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PRECAST CONCRETE PANELLING ENHANCES STELLENBOSCH UNIVERSITY BUILDING

April 6, 2023 641 641

Reinforced precast concrete facade panels, manufactured by Concrete Manufacturers Association member, Concrete Units, have been used to dress the external elevations of two U-shaped service shafts which flank the northern entrance of Stellenbosch University’s Civil, Electrical and Electronic Engineering building. The installation forms part of an overall face-lifting and refurbishment of the five-storey structure which is being undertaken on behalf of the university by main contractor, GVK-Siya Zama Construction, in collaboration with project architect, KMH Architects, and structural engineers, Edifice Consulting Engineers.

Forty panels in six sizes were attached to each shaft’s three exterior elevations over eight segments, five panels dressing each segment. All the panels are 2.2m high, apart from the top or eighth segment units which are 1.4m, and they vary in width from 400mm to 1 700mm. The front or north-facing elevations of each shaft took 16 panels as did the two inner side-facing facades. The two outer side-facing elevations were each dressed with eight narrower panels.

A side view of the steel bracket installation.

Rynhard Zwarts of KMH Architects said he specified precast concrete panelling for the service shaft facades to create a point of interest at the building’s northern entrance and because precast concrete has a much cleaner finish than in-situ concrete.

“The finish on Concrete Unit’s precast panels is beautiful and panelling emulates the facade of the New Paving Laboratory (NPL) which is adjacent to the engineering building. We established a language of materiality for the NPL which is being adopted for the engineering block’s northern façade. Moreover, we requested that the panels be cast with ferrule holes as cosmetic embellishments which mimic the holes in the in-situ concrete finish of the NPL,” said Zwarts.

Housing the building’s distribution boards, the shafts comprise reinforced concrete walling on the front and outer elevations, and reinforced concrete with a brick in-fill walling, on the inner-facing walls.

The panelling shortly after installation.

Edifice structural engineer, Ryno Thiart, said that one of the main challenges was establishing the most effective method of attaching the panels to the walling.

“We were fortunate in that the shafts are housed in a Reinforced Concrete (RC) frame which meant they had the strength to support the precast panelling.

“Our design geometry embraced KMH Architects’ visual input as well as practical installation considerations, and was premised on a shared panel loading between the reinforced concrete corbels, attached to the bottom of the existing concrete shafts, and galvanised steel angle brackets, which were mounted on the shaft walling. The angle brackets were designed for lateral connectivity and for handling the panels’ vertical loading in the event that some loading would not be distributed to the concrete footings. In addition, the corbels were designed to support the total vertical panel loading. Apart from the base level panel sections which rest on the corbels, each panel section sits on the segment below through keyway joints cast into the panels.

The panelling shortly after installation.

“We kept the weight of the panels to a minimum to reduce the loading. And we made the panel walls a relatively thin 100mm because they are not subject to the same forces as the end sections which were required to be thicker for bracket hanging and inter-panel connectivity,” advised Thiart.

Once the ground level facade panels were installed by VBD Steel Construction, Concrete Units took laser levels and calculated bracket positions. This process was assisted by the fact that the building had been constructed to very tight tolerances in the 1970s.

“The structure and brickwork were within a 5-10mm tolerance which one rarely sees these days,” said Concrete Units production manager, Alwyn Carstens. “This meant our lines and levels worked out very well and allowed us in turn to operate within tight tolerances.”

Scaffolding with platforms in line with each segment was erected around the shafts which made the installation process relatively easy. A 25 tonne mobile crane hoisted the panels above the top of the scaffolding and lowered them between the scaffolding and the walling onto the angle brackets.

The panels were cast with corbels/beams which run the full width at the top of the panel and provide a 170mm anchor ledge for hanging them off the steel angle brackets. In addition, V-shaped grooves were cast into the top of the corbels and V-shaped ridges were cast into the bottom panel beams to facilitate the keyway connections.

One of the galvanised steel brackets showing slotted steel nuts.

GVK contracts manager, Deon Terblanche, said that in order to achieve the shared load distribution between the brackets and the panels, HDPE shims were inserted between the brackets and the corbels.

“Shim placement involved lifting the panels off the brackets to provide access. The brackets were installed 10mm below their designated levels to allow for the height and load-sharing adjustments. In addition, rubber sealing was used in the keyway joints to further assist with the alignment process and ensure tight joints.

“Once the panels were aligned they were permanently secured to the brackets with 20mm stainless steel bolts. Each bracket was purpose made, because once the panels were installed there was no space to secure the bottom nuts in position while the bolts were tightened from the top. To overcome this problem purpose-made square nuts were used; they were kept in position by steel guides welded to the underside of the angle and the angle bolt holes were slotted to allow for the lateral alignment and adjustment of the panels. Further bolt insertion flexibility was provided by Concrete Units casting extra-large 40mm bolt sleeves in the panel corbels,” said Terblanche.

One of the galvanised steel brackets showing slotted steel nuts.

The angle brackets were attached to the RC walls with stainless steel bolts. They penetrate through to the back of the RC walls where they are secured to purpose made steel square washers. In cases where the brackets were close to shaft corners, chemical anchoring was used.

The in-fill brick walls were not sufficiently strong to support the eccentric vertical panel loading, therefore channel brackets were attached on the inside of the building to two existing RC columns which flanked each infill wall. Stainless steel bolts were inserted through both sets of walling, fixing the external angle bracket to the internal steel channel. The brick walls were three-skinned and 330mm thick as opposed to the 220mm reinforced concrete columns on either side of them. Therefore the internal brick skins, three courses deep, had to be removed to enable the installation of the channel brackets. The voids between the brackets and the walls were filled with Sika grout to conceal the steel channels on the inside of the building.

One of the top level panels cast with a recess to fit around the concrete beam at the top of the building.

A further complication occurred on segment eight on the outer wall of the shaft, where concrete beams intersected with the shafts. In this instance panels with recesses were cast to fit around the beams.

Once all the panels had been installed they were capped with precast coping cast by Concrete Units. As well as being easy on the eye, the coping also prevents water seepage. Additional water-proofing was achieved by applying a Sika sealant to the horizontal and vertical panel jointing.

After gaining Edifice approval for the rebar layout, Concrete Units cast the panels with 40MPa concrete which was cured with a wax-based curing compound.

“We positioned the rebar in the centre of the panels to achieve 40mm cover. Three new moulds were utilized to achieve an off-shutter finish on the front face and all the sides. In addition we used 15x15mm chamfers on all the corners which created smooth edges and a groove which was filled with the Sika sealant.”

A freshly cast panel showing the V-shaped connection groove at the bottom of the panel.

“After the panels were cast they were joined together at our factory to ensure that the front alignment was 100% and that the jointing worked correctly. Each panel had four lifting holes and we calculated the centre of gravity for each panel so that they hung vertically during installation,” said Carstens.

The panels were transported to site using special transport frames and every frame was vertically loaded with four panels.

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Project Team
Client	Facilities Management - Stellenbosch University
Principal agent	AL&A
Architect	KMH Architects
Consulting structural engineer	Edifice Consulting Engineers
Main contractor	GVK- Siya Zama Construction
Panel Producer	Concrete Units
Panel installation	VBD Steel Construction
Civil engineering	SMEC
Electrical engineer	Triocon
Electronic engineer	TTA
Fire consultant	STAC
Mechanical and wet services engineer	BVi