US3340659A

US3340659A - Blast shield for building structures

Info

Publication number: US3340659A
Application number: US287592A
Authority: US
Inventors: Trygve W Hoff
Original assignee: Hoff Res & Dev Lab Inc
Current assignee: Hoff Res & Dev Lab Inc; Hoff Research & Development Laboratories Inc
Priority date: 1963-06-13
Filing date: 1963-06-13
Publication date: 1967-09-12
Anticipated expiration: 1984-09-12

Description

p 1967 T. w. HOFF BLAST SHIELD FOR BUILDING STRUCTURES Filed June 13, 1963 2 SheetsSheet 1 m T m V m [em/4. W HUFF wfiw Sept. 12, 1967 T. w. 'HOFF 3,340,659

BLAST SHIELD FOR BUILDING STRUCTURES f1 g- .7 INVENTOR.

Arm/ways United States Patent 3,340,659 BLAST SHIELD FOR BUILDING STRUCTURES Trygve W. Hoff, Cleveland Heights, Ohio, assignor t0 Holf Research & Development Laboratories Incorporated, Cleveland, Ohio, a corporation of Ohio Filed June 13, 1963, Ser. No. 287,592 9 Claims. (Cl. 52-261) This invention relates to the protection of building structures from damage by airborne shock waves and more particularly to blast-resistant'shielding means for building structures.

Conventional buildings are subject to severe damage from atmospherically transmitted shock waves and/ or disturbances produced by blasts. The nature and extent of the damage to the building, inter alia, depends upon the type and nature of the blast that produces the destructive forces. Ordinary blasts and blasts of less power than produced by nuclear devices set up high atmosphericallyborne transient forces classified as shock waves or diffraction pulses. Nuclear devices produce two additional forces and effects of greater time duration than the relatively short-lived transient diffraction effect. These are a uniform isotropic crushing pressure having a generally enveloping and crushing effect upon structures in the region of the blast and a dynamic pressure or drag force effect due to the movement of large masses of air at high velocities imparted to them by the blast. Often the sup porting framework of buildings will withstand shock waves and generally enveloping crushing pressures which effectively destroy the outside shell and particularly the vertical outside walls of the buildings. Thus, a building otherwise undamaged by blast forces may be rendered useless and its contents and interior greatly damaged through failure of its outside shell.

The most severe damage generally occurs to a buildings vertical outside walls which have large areas of exposure ormal to the blast forces or substantial components theref. These outside walls generally are best adapted to withstand forces acting in directions substantially parallel to e plane of the wall and are relatively Weaker in beam str ngth for resisting forces directed normal to them. This is articularly true of glass panels and/ or windows which are easily broken by airborne shock waves directed against the Roofs or the upper faces of buildings may also be da aged by blast forces, but sometimes to a lesser extent if their orientation minimizes those components of the forces directed normally to their surface.

In he case of a relatively tall building, even the supporting jfamework may fail as well as the exterior shell if the dyn mic pressures are sufiicient to topple or break by ben ing the entire building. Considering this effect, a tall buil ing can be thought of as a longitudinal structure having free and a fixed end anchored to earth in the general ma ner of a cantilevered structure.

One of the objects of this invention, therefore, is to provide a building construction adapted to prevent and/ or reduce damage to building structures by airborne forces su h as are generated, for example, by blasts or explosions.

Another object is to provide a building construction dapted to shield the outer shell of a building structure from blast-produced forces or components thereof directed g nerally normal to the surface planes of the shell.

Another object is to provide a building construction adapted to shield the outer shell of a building structure from blast-produced crushing and enveloping pressures or components thereof directed generally normal to the surface planes of the shell.

Another object is to provide a building construction adapted to aid the supporting framework of a building structure in resisting blast-produced dynamic forces.

Another object is to provide such a building construction that is blast resistant and is supported by and cooperates with the supporting framework of the building structure whose outer shell is protected thereby.

Another object of my invention is to provide such a building construction that is adapted to resist in tension blast-produced forces or components thereof directed generally normal to the exterior surface planes of the building structure shielded and to transfer the tension forces produced in resistance to the supporting framework and/ or floors of the shielded building structure.

Another object is to provide such a building construction that is readily adapted for use in protecting existing building structures through cooperation and coaction with conventional structure elements of existing buildings.

Another object is to provide such a building constructhat may readily be incorporated in newly erected buildings.

In brief, I accomplish the foregoing objects of my invention by providing a blast-resistant shield overlying and standing between the building faces and force producing blasts. The shield comprises a number of panels of flexible and somewhat elastic sheet material further characterized as having a relatively high tensile strength. The sheet material is fastened along at least two opposite marginal portions to longitudinal portions of suitably arranged framing members. The framing members are structurally related and tied to the conventional structural framework of the building and extend longitudinally along the faces of the building and laterally outwardly from the exterior faces thereof. The panels of sheet material are thus supported in a plane substantially parallel'to and spaced away from the exterior surface of the building faces and anchored along their marginal portions to and through the framings to the structural framework of the shielded building.

The flexible and somewhat elastic panels of sheet material are capable of acting in the manner of a catenary in the spaces between framing members when subjected to loads directed against the large surface areas of the sheets. By utilizing sheet material capable of substantial deflection beween its supported and anchored opposite marginal edges, I achieve a covering of substantial area which, under normal or unloaded conditions, assumes a relatively fiat plane position; but which, under relatively high loading by normally directed forces or components of forces, assumes a curved or bowed position. By permitting the sheets to assume such a curved position under load, they are stressed predominantly in tension. In this manner, the flexible, lightweight panels of sheet material are able to withstand a large total load equal to the capacity of much heavier and more massive and expensive constructions constrained in a generally plane attitude and required to support a load as a beam or flat slab. It will be apparent that when the blast-resistant shield is under load, the framing members anchoring opposite marginal edges of a panel of flexible sheet material tend to be drawn toward each other and are subjected to forces acting in a plane parallel to the blast-resistant shield and the exterior wall of the shielded building. These forces are resisted by the conventional supporting framework of the building and by the other structural elements integrated therewith, such as floors.

My invention also comprehends employing resiliently bendable longitudinal rib means in conjunction with the high tensile strength panels of flexible sheet material which, through their bending stiffness, tend to maintain the sheets in a generally plane attitude under dead load and light load conditions but which permit the abovedescribed catenary type action or bowing of the sheet material under live load conditions. The rib means comprise longitudinal elements characterized by their resilient stiffness or resistance to bending and which lie along and are suitably secured to one or both surfaces of the sheets.

Such a building construction as I have described above, when employed in continuous fashion on all exterior surfaces of the building to be protected, acts together to produce a total effect and strength analogous to that of a box girder. This box girder type of strength achieved through the construction of my invention provides substantial aid to the supporting framework of the building being protected in resisting the dynamic pressures and forces produced, for example, by nuclear devices tending to bend and topple a tall building.

My invention is more particularly set forth in the following description of a preferred and modified form thereof and by the accompanying drawings in which:

FIGURE 1 is a prspective view of a conventional building structure provided with a preferred form of blast-resistant shield embodying my invention shown with some of the panels of flexible sheet material removed or broken away in order to more fully disclose the details of the shields construction and its relationship to the protected building structure;

FIGURE 2 is an elevational view of an enlarged scale of a typical portion of a wall of the building of FIG- URE 1;

FIGURE 3 is a cross-sectional view on an enlarged scale of the blast-resistant shield as shown in FIGURE 2, taken along the line 33 therein;

FIGURE 4 is the same view as FIGURE 3 but with the shield loaded or subjected to shock waves as indicated by the arrows; and 7 FIGURE is a view similar to FIGURE 3 and showing a modified form of the blast-resistant shield embodyiny my invention.

Referring now to the drawings, the blast-resistant shielding means comprises a number of longitudinal framing members F appearing on the exterior surface of the outside walls of the building structure B to be protected and a number of panels P of sheet material supported by and extending between framing members F and together forming a substantially complete and continuous covering for the exposed faces of building B.

As seen generally in FIGURE 1 and more particularly in FIGURE 2, framing members F extend longitudinally in a vertical direction and in parallel spaced apart fashion across the face of the outside wall. The interval between each vertically rising framing member F depends in part upon the physical dimensions of the building protected and its supporting framework, the spacing and size of window and door openings in the wall of the building and, as will be explained more fully below, the extent which framing members F extend outwardly from the wall. Inasmuch as the force of the shock waves resisted by the shielding structure and from which the building is thereby insulated is transmitted ultimately to the integrated structural element of the building such as the supporting framework and floors of the building, it is desirable to locate framing members F along vertical columns or piers of the building. Thus, a framing member F is generally placed at each end of an exposed face of the building or at the building corners and at selected intervals therebetween in accordance with the factors noted above. While the method and means for attaching the framing members to the structurel framework of a building form no part of the invention, it will be understood that they must be tied securely into the structure and in a manner enabling them to resist displacement when the shield is subjected to shock waves and to support and sustain the plurality of panels of flexible sheet material with their marginal edges anchored in a relatively fixed position.

In the case of an existing building to be protected with a blast-resistant shield of my invention, framing members F may be practicably made of structural steel of any suitable sections such as wide flange, I or channel sections or special hat sections. The section of the framing members F employed should be able to be fastened or attached to the building as described above and to provide an adequate longitudinal portion at a spaced distance from the exterior surface of the building to permit the convenient and satisfactory attachment or fastening of the panels P to the framing members F.

As shown in the drawings, framing members F are structural beams of wide flange section. As seen most clearly in FIGURES 3, 4 and 5, one flange of each of the members F provides a longitudinal anchoring portion 10 having a wide bearing surface for engagement with the exterior surface of building B and has adequate material to permit fastening members F to the framework or supporting structure of building B by means of long bolts, tie rods or the like. The other flange of each of members F comprises a longitudinal supporting portion 11 with sufficient lateral dimension to permit marginal portions 12 of two adjacent panels P to be anchored to each framing member F as by lapping each marginal portion 12 over a substantial part of a longitudinal supporting portion 11 and bolting or welding the parts together. The webs of framing members F comprise spacing portions 13 serving to

space portion

10 and 11 apart and particularly to support and position portion 11 and thereby panels P and their marginal portions 12 outwardly of and away from the exterior faces of building structure B to permit deflection of panels P toward the exterior faces without engagement therebetween.

In the case of newly constructed buildings, the sections or shapes employed in the structural framework of the building itself or in vertically aligned structural elements of the building may be chosen to provide suitably integrated framing members F having vertically extending longitudinal portions extending and supported outwardly of the exterior surfaces of the building and to which marginal portions of panels P may be anchored.

Panels P of flexible sheet material are preferably of lightweight sheet metal material such as 16 gauge sheet steel and of a quality having relatively high tensile strength. For buildings such as shown in FIGURE 1, panels P are preferably rectangular in shape and of convenient size and so proportioned and dimensioned as to extend between vertical framing members F and permit the suitable fastening or attachment of their opposite marginal edges to the longitudinal portions of framing members F standing away from the exterior surface of the building.

Each of the sheets is fastened or attached to supporting framing members F by conventional means such as bolts. The particular means and manner of fastening the opposite marginal portions of the sheets to framing members F forms no part of this invention and any one of several well-known means, such as bolts with floating nuts, self-tapping screws or welds, may be employed. The fastenings between the sheet and framing members F should be at suitable intervals along each of two opposite marginal portions 12 so that when each panel P is loaded and stressed in tension, the stress in the sheet is transmitted and distributed relatively uniformly and without undue concentration at the fastening points to framing members F.

As seen in greater detail in FIGURE 2, the vertical marginal portions 12 of panels P overlie a suflicient width of the outwardly facing surfaces of longitudinal supporting portions 11 of framing members F to permit their attachment. The horizontal dimension of panels P may be such that they extend only between two adjacent vertical framing members F, or they may be long enough to span the interval between several members F. In either event, the vertical marginal portions 12 of each panel P must be secured to framing members F and it is preferred that panels which span more than one interval between vertical members F be secured to the intervening members F also. The horizontal marginal portions 14 of each of panels P are butted together. The abutting horizontal marginal portions of panels P may be restrained against relative movement by any means that does interfere with the deflection of the panels under blast force loading.

The operation of the blast-resistant shield of my invention can be best illustrated in connection with FIGURES 3 and 4 of the drawings. In these figures, a portion of the exterior wall of building B is indicated in cross-hatched section. Framing members F, seen in transverse cross section, are, in this embodiment, I beams arranged vertically of the outside Wall with one flange fastened to and adjacent the wall and the otherflange spaced away from the wall by the intervening web portion of the beam and providing a longitudinal supporting portion 11 for supporting and securing opposite marginal portions 12 of panels P. As illustrated in FIGURE 3, the panels P assume and retain a relatively flat position spanning the space between framing members F and spaced away from the exterior of the outside wall of the building in a plane substantially parallel thereto. When uniformly distributed high transient loads, such as shock waves generated by blasts or explosions transmitted through the air, are applied to panels P, their flexible and somewhat elastic nature permits them to deflect in the manner of a catenary as seen most clearly in FIGURE 4. These uniformly distributed and high transient loads are sustained primarily and to a substantial extent by the tensile strength of panels P of sheet material acting in the manner of a catenary. Tension produced in panels P is resisted by framing members F and in turn by the entire integrated structural and sup porting framework of the building being protected. It is believed that a substantial amount of stress developed in the sheets by high transient loads is transmitted to and sustained by. the floors of the building. It will be noted that the longitudinal supporting portions 11 of framing members F must be spaced outwardly from the protected building a sufficient distance to keep panels P from lying against the building when deflected by blast loads. This permits the blast-resistant shield to act in the intended way and prevents panels P from striking and damaging windows, for example.

At the corners of each building, I believe it to be desirable, though not necessary, to join or tie together the outwardly spaced longitudinal portions 11 of framing members F adjacent each corner of the building. This can be accomplished by means of corner panels C as shown in FIGURE 1 and in transverse cross section in FIG-

URES

3 and 4 and 5, for example. Such corner panels C have a relatively short span between the supporting longitudinal portions 11 of the corner framing members F and will exhibit little deflection or action in the manner of panels P, but they serve to tie together each pair of corner framing members F and to resist and balance the stress imposed on these framing members by the panels P secured to one side of and extending in one direction therefrom. Corner panels C, when employed to join together the blast-resistant shield applied to each of the exterior walls of a tall building, for example, tie together the shielding parts of the construction on all sides of the protected building so that it acts in the manner of a box girder and, as such, enhances the constructions resistance to high dynamic pressures that may be produced by a blast. While it might seem that this box girder-like conception of my blast-resistant shield would require anchoring and footing in and on the earth, I do not believe this is necessary. The dynamic pressures produced by nuclear devices are not uniform and homogeneous in magnitude nor direction nor are they of a very great duration. It appears, therefore, that the maximum bending moment produced in the building by the highly complex dynamic pressures might or might not occur at ground level, for example, and that, in any event, it is probably constantly shifting up and down the height of the building structure.

A modified form of blast-resistant shield comprehending my invention can be understood from the foregoing description of a preferred embodiment together with FIG- URE 5 of the drawings in which elements common to both embodiments are identified by like reference characters. As seen in FIGURE 5, the modified form of shield consists of vertical framing members F and panels P of flexible sheet material arranged and related in the same manner as in the previously described embodiment. Panels P, however are additionally provided with resiliently bendable longitudinal rib means 15 arranged in parallel spaced apart fashion between marginal portions 14 and extending longitudinally between secured marginal portions 12 of each panel.

The ribs 15 comprise longitudinal elements characterized by their resilient stiffness or resistance to bending and lie along and are suitably secured only to one or both surfaces of panels P and not to framing members F.

The useful function performed by rib elements 15 is to maintain the sheets of the panels P in a relatively plane attitude when the blast-resistant shield is not stressed by high transient loads and to maintain any rattling or Waving of the panels P as might otherwise be experienced under certain wind loads. Thus upon deflection of panels P by high transient loads, ribs 15 are subjected to no appreciable tension stress but only to a banding stress. The ribs 15 thus act and tend to maintain panels P in a generally plane attitude under dead or light load conditions but permit the above-described deflection or catenary type aciton or bowing of the sheet material of panels P under live load or high transient load conditions.

Framing members F of the blast-resistant shield of my invention are preferably permanently attached to or incorporated in the structure of the building to be protected, ready at all times to receive and support the panels P. The panels P of flexible sheet material may be permanently or removably attached to framing members F over all or part of the outside faces of the building to be protected depending upon the nature of the blast-producing circumstance or condition against which protection is sought. To adequately resist and shield a building from shock waves of an explosion, the entire surface of the outside walls of the building should be covered by the blast-resistant shield so that failure and destruction at one portion of the outside Walls of the building leading to further collapse or damage will be prevented.

While I have described my invention particularly in terms of the framing elements having a vertical orientation to which the horizontally opposite marginal portions of the flexible panels are attached, it is to be understood that the invention also comprehends other orientations of the framing members and cor-responding in appropriate marginal portions of attachment of the panels thereto.

For example, in a building structure having floor slabsthat may be conveniently and practically employed to protect and insulate existing buildings or incorpated in the structure of newly constructed buildings and which acts to prevent the blowing out or in of outside walls and windows when the building is subjected to airborne shock waves generated by blasts or explosions. The shield itself is blast-resistant and, through the permitted deflection of a large part of its surface area, tends to ride with the blow and resolve the destructive forces of blasts and explosions into tension acting in a structure highly adapted to resist them. Thus the building protected by the blast-resistant shield of my invention is insulated and protected from the force and effect of highly destructive, normally directed forces or components of forces on its outside walls and is able to withstand the force of blasts and explosion without damage by resisting these 'forces by the strength of materials commensurate with the forces experienced.

Changes, modifiications and improvement may be made to the above-described preferred and modified forms of my invention without departing from the precepts and principles of the invention. Therefore, I do not wish my patent to be limited to any particular form of my invention specifically illustrated and described nor in any manner inconsistent with the extent to which my invention has promoted the art.

Iclaim:

1. A blast shield for and in combination with a building structure having plane outside walls meeting together and terminating at corners, said blast shield comprising:

a plurality of longitudinal framing members laterally spaced at intervals along the outside of walls of the building structure and structurally secured to the building structure, said plurality including at least a framing member adjacent each corner on each wall, each of said framing members having a-spacing portion extending outwardly from the building structure and longitudinal portion spaced and supported by said spacing portion outwardly and away from the building structure,

a plurality of panels of flexible, resilient sheet material arranged together to substantially cover the outside walls of the building structure, each of said panels having opposite marginal portions secured to longitudinal portions of a pair of laterally spaced framing members lying along the same outside wall so as to tend to maintain the panel substantially flat and spaced outwardly from the outside wall of the building structure and to permit said panel to belly toward the wall from which it is spaced and be stressed in tension between its secured marginal portions under high dynamic and externally applied loads.

2. The blast shield of claim 1 with tension means interconnecting the longitudinal supporting portions of the framing members adjacent each corner of the building.

3. The blast shield 'of claim 1 with a resiliently bendable rib element extending longitudinally between the secured marginal portions of each panel and engaging only the panel so as to constrain it to remain substantially flat and inflexible under normal light loads while permitting it to belly between its secured marginal portions without fracture.

4. A blast shield for and in combination with a building structure comprising:

a plurality of longitudinal framing members disposed in a laterally spaced arrangement over the exterior faces of the building to be shielded, said framing members having a portion structurally connected to the building to be shielded and a longitudinal portion standing outwardly and spaced away from the exterior faces of the building,

a plurality of panels of flexible, resilient sheet material arranged together to substantially cover the exterior faces of the building, each of said panels having opposite marginal portions secured to said longitudinal portions of a pair of laterally spaced framing members so as to tend to maintain the panel substantially flat and spaced outwardly from an exterior face of the building and to permit said panel to belly toward the exterior face and be stressed in tension between its secured marginal portions under high dynamic and externally applied loads.

5. The blast shield of claim 4 with a resiliently bendable rib element extending longitudinally between the secured marginal portions of each panel and engaging only the panel so as to constrain it to remain substantially flat and inflexible under normal light loads while permitting it to belly between its secured marginal portions Without fracture.

6. A blast shield for and in combination with a building structure having a plurality of longitudinal framing members disposed in a laterally spaced arrangement, each of said framing members having a longitudinal portion standing outwardly and spaced away from the exterior face of the building, said blast shield comprising:

a plurality of panels of flexible, resilient sheet material arranged together to substantially cover the exterior faces of the building, each of said panels having opposite marginal portions secured to said longitudinal portions of a pair of laterally spaced framing members so as totend to maintain the panel substantially flat and spaced outwardly from an exterior face of the building and to permit said panel to belly toward the exterior face and be stressed in tension between its secured marginal portions under high dynamic and externally applied loads.

7. The blast shield of claim 6 with a resiliently bendable rib element extending longitudinally between the secured marginal portions of each panel and engaging only the panel so as to constrain it to remain substantially flat and inflexible under normal light loads while permitting it to belly between its secured marginal portions without fracture.

8. A blast shield for and in combination with a building structure comprising:

vertically extending framing members laterally spaced at intervals along the exterior faces of the building to be shielded and secured to the building structure, each of said framing members having spacing means extending outwardly from the building structure and a longitudinal portion spaced and supported by said spacing means outwardly and away from the exterior faces of the building structure,

a plurality of panels of flexible, resilient sheet material arranged together to substantially cover the exterior faces of the building structure, each of said panels having opposite marginal portions secured to said outwardly spaced and longitudinal portions of a pair of laterally spaced framing members lying along the same outside wall so as to tend to maintain the panel substantially flat and in a plane spaced outwardly from an exterior face of the building and to permit said panel to belly toward the building face from which it is spaced and be stressed in tension between its secured marginal portions under high dynamic and externally applied loads.

9. A blast shield for and in combination with a building structure comprising:

a plurality of rectangular panels of flexible, resilient sheet material arranged in horizontally adjacent vertical columns so as to substantially cover the exterior References Cited UNITED STATES PATENTS Lundvall 52508 X Wood 52506 X Atkin 52508 X Connor 52508 X Sklarotf 52483 X FRANK L. ABBOTT, Primary Examiner.

RICHARD W. COOKE, JR., Examiner.

R. S. VERMUT, Assistant Examiner.

Claims

1. A BLAST SHIELD FOR AND IN COMBINATION WITH A BUILDING STRUCTURE HAVING PLANE OUTSIDE WALLS MEETING TOGETHER AND TERMINATING AT CORNERS, SAID BLAST SHIELD COMPRISING: A PLURALITY OF LONGITUDINAL FRAMING MEMBERS LATERALLY SPACED AT INTERVALS ALONG THE OUTSIDE OF WALLS OF THE BUILDING STRUCTURE AND STRUCTURALLY SECURED TO THE BUILDING STRUCTURE, SAID PLURALITY INCLUDING AT LEAST A FRAMING MEMBER ADJACENT EACH CORNER ON EACH WALL, EACH OF SAID FRAMING MEMBERS HAVING A SPACING PORTION EXTENDING OUTWARDLY FROM THE BUILDING STRUCTURE AND LONGITUDINAL PORTION SPACED AND SUPPORTED BY SAID SPACING PORTION OUTWARDLY AND AWAY FROM THE BUILDING STRUCTURE, A PLURALITY OF PANELS OF FLEXIBLE, RESILIENT SHEET MATERIAL ARRANGED TOGETHER TO SUBSTANTIALLY COVER THE OUTSIDE WALLS OF THE BUILDING STRUCTURE, EACH OF SAID PANELS HAVING OPPOSITE MARGINAL PORTIONS SECURED TO LONGITUDINAL PORTIONS OF A PAIR OF LATERALLY SPACED FRAMING MEMBERS LYING ALONG THE SAME OUTSIDE WALL SO AS TO TEND TO MAINTAIN THE PANEL SUBSTANTIALLY FLAT AND SPACED OUTWARDLY FROM THE OUTSIDE WALL OF THE BUILDING STRUCTURE AND TO PERMIT SAID PANEL TO BELLY TOWARD THE WALL FROM WHICH IT IS SPACED AND BE STRESSED IN TENSION BETWEEN ITS SECURED MARGINAL PORTIONS UNDER HIGH DYNAMIC AND EXTERNALLY APPLIED LOADS.