Cost and CO2 Emission Optimization of Steel Reinforced Concrete Columns in High-Rise Buildings

Analysis of composite concrete steel column using "X" shape steel section

In this paper, a new structural steel shape is proposed to be used in composite columns. The model is made of a concrete column with the proposed steel section embedded in concrete with four angles "L shape", welded together to form the shape "X". The equivalent compressive strength capacity of this "X" shape was compared to the conventional steel "W shape" section. The main goal of the research is the strength enlargement of composite columns. Three 6 ft long columns were analyzed: one conventional "W" section (W100 × 330), one with two angles (2 L 89 × 76.5 × 8), and one with four angles (4 L 50 × 50 × 6.5). Finite element analysis was completed using ABAQUS software and theoretical analysis was performed using AISC and Eurocode4. The deflection control analysis using ABAQUS was validated first on samples from a previously published experimental study conducted in the laboratory, and results from ABAQUS were aligned with the experimental study outcomes. This study found that the proposed "X" shape steel section has comparable compressive strength values to the conventional "W" section.

Embodied Energy Optimization of Prestressed Concrete Road Flyovers by a Two-Phase Kriging Surrogate Model

This study aims to establish a methodology for optimizing embodied energy while constructing lightened road flyovers. A cross-sectional analysis is conducted to determine design parameters through an exhaustive literature review. Based on this analysis, key design variables that can enhance the energy efficiency of the slab are identified. The methodology is divided into two phases: a statistical technique known as Latin Hypercube Sampling is initially employed to sample deck variables and create a response surface; subsequently, the response surface is fine-tuned through a Kriging-based optimization model. Consequently, a methodology has been developed that reduces the energy cost of constructing lightened slab bridge decks. Recommendations to improve energy efficiency include employing high slenderness ratios (approximately 1/28), minimizing concrete and active reinforcement usage, and increasing the amount of passive reinforcement.

Non-Iterative Optimal Design Method Based on LM Index for Steel Double-Beam Floor Systems Reinforced with Concrete Panels

Steel double-beam floor systems reinforced with concrete panels can improve the structural and environmental performance of buildings by reducing moment demands and embodied CO₂ emissions. However, for steel double-beam floor systems, a time-consuming iterative analysis is required to derive an optimal design proposal owing to the rotational constraints in the composite joints between the concrete panel and steel beams. In this study, a non-iterative optimal design method using the LM index is proposed to minimize the embodied CO₂ emissions of steel double-beam floor systems. The LM index is a measure that can be used to select the optimal cross-section of the steel beams considering the decreased moment capacity according to the unbraced length. The structural feasibility of the proposed design method was verified by investigating whether safety-related constraints were satisfied by the LM index with respect to the design variables under various gravity loads. The applicability of the proposed optimal design method is verified by comparing the embodied CO₂ emissions derived from the proposed and code-based design methods. Applicable design conditions were presented based on the LM index to aid engineers. The proposed design method can provide environmentally-optimized design proposals to ensure structural safety by directly selecting the LM index of steel beams.

Modified Harmony Search Algorithm-Based Optimization for Eco-Friendly Reinforced Concrete Frames

Cost and CO2 are two factors in the optimum design of structures. This study proposes a modified harmony search methodology for optimization of reinforced concrete beams with minimum CO2 emissions. The optimum design was developed in detail by considering all possible combinations of variable loads, including dynamic force resulting from earthquake motion. Moreover, time-history analyses were performed, and requirements of the ACI-318 building code were considered in the reinforced concrete design. The results show that the optimum design based on CO2 emission minimization is greatly different from the optimum cost design results. According to these results, using recycled members provides a sustainable design.

Comparison of Environmental Impact of Three Different Slab Systems for Life Cycle Assessment of a Commercial Building in South Korea

The environmental impacts of the construction stage should be considered since a large amount of building materials are used to construct a building at this stage. Studies on the improvement of construction techniques or the application of newly developed construction methods for reducing the environmental impacts are relatively scant compared to other topics of studies. This study aimed to assess and compare the environmental impacts of the ordinary solid slab, the flat plate slab and the voided slab system during the construction phase. A process-based quantitative model was adopted to evaluate the environmental impacts and the comparative results were analysed to demonstrate the significant characteristics of the environmental impacts of the construction of slab in a building. The assessment results show that the environmental impacts from the ordinary solid slab are the highest and the voided slab system is the lowest among three slab systems. As the slab system of the studied building was replaced, it was shown that the environmental impact indicators showed the decreased tendency. Based on the results of environmental impact reduction from the ordinary solid slab, the flat plate slab and the voided slab system, the voided slab system would have the least environmental impact in all indicators.

Effect of Carbon Pricing on Optimal Mix Design of Sustainable High-Strength Concrete

Material cost and CO2 emissions are among the vital issues related to the sustainability of high-strength concrete. This research proposes a calculation procedure for the mix design of silica fume-blended high-strength concrete with an optimal total cost considering various carbon pricings. First, the material cost and CO2 emission cost are determined using concrete mixture and unit prices. Gene expression programming (GEP) is used to evaluate concrete mechanical and workability properties. Second, a genetic algorithm (GA) is used to search the optimal mixture, considering various constraints, such as design compressive strength constraint, design workability constraint, range constraints, ratio constraints, and concrete volume constraint. The optimization objective of the GA is the sum of the material cost and the cost of CO2 emissions. Third, illustrative examples are shown for designing various kinds of concrete. Five strength levels (from 95 to 115 MPa with steps of 5 MPa) and four carbon pricings (normal carbon pricing, zero carbon pricing, five-fold carbon pricings, and ten-fold carbon pricings) are considered. A total of 20 optimal mixtures are calculated. The optimal mixtures were found the same for the cases of normal CO2 pricing and zero CO2 pricing. Optimal mixtures with higher strengths are more sensitive to variation in carbon pricing. For five-fold CO2 pricing, the cement content of mixtures with higher strengths (105, 110, and 115 MPa) are lower than those of normal CO2 pricing. As the CO2 pricing increases from five-fold to ten-fold, for mixtures with a strength of 110 MPa, the cement content becomes lower. Summarily, the proposed method can be applied to the material design of sustainable high-strength concrete with low material cost and CO2 emissions.

Optimal Design of the Cement, Fly Ash, and Slag Mixture in Ternary Blended Concrete Based on Gene Expression Programming and the Genetic Algorithm

Concrete producers and construction companies are interested in improving the sustainability of concrete, including reducing its CO₂ emissions and the costs of materials while maintaining its mechanical properties, workability, and durability. In this study, we propose a simple approach to the optimal design of the fly ash and slag mixture in blended concrete that considers the carbon pricing, material cost, strength, workability, and carbonation durability. Firstly, the carbon pricing and the material cost are calculated based on the concrete mixture and unit prices. The total cost equals the sum of the material cost and the carbon pricing, and is set as the optimization’s objective function. Secondly, 25 various mixtures are used as a database of optimization. The database covered a wide range of strengths between 25 MPa and 55 MPa and a wide range of workability between 5 and 25 cm in slump. Gene expression programming is used to predict the concrete’s strength and slump. The ternary blended concrete’s carbonation depth is calculated using the efficiency factors of fly ash and slag. Thirdly, the genetic algorithm is used to find the optimal mixture under various constraints. We provide examples to illustrate the design of ternary blended concrete with different strength levels and environmental CO₂ concentrations. The results show that, for a suburban region, carbonation durability is the controlling factor in terms of the design of the mixture when the design strength is less than 40.49 MPa, and the compressive strength is the controlling factor in the design of the mixture when the design strength is greater than 40.49 MPa. For an urban region, the critical strength for distinguishing carbonation durability control and strength control is 45.93 MPa. The total cost, material cost, and carbon pricing increase as the concrete’s strength increases.

Multi-objective green design model to mitigate environmental impact of construction of mega columns for super-tall buildings

The mega columns used in super-tall buildings are several meters in size; thus, a greater quantity of construction materials are required than for a general column. Considering the environmental impact, research on a green design model for super-tall buildings is necessary. This design model should minimize both CO₂ emissions and cost in the mega-column construction and design phases with consideration of the member or building size. In this regard, a multi-objective green design model (MOGDM) capable of minimizing construction cost and reducing CO₂ emissions is proposed in this study. The MOGDM is applied to the design of mega columns for a super-tall building and its performance is evaluated based on the average environmental impact reduction rate (AER) and the average increase-in-cost reduction rate (AICR); these indexes are developed to assess the CO₂ emission and construction cost reduction capability. Under the loading scenarios considered in this study, the average AER and AICR for the MOGDM output are 6.76% and 58.02%, respectively. Thus, the evaluation results confirm that the MOGDM proposed in this study can effectively reduce CO₂ emissions and cost in the design and construction phases of mega columns for super-tall buildings.

Optimization of Concrete Mixture Design Using Adaptive Surrogate Model

The increase in urban construction in China has been accompanied by increasing concrete output, which has reached 2250 million m3 in recent years, ranked as the highest in the world. Consequentially, its environmental burden is significant in terms of resource use and carbon emissions. An adaptive surrogate model based on an extended radial basis function and adaptive sampling method was used to optimize the design of a concrete mixture in order to reduce its CO2 emissions and cost. The adaptive sampling method based on the multi-island genetic algorithm was adopted in order to improve the adaptive capability and accuracy of the surrogate model by selecting the proper sample size and ensuring uniform distribution of the sample points in the designed space. Three types of concrete with different strength, that is, C70, C40 and C30, were optimized by controlling the amount of fly ash and phosphorous slag in the samples. The optimized results showed that fly ash and phosphorous slag have a significant influence on the CO2 emissions of concrete and optimized concrete’s cost, while CO2 emissions were less than that of the reference samples. Therefore, the optimal mixture is with great significance to reduce the carbon emission of concrete, which also has implications for decreasing the environmental burden of concrete. In this way, we can optimize concrete of different strength to reduce carbon dioxide emission.

The Reduction of CO2 Emissions by Application of High-Strength Reinforcing Bars to Three Different Structural Systems in South Korea

The architecture, engineering, and construction (AEC) industry consume approximately 23% of the national energy annually, and are considered among the highest energy consuming industries. Recently, several studies have focused on establishing strategies to reduce the emissions of carbon dioxide in the AEC industry by utilisation of low-carbon materials, material reuse, recycling and minimal usage; selection of an optimal structural system and structural optimisation; and optimisation of construction operations. While several studies examined material selection and replacement in concrete, there is a paucity of studies investigating the replacement and implementation of high-strength re-bars to lower the carbon dioxide emissions in buildings. To fill this research gap, the purpose of this study involves calculating the emissions of carbon dioxide by applying high-strength reinforcement bars in three different types of buildings. The input–output analysis method was adopted to compute the emissions of carbon dioxide by using the yield strength and size. This study showed that the application of the high-strength re-bars is beneficial in reducing the input amount of materials, although the quantity of reinforcing bars on the development and splice increased. Furthermore, the application of high-strength deformed bars is also advantageous as a means of carbon dioxide reduction in the studied structural systems. In this study, the CO2 emissions of three different structural systems indicated that implementing SD500 re-bars is the most effective method to reduce carbon dioxide emissions.