Controlled release wall structure

A controlled release wall structure is provided which relies on controlled strength distribution and which disengages from a building framework at a selected applied load -- failure load -- and collapses in the direction of the applied load, that is, inwardly or outwardly of the building. Under normal wind load conditions, the present wall structure will safely sustain the expected elastic deflection and working stresses. However, under abnormally high loadings such as applied by explosion forces or by tornado and hurricane wind forces, the present wall structure collapses to create a substantial open area whereby a minimal loading is transmitted to the structural framework. The present wall structure protects the building framework from being overstressed during tornadoes or hurricanes; and also is capable of quickly relieving excessive pressures generated by an explosion within or without the building. The present wall structure includes at least one composite panel which spans the distance between at least first and second frame members, and which has one panel end releasably retained on the first frame member. According to this invention the composite panel is provided with a discontinuity in the region between the first and second frame members, which reduces the bending strength of the composite panel. The discontinuity extends parallel with and is spaced at a "selected distance" from a proximate edge of the first frame member. The "selected distance" determines the failure load of the wall structure.

BACKGROUND OF THE INVENTION 
1. Field of the Invention: 
This invention relates to building wall structures, and more particularly 
to controlled release wall structures adapted to collapse inwardly or 
outwardly relative to the building framework when acted upon by abnormally 
high positive or negative wind pressures. 
2. Description of the Prior Art: 
In the past, building wall structures have been adapted to be separated 
from the structural framework -- usually away from the framework -- when 
the wall structure experiences a selected elevated pressure. Such elevated 
pressure may be created by explosions occurring within the confines of the 
building or by abnormally high negative wind pressures. Such wall 
structures have been provided wherein the panels. 
(a) are held in place by resilient members, see, for example, U.S. Pat. 
Nos. 3,112,535; 3,150,749; 3,258,890; 
(b) are secured to the frame members by releasable fastening means of the 
type which will fail in shear or in tension, see, for example, U.S. Pat. 
Nos. 3,258,887; 3,807,106; and 
(c) are secured to the structural framework by pressure release fasteners 
which incorporate a deformable metal washer which is forced over the 
fastener head during release of the panel, see, for example, U.S. Pat. No. 
3,828,493. 
In a recent development, a wall structure is provided which spans across at 
least two frame members and which is adapted to collapse (inwardly or 
outwardly) in the direction of and at a predetermined applied load. The 
wall structure includes a liner sheet having one end releasably retained 
to a first frame member, an outer facing sheet, and at least two subgirts 
disposed between and secured to the liner sheet and to the facing sheet. 
The failure load of the wall structure is controlled by the distance 
between the first frame member and the subgirt adjacent thereto. The 
failure load of the wall structure is regulated by controlling the force 
distribution in the wall structure components. See, for example, U.S. Pat. 
No. 3,998,016. 
Transparent laminated window closures are known which, in response to 
excessive pressures, rupture or yield inwardly or outwardly from the 
original plane of the window. In one arrangement, one or both of the glass 
plates of the laminate may be split or scored along predetermined lines 
such that the closure ruptures into a selected number of segments, each 
segment having marginal edges hinged to the frame. See, for example, U.S. 
Pat. No. 2,679,467. In a second arrangement, the closure comprises 
triangular segments having a yieldable strip, such as elastic tape or the 
plastic interlayer of the laminate, which bridges across the adjacent 
edges of the segments. The yieldable tape flexes during application of 
excessive pressures, thereby allowing the triangular segments to move in 
the direction of the applied pressure. See, for example, U.S. Pat. No. 
2,721,157. 
SUMMARY OF THE INVENTION 
The principal object of this invention is to provide a wall structure 
comprising at least one composite panel, which safely sustains the 
expected deflection and working stresses encountered under normal wind 
loadings but which is adapted to collapse at abnormally high loadings, 
such as produced during tornadoes or hurricanes and such as generated by 
explosions within or without the building. 
Another object of this invention is to provide a controlled release wall 
structure which prevents overloading the building structural framework and 
hence the building structural framework need not be designed for full 
tornado and hurricane loads. 
Another object of this invention is to provide a controlled release wall 
structure which is adapted to collapse at a specified applied load but 
which remains positively connected to the structural framework. 
Another object of this invention is to provide a controlled release wall 
structure wherein the collapse of the wall structure at a predictable 
failure load relies on controlled strength distribution within the 
composite panel. 
Still another object of this invention is to provide a controlled release 
wall structure incorporating a composite panel having a discontinuity 
extending substantially parallel with and spaced at a selected distance 
from an adjacent frame member, wherein the discontinuity reduces the 
bending strength of the composite panel in the plane of the discontinuity 
-- the "selected distance" determining the failure load at which the 
composite panel will collapse. 
The present invention provides a wall structure of the type incorporating 
at least one composite panel and having a blow-in/blow-out feature which 
protects the building structural framework from being overloaded when the 
wall structure experiences abnormally high wind loadings such as produced 
during tornadoes and hurricanes. The present wall structure may also 
operate to release excessive pressures, such as generated by an explosion 
within the interior of the building. 
The present wall structure may be erected as a single-span or double-span 
structure. At a selected failure load, the wall structure fails in 
bending, disengages from one end support, and collapses inwardly or 
outwardly depending on the direction of the applied load. In its collapsed 
configuration, the wall structure transmits a minimal wind loading to the 
structural framework. Positive fasteners placed at one end of the panel in 
the case of a single-span condition or at the central support in the case 
of a double-span condition prevent the wall structure from becoming 
completely disengaged from the structural framework. 
In a single-span condition, the present wall structure comprises a 
composite panel spanning the distance between first and second frame 
members. Confinement means releasably retain one panel end on the first 
frame member. Fastening means positively secure the panel to the second 
frame member. The composite panel comprises spaced-apart inner and outer 
skins which are secured in shear-transferring relation by means of a 
structural core, such as a foam core, a honeycomblike core or the 
equivalent. The composite panel incorporates a discontinuity in at least 
one surface of one skin along a line extending generally parallel with and 
spaced at a selected distance from a proximate edge of the first frame 
member. The discontinuity reduces the bending strength of the composite 
panel in the plane of the discontinuity whereby the wall structure is 
adapted to disengage from the confinement means at an applied load 
determined by the selected distance and to collapse in the direction of 
the applied load, but remain positively connected to the second frame 
member. 
In a double-span structure, the composite panel is supported on three frame 
members, i.e., two end frame members and a central frame member. Two 
discontinuities are provided, one adjacent to each end of the composite 
panel. 
Where the two spans are of equal length, the discontinuities are spaced at 
substantially identical selected distances from the proximate edges of the 
adjacent end frame members. The two equal spans will collapse at 
substantially identical selected failure loads. 
Occasionally due to structural steel conditions, the two spans are of 
unequal length. In this instance, the discontinuities are spaced at 
different selected distances from the proximate edges of the adjacent end 
frame members. However the different selected distances are chosen such 
that the two unequal spans will collapse at substantially identical 
selected failure loads. 
In accordance with this invention, the elastic properties of the wall 
structure, that is, the elastic deflection and the working stresses, are 
essentially the same as those of a conventional wall structure. Hence, the 
ability of the present wall structure to resist normal wind loadings is 
not significantly reduced despite the introduction of the discontinuity. 
While the bending strength of the panel in the plane of the discontinuity 
is reduced, the effects of the reduced bending strength are exhibited only 
under abnormally high loading conditions. That is, only after the 
composite panel fails by buckling or yielding at the maximum moment region 
and after the load is redistributed does the discontinuity trigger the 
release mechanism which forces collapse of the panel at the location of 
the discontinuity. 
The present wall structure may also be erected as a single-span wall 
structure wherein the opposite ends thereof are slideably retained on the 
adjacent frame members. In accordance with this second embodiment, the 
composite panel is provided with at least one discontinuity extending 
generally parallel with and spaced at a selected distance from a proximate 
edge of a first frame member. The arrangement is such that the wall 
structure is adapted to disengage from the confinement means at an applied 
load determined by the selected distance and to collapse in the direction 
of the applied load.

DESCRIPTION OF THE PREFERRED EMBODIMENT(S) 
FIG. 1 illustrates a controlled release wall structure 25 of this invention 
erected on a structural framework 26 of which only a vertical column 27 
and horizontal frame members or girts 28 through 31 are illustrated. The 
present wall structure 25 includes at least one and preferably a plurality 
of composite panels 32 erected in side-by-side lapped relation. The 
present wall structure 25 may be erected as a double-span wall section 33 
wherein each of the composite panels, for example, the composite panel 
32', has opposite or first and second panel ends 34, 35 lapping the first 
and third frame members 28, 30. Confinement means 36 is provided for 
releasably retaining each of the panel ends 34, 35 on the first and third 
frame members 28, 30. Fastening means 37 is provided for positively 
securing the composite panel 32' to the second or central frame member 29. 
The composite panel 32' presents a first panel segment 40 spanning between 
the first and central frame members 28, 29; and a second panel segment 41 
spanning between the central and third frame members 29, 30. The first and 
second panel segments 40, 41 have span lengths indicated by the dimension 
lines L. 
In accordance with the present invention, the composite panels 32 have 
first and second discontinuities 65 (see FIG. 5), one positioned between 
the first and central frame members 28, 29 and the other positioned 
between the central and third frame members 29, 30, respectively. As will 
hereinafter be described, each of the discontinuities is formed in at 
least one surface of one skin along a line indicated by the dash-dot line 
38 in FIG. 1, which extends generally parallel with and which is spaced at 
a selected distance "D" from a proximate or adjacent edge 39 of the first 
and third frame members 28, 30. The arrangement is such that each of the 
discontinuities reduces the bending strength of the composite panel 
segments 40, 41, whereby the wall structure is adapted to disengage from 
the confinement means 36 at an applied load determined by the selected 
distance "D" and to collapse in the direction of the applied load. During 
collapse the fastening means 37 maintains the composite panel 32 
positively connected to the second or central frame member 29. 
Preferably the span lengths L are substantially identical so that the 
applied load and the working stresses resulting therefrom are distributed 
substantially equally between the first and second panel segments 40, 41. 
In this instance the discontinuities 65 (FIG. 5) in the panel segments 40, 
41 are provided at substantially identical selected distances "D". The 
equal length panel segments 40, 41 will collapse at a single selected 
failure load. 
Occasionally the position of the horizontal frame members or girts 28 to 30 
will be such that the span lengths L are unequal; and the applied load and 
the working stresses resulting therefrom will be distributed unevenly 
between the first and second panel segments 40, 41. Consequently the 
discontinuities 65 (FIG. 5) in the panel segments 40, 41 are provided at 
different selected distances "D" -- the selected distance "D" for the 
shorter span being greater than the selected distance "D" of the longer 
span. It will be appreciated that the different selected distances "D" are 
chosen such that each of the two unequal spans will collapse at the same 
selected failure load. 
It will also be observed in FIG. 1 that wall sections 33A and 33B, each 
comprising a plurality of the composite panels 32A, 32B, respectively, may 
be erected above and below the wall section 33. The wall sections 33A and 
33B may be single-span or double-span wall sections. 
COMPOSITE PANEL 32: The present controlled release wall structure 
incorporates panels of the type known as composite panels which comprise 
spaced-apart inner and outer skins which are secured in shear-transferring 
relation by means of a structural core. In general the strength of the 
skins is equal to or greater than that of the structural core. The skins 
sustain bending stresses whereas the core sustains shear stresses. The 
bonds between the core and each of the skins develop the shear-transfer 
mechanism. 
Skins suitable for use in composite panels exhibit a modulus of elasticity 
of at least 500,000 psi, and tensile and compressive strengths of at least 
1,000 psi. Suitable skins may be formed from metals such as sheet steel, 
aluminum and the like, wood including laminates such as plywood, glass 
fiber reinforced plastics, glass fiber reinforced gypsum, and fiber 
reinforced concrete. 
Structural cores suitable for use in composite panels exhibit a shear 
modulus of at least 100 pounds per square inch and a shear strength of at 
least 10 pounds per square inch. Suitable core materials include 
foamed-in-place plastics, metal and paper honeycomb members and the like. 
The bonds between the skins and the core must exhibit a bond strength of at 
least 10 pounds per square inch. Adequate bonds are formed between the 
skins and foamed-in-place plastic materials. Well-known structural 
adhesives such as an epoxy structural adhesive normally are employed to 
secure the honeycomb member to the inner and outer skins. 
Typical composite panels 42, 42', and 43 are illustrated in FIGS. 2 to 4. 
The composite panel 42 (FIG. 2) may comprise substantially flat outer and 
inner skins 44, 45 and a structural core 46. The core 46 may comprise a 
foamed plastic core 47 of the foamed-in-place type which during expansion 
self-adheres to the skins 44, 45. Alternatively, the foamed plastic core 
47 may be provided in the form of a slab which is profiled and secured to 
the skins 44, 45 by means of a structural adhesive, in the manner 
suggested in U.S. Pat. No. 3,555,756. For a complete description of the 
composite panel 42 attention is directed to U.S. Patent No. 3,777,430 
which is incorporated herein by reference. 
The composite panel 42' (FIG. 3) comprises a profiled outer skin 44', a 
substantially flat inner skin 45, and a structural core 46. The profiled 
outer skin 44' presents alternating crests 75 and valleys 76 connected by 
webs 77. The structure core 46 may comprise a foamed plastic core 47' 
which fills less than the entire space between the skins 44', 45. For a 
complete description of the composite panel 42' attention is directed to 
U.S. Pat. No. 3,849,959 which is incorporated herein by reference. 
The composite panel 43 (FIG. 4) comprises substantially flat outer and 
inner skins 44, 45 and a structure core 46. The core 46 comprises a 
honeycomb-like core member 48 having its opposite faces secured to the 
skins 44, 45 by a structural adhesive 49. If desired, the cells of the 
core member 48 may be filled with a thermal insulation, e.g., expanded 
silicate such as perlite, foamed plastics material and the like. For a 
complete description of the composite panel 43 reference is directed to 
U.S. Pat. No. 3,998,023 and 3,998,024 which are incorporated herein by 
reference. 
The outer skins 44, 44' and the inner skins 45 of the composite panels 42, 
42' and 43 may, when formed from sheet metal, have a thickness in the 
range of 0.0179 to 0.0598 inches (0.45 to 1.52 mm). 
FASTENING MEANS 37: Referring to FIGS. 5 through 7, the fastening means 37 
may comprise an angle member 51 having a first leg 52 overlying a flange 
53 of the composite panel 32; and a second leg 54 extending through the 
structural core 46 and having a remote end engaging the inner skin 45. 
Fasteners 55 extend through the first leg 52, the flange 53, the 
structural core 46, the inner skin 45 into threaded engagement with the 
central frame member 29. The clip members 51 and the fasteners 55 
cooperate to positively secure the panel 32 to the central frame member 
29. 
CONFINEMENT MEANS 36: In wall structures which incorporate composite panels 
of the type illustrated in FIGS. 2 and 3, individual confinement means 36 
(FIGS. 5 and 8) may be provided for releasably retaining each of the panel 
ends 34, 35 to the first and third frame members 28, 30. Each of the 
confinement means 36 may comprise an angle member 56, similar to the angle 
member 51, and a cooperating fastener 57. 
The angle member 56 has a first leg 58 overlying the flange 53 of the 
composite panel 32; and a second leg 59 extending through the structural 
core 46. The inner sheet 45 is provided with a slot 61 which exposes an 
upper surface of the frame member 30. As best shown in FIG. 5, the second 
leg 59 of the angle member 46 has a remote end 62 engaging the upper 
surface of the frame member 30. The confinement means 36 adequately 
retains the panels on the frame members when the wall structure is 
subjected to normal positive and negative wind loadings. However, during 
collapse the panel ends 34, 35 slide free of the confinement means 36. 
Since the fasteners 57 extend through the recesses 60 and the slots 61, no 
tearing or rupturing of metal is required as the panel ends slide free of 
the confinement means 36. 
Alternatively, as shown in FIG. 9, confinement means 36' may be provided 
comprising a single angle member 56' which bridges the gap between the 
panel ends 34, 35 of the adjacent composite panels 32 and 32A. 
It will be observed in FIGS. 5 and 9 that the panel ends 34, 35 of the 
panels 32 and 32A (and of the composite panels 32 and 32B) are 
spaced-apart and present a gap 63 therebetween. During erection, a 
suitable sealant 64 is introduced into the gap 63 to provide a vapor-tight 
seal. 
Referring to FIG. 5, each of the panel ends 34, 35 is provided with a 
discontinuity identified generally by the numeral 65 which extends along 
the line 38. 
An alternative embodiment of the present controlled release wall structure 
is illustrated in FIG. 10 and designated generally by the numeral 25'. In 
this embodiment, the composite panel 32 is erected on a single-span 
condition. Individual confinement means 36 releasably retain each of the 
panel ends 34, 35 to the first and second frame members 28, 29. In 
accordance with this embodiment, the composite panel 32 is provided with 
at least one discontinuity 65 which is spaced at a selected distance "D" 
from the proximate or adjacent edge 39 of the first frame member 28. If 
desired a second discontinuity 65' may be formed in the composite panel 32 
along a second line 38' which is spaced at a selected distance "D" from 
the proximate or adjacent edge 39' of the second frame member 29. The 
overall arrangement is such that the composite panel 32 disengages from 
the confinement means at an applied load determined by the selected 
distance and collapses in the direction of the applied load. In the 
preferred arrangement, the selected distances "D" are substantially 
identical. 
The opposite ends of the composite panel 42' of FIG. 3 may be adapted for 
use in the present controlled release wall structure in the manner 
illustrated in FIGS. 11 to 13. Slots 84 (FIG. 13) may be provided which 
extend longitudinally from the panel end 82 in the region of each of two 
spaced-apart valleys 76 of the outer skin 44'. The slots 84 may be formed 
prior to or after the panel 42' is assembled. If formed prior to assembly, 
the slots 84 are provided solely in the outer skin 44' and the inner skin 
45 as shown in FIG. 13. If formed after assembly, the slots 84 may also 
extend through the core 47'. The opposite panel end 83 (FIGS. 11, 12) 
comprises an end segment of the outer skin 44' which extends beyond the 
core 47' and inner skin 45 and constitutes a lapping end. At least two 
additional slots 85 may be provided in the same valleys 76 at the opposite 
panel end 83. The slots 85 extend longitudinally from the terminal edge of 
the panel end 83. If the panel 42' (FIG. 11) is to be erected on a 
two-span condition, openings 86 are provided in the same valleys 76 and in 
a central portion 87 of the panel 42'. The openings 86 normally are 
drilled in the field and are adapted to receive fasteners (not 
illustrated) which positively secure the panel 42' to a central frame 
member represented by the dash-dot line 88. 
It will be observed in FIG. 12 that the upper panel 42'A -- also the 
subjacent panel 42'B -- presents a tongue 89 and a complementary groove 90 
along the opposite longitudinal edges thereof. In the region of the tongue 
89, the valley 77 of the outer skin 44' presents a downturned flange 91 
which penetrates the core 47'. The complementary groove 90 is defined in 
part by a laterally inwardly extending two-step flange 92. 
It will further be observed in FIG. 12 that the downturned flange 91 and 
two-step flange 92 have been eliminated along the entire length of the 
panel end 83 of the upper panel 42'B. In the absence of the flanges 91, 92 
the panel end 83 of the upper panel 42'B may be erected in overlapping 
relation with the panel end 82 of the subjacent panel 42'A as illustrated 
in FIG. 13. 
As illustrated in FIG. 13, confinement means 36" in the form of a fastener 
93 extending through the registered slots 84, 85 releasably retains the 
overlapped panel ends 82, 83 on a frame member 94. The frame member 94 
corresponds to either the first or second frame member 28, 30 of FIGS. 1 
and 5. It will be appreciated that as the panels 42'A, 42'B undergo 
bending buckling when subjected to the selected applied load, a dragging 
force is produced which pulls the panel ends 82, 83 free of the fastener 
93. The resistance to release produced by the clamping force of the 
fastener 93 is insignificant compared to the magnitude of the aforesaid 
dragging force. 
DISCONTINUITY: The collapse of the present controlled release wall 
structure at a predictable failure load is accomplished by controlling the 
strength distribution within each of the composite panels. As is known, 
the ultimate bending strength of a composite panel can be calculated and 
depends on the configuration of the panel and the strength properties of 
its components. The moment coefficient of the panel at mid-span 
establishes the load at which the panel will undergo bending failure. In 
accordance with this invention, a discontinuity is introduced which 
weakens, i.e., reduces the bending strength of the panel in a plane P 
(FIG. 5). The plane P extends transversely of and is generally 
perpendicular to the panel and also passes through the discontinuity. The 
moment coefficient of the panel in the plane P, that is, at the 
discontinuity, is less than the moment coefficient of the panel at 
mid-span. Thus a composite panel provided with an appropriately positioned 
discontinuity will fail at a predictable failure load or pressure 
threshold. Also, a composite panel of given configuration can be caused to 
fail predictably at any failure load within a range of failure loads by 
positioning the discontinuity at a preselected distance "D" (FIG. 5). The 
general relationship between the failure load of the present controlled 
release wall structure is discussed hereinafter in connection with FIG. 
23. 
FIG. 14 illustrates a composite panel 32 having a covering width W and 
which, for the purposes of illustration, is provided with discontinuities 
of various forms. It should also be appreciated that the discontinuity may 
be provided in either the inner skin 45 or the outer skin 44. Also, the 
discontinuity preferably is formed in the panel at the factory. 
Alternatively the discontinuity may be formed in the panel at the erection 
site. 
The discontinuity 65 preferably comprises a cut 66 (FIGS. 14 and 15) such 
as made by a saw blade prior to assembling the panel 32 or such as made by 
an electric shear after the panel 32 has been assembled. The cut 66 
preferably is formed in the skin 45(44) without penetrating the core 47 by 
more than 1/8 inch (3.2 mm). If desired, a sealant 60 or other suitable 
material may be introduced into the cut 66. Where the cut 66 is provided 
in the inner skin 45, the sealant 60 serves solely to conceal the cut 66. 
Where the cut 66 is provided in the outer skin 44, the sealant 60 not only 
conceals the cut 66 but also provides weather protection for the core 47. 
As illustrated in FIG. 14, the cut 66 may extend substantially entirely 
across the full covering width W of the composite panel 32. Alternatively, 
the cut 66' may have a length which is less than the full covering width 
W. It has been determined that the positive and negative failure loads of 
the present composite panel are not only a function of the selected 
distance "D" but also are a function of the length of the cut 66. For 
example, the composite panel can be caused to fail predictably at a 
selected negative failure load by appropriate choice of the selected 
distance "D". The positive failure load at which the same composite panel 
will fail can be rendered substantially equal to, greater than or less 
than the selected negative failure load by adjusting the length of the cut 
66. In general, the positive failure load decreased curvilinearly as the 
length of the cut 66 is increased. It will be appreciated that the present 
invention provides a means by which a composite panel can be adapted to 
fail predictably over a wide range of selected applied loads, and further 
a means by which the positive and negative loads at which the panel will 
fail can be regulated. 
The discontinuity 65 may also comprise a cut 66" (FIG. 16) such as formed 
by shearing the skin 45(44) wherein adjacent skin portions 95, 96 are 
laterally offset relative to each other. In the preferred arrangement, the 
skin portion 95 is substantially entirely laterally offset from the skin 
portion 96 thereby to preclude a bridging effect when the skin 45(44) is 
in compression. 
The discontinuity 65 may extend intermittently along the line 38 and 
comprise spaced slots 67 (FIGS. 14, 17) of identical lengths or of 
different lengths. 
The discontinuity 65 may also take the form of spaced perforations or 
openings 68 (FIGS. 14, 18, 19). Each of the perforations or openings 68 
may be formed, for example, by drilling, after the panel 32 has been 
assembled. Alternatively, the skin 45(44) may be provided with openings or 
perforations 68' (FIG. 19) prior to assembling the panel 32. Where a 
structural core of foamed plastic materials 47 is provided, the foamed 
plastics material may extend into the perforations or openings 68'. 
The discontinuity 65 may also comprise a groove 69 (FIGS. 14, 20) formed in 
an exterior face 70 of the skin 45(44). The groove 69 presents an open end 
71 in the plane of the exterior face 70 and a bottom 72 proximate to the 
interior face 73 of the skin 45(44). Alternatively, a groove 69' (FIG. 21) 
may be provided in the interior face 73 of the skin 45(44). 
The discontinuity 65 may also take the form of spaced grooves 74 (FIGS. 14, 
22). The spaced grooves may be provided in the exterior face 72 (FIG. 22) 
of the skin 45(44). Alternatively, the grooves may be provided on the 
interior face of the skin 45(44). 
In composite panels wherein either or both of the skins 44, 45 are 
profiled, the discontinuity is formed at least in the crests. For example, 
in the composite panel 42' (FIG. 3) the discontinuity may be formed at 
least across the full width of each of the crests 75. If desired, the 
discontinuity may also be provided in the webs 77 and/or in the valleys 
76. 
SELECTED DISTANCE "D": A general relationship between the failure load of 
the present controlled release wall structure and the selected distance 
"D" is graphically presented in FIG. 23. For this discussion consider a 
wall structure assembled from plural composite panels, such as illustrated 
in FIG. 2, erected on a span of length L as in FIG. 5. Two modes of panel 
failure are possible. The panel may fail at mid-span (L/2) or at the 
discontinuity 65. 
Panel failure at mid-span (L/2) is governed by the moment coefficient of 
the composite panel at mid-span. Thus, if only failure at mid-span is 
considered, the failure load is constant and is represented by the dotted 
line 78 in FIG. 23. 
Panel failure at the discontinuity is governed by the moment coefficient of 
the composite panel at the discontinuity and by the selected distance "D". 
Thus, if only failure at the discontinuity is considered, the failure load 
decreased curvilinearly, for example, in the manner represented by the 
dotted line 79 in FIG. 23, as the selected distance "D" is increased. It 
will be observed from line 79 that as the selected distance approaches 
zero, the failure load approaches infinity. However, at a selected 
distance of L/n (n being greater than 2), the ultimate bending strength of 
the composite panel is exceeded and the failure load equals that 
represented by line 78. At a selected distance "D" of L/n, the composite 
panel may fail either at mid-span or at the discontinuity. 
The failure load of the present controlled release wall structure as a 
function of the selected distance "D" is represented, in FIG. 23, by the 
solid line 80 which consists of segments of the lines 78 and 79. As the 
selected distance "D" is increased from zero to L/n, the failure load is 
constant. As the selected distance "D" is increased from L/n to L/2, the 
failure load decreases curvilinearly along the line 80. For selected 
distances "D" greater than L/2, the failure load increases along a line 
represented by the dotted line 80', the dotted line 80' being a mirror 
image of the solid line 80. 
It will be appreciated that the span length also affects the failure load 
versus distance "D" relationship. In FIG. 23, the line 80 represents the 
failure load curve of a composite panel of span length L. For span lengths 
larger than L, the line 80 will assume positions below that in FIG. 23. 
Conversely, for span lengths less than L, the line 80 will assume 
positions above that in FIG. 23. 
Since the bending strengths at mid-span and at the discontinuity of one 
composite panel configuration will differ from those of a different 
composite panel configuration, numerical values of the minimum and maximum 
selected distances "D" cannot be given. However, since the selected 
distance "D" also varies with the span length for each composite panel 
configuration, the selected distance "D", in general, may vary from about 
L/40 to about L/2. 
Failure loads ranging from about 20 pounds per square foot to more than 150 
pounds per square foot can be provided. In buildings where the principal 
concern is occupant safety against rapidly increasing pressures generated 
by explosions within the building, a failure load range of from 20 to 40 
pounds per square foot is desired. In buildings where the structural 
framework is to be protected against stresses created by abnormally high 
wind pressure generated during tornadoes, hurricanes and the like, a 
failure load range of from 40 to 120 pounds per square foot appears to be 
adequate. 
When a wall structure of the type illustrated in the drawings experiences 
abnormally high wind pressure corresponding to the selected failure load, 
the composite panel undergoes bending buckling and produces a dragging 
force which pulls the panel ends 34, 35 free of the confinement means. The 
resistance to release offered by the confinement means is insignificant 
compared to the magnitude of the aforesaid dragging force. Consequently, 
the failure load of the present controlled release wall structure is not 
affected by the confinement means. 
In accordance with the present invention, a controlled release wall 
structure having a specified failure load requirement can be provided by 
(a) selecting, for a given span, the type of composite panel which will 
sustain the deflection and working stresses expected under normal wind 
load conditions; and 
(b) thereafter selecting the discontinuity spacing -- the selected distance 
"D" -- which will provide the specified failure load. 
EXAMPLE: Two samples of a composite panel of the type illustrated in FIG. 2 
were prepared and tested. Each of the composite panels was assembled from 
22 gage (0.076 cm) inner and outer skins and a foamed-in-place 
polyurethane core having a core density of 3.48 pounds per cubic foot. The 
composite panels each had a length of 20.25 feet (6.17 meters) and had a 
covering width W (FIG. 14) of 297/8 inches (75.9 cm). A discontinuity in 
the form of a cut 1/4 inch (0.64 cm) wide and 29 inches (73.7 cm) long was 
provided in the inner skin at a distance of 25 inches (63.5 cm) from the 
end of the panel. Each composite panel was supported on three 5 inch (12.7 
cm) wide beams at a center-to-center distance of 10.25 feet (3.57 meters). 
The opposite ends of the composite panel overlapped the end beams by 1 
inch (2.54 cm) resulting in a selected distance of 24 inches (61 cm). The 
first composite panel failed at a positive loading of 72.1 pounds per 
square foot (352 kilograms per square meter). The second composite panel 
failed at a negative loading of 77.9 pounds per square foot (380 kilograms 
per square meter). The average failure load was 75 pounds per square foot 
(366 kilograms per square meter) resulting in a deviation of plus or minus 
4%.