GLUED LEDGER HEAD

Abstract

A modular scaffold component of different material components advantageously uses the durability and reliability of conventional type steel ledger heads adhesively secured to by an aluminum or aluminum alloy structural member. In a preferred embodiment the structural member is an extruded elongate tube and in a further preferred structure the elongate tube is of a non circular cross section having thickened top and bottom portions preferably interior to a circular outer surface. These thickened portions provide additional strength and structural characteristics such that the component can be freely substituted for the equivalent steel component. In this way the component may be added to existing systems to take advantage of the reduced weight thereof without requiring a dedicated system or rendering an existing system obsolete.

Description

FIELD OF THE INVENTION

The present invention relates to components for modular scaffolding systems and in particular relates to components made of two different materials.

BACKGROUND OF THE INVENTION

Modular scaffolding systems are extensively used in the building and repair industries and provide safe and efficient access to elevated areas. Modular scaffolding systems have advantages over the conventional tube and clamp systems in that the components connect to one another at predetermined positions and the systems are more cost effective to erect and tear down.

Typically modular scaffolding systems are made of galvanized steel components. There are a number of well known proprietary arrangements that allow the components to be securely fixed to each other. In most cases the systems are not cross compatible.

Galvanized steel is the material of choice as it is robust and able to withstand shock impacts and provide good structural strength required to support the loads that are applied to the scaffolding from wind, materials and personnel.

In some industries there is an increasing tendency to favour the use of lighter weight scaffolding systems in general and in particular to use aluminum scaffold products. For example, aerospace applications and computer/IT applications often use aluminum scaffolding products as such components are lighter in weight and if accidentally dropped are less likely to cause extensive damage to the surroundings compared to the heavier galvanized steel product.

All aluminum modular scaffolds have not been considered acceptable for industrial applications (such as refineries) as the end connections (ledger heads etc.) of these components are prone to damage or need to be of a significantly larger size to resist abuse and shock loads that are common in the work place. In Canada the use of aluminum scaffold products in the industrial market has generally been restricted to aluminum tube and clamp systems that use aluminum tube and steel tube couplers.

Although aluminum scaffolding systems have not been generally accepted, such systems are considered desirable due to the lighter weight of the components. Workers who are erecting the system or tearing it down certainly prefer the lighter weight of the components. Therefore in general the assemblers would prefer to use lighter weight components for ease of assembly however the actual labour component for erecting aluminum tube and clamp systems is much higher.

A hybrid system that proposed using steel connecting heads mechanically pinned or fastened to aluminum tubes was not successful or accepted as the softer aluminum tube deforms at the pin or fastening point compromising the mechanical connection and rendering the system prone to damage.

The present invention seeks to overcome a number of deficiencies with respect to the prior art and advantageously use a combination of steel elements secured to aluminum tubes to provide a system which is both effective and convenient to install due to the reduce weight thereof.

SUMMARY OF THE INVENTION

A modular scaffold component according to the present invention comprises first and second steel ledger heads with each ledger head including a fastening element to mechanically connect the ledger head to spaced scaffold support members. An elongate tube extrusion of an aluminum or aluminum alloy is adhesively secured to each ledger head and forms a structural element therebetween. The elongate tube extrusion in each ledger head has an overlapping sleeve type relationship with opposed overlapping surfaces secured by an adhesive structurally connecting the ledger heads and providing a secure mechanical connection of each ledger head to the tube extrusion for use in a scaffold system.

According to an aspect of the invention the modular scaffold component includes a steel tube connecting stub sized for receipt in the elongate tube extrusion with the adhesive securement therebetween.

According to a further aspect of the invention the steel tube connecting stub overlaps with the elongate tube extrusion over at least one and a half inches in the length of the elongate tube extrusion.

In a further aspect of the invention the steel tube connecting stub is welded to a rear surface of the ledger head.

In a modular scaffold component according to the present invention the component includes at least a ledger head and a connected elongate tube. The improvement comprises an adhesive securement of the ledger head to the elongate tube and each ledger head includes a connecting portion having an overlapping sleeve type relationship with an end of the elongate tube. Preferably an adhesive component is provided within a gap of the overlapping sleeve type relationship and forms a distributed mechanical connection of the elongate tube to the at least one ledger head. The elongate tube is of an aluminum or an aluminum alloy material and the ledger head is of a steel material.

In a preferred aspect of the modular scaffold component the adhesive is a two part adhesive forming a permanent rigid connection of the ledger head to the elongate tube.

With the present invention it is preferable that the elongate tube includes interior reinforcing at the top and bottom thereof to improve the characteristics of the elongate tube with respect to bending. Reinforcing on the interior is preferred as the outer diameter of the aluminum tube can be the same as an equivalent steel component. This allows the composite modular component to be used throughout the system and in particular allows clamping arrangements used with most modular systems to also engage the aluminum tube component.

Preferably the reinforcing on the interior of the aluminum tube is also designed to allow a particular registration with the ledger head. The ledger head preferably includes a portion that is inserted into the elongate tube and cooperates therewith to provide a predetermined registration. In this way the orientation of the ledger head with respect to the elongate tube is simplified and the manufacture of the component is also simplified.

Reinforcing of the elongate tube also has the desirable characteristic that the strength of the component will be the same or approximately the same as the corresponding steel component. The composite component is lighter weight and easier to use, however there is no requirement to retrain the labour or to have a composite component which is of reduced strength relative to a steel one. Providing a lighter component that is a replacement for the heavier steel component while still providing the same functionality is a highly desirable feature of the present invention.

Adhesive securement of the ledger heads to the elongate tube or other structural connecting component of a reduced weight is the preferred arrangement. It is possible to use other arrangements including the mechanical securement of these components while providing the particular advantages. If an alternate arrangement is to be considered a filler type material is preferable between the connecting portion of the ledger head and the tube to avoid play or movement between these components. For example a bonded type filler arrangement can reduce play and can rely on mechanical securement of a pin type connection or dimple type connections to maintain the rigidity of the system.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention are shown in the drawings, wherein:

FIG. 1 is a schematic view of a ledger as used in scaffolding systems;

FIG. 2 is a partial sectional view of a scaffold ledger showing the connection of a ledger head to an aluminum tube;

FIG. 3 is a front view of a guard rail component made of generally aluminum tubes with steel ledger heads for releasable connection to the scaffolding structure;

FIG. 4 is a further view of a scaffold component made of generally aluminum tubes and having steel ledger head connectors;

FIG. 5 is a side view showing an aluminum tube connected to a ledger head having a downwardly extending drop pin;

FIG. 6 is a side view of a scaffold component having an aluminum tube and an inner steel tube for connection to a scaffold connecting member;

FIG. 7 is a partial perspective view showing the connection of a ledger head to an aluminum tube;

FIG. 8 is a perspective view similar to FIG. 7 without a mechanical pin connection between the ledger head and the aluminum tube;

FIG. 9 is a partial perspective view of an alternate arrangement where the aluminum tube includes thickened top and bottom sections and the ledger head includes an extending spigot designed to have a particular registration with the aluminum tube;

FIG. 10 is a view similar to FIG. 9 without a connecting pin;

FIG. 11 is a perspective view of a 5×5 foot scaffold tower with raised work platform; and

FIGS. 12 a and 12b are perspective views of a preferred cast ledger head alone in FIG. 12a and as a cutaway of a completed connection in FIG. 12b.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 generally illustrates a ledger 2 that is a modular component that is commonly used in scaffolding systems and is sometimes used as a brace member in shoring systems. There are a number of scaffolding systems commonly used and typically these proprietary systems use their own arrangement for connecting of a modular bracing component to a scaffold leg or to a scaffold frame. One common connecting system as shown in FIG. 3 uses a circular connecting rosette 104 that is welded to the uprights 103 of a scaffolding frame 102 at predetermined points. These rosettes 104 allow convenient connection with a ledger head 4 or 4a as generally shown in FIGS. 2 and 3. A drop wedge 5 passes through the ledger head and through the rosette and positively secures the ledger head 4a to the upright 103 of the scaffold frame 102. Typically the drop wedge 5 is captured or retained in the ledger head. These rosettes can also be used on the uprights of scaffold frame members to simplify connection. Other common connection arrangements include a cup and prong type arrangement where the prong is inserted into an upwardly extending cup and a top member moves downwardly to retain the prong in the cup. As can be appreciated, the present invention as subsequently described can be used with different scaffolding connecting arrangements and is not limited to the particular ledger head design shown in the drawings.

Ledgers of the general structure as shown in FIG. 1 are commonly used in modular scaffolding systems. One of the desirable features of a modular scaffolding system is the convenience and labour saving in erecting the system. Modular systems are based on fixed positions of various components that interconnect in a simplified manner. In contrast, tube and clamp scaffolding arrangements are custom designed and require more skilled labour. In modular scaffolding systems it is cost effective to use relatively large spacing between the upright components. Many systems use a 5 foot, 7 foot or 10 foot bay spacing between frames. Conventional ledgers made of steel tube with a cast or formed steel ledger head either end thereof can easily be carried by a labourer and steel frames can be carried by two labourers.

FIG. 11 is an example of a 5 foot×5 foot tower 200 commonly used in oil refinery maintenance applications. The tower includes a raised work platform 202 having guard rails 204 thereabout. The tower includes elongate legs or uprights 206 connected via rosettes to the guard rails 204, the ledgers 208 and the diagonal braces 210. The ledgers 208 preferably use the higher load carrying capability of the tubes shown in FIGS. 9 and 10. With this arrangement it is not necessary to distinguish between steel and steel/aluminum components as the load carrying capacities are designed to be similar to allow free substitution. In the case of a 7 foot load carrying ledger a double tube aluminum ledger will be used. These components all use the steel ledger heads or connectors in combination with adhesively secured aluminum or aluminum alloy tubes.

In essentially all applications, the workmen used to erect these systems prefer a small bay spacing as the components are lighter and therefore easier to carry and assemble. In applications or industries where the labour component has a significant influence in determining an acceptable system, the smaller separation distances such as 7 foot bay separation is often used where it would be more cost effective to use the larger 10 foot bay spacing. For higher load applications a 5 foot bay spacing is used.

In order to overcome this bias while still being able to achieve the desired labour savings in erecting of a modular scaffolding system, the present invention uses aluminum tubes that have a specific connection with a steel ledger head or similar steel connecting component.

The ledger head 4 shown in FIG. 2 is of a steel material and can be formed from plate or may be a cast component. The steel of the ledger head is desirable due to its high strength and also its tolerance with respect to potential damage on the work site. These steel ledger heads are very durable and are not prone to damage.

The ledger head 4 as shown in FIG. 2 includes a system connecting end 6 which will have the particular shape for engaging the intended modular scaffolding system. In this case there is a central slot 7 which receives part of the flange of a connecting rosette 104. A wedge member will pass through the center passage 9 to effectively lock the ledger head to a scaffold component as shown in FIG. 3.

Directly opposite the system connecting end 6 is the tube connecting end 8. This end of the ledger head 4 is designed to cooperate and engage the aluminum tube 14. The aluminum tube 14 replaces the conventional steel tube that would be used for such a ledger. In the structure shown in FIG. 2, the tube connecting end 8 includes an inner stub collar 20 which is received interior to the steel tube connecting stub 10. The length of the steel tube connecting stub 10 is relatively short and is typically in the range of 2 to 6 inches. The length of this steel tube connecting stub provides a large adhesive securement area with the aluminum tube 14. A suitable adhesive 22 is shown that connects the steel tube connecting stub 10 to the end of the aluminum tube 14. The adhesive 22 is preferably a two part epoxy type adhesive.

The steel tube connecting stub 10 in this case is shown secured to the ledger head 4 by a weld 12. It can also be seen that the inner stub collar 20 projects into the steel tube connecting stub 10 a sufficient distance to overlap with the end of the aluminum tube 14. The inner stub collar 20 provides support for both the connecting stub 10 and the end of the aluminum tube 14. This overlap arrangement provides an effective cooperation between the elements and opposes shear. The adhesive 22 is selected to provide strong securement of the aluminum tube 14 to the connecting stub 10. The adhesive is also preferably selected to electrically isolate the steel tube connecting stub 10 from the aluminum or aluminum alloy tube 14. This reduces the possibility of corrosion due to the dissimilar metal materials.

It has been found that the adhesive 22 can provide a durable fixed securement of the aluminum tube to the ledger head that is not prone to damage. The length of the steel tube connecting stub 10 in a preferred embodiment is of a length of about 2 to 3 inches and provides sufficient area for adhesive securement of the aluminum tube to the ledger head. This adhesive securement provides effective connection for the design loads for ledgers and other scaffold connecting components. The adhesive is selected to comply with the appropriate temperature ranges. For example, scaffolding systems used in large refineries in northern Canada can encounter winter conditions of −45° F. whereas scaffolding systems in the southern United States encounter summer temperatures in excess of 100° F. The adhesive is selected to be effective for the temperature ranges and satisfy typical loads caused by dropping or otherwise onsite job conditions that the components experience at all temperatures within the predetermined ranges.

As can be appreciated from a review of FIG. 2, the steel tube connecting stub 10 provides an effective arrangement for distributing forces exerted on the ledger head to the aluminum tube without damage thereof.

It has been found desirable to increase the wall thickness of the aluminum tube that would otherwise replace the commonly used steel tube. For example, it is common to use a steel tube with a 3.2 mm thickness and to provide additional strength the aluminum tube has a thickness of approximately 3.7 mm. As can be appreciated there will be more aluminum material however the overall weight of the ledger will be significantly reduced. This lighter system component (i.e. the conventional type steel material for the ledger head in combination with an aluminum tube type member connected thereto) acts as a equivalent component with the desirable reduced weight. This has significant advantages to the workforce responsible for erecting and dismantling of such modular systems. Typically ledgers are divided into load bearing ledgers and non load bearing ledgers. A 10 foot ledger is non load bearing and the thicker aluminum type is satisfactory for this application. For load bearing applications common in 5 foot ledgers a different structure of the aluminum tube and ledger is used.

From the above, it might be considered that an all aluminum system would be preferable. Unfortunately an all aluminum system with aluminum ledger heads is prone to damage or the ledger heads must be greatly oversized to provide the required durability. This results in a component that is less desirable and/or more expensive to make. The steel/aluminum hybrid system as described herein having steel ledger heads in combination with an elongate aluminum tube extrusion is both cost effective to manufacture and light weight.

FIGS. 3, 4, 5, 6, 7 and 9 show a ledger connected to a ledger head that also includes securing ports for a pin connector to provide additional mechanical securement of the ledger head to the tube. This pin type connection is normally not necessary as the adhesive securement of the components is sufficient, however it does provide a further well recognized connection. There may be some reluctance to initially accept the high structural integrity of the adhesive securement and therefore a mechanical pin connection is also provided. Furthermore the adhesive and mechanical connections complement one another particular during assembly. For example, the pin connection maintains the position of the components as the adhesive cures or otherwise sets. With the pin connection the core after initial gluing is reduced. FIGS. 8 and 10 show a ledger head and aluminum tube connection that relies solely on the adhesive securement of the component.

The ledger head as shown in FIG. 2 has been described with respect to a separate steel tube connecting stub 10. This arrangement is desirable for existing ledger head designs that can be used directly or require only a small modification to receive the steel tube connecting stub. As the system becomes more widely accepted it is anticipated that the ledger head and the connecting stub 10 will be an integral component of the ledger head. In this case the ledger head would not include the stub collar 20 as basically the stub collar 20 and the steel tube connecting stub 10 are an integral component of the ledger head 4.

The particular connection of the ledger head 4 to the aluminum tube 14 can also be used for connecting of other modular dual material scaffolding components. FIG. 3 shows a guard rail frame 30 connected between two uprights 100 and 102 shown with rosette connections 104. This is one particular type of scaffolding connection system however it can be appreciated that other arrangements are also possible. In this case the upper rail of the guardrail frame 30 includes steel ledger heads 4a including drop wedges 5. The steel connectors 4b associated with the lower rail of the guard rail frame 30 are drop pin connectors having a fixed extending pin 9 which is received in a slot of the rosette 104. The upper rail 32, the lower rail 34 and the connecting tubes 36, 37 and 38 are of an aluminum tube construction. The connection between the upper rail 32 and its connecting components are similar to the structure as described in FIG. 2. This is also true for the lower rail 34 and the connectors 4b.

As can be appreciated from a review of FIG. 3, the ends of the guard rail frame 30 (i.e. the connecting components 4a and 4b) are of a conventional steel configuration and are typically of galvanized steel. These connections provide a robust structure that is not prone to damage. The intermediate components connecting these connectors to the uprights 100 and 102 are of a lighter weight aluminum tubing and as such the guard rail frame 30 will be of significantly reduced weight relative to a similar guard rail frame that uses steel tubing.

FIG. 5 shows further details of the connector 4b shown in FIG. 3. This connector includes an inner steel tube connecting stub 10, an outer aluminum tube 14 and a suitable adhesive provided between these two components. A connecting pin 15 has been shown.

An aluminum frame 40 is shown in FIG. 4 attached to steel vertical members of a scaffold frame 100 and 102. The tubular members of the frame 40 as well as the center connecting member are of an aluminum material and thus provide a significant weight advantage. The downwardly angled diagonal tubes 42 and 44 are also of aluminum and connected to the short aluminum tube 46 and 48 associated with the steel leg engaging members 47 and 49. This aluminum frame provides the weight advantages while still providing good load bearing capabilities. Designing the combination steel/aluminum components to have equivalent strength as the existing steel components allows mixing of components without regard to type.

The connector 110 shown in FIG. 6 includes the outer aluminum tube 14 in combination with the inner steel tube connecting stub 10. These components are secured by an adhesive. The end 112 of the steel tube connecting stub 10 has been adapted for welded securement to a similar steel tube. As can be appreciated the steel tube connecting stub 10 can take different configurations appropriate for connection to a steel component.

Additional details of the hybrid system can be appreciated from a review of FIGS. 7, 8, 9 and 10. FIG. 7 shows the described connection arrangement with two ports for receiving a connecting pin that is used in addition to the adhesive securement. FIG. 8 is a prospective view essentially the same as FIG. 7 but without a connecting pin securement. Adhesive securement can be supplemented with a mechanical securement to meet any design or safety requirements. As a steel stud or tube is stronger than an equivalent sized aluminum tube, it is generally preferred to have the aluminum tube sleeve the steel connecting stud or tube. This relationship can be reversed as the more important issue is the adhesive securement therebetween.

The structures of FIGS. 9 and 10 are similar to FIGS. 7 and 8 however the cross section of the aluminum tube has been modified. FIG. 9 again includes ports for a connecting pin whereas FIG. 10 relies solely on the adhesive securement. Other securing arrangements can be used in combination with the adhesive if desired, however the adhesive on its can provide the required strength as the adhesive securement area can be increased when necessary.

In FIGS. 9 and 10 both the steel tube connecting stub 10a and the aluminum tube 14a have been modified to provide several advantages. Basically the ledger head with the steel tube connecting stub secured thereto can only be received in the modified aluminum tube 14a in one of two orientations. With this arrangement it is easy to assemble the ledger heads to the aluminum tube and provide accurate alignment of the two ledger heads.

The modified cross section of the aluminum tube 14a provides additional strength with respect to bending. A thickened portion is provided at the top surface of the modified aluminum tube 14a and the bottom surface of the tube has also been increased. This structure provides a reinforced or higher strength top and bottom flange joined by the side members. Similarly the connection to the ledger head is also improved. This modified tube also cooperates with the ledger head to provide registration and thus simplifies assembly of the components. The steel tube connecting stub 10a includes a top and bottom surface that closely corresponds to the modified tube 14a to provide the registration function.

A modified ledger head 304 is shown in FIGS. 12a and 12b and is a one piece cast steel material with the connecting stub 310 including a flattened top surface 330 and a corresponding flattened bottom surface 332.

The sides 340 and 342 of the connecting stub 310 each include a pair of shallow grooves 336 and 338 that preferably have a depth of approximately 2 mm. The grooves 336 and 338 are positioned either side of the connecting port 350. Each of the sides 340 and 342 include a center flattened portion 354.

The purpose of the flattened portions 354 and the shallow grooves 336 and 338 are to assist in the distribution of the adhesive (preferably an epoxy adhesive and most preferably an acrylic epoxy adhesive). These flattened portions 354 and the grooves 336 and 338 provide channels that allow the epoxy to flow and provide a large adhesive securing surface about the connecting stub 310. As can be appreciated from a review of FIG. 9, the modified aluminum tube extrusion 14a includes a flattened top surface 360 and bottom surface 362 interior to the pipe for closely engaging surfaces 330 and 332 of the cast ledger head. These grooves and flattened area provide additional space to receive excess epoxy while still providing efficient coating about the connecting stub. In addition these grooves will act to further improve the attachment of the tube to the ledger head. As can be appreciated, the ledger head of FIGS. 9, 10, 12a and 12b with the modified aluminum pipe extrusion as shown in FIGS. 9 and 10 provide a simple arrangement where the ledger heads are registered with the tube and thus improve the assembly of the components. The grooves 336 and 338 provided either side of the connecting stub in combination with the flattened portions 354 also simplify securement of the ledger head to the tube and also assist in providing excellent locking of the ledger head to the tube extrusion. FIG. 12b shows a completed connection.

The modified tube extrusion as shown in FIGS. 9 and 10 include the thickened top area 380 and the thickened bottom area 382 that provides additional strength for the tube extrusion to oppose bending of the tube in the vertical plane assuming the tube was horizontal. These act in a way similar to the top and bottom flanges of an I-beam type shape. The size of the areas 380 and 382 can be adjusted to provide the desired structural characteristics of the tube while also simplifying the registration of the ledger head with the tube. The opposed curved side walls 384 and 386 of the tube 14a closely correspond to the side walls 340 and 342 of the ledger head. These sidewalls are somewhat thinner, preferably about 3.20 mm with an outside tube diameter of 48.30 mm.

It is highly desirable to maintain the common outside steel tube diameter of 48.30 mm to allow compatibility with a host of existing clamps and other components designed for this tube diameter.

The following is a comparison of a ten foot aluminum ledger with the modified tube extrusion shown in FIGS. 9 and 10 to an all steel ten foot ledger:

		Aluminum
		Bearer
	Regular	w/Glued
	Steel	Ledger	Limiting
Attribute	Ledger	Heads	Factor
Weight of Aluminum 10 ft	11.1	5.98	—
Ledger c/w ledger heads
and wedges (kg)
Calculated Safe Bending	0.50	0.52	Allowable
Moment (kN · m)			Bending
			Stress in
			Tube
End Vertical Load	8.9	8.9	Rosette
Capacity (kN)			Capacity
Safe tensile strength	14.19	14.19	Rosette/Wedge
of ledger head to			Capacity
rosette connection (kN)

Ten and seven foot ledgers are not designed for substantial load carrying capability. In contrast a five foot steel ledger is often referred to as a bearer for significant load carrying capacity. The modified aluminum tube ledger is designed to have properties generally the same as the conventional steel tube and significantly stronger than conventional or regular aluminum scaffold tube.

The following tables provide a comparison of the modified aluminum tube to a regular aluminum tube, an equivalent high strength aluminum tube having a thickened wall to provide properties similar to a conventional steel tube and the conventional steel tube section.

REGULAR ALUMINUM SCAFFOLD TUBE
SECTION PROPERTIES
SECTION MODULUS: 5330 mm{circumflex over ( )}3
MOMENT OF INERTIA: 128730 mm{circumflex over ( )}4
WEIGHT: 1.392 kg/m
OPTIMIZED ALUMINUM LEDGER TUBE
                                 COMPARISON TO
                                 REGULAR ALUMINUM
SECTION PROPERTIES               SCAFFOLD TUBE
SECTION MODULUS: 7746 mm{circumflex over ( )}3 45% Stronger
MOMENT OF INERTIA: 187085 mm{circumflex over ( )}4 45% Stiffer
WEIGHT: 1.872 kg/m               34% Heavier

The table above shows the section properties of aluminum scaffold tube, commonly used in Canada, compared to the optimized version referred to in the present patent application. It can be seen that, although the optimized version is 34% heavier, it is 45% stronger and 45% stiffer. The optimized section is as strong as the regular steel scaffold ledger tubes when subjected to bending stresses.

EQUIVALENT STRENGTH ALUMINUM TUBE
SECTION PROPERTIES
SECTION MODULUS: 7746 mm{circumflex over ( )}3
MOMENT OF INERTIA: 187085 mm{circumflex over ( )}4
WEIGHT: 2.249 kg/m
OPTIMIZED ALUMINUM LEDGER TUBE
                                 COMPARISON TO
                                 REGULAR ALUMINUM
SECTION PROPERTIES               SCAFFOLD TUBE
SECTION MODULUS: 7746 mm{circumflex over ( )}3 Identical strength
MOMENT OF INERTIA: 187085 mm{circumflex over ( )}4 Identical Stiffness
WEIGHT: 1.872 kg/m               17% lighter

The table above shows the section properties of an aluminum scaffold tube with a constant wall thickness and with the same strength and stiffness as the optimized aluminum ledger tube. It can be seen that, because the aluminum is not distributed in the most favourable manner, the regular tube is 17% heavier compared to the optimized section.

STEEL SCAFFOLD LEDGER TUBE
SECTION PROPERTIES
SECTION MODULUS: 4774 mm{circumflex over ( )}3
MOMENT OF INERTIA: 115292 mm{circumflex over ( )}4
WEIGHT: 3.539 kg/m
OPTIMIZED ALUMINUM LEDGER TUBE
                                 COMPARISON TO
                                 REGULAR ALUMINUM
SECTION PROPERTIES               SCAFFOLD TUBE
SECTION MODULUS: 7746 mm{circumflex over ( )}3 62% Higher
MOMENT OF INERTIA: 187085 mm{circumflex over ( )}4 62% Higher
WEIGHT: 1.872 kg/m               47% Light er

The table above shows the section properties of a typical steel scaffold ledger tube with the same bending strength as the optimized aluminum ledger tube. It can be seen that the optimized aluminum ledger tube is 47% lighter compared to the steel tube.

As can be seen the modified tube is lighter and structurally stronger by providing more material on the interior of the top and bottom areas of the tube (preferably of equal size). The side walls have been slightly reduced (relative to conventional aluminum tube) to a thickness of 3.20 mm.

From the above, it can be seen that the safe load capacities of ledgers is limited by the strength of the rosette connection. This means that the performance of the aluminum ledger is equivalent to steel ledgers. The aluminum ledger will deflect more under load, but there is no regulatory limit imposed upon the maximum allowable deflection of scaffold ledgers. As can be appreciated as the length of the ledger decreases the strength will increase as it is preferred to use the same tube extrusion. With this arrangement the aluminum bearer with glued ledger head can be freely used as a replacement for the conventional all steel bearer.

Two part acrylic adhesives are normally available in different grades having different working times. The adhesive is preferably selected to be operative once cured in a temperature range from −40° C. to 149° C. Desirably the adhesive resists dilute acids, alkalies, solvents, greases, oils, moisture, salt spray and weathering. Furthermore it is preferable that the adhesive is nonconductive and provides an electrical insulating property separating the steel ledger head from the aluminum tube and thus reduces possible galvanic action therebetween.

Due to the scaffold application the adhesive must be tolerant to vibration and a more flexible adhesive is preferred. More brittle adhesives can crack under impact load that can occur by dropping or striking with a hammer that may occur during connection to a scaffold leg.

Two suitable adhesives for the glued ledger head and pin structure are as follows:

Adhesive 1:
Manufacturer:       Extreme Adhesives Inc.
Type:               Methacrylate 2-part Adhesive System
Product Name:       Extreme 310
Shear strength      3,300 psi
as rec'd aluminum):
Tensile Elongation: 60%
Thermal Service     −65 F. to +260 F.
Range:
Mix Ratio:          1:1
Working Time        13 to 17 minutes
at 75 degrees F.):
Colour:             Straw or Black
Clean-up Solvents:  MEK, Acetone

Adhesive 2:
Manufacturer:       Parsons Adhesives Inc.
Type:               Methacrylate 2-part Adhesive System
Product Name:       7120
Shear strength      3,000 to 3,300 psi
as rec'd aluminum):
Tensile Elongation: 45% to 50%
Thermal Service     −40 F. to +260 F.
Range:
Mix Ratio:          1:1
Working Time        120 to 130 minutes
at 75 degrees F.):
Colour:             Cream or White
Clean-up Solvents:  MEK, Acetone

It is believed an appropriate amount of tensile elongation is desired to avoid brittle fracture of the adhesive by vibration or shock load during use of the components. A tensile elongation of the adhesive of at least about 20% is considered appropriate. The preferred adhesives above have much higher elongation and still provide sufficient tensile strength in excess of 20,000 lbs. The following is an example of the assembly procedure:

Surface Preparation:

IMPORTANT: In order to maximize joint strength, preparation of the joint mating surfaces take place preferably not more than two hours before assembly or as specified by the manufacture. Preparation of the surfaces and the timing thereof are chosen to achieve effective bonding of the components.

STEP 1: Clean the ends and interior surfaces of the aluminum ledger tube and the mating surfaces of the ledger head castings with MEK or Acetone for a length of 2″. Allow to dry.

STEP 2: Abrade the internal mating surfaces of the aluminum bearer with a flapper wheel or by hand sanding using 100 grit abrasive paper. Carefully remove all grit and dust from inside the ledger tube.

STEP 3: Carefully abrade the galvanized mating surfaces of the ledger head by hand using 100 grit abrasive paper, taking care not to break through the zinc galvanized coating.

Application of Adhesive:

Note: To be undertaken in a working temperature of 70 degrees F. to 75 degrees F.

STEP 4: Mix a sufficient amount of adhesive in accordance with the manufacturer's recommendations.

STEP 5: To achieve an even layer of adhesive, trowel the material onto both ledger heads and inside the aluminum extrusion using a 24 tpi hacksaw blade, or similar, as the trowel.

STEP 6: Apply adhesive to all mating surfaces inside both ends of the aluminum profile, for a length of at least 2″, making sure that there is a build-up at the curved inside portions on the inside of the aluminum profile (where there is a wall thickness 3.2 mm). Adhesive must also be applied to end surfaces of the aluminum profile to provide a sealed joint against the rear of the ledger head casting.

STEP 7: Apply the adhesive to the mating surfaces of both ledger heads, making sure that all surfaces are covered and that there is a build-up of adhesive on the curved sides of the ledger head mating surfaces. Adhesive must also be applied to the flat mating surface where the end of aluminum ledger tube will butt against the rear of the ledger head.

Assembly of Ledgers:

Note: Assembly must be carried-out within the working time of the selected adhesive, after mixing and in temperatures that comply with the adhesive manufacturer's recommendations.

STEP 8: Push the ledger head fully into the end of the aluminum ledger tube until it will go no further. Ensure that the end of the aluminum ledger tube is fully in contact with the flat surface at the rear of the ledger head.

STEP 9: Immediately secure the joint with the specified zinc plated steel coil pin to hold the ledger head in place while the adhesive cures.

STEP 10: Repeat steps 8 though 10 for the second ledger head.

STEP 11: Clean off any excess adhesive that has been squeezed out the end of the aluminum ledger tube during assembly with acetone or MEK.

STEP 12: Secure Wedges to both ledger heads.

STEP 13: Store the assembled ledger assembly horizontally, in a warm area, during the curing period.

As can be appreciated, particularly with the designs shown in FIGS. 9, 10, 12a and 12b, the connecting stubs of the ledger heads may be coated with a mixed two part adhesive and then subsequently inserted in an appropriate length of the aluminum tube. Registration of the ledger head with the aluminum tube is achieved due to the particular cooperation therebetween. Once the stub is inserted, a suitable pin connector can be inserted if the ports are provided or the components may merely be maintained in the assembled orientation until such time as the adhesive has cured. The connecting stub overlaps with the end of the tube 14a and includes a large area for adhesive securement therebetween. Basically this area determines the mechanical strength of the connection. Furthermore the required skill to make the connection is low and reliability is high.

In the preferred arrangement the entire surface of the connecting stub is coated with adhesive whereby a strong mechanical connection of the components is achieved. The particular level of this mechanical connection is a function of the surface area of the adhesive securement between the aluminum tube and the ledger head. A connecting stub of approximately one and a half inches in length coated thereabout and cooperating with an appropriate sized aluminum tube will provide a mechanical securement having a shear strength of 3000 to 4000 psi. As can be appreciated there is some tolerance between the connecting stub and the interior of the aluminum tube which is essentially filled by the two part adhesive. The two part adhesive will also assist in the insertion of the connecting stub into the tube. It is anticipated that if the epoxy has a working time of about 10 to 20 minutes that the epoxy can be dispensed in an automated manner such that the two parts mix upon application to the connecting stub and this will provide more than sufficient time to allow the ledger head to be properly positioned either end of the tube. Typically the assembled parts will be placed on a rack or other suitable structure to avoid inadvertent forces until such time as the epoxy is cured or partially cured.

It is also possible to use the modified aluminum or aluminum alloy tube section and the cooperating steel ledger heads in a mechanically secured configuration. The close fit of the ledger heads in or about the aluminum tube provides a larger area for distributing loads therebetween. It is preferable to fill any gap or tolerance between the overlapping surfaces of the tube and ledger head with a filler material that need not provide the adhesive securement earlier specified. A pin or other mechanical securement can be used. With this arrangement a ledger or other scaffold component that previously used a steel connecting arrangement can be modified using the modified tube to provide weight advantages while be generally equivalent or allowing substitution for the conventional heavier steel component.

A vertical pin securement through the thickened portions may be preferred for both the mechanical and the mechanical adhesive securement.

With this arrangement it is desirable to provide a mechanical securement that distributes the load and avoids high stress areas or a loose connection. It is also desirable to electrically separate the steel ledger from the aluminum tube.

In some all steel scaffold systems, a ledger is fabricated as a single piece component with the ledger heads formed by cutting and deforming the ends of the tube. Basically the ends are slotted and flattened to form ledger heads. For this type of system an aluminum/steel system would use short steel tubes with integral ledgers adhesively secured to an aluminum tube. In this way the same type of ledger head connection is maintained.

The present arrangement allows effective integration of steel scaffolding posts or frames that use conventional mechanical connection of components with the hybrid dual material scaffold components. The connecting components such as guard rails, guard rail frames, ledger members, diagonal bracing members, and other components which connect to such uprights, advantageously use a steel head or connecting portion to form the mechanical connection. The steel connecting components have been modified to include an adhesive securement of an aluminum tube to one side of the component. Thus a significant portion of each of these connecting members are made of aluminum or aluminum alloy and are of reduced weight relative to the same component fabricated using steel tubing. Advantageously the system is lighter weight and as such it is possible to use greater separation between the upright members (more cost effective) or more favorable conditions for the labour erecting the system if they choose to use a smaller separation distance between uprights.

In refineries in northern Canada modular scaffolding systems are used extensively and 10 foot base spacings could be used for many applications. However in most cases smaller bay separation is used as the work force assembling the systems prefers the smaller and lighter weight components. The hybrid system as disclosed herein can be used to allow a larger spacing to be used while also providing a system which is lightweight and thus more acceptable to the installing workmen. The modified system does not need to replace all of the existing steel components as the upright members continue to be of steel and only the connecting components are replaced or added. Furthermore it can be appreciated that the system is fully compatible with a mixture of steel and aluminum hybrid components particularly the reinforced aluminum tubes that are designed to have the same load carrying capacities as the equivalent all steel component. This allows mixing of the system components without concern regarding different load ratings. This provides a gradual turnover of the equipment to the new hybrid system components.

Although various preferred embodiments of the present invention have been described herein in detail, it will be appreciated by those skilled in the art, that variations may be made thereto without departing from the spirit of the invention or the scope of the appended claims.

Claims

1. A modular scaffold component comprising first and second steel ledger heads including a fastening element to mechanically connect the ledger head to spaced scaffold support members,an elongate tube extrusion of an aluminum or aluminum alloy material adhesively secured to each ledger head and forming a structural element therebetween,said elongate tube extrusion and each ledger head having an over sleeve type relationship with opposed overlapping surfaces secured by an adhesive structurally connecting said ledger heads and providing a secure mechanical connection of each ledger head to said tube extrusion for use in a scaffold system.

2. A modular scaffold component as claimed in claim I wherein each ledger head includes a steel tube connecting stub sized for receipt in said elongate tube extrusion with said adhesive securement therebetween.

3. T modular scaffold component as claimed in claim 2 wherein said steel tube connecting stub overlaps with said elongate tube extrusion over at least one and a half inches in the length of said elongate tube extrusion.

4. A modular scaffold component as claimed in claim 3 wherein said steel tube connecting stub is welded to a rear face of said ledger head.

5. A modular scaffold component as claimed in claim 3 wherein said steel tube connecting stub and said ledger head are an integral casting.

6. A modular scaffold component as claimed in claim 2 wherein said component is a ledger, a diagonal brace, a reinforced load carrying member, a frame member or a guard rail.

7. A modular scaffold component as claimed in claim 1 wherein each ledger head includes a connecting part that receives an end of said elongate tube extrusion and forms said overlapping sleeve relationship therewith.

8. A modular scaffold component as claimed claim 7 wherein said adhesive is a two part adhesive forming a rigid connection of said ledger head to said tube extrusion.

9. A modular scaffold component as claimed in claim 7 wherein said overlapping sleeve relationship is of a length of at least one and a half inches.

10. in a modular scaffold component having at least a ledger head and a connected elongate tube, the improvement comprising an adhesive type securement of the ledger head to said elongate tube, each ledger head including a connecting portion having an overlapping sleeve type relationship with an end of said elongate tube, and an adhesive component within a gap of said overlapping sleeve type relationship forming a distributed mechanical connection of said elongate tube to said at least one ledger head; said elongate tube being of an aluminum or aluminum alloy material and said ledger head being of a steel material.

11. In a modular scaffold component as claimed in claim 10 wherein said adhesive is a two part adhesive forming a permanent rigid connection of said ledger head to said elongate tube.

12. In a modular scaffold component as claimed in claim 10 wherein said scaffold component is a ledger, guard rail or reinforced ledger and said component includes at least two ledger heads at opposite ends of said elongate tube.

13. In a modular scaffold component as claimed in claim 10 wherein said adhesive is an epoxy adhesive.

14. In a modular scaffold component as claimed in claim 10 wherein said adhesive forms an electrical insulating layer sufficient to avoid a dielectric current between said elongate tube and said at least one ledger head.

15. In a modular scaffold component as claimed in claim 10 wherein said connecting portion is tubular and is received in said elongate tube or said elongate tube is received in said connecting portion.

16. In a modular scaffold component as claimed in claim 15 wherein said adhesive component between said connection portion and said elongate tube is a two part epoxy adhesive.

17. In a modular scaffold component as claimed in claim 16 wherein said connection portion and said elongate tube have cooperating non circular cross sections requiring a particular registration of said connection portion and said elongate tube to form said overlapped relationship.

18. In a modular scaffold component as claimed in claim 10 wherein each ledger head additional includes a pin type mechanical connection of the ledger head to said elongate tube.

19. In a modular scaffold component as claimed in claim 18 wherein the pin connection of each ledger head when considered independent of said adhesive securement is of less strength or durability compared to the adhesive securement of the ledger head to said elongate tube.

20. In a modular component as claimed in claim 10 wherein said sleeve type relationship extends at least one and half inches in the length and about an interior or exterior surface of the end of said elongate tube.