Minor repairs to this multi-story building were required following the 4 September 2010 Darfield earthquake. Concrete window surrounds and sections of floor slab required patch repairs, and areas of brickwork needed to be dismantled and rebuilt. The entire building was scaffolded and wrapped in plastic to allow safe access to the damaged areas. Problems with the original wall tie system were soon uncovered and a solution sought.

The project engineers had already specified PatchPin to be used to provide a mechanical key in areas selected for concrete patch repair. Small holes were being drilled into these areas and stainless steel PatchPins were being driven into position using a support tool fitted to an SDS drill. DryFix was soon added to the scope of works when concerns were raised over the state of connection between the external brick cladding and the internal reinforced concrete superstructure.

To retie the panels, small holes were again drilled, this time through the existing brickwork panels and into the concrete behind at regular vertical and horizontal spacings. Several thousand self-tapping, stainless steel DryFix ties were then driven into position to produce a secure mechanical connection. Entry points were patched with an oxide-coloured mortar to leave a near invisible retrofit. Installation took less than a week with contractors working outside normal business hours to minimise disruption to building occupants.

This Christchurch CBD heritage building was one of only a small number for its age, type and location to survive the 2010/2011 Canterbury earthquake swarm in repairable condition. It was also among the first to re-open in the CBD after repairs were quickly organised and conducted. A steel frame retrofitted in 2008 saved the building from serious structural damage, but numerous cracks and other mostly superficial damage developed, particularly around doors, windows and the internal stairwell, and work was needed to restore structural integrity to these areas.

Cracks in the brickwork were stitched using the HeliBar-HeliBond Crack Stitching system. HeliBar stainless steel reinforcing bars were bonded into channelled-out mortar beds with HeliBond grout at all locations around the building where cracking had occurred. Where cracks in the façade were stitched, a suitably coloured repointing mix was used to cover the slots and completely conceal the location of the installed bars. Concealment of stitches to internal walls was achieved through a fresh application of plaster and paint.

In other areas of the building, DryFix ties were used to improve the connection between the external and internal brick leaves. To minimise damage to the existing brickwork and to help achieve an optimal result, small rotary percussion drills holding straight-shanked 5mm diameter drill bits were used to drill the pilot holes necessary for DryFix installation. Holes were drilled through the internal leaf and into the external leaf. DryFix were then installed using a Power Driver Attachment fitted to a light-weight SDS drill. Plaster and paint applied to the internal walls now conceals all DryFix entry points.

The pictured two storey brick building was seismically retrofitted in 2007.1 Alterations to the interal layout were made. Selected internal walls were removed and replaced with secondary moment resisting steel frames. These strengthened the building and created large openings and a new dynamic to the ground floor operations. The design won a prestigious architectural prize and helped the building withstand the recent Canterbury earthquake swarm.1 Cracked brickwork was among the short list of observed earthquake damage.

Crack Stitching was specified as part of a repair programme designed to mend damaged areas and restore strength to the cracked brickwork. Slots spaced at regular vertical intervals were cut into the mortar joints at each location where cracking had occurred. These were then cleaned and primed. A bead of HeliBond grout was then injected to the back of each slot, before lengths of HeliBar reinforcement were pushed into position and a second bead of HeliBond injected over the top to cover. Slots cut into the external brickwork were repointed to finish. Plaster was used to cover those cut into the internal walls and complete the hidden repair.

Many thousands of aftershocks have since tested the performance of the installed HeliBars at this location, with none larger (to date of publication) than the M6.3 aftershock of 13 June 2011. This event was large enough to cause significant new damage to much of Christchurch's remaining building stock, including new damage to this building. Cracking was observed once again in several areas. Significantly, however, no new damage was observed in any of the areas where Helifix repairs had taken place. Not surprisingly, the specification for a second round of repairs includes Helifix Crack Stitching.

A similar Crack Stitching story has been played out at this large commercial site (pictured opposite). Crack Stitching repairs designed to restore integrity to sections of cracked brickwork around this building had been underway for several weeks prior to the 13 June quake and following the buildings closure on the day of the devastating M6.3, 22 February quake. The sequence of events allowed the project engineers and contractors alike the opportunity to scrutinise the performance of the Helifix Crack Stitching System against strong, real world seismic conditions. The system performed extremely well, and the engineers for this undertaking have since specified Crack Stitching to be used in several other projects on their books.

Cracks in masonry may lengthen, open and close as a result of numerous everyday factors, including on-going shrinkage and heave in foundation soils, and seasonal wet and dry, hot and cold environmental conditions. Under conditions such as these, crack stitching contributes improved masonry stability and the redistribution of tensile loads and wall movement to help minimise the chance of crack development. Under seismic conditions, Helifix Crack Stitching contributes further by adding strength to areas that might otherwise act as paths of least resistance.

1. Ingham, J. and Griffiths, M. (2011). The performance of unreinforced masonry buildings in the 2010/2011 Canterbury earthquake swarm. Report to the Royal Commission of Inquiry.

This attractive chapel, constructed from volcanic stone and clad internally with soft limestone (Oamaru stone) panels, became the interim home for the Anglican community in Christchurch following the 22 February 2011 earthquake and subsequent partial collapse of the Cathedral. To help ready the chapel for the upcoming easter services, a method had to be quickly devised and implemented to improve the strength of connection between the cladding and the volcanic stone. Stabilisation of the vestibule wall was also required.

The RetroTie system was chosen by the project engineers to perform the first task. Small pilot holes were first drilled through the cladding and into the stone. The holes in the limestone were then expanded and cleaned. Finally, RetroTies were power-driven into the pilot holes in the external stone wall before resin was injected to bond their exposed tails to the limestone cladding. Patching using a lime-based mortar, specially prepared on site by the project stonemasons, produced a near invisible fix.

Long-series ResiTies were then used to pin the rubble-filled vestibule walls. Blind holes were first drilled through the external stonework and deep into the back-up materials. Resin was then pumped into the holes. Helical stainless steel ResiTies were then wound into the resin-filled hole.

Seismic strengthening of the Scott Building at the University of Otago recently commenced following a detailed seismic assement. As part of a comprehensive strengthening program scheduled to run over at least the next decade, DryFix were used to tie the two whythes of the buildings second floor unreinforced masonry (URM) brick wall.

Completed in 1918, the Scott Building was identified by the University as a URM building of considerable material and cultural value. Situated near the entrance to the emergency department of the Dunedin Hospital, it was also identified as a building in need of a seismic retrofit since failure of the façade could severely disrupt the smooth functioning of the hospital.

Fibre-reinforced polymer sheeting was used to clad the internal brick wall. New structural diaphragms were added at floor and ceiling levels.

The DryFix system was used to strengthen connection between the internal and external wythes.

Undersize pilot holes were drilled at regular intervals through the near wythe and into the remote wythe. Stainless steel, 8mm diameter DryFix pins were then driven into position on the hammer action of a drill to provide a fully mechanical connection. The ties were installed from the inside of the building, leaving the façade untouched and an invisible structural solution.

Unreinforced masonry (URM) buildings form a significant and rapidly diminishing part of New Zealand's collective heritage and there is a growing concern that appropriate retrofit repair and reinforcement steps be taken to preserve these structures for future generations.1 In Auckland, threats to the longevity of URM structures include salt, wind and seismic loading.

Using a range of Helifix remedial systems, structural integrity was re-introduced into this building, situated in central Auckland, and strength added in anticipation of future seismic events. The original construction materials and character were retained through the use of non-disruptive Helifix installation techniques. The deterioration of the façade included corroded wall ties, failed lintels, cracked, bowed and unstable brickwork.

The Helifix repair scheme involved installing HeliBar stainless steel reinforcing bars into channelled-out mortar beds at various levels and locations along the façade. These tied the masonry together, stitched cracks, and formed masonry beams that reinforced the structure and spread the loads. A suitably coloured repointing mix was used to cover the slots and completely conceal the location of the installed bars.

StarTies were used to connect sections of the external brickwork leaf that needed to be reset back to the internal leaf. In these instances, undersize, 5mm pilot holes were drilled 70mm deep into the internal leaf before 8mm diameter StarTies were driven into position and their exposed tails bonded into the mortar beds of the newly constructed external leaf section.

DryFix ties were used to tie all other areas of the façade back to the internal leaf. To minimise damage to the existing brickwork, small rotary percussion drills holding straight-shanked 5mm diameter drill bits were used to drill the pilot holes necessary for DryFix installation. Holes were drilled through the external leaf and 70mm deep into the remote leaf. DryFix ties were then installed using a Power Driver Attachment fitted to a light-weight SDS drill. A coloured patching mortar mix was used to patch all DryFix entry points to leave a near invisible repair.

1. Goodwin C., Tonks G. and J. Ingham (2009). Identifying heritage value in URM buildings. URL: retrofitsolutions.org.nz (Accessed: March 2010)

A collaborative project investigating the seismic retrofitting of masonry buildings, involving researchers from both sides of the Tasman, continues to make headway. Led by engineers at the Universities of Auckland and Canterbury in New Zealand, in conjunction with colleagues at the Universities of Newcastle and Adelaide in Australia, the Seismic Retrofit Solutions project has targeted the development of cost-effective guidelines and solutions to retrofit unreinforced masonry (URM) structures.

The wording and implementation of a full list of solutions and formal provisions has yet to reach fruition, but the research, which is now at an advanced stage, has produced compelling results and there is a growing expectation that a suite of technical seismic manuals will result. As part of the project, researchers have investigated the performance of a number of different retrofitting systems. Shotcrete, fibre-reinforced polymer (FRP) sheeting and shear truss systems, among others, have received attention. Helifix has also supported a coordinated series of studies into its own Helibeam System of masonry reinforcement.

Unreinforced masonry panels, cut from condemned buildings in Gisborne, the site of a significant earthquake in 2007, provided the raw material for Helifix testing in New Zealand. In Australia, tests conducted using newly constructed masonry panels reinforced with HeliBar and HeliBond grout have fueled research at the University of Newcastle.

Results to the date of publication (November 2009) confirm much of what is already known about the Helibeam System, and which has been confirmed previously at numerous different sites and laboratories around the world. And that is: the Helibeam System can be used to provide tremendous strength and greatly enhanced seismic performance to existing masonry structures.

The Helibeam System, which builds around the bonding of specially formed stainless steel HeliBars into existing masonry with a specially formulated cementitious grout, HeliBond, also offers great versatility. Available in a range of different diameters and cross-sectional areas, different combinations of HeliBars and installation patterns may be used in pursuit of a variety of different solutions. Their unique helical profile ensures that HeliBars can be bonded into slots and clearance holes cut and drilled into masonry without workmanship difficulty. Complete results of the tests will be published through a series of papers presented at various international seismic and engineering conferences and symposiums in the new year. Current results confirm that, critical to the performance of the Helibeam System is the high quality and strength of the bond created between the HeliBar reinforcement, the HeliBond, and the masonry itself. Further, results indicate a significant increase in the performance of the tested masonry wallettes when subjected to simulated seismic loads.

Helifix is looking forward to its on-going involvement with the project.