CONCRETE TECHNOLOGY
THE FUTURE OF SUSTAINABILITY IN THE ACI 318 CONCRETE BUILDING CODE by Andrew W Taylor and Shana T Kelley, KPFF Consulting Engineers, USA Traditionally, structural building codes have been viewed as pertaining only to the regulation of structural engineering practice, without particular regard for the impacts of building design and construction on the environment. With the recent increase in attention to the sustainability of manufactured building materials, building construction, and building demolition, the writers of building codes and standards have started to examine all aspects of the building design process, looking for ways to reduce environmental impacts, particularly the emission of carbon dioxide. One may naturally ask how structural building codes, which deal primarily with regulations for the proper application of engineering principles to achieve adequate strength, stiffness, and serviceability of buildings, can be expected to address environmental concerns. Upon closer examination of structural building codes, however, it can be understood that structural codes can be written in such a way that they support and promote sustainable building practices. This article explores the ways in which structural engineering regulations can be modified to reduce the environmental impacts of concrete buildings. The focus of this article is the American Concrete Institute’s ‘ACI 318: Building Code Requirements for Structural Concrete’, but the ideas explored here can be applied to any building code that regulates the structural design of concrete buildings. INTRODUCTION Before the last decade, structural engineers were seldom involved in consideration of the environmental impacts of the structures they designed. In recent years, however, this has changed. Many of the reasons that the environment is adversely affected by the creation of a new building are related to the production, transportation, and assembly of structural materials and components. It stands to reason, then, that the structural engineer should be an active participant in the movement towards creating building projects that are less detrimental to the environment. Until very recently, structural building codes - the regulations that ensure the strength, stiffness, and serviceability of a structure - have had little or nothing to say about environmental concerns. Structural codes have been almost exclusively concerned with public safety, while the environmental impacts of building construction have been the subject of other codes, guidelines and sustainability rating systems. Major structural design codes have, however, started to address environmental aspects of construction. An important example is the fib Model Code for Concrete Structures 2010 [1]. In section 3.4 ‘Performance Requirements for Sustainability’ of the fib model code, the general principles of design for sustainability are outlined, and performance categories related to environmental impact and to impact on society are listed. Section 3.4 presents a brief, innovative framework for consideration of sustainability in structural design. This effort will be 22
THE SINGAPORE ENGINEER July 2020
expanded in the next edition of the 2020 fib model code (MC2020). The current proposed outline of MC2020 includes Section 3 ‘Sustainability Perspective’, Section 28 ‘Evaluation of Environmental Performance’, and Section 30 ‘Sustainability Evaluation’. MC2020 will adopt a holistic plan for building life cycle performance, including initial design for sustainability, through-life management and care, assessment of environmental performance, and eventual dismantlement and reuse. Sustainability considerations were first introduced in the 2014 edition of the American Concrete Institute building code, ACI 318-14 [2]. Although these provisions essentially consist of a statement expressing the desirability of considering sustainability in structural design, this represented a modest start on the path towards creating more comprehensive sustainability provisions. The same provisions on sustainability appear in ACI 318-19 [3], but these were supplemented by new rules permitting the use of alternative cementitious materials and recycled aggregates. Looking forward, plans are underway to create an ACI 318 subcommittee charged with writing expanded sustainability provisions for the 2025 edition of the ACI 318 code. In this article, we describe why sustainability should be considered in the design of reinforced concrete structures, we outline the initiatives that the American Concrete Institute (ACI) has undertaken to address the challenges of sustainable structural design, and we provide information on recent plans to expand sustainability provisions in future editions of the ACI 318 code.
