Periodic Reporting for period 1 - RECOMPOSE (Resource Efficient Steel - Recycled Aggregate Concrete Composite Floor Systems)
Período documentado: 2023-05-15 hasta 2025-07-14
The construction sector plays a significant role in the economy, raw material extraction, and waste generation. In the conventional linear economy model, extracting raw materials for construction and disposal of construction and demolition waste undermine sustainable development. Concrete is a predominant construction material made of graded aggregates (i.e. sands and gravel, accounting for 60-80% of the concrete volume), water, and cement. Recycling the demolition construction waste by crushing it into aggregate effectively mitigates the problems of waste generation and raw resource depletion. In the past, recycled aggregate (RA) is mainly used in non-structural construction such as pavement and backfill, due to its lower quality than the natural aggregate. Currently, the EN 206 and its revised national annexes allow the limited percentages of the coarse aggregate in concrete to be substituted by RA, e.g. at most 0-50% depending on the exposure classes and national limitations. Further, reduction factors for mechanical properties of recycled aggregate concrete (RAC) have been introduced into the new second generation of Eurocode 2 (FprEN 1992-1-1: 2023), enabling the application of RAC in concrete structures. However, to date, no application rules for RAC have been incorporated into the standards for steel–concrete composite structures.
Aiming to promote more applications of RA, the RECOMPOSE project is exploring the possibility of using higher percentages of RA in steel-concrete composite floor systems upon satisfactory structural safety. The research focuses on the shear resistance of headed stud connectors embedded in RAC slabs governing the structural performance and integrity of the composite floor systems. In addition, whether applying the reduced RAC properties recommended by the upcoming Eurocode 2 into the resistance model of headed stud shear connections in second generation of Eurocode 4 (FprEN 1994-1-1) leads to a safe design is questionable. Accordingly, the RECOMPOSE project is working to answer this question by performing reliability analyses.
The host professor of the RECOMPOSE project served as the convenor of project team CEN/TC250/SC4.T6 within the EU-Mandate M515 which is responsible for developing the second generation of Eurocode 4. He guides the project with standardization-related expertise and engages the project with standardization processes. The standardization-oriented strategy facilitates the dissemination and exploitation of the project outputs and maximizes their impacts. It will trigger the research for the development of Eurocode 4 considering RAC for composite floor systems, which will have a huge impact making possible a large-scale application of RAC in buildings in the future.
Aiming to promote more applications of RA, the RECOMPOSE project is exploring the possibility of using higher percentages of RA in steel-concrete composite floor systems upon satisfactory structural safety. The research focuses on the shear resistance of headed stud connectors embedded in RAC slabs governing the structural performance and integrity of the composite floor systems. In addition, whether applying the reduced RAC properties recommended by the upcoming Eurocode 2 into the resistance model of headed stud shear connections in second generation of Eurocode 4 (FprEN 1994-1-1) leads to a safe design is questionable. Accordingly, the RECOMPOSE project is working to answer this question by performing reliability analyses.
The host professor of the RECOMPOSE project served as the convenor of project team CEN/TC250/SC4.T6 within the EU-Mandate M515 which is responsible for developing the second generation of Eurocode 4. He guides the project with standardization-related expertise and engages the project with standardization processes. The standardization-oriented strategy facilitates the dissemination and exploitation of the project outputs and maximizes their impacts. It will trigger the research for the development of Eurocode 4 considering RAC for composite floor systems, which will have a huge impact making possible a large-scale application of RAC in buildings in the future.
1. Experimental programme
Twelve push-out specimens in accordance with Annex B of FprEN1994-1-1 have been investigated, and test results have been analysed. The load-bearing performance of headed stud connectors in RAC slabs containing 100% RA has been revealed for the first time.
2. Numerical simulations
Finite element (FE) models of headeds stud connections have been calibrated by experimental results. Parametric studies have been performed using the verified FE models. A dataset of stochastic responses of headed-stud connections has been created.
3. Design methods considering structural reliability
A novel computational model, polynomial chaos expansion (PCE), has been derived for predicting the resistance of headed stud connections in solid RAC slabs. Four machine learning models have been trained with the data of headed stud connectors in NAC slabs. The PCE and machine learning models, and the existing popular mechanics-based models have been statistically evaluated with the available test results of headed stud connections using RAC towards the required reliability within the European design practice. It was found that the PCE model leads to the highest design resistance among all the models. The results also indicated that using the resistance model for headed stud connections in FprEN 1994-1-1 with the reduced RAC strength recommended by FprEN 1992-1-1 cannot ensure structural reliability.
Furthermore, based on experimental data generated within RECOMPOSE, the fellow assessed the newly developed design model in Annex G of the FprEN 1994-1-1, which addresses headed stud connectors in composite beams with transversal narrow profiled sheeting. As a result, a modification factor was proposed for the design model while maintaining the same partial safety factor (i.e. 1.25) to meet the structural reliability requirements defined in EN 1990, specifically, a target failure probability of less than 0.0012.
Twelve push-out specimens in accordance with Annex B of FprEN1994-1-1 have been investigated, and test results have been analysed. The load-bearing performance of headed stud connectors in RAC slabs containing 100% RA has been revealed for the first time.
2. Numerical simulations
Finite element (FE) models of headeds stud connections have been calibrated by experimental results. Parametric studies have been performed using the verified FE models. A dataset of stochastic responses of headed-stud connections has been created.
3. Design methods considering structural reliability
A novel computational model, polynomial chaos expansion (PCE), has been derived for predicting the resistance of headed stud connections in solid RAC slabs. Four machine learning models have been trained with the data of headed stud connectors in NAC slabs. The PCE and machine learning models, and the existing popular mechanics-based models have been statistically evaluated with the available test results of headed stud connections using RAC towards the required reliability within the European design practice. It was found that the PCE model leads to the highest design resistance among all the models. The results also indicated that using the resistance model for headed stud connections in FprEN 1994-1-1 with the reduced RAC strength recommended by FprEN 1992-1-1 cannot ensure structural reliability.
Furthermore, based on experimental data generated within RECOMPOSE, the fellow assessed the newly developed design model in Annex G of the FprEN 1994-1-1, which addresses headed stud connectors in composite beams with transversal narrow profiled sheeting. As a result, a modification factor was proposed for the design model while maintaining the same partial safety factor (i.e. 1.25) to meet the structural reliability requirements defined in EN 1990, specifically, a target failure probability of less than 0.0012.
The developed Polynomial Chaos Expansion (PCE) model represents a promising approach for the design of headed stud connectors, enabling material savings and potential economic benefits. This method also shows potential for extension to the design of other structural components. The identification of the load-bearing performance, particularly the significant load relaxation, of headed stud connectors in RAC slabs containing 100% RA, along with the reliability assessment of existing mechanics-based models and design models in FprEN 1994-1-1, may encourage standardization bodies to revise the current design models to account for RAC. The next step is to disseminate the results as widely as possible by publishing the results on influential platforms in the open-access form, presenting to standardization committees/working groups, and at international conferences.