Carbon embodied optimization for buttressed earth-retaining walls: Implications for low-carbon conceptual designs

Abstract

This paper shows the differences between the design of a reinforced concrete structure considering two objectives to minimize; economic cost and CO2 emissions. Both objectives depend on the amount of two high carbon intensive materials: cement in the concrete and steel; therefore, these objectives are related. As the balance between steel and cement per m 3 of concrete depends on several factors such as the type of structure, this study focuses on buttressed earth-retaining walls. Another factor that determines the balance between steel and concrete is the height of the wall. Thus, the methodology considers a parametric study for optimal designs of buttressed earth-retaining walls, where one of the parameters is the wall height. One of the objectives is to show the variation in cost when CO2 is minimized, respectful of minimizing the economic cost. The findings show that wall elements under bendingcompressive strains (i.e. the stem of the buttressed retaining wall) perform differently depending on the target function. On one hand, the study reveals an upward trend of steel per unit volume of concrete in emission-optimized earth-retaining buttressed walls, compared to the cost-optimized. On the other hand, it is checked that unlike the cost-optimized walls, emission-optimized walls opt for a higher concrete class than the minimum class available. These findings indicate that emission-optimized walls penalize not only concrete volume, but also the cement content, to the extent that a higher concrete class outperforms in reduced emissions. Additionally, the paper outlines how and to what extent the design of this typology varies for the two analysed objectives in terms of geometry and amount of materials. Some relevant differences influencing the geometry of design strategies are found.

A Hybrid k-Means Cuckoo Search Algorithm Applied to the Counterfort Retaining Walls Problem

“…These construction units correspond to formwork, materials, excavation and earth-fill. The cost and emission functions are based on a 1 m wide strip [34]. The emission and cost values were obtained from [34,66] and are shown in Table 1.…”

“…The cost and emission functions are based on a 1 m wide strip [34]. The emission and cost values were obtained from [34,66] and are shown in Table 1. Then, in a general way, our optimization problem is defined according to Equation (1).…”

“…To evaluate our algorithm in a different scenario than that of a random operator, in this Section we compare the results obtained by the algorithm that uses discretization by k-means, with the results published in [34,67]. In these works, the harmony search algorithm was used to optimize the buttress retaining wall.…”

“…Optimization is carried out for cost and emissions of CO 2 . A comparison is made between the proposed hybrid algorithm and an adaptation of the harmony search (HS) proposed in [34]. The design of the counterfort retaining walls will be detailed in Section 3.…”

Heuristic Techniques for the Design of Steel-Concrete Composite Pedestrian Bridges

“…In recent years, databases measuring the environmental impact of materials have been elaborated, because of the importance of incorporating the design criteria to consider the impact on CO 2 emissions [38][39][40]. Many researchers, such as Yepes et al [41] and Molina-Moreno et al [42], have used these databases to study the difference between the cost and the CO 2 emission optimization for reinforced concrete (RC) structures.…”