۱- Introduction

۲- Limit states

۳- Design approach

۴- Illustration of concept; impact minimization of façade element

۵- Discussion

۶- Conclusions

References

Abstract

Probability-based limit state design is a hallmark of modern civil engineering practice. Code requirements to meet both ultimate limit states (ULS) and serviceability limit states (SLS) have vastly improved the safety and usefulness of concrete structures. To meet increasing challenges of triple bottom line sustainability (covering social, environmental and economic aspects), a new class of design limit states are needed within code-based engineering design practice. A framework for sustainable design and management considering environmental impacts was earlier developed, and a multi-physics and multi-scale deterioration model for reinforced concrete affected by chloride-induced corrosion was established. A simplified case study is presented in which a reinforced concrete panel is exposed to a marine environment. The multi-physics deterioration model is used to determine the time until an engineering limit state (cracking due to reinforcement corrosion) is reached, and a design and maintenance optimization is performed with regard to sustainability (global warming potential footprint).

Introduction

Sustainability-focused innovation is required in the construction industry to meet future climate goals, e.g. [1–۳]. To facilitate such innovation and allow for the sustainable design and management of concrete structures, both engineering (i.e. commonly used ultimate limit states (ULS) and serviceability limit states (SLS)) and sustainability limit states (e.g. maximum carbon footprint over a concrete structure’s operational service life) need to be considered [4]. The European-funded DuraCrete project led to the formulation of a durability design framework resembling the probabilistic and factorial design approaches established for structural design [5]. This durability design framework was further developed and formalized in the fib Model Code for service life design [6] and the ISO standard 16204 [7]. In addition to including the durability design guidelines given in [6], the updated fib Model Code for concrete structures 2010 (MC2010) [8] also provides design principles for sustainability,1 including environmental impacts, social impacts, and aesthetics (see [8] Section 3.4), and suggests verification of sustainability metrics to be undertaken using rigorous life cycle assessment methods adhering to ISO 14040 [9] (see [8] Section 7.10). However, no specific guidelines or methodologies for undertaking the design are given in [8]. Complying with the intent of [8], a framework for sustainable design and management considering environmental impacts was, based on Lepech [10], proposed by Lepech et al. [11]. Using this framework for sustainability assessment and only considering engineering limit states at the materials level, Lepech et al. [12] illustrated the impact of the selected engineering limit state on the cumulative environmental impact of a single structure. Further exploring the role of material engineering limit states, Lepech [4] performed environmental impact minimization for 100,000 bridges over 100 years, which indicate a counter-intuitive sequence of different engineering SLS limit states to be optimal. Both studies [4,12] were undertaken using simplified deterioration models for reinforced concrete (i.e. Fickian transport models and uniform steel corrosion according to Faraday’s Law). To allow for improved modeling of engineering limit states and thus improved assessment of sustainability, a multi-physics and multi-scale deterioration modeling framework for reinforced concrete affected by chloride-induced corrosion is being built [13].