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REMEDIAL OR SUPPLEMENTARY TIE SYSTEMS FOR BVlSS WALL SYSTEMS

E.F.P. Burnett1, M.A Postma2, C. Wegner3

Two problems related to the lateral tie system in existing veneer walls, incJuding Brick Veneer Steel Stud (BV/SS) walls, are :

• insufficient lateral attachment between the brick veneer and steel stud as a result of design andJor construction inadequacies

• deterioration in the lateral attachment often as a result of corrosion

Remediation may incJude the provision of new ties either to supplement, restore, or enhance existing lateral attachment between the brick veneer and steel stud.

This paper documents some of the resuIts from a project to assess various remedial strategies for providing supplemental ties in BV/SS wall systems. The mam objectives were :

• to establish what remediaJ tie systems were commerciaJly available • to assess and compare each system

Eleven remedial tie systems were evaluated based on demonstrations of their installation in a BVlSS cJad building. The evaluation of the remediaJ tie systems included such issues as the ease and time of installation, the strength of the connection and the potential for and the effect of corrosion on the connection. Procedures for locating the steel stud from both the exterior and interior have also been identified and documented. lt was concluded that some of these remedial tie systems may be feasible but require additional development work and testing.

Keywords: ties, brick veneer, steel stud, remedial, masonry c1adding

Professor of Civil Engineering and Director Building Engineering Group, University of Waterloo, Waterloo, Ontario, Canada, N2L 3G I

2 RestorationlStructuraJ Engineer, Carl Walker Inc., 445 West Michigan Ave, Suite 101 , Kalamazoo, Ml49007

3 Research Assistant, Building Engineering Group, University of Waterloo, Waterloo, Ontario, Canada, N2L 3Gl

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INTRODUCTION

Over the last 10 years, the performance of the clay brick veneerlsteel stud (BV/SS) enclosure system for multi-storey residential buildings has received a great deal of attention. Many buildings have BV/SS enclosures and many of these have experienced or are experiencing problems. Repair is expensive and there is also considerable uncertainty as to the levei and extent of deterioration and darnage, especially the corrosion of metal components--i.e., the ties, the stud system and the self-tapping screws. Therefore, it is particularly difficult to decide on the form and extent of remedial action. The design professional faces a real dilemma when choosing an appropriate building repair strategy. If legal action is involved, there is considerable pressure to prescribe a conservative and thus relatively expensive solution. There is also the question of knowing what to do about those BVlSS waIls that have yet to exhibit a visible problem but are known to be vulnerable and likely to experience problems. The Canada Mortgage and Housing Corporation (CMHC) initiated a multi-task project to address these topics.

The primary objective of this research project was to develop various strategies for the remediation and thus the control or avoidance of problems in existing BV ISS wall systems. This paper summarizes the work that is reported in detail in a report entitled "Task 1: Brick Ties - Options For Remediation" issued by CMHC, December 1992. 1

The main objective in this R&D task was to identify, demonstrate and assess the methods of providing supplemental ties to BVlSS buildings. Of particular interest were retrofit procedures that could be conducted from the interior. A secondary objective, common to ali repair systems, was to develop procedures for locating the steel stud from both the interior and the exterior.

PROCEDURE

Four related steps were involved. First, the major manufacturers and distributors of masonry tie systems in Canada were canvassed to identify those systems that are commercially available and suitable for tie retrofit in BV/SS systems. The following companies were approached :

Dur-O-Wal Ltd., Mississauga, Ontario Fero Holdings Ltd., Edmonton, Alberta Cintec Canada, Nepean, Ontario Blok-Lok Ltd., Weston, Ontario Hilti Fastening Systems, Bramalea, Ontario

The second step involved the actual on-site demonstration of installation procedures on an existing BV/SS building by the tie manufacturers and distributors. In this demonstration task the practical difficulties of locating the steel studs for both exterior and interior retrotit were assessed. Three of the tive companies participated in these demonstrations. In total 11 tie systems, 4 installed from the interior and 7 installed from the exterior were assessed.

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After the installation demonstrations, the third step involved opening up the walls and investigating each repair method. Large sections of interior gypsurn board were removed to inspect the connections of the tie systems in the brick and the steel stud and to assess the damage to the vapour retarder, the exterior sheathing and other building components. Most of the repair systems were also examined from the exterior.

The fourth and final step was to compare each retrofit system, to describe the method of installation and to assess the effectiveness of each retrofit procedure.

DESCRIPTION OF BUILDING AND BRICKWORK

The building used for the demonstrations is a 9 storey multi-unit residential building located in southwestern Ontario. The building is approximately 5 years old. The building structure comprises cast-in-place reinforced concrete floor slabs, colurnns and shear waIls. The section of non-structuraI externaI wall on which the demonstrations were made is located on the ground floor.

Figure 1 and 2, show the composition of the wall : 90 mm c1ay brick veneer 25 mm cavity 25 mm expanded polystyrene sheathing 89 mm steel stud backup (0.9 mm or 20 gauge) 89 mm fibreglass batt insulation 6 mil polyethylene vapour retarder 12.5 mm gypsum board

The brick veneer is interrupted at every floor, supported on shelf angles. Although this is a 9 storey building, the ties that were used are residential corrugated strip ties. The CSA Standard CAN3-A370-M842 restricts the uses of standard corrugated strip ties as follows :

1) use in buildings not exceeding 11 metres in height (Clause 9.2.1. 1) 2) use with the maximum unsupported length of tie between the

veneer and its structural backing of25 mm (Clause 9.2.1.2 (b))

Since the ties did not conform to code and they were not instaIled properly, the instaIlation of supplementary ties wiIl likely be one component of remediation of this building. These deficiencies made this building suitable for this project to physicaIly demonstrate various remedial methods for installing supplementary ties.

Complete replacement of the brick veneer can be very expensive. Adding remedial ties, provided the brickwork can be properly re-attached to the steel studs with minimum damage, will be quicker and less cost1y than complete replacement of the veneer. For these reasons remediaI ties need to be assessed as a practical means of repalr.

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FIGURE 1 --- Helifix Interior Repair - HRT80 Tie Dry Fix

6.Om.m dia. bole I.Q bnd:

M«b .. iuJ CoaD«I.io. la Briclr. VCDt'I!r

6.Smm dLa. bole iD J~I Jl\Iod nMlgc and sbcal.hi.Dg

HRnGlie 220mm 100g

~c<h.nkal ConD«tioQ in Slcd Stud

o 89:r. 22S o.y &ia

~ R12BauWulauOll.

6 mil Polyetbyk:nc Vapour Rcu.n:lcr

:t..::: .. ~J:.l.P>:~. ~tõ~ .~Y;?~)i(-:; ~ 12.5rnm Gypsw:n Boud.

FIGURE 2 --- Dur-O-Wal Exterior Repair - Threaded Bolt and Expansion Anchor

Mcc .... atal COOA«Uoa 111 Brkk v cn«r

Mcchanical Conncchon in Slttl Slud

o 89:1 22S Oay Bric.k

~15mmC..,iry

..... ;.-t--t--t--cf--- 90mm Steel Stud 20 ,aLlge

~ R12 Bau ItuuJ.atiOQ

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LOCATING THE VERTICAL STEEL STUDS

Properly locating and penetrating the steel stud has a bearing on the reliability and effectiveness of any of the repair procedures. Therefore a common concem with ali the retrofit tie systems was how to locate the vertical steel studs. The objective is to locate the stud with a reasonable degree of precision, to establish on what side the web lies (if possible) and to do so as quickly and with as little physical damage as possible. The ease with which this can be done is very much dependent whether done from the interior or the exterior, on floor height and the nature of the facade, i.e., many windows, straight runs etc. The degree of precision in locating the stud and the determination of the position of the web are. important in order to ensure that the tie is installed in the flange as close to the web as possible without damaging the web. In this demonstration project, various methods of steel stud location were used.

From the interior the following methods were found useful in locating the steel studs : I) Locate and mark the likely positions of steel studs at known

positions, i.e., adjacent to windows, doors etc. 2) If possible obtain design drawings for approximate stud

location 3) a) Confirm these positions with a metal detector, or

b) Confirm the location of the flange and the direction of the C channel with a hammer and nail or spike, etc.

Locating the steel studs from the exterior was found to be more difficult than from the interior. Two methods of locating the steel studs were demonstrated. The frrst involved the use of a metal detector to locate the steel studs while the second method involved saw-cutting the mortar joint in the expected vicinity of the steel studs.

The success of the method involving the metal detector will depend to a large degree on the particular metal detector, the experience and competence of the user, and the type of the tie system. In some respects, the small diameter ties in some of the retrofit systems allow for a larger margin of error in locating the extremities of the steel stud flange than the larger diameter tie systems, as the larger diameter ties require greater precision in locating the flange of the steel stud in order to make an effective connection and to avoid drilling into the web section of the steel stud. However, when using a metal detector to locate the steel stud it was found that the steel studs could not be located accurately enough and the use of a metal detector to locate the steel studs may result in missing the steel stud altogether. To locate the steel studs from the exterior the following methods were found useful :

1) Guess/assess the location of those steel studs of known position i.e. adjacent to windows, doors etc.

2) Use nondestructive methods of locating the steel studs on the interior described earlier and transfer these locations to the exterior.

3) Saw-cut the mortar joint in the estimated vicinities of the steel studs and prod with a thin rod to determine the exact location of the steel stud, as well as the position of the web of the steel stud.

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INTERIOR REP AIR :METHODS

Four different interior retrofit systems were demonstrated, namely : INIl Cintec Cementitious Sock with a 22 mm hole 1NT2 Dur-O-Wal side mounting bracket and expansion anchor 1NT3 Dur-O-Wal Stainless Steel Rod and Sleeve with Epoxy 1NT4 Helifix HRT80 tie Dry Fix (see Figure 1)

The four interior retrofit methods were alI demonstrated relatively successfulIy. Each method is different and each has advantages and disadvantages. The table "Comparison of Interior Retrofit Systems", summarizes and qualifies the attributes of each method.

With the exception of INT2, the web mounted bracket, the repair methods demonstrated were alI feasible. The use of repair method INT2 would only be practical if large amounts of the interior gypsum board were to be removed.

An estimate ofthe cost per tie for each remedial tie system has been given. However, too much weight should not be put on the cost of an individual tie as tie spacing, the total number of ties, and the instalIation cost will have a significant impact on the overall cost of the remediation. A major cost of remediation will be the labour to install the ties and to return the wall to its intended state.

The aesthetics of the repair, or visibility, will undoubtedly be an important factor in the choice of a repair system, particularly when the repair is conducted from the interior. The size of hole in the interior gypsum board with repairs INT3 and 1NT4, approximately l5mm diameter, can be patched fairly readily. The much larger hole, approx. 35 mm, for the Cintec anchor is not easily repairable but the end washer diameter could be decreased.

AlI individual remedial tie methods involve damage to the air barrier and vapour retarder. While the drywall can be repaired, the 4 or 6 mil poly, if any, cannot be repaired as readily. However proper sealing of all holes can be done and suitable finishes can be specified and used. In most wall remediation, the provision of ensuring an adequate air barrier involving the sealing of the interior perimeter joints, is likely to be a requirement. Tie remediation and air sealing can be conducted at the same time as part of a good overaIl repair.

No damage to the brick veneer should occur with an interior repair but care must be taken to limit the depth ofthe pre-driIled hole to 2/3 or 3/4 ofthe brick depth to avoid punching through. Also impact drills should not be used as spalling of the brick wiIl occur.

Thermal bridging, although it cannot be eliminated, can be rninimized with the use of ties with small mass. As with other components in a steel stud system, corrosion is a concem. The repair method used should not promote or accelerate corrosion, although the consequences of breaking the galvanizing near the tie connection needs to be studied further. For these reasons a stainless steel tie is preferred especiaIly if the remedial tie is being introduced into a less than ideal environrnent.

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Comparison of Interior Retrofit Systems

INTl INT2 INT3 INT4 Cintec Dur-O-Wal Dur-O-Wal Blok-Lok

Cementitious Bracket & S.S. Rod in Helifix Sock (22mm) Exp. Epoxy HRT80

Anchor INST ALLA TlON

Ease * - * * Time * * * +

Visibility ofDamage * - + + Weather Limitations - * - *

Effect on Tenant - - - -REPAIR

CHARACTERISTlCS Strength of * + * ? Connection

Ductility of Connection - + - + AirLeakage * + * *

Various Thicknesses * * * ? ofStud

Moisture Drip + + - + Potential for Corrosion + + + * Effect of Corrosion on * * * -

Connection Thennal Bridging - - - -

COSTS Cost ofTie +/- $ 9.00 +/- $ 4.00 +/- $ 3.00 +/- $ 3.75

Cost ofLabour** ? ? Relative Cost of * -

MakingGood

* satisfactory, or of no relative difference + relatively positive, or beneficiai or better

relatively negative, or worse

? not known, or still to be detennined

? +

** the scale of the repair and the current status of these approaches affect this answer and make it difficult to provide any kind of assessment.

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? +

EXTERIOR REPAIR METHODS

Seven different exterior retrofit systems were demonstrated, namely : EXTl Cintec Cementitious Sock with 65 mm Hole EXT2 Cintec Cementitious Sock with 22 mm Hole EXT3 Dur-O-Wal Toggle Clips and Expansion Anchor EXT4 Dur-O-Wal Threaded Bolt and Expansion Anchor (see Figure 2) EXT5 Dur-O-Wal Drill and Tap Bolt and Expansion Anchor EXT6 Dur-O-Wal Stainless Steel Rod and Sleeve with Epoxy EXT7 Helifix HRT80 Dry Fix in SS, Polyester Resin in BV

The seven exterior retrofit methods were ali demonstrated relatively successfully. As with the interior repairs, each repair is different and each has advantages and disadvantages. The table, "Comparison of Exterior Retrofit Systems", summarizes and qualifies the attributes of each method.

All repair methods, with the possible exception of the larger Cintec repair (EXTl), are feasible methods to tie the brick veneer to the steel stud. The large 65 mm dia. hole needed for the Cintec tie in repair method EXT 1 is aesthetically unacceptable and expensive. This repair would possibly be suitable if existing ties have to be removed and replaced.

The unit cost of the Cintec anchors are considerably more than the other tie systems. These unit prices do not include the cost to instaIl the ties and to return the walI to its intended condition.

Except for the Cintec anchors, damage to the brick veneer is usually restricted to the mortar joint and this can readily be filled with mortar. However the damage to the exterior sheathing, the air barrier (if involved) and the steel stud is both difficult to assess and difficult to avoid. Repair EXT3, the Dur-O-Wal toggle clips, is unacceptable for use with compressible exterior sheathings as the toggle clips will either cut a Jarge hole in this sheathing (providing a passage for air leakage) or the sheathing will have to be relied upon for compression in the connection.

The strength of the tie connection will typically depend on the strength of the connection of the tie to the steel stud, rather than to the brick. The three connectors, EXT4, EXT5 and EXT7, that reiy on a screw type connection need to be adequately tested for strength under both static and cyclic loading. The threaded connections are also more vulnerable to corrosion.

The ease ofinstallation ofthe various repair methods varied considerably. The screw type tie systems were relatively easy to install. The anchors utilizing epoxy or grout filIer were easy to instalI but the preparation and use of filIers adds complication. The toggle clip anchor should be easy to install but the chance for problems is increased as the installation is done blindo

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Comparison of Exterior Retrofit Systems

EXTI EXT2 Cintec Cintec

Cementitious Cementitious Sock Sock (22mm)

(65mm)

INSTALLA TlON

Ease - * Time - *

Visibility ofDamage - -Weather Limitarions - -

Effect on T enant * * REPAIR

CHARACTERISTlCS Strength of * * Connection

Ductility of Connection - -AirLeakage * *

Various Thicknesses * * ofStud

Moisture Drip + + Potential for Corrosion + + Effect of Corrosion on * *

Connection Thermal Bridging * *

COSTS CostofTie +/- $ 15.00 +/- $ 9.00

Cost of Labour** ? ? ReIative Cost of - *

Making Good

* satisfactory, or of no relative difference

+ relatively positive, or beneficiaI or better

relatively negative, or worse

? not known, or still to be determined

EXT3 EXT4 Dur-O-WaJ Dur-O-Wal

Toggle Threaded Clips & Bo1t& Exp.

Exp. Anchor Anchor

* * * * * * * * * *

? ')

* * * * * ?

+ + * * * -

* *

+/- $ 3.00 +/- $ 3.00

? ? + +

** the scale of the repair and the current status of these approaches affect this answer and make it difficult to provi de any kind of assessment.

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Comparison of Exterior Retrofit Systems (Continued)

EXT5 EXT6 Dur-O-WaI Dur-O-WaI

DrilI and Tap S.S. Rod in & Exp. Epoxy Anchor

INST ALLA TION

Ease * * Time * *

Visibility ofDamage * + Weather Limitations * -

Effect on Tenant * * REPAIR

CHARACTERISTICS Strength of ? * Connection

Ductility of Connection * -AirLeakage * +

Various Thicknesses ? * ofStud

Moisture Drip + -PotentiaI for Corrosion * + Effect of Corrosion on - *

Connection ThermaI Bridging * +

COSTS Cost ofTie +/- $ 2.50 +/- $3.00

Cost ofLabour** ? ? Relative Cost * +

of Making Good

* satisfactory, or of no relative difference

+ reIatively positive, or beneficiaI or better

- relativeIy negative, or worse

? not known, or stilI to be determined

EXT7 Blok-Lok HeIifix HRT80

* * + -*

?

+ * ?

+ * -

*

+/- $ 3.75

? +

** the scale of the repair and the current status of these approaches affect this answer and make it difficult to provi de any kind of assessment.

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CONCLUSIONS

This paper identifies various tie systems that are eommereially available for use as supplementary briek ties in briek veneerlsteel stud walls. Eaeh repair strategy has been physieally demonstrated and then assessed.

Procedures for loeating the steel stud from both the exterior and the interior have been identified and doeumented. It was found that loeating the studs from the interior is generally easier than doing so from the exterior, but proeedures are available to address both situations.

Whether the need for remedial briek ties is due to improper tie seleetion or inadequate spaeing does not signifieantly affeet whieh supplementary tie system shouId be used. However the ehoice of tie system and whether an interior or exterior repair method should be used, does depend on the nature and extent of ali the repair work needed on the building. The impact of other building defieieneies may affeet the choiee of tie repair method. The ehoiee of whether an interior or an exterior repair method is used will depend on numerous faetors ineluding cost, aeeess, timing, and the type of other wall repairs that are needed. AlI things eonsidered, the ehoice of a repair system depends on the overall state of the building, the eomparison of the eosts and benefits of alternative strategies and the needs of the owners and tenants of the building.

It is important to stress that the presentation of these remedial tie systems does not neeessarily endorse the use of any of these remedial tie systems. There are many issues related to the installation of remedial tie systems and their feasibility in relation to other repairs that are needed for the wall that have not been eonsidered in this paper and that may be building specifie. Before using the tie systems demonstrated, some key questions need to be answered. The perfonnanee eharaeteristies and reliability of the eonneetions in the steel stud flange need to be assessed. The potential for eorrosion and its impaet on the perfonnance of the eonneetion needs to be detennined. Other eonsiderations including the impaet on air leakage and thennal bridging shouId also be studied. These questions are the foeus in later tasks of this CMHC funded R&D projeet.

REFERENCES

Postrna, M.A. , Burnett, E.F.P., "Taskl: Briek Ties - Options For Remediation," A report prepared for the Canadian Mortgage and Housing Corporation (CMHC), Ottawa, Ontario, 1992

2 Canadian Standards Association, CAN3-A270-M84, "Conneetors for Masonry", Ottawa, Ontario, 1984

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