Pre-Stressed Open (Curtain-) Side Container Fabrication Transport and storage containers are typically fabricated from an assembly of discrete rails or beams and infill panels, welded together at localised spot joins or seams.

Moreover, deck beams themselves are also fabricated, rather than say hot rolled in a strip mill, to a desired cross-section, to allow thin plate sections for weight saving.

Residual Stress Entrapment This introduces residual stresses, attendant local welding heat-which are'trapped'in the structure, impacting upon structural performance under load.

Residual or trapped stresses can admit local yield upon initial loading-re-distributing residual stresses and engendering a permanent deformation or set.

Moreover, residual stresses undermine component and overall structure fatigue life.

Residual stresses also allow the structure to perform in a plastic, rather than elastic way-and thus deflect more than an equivalent elastic structure, thus requiring more tolerance for operating deflections.

If located at operational stress concentration regions, such as deck beam ends and deck to end post or wall corner joints, accumulated stressing is aggravated-leading to fatigue cracking and structural failure.

Platform Deck-Flat Rack In a minimal container format, such as a platform deck, in particular one surmounted by bounding end posts or walls, and commonly known as a flat rack, longitudinal deck beams extend unsupported over an entire container span or footprint, between opposite ends and attendant end posts and/or walls.

Deck Sag Deck cargo loading (between deck beam end support) tends to induce a'downward'bow or sag between supported ends.

Arch Camber Excessive such sag can impede stacking but can be countered or offset by contriving in construction an upward-shallow arch-pre-camber deck profile.

The beam can be made with an upward camber in which during fabrication residual stresses become embedded, due to (differential weld) expansion and shrinkage.

After welding, the camber can be reduced by pre-loading to a smaller camber or preferably none

at all (particularly in the case of a curtain side container).

Elastic Deformation In successive cargo loading and unloading cycles the intention is that deck beams transition elastically between upward bowed and flatter, albeit not flat, profiles.

End Wall Flex Any end walls would be allowed to flex by movement of deck ends.

Permanent Set However, with a fabricated (welded) plate beam construction, an initial gross and permanent set can arise, even when a cargo load within design limit is applied.

Yield This is associated with yielding beyond the material elastic limit as welding stresses are re- distributed, before reaching a (re-) stabilised, (re-) set condition-beyond or after which elastic bending under live cargo loading can arise.

Absent special measures, such as those which the present case addresses, this would create a pronounced and excessive'yield'sag, beyond that for which standard pre-curvature was intended to compensate.

Thus, using a traditional counter profile constructional approach, additional bow or curvature would have to be introduced into a deck beam.

Prior Art The broad principle of loading to contrive stress (re-) distribution is well established.

A related case US 6,317, 981 employed pre-stressing individual flat rack (deck) beams to re- distribute welding-induced local stresses to counter initial yield.

Pre-stressing was applied selectively over the beam profile in this same (downward) direction of normal cargo loading in use.

Thereafter somewhat improved material behaviour was achieved through work hardening of material taken beyond the elastic limit-attendant compressive and tension stresses in lower and upper beam flanges upon loading deformation.

Pre-Stressing Pre-stressing deformation post fabrication can: counter initial'permanent yield'tendency or susceptibility under initial cargo loading ; reduce, take out, or consume some pre-camber profiling incorporated in fabrication; yet

'leave sufficient residual (arch) pre-camber to counter or accommodate flexing under cargo load.

Pre End Frame Fitment If end frames, posts or walls, are fitted before pre-loading, they may not remain orthogonal to the base after pre-loading.

Thus, in order to prevent end frames from being splayed outwards or canted inwards-beyond tolerable modest flexing in cargo (un) loading cycles-it may be necessary to pre-load a flatrack base before end frames are fitted.

Thus the Applicant has fitted end frames, set initially square or orthogonal to the ends of a pre- cambered deck profile-after an initial pre-stress settling or yield load has been applied and relieved.

Corner Stress US 6,317, 981 is not concerned with closed frame containers, such as curtain sided, roofed between end wall formats, nor with stresses at corners, in particular end wall base to deck beam ends.

Such corner stresses remain unrelieved by hitherto known techniques and represent vulnerable weak point.

Thus, loading cycles-and attendant longitudinal beam flexing can have a progressive adverse fatigue life impact.

Open (Curtain) Side Whilst the above approach might be tenable in a platform deck or open-top flat rack, it is not so when a roof is present, as in an open (curtain) sided configuration-where more severe geometric constraints arise on cross-sectional form.

Deformation is critical for a so-called'curtain-side'container format, with a roof overlying a platform deck and surmounting opposite end posts and/or walls.

Roof rails brace overall open-sided form by holding the end frames or posts against rotational deflection and thus inducing in the posts and on to deck side rails a bending moment which counters bending induced by vertical cargo loads.

Side rails can therefore be of somewhat less deep section than, say, for a minimal open-topped flatrack.

End posts or walls can be less robust than, say, for a collapse fold flat rack, with no upper span brace such as a roof.

Reliance is placed upon open longitudinal side access-and so any deformity, such as bowing or lozenging, impacts adversely upon loading access and so capacity.

Rather, a rectangular or orthogonal sided access aperture profile must be preserved.

Deck bending while ends are constrained by a roof between end walls can stress bottom corner end joints between end wall bases and deck beam ends.

Thus a roof is under compression, which is more readily withstood, while a deck is under tension by stretch and which is less readily withstood.

In fact, with an l-section deck beam differential compression and tension stresses are experienced by top and bottom flanges respectively.

These can remain unresolved at bottom corner joints with end walls-with attendant stress concentration and imbalance, undermining fatigue (cyclical loading) strength.

Longitudinal bending loads are aggravated with extended container formats-to counter which inset bracing/support posts and/or side stub walls or even an'I'beam profile through intermediate divider wall have been devised.

Similarly, structural bracing is even more critical with wholesale (re-) movable roof and local removable roof access panels which have been devised.

Curtain Side Pre-loading Considerations Pre-loading (deck platform curvature) deformation, such as employed with open top flat racks, cannot simply be ported to a curtain-side format-not least without special consideration of corner joint stresses.

Another consideration is that container test standards limit maximum tolerable deck deformation upon and after test loading.

Pre-stressing load and attendant curvature or camber must address an initial permanent set tendency, yet preserve a stable flat loading platform.

End posts or walls can be fitted after deck pre-loading deformation to preserve an upright stance - or at least inhibit excessive toe-in upon deck loading.

Statement of Invention A method of using permanent yield or set in a fabricated frame, to bolster ongoing behaviour under load including the steps of incorporating an arched curvature or bow profile upon fabrication, pre-loading to settle the profile and counter pre-profile curvature, to contrive a flatter, straighter, squarer or more orthogonal geometrical form, by relieving, re-distributing, re-disposing or re-aligning residual stresses preparatory to active loading cycles in operational use.

A method of structure construction with a prefabricated beam, including the step of incorporating a camber profile in fabrication sufficient to encompass initial, one-off, pre-loading deformation and yield set and cyclical loading elastic deflection upon active (un) loading in operation.

A method of structure construction with a prefabricated beam including the step of pre-loading to re-deploy inherent stress upon fabrication, to achieve residual stress character and distribution favourable to ongoing operational loading.

A prefabricated structure constructed by the method of any preceding claim.

A pre-fabricated structure of individual elements joined by local heat welding with attendant induced internal stresses, an a preliminary arched curvature or camber, reduced or countered by preliminary loading, beyond an elastic limit to permanent yield.

A platform deck container, with deck beams and/or related superstructure pre-fabricated with an arched curvature or bow and pre-loaded beyond an elastic threshold into plastic deformation, in turn to (re-) align fabrication induced stress better to counter loading deformation.

A pre-fabricated flat rack container, with pre-loading of corner joints, between end posts and/or walls and platform base for favourable stress re-disposition A container, pre-loaded, after fabrication and assembly, and before end or super-structure mounting. to relieve and/or re-align stresses introduced by fabrication and assembly, such as local welded joint heating.

A container, stressed by pre-ioading, through initial elastic stress/strain (recoverable deformation) range, to somewhat (20%) beyond a yield point to plastic deformation (permanent change-internal structure realignment), to achieve work hardening/toughening (stored strain energy), and/or re-disposition or re-alignment of stress introduced upon fabrication, such as by local welding heat, better to withstand fatigue from ongoing (un) loading cycles.

A container, configured as closed frame, such as a curtain-side format,

with platform base, opposite end posts and/or walls, roof overlying base and surmounting end posts/walls, pre-stressed to flatten initial deck curvature or bow, and maintain generally orthogonal configuration in use.

A container, with roof pre-tensioned, by inter-coupling end walls splayed by deck beam bow upon pre-loading, to counter compression otherwise arising from deck deformation under cargo loading, with attendant inward end post/wall tendency.

A container pre-loaded after fabrication such that fabrication stresses, as from local heat by welding, are re-distributed by pre-loading, to contrive an assembled form better able to withstand deformity and preserve geometry under operational fatigue loading.

A method of container pre-stressing or stress (re-) alignment, comprising the steps of applying pre-load across a deck beam and/or between deck beam and end posts or walls.

A pre-stressing method, taken somewhat (say some 20%) beyond an initial material elastic limit, into a permanent yield region, but in which ongoing loading and deformation recovery can take place elastically, albeit at a higher stress range, whereby the structure is effectively work hardened or stiffened better to resist loading cycle fatigue.

A fabricated container deck beam pre-stressed overall after beam fabrication.

In this context, overall can signify selectively locally applied stress at, over or around beam mid- span and at or towards each end.

A method of flat rack container construction including the step of pre-loading a pre-fabricated deck beam selectively at, over or around beam mid-span and/or at or towards beam ends, to redistribute stresses-including corner joints-induced upon fabrication, such as localised welding heat.

More specifically, beam fabrication stresses, such as from local welding heat, are re-distributed by pre-loading, to contrive a beam better able to withstand deformation, operational fatigue loading and preserve geometry.

Preferably, such pre-load counters (pre-) fabrication camber and achieves a generally straight deck profile Modest camber may be allowed in some designs although it does restrict the side loading height (in a curtain side container) between top roof rail and base side rail.

Thus, it is desirable to achieve a level horizontal floor.

Analysis & Rationale Under normal circumstances a welded joint in a structure is stressed to tensile yield after manufacture (fabrication).

If the structure is then operated under normal service conditions, welds are stressed beyond yield.

When unloaded, any surrounding structure that has remained within material elastic limit pulls the overall structure back to approximately the original geometry.

This leaves the weld with a residual compression.

Such compression is taken account of in standard fatigue analysis.

Provided the structure is not loaded beyond'normal' (prescribed standard, such as CE), residual stress will remain constant.

However, application of an initial overload well beyond normal in-service loads, will generate an additional compressive stress-over and above that generated by in-service loading.

Standard fatigue analysis techniques allow factoring down of compressive stress range, as it causes much less damage.

Extra residual stress-over and above normal (prescribed standard) value-incurred by the over load will effectively reduce the maximum tensile stress that a weld'sees'-and as a result will increase structure fatigue life.

Thus, some aspects of the invention are concerned with introducing-by judicious localised pre- loading-a new residual stress which: enhances fatigue life ; enhances elastic limit to inhibit further permanent deformation or set; and re-aligns residual weld stress; so stabilising the structure in service.

In practice, local material working or pre- (di) stressing can include diverse techniques, such as shot peening, dead weight, hydraulic rams, rollers, combined pre-load and shot peening; to rail bracing with struts to end walls.

Terminology-Pre-Stressing/Pre-Loading Pre-stressing or pre-loading can be taken to embrace stress (re-) alignment, stress (re-) disposition, (re-) deployment or even stress relief of earlier induced stresses.

Pre-loading Deck Beams, End Posts/Walls, Corner Joints Primarily, it is envisaged that such pre-stressing would address deck beams.

That said, pre-stressing of deck beams in relation to end post or end wall fitment-effectively corner joint pre-stressing-is envisaged.

In addition, pre-loading and/or pre-stressing of deck beams through attached corner posts and/or end walls could be contemplated.

A curtain-side container format, with platform base, could be pre-stressed, to work through, absorb or counter certain (excess) preliminary deck curvature or bow introduced in fabrication and re-distribute internal stresses, before fitment of opposite end posts and/or walls, and/or roof overlying base and surmounting end posts/walls.

In practice, such pre-stressing, (pre-) stress (re-) alignment or (re-) disposition can introduce residual tension stresses at deck beam centre or mid-span and residual compression stresses at beam ends.

The latter have a beneficial effect upon fatigue life, given operational stress concentration at beam ends.

In a curtain-side container, base pre-stressing re-distributes residual stresses, so that, when fitted with corner posts/walls and roof, these stresses are translated to this super-structure.

In a particular construction, a curtain-side container features an upwardly cambered deck, fitted with end frames only, before pre-loading.

Preferably end frames, posts or walls, are fitted before pre-loading, and are contained so that they may remain orthogonal to the base after pre-loading, and still benefit from pre-stressing of connections between end frame and base.

Pre-loading can be performed while holding the tops of end frames or walls at a desired span.

This may be achieved by clamping top corner castings of end frames or walls to a dedicated jig, itself set to a desired span, or by welding temporary tie bars between opposed corner castings.

In this way, critical top profile rectangular geometry is preserved.

Reliance is placed upon sturdy roof beams, robust top corner joints and sufficiently stiff end walls-albeit typically the latter are still somewhat less robust than employed in an open top flat rack.

Some leeway in modest deck flexing can be admitted, without conflict with a mounting surface or a stacked underlying container.

Pre-loading is desirably applied adjacent deck beam ends, and at mid-span.

The pre-load will be calculated to level deck beams and re-distribute stresses within base and end frames-including intervening corner joints.

Once pre-load is complete, the deck could either retain a modest arch camber, or have a generally flat and level surface, with end frames set at approximately 90 degrees to the base.

In either case, elastic deformation and beam deflection upon cargo (un) loading does not take the deck or overall profile unduly out of tolerable geometry.

On a curtain-side container, a roof may then be fitted between end frame tops-without introducing further stresses to the structure.

Alternatively, the base alone may be pre-loaded and then end frames and then roof fitted.

This would preclude post to base joint pre-load, but attendant unresolved corner stress concentration could be tolerated by fitment of corner reinforcements.

If the end frames are required to be pulled towards one another as the roof is fitted, base centre stress increases, but a pre-stress is also induced in post to base corner joints in a direction opposite to that induced during cargo loading.

If end frames are pushed outwards (splayed) during assembly, opposite stresses arise.

Either may be advantageous, however, the first method would be more likely to prevent cracking.

Pre-Loading/Pre-Stressing It is envisaged that localised, support, jacking and (counter-) bracing could be employed in container production.

The intention is to create desired pre-loading and attendant pre-stressing, or rather pre-stress (re-) alignment or (re-) disposition, after fabrication and (sub) component welding assembly.

Thus, local support, spreader beams and hydraulic jacks would be deployed to apply pre- loading.

Pre-load Limit Care is taken not to apply too much pre-load to a base, as this may result in more strain at the post-base corner joint rather than less.

Thus, for example, some 30mm of pre-load deformation will likely reduce corner stresses, whereas 40mm will likely increase them.

Embodiments There now follows a description of some particular embodiments of the invention, by way of example only, with reference to the accompanying diagrammatic and schematic drawings, in wh ich : Figure 1A shows pre-loading of a container base by bending the base platform from a slightly upwardly cambered form into a somewhat flatter or more level form;

Figure 1 B shows pre-loaded or stress-adjusted container of Figure 1 A-a marginal residual arch, bow or curvature may be retained, albeit not apparent, to counter or accommodate deck (elastic) flex deformation under cargo loading ; Figure 1 C shows roof fitment to pre-loaded container of Figure 1 A to create a re-configured orthogonal profile as an open (curtain) sided format; the roof beam serves as tie to counter relative movement of end post or wall top fittings.

Figure 2A shows a plan view of a curtain-side container format embodying pre-loading or stress re-distribution according to the invention; Figure 2B is a side elevation view of the container of Figure 2A; Figure 2C is an end elevation of the container of Figures 2A and 2B, taken from an access end; Figure 3A shows a 3-D isometric view-taken somewhat from above and to one longitudinal side - of the container of Figures 2A through 2C; Figure 3B shows another 3-D isometric view of the container of Figure 3A-taken from below and one side; The container of Figures 2A through 3B also features an extended span format and 1'-section intermediate stub wall bracing at the opposite end to the access end.

Figures 4A through 4C depict pre-loading a curtain-sided container according to the present invention; More specifically: Figure 4A shows a deck with end posts/walls mounted upon a jig or fixture to hold end post or wall tops at a desired separation or span, preparatory to pre-load stressing; Figure 4B shows the arrangement of Figure 4A with pre-load applied to deck centre (mid-span) and ends; Figure 4C shows the container of Figure 4B once pre-load is complete and with permanent roof fitted.

Figures 5A through 5C show an alternative pre-loading sequence according to the invention, for a curtain-sided container; More specifically : Figure 5A shows a deck or base with built-in arch camber, pre-loaded at mid-span (longitudinal centre) and ends; Figure 5B shows the base of Figure 5A after pre-load, being fitted with end posts/walls and overlying and intervening roof; Figure 5C shows the container of Figure 5B with all elements secured in place.

Referring to the drawings, double-headed arrows are used to represent deck beam 11 and end post or wall 12 pre-loading or pre-stressing.

This is undertaken in order to re-align, re-dispose or re-deploy stresses originally introduced upon fabrication and local heat welding component assembly-particularly, where l-profile deck beams 11 are employed.

Thus, the intention is to contrive a more favourable residual stress regime-but not necessarily to extinguish altogether residual or trapped stress if this can lead to a favourable ongoing behaviour under load.

Deck beams 11 are conveniently (pre-) fabricated with an upward camber or arch-shown in broken line in Figure 1A.

The intention is to counter or accommodate downward deformation, bending or sag, upon cargo loading.

Generally, a rectangular outer profile limit is desirable for compatibility with other such containers and handling facilities.

Excessive base deck sag could contact and interfere with a juxtaposed underlying container or a cargo carried thereby.

Even before cargo loading, some entrained residual stress arises from deck beam pre- fabrication by localised welding heat.

Thus, say, an l-section, U-section, C-section, or box beam can be fabricated with an inherent bow or curvature.

(Post-fabrication) pre-load of a platform deck or individual deck beam 11 serves to counter or re- configure this camber, to produce a generally flatter, even if still not entirely straight and level surface profile.

Without initial (upward) counter camber, normal (within design limit) cargo loading could produce undesirable sag or downward bow of deck 11.

In a curtain-sided container format 10, any base 11 deformation is critical, as it impacts adversely upon overall rigidity and profile uniformity or symmetry.

More specifically, the joint 17 between a base 11 and end frame 12 in a curtain-side container 10 can be put under severe stress if the base 11 itself is stressed.

This is because the tops of the side walls or posts 12 are constrained from movement by an intervening and bracing roof element 14.

The intention is to preserve orthogonal roof 14 and deck 11 to end post or wall 12 corner geometry and a rectangular side (un) loading access aperture.

Load Distribution-Flatrack vs Curtain Side In an open top flatrack deck bending induces most severe loading at mid-span, where bending deformation is greatest.

In contrast, in a curtain side, loading is severe not only at mid-span, but at bottom corner joints.

Roof rails 14 are also subject to compression, by inward deflection of end posts or walls 12 through deck 11 sag upon cargo loading.

Although pre-load or pre-stress has been employed in open top flatrack construction, no special consideration has been given to base 11 and post 12 corner joint 17-of critical concern in a closed frame format such as a curtain side.

Thus, previously pre-loading has generally been applied to a centre region or mid (longitudinal) span of a deck beam 11-as this is the area most prone to sag.

Figures 1 A through 1 C show one method of pre-loading a curtain-side container 10 according to the present invention.

Figure 1A shows pre-loading of deck 11, to deform it from an initially (pre-fabricated) upward camber (depicted in broken line) into a generally somewhat flatter-if still not entirely flat base 11.

In this example, side posts/walls 12 are fitted prior to deck 11 pre-loading, with roof 14 fitted afterwards.

Thus, some flexing of post/walls 12 is permitted relative to base 11 with inward cant or lean upon loading and outward splay upon recovery or relaxation.

Marginal deflection can be countered or suppressed upon roof 14 fitment, through tension or compression load transfer.

Figures 2A through 3B show more detailed views of a constructed curtain-sided container 10, comprising a pre-loaded base 11, roof 14, end access doors 15, and side curtain 16-which is shown drawn to one end for side access.

Figures 4A through 4C show an alternative method of pre-loading a curtain-side container 10 to that of Figures 1A through 1C.

In this example, base 11 is again pre-loaded once end frames 12 have been attached, however, in this case the top corner castings 13 of each end post/wall 12 are held in position during pre- loading.

Thus, as shown in Figure 4A, base 11 has an initial upward camber such that end posts/walls 12 are slightly outwardly splayed.

Top corner castings 13 are first pulled into alignment with jig 18 which is configured to hold (tops of) end posts/walls 12 at a desired finished span.

For example, for a 45ft (1 3. 7m) container, corner castings 13 will be held an appropriate distance apart.

Jig 18 may comprise opposed end capture fittings with intervening bracing, or may be a temporary tie bar of appropriate length.

While end posts/walls 12 are held in position by jig 18, pre-loading is applied to base 11 at both central (mid-span) and end regions.

As tops of end frames 12 are constrained from movement, pre-loading of base 11 will re- distribute stresses-not only within base 11 itself but also at corner joints 17 between base 11 and end frames 12.

After pre-loading, top corner castings 13 should be aligned for container roof 14 fitment- without introducing further stresses or strains.

Figures 5A through 5C show yet a further method of pre-loading a curtain-side container 10 to that shown in Figures 1A through 1C and 4A through 4C.

In this example, a base 11 is pre-loaded prior to end frame 12 fitment.

Again, pre-load is performed at the centre (mid-span) and ends of deck beams 11.

Once pre-load is complete-and initial (fabricated) camber of deck beams 11 has been somewhat reduced suppressed or countered-end frames 12 and roof 14 are fitted.

These can be attached sequentially, or as a single pre-fabricated unit-as shown in Figure 5B.

Critical high stress regions, such as beam ends, and deck 11 to end post or wall 12 corner joints 17, can be'favourably're-stressed or stress (re-) aligned according to the invention.

Thus loads can be applied between end posts or walls 12 and deck beams 11.

For clarity, deck beam 11 and end post or wall 12 deformation is exaggerated somewhat in Figures 1A through 1C and 4A through 5C.

Mix and Match Features Generally, in the embodiments, where feasible and appropriate, features may be mixed and matched to suit circumstances.

It is not feasible to describe every such feature combination.

Claim Brackets In the claims, phrases in brackets, vis {...}, alongside claim numbering are for ease of reference and themselves form no part of claim scope or interpretation.

Component List 10 container (curtain side format) 11 platform base 12 end post/wall 13 handling capture fitment 14 roof 15 access end 16 curtain 17 corner joint 18 jig