| 1. |
- Andersen, Lars V., et al.
(författare)
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Mitigation of ground vibration from pile driving by circular arrays of rigid blocks placed on the ground surface
- 2020
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Ingår i: EURODYN 2020 - 11th International Conference on Structural Dynamics, Proceedings. - 2311-9020. - 9786188507210 ; 2, s. 2966-2984
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Konferensbidrag (refereegranskat)abstract
- Ground vibration associated with pile driving causes annoyance to inhabitants of the neighbouring environment and may possibly lead to damage on existing structures in the proximity of a construction site. Vibration mitigation near the source can reduce the problem. The paper investigates the effect of circular arrays of blocks, placed on the ground surface around the position at which the pile is driven. A semi-analytical model of a layered soil has been used for the analysis, and the blocks have been modelled as monolithic structures, accounting for the full structure-soil-structure interaction. Two different sites have been studied: a layered soil with three metres of soft sand over a half-space of till, and a five metres deep layer of soft clay overlying a half-space of lime. The block arrays consist of one to three concentric rings with radii 4, 8, and 12 m, respectively. The rings contain 6, 12, and 24 blocks, respectively, and the size of the blocks have been scaled such that each ring has the same total mass. The pile has not been modelled explicitly; instead vertical excitation has been applied in different depts over a circular area corresponding to the cross section of a pile. For the considered cases it has been found that an array of blocks, shaped as a "Stonehenge ", may provide significant mitigation of the ground vibration level in a receiver zone placed 20-40 m from the pile. When a load is applied within the soft tops oil layer, the array provides an insertion loss in the order of 5-20 dB, depending on the size of the blocks and the configuration of the arrays. For loads applied deeper in the soil, within the stiffer half-space, the insertion loss is small and may in some situations be negative. However, this must be seen in the context that the transfer mobility in the reference state without the blocks, i.e. the greenfield, is low when the load is applied within the stiff half-space.
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| 2. |
- Andersen, Lars V., et al.
(författare)
-
Mitigation of ground vibrations by circular arrays of rigid blocks
- 2019
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Ingår i: COMPDYN 2019 - 7th International Conference on Computational Methods in Structural Dynamics and Earthquake Engineering, Proceedings. - 2623-3347. - 9786188284470 ; 2, s. 3422-3447
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Konferensbidrag (refereegranskat)abstract
- Pile driving and other activities in the built environment cause ground vibration at low frequencies. This may result in annoyance to people as well as damage to civil structures. It is known that masses added on the ground surface can have an impact on the vibration levels in the surrounding environment. Hence, employing a semi-analytical model for rigid blocks on the surface of a layered ground, this paper investigates whether circular arrays of such blocks can be used as a means of vibration mitigation. The frequency range 0–80 Hz is considered, since this is relevant to whole-body vibrations of humans as well as the fundamental modes of resonance in building elements, e.g., floors and walls. Two different soil profiles are analysed: a soft dry sand layer over a till half-space and a soft wet clay layer over a lime half-space. Further, three configurations of the block arrays are taken into consideration, and for the first soil profile also the height of the blocks is varied to test its influence on the insertion loss in a zone 20–40 m away from the source. The aim is to quantify the overall insertion loss that can be expected using the proposed methodology. Further, the variation in insertion loss caused by changes in the block array configuration is examined.
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| 3. |
- Andersson, Linus, et al.
(författare)
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Model reduction for structures subjected to blast loading by use of dynamic substructuring
- 2020
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Ingår i: EURODYN 2020 - 11th International Conference on Structural Dynamics, Proceedings. - 2311-9020. - 9786188507210 ; 2, s. 2544-2564
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Konferensbidrag (refereegranskat)abstract
- In the present study, strategies are developed to enable time-efficient models for structures subjected to blast loading, appropriate for use in a structural design process. Dynamic sub structuring is employed to obtain reduced models with localized nonlinearities, such as predefined plastic hinges in a beam column structure. The parts of the substructures that remains linear elastic are modeled by Ritz-vectors whereas parts with a nonlinear response are retained as physical degrees-of-freedom. Furthermore, a time-stepping method is presented that is shown to be suitable for reduced models including local and predefined rigid-plastic behavior. The proposed methodology is applied and demonstrated in a numerical example of a concrete frame structure. Both the well-established Craig-Bampton method and reduction bases enriched by so-called correction modes are evaluated. For the load case studied, it is shown that the standard Craig-Bampton technique is suitable for reducing the substructures. Furthermore, it is shown that only a few Ritz-vectors are needed to sufficiently describe the deformation of the structure. However, additional modes are needed to ensure an accurate representation of the interface forces between the substructures.
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| 4. |
- Andersson, Linus, et al.
(författare)
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Reduced order modeling for the dynamic analysis of structures with nonlinear interfaces
- 2019
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Ingår i: COMPDYN 2019 - 7th International Conference on Computational Methods in Structural Dynamics and Earthquake Engineering, Proceedings. - 2623-3347. - 9786188284470 ; 2, s. 2395-2406
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Konferensbidrag (refereegranskat)abstract
- In the present paper, linear substructures with nonlinearities localized at their interfaces, such as the joints in a beam structure, are studied. By subdivision of the total structure into substructures, reduced subsystems are obtained by component mode synthesis. Nonlinear elements are introduced at supports or between substructures. A numerical example is presented where a beam subjected to blast loading is studied. The influence of the nonlinear behavior as well as the number of retained fixed-interface normal modes in the reduced subsystems are evaluated. The response is also compared to the response of equivalent single-degree-of-freedom systems, which are frequently employed in blast load design calculations. For the load cases studied, the displacement computed from an equivalent single-degree-of-freedom system correspond fairly well to the displacement given by a refined two-dimensional beam model, reduced by substructuring. In contrast, the shear force differs significantly due to that higher order modes are neglected in the single-degree-of-freedom system.
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| 5. |
- Malmborg, J., et al.
(författare)
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Modeling train-induced ground-borne vibrations using FEM in a moving frame of reference
- 2019
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Ingår i: COMPDYN 2019 - 7th International Conference on Computational Methods in Structural Dynamics and Earthquake Engineering, Proceedings. - Athens : Institute of Structural Analysis and Antiseismic Research School of Civil Engineering National Technical University of Athens (NTUA) Greece. - 2623-3347. - 9786188284456 ; 3, s. 5899-5912
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Konferensbidrag (refereegranskat)abstract
- To predict ground-borne vibration levels caused by railway traffic, models for estimating the load from the vibration source, as well as the vibration transmission through the ground, are needed. In the present paper, a finite element formulation in a frame of reference following the moving load, is used for modeling a railway slab track. The response of the underlying soil is represented through a dynamic stiffness matrix, obtained via the Green’s function for a horizontally layered visco-elastic half-space in a moving frame of reference in the frequency–wavenumber domain. The track can be modeled as continuously connected beams, but the use of plate elements allows for more general stress and displacement distributions in the transverse direction of the slab to be resolved. Here, the free-field response due to a harmonic load moving along a slab track, is evaluated and compared using different modeling strategies for the slab.
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| 6. |
- Peplow, Andrew T., et al.
(författare)
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Computation of axisymmetric vibration transmission using a well-conditioned system for elastic layers over a half–space
- 2019
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Ingår i: COMPDYN 2019 - 7th International Conference on Computational Methods in Structural Dynamics and Earthquake Engineering, Proceedings. - Athens : Institute of Structural Analysis and Antiseismic Research School of Civil Engineering National Technical University of Athens (NTUA) Greece. - 2623-3347. - 9786188284456 ; 3, s. 4548-4556
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Konferensbidrag (refereegranskat)abstract
- In the context of range-independent solid media, we propose a well-conditioned dynamic stiffness matrix for an elastic layer sitting over an elastic half-space. This formulation overcomes the well-known problem of numerical ill-conditioning when solving the system of equations for deep-layered strata. The methodology involves the exact solutions of transformed ordinary differential equations in the wavenumber domain, namely a projection method based on the transformed equations with respect to the depth coordinate. By re-arranging the transformed equations, the solutions remain numerically well-conditioned for all layer depths. The inverse transforms are achieved with a numerical quadrature method and the results presented include actual displacement fields in the near-field of the load in plane-strain and three-dimensional axisymmetric cases. Verification against finite element method (FEM) calculations demonstrates the performance and complexity of the two approaches.
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| 7. |
- Persson, Peter, et al.
(författare)
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How building adjacency affects occupant-perceivable vibrations due to urban sources : A parametric study
- 2019
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Ingår i: COMPDYN 2019 - 7th International Conference on Computational Methods in Structural Dynamics and Earthquake Engineering, Proceedings. - Athens : Institute of Structural Analysis and Antiseismic Research School of Civil Engineering National Technical University of Athens (NTUA) Greece. - 2623-3347. - 9786188284456 ; 3, s. 5610-5621
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Konferensbidrag (refereegranskat)abstract
- Urban densification, despite the economic and social opportunities it offers, brings with it challenges to the well-being of citizens. A direct effect of densification is the rise in noise- and vibration-producing sources, which can lead to both health and comfort issues. In determining the risk associated with excessive vibration levels, the distance between the source and the receiver or target building, the ground properties, and the building type, are all important factors. In this paper, we are concerned with the effect that adjacent buildings have on the prediction of the vibration levels in a residential building, caused by external ground surface loads. The parametric studies were conducted using a coupled finite element model of the ground and the buildings. The analyses were conducted in the frequency domain, and vibrational velocity levels were computed at the receiver building in order to assess how building adjacency affects the receiving building’s vibrational response.
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