F. Cedrón

Bio: F. Cedrón is an academic researcher from Imperial College London. The author has contributed to research in topics: Seismic loading & Nonlinear system. The author has an hindex of 1, co-authored 2 publications receiving 7 citations.

Seismic performance of single layer steel cylindrical lattice shells

Abstract: This paper examines the elastic and inelastic seismic behaviour of single layer steel cylindrical lattice shells. The main dynamic characteristics for this form of structure are firstly examined through a parametric assessment, which also leads to proposed expressions for estimating the fundamental period and mode of vibration. The seismic response of five typical shell configurations, representing a wide range of rise to span ratios, is then assessed within the linear elastic range under selected earthquake excitations. Particular focus is given to the relative influence of the horizontal and vertical seismic components on the internal actions. In order to provide a means for evaluating the underlying inelastic behaviour, a simple pushover approach, which is suitable for this structural form, is suggested using the forces obtained from the fundamental mode shape. The peak angle change is proposed as a damage parameter within the nonlinear analysis for characterising the inelastic global and local demands in shells of different geometries. Incremental dynamic analysis is subsequently carried out in order to evaluate the detailed nonlinear time history response. The results provide detailed insights into the influence of the horizontal and vertical excitations on the nonlinear seismic response, and illustrate the suitability of the peak angle change as an inelastic deformation measure for shells of different geometric configurations. The main findings from the linear and nonlinear assessments are highlighted within the discussions, with a view to providing guidance for performance based assessment procedures as well as simplified design approaches.

Assessment and design considerations for single layer cylindrical lattice shells subjected to seismic loading

Abstract: This paper examines the main considerations related to the seismic design and assessment of single layer steel cylindrical lattice shells, and offers recommendations for their practical application. Geometric configurations covering a wide range of rise to span ratios are considered within the investigation. An insight into the relative influence of seismic loading on shell design, in comparison to gravity conditions, is firstly provided through the use of digital parametric engineering procedures. This is followed by linear elastic response assessments which are used to propose a simplified procedure for estimating the internal seismic forces for the purpose of member sizing in early design stages. Suitable approaches for pushover analysis are then discussed and used to identify inherent plastic mechanisms. The results of incremental nonlinear dynamic analysis, using a suite of fourteen records, are also employed in order to validate the findings and to further assess the ultimate response under realistic seismic loading conditions. Based on the findings, representative ranges for behaviour factors and displacement modification coefficients are derived alongside discussions on their implementation within codified seismic design procedures. Apart from providing recommendations for simplified design approaches, the assessments presented in this paper can also be used to support detailed performance based guidelines as well as for informing geometry and size optimisation strategies.

Confinement effects for rubberised concrete in tubular steel cross-sections under combined loading

Abstract: This paper describes an experimental investigation into confinement effects provided by circular tubular sections to rubberised concrete materials under combined loading. The tests include specimens with 0%, 30% and 60% rubber replacement of mineral aggregates by volume. After describing the experimental arrangements and specimen details, the results of bending and eccentric compression tests are presented, together with complementary axial compression tests on stub-column samples. Tests on hollow steel specimens are also included for comparison purposes. Particular focus is given to assessing the confinement effects in the infill concrete as well as their influence on the axial–bending cross-section strength interaction. The results show that whilst the capacity is reduced with the increase in the rubber replacement ratio, an enhanced confinement action is obtained for high rubber content concrete compared with conventional materials. Test measurements by means of digital image correlation techniques show that the confinement in axial compression and the neutral axis position under combined loading depend on the rubber content. Analytical procedures for determining the capacity of rubberised concrete infilled cross-sections are also considered based on the test results as well as those from a collated database and then compared with available recommendations. Rubber content-dependent modification factors are proposed to provide more realistic representations of the axial and flexural cross-section capacities. The test results and observations are used, in conjunction with a number of analytical assessments, to highlight the main parameters influencing the behaviour and to propose simplified expressions for determining the cross-section strength under combined compression and bending.

A new damage detection method of single-layer latticed shells based on combined modal strain energy index

Abstract: The existing damage detection methods are challenging to be directly applied to single-layer latticed shells due to the complex mechanical mechanism and modal characteristics of such structures. In this regard, an effective damage detection method based on the combined modal strain energy index is proposed in this paper to detect the location of the damaged members in such structures. Based on the vibration modal features before and after damage of structures, the modal matching and combination method is presented to generate the combined mode, which include the modal matching procedure based on the modal assurance criterion and the modal combination procedure using the Kriging interpolation. Compared with the damaged mode, the specially constructed combined mode can significantly reduce the mode shape discrepancy in the undamaged region on the basis of retaining the characteristic differences in the damaged members. On this basis, the combined modal strain energy change index is proposed according to the modal strain energy difference between the original mode and the combined mode. Since the proposed index is established according to the difference between the combined vibration mode and the original vibration mode, the values of damage index of the undamaged members are greatly reduced, so as to effectively avoid the occurrence of misjudgement. Several numerical examples with different damage scenarios are studied in order to evaluate the proposed approach. The results clearly indicate that the proposed method features high damage localization accuracy compared with traditional methods and good measurement noise robustness.

Shape optimization and buckling analysis of novel two-way aluminum alloy latticed shells

Abstract: The circumferential profile of cylinder, as a classic shape, has been widely adopted in single-layer latticed shells. Previous research into these structures primarily concentrated on their buckling behavior. In this work, a novel two-way aluminum alloy cable-stiffened single-layer latticed shell is proposed to explore a shape optimization procedure of such structure. In addition, the buckling behavior of the optimized structures and classic cylindrical latticed shells are examined and compared. The optimization procedure adopts a linear algorithm, in which the structural strain energy is selected to be the optimization objective. Buckling analyses are also performed to compare the buckling behavior of this novel latticed shell with classic cylindrical and optimized shapes. The comparisons show that the load-carrying capacities are clearly enhanced by optimizing the shell shapes. The results presented in this article are anticipated to aid engineers in the design of two-way aluminum alloy latticed shells with an optimal shape.

Assessment and design considerations for single layer cylindrical lattice shells subjected to seismic loading

Abstract: This paper examines the main considerations related to the seismic design and assessment of single layer steel cylindrical lattice shells, and offers recommendations for their practical application. Geometric configurations covering a wide range of rise to span ratios are considered within the investigation. An insight into the relative influence of seismic loading on shell design, in comparison to gravity conditions, is firstly provided through the use of digital parametric engineering procedures. This is followed by linear elastic response assessments which are used to propose a simplified procedure for estimating the internal seismic forces for the purpose of member sizing in early design stages. Suitable approaches for pushover analysis are then discussed and used to identify inherent plastic mechanisms. The results of incremental nonlinear dynamic analysis, using a suite of fourteen records, are also employed in order to validate the findings and to further assess the ultimate response under realistic seismic loading conditions. Based on the findings, representative ranges for behaviour factors and displacement modification coefficients are derived alongside discussions on their implementation within codified seismic design procedures. Apart from providing recommendations for simplified design approaches, the assessments presented in this paper can also be used to support detailed performance based guidelines as well as for informing geometry and size optimisation strategies.

Higher mode effects of multistorey substructures on the seismic response of double-layered steel gridshell domes

Abstract: The seismic response of gridshell roofs with substructures is strongly influenced by the relative mass and stiffness of the roof and substructure, and particularly by how close the periods of the dominant roof and substructure modes are. Multistorey substructures may exhibit a significant higher-mode acceleration response, primarily due to the contribution of the shorter second translational substructure mode to the roof response. This paper presents parametric studies conducted on steel gridshell domes with 60, 100 and 150 m spans and six-storey substructures to investigate the interaction between the higher substructure modes and dominant roof modes. The contribution of each substructure mode to the overall response was characterised by a newly proposed dominance response ratio. In contrast to previous studies of long-period single-storey substructures, which only minimally excited the roof modes, the higher modes of the long-period multistorey substructures investigated in this study significantly contributed to the roof response. The roof vertical accelerations were amplified by up to three times the substructure roofline acceleration, as the curved roof geometry couples the horizontal substructure and vertical roof response. The substructure higher-mode contribution was quantified using amplification factors and developed into equivalent static loads that were found to be in good agreement with response spectrum analysis results. The proposed equivalent static loads provide insight into the complex dynamic characteristics of gridshell roofs with multistorey substructures and offer an efficient method for preliminary seismic design.