Construction World December 2021

AFRISAM INNOVATION AWARD FOR SUSTAINABLE CONSTRUCTION

Consul t ing Eng ineeres

AfriSam Innovat ion Award for Sustainable Construct ion

I n response to a strong demand for qual i ty res ident ial apartments in Cape Town, FWJK Developments conceived the development of an iconic high- ri se in the foreshore area. A key requi rement for the Ci ty of Cape Town’s development approval was to retain a 12-metre- high exi st ing heri tage façade on the s i te. Preser ving thi s f ragi le hi storic feature, which had been bui l t us ing rock , clay and l imestone, at ground level of the proposed tal l bui lding requi red innovat ive structural solut ions to fi t wi thin the project budget and t imef rame. Appointed the structural and civi l engineer on the project , Zutari (previously Aurecon South Af rica) was respons ible for des igning the tal l bui lding. Innovat ive structural solut ions were also requi red to create suf ficient parking wi thin the bui lding’s constrained footprint , and to break away f rom tradi t ional high- ri se des ign in order to mi t igate lateral dri f t under wind load. At 120 m and 36 storeys high, 16 on Bree i s the tal lest res ident ial and second-tal lest mixed-use development in Cape Town over the last 20 years . I t of fers unrival led views of the ci ty’s natural beauty, whi le st i l l being in walking di stance to the V&A Water f ront commercial hub and the CBD. Keeping wi thin the project budget and t imef rame was a tribute to the successful col laborat ion between the structural engineers , the developers and the rest of the project team. Due to the relat ively smal l s i ze of the s i te, the archi tectural scheme for 16 on Bree did not al low suf ficient space for a core that was able to res i st the lateral loads that the structure had to accommodate. Consequent ly, the lateral des ign of the bui lding cal led for out-of-the box thinking to ensure that the geometric archi tectural requi rements , as wel l as the structural requi rements , could be sat i sfied s imul taneously. 16 ON BREE STREET

The solut ion adopted was a lateral system cons i st ing of a substant ial ly smal ler reinforced concrete core s i tuated in the middle of the bui lding ( in plan) , wi th outrigger wal ls at two di st inct locat ions that were connected to two perimeter columns . Thi s meant that when the structure was loaded lateral ly the core would want to overturn; however, the perimeter columns would be engaged to the core through the outrigger wal ls . They would aid in res i st ing the overturning moment due to the lever arm between them and the core centroid. The elegance of the solut ion was that the outrigger wal ls did not need to be placed in the parking levels hampering the vehicle flow. Rather, the outrigger wal ls were located in the res ident ial levels and al igned wi th apartment wal ls to avoid los ing any saleable res ident ial area. The s i ze and complexi ty of the bui lding, as wel l as the unconvent ional lateral system and large number of load cases and combinat ions that had to be cons idered, meant the structure requi red a more substant ial analys i s than i s typical ly carried out for standard bui ldings . To cater for al l of the complexi t ies , a three-dimens ional fini te element model of the ful l bui lding was produced. The model l ing was also used to opt imi se the number and pos i t ion of the outriggers to mi t igate the ef fects of stabi l i sat ion and vibrat ion f rom the central l i f t and stai r core. The fini te element model included al l combinat ions of gravi ty and vert ical loads that were requi red to be cons idered. Furthermore, envelopes of the load combinat ions were included, which made i t poss ible to ver y eas i ly and quickly determine the requi red des ign forces for any element in the model for al l load combinat ions . The foundat ions and columns were des igned us ing the fini te element model as i t provided a more accurate contribut ing area, and therefore provided a better est imate of the axial loads . The ingenious solut ion for protect ing and preser ving the hi storic façade was to construct a steel bracing

84 20 th Best Project Awards 2021