•Cut-and-cover shallow metro and railway stations are seismically vulnerable.•This is due to the internal hyperstaticity of its rigid transverse box section.•This paper proposes an alternative ...solution with low lateral stiffness.•The proposed technology is applied to a relevant actual case study.•This case is deeply analyzed, and the offered solution proofs feasible.
Underground cut-and-cover structures are commonly designed as rigid box sections; however, in practical applications, connections between walls and slabs are frequently rather hinged (because of ease of construction). The abovementioned rigid configurations are highly sensitive to seismic ground motions, due to their important lateral stiffness and internal hyperstaticity; conversely, structures with articulated (or sliding) members have a smaller lateral stiffness, and would be significantly less affected by seismic waves, as would simply accommodate the imposed strains. This flexible solution has been widely considered in practice, but has received little attention from the academic community; this paper tries to close this gap by investigating preliminarily the seismic performance of box-section underground structures with hinged or sliding members. The well-known Daikai Station, damaged by the 1995 Kobe earthquake is analyzed in this paper as a highly relevant case study. An alternative solution is proposed for that station; both simplified and precise calculations have been performed. The simplified calculations are linear static analyses of the station-soil system; the soil-structure interaction is represented by a simple classical model. The precise calculations are nonlinear time-history analyses of an integrated finite element model of the station and the surrounding soil. Both types of analyses refer to the traditional and the proposed solutions of the station. The results of the static and dynamic analyses are satisfactorily compared; they prove that the proposed flexible solution is fully feasible and provides better seismic performance. Finally, another paper by the same authors presented a supplementary case study on a 2-story 3-bay subway station; the outcomes of these two studies could contribute to ground this constructive solution for shallow underground rectangular cut-and-cover structures in seismic areas (both for new construction and retrofit). Noticeably, this approach can be utilized for both cast-in-place and precast structures.
•This work assesses the influence of various weld patterns between beam and end-plate on the global ductile behavior of pallet racks, being one of them a novelty.•This assessment is performed by ...means of pushover analysis.•The influence of the level height is studied throughout two rack configurations.•Different numerical models for racks are presented, aiming to capture the influence of upright perforations and 3D effects.
This paper presents numerical pushover analyses on multiple bay pallet racks, aiming to quantify variations in global ductility when using different beam-to-upright connections. The connections differ in the layout of the beam-to-endplate welding, being one of them a technological novelty. They are modeled with envelopes of monotonic and cyclic moment-rotation curves obtained from component tests and presented in previous research. Moreover, the influence of the level height is studied throughout two different rack configurations. A single-column model for multiple bay racks, made with 3D beams and shells, is presented and compared with simpler 2D models to quantify the influence of 3D effects and upright perforations. Results exhibit that the novel connection improves the capacity to absorb energy, but an inappropriate rack configuration can lead to a soft-story mechanism, thus not taking full advantage of its ductility.
This paper presents a parametrical study on seismic pounding between pairs of RC frames with 3 and 5 stories and aligned slabs. The performance indices are the maximum inter-story drift, absolute ...acceleration, and story shear force, and the cumulated hysteretic energy. The distinctive features are the selection of parameters and of performance indices, the soil-structure interaction, a modified Kelvin-Voigt pounding model, and, the careful selection of the discretization period. The findings of this study are the corroboration of remarks from previous researches and the formulation of new conclusions.
•Seismic pounding between buildings with aligned slabs is important, and its numerical simulation is far from trivial.•A considerable number of researches have been reported; however, there are still many open questions, given that the pounding behavior is somehow chaotic.•This work presents a parametric study on pounding between pairs of low-rise RC buildings with aligned slabs.•The main distinctive features of the study are the careful selection of the buildings and the seismic inputs, the simulation of pounding with an advanced model, the consideration of SSI, and the examination of results through a comprehensive set of performance indices.•This study confirms and deepen the conclusions of previous researches and provides new remarks.
Collision between adjoining buildings with aligned slabs is relevant, since the huge impact forces significantly modify the buildings dynamic behavior. The separation required by the regulations ...avoids pounding; however, even in recent buildings, impact can occur due to not fulfillment of codes and seismicity underestimation. Given the importance of this issue, a significant research effort has been undertaken worldwide, and a considerable number of papers are available. The complexity of this field and this abundance of information might require a review task. This paper presents a summary of the theoretical developments, discusses the most common simulation software, provides an overview of the previous research, offers recommendations to researchers, and identifies research needs.
This paper presents a state-of-the-art review on seismic tests of adjustable pallet rack systems: on particular components of racks, subassemblies, full racks and stored goods. The tested particular ...components are the most critical connections: beams-to-uprights, braces-to-uprights, and floor-to-uprights; subassemblies also include beam-to-upright connections, among other components. Tests on full racks can be static (pushover), pseudo-dynamic, or dynamic (pullout and shaking table). Finally, tests on stored goods are sliding (aimed to identify the friction coefficient with the supporting members) and tilting (to check their confinement). The examination of the discussed experiments provides relevant conclusions and allows identifying research needs.
•This paper presents a state-of-the-art review on racks testing for seismic design.•The study focuses on adjustable pallet racks.•The major worldwide design codes are analyzed.•Global remarks are derived, and further research needs are identified.
•The beam-upright connections of racks play a relevant role in their seismic capacity.•This work supplements a previously-conducted testing campaign on such connections.•In those tests, different ...weld paths were compared, looking for ductile break modes.•In this paper, numerical simulations are performed in order to deepen the tests observations.•The influence of the weld paths on the connection stiffness, stress elastic distribution, and yielding onset is studied.
This paper presents numerical simulations of a suite of cantilever seismic tests of speed-lock connections between beam and upright members of adjustable pallet rack systems. The tested specimens differ in the endplate-to-beam weld beads geometric configuration; the experimental results show that each weld configuration leads to different behavior, significantly affecting the connection capacity and ductility. As a result, the performed numerical simulations aim to better understand and deepen these observations. Special attention is paid to the initial (elastic) behavior of the tested assembly, albeit the stress redistribution after the first yielding has also been studied and found to be relevant. The numerical results are satisfactory compared with the experimental ones, and specific remarks are derived. This work is a part of a broader research effort aimed to improve the dissipative seismic behavior of racks; such research activity involves also upright-base plate connections testing, advanced numerical simulation, and proposal of rack ductility behavior factors.
Summary
The behavior of reinforced concrete structures under severe demands, as strong ground motions, is highly complex; this is mainly due to the complexity of concrete behavior and to the strong ...interaction between concrete and steel, with several coupled failure modes. On the other hand, given the increasing awareness and concern on the worldwide seismic risk, new developments have arisen in earthquake engineering; nonetheless, some developments are mainly based on simple analytical tools that are widely used, given their moderate computational cost. This research aims to provide a solid basis for validation and calibration of such developments by using computationally efficient continuum mechanics‐based tools. Within this context, this paper presents a model for 3D simulation of cyclic behavior of RC structures. The model integrates a bond‐slip model developed by one of the authors and the damage variable evolution methodology for concrete damage plastic model developed by some authors. In the integrated model, a new technique is derived for efficient 3D analysis of bond‐slip of 2 or more crossing reinforcing bars in beam‐column joints, slabs, footings, pile caps, and other similar members. The analysis is performed by implementing the bond‐slip model in a user element subroutine of Abaqus and the damage variable evolution methodology in the original concrete damage plastic model in the package. Two laboratory experiments consisting of a column and a frame subjected to cyclic displacements up to failure are simulated with the proposed formulation.
This paper presents seismic cantilever monotonic and cyclic tests of speed-lock (boltless) beam-to-upright connections of adjustable pallet rack systems; the objective of the monotonic tests is to ...obtain the bounds that are employed to define the loading protocol of the subsequent cyclic tests. The beam-to-upright connections consist of welding the beam to an intermediate end-plate (L-shaped) that, in its turn, is linked to the upright through a hooked assembly. The performed experiments investigate the connections hysteretic behavior, as it contributes to the rack lateral strength, stiffness, and ductility. More precisely, the main objective of this research is to propose a new strengthened design of the weld beads geometric configuration. This design is oriented for the connection failure not to arise in the weld, but the hooked assembly. This shift is expected to increase the connection ductility; in this sense, specimens with traditional and novel weld geometric designs are tested. In most of the tests performed, the results confirm that the new weld design leads to more ductile failure modes; preliminary evaluations state that the ductility increase might be sufficient to absorb most of the input seismic energy. On the other hand, tests are conducted according to two loading protocols: the traditional one by following European regulations and a new strategy proposed by Prof. Castiglioni accounting for the influence of gravity loads. Comparison between their results shows that the Castiglioni approach is more demanding and seems to reproduce the actual seismic behavior of racks better.
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•The beam-upright connections play a relevant role in their seismic capacity.•Their cyclic behavior, given its complexity, needs to be investigated by testing.•This paper presents cyclic tests on boltless beam-upright connections of racks.•Different welding strategies are compared aiming to redistribute the stresses and improve the ductility.•The influence of the testing protocol is also investigated.
Ordinary (customary) light gauge steel framing is a convenient construction technology; however, given the studs low axial capacity, it has been considered mainly for low-rise buildings in low ...seismicity regions. This paper investigates the boundaries of application of this type of steel framing (in moderate and high seismicity areas) by designing the structures of three representative 5, 7 and 10-storey buildings in order to examine their feasibility. The necessity of using built-up columns consisting of two or more sections is investigated. The axial capacity of studs is estimated by code-type analyses. The critical buckling stress is determined with well-known closed-form expressions; as they do not contemplate the flexibility of the screwed connections (in built-up sections), the obtained results are complemented with those of the finite strip method and generalized beam theory formulations.
In simplified seismic structural analyses, not all the deterioration modes are adequately considered. This work discusses the relation among the hidden failure modes of columns of non-ductile ...reinforced concrete building frames and their global collapse mechanism. With this aim, a numerically efficient model is developed and implemented in OpenSEES. Two benchmark problems are analyzed with this model: the well-known Van Nuys Hotel and a prototype building designed for gravity loads only; in this last case, the results are compared with experiments on a one-third scale model. The obtained results confirm that simplified models grossly overestimate the building capacity.
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