Rigid Superstructure Research Articles

Vibration analysis of double elastomer layered superstructures with extended locally continuous support model

In this study, a distributed rail pad (RP) model of rail supported by double elastomer layers for rigid superstructures like light metro is presented, and a semi-analytical solution is derived via the Galerkin's method. Apart from existing distributed RP models that contain multiple individual spring-dampers, the proposed method offers locally continuous rail bedding. The new model assumes that the rail bedding is not pointwise and connects the continuous bedding and lumped baseplate mass with a derived function, which is the first novelty of the paper. Results of the single-spring model (SSM) and extended locally continuous support models (ELCSM) are obtained and compared to indoor and outdoor measurements in the time and frequency domains. The proposed model shows similar results to the conventional model for dynamic response; however, the clear difference between the models is seen at high resonant frequencies because of the stiffer bedding of the rail. Another point is that rail stresses and displacements can be calculated more accurately compared to SSM, due to including the length of RP. The findings of the study highlight the importance of considering RP length and stiffness when designing and maintaining railway tracks and provide insights into how to optimize these parameters for better performance and durability.

Cluster-Spin-Glass Magnetic Behavior and Morphology in the Coordination Polymer Alloys FeyCo1-yBTT.

We report the synthesis of a series of pseudo-1D coordination polymer (CP) materials with the formula FeyCo1-yBTT (BTT = 1,3,5-benzenetrithiolate). These materials were structurally characterized by PXRD Rietveld, EXAFS, and PDF analyses, revealing that the CP superstructure enables a continuous and isomorphous alloy between the two homometallic compounds. Lower Fe loadings exhibit emergent spin glass magnetic behavior, such as memory effects and composition-dependent spin glass response time constants ranging from 6.9 × 10-9 s to 1.8 × 10-6 s. These data are consistent with the formation of spin clusters within the lattice. The magnetic behavior in these materials was modeled via replica exchange Monte Carlo simulation, which provides a good match for the experimentally measured spin glassing and magnetic phase transitions. These findings underscore how the rigid superstructure of CP and MOF scaffolds can enable the systematic tuning of physical properties, such as the spin glass behavior described here.

PREDICTION MODEL FOR BASE SHEAR INCREASE DUE TO VERTICAL GROUND MOTION IN FRICTION PENDULUM ISOLATED STRUCTURES

Seismic isolation is one of the most effective seismic hazard mitigation techniques, which has been implemented in many structures. Friction pendulum isolators are one of the most popular isolation devices to achieve energy dissipation and shear resistance that depends on the effective radius and instantaneous vertical force on them. So, the horizontal response of this type of isolators is coupled with the axial load on them, which could change due to vertical acceleration during ground shaking. Thus, it makes consideration of the vertical excitation in the design and analysis phase inevitable, especially for structures in those regions where vertical ground accelerations are more pronounced. In this study a model for the prediction of increase in base shear due to vertical motion for friction pendulum isolated structures is proposed. A simple single friction pendulum isolator system is utilized with the assumption of rigid superstructure on top and subjected to a hundred earthquake ground motions with different characteristics. A multi-layer perceptron model with three layers is utilized, and a simple computer program, which is open-source, is prepared to construct probability curves. With the help of the program, within the range of the considered structural parameters in the study, probability curves related to increase in base shear, maximum isolator displacement and residual isolator displacement can be constructed, and designers can have a rough estimation on modification of these parameters due to vertical ground motion.

Investigation of soil–pile–structure interaction induced by vertical loads and tunnelling

The response of pile groups and piled structures to vertical and tunnelling-induced loads is studied. A two-stage model is adopted that can efficiently consider external actions, greenfield tunnelling movements, superstructure stiffness, ultimate pile shaft and base stresses, pile-soil interactions in uniform or layered soils, and local soil behaviour (as either linear elastic, elastic perfectly-plastic, or nonlinear). Several scenarios are analysed: namely, piles subjected to vertical loads; piles and piled structures that are affected by tunnelling induced ground movements. Model results for piles under vertical loads compare well with field and other analytical models, confirming the robustness of the model. For tunnelling adjacent to or beneath single piles and pile groups, the impact of layered soils, soil yielding, and hyperbolic transfer mechanisms are shown to be significant, indicating that these aspects should be considered in risk assessments when using simplified models. Analyses of tunnelling beneath free-head piles and piled equivalent beams (describing flexible slabs or stiff buildings) confirm that pile-foundation connections and superstructures decrease tunnelling-induced displacements and deformations at the surface level; however, their action can also worsen the foundation distress with respect to force-moment structural capacity. Considering that the envelopes of fully-flexible and perfectly rigid superstructures will not always be conservative, soil-pile-structure interaction models are recommended for design.

Insights into inter-story isolation design through the analysis of two case studies

Inter-story isolation system (IIS, also appointed as mid-story isolation), is currently spreading and gaining significant popularity, mainly in Japan. However, while more than sixty applications have been realized in nearly twenty years, the conceptual framework for dealing with the design problem of IIS is not well established, since the IIS combines isolation and mass damping control strategies.In this paper two case studies of real inter-story isolated buildings are in depth examined for interpreting the latest design practice in the light of approaches and indications coming from the world of research. The two buildings, very different from each other, cover the wide applicability of IIS. One of them is a paradigmatic example of ideal IIS, with dynamic characteristics commonly adopted in the scientific community, i.e. a very rigid superstructure, and frequencies of the two structural parts well separated from the isolation frequency. The other building is a non-typical case of IIS, with the upper structures less rigid than the lower one, and both structural portions quite flexible. Modal and frequency response analyses are carried out on simplified two- or three- degree-of-freedom models, representing the reduced-order models utilized in the inherent scientific literature for grasping the influence of the main design parameters governing the dynamic problem. Modal and non-linear time history analyses are then carried out on multi degree-of-freedom models, for the seismic assessment of the buildings. The main results are reported and design implications are discussed.

The Usability of Pumice Powder as a Binding Additive in the Aspect of Selected Mechanical Parameters for Concrete Road Pavement.

In this study, the usability of pumice powder and lime in concrete production as a binding additive for rigid superstructure concrete road pavement was investigated. Following the determination of the optimum binder ratio, these new binder ratios were used in crushed limestone concrete production. The concrete thus formed was named concrete containing cement, pumice powder and lime (PPCC). The normally produced concrete, without pumice powder and lime binder was selected as reference concrete (RC). Regarding the total binder amount of the most appropriate binder ratio 50% was found to be cement, 30% pumice powder and 20% lime in the result of the study. In consequence of the study, the 20 ± 2 °C and 7–28 days compressive strengths of the reference concrete were found to be 33.8 MPa and 38.2 MPa and its bending strengths were 4.2 MPa and 4.7 MPa. The 20 ± 2 °C and 7–28 days compressive strengths of PPCC were found to be 25.1 MPa and 28.3 MPa and its bending strengths were 3.2 MPa and 3.5 MPa. The results of the study showed the usability of PPCC in concrete pavement.

Seismic Performance of Rocking Oscillators on a Soft Story: Inelastic Response

AbstractThe inelastic response of a class of nonlinear oscillators, characterized by a relatively rigid superstructure on a soft ground story under base seismic excitation, is numerically investiga...

Mechanical Properties of Reactive Powder Concretes Produced Using Pumice Powder

We examined the applicability of the pumice aggregate on the concrete formed by considering the reactive powder concrete mixture ratios, for the rigid superstructure concrete road pavement and building construction. The natural pumice aggregate in fibrous and non-fibrous concrete samples was used in the production of concrete by fracturing in 0.1-0.6 mm dimensions in rotor mill. The concreted formed in this way is named after the pumice powder concrete (PPC). The PPC samples produced were taken 7 days as 20 °C standard water cure, 28 days as 20 °C standard cure and 9 different types of combined cures. The combined cures were applied different temperatures in different durations. PPC samples were subjected to some pressure and flexural tests at the end of the standard water and combined cures. The highest compressive and flexural strengths of PPC samples were obtained after the combined cures: 3 days in 20 °C as standard water curing + 2 days in 180 °C in drying-oven. The highest compressive strength of PPC samples without any fiber was found to be 47.27 MPa, as for the highest flexural strength, it is found to be 5.23 MPa, in the end of the study. The highest compressive strength of fibrous PPC samples was 51.12 MPa, while flexural strength was 6.57 MPa.

Slow Magnetic Relaxation of Co(II) Single Chains Embedded within Metal-Organic Superstructures.

Two coordination polymers of the type Co(BPDC)(N-ox), with BPDC being 4,4'-biphenyldicarboxylate and N-ox being pyridine N-oxide (PNO) or isoquinoline N-oxide (IQNO), have been synthesized and characterized. The compounds feature 2D and 3D metal-organic networks that encapsulate Co(II)-based chains in a rigid superstructure. The dc and ac magnetic properties of these Co(BPDC)(N-ox) materials have been investigated alongside those of a related Co(BDC)(PNO) compound (where BDC is 1,4-benzenedicarboxylate), which contains a smaller dicarboxylate linker. These Co(II)-containing coordination polymers exhibit slow magnetic relaxation, as observed by ac susceptibility measurements. The observed magnetic behavior of all compounds is consistent with an antiferromagnetic interaction between canted Co spins along the 1D skeleton, resulting in single-chain magnet behavior. In the case of Co(BPDC)(IQNO), weak interchain magnetic interactions yield 3D antiferromagnetic order while the inherent magnetic behavior stemming from the chain component is maintained. The combination of these effects in this material puts it at the frontier between single-chain magnets and classical bulk antiferromagnets. This work contributes to the limited group of materials featuring the organization of single-chain magnets within a coordination polymer superstructure.

Seismic response evaluation of base-isolated reinforced concrete buildings under bidirectional excitation

This paper reports on an investigation of the seismic response of base-isolated reinforced concrete buildings, which considers various isolation system parameters under bidirectional near-fault and far-fault motions. Three-dimensional models of 4-, 8-, and 12-story base-isolated buildings with nonlinear effects in the isolation system and the superstructure are investigated, and nonlinear response history analysis is carried out. The bounding values of isolation system properties that incorporate the aging effect of isolators are also taken into account, as is the current state of practice in the design and analysis of base-isolated buildings. The response indicators of the buildings are studied for near-fault and far-fault motions weight-scaled to represent the design earthquake (DE) level and the risk-targeted maximum considered earthquake (MCER) level. Results of the nonlinear response history analyses indicate no structural damage under DE-level motions for near-fault and far-fault motions and for MCER-level far-fault motions, whereas minor structural damage is observed under MCER-level near-fault motions. Results of the base-isolated buildings are compared with their fixed-base counterparts. Significant reduction of the superstructure response of the 12-story base-isolated building compared to the fixed-base condition indicates that base isolation can be effectively used in taller buildings to enhance performance. Additionally, the applicability of a rigid superstructure to predict the isolator displacement demand is also investigated. It is found that the isolator displacements can be estimated accurately using a rigid body model for the superstructure for the buildings considered.

Out-of-plane (SH) soil-structure interaction: a shear wall with rigid and flexible ring foundation

Soil-structure interaction (SSI) of a building and shear wall above a foundation in an elastic half-space has long been an important research subject for earthquake engineers and strong-motion seismologists. Numerous papers have been published since the early 1970s; however, very few of these papers have analytic closed-form solutions available. The soil-structure interaction problem is one of the most classic problems connecting the two disciplines of earthquake engineering and civil engineering. The interaction effect represents the mechanism of energy transfer and dissipation among the elements of the dynamic system, namely the soil subgrade, foundation, and superstructure. This interaction effect is important across many structure, foundation, and subgrade types but is most pronounced when a rigid superstructure is founded on a relatively soft lower foundation and subgrade. This effect may only be ignored when the subgrade is much harder than a flexible superstructure: for instance a flexible moment frame superstructure founded on a thin compacted soil layer on top of very stiff bedrock below. This paper will study the interaction effect of the subgrade and the superstructure. The analytical solution of the interaction of a shear wall, flexible-rigid foundation, and an elastic half-space is derived for incident SH waves with various angles of incidence. It found that the flexible ring (soft layer) cannot be used as an isolation mechanism to decouple a superstructure from its substructure resting on a shaking half-space.

Character Analysis of Balance and Imbalance of Varying Rigidity of Rigid Pile Composite Foundation under Seismic Load

Based on ABAQUS finite element analysis software simulation, the finite element model for dynamic analysis of rigid pile composite foundation and superstructure interaction system is established, which selects the two kinds of models, by simulating the soil dynamic constitutive model, selecting appropriate artificial boundary.The influence of rigid pile composite foundation on balance and imbalance of varying rigidity is analyzed under seismic loads. The result shows that the maximum bending moment and the horizontal displacement of the long pile is much greater than that of the short pile under seismic loads, the long pile of bending moment is larger in the position of stiffness change. By constrast, under the same economic condition, the aseismic performance of of rigid pile composite foundation on balance of varying rigidity is better than that of rigid pile composite foundation on imbalance of varying rigidity.

Soil, Foundation, and Superstructure Interaction for Plane Two-Bay Frames

AbstractGeotechnical analyses are usually made before superstructure members are fully defined. The behavior of long-span buildings differs from the behavior of short-span buildings. Expensive solutions to the differential settlement that is calculated in geotechnical reports may be preferable but do not necessarily consider the superstructure’s rigidity effect. This paper examines the effect of the superstructure’s rigidity on the contact stress and the differential settlement for plane 2-bay frames. The plane frames consisted of flat slabs with hinged or fixed connections to the walls. The foundation system consisted of strip footings without tie beams to connect the footings due to the large span of the frames. The effect of superstructure rigidity on the damping of differential settlement owing to the redistribution of loads was investigated. The use of a slightly rigid superstructure may be the solution to differential settlement without the need for additional, more expensive methods. Five groups wi...

Seismic Response of Rocking Oscillators on a Soft Story: Elastic Response

AbstractThe elastic response of a class of nonlinear oscillators that represent structural systems with a relatively rigid superstructure on a soft ground story is evaluated under lateral base excitation. The governing equations of motion are developed, accounting for both lateral translation and overturning rocking of the rigid superstructure relative to the flexible ground story. In this work, the system parameters are identified initially for linear elastic response and, subsequently, in a companion publication, for the case of the base exhibiting nonlinear resistance–deformation characteristics. The dynamic coupling between lateral and rocking modes is evaluated under a base excitation for different system period and resistance parameters, and the deformation and force demands are compared with the single-degree-of-freedom lateral-response-only predictions, as typically considered in seismic design. It is shown that the presence of rocking of the rigid superstructure causes an increase in the transver...

Observation of Sublattice Disordering of the Catalytic Sites in a Complex Mo–V–Nb–Te–O Oxidation Catalyst Using High Temperature STEM Imaging

A Mo–V–Nb–Te–O oxidation catalyst has been imaged using scanning transmission electron microscopy at 780 K, which is slightly above its operating temperature. We observe a sublattice disordering of the corner-sharing octahedra forming the catalytic sites containing V5+ while the edge-sharing pentagonal bipyramidal {Nb(Mo5)} sublattice remains structurally more rigid and thereby maintains the overall structural integrity of the catalyst. Imaging the termination of the edges of the [001] basal zones at room temperature reveal a preference for presence of a closed network of secondary structural {Nb(Mo)5} units providing further evidence of the stability of this sublattice structure. We propose that sublattice disordering of catalytic sites enables structural flexibility to accommodate different oxidation states during multistep chemical reactions within a more rigid superstructure and presents a new paradigm for compositionally and structurally complex catalysts.

Spreading-Induced Damage to Short-Span Bridges in Christchurch, New Zealand

This paper discusses the performance of road bridges during the 2010–2011 Canterbury earthquakes and focuses on the response of bridges in liquefying soils undergoing lateral spreading. A characteristic spreading-induced mechanism for short-span bridges with rigid superstructures is presented and explored using four well-documented case studies. A series of pseudo-static analyses are then used to investigate the observed response of the bridges and their pile foundations in particular. Deformations and damage to the piles are evaluated and correlated with the spreading displacements, and key factors controlling the pile response and the development of the spreading-induced damage mechanism are identified.

Experimental evaluation of supplemental viscous damping for a sliding isolation system under pulse-like base excitations

Near-fault earthquakes that usually contain a long-period pulse component may cause excessive responses to a base-isolated structure, especially with regard to its peak isolator displacement. Viscous-type dampers, whose damping force is proportional to the excitation velocity, can be used to mitigate the excessive responses of the isolated structure. In this study, the effect of viscous-type supplemental damping on a sliding isolation system subjected to pulse-like ground excitations is evaluated experimentally by a shaking table test. The test program involves a relatively rigid structure isolated by sliding-type isolators and a fluid viscous damper installed within the isolation layer. Seismic excitations with and without a long-period pulse component were imposed on the isolated system, and the experimental responses of the system with and without installation of the fluid damper were compared. The test results demonstrate that, for a rigid superstructure, the viscous damper is able to effectively suppress the peak isolator displacement induced by the long-period pulse component without increasing the acceleration level of the superstructure; however, it also slightly increases the structural acceleration in the seismic excitation without the pulse component. The results also show that a pulse-like ground motion is able to induce resonance-like behavior for the isolator displacement of a sliding system when the pulse period is close to the isolation period. However, this resonance-like behavior can be effectively mitigated by adding viscous damping to the isolation system. Finally, by using linear and nonlinear viscous models to simulate the experimental responses, the influence of the damper nonlinearity on the test results was also investigated.

Effect of two horizontal components of earthquake on nonlinear response of torsionally coupled base isolated structures

SUMMARYTorsion in base‐isolated structures using bilinear rubber isolators effected by two horizontal components of earthquake simultaneously is investigated under various principal parameters including number of storeys; ratio of uncoupled torsional frequency to lateral frequency in the superstructure; ratio of uncoupled torsional frequency to lateral frequency in the isolation system; mass eccentricity in the superstructure and isolation system; and, in addition, the direction of eccentricity. Structure was supposed a shear structure and it was modeled by using concentrated mass and springs. Isolators are modelled by using nonlinear springs considering the interaction of isolator behaviour in two directions. The effect of variation in considered parameters on the behaviour of the superstructure and isolation system is investigated under seven ground motions. It is demonstrated that the parameters affect asymmetric structure behaviour with respect to symmetric one. The results of our investigations help us to understand the asymmetric structure behaviour under bidirectional earthquake by comparing it with a symmetric one. These results demonstrate that asymmetry in the superstructure or isolation system could have a significant effect on the torsional behaviour of isolated structures. In addition, the results show that the use of rigid superstructures and calculation of dynamic torsion by multiplying eccentricity by the dynamic base shear are unacceptable assumptions. Torsional effect on the isolated structural behaviour is amplified by considering two horizontal components of earthquake and comparing them with just one horizontal component. Copyright © 2010 John Wiley & Sons, Ltd.

Non-Linear Behaviour of Base-Isolated Building Supported on Flexible Soil under Damaging Earthquakes

Seismic isolation is a strategy to reduce damage of structures exposed to devastating earthquake excitations. Isolation systems, applied at the base of buildings, lower the fundamental frequency of the structure below the range of dominant frequencies of the ground motion as well as allow to dissipate more energy during structural vibrations. The effectiveness of the base-isolated buildings in damage reduction has been confirmed numerically for the models of structures with fixed supports. The aim of the present paper is to show the results of the non-linear analysis of the response of a base-isolated building supported on soft soil incorporating soil-structure interaction. The detailed study has been conducted for the building equipped with high damping rubber bearings used as isolation devices. The results of numerical simulations demonstrate that soil flexibility has a significant influence on the behaviour of isolated base of the structure. Considering the flexibility of soil significantly affects the rigid superstructure response lowering its potential to reduce structural damage.

Analysis of connection element classes and locations and of some structural requirements for the mounting of different superstructure types on transport vehicles

Analysis of connection element classes and locations and of some structural requirements for the mounting of different superstructure types on transport vehicles