontal flange of a corresponding main beam, a first nose projection extending from one end of said cross T web beyond said abutment shoulder and arranged to enter a respective transverse slot in the adjacent main beam web, a second nose projection extending from the other end of said cross T web beyond said abutment shoulder and arranged to enter a respective transverse slot in the adjacent main beam web, said cross T web having a longitudinally extending slot adjacent said one end thereof, a first tongue projecting from the end of said second nose and arranged to be bent through the longitudinally extending slot of a corresponding cross T for locking said cross Ts together and to the corresponding main beam, and a pair of deformable tongues projecting from opposite ends of said cross T beyond said abutment shoulders and each being arranged to contact the adjacent main beam web, the heights of said first and second noses being less than the height of the main beam web transverse slot whereby to permit the cross T ends to become lifted by the overriding of said abutment shoulders onto the flanges of said main beam as said cross Ts expand when exposed to elevated temperatures.

8. In a fire-retarding structural ceiling system, the combination of abutting beams each formed as an inverted T having a web with a rib along the upper edge and laterally extending tile-supporting flanges along the lower edge, the rib being cut back into the web to define a generally horizontal upper edge of an integral horizontally extending abutment lug, the central portion of the web being deeply cut back to define a generally horizontal lower edge of the abutment lug, the latter cut back portion extending downwardly from the lug substantially to the flanges, the lug thus formed being sufliciently narrow in the vertical direction and sufiiciently long in the horizontal direction as to collapse laterally with column action when subjected to the excessive end loading accompanying expansion due to a fire.

9. The combination as claimed in claim 8 including 9. splice plate spanning the ends of the beams and hookingly engaging the same to prevent separation of the beam ends under normal temperature conditions while permitting expansion of said beam ends toward each other when exposed to elevated temperatures.

References Cited UNITED STATES PATENTS 3,159,252 12/1964 Cotts 52573 3,175,655 3/1965 Brown et al. 52573 3,189,139 6/ 1965 Znamirowski 52573 3,239,035 3/1966 Znamirowski 52484 3,284,977 11/1966 Lickliter et a1 52573 ROY D. FRAZIER, Primary Examiner R. D. KRAUS, Assistant Examiner US. Cl. X.R. 287-18936