12 research outputs found
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Seismic design of reinforced concrete frames for minimum embodied CO2 emissions
Optimum structural design of reinforced concrete (RC) frames has been the focus of extensive research. Typically, previous studies set economic cost as the main design objective despite the fact that RC structures are major contributors of CO2 emissions. The limited number of studies examining optimum design of RC frames for minimum CO2 emissions do not address seismic design considerations. However, in many countries around the world, including most of the top-10 countries in CO2 emissions from cement production, RC structures must be designed against earthquake threat. To bridge this gap, the present study develops optimum seismic designs of RC frames for minimum cradle to gate embodied CO2 emissions and compares them with optimum designs based on construction cost. The aim is to identify efficient design practices that minimize the environmental impact of earthquake-resistant RC frames and examine the trade-offs between their cost and CO2 footprint. To serve this goal, an RC frame is optimally designed according to all ductility classes of Eurocode 8 and for various design peak ground accelerations (PGAs), concrete classes and materials embodied CO2 footprint scenarios. It is found that the minimum feasible CO2 emissions of RC frames strongly depend on the adopted ductility class in regions of high seismicity, where low ductility seismic design can generate up to 60% more CO2 emissions than designs for medium and high ductility. The differences reduce, however, as the level of seismicity decreases. Furthermore, CO2 emissions increase significantly with the design PGA. On the other hand, they are less sensitive to the applied concrete class. It is also concluded that, for medium to high values of the ratio of the unit environmental impact of reinforcing steel to the respective impact of concrete, the minimum CO2 seismic designs are very closely related to the minimum cost designs. However, for low values of the same ratio, the minimum cost design solutions can generate up to 13% more emissions than the minimum CO2 designs
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Sustainable seismic design of RC frames with structural optimisation techniques
In conventional engineering practice, the sustainable seismic design of reinforced concrete (RC) frames is pursued with the aid of the designer’s experience and/or trial and error approaches. Nevertheless, the complexity of this structural design task, as well as the demand for sustainable solutions in limited time, set the use of automated structural optimization methodologies as an attractive alternative approach. In this study, it is shown that the use of structural optimization techniques in seismic design of RC frames can lead to significant reductions not only in economic costs but also in environmental impacts expressed in terms of embodied CO2 emissions. The latter is significant because in many countries around the world, including most of the top-10 countries in CO2 emissions from cement production, RC structures are designed to resist earthquake loads. Moreover, the trade-offs between the economic costs of earthquake-resistant RC frames and the embodied CO2 emissions are presented. It is concluded that, typically, the designs of RC frames for minimum construction cost and embodied CO2 emissions are closely related. Therefore, both objectives can be achieved almost simultaneously in the framework of optimum seismic design of RC frames
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The anchorage-slip effect on direct displacement-based design of R/C bridge piers for limiting material strains
Direct displacement-based design (DDBD) represents an innovative philosophy for seismic design of structures. When structural considerations are more critical, DDBD design should be carried on the basis of limiting material strains since structural damage is always strain related. In this case, the outcome of DDBD is strongly influenced by the displacement demand of the structural element for the target limit strains. Experimental studies have shown that anchorage slip may contribute significantly to the total displacement capacity of R/C column elements. However, in the previous studies, anchorage slip effect is either ignored or lumped into flexural deformations by applying the equivalent strain penetration length. In the light of the above, an attempt is made in this paper to include explicitly anchorage slip effect in DDBD of R/C column elements. For this purpose, a new computer program named RCCOLA-DBD is developed for the DDBD of single R/C elements for limiting material strains. By applying this program, more than 300 parametric designs are conducted to investigate the influence of anchorage slip effect as well as of numerous other parameters on the seismic design of R/C members according to this methodology
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Multi-objective optimum selection of ground motion records with genetic algorithms
Existing ground motion selection methods for the seismic assessment of structural systems consider only spectral compatibility as selection objective. Other important earthquake parameters such as those related to regional seismicity, local soil conditions, strong ground motion intensity and duration are considered indirectly by setting them as selection constraints. This study presents a new framework for the optimum selection of earthquake ground motions, where more than one objectives are considered explicitly in the selection procedure including objectives that are not directly related to spectral matching. To address the multi-objective nature of the optimization problem examined herein, the weighted sum method is used that supports decision making both in the pre-processing and post-processing phase of the selection procedure. The optimum selections are conducted by the use of a mixed-integer genetic algorithm that is able to track near-global optimal solutions of constrained problems with both discrete and continuous design variables. It is found that proposed methodology is able to select ground motion sets that are both spectrum compatible and representative of the seismic conditions of the structural system under investigation
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A combined damage index for seismic assessment of non-ductile reinforced concrete structures
Existing seismic damage indices have been formulated and verified almost exclusively on the basis of flexural damage mechanisms. In this paper, a local damage index proposed previously by the authors for assessing existing reinforced concrete (RC) structures is described. According to its formulation, deterioration caused by all deformation mechanisms (flexure, shear, anchorage slip) is treated separately for each mechanism. Moreover, the additive character of damage arising from the three response mechanisms, as well as the increase in degradation rate caused by their interaction, are fully taken into consideration. The proposed local damage index is first calibrated against experimental recordings and then is applied to predict seismic damage response of one RC column and one frame test specimen with substandard detailing. It is concluded that in all cases and independently from the prevailing mode of failure, the new local damage index predicts well the damage pattern of the analysed specimens
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A gradual spread inelasticity model for R/C beam-columns, accounting for flexure, shear and anchorage slip
A new beam-column model is developed for the seismic analysis of reinforced concrete (R/C) structures. This finite element consists of two interacting, gradual spread inelasticity sub-elements representing inelastic flexural and shear response and two rotational springs at the ends of
the member to model anchorage slip effects. The flexural sub-element is able to capture gradual spread of flexural yielding in plastic hinge regions of R/C members. The shear sub-element interacts throughout the analysis with the flexural sub-element, in the location of the plastic hinge regions, in order to capture gradual spread of inelastic shear deformations as well as degradation of shear strength with curvature ductility demand based on an analytical procedure proposed herein. The skeleton curves and hysteretic behaviour in all three deformation mechanisms are determined on the basis of analytical procedures and hysteretic models found to match adequately the experimental
results. Empirical formulae are proposed for the shear distortion at onset of stirrup yielding and onset of shear failure. The proposed element is implemented in the general finite element code for damage analysis of R/C structures IDARC and is validated against experimental results involving R/C column and frame specimens failing in shear subsequent to yielding in flexure. It is shown that the model can capture well the hysteretic response and predict reliably the type of failure of these specimens
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Seismic damage analysis including inelastic shear-flexure interaction
The paper focusses on seismic damage analysis of reinforced concrete (R/C) members, accounting for shear-flexure interaction in the inelastic range. A finite element of the beam-column type for the seismic analysis of R/C structures is first briefly described. The analytical model consists of two distributed flexibility sub-elements which interact throughout the analysis to simulate inelastic flexural and shear response. The finite element accounts for shear strength degradation with inelastic curvature demand, as well as coupling between inelastic flexural and shear deformations after flexural yielding. Based on this model, a seismic damage index is proposed taking into account both inelastic flexural and shear deformations, as well as their interaction. The finite element and the seismic damage index are used to analyse the response of R/C columns tested under cyclic loading and failing either in shear or in flexure. It is shown that the analytical model and damage index can predict and describe well the hysteretic response of R/C
columns with different types of failure
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Analytical study on the influence of distributed beam vertical loading on seismic response of frame structures
Typically, beams that form part of structural systems are subjected to vertical distributed loading along their length. Distributed loading affects moment and shear distribution, and consequently spread of inelasticity, along the beam length. However, the finite element models developed so far for seismic analysis of frame structures either ignore the effect of vertical distributed loading on spread of inelasticity or consider it in an approximate manner. In this paper, a beam-type finite element is developed, which is capable of considering accurately the effect of uniform distributed loading on spreading of inelastic deformations along the beam length. The proposed model consists of two gradual spread inelasticity sub-elements accounting explicitly for inelastic flexural and shear response. Following this approach, the effect of distributed loading on spreading of inelastic flexural and shear deformations is properly taken into account. The finite element is implemented in the seismic analysis of plane frame structures with beam members controlled either by flexure or shear. It is shown that to obtain accurate results the influence of distributed beam loading on spreading of inelastic deformations should be taken into account in the inelastic seismic analysis of frame structures
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Optimum design of 3D reinforced concrete building frames with the flower pollination algorithm
The flower pollination algorithm (FPA) is a highly efficient metaheuristic optimization algorithm that is inspired by the pollination process of flowering species. FPA is characterised by simplicity in its formulation as well as high computational performance and it has been found to outperform other well-established algorithms in a range of diverse optimization problems. The present study applies, for first time, the FPA to the computationally challenging optimum design of real-world 3D reinforced concrete (RC) building frame structures after a set of appropriate modifications to its original formulation. To serve this goal, a new computationally efficient framework for the optimum design of 3D RC frames is developed that is interacting with the well-known software SAP2000 for the purposes of structural analysis and design. The framework is then applied to the minimum material cost design of a 4-storey and a 12-storey RC building in accordance with Eurocode regulations. It is found that the FPA exhibits better or similar computational performance than other well-established algorithms in these optimization tasks. Furthermore, parameter tuning analysis reveals the FPA parameter values that maximize its computational performance in the optimum structural design of 3D RC building frames
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Sustainable and resilient seismic design of reinforced concrete frames with rocking isolation on spread footings
The rapidly evolving climate change together with the urgent need of modern societies for resilience against catastrophic threats set the sustainable and resilient seismic design of reinforced concrete (RC) structures as a priority. Rocking isolation of RC frames resting on spread footings has been proven numerically and experimentally to offer superior seismic performance with reduced seismic demands in the superstructure. At the same time, rocking footings do not require special construction solutions and can be readily implemented in the current state of practice. To exploit these benefits, the present study, for first time, utilizes rocking footings in the optimum design of RC frames for high seismic resilience and reduced environmental impact. This is achieved by incorporating a resilient seismic design methodology into a numerical optimization procedure that is aiming to minimize embodied carbon. Applications of the proposed approach show that the carbon footprint of RC frames can be reduced by 40% due to rocking isolation on spread footings. The benefits become more important as the level of seismic hazard increases. It is also found that the environmental benefits of rocking footings for RC frames are rather insensitive to the characteristics of ground motions and the uncertainties of soil properties