Engineering Design & Construction

CIVL9903 - University of Sydney

Project Overview

This project involved the structural concept and preliminary design of a 32-storey commercial tower in Sydney CBD. The project included designing the foundation on sandstone, building a reinforced concrete core and steel bracing systems for lateral stability, developing three different types of floor systems (post-tensioned, composite steel, and mass timber), and building a 25 m architectural roof structure.

The design process was all about making sure the load path was clear, the building could withstand wind and earthquakes according to AS1170, and checking its strength and serviceability, as well as taking into account how easy it would be to build. The project is a good example of a whole-system approach to designing high-rise buildings, balancing efficiency, ease of construction, and material performance.

Figure.1 Layout and Elevation of the commercial tower.

Problem Statement

The challenge was to design a high-rise structure capable of resisting significant wind loads, while ensuring stability, serviceability, and efficient load transfer from roof to foundation. The design also required selecting optimal structural systems for foundations, lateral stability, and floor systems under real site constraints.

Design Scope

Foundations

Raft base on sandstone
CFA piles with rock sockets
Checks for uplift and tension piles
The idea of basement retention

Figure.2 Geotechnical Cross-section

Lateral Stability

Wind design (AS1170.2)
Seismic base shear (AS1170.4)
RC core and steel bracing system
Core stress tests when the core flips over

Figure.3 Figure 3. RC core and steel X-bracing system used to resist lateral wind loads and control building drift.

Systems for the Floor

Multi-system floor design comparison (P/T, steel composite, mass timber).

Rooftop Canopy

Consideration of uplift wind
Integration of architecture and structure

Figure.4 Floor and Roof Elements

Foundation Strategy

The tower foundation system was designed to suit sandstone bedrock conditions in Darling Harbour. A reinforced concrete raft foundation was analysed for vertical load and wind overturning effects, verifying full compression under service loads.

For heavily loaded columns and braced-frame elements, 900 mm diameter CFA piles with 1.5 m rock sockets were designed to resist both compression and uplift forces. Pile capacity checks included shaft adhesion and end bearing resistance.

Basement retention was addressed using a hybrid system of secant and contiguous bored pile walls with ground anchors to control lateral earth pressures and groundwater intrusion in the dense CBD environment.

Figure.5 Four-pile cap foundation layout (Ø900 mm CFA piles).

Lateral Stability System

32-Storey Tower (124 m)

Reinforced concrete core (10 m × 10 m, 450 mm) combined with perimeter steel X-bracing to resist lateral loads.

Wind governs design (1000-year return period)
Wind base moment ≈ 376,900 kNm
Seismic base shear ≈ 2% of building weight
Ultimate overturning ≈ ±450,000 kNm
Brace axial force ≈ 4,500 kN

Key Learning:
Wind controls high-rise performance in Sydney; core stiffness and bracing configuration are critical for drift and overturning resistance.

Floor System Design

A comparative study was undertaken for three floor systems: post-tensioned (P/T) concrete band beams, composite steel framing with metal deck slab, and mass timber (CLT with glulam beams). Each system was assessed for span capability, structural depth, weight, constructability, and service integration.

The exercise highlighted trade-offs between efficiency and sustainability — with P/T offering reduced depth for long spans, composite steel providing faster erection, and mass timber delivering lower embodied carbon and architectural warmth for upper levels.

My Contribution

Developed load calculations and combinations in accordance with AS 1170 (wind and seismic)
Designed foundation systems including raft and CFA piles with uplift and compression checks
Analysed lateral stability system using RC core and steel bracing
Compared floor system alternatives (post-tensioned, composite steel, mass timber)
Evaluated roof canopy structural behaviour, including uplift and load reversal effects
Interpreted structural behaviour and validated design decisions based on performance

Tools & Analysis

Excel – load calculations and design checks
Structural modelling (concept-level analysis)
Australian Standards: AS 1170, AS 3600, AS 4100

Rooftop Canopy – Structural Behaviour Summary

The proposed rooftop canopy is a 43.5 m × 25 m modular glulam structure inspired by PHIVE’s geometric grid logic. The system consists of primary and secondary glulam beams forming diamond-shaped panels supporting solar panels and glass modules.

Key Learning

This project reinforced understanding of:

Load reversal in roof structures
Uplift-critical connection design
Moment and shear redistribution under changing load directions
Importance of anchorage in lightweight canopy systems

Figure. 5 Bending, shear, and axial force response under downward wind loading (1.5 kN/m), demonstrating sagging behaviour and peak support reactions.

Key Engineering Outcomes

Identified wind loading as governing design case for high-rise performance in Sydney
Verified structural stability under overturning moments (~450,000 kNm)
Assessed efficiency of different floor systems based on span, weight, and constructability
Developed integrated structural system ensuring continuous load path from roof to foundation
Evaluated foundation solutions under combined vertical and uplift forces

Key Engineering Learning

Wind loading governs high-rise design more than seismic effects in Sydney
Core stiffness and bracing configuration are critical for drift and overturning resistance
Structural design must balance efficiency, constructability, and material performance
Load path continuity is essential for safe and realistic structural behaviour
Foundation design is heavily influenced by overturning effects and ground conditions