Simplicity is Deceiving

Jumbo Glass at High-rise Podium

Overview

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Abstract

The case study presented is a 195 meters tall office tower with a raised podium made of 16 meters full height glass panels (and smaller). The panels are only restrained by prestressed high-strength stainless-steel rods, lying entirely in the glass panel build up, composed by four 12 mm thick plies, laminated with 1.52 mm thick sheets of ionoplast interlayer, with an overall thickness of approx. 52 mm. Due to the facade geometry and the high wind expected, movement joints between rods are introduced, allowing for differential movement to avoid peak stresses in the glass panels. Also, smooth transition between a rod rectangular section at the interface with glass panels to circular section at anchor points needs to be ensured by CNC machining to avoid failure of the rod anchors due to fatigue. Sophisticated non-linear 3D FEM models had to be analyzed to predict glass stresses, differential movement to be accommodated by the joints and geometrical transition between rod sections.

The main innovation of this facade was the use of prestressed rods in conjunction with jumbo size glass panels. As tension structures experience large movement, it was crucial to understand the effect of these deformations imposed by the rods onto the full height glass panels, analyzing steel and glass members together as a single facade entity. Furthermore, in contrast to typical cable wall facade where the prestressed elements (cables) are offset form the glass line, here the rods are located in the plane of the glass panels and completely flush with them, ensuring the thinnest possible build-up in relation to the large facade span. A rocking portal frame, moving together with the rods to avoid excessive warping in the glass panels, has been used as a solution to deal with the required opening in the facade. An additional complication was given by the high wind load (typhoon) applied on the facade which required rods’ prestress in the order of 1000 Kilonewton in order to limit glass stresses and deflection.

Introduction

Architects’ desire for taller and more transparent façades has pushed the Structural Engineers into a more structural use of glass and research of alternative structural systems. The three main current

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Background

Facades with glass fins are the most immediate alternative to typical aluminum or steel mullions system, as they simply “replace” the metal member with a glass one. Fins are typically

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Case Study

Two Taikoo Place is 195 m tall office tower which will be located in Quarry Bay, Hong Kong Island (Figure 1A). The current plan of the tower has a rectangular

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Structural Narrative

The podium design strategy is based on pre-tensioned rods and full height glass panels. The rods act as mullions, albeit more flexible, via catenary action and non-linear behavior. The glass

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Analysis: Global Model

A three-dimensional finite element model of the podium façade is built in Strand7 to assess its structural performances (Figure 5). The in-plane and out-of-plane behavior of the glass panels is

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Analysis: Local Models

Three-dimensional finite element models for the full-height flat panel and the full-height curved panel are built to assess more in detail the structural performance of the glass (Figure 9). The

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Results

Results: Summary

A number of 60 serviceability combinations and 120 ultimate limit state combinations are analyzed as a result of the permutations of the different wind load cases, prescribed by the

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Conclusion

This case study has shown how this innovative structural system for high-rise glass façade can be used to ensure maximum transparency and structural safety, even in a typhoon area such

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Rights and Permissions

BS EN 1993-1-11. Eurocode 3 – Design of steel structures. Design of structure with tension components, 2006.

BMT. Taikoo Place Podium Cable Glass Wall Wind Loading Study, 2018.

Code of Practice for the Structural Use of Glass, Building Department, Hong Kong, 2018.

Code of Practice for the Structural Use of Steel, Building Department, Hong Kong, 2011.

Code of Practice on Wind Effects, Building Department, Hong Kong, 2004.

Strand7. User Manual - Release 2.3, 2005.