GB2539469A

GB2539469A - Brace assembly

Info

Publication number: GB2539469A
Application number: GB1510647.9A
Authority: GB
Inventors: Karavasilis Theodore; Tzimas Angelos
Original assignee: University of Warwick
Current assignee: University of Warwick
Priority date: 2015-06-17
Filing date: 2015-06-17
Publication date: 2016-12-21
Also published as: GB201510647D0

Abstract

A brace assembly (5) for interconnecting first and second structural members (2, 3) in a building structure (1) is disclosed. The brace assembly comprises a brace member (6) having first and second ends (7, 8). A damping element (13) is coupled to the second end of the brace member for linking the brace member to the second structural member. The first end of the brace member has a first joint portion (14) for cooperating with a second joint portion (15) on the first structural member via a yielding fuse member (11) having at least one weak section (12; Figure 6). The yielding fuse member is removably insertable into the first and second joint portions to form a joint. The joint is configured to provide a space (17) around each weak section so as to permit plastic deformation of the fuse member. The fuse member may be a pin and the first and second joint portions may be interdigitating flange and gusset plates. The assembly can be serviced by replacing the fuse member only.

Description

Brace assembly

Field of the invention

The present invention relates to a brace assembly for a building structure, such as a steel frame building or wind turbine.

Background

Building structures, in particular slender building structures, such as bridges, tall buildings, wind turbines and other similar building structures, use damping to prevent destructive excitation of oscillatory modes caused by wind or other sources of mechanical excitation. Such damping is often achieved using brace assemblies which incorporate energy dissipation mechanisms, for example, elastomeric coupling between elements, sealed pistons containing fluid or semi-fluid, buckling restrained braces ("BRB") and similar elements.

Building structures may also require protection against exceptional loadings which exceed normal tolerances, such as a building which experiences an earthquake or a wind turbine which experiences exceptionally high gusts during a storm. Building structures may be designed to improve safety by using structural fuses which are designed to undergo plastic deformation so as to absorb energy during such exceptional loading.

Whilst structural fuses are effective in preventing catastrophic damage and improve safety by allowing engineers to control the failure modes of building structures, they are frequently difficult or impossible to replace, so that building structures require extensive or complete re-building following an exceptional loading event. Thus, there is interest in developing structural fuse elements which are more readily replaceable.

Buckling restrained braces can be complex and/or expensive to manufacture.

US 2010/0205876 Al describes structural fuse elements which are eccentric yielding arms manufactured from cast steel. The eccentric yielding arms are integrally formed as part of the brace and undergo gross flexural yielding in response to a seismic event. WO 2012/094756 Al describes a bracing member which includes a central damping element and which incorporates yielding members integrally formed as part of the bracing element. However, these arrangements may require the entire bracing element (or at least a substantial part thereof) to be replaced following an exceptional loading event.

US 2008/0289267 Al describes a pin-fuse frame in which diagonal bracing elements are bolted together such that one member includes a hole and the corresponding member includes a slot. When a load exceeding the frictional force due to the bolts is experienced, the diagonal brace may slip and change in length. Similar joints at corners permit the angle of horizontal and vertical members to slip. However, such pin-fuse frames may experience slippage issues dues to long term vibrations and a /0 relatively large number of bolts and elements may need to be inspected, loosened and repositioned following an exceptional loading event.

Summary

The present invention seeks to provide a brace assembly and a building structure which include yielding fuse members which can be easily tested for integrity and easily replaced when required. The present invention also seeks to provide a yielding fuse which is simple to produce.

According to a first aspect of the invention there is provided a brace assembly for interconnecting first and second structural members in a building structure. The brace assembly comprises a brace member having first and second ends. The brace assembly also comprises a yielding fuse member having at least one weak section. The brace assembly also comprises a damping element coupled to the second end of the brace member, for linking the brace member to the second structural member. The first end of the brace member has a first joint portion for cooperating with a second joint portion on the first structural member via the yielding fuse member. The yielding fuse member is removably insertable into the first and second joint portions to form a joint. The joint is configured to provide a space around a weak section so as to permit plastic deformation of the fuse member. The yielding fuse member preferably has at least two weak sections. More preferably, the yielding fuse member has two weak sections.

The joint may comprise a knuckle joint comprising an eye, a fork and a pin, wherein the fuse member comprises the pin. The first joint portion may comprise the knuckle joint fork and the second joint portion may comprise the knuckle joint eye. The fuse member may comprise a shaft having first and second ends. The shaft is preferably elongate. The shaft is preferably cylindrically symmetric. -3 -

The shaft may include first, second, third, fourth and fifth sections between the first and second ends. The first, third and fifth sections may have relatively large respective cross sectional areas and the second and fourth sections may have relatively small respective cross sectional areas, thereby defining first and second weak sections.

The first joint portion comprises at least one flange plate, and the second joint portion comprises at least one gusset plate, wherein the flange plate(s) and gusset plate(s) interdigitate.

The fuse member and damping elements may be configured such that, in response to axial loading of the brace member, the fuse member undergoes plastic yielding before the damping element is damaged.

The damping element may comprise a plurality of viscoelastic or elastomeric layers, and a plurality of metal plates, wherein the viscoelastic or elastomeric layer and metal plates are interdigitated and wherein the viscoelastic or elastomeric layer and metal plates are bonded.

The fuse member may comprise mild steel or stainless steel.

According to a second aspect of the invention there is provided a building structure comprising first and second structural members, and a brace assembly as hereinbefore described interconnecting the first and second structural members. -0or

According to a third aspect of the invention there is provided a building structure comprising first and second structural members, and a brace assembly interconnecting the first and second structural members. The brace assembly comprising a brace member having first and second ends, a yielding fuse member having at least one weak section, and a damping element linking the second end of the brace member to the second structural member. The first end of the brace member and the first structural member are connected by a joint comprising the yielding fuse which is removably insertable, the joint configured to provide space(s) around the weak section(s) to permit plastic deformation. The yielding fuse member preferably has at least two weak sections. -4 -

The building structure may include a brace assembly suitable for use in the building structure.

According to a fourth aspect of the invention there is provided a method of servicing a building structure. The method comprises urging the yielding fuse member with a force below a predetermined force threshold so as to attempt to remove the fuse member. The method further comprises determining whether the fuse member is displaced by a distance exceeding a predetermined distance threshold, and on a negative determination, replacing the fuse member. -5 -

Brief Description of the Drawings

Certain embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings in which: Figure 1 is a perspective view of a building structure including a brace assembly. 5 Figure 2 is a side view of a brace assembly; Figure 3 is a plan view of a brace assembly shown in Figure 2; Figure 4 is a cross sectional view of a brace assembly along A-A' in Figure 3; Figure 5 is a side view of a brace member include in the brace assembly shown in Figure 2; /0 Figure 6 is a plan view of a brace member include in the brace assembly shown in Figure 2; Figure 7 is plan view of a yielding fuse member included in a brace assembly shown in Figure 2; Figure 8 is a cross sectional view of a fuse member along B-B' in Figure 7; Figure 9 is a partial cross sectional view of damping element shown in Figure 2; Figure 10 is a side view of a first end of a brace assembly shown in Figure 2; Figure 11 is a cross sectional view along C-C' in Figure 10; Figure 12 is a cross sectional view along D-D' in Figure 10; Figure 13 is a cross sectional view along E-E' in Figure 10; Figure 14 is a cross sectional view along F-F' in Figure 10; Figure 15 is a side view of a second end of a brace assembly shown in Figure 2; Figure 16 is a cross sectional view along G-G' in Figure 15; Figure 17 is a cross sectional view along H-H' in Figure 15; Figure 18 is a cross sectional view along I-I' in Figure 15; Figure 19 is a cross sectional view along J-J' in Figure 15; Figure 2oA is a schematic plan view of the mechanical loading of a fuse member; Figure 2oB is a schematic plan view of a deformed fuse member; Figure 21A is a schematic plan view of testing a fuse member; Figure 21B is a schematic plan view of testing a fuse member; Figure 22 is a side view of a second weak section of a fuse member; Figure 23 is a side view of a third weak section of a fuse member; Figure 24 is a side view of a fourth weak section of a fuse member; Figure 25 is a plan view of an alternative first end of a brace assembly shown in Figure 2; and Figure 26 is a plan view of an alternative first end of a brace assembly shown in Figure 2. -6 -

Detailed Description of Certain Embodiments

In the following description, like parts are denoted by like reference numerals.

Referring to Figure 1, a part of a building structure 1 in the form of a building having a steel frame is shown. The building structure 1 includes a number of upright structural members 2 which are fixedly connected to a number of horizontal structural members 3 to form a frame. The frame includes a number of rectangular apertures 4, each bounded by a pair of upright structural members and a pair of second horizontal /o structural members. Brace assemblies 5 run diagonally within the rectangular apertures 4 to interconnect the pair of upright structural members 2 and/or the pair of horizontal structural members 3.

Referring to Figure 2, a side view of a brace assembly 5 for interconnecting structural members 2, 3 in a building structure 1 is shown. The brace assembly 5 includes a brace member 6 having a first end 7 and a second end 8. The first and second ends are separated along a brace member axis 9 by an elongate brace beam member to. The brace assembly 5 also includes a yielding fuse member it having two weak sections 12a, 12b (Figure 6) and a damping element 13. The brace assembly 5 is generally made from steel components. The structural members 2, 3 interconnected by the brace assembly 5 may be formed of materials such as steel, steel reinforced concrete or any other suitable structural materials. The structural members 2, 3 are interconnected by the brace assembly 5, but do not form part of the brace assembly 5.

The first end 7 of the brace member 6 is coupled to the brace beam member 10 and has a first joint portion 14 for cooperating with a second joint portion 15, via the yielding fuse member 11 which is removably insertable into the first and second joint portions 14, 15 to form a fused joint 16. The second joint portion is fixedly attached to the structural members 2, 3 at a first point. The second joint portion 15 is a gusset plate fixedly attached at the intersection of an upstanding structural member 2 with a horizontal structural member 3. The second joint portion 15 may be attached to the structural members 2, 3 using, for example, welding, bolting or riveting. Alternatively, the second joint portion 15 may be integrally formed with one of the structural members 2, 3. The fused joint 16 is arranged so that there is a space 17a, 17b (Figure 6) 35 around a weak section 12a, 12b of the fuse member it The space 17a, 17b permits plastic deformation of the fuse member it. -7 -

The yielding fuse member 11 is not fixedly coupled to either of the first or second joint portions 14, 15. The yielding fuse member 11 may be held in place by friction, or by a retaining member such as a split pin 56 (Figure 6), a cap, a bolt, an 0-ring or a length of wire inserted through an end of the fuse member 11 and bent. The friction may arise from the weight of the brace member 6.

The second end 8 of the brace member 6 is coupled to the brace beam member to and includes the damping element 13. The damping element 13 is fixedly attached to a second gusset plate 18 via bolted plates 19. The second end 8 of the brace member 6 is attached to the structural members 2, 3 at a second point which is diagonally opposite the first point. The brace member 6 spans between a pair of upstanding structural members 2.

Referring also to Figures 3 and 4, the structural members 2, 3 and the brace beam member to are steel I-beams. However, structural members 2, 3 and brace beam member to need not be T-beams and other shapes may be used for the structural members 2, 3 and brace beam member 6 such as, for example, U-beams, or square, rectangular or cylindrical sections.

Referring to Figures 5 and 6, the first end 7 of the brace member 6 includes a cross piece 20. The cross piece 20 is a rectangular steel sheet which is oriented perpendicular to the brace member axis 9 and which is fixedly attached to the end of the brace beam member 10. The first joint portion 14 is provided by a pair of parallel flange plates zia, 21b which project parallel to the beam member axis 9. The pair of flange plates zia, 21b lie parallel to, and are located adjacent to, opposed edges of the rectangular cross piece zo. When the fused joint 16 is assembled, the flange plates zia, 21b are disposed either side of and parallel with, the second joint portion 15. In this way, the fused joint 16 forms a knuckle joint including a fork, an eye and a pin, whereby the flange plates 21a, 21b of the first joint portion 14 provide the tines of the fork, the second joint portion 15 provides the eye and the yielding fuse member 11 provides the pin. The yielding fuse member 11 is received by corresponding through holes in the pair of flange plates 21a, 21b providing the first joint portion 14 and a through hole in the gusset plate providing the second joint portion 15. -8 -

Spaces 17a, 17b are provided between each of the flange plates 21a, 21b and the second joint portion 15 as a result of the separation between the flange plates 21a, 21b being larger than the thickness of the gusset plate providing the second joint portion 15.

Referring also to Figures 7 and 8, the yielding fuse member 11 is a shaft having a first end 22 and a second end 23. The first and second ends 22, 23 of the fuse member it are received by corresponding through holes in the pair of flange plates 21a, 21b. A central portion 24 of the fuse member is received by a corresponding through hole in the gusset plate providing the second joint portion 15. A pair of weak sections 12a, 12b are provided either side of the central portion 24. When the fused joint 16 is assembled, one weak section 12 is provided between the second joint portion 15 and each of the first and second flange plates 21a, 21b. The first and second end portions 22, 23 and the central portion 24 have relatively respective large cross sectional areas and the pair of weak sections 12a, 12b have relatively small respective cross sectional areas. In this case, the weak sections 12a, 12b are defined by the reduced cross sectional areas, which serve to increase the probability that plastic deformation of the fuse member 11 will first occur within the weak sections 12a, 12b. The fuse member comprises mild steel or stainless steel. Stainless steel may be preferred in a case where the cross section of the fuse member 11 is to be reduced. However, the fuse member 11 need not be made of mild steel or stainless steel, and may comprise any material having suitable strength and energy dissipation capacity. Material for forming the fuse member 11 preferably exhibits predictable inelastic behaviour above the yield point.

The shaft of the fuse member 11 is elongate. The shaft of the fuse member it is cylindrically symmetric about a fuse member axis 25. The cross sectional area of the fuse member 11 tapers within each weak section 12 to a waist 26 which is located at the midpoint of the weak section 12. The variation of the radius of the fuse member 11 with distance along the fuse member axis 25 within the weak section 12 produces a shape, or profile, when viewed perpendicular to the fuse member axis 25. Each of the weak sections 12a, 12b of the fuse member 11 has a profile which is generally hourglass shaped and symmetric about the respective waist 26. The profile of each weak section 12 includes sharply-curved portions 27 leading into generally straight tapering portions 28 which intersect and make an obtuse angle at the waist 26. The sharply-curved portions 27 are tangential to a generally straight tapering portion 28 at one end, and make an angle with the straight sides of the first portion 22, second portion 23 or central portion 24 at another end. The profile of the weak section 12 may vary -9 -smoothly at the intersection of the generally straight tapering portions 28 to avoid a stress concentrating kink. The cross-sectional area of the waist 26 may be selected to be the minimum required sectional area in order to avoid shear failure of the fuse member 11 by brittle fracture.

Referring again to Figures 5 and 6, and also referring to Figure 9, the second end portion 8 of the brace member 6 includes a cross piece 29. The cross piece 29 is a rectangular steel sheet which is oriented perpendicular to the brace member axis 9 and which is fixedly attached to the end of the brace beam member 10. A pair of damping dement outer plates 3oa, 3ob project from the cross piece 29 parallel to the brace member axis 9. The pair of damping element outer plates 3oa, Sob lie parallel to, and are located adjacent to, opposed edges of the rectangular cross piece 29. A pair of damping element inner plates 3m, 31b are bolted together and positioned between and parallel to the damping element outer plates 3oa, 3ob. The damping element inner plates 3m, 31b are connected to the damping element outer plates 3oa, 3ob via a pair of damping assemblies 32a, 32b arranged on either side of the damping element inner plates 31a, 31b.

The damping element inner plates 31a, 31b are bolted together using bolts 33, and also fixedly connected to the second gusset plate 18 via bolted plates 19 and bolts 33. A damping assembly 32 includes a number of metal plates 34 interdigitated with and bonded to a number of layers of viscoelastic or elastomeric material 35. In this case, each of the damping assemblies 32a, 32b include a single layer of viscoelastic or elastomeric material bonded between a pair of metal plates 34. The metal plates 34 include threaded through holes 36, which align with corresponding countersunk through holes 37 in the damping element inner and outer plates 3oa, 3ob, 3m, 31b. Bolts with countersunk heads 38 are received through the countersunk through holes 37 and tightened into the threaded through holes 36.

Referring to Figures 10 to 14, further views and cross sections of the configuration of the fused joint 16 connecting the first end 7 of the brace member 6 to the gusset plate providing the second joint portion 15 are shown.

Referring to Figure 15 to 19, further views and cross sections of the configuration of 35 connecting the second end 8 of the brace member 6 to the second gusset plate 18 via the bolted plates 19 are shown.

-10 -Operation of the brace assembly A building structure 1 will first fail when the loading of the weakest element in the building structure 1 exceeds a maximum loading for that element. During normal loading, that is say when a building experiences the loading for which it was designed, a building structure 1 will not experience failure loading of any element. However, loads significantly in excess of the design loads, that is to say extreme loads, may be experienced by a building structure 1 as a result of external event, for example wind loading or seismic activity. Such loadings may, if not damped, cause excitation of the dynamic modes of the building structure 1. Undamped excitation of the building structure 1 dynamic modes can result in large displacements of the building structure 1 and correspondingly large loads. This is particularly the case for slender building structures 1.

Structural fuses are incorporated into building structures lto provide predictable locations for deformation to occur in response to an extreme loading event. Structural fuses are designed to fail and plastically deform before other structural elements. Structural fuses are designed and positioned so that a building structure 1 can accommodate significant displacements and distortions in a planned fashion, so as to minimise the impact on the overall integrity of a building structure 1.

Referring to Figures 1 and 2, when a loading is applied to a building structure 1 including a frame assembled from upright structural members 2 and horizontal structural members 3, the structural members 2, 3 may be urged to undergo shear or displacements relative to one another. Such shear displacements may be opposed by using brace members 6 which span between adjacent upright structural members 2 and/or adjacent horizontal structural members 3. The resulting loading of the brace members 6 is primarily axial, which is to say that the component of a force transmitted by each brace member 6 parallel to the respective brace member axis 9 is substantially larger than the component of the force in any perpendicular direction.

Referring to Figure 2oA, when an axial load 39 is applied to a brace member 6, it is transmitted from the gusset plate providing the second joint portion is to the pair of flange plates 21a, 2117 providing the first joint portion 14 via the yielding fuse member 11. The weak sections 12a, 1217 of the fuse member 11 are designed to undergo plastic yielding in response to an axial load 39 which exceeds a threshold limit. The fuse member 11 is designed to have a threshold limit which ensures that the fuse member ii will fail before any other structural element, in particular the structural members 2, 3, or any part of the brace assembly 5 other than the fuse member n such as, for example, the brace beam member 10 or the viscoelastic / el astomeri c material 35.

The brace member 6 may be subjected to a design load during normal operation of the building structure 1. The threshold limit of the fuse member 11 may be designed to be a multiple of the design load of the brace member 6. For example, the threshold limit of the fuse member 11 may be five times the design load of the brace member 6. As to another example, for a building structure 1 in a seismically active region which experience frequent low-level events, the threshold limit of the fuse member 11 may be three times the load which would from a typical low-level seismic event.

Referring to Figure 2oB, when an axial load 39 exceeding the designed threshold limit of the fuse member 11 is applied to the brace member 6, the weak sections 12a, 12b undergo plastic deformation and deform into the spaces 17a, 176 provided about each weak section 12a, 12b. Once the axial load is removed, or has reduced sufficiently to lower the stresses in the deformed fuse member if below the local yield point, the deformed fuse member if will stop plastic deformation.

The material for the fuse members 11 and the profiles of the weak sections may be selected such that the deformed fuse member 11' is capable of elastically sustaining the design load of the brace member 6, at least over a certain range of displacements of the first and second joint portions 14, 15. However, even when the deformed fuse member -0or 11' may sustain the design load, in the longer term after an extreme loading event the deformed fuse member if will need to be replaced according to the procedure described hereinafter.

Spaces 17a, 17b provided around the weak sections 12a, 12b should be sufficient to allow the fuse member ii to undergo plastic deformation to accommodate displacements/distortions of the building structure 1. If insufficient space 17 is provided, then concentration of plastic deformation into small volumes of the fuse member 11 may lead to fracture of the fuse member 11 for small displacements of the first and second joint portions 14, 15. Use of weak sections 12 having profiles that include stress concentrating features may also result in fracture of the fuse member ii for small displacements of the first and second joint portions 14, 15.

-12 -The hourglass profile 26, 27, 28 of the weak sections 12a, 12b is designed to spread the plastic deformation evenly throughout the weak sections 12a, 12b. Evenly spreading the plastic deformation improves the energy absorbed and/or the maximum displacement of the first and second joint portions 14, 15 prior to failure of the fuse member 11. The cross-sectional area of the waist 26 may be selected to be the minimum required sectional area in order to avoid shear failure of the fuse member n by brittle fracture.

/0 After a fuse member n is first deformed, the precise axial load 39 at which the deformed fuse member n' will cease/resume plastic deformation will be different to the designed threshold limit of the undeformed fuse member n. This arises as a result of both the strain hardening characteristics of the material comprising the fuse member n and of geometric changes in the shape of the weak sections 12, sometimes referred to as "geometric softening".

The material for the fuse members n and the profiles of the weak sections may be selected such that the effects of strain hardening and geometric softening substantially cancel each other out. This may allow the threshold limit of the deformed fuse member n' to be controlled within a certain tolerance of the original designed threshold limit of the fuse member 11, at least over a certain range of displacements of the first and second joint portions 14, 15.

The material for the fuse members n and the profiles of the weak sections may be selected such that, in addition to yielding at an axial load 39 exceeding a threshold limit, each fuse member 11 may absorb a designed for quantity of energy and/or accommodate a designed for maximum displacement of the first and second joint portions 14, 15 prior to ultimate failure of the fuse member n.

Axial loading 39 of the brace member 6 causes the damping element outer plates 3oa, 3oU to Ue laterally displaced with respect to the damping element intter plates 3m, 31U. This produces shear displacements in the viscoelastic material layers 35 of the damping assemblies 32a, 32b. Larger axial loadings 39 result in larger shear displacements. During dynamic loading of a building structure 1, the viscoelastic material layers 35 absorb energy, thereby damping oscillations of the building structure 1 and preventing -13 -or reducing potentially destructive excitation of the dynamic modes of the building structure 1.

Above a threshold level of shear displacement, corresponding to an axial load 39 exceeding a damping element threshold limit, the viscoelastic material layers 35 will fail by rupturing of the viscoelastic material or by delamination from the metal layers 34. If the damping assemblies 32a, 32b of a brace assembly are degraded or broken during an extreme loading event, then that brace assembly 5 may be unable to provide bracing and/or damping to the building structure 1 in a subsequent extreme loading o event. For example, during an aftershock following a primary seismic event. For this reason, preserving the integrity of the damping assemblies 32a, 32b may be important. Additionally, replacement of the damping assemblies 32a, 32b may be difficult and/or expensive.

In order to protect the damping assemblies 32a, 32b, the threshold limit of the fuse members 11 may be designed to correspond to an axial load 39 which is less than the axial load 39 corresponding to the damping element threshold limit.

The material for the fuse members it and the profiles of the weak sections may be selected so that the effects of strain hardening and geometric softening are such that the threshold limit for the deformed fuse member 11' remains below the damping element threshold limit, at least over a certain range of displacements of the first and second joint portions 14, 15.

Testing and replacement of yielding fuse members As described hereinbefore, the yielding fuse member 11 is removably insertable into the first and second joint portions 14, 15 to form a fused joint 16, and the yielding fuse member 11 is not fixedly coupled to either of the first or second joint portions 14, 15. The yielding fuse member 11 may be held in place by friction, for example, friction may arise from the weight of the brace member 6. Alternatively, the yielding fuse member 11 may be held in place by a retaining member such as a split pin 56 (Figure 11), a cap, a bolt, an 0-ring or a length of wire inserted through an end of the fuse member 11 and bent.

After an extreme loading event, for example, especially strong winds or a seismic event, the integrity of fuse members 11 included in a building structure 1 may be tested. Any damaged fused joints 16 discovered may be restored by removing the deformed fuse members if and inserting undeformed yielding fuse members 11 as replacements.

It is important to identify and replace the deformed fuse members if because the building structure 1 will be distorted whilst brace members 6 are deviated from the designed positions. Additionally, as described hereinbefore, a deformed fuse member 11' may yield at an axial load 39 which is different to the designed threshold limit, which may result in unplanned and unpredictable behaviour of a building structure 1 in response to a subsequent extreme loading event.

Referring to Figure 21A, an operative may test the integrity of a removably insertable fuse member 11 by urging the yielding fuse member with a test force 4o below a predetermined force threshold, the test force 4o directed so as to attempt to remove the fuse member ii. When the fuse member 11 is held in place by friction, the test force may be applied directly to the first or second end 22, 23 of the fuse member 11.

Alternatively, when the fuse member 11 is held in place by a retaining member such as a split pin 56, cap, bolt, 0-ring or length of wire, the split pin 56, cap, bolt, 0-ring or length of wire is removed before application of the test force 40. The test force may be applied using a variety of different tools including, for example, a hammer or mallet.

This can allow an operative to test the integrity of yielding fuse members 11 quickly and easily, even when access space around the brace assembly 5 is limited.

Referring to Figure 21B, an operative may determine whether application of the test force 40 has resulted in the fuse member ii being displaced by a distance exceeding a -0or predetermined distance threshold. If the fuse member 11 is undeformed, then application of the test force 4o will result in a displacement of the fuse member ii. In such a case, the operative can restore the fuse member 11 to the starting position and the testing of that fuse member 11 is completed.

However, in the case of a deformed fuse member if, such as shown in Figure 20B for example, the deformed shape of the deformed fuse member if will prevent it from being displaced by a distance exceeding the predetermined distance threshold. In such a case, the failure to displace the deformed fuse member ii will indicate to the operative that the fuse member is a deformed fuse member if and must be replaced.

-15 -Removing the deformed fuse member 11' may require operations such as, for example, cutting or sawing through the shaft or the weak sections 12a, 12b which are exposed between each of the flange plates 21a, 21b and the gusset plate providing the second joint portion 15.

Depending upon the condition of the rest of a building structure 1, removal of a deformed fuse member 11' may allow the relative positions of the first and second joint portions 14, 15 to return to a correct position in which the respective through holes are aligned to allow insertion of the replacement undeformed fuse member it However, to the first end 7 of the brace member 5 and the second joint portion 15 may need to be moved into, and temporarily secured in, the correct position in order to allow insertion of the replacement undeformed fuse member 11.

Moving and or temporarily securing the brace member 6 in the correct position may be facilitated by the inclusion of the damping element 13 at the second end 8 of the brace member 6. The viscoelastic or elastomeric material layers 35 permit the brace member 6 to be more readily deflected than if the second end 8 of the brace member 6 was made from rigid material such as steel. As a result, the brace member 6 may be moved into and temporarily secured in the correct position without power tools/equipment, for example, using a wedge and hammer, a hand operated winch and rope, a crowbar, a scissor lift or a hand pumped hydraulic or pneumatic ram.

Alternatively, when the required correction is larger and/or when the force required is greater, moving and or temporarily securing the brace member 6 in the correct position 25 may use equipment such as, for example. motorised winches or powered hydraulic or pneumatic rams.

Modifications It will be appreciated that many modifications may be made to the embodiments hereinbefore described.

For example, removably insertable yielding fuse members n have been described as having weak sections 12 having an hourglass shaped profile with a sharply curved initial portions 27 leading into generally straight tapering portions 28 which intersect at a waist 26. However, other profiles of weak section 12 may be used. Referring to Figure 22, a fuse member 11 may alternatively include a second weak section 41 which has a continuously curved portion 42. The continuously curved portion 42 narrows to a waist 26 at the midpoint of the second weak section, and is symmetric about the waist 26. The continuously curved portion 42 makes an angle to the straight sides at either end of the second weak section 41. The profile of the continuously curved portion 42 may described a curve such as, for example, a segment of a circular arc, a parabola or a polynomial spline.

Referring to Figure 23, a fuse member 11 may alternatively include a third weak section 43 which is the same as the second weak section 41 except that the third weak section 43 has a second continuously curved portion 44 which is tangential to the straight sides at either end of the third weak section 43.

Referring to Figure 24, a fuse member 11 may alternatively include a fourth weak section 5o, formed as a notch 51. Alternatively, a fuse member 11 may include further types of weak section 12, characterised by any profile having a reduced cross sectional area with respect to the first end 22, second end 23 or central portion 24 of the fuse member 11. Weak sections 12 may have profiles which include kinks or discontinuities in the surface of the weak sections.

The brace assembly 5 has been described with the first joint portion 14 and the second joint portion 15 being coupled by one removably insertable yielding fuse member H. However, the first joint portion 14 and the second joint portion 15 may alternatively be coupled by more than one removably insertable yielding fuse member 11. For example, two, three, four or more removably insertable yielding fuse members 11 may couple the first joint portion 14 and the second joint portion 15.

The brace assembly 5 has been described with the first joint portion 14 provided by a pair of flange plates 21a, 21b disposed either side of and parallel with, the gusset plate providing the second joint portion 15. Referring to Figure 25, the first joint portion 14 may alternatively be provided by the brace beam member to and the second joint portion 15 may be provided by a pair of bracketing gusset plates 52a, 52b disposed either side of the brace beam member 10. The first end 22 of the fuse member 11 may be received by a through hole in a first bracketing gusset plate 52a, the central portion 24 of the fuse member 11 may be received by a through hole in the brace beam member 10 and the second end 23 of the fuse member 11 may be received by a through hole in a second bracketing gusset plate 52b. The first and second joint portions 14, 15 need not -17 -be provided by gusset plates, and may instead be integrally formed with one or more structural members 2, 3.

The fuse member 11 has been described with a pair of weak sections 12a, 12b.

Alternatively, the fuse member 11 may have only one, or three or more weak sections 12. For example, referring to Figure 26, the first joint portion 14 may be provided by a number of flange plates 53 and the second joint portion 15 may be provided by a number of gusset plates 54. The flange plates 53 and the gusset plates 54 may be interdigitated, and coupled together by one or more second fuse members 55 received into corresponding through holes in each flange plate 53 and gusset plate 54. The second fuse members 55 may include a weak section 12, 41, 43, 5o positioned between each flange plate 53 and each gusset plate 54. The first joint portion may be provided by at least one flange plate 53, and the second joint portion may be provided by at least one gusset plate 54. The arrangement of the flange plate(s) 53, gusset plate(s) 54 and weak section(s) 12 is preferably symmetric in order to reduce or eliminate distortions and to reduce or prevent displacements parallel to the fuse member axis 25. However, the arrangement of the flange plate(s) 53, gusset plate(s) 54 and weak section(s) 12 need not be symmetric, and the number of flange plates 53 may be equal to the number of gusset plates 54.

Claims

-18 -Claims 1. A brace assembly for interconnecting first and second structural members in a building structure, the brace assembly comprising: a brace member having first and second ends; a yielding fuse member having at least one weak section; a damping element coupled to the second end of the brace member for linking the brace member to the second structural member; wherein the first end of the brace member has a first joint portion for cooperating to with a second joint portion on the first structural member via the yielding fuse member which is removably insertable into the first and second joint portions to form a joint, the joint configured to provide a space around a weak section so as to permit plastic deformation of the fuse member.
2. A brace assembly according to claim 1, wherein the joint comprises: a knuckle joint comprising an eye, a fork and a pin, wherein the fuse member comprises the pin.
3. A brace assembly according to claim 2, wherein the first joint portion comprises the knuckle joint fork and the second joint portion comprises the knuckle joint eye.
4. A brace assembly according to any preceding claim, wherein the fuse member comprises a shaft having first and second ends.

-0or
5. A brace assembly according to claim 4, wherein the shaft includes first, second, third, fourth and fifth sections between the first and second ends, wherein the first, third and fifth sections have relatively large respective cross sectional areas and the second and fourth sections have a relatively small respective cross sectional areas thereby defining first and second weak sections. 3°
6. A brace assembly according to any preceding claim, wherein: the first joint portion comprises at least one flange plate; and the second joint portion comprises at least one gusset plate; wherein the flange plate(s) and gusset plate(s) interdigitate.
7. A brace assembly according to any preceding claim, wherein the fuse member and damping elements are configured such that, in response to axial loading of the brace member, the fuse member undergoes plastic yielding before the damping element is damaged.
8. A brace assembly according to any preceding claim, wherein the damping element comprises: a plurality of viscoelastic or elastomeric layers; and a plurality of metal plates; wherein the viscoelastic or elastomeric layer and metal plates are interdigitated and wherein the viscoelastic or elastomeric layer and metal plates are bonded.
9. A brace assembly according to any preceding claim, wherein the fuse member comprises mild steel or stainless steel.to. A building structure comprising: first and second structural members; and a brace assembly according to any preceding claim interconnecting the first and second structural members.it A building structure comprising: first and second structural members; and a brace assembly interconnecting the first and second structural members, the brace assembly comprising: a brace member having first and second ends; a yielding fuse member having at least one weak section; and a damping element linking the second end of the brace member to the second structural member; wherein the first end of the brace member and the first structural member arc connected by a joint comprising the yielding fuse which is removably insertable, the joint configured to provide space(s) around the weak section(s) to permit plastic deformation.12. A brace assembly for use in the building structure according to claim it.13. A method of servicing a building structure according to claim 10 or 11, the method comprising: urging the yielding fuse member with a force below a predetermined force threshold so as to attempt to remove the fuse member; determining whether the fuse member is displaced by a distance exceeding a predetermined distance threshold; and on a negative determination, replacing the fuse member.