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THE LaPALLE DUCTILE TIE CONNECTOR

David Allen Technical Consultant

37 Ladies Mile Auckland 5, New Zealand

ABSTRACT

Structural analyses of anchorages of non-structural cladding elements to a main loadbearing frame require consideration of the in-service effects of long term differential building movements, together with an accommodation for in-plane and faceloads arising from severe wind or seismic effects.

The LaPalle ductile Tie Connector is a New Zealand invention wherein the geometry of the three interlinked parts allows for code-imposed degrees of vertical, horizontal and pivotal in-plane movements. Conjointly, the device makes use of the ductile properties of metal to achieve a response mechanism to faceloads that can be so structured as to cater for a number of end-uses.

The LaPalle Tie Connector is the precursor of a generation of masonry anchorages which, being rationally designed, will integrate successfully with modern engineered masonry cladding systems.

KEY WORDS

Brick, corrosion, ductility, differential movement, masonry, ties, veneer.

I NTRODUCTION

"Wall tie performance, or the lack of it, has been shown to be the critical factor in determining the service life of cavity masonry walls and masonry veneer constructions. The integrity of both forms of construction will depend not only on the proper fixing of wall ties, but also on the correct choice of tie to be used in satisfying the requirements of the building regulations. Until such time as the importance of the material character­istics of wall ties and their performance criteria are acknowledged by both the tradesman and the designer, masonry wall ties will continue to be the 'Achilles heel' ofcavity wall and masonry veneer construction. In recent years, attention has been focused on the performance of wall ties, resulting in the promulgation of a number of comprehensive national Standards governing the use of wall ties used in masonry constructions."

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These comments are taken verbatim from the foreword to SANl Dl 4210 [1] 1988, which addresses the problem of in-service and seismic displace­ments between veneers and various stiffnesses of support structures, codifying wall tie types by performance and by classifications of duty so as to meet the varying load and displacement cri teria which are contained in the current and proposed Codes of Practice for General Structural Design and Design Loadings for Buildings, NlS 4203 [2] and Dl 4203.[3]

Performance criteria for tie stiffness, ductility and ultimate strength are set forth in Dl 4210, with the intention of attaining higher levels of safety than those demonstrated in the past by empirical wall tie anchorages where manufacture and design has been based on incremental stages of improvement to either round wire or to strip metal fabrications.

OEFINITION ANO WALL TIE FUNCTION

In this paper a wall tie connector is defined as a wall tie with two or more interlinked components, exclusive of fixings. In further discussion, the LaPalle Tie Connector will be shown to have developed within the framework of NlS 4203 and Dl 4210, and that its performance can be quantified in terms ofaxial characteristic strength, characteristic cyclic strength, characteristic stiffness and axial ductility.

BACKGROUNO TO THE LaPALLE TIE CONNECTOR OEVELOPMENT

Prior to, but more so during the 1970's, the shortcomings of masonry anchorages came under increasing scrutiny, as did other aspects of the then bUilding scene where some high-rise masonry claddings were exhibiting signs of distress.

In seismic areas, masonry ties and connectors would predictably be revealed as ineffectual links between a support structure and its veneer, with the attendant spectacular failures certain to find their way into the literature.

Commenting on damage to buildings in Coalinga during the 2 May 1983 earthquake, Mr James Amrhein, Executive Director of the Masonry Institute of America, in his address to the New lealand Institution of Engineers Annual Conference 1984, is reported as saying, 'The earthquake showed too that veneer anchorages must be improved. More adequate anchorage to supporting walls was required as corrugated metal ties did not hold the masonry. '

Given the design imperfections of masonry tie anchorages where increased dynamic axial loadings are relieved only by tie failure, it is understandable that as the maximum load capacity of conventional ties is over-reached, masonry fails. Such a failure mode leads to shedding of veneers in the now familiar pattern whereby tie failure at the top of a masonry veneer 'unzips' the remaining tie connections progressively down the wall.

In a non-seismic situation of 1976, it is informative to quote Grimm [4], " ..... but these empirical building standards represent only guesses, rather than rigorous rational performance criteria. Because these guesses are occasionally not very good, masonry walls have fallen off buildings."

Pertinent chronological extracts relating to the interplay of the various factors which influence the performance of masonry claddings are examined to round out the background material which has led to the development of the LaPalle Tie Connector.

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Thomas [5] (1970) presented 1968 data on the strength, function and other properties of wa11 ties. The material relates to British practice for cavity wall ties and dovetail in-slot anchors. The properties of wall ties and their suitability in respect of differential movement, fire resistance, corrosive conditions and frost effects were discussed. Results of research work on the shear and pullout values of wall ties used as peripheral fixings for brickwork panels were described, together with a table of recommended safe loads. The tensile strength of wall ties with varying degrees of embedment and precompression due to wall deadload were included, as well as a discussion on the suitability of polypropylene ties. Thomas commented that under tensile loadings polypropylene failed by extension or by fracture, and at relatively low loadings. (In-plane racking tests on polypropylene ties undertaken as part of this project have confirmed brittle failure at low lateral displacements.)

Grimm [4] (1976) in discussing metal ties and anchors for brick walls said, " ••••• the growing use of brick masonry bearing wa11 structural systems for high-rise frameless buildings requires that structural engineers give increasing attention to masonry construction details, among the more important of which are the material, size, shape, and position of metal ties and anchors, on which the structural integrity of masonry walls is highly dependent. Structural design practice in selecting from the array of available materials has been largely heuristic and intuitive. Rational analysis of the physical and chemical properties of metal ties and anchors in masonry walls has not kept pace with the structural engineering analysis of masonry, which has developed rapidly in the last decade."

Ongoi ng, Grimm offers thi s penetrat i ng comment, "Des i gn of wa 11 anchorage systems is frequently in the gray area of professional responsibility between architects and engineers and is frequently neglected by both, whi~h results in the use of anchorage systems having factors of safety moch lower than that of the walls and frequently results in structural failure, particularly in nonbearing curtain walls."

Grimm opines, "The reason that more disasters are prevalent can be attributed only to the fact that buildings are designed to resist assumptions rather than forces."

Borchelt [6] (1979) in listing design considerations for masonry curtain walls on tall buildings, recoçnised previously documented causes of differential movement such as (i) elastic deformation; (ii) shrinkage in concrete and concrete masonry; (iii) creep; (iv) thermal movement and (v) moisture expansion of clay masonry. In the transfer of wind loads to the backup frame, flexible ties were mentioned as requiring only to transfer direct tension and compression forces, not shear or flexure.

Borchelt commented also that most stud manufacturers' recommendations for steel stud sizes and spacings were based solely on steel stress and steel buckling values and therefore, to reduce cracking of masonry bedjoints because of the disparate stiffnesses of veneer and backup framing, stud span lengths should be divided by 600 to limit stud defl ect i ons.

Monk [7] (1980) in developing the historical changes in masonry from a major structural loadbearing material to a nonloadbearing cladding outlined the progression of (i) walls becoming thinner; (ii) mortar becoming more cementitious and (iii) skeleton frames becoming the support structure -leading to increased occurrences of water leakage, cracking failures and problematic anchorage security.

In his section, 'Causes of Failure', Monk highlighted SOme masonry faults arising from differential building movements where clay masonry is attached without due regard for flexible anchorages, as (i) racking cracks

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in brick walls with few openings due to forced participation as a shear wall; (ii) shearing at window or door openings causing sill, jamb and head splitting as the exterior wythe moves relative to the interior construction to which the window or door is rigidly attached and (iii) vertical cracking at external corners of long walls as intersecting walls move relative to a fixed corner.

Hastings [8] (1980) reporting on connectors for masonry recorded that although the design of masonry buildings had become increasingly sophisticated in recent years, the design of connectors which join one masonry wythe to another or to the building frame had not kept pace, and attention was being drawn to the importance of this topic by the occurrence of hazardous and costly building failures. The outcome was CSA A370 [9], perhaps the first North American Standard devoted exclusively to the subject of masonry connectors. In recognising the importance of connectors, the view of the development committee was that CSA A370 would bring some order into the field of connections and encourage research on the subject.

Comments from Hastings illustrate problems perceived at that time.

(a) "Masonry design based on engineering analysis has reached an advanced stage of development. Tall masonry buildings have been built with thin walls stressed to levels unimagined a few years ago. This sophistication in the design of the masonry elements has not been matched by progress in the design of the connectors which must tie these elements to each other and to building frames. A need has arisen for specialised connectors which can be built into these thin walls and which can resist specific forces."

(b) "More stringent requirements for wind and seismic design have focused attention on the need for effective connectors which can literally 'hold buildings together' in the face of strong lateral and uplift forces."

(c) "Masonry is now being used in ways not foreseen by many building codes. Examples are prefabricated masonry panels, and the use of masonry veneer secured to metal studs in high-rise buildings. Such novel uses generate a need for specialised connectors."

(d) "The current necessity of reducing the heat loss in building envelopes has resulted in a demand for wider cavities in masonry walls to accommodate more insulation. This in turn has given rise to a search for special ties which can 'bridge the gap'."

(e) "The detailing of some modern buildings has led to increased water penetration of masonry walls on the one hand, and higher internal humidity has increased the incidence of condensation within the walls, on the other hand. Some of the cladding failures referred to earlier have been traced to the early corrosion of connectors. It is clear that there is a need for more information on this subject."

Warren, Ameny and Jessop [10] (1983) in their report on the state of the art of masonry connectors, cited certain areas where further research work was urgently needed. Among those issues deemed either not to have been addressed or not covered in adequate detail were (i) the behaviour of rigid connectors; (ii) the effect of wall connectors on wall lateral strength; (iii) required factors of safety for connectors; (iv) fire resistance of connectors, and (v) procedures for evaluating the durability of connectors.

In their 1985 report, Ameny and Jessop [11] were further drawing attention to the causes and effects of failures of masonry claddings.

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The section devoted to ties, anchors and shelf angle details quoted instability and rain penetration resulting from (i) ties having inadequate embedment in the mortar; (ii) ties sloped to the inside of the building; (iii) ties pushed into green mortar instead of being built in; (iv ) mortar sticking to ties and (v) moisture drips in ties not positioned in the centre of the cavity. The foregoing faults would be magnified by the effect of corrosive attack on ties and fixings.

Allen and Lap i sh [12] (1985) in their analysis of the interaction of (2.4 m square) timber-framed walls with a tied clay masonry veneer under cyclic racking loads concluded that (i) the integrity of such veneers if subjected to in-plane loads could be preserved by achievable 400 kPa masonry-to-mortar bond strengths; (ii) mandatory data for designers should be required from manufacturers of masonry ties and connectors in respect of material properties and performance characteristics under face and in-plane loadings, and (iii) code imposed performance characteristics parameters should specify minimums for accommodating differential in-plane movements between the structural wall and the tied veneer whilst maintaining faceload capacities of wall tie assemblies.

Walazek and Gerstner [13] (1987) in their recent historical survey of the develop~ent of masonry cladding design, focused on unresolved problem areas by enumerating some of the perceived causes as (i) moisture expansion and shrinkage of the masonry cladding; (ii) thermal expansion and shortening of masonry; (iii) creep deformation, and (iv) weathering of brick masonry. In attributing the principal cause of cladding failures as arising from restricted differential movement between a building structure and its envelope, the authors made a number of important recommendations in respect of expansion joints, both vertical and horizontal, but touched upon the role of connectors only in passing in their conclusions.

They did, however, raise an interesting point concerning a lack of dialogue between interdisciplinary areas of a construction team, making the observation that while architects and cladding suppliers share the primary responsibility for designing cladding details, they cannot realistically do so without relevant information from the structural engineer. They stated further that it would be desirable for the engineer to go to the additional step of acquainting the contractor and masons with the importance of various connection details at preliminary design meetings. The authors then touched upon the legal complications arising from divided responsibilities, quoting from reference [14] 'a lawyer's attitude will be that the structural engineer had an overall understanding and control of the project, as opposed to the cladding designer who knows only his product. I

The foregoing recitations of cause and effect as related to masonry cladding failures have, because of the gravity of such events, impacted on the wider scene of professional liability.

The legalities of apportioning responsibilities for cladding failures are beyond the purview of this paper. However, Bulletin #75 [15] (December 1985) devoted to a Professional Liability Loss Control Program prefaced an overview of the situation with the heading, "Application of New CSA Masonry Standard Could Avoid Catastrophe" and, in the introduction, voiced this concern: 'During the last five years a number of architects and structural engineers have unfortunately been in major professional liability claims emanating from problems with connectors. Most of these claims involved high-rise masonry buildings. A prominent Toronto consulting engineer has kindly agreed to write the following text which we highly recommend as required reading for all designers and specification writers. I

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Notwithstanding the inability of the loss control administrators to outline mandatory 'thou shalt not' clauses, the role and importance of connections has now progressed beyond the 'gray area' of Grimm [4]. Connectors henceforth will be a rational design detail in the literature which designers may overlook, but only at the implied risk of future litigation.

DESIGN PHILOSOPHY OF THE LaPALLE DUCTILE TIE CONNECTOR

The background notes have offered a useful insight into the nature and the complexities of the problems encountered in the design, construction and the performance of masonry veneer claddings. Notwithstanding the previous recitation of cause, effect, and likely remedies, in the New Zealand Codes of Practice, the seismic design of masonry veneers and their wall tie connections is governed by two basic considerat i ons, viz:

(1) In-plane separations between the veneer and the seismic resisting structure shall be provided where the interstorey lateral drifts lie between 0.0006 and 0.01 of the storey height.[2.3]

New Zealand codes intend that the designed seismic response of the basic earthquake-resisting structure be not modified by bracing effects arising from stiff brittle nonloadbearing elements such as masonry veneers. Veneers are, therefore, to be adequately separated from the structure to allow for the required independent in-plane movements to take place between the veneer and the structure.[2,3.16] Inter-storey drifts of up to 1/100th of the storey height are permitted per floor. Current building structures may sustain lateral drifts of between 15 mm and 30 mm per floor, whereas the in-plane seismic drift of masonry veneers would be in the order of a few mil 1 imetres only. In-plane deflections of flexible support members (t imber or steel frame) will be significantly greater than those induced in masonry veneers. Masonry ties and connectors which are inflexible or very stiff in the horizontal plane will attract significant shears, moments or axial forces into themselves and their fixings, as well as into the veneer when used in flexible structures. Effectively this means that in the event of an earthquake, wall tie connections which during their early in-service life would have undergone some differential vertical movement , must be further capable of accommodating significant lateral in-plane differential seismic movements between the deforming structure and the veneer, yet without destroying the faceload capacity of the wall tie or its connections.[16]

It should be noted that high axial forces will be induced into simple round-wire flexible ties at extension, to accommodate maximum differential diagonal movements between the attached elements when undergoing seismic attack. Flexible ties preferably should have a sliding configuration which will not alter the axial load capacity of the tie assembly.

In the interests of public safety, veneers ought not to be subjected to large in-plane forces from the structure, and should be designed and built to survive a seismic event with a minimum of damage and consequent restoration costs .

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Timber Stud Framlng------t---'I-i<'

Fixing Bracket----,?=---t--o

Fixlng Screws---::;;,.jf--H---+-~

Locking Bar---1!>T

Dralnage ca~"", ~--,

Locking Tonque----""Ir--o

Figure 1. Isometric view of the LaPalle ductile Tie Connector illustrating the geometry of achieving the following in-plane movements over a clear cavity of 55 mm to 65 mm -

± 40 mm horizontally, total 80 mm; ± 10 mm vertically, total 20 mm; Pivotal movement, approximately 30° left or right.

(2) Seismic induced face10ads within the mass of a masonry veneer wi11 vary with the height of the structure.[2,3]

These loads will range from one times gravity at ground level, to; twice the gravity equivalent at the top of the structure. The New lealand Limit State Loadings Code, [3] replacing the present code, [2] varies tie loads considerably, depending on (a) the ductility and the seismic response of the earthquake resisting structure; (b) the ductile capacity of the wall tie connections, and (c) the natural period of the veneer and its positioning within the height of the structure.

In some cases, the new code faceloads on veneers exceed present code requirements with levels approaching 3g. Such requirements are based on a paper by Kelly [17] giving the results of comprehensive computer-based studies using actual earthquake records.

In the following tables, faceload forces and tributary loads are placed in context with NlS 4203 and Dl 4203.

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TABLE 1 Faceloads on three New Zealand brick types

Faceloads kPa/psf Brick width Mass 19 29 39 70 mm Clay 135 kg/m' 1. 35 2.7 4.05 perforated 28.18 ,sf 28.18 56.37 84.56 90 mm Clay 170 kg m' 1.7 3.4 5. 1 perforated 35.49 ,sf 35.49 70.8 106.1 90 mm Concrete 200 kg m' 2 4 6 solid, frogged 41.76 psf 41.76 83.5 125.25

TABLE 2 Tributary loads adjacent to each tie when

spaced at 600mm x 350mm (2ft x 1.15ft).

Tributary Loads Brick width Force 19 29 39 70 mm Clay N 283 567 850 ~erforated 1bf 64.8 129.62 194.4 90 mm Clay N 357 714 1071 !;!erforated 1bf 81.6 163.25 244.88 90 mm Concrete N 420 840 1260 solid, fro.9.ged 1bf 96.04 192 288

When such loads are transferred from the veneer through the ties and into the support stud walls, loads on the ties are changed from the adjacent tributary areas by the stiffness and the inherent strength of the various component parts (veneer, wall tie connections and stud framing) of the composite structure. Maximum loads in wall tie connections may be up to three to eight times greater than the tabulated values given previously, in locations adjacent to floor levels.[18] Where faceload deflections of the supporting structure are likely to be significant as in the case of light gauge steel channel sections, measures are required to either adequately match stiffnesses or, alternatively, to provide highly ductile connections to limit the axial load in wall ties adjacent to floors and to allow for load redistribution throughout the veneer cOhstruction.[18]

Additionally, DZ 4203 requires that connections which respond elastically must have a safety facto r of 1.2 over and above the code tie loads. Where veneers and ductile ties have been designed by capacity design procedures, loads on wall tie connections may be substantially reduced. This is consistent with the seismic design philosophy which assumes that the structure will perform as a ductile mechanism. Ductile hinges may be regarded as fuses which deform without increasing the stresses in the connecting members beyond their ultimate strength. The system can be likened to a glass-framed building with lead joints. Where ductile hinges are not provided, a glass building must be strong enough to resist the full elastic response generated within the structure by an earthquake - which may be some six times greater than if designed for ductility.

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o----+-- St u d F r a m! n 9 ---!--- --<;>

Flx ing Sc r e ws

F1 xing Bracket

Locking Bar

'-:,

_~ __ ~ __ ~t-~==~==~,LockTng TOngue~=:~:271~~~r-~~ Veneer Claddlng

Figures 2 and 3. Plan views of the ductile deformation mechanism of the LaPalle Tie Connector illustrating positive and negative faceloads applied

to the centre, and to one end of the square locking bar.

Figure 4.

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LO A O/ (N)

2000

2000

Hysteretic modelling ofaxial ductility and cyclic strength of the LaPalle Tie Connector.

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MATERIAL PROPERTIES - LaPALLE DUCTILE TIE CONNECTOR

(1) Metal Components: In accordance with the relevant bUilding regulations, the sheet metal components of the LaPalle Tie Connector and the square-section connecting tie rod (Figure 1) are fabricated from thicknesses of metal sufficient to give an appropriate strength and stiffness to accommodate specific combinations of in-plane and out-of-plane loads and building movements. Commonly, 2 mm stainless or 2.5 mm mild steel sheet is used, with a 6.3 mm square connecting tie rod o Other weights of metal will depend on the structural analysis of the intended end-use . (2) Fasteners: Two fixing screws of material properties sufficient to secure the tie connector are normally supplied. The fixings are compatible with the corrosion-resistant material of the tie connector components. (3) Corrosion Resistance: CSA A370 (D5) stated in 1984 that, "many connectors currently sold as corrosion resistant may provi de only token resistance against corrosion". Clearly the starting point in combatting corrosion is the attitude adopted by tie manufacturers in the merchandising of masonry ties.

The degree of protection to the component parts of the LaPalle Tie Connector as manufactured under licence is governed by the appropriate standards in the country of use, but is not less than that provided by hot-dip galvanizing to BS 729, after forming, or by fabrication in austenitic stainless steels.

PERFORMANCE CHARACTERISTICS - LaPALLE DUCTILE TIE CONNECTOR

The Brick Institute of America, BIA Technical Note 44B [19] (March 1987) stated that present analysis techniques that might accurately model metal-tied wall systems were still in the developmental stage and would require further refinement and verification through testing.

Guideline recommendations were, however, offered for achieving acceptable strength and deformation characteristics. The LaPalle ductile Tie Connector can be shown to comply fully with the following parameters. (1) Tolerances. The mechanical tolerances of the assembled LaPalle Tie Connector component parts can be held within a total of 1.2mm (O.05in). (2) Controlled Yield. The LaPalle Tie Connector is capable of undergoing a controlled yield at a predetermined load and dêflection level. This feature may be used so as to be compatible with the forces imposed on a veneer by the bowing of the stud support system, wherein inward or outward bowing may result from vertical loads imposed on the studs by the structural deflections of the main frame members. (3) Adjustment Eccentricities. .The fixing of the LaPalle Tie Connector is normal to the plane of the support structure, and is independent of masonry wythe coursings . Vertical and horizontal spacings can be those required by the relevant specification clauses . (4) Connector Integrity. When the component parts of the LaPalle Tie Connector are assembled and interlocked, disengagement of the adjustable parts cannot occur even when the Tie Connector is at full horizontal or at full vertical extension. (5) Moisture Barriers. The LaPalle Tie Connector assembly is provided with water drip devices which do not interfere with structural performance and which prevent the transfer of free water to the inner wythe or to the support member.

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(6) Tie Stiffness. The LaPalle Tie Connector can be so proportioned that it has a near constant stiffness with acceptable mechanical tolerances over the full range of specified horizontal and vertical adjustments. A stiffness of the Tie Connector in excess of 377 N/mm (100 lbf/0.05 in) is being achieved with the model being presently developed for the New Zealand market. (7) Non-seismic Effects. For very high wind situations or for multi-storey continuous masonry veneers, the LaPalle Tie Connector could be used to distribute or to share applied loads into the less stiff parts of the structure. This design approach would reduce the high out-of-plane moments in a veneer adjacent to floors and at roof level, and would minimise movement in a veneer to below crack formation levels, hence reducing moisture ingress and weathering problems. The ductility mechanism of the LaPalle Tie Connector at ultimate loads has been specially contrived to control extreme seismic lateral loads and could be utilised in a similar manner to resist very high wind loads.

SUf>fo1ARY

This pape r traverses two decades of selected reference extracts which outline shortcomings in masonry cladding constructions and their connections. A rational design philosophy covering assessments of differential in-plane and out-of-plane building movements is discussed. An exposition of the LaPalle Tie Connector configuration and hysteretic modelling indicates that because the device is the product of rational design, those performance criteria demanded by the relevant building regulations can be satisfied.

The geometry of the LaPalle Tie Connector allows for significant degrees of in-plane differential building movements while exhibiting structured levels of stiffness and ductility to cater for varying degrees of moderate or extreme faceloads.

The LaPalle Tie Connector complies with the governing seismic requirements of the New Zealand Codes of Practice. Moreover, in the further pursuit of safer levels of masonry veneer connections, the LaPalle Tie Connector offers an anchorage system fully able to satisfy the Brick Institute of America recommended guidelines for better masonry cladding constructions, as given in their Technical Note 44B, 1987.

REFERENCES

1. Standards Association of New Zealand. Draft for comment: code of practice for masonry struction: materials and workmanship. SANZ DZ 4210, February 1988.

2. Standards Association of New Zealand. Code of practice for general structural design and design loadings for buildings. SANZ NZS 4203:1984.

3. Standards Association of New Zealand. Draft for comment: general structural design and design loadings for buildings. SANZ DZ 4203:1986.

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4. Grimm, C.T. Metal ties and anchors for brick wa11s. Journa1 Structura1 Division, Proceedings of ASCE, Vo1. 102, No. ST4, Apri1 1976, pp. 850, 839, 852.

5. Thomas, K. The strength, function and other properties of wa11 ties. Brick Deve10pment Assoe., Research Notes, Vo1. 1, No . 2, March 1970.

6. Borche1t, G.J. Masonry curtain wa11s on ta11 bui1dings. BIA Proceedings, Fifth Internationa1 Brick Masonry Conference, October 1979, pp. 573.

7. Monk, C.B., Jr. Masonry facade and paving fai1ures. Proceedings Second Canadian Masonry Symposium, June 1980, pp. 470, 477, 478.

8. Hastings, B.A. Connectors for masonry. Proceedings, Second Canadian Masonry Symposium, June 1980, pp. 165.

9. Canadian Standards Association. Connectors for masonry. CAN = A370 = M84, March 1984.

10. Warren, D. J. N., Ameny, P., and Jessop, E. L. Masonry connectors: a state of the art reporto Proceedings, 3rd Canadian Masonry Symposium, June 1983, pp. 17-12.

11. Ameny, P. and Jessop, E. L. Masonry c1adding: a report on causes and effects of fai1ures. Proceedings, Seventh Internationa1 Brick Masonry Conference, February 1985, pp. 266.

12. A11en, D. and Lapish, E.B. The interaction of timber framed wa11s with a tied masonry veneer under cyc1ic racking loads. Proceedings, Fourth Canadian Masonry Symposium, June 1986, pp. 7.

13. Walazek, J.M. and Gerstner, R.W. The development of masonry cladding design: an historical survey. Proceedings, Fourth North American Masonry Conference, August 1987, pp. 35-4, 35-13.

14. Becker, R.J. and Robison, R. Get involved with cladding design~ Civil Engineering, Vol. 55, June 1985, pp. 70-73.

15. National Program Administrator and Simcoe Erie General Insurance Company, Canada. Application of new CSA masonry standards could avoid catastrophe. Loss Control Bulletin ~ 75, December 1985.

16. Standards Association of New Zealand. Code of practice for the design of masonry structures. SANZ NZS 4230:1985.

17. Kelly, T.E. Floor response of yielding structure. Proceedings Second South f?cific Regional Conference on Earthguake Engineering, Volo 1, May 1979.

18. Lapish, E.B. and Allen, D. Variability of tie loads in brick masonry veneer construction. Proceedings, Fourth Canadian Masonry Symposium, June 1986.

19. Brick Institute of America. Wall ties for brick masonry. . BIA Technical Note 44B, March 1987, pp ~ 6.