Stiffness reduction in soft Chicago clay during deep urban excavations

2014 ◽  
pp. 287-291
Author(s):  
Young-Hoon Jung ◽  
Taesik Kim
Keyword(s):  
Chicago Clay ◽  
Stiffness Reduction

scholarly journals Laser-excited elastic guided waves reveal the complex mechanics of nanoporous silicon

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Marc Thelen ◽  
Nicolas Bochud ◽  
Manuel Brinker ◽  
Claire Prada ◽  
Patrick Huber
Keyword(s):  
Guided Waves ◽  
Laser Ultrasonics ◽  
Bulk Silicon ◽  
Nanoporous Silicon ◽  
Stiffness Reduction ◽  
Mechanical Characterisation ◽  
Isotropic Elasticity ◽  
On Chip ◽  
Non Destructive

AbstractNanoporosity in silicon leads to completely new functionalities of this mainstream semiconductor. A difficult to assess mechanics has however significantly limited its application in fields ranging from nanofluidics and biosensorics to drug delivery, energy storage and photonics. Here, we present a study on laser-excited elastic guided waves detected contactless and non-destructively in dry and liquid-infused single-crystalline porous silicon. These experiments reveal that the self-organised formation of 100 billions of parallel nanopores per square centimetre cross section results in a nearly isotropic elasticity perpendicular to the pore axes and an 80% effective stiffness reduction, altogether leading to significant deviations from the cubic anisotropy observed in bulk silicon. Our thorough assessment of the wafer-scale mechanics of nanoporous silicon provides the base for predictive applications in robust on-chip devices and evidences that recent breakthroughs in laser ultrasonics open up entirely new frontiers for in-situ, non-destructive mechanical characterisation of dry and liquid-functionalised porous materials.

scholarly journals Vision-Based Structural FE Model Updating Using Genetic Algorithm

2021 ◽  
Vol 11 (4) ◽  
pp. 1622
Author(s):  
Gun Park ◽  
Ki-Nam Hong ◽  
Hyungchul Yoon
Keyword(s):  
Genetic Algorithm ◽  
Model Updating ◽  
Structural Parameters ◽  
Fe Model ◽  
Structural Members ◽  
Stiffness Reduction ◽  
Before And After ◽  
Scale Test ◽  
Fe Model Updating ◽  
Story Building

Structural members can be damaged from earthquakes or deterioration. The finite element (FE) model of a structure should be updated to reflect the damage conditions. If the stiffness reduction is ignored, the analysis results will be unreliable. Conventional FE model updating techniques measure the structure response with accelerometers to update the FE model. However, accelerometers can measure the response only where the sensor is installed. This paper introduces a new computer-vision based method for structural FE model updating using genetic algorithm. The system measures the displacement of the structure using seven different object tracking algorithms, and optimizes the structural parameters using genetic algorithm. To validate the performance, a lab-scale test with a three-story building was conducted. The displacement of each story of the building was measured before and after reducing the stiffness of one column. Genetic algorithm automatically optimized the non-damaged state of the FE model to the damaged state. The proposed method successfully updated the FE model to the damaged state. The proposed method is expected to reduce the time and cost of FE model updating.

scholarly journals Numerical Study of the Seismic Response of an Instrumented Building with Underground Stories

2021 ◽  
Vol 11 (7) ◽  
pp. 3190
Author(s):  
Edmundo Schanze ◽  
Gilberto Leiva ◽  
Miguel Gómez ◽  
Alvaro Lopez
Keyword(s):  
Seismic Response ◽  
Soil Structure ◽  
Numerical Study ◽  
Time History ◽  
Building Design ◽  
Average Height ◽  
The Real ◽  
Vibration Data ◽  
Finite Element Software ◽  
Stiffness Reduction

Engineering practitioners do not usually include soil–structure interactions in building design; rather, it is common to model and design foundations as embedded joints with joint–based reactions. In some cases, foundation structures are modeled as rigid bodies, embedding the first story into lower vertical elements. Given that the effects of underground floors on the seismic response are not generally included in current building design provisions, it has been little explored in the literature. This work compares and analyzes models to study the effects of different underground stories modeling approaches using earthquake vibration data recorded for the 16–story Alcazar building office in downtown Viña del Mar (Chile). The modeling expands beyond an embedded first story structure to soil with equivalent springs, representing soil–structure interaction (SSI), with varying rigid soil homogeneity. The building was modeled in a finite element software considering only dead load as a static load case because the structure remained in the framing stage when the monitoring system was operating. The instruments registered 72 aftershocks from the 2010 Maule Earthquake, and this study focused on 11 aftershocks of different hypocenters and magnitudes to collect representative information. The comparisons between empirical records and models in this study showed a better fit between the model and the real vibration data for the models that do consider the SSI using horizontal springs attached to the retaining walls of the underground stories. In addition, it was observed that applying a stiffness reduction factor of 0.7 to all elements in deformation verification models for average–height buildings was suitable to analyze the behavior under small earthquakes; better results are obtained embedding the structure in the foundation level than embedding in the street level; the use of horizontal springs with Kuesel’s model with traction for the analysis of the structure yields appropriate results; it is necessary to carefully select the spring constants to be used, paying special attention to the vertical springs. Even though the results presented herein indicate that the use of vertical springs to simulate the SSI of the base slab can result in major differences concerning the real response, it is necessary to obtain more data from instrumentation across a wider variety of structures to continue to evaluate better design and modeling practices. Similarly, further analyses, including nonlinear time–history and high–intensity events, are needed to best regulate building design.

scholarly journals Association arterial stiffness reduction with improved left ventricular longitudinal and torsional deformation after 3 years of antihypertensive treatment

2020 ◽  
Vol 41 (Supplement_2) ◽  
Author(s):  
S Tzortzis ◽  
I Ikonomidis ◽  
H Triantafyllidi ◽  
J Thymis ◽  
A Frogoudaki ◽  
...  
Keyword(s):  
Blood Pressure ◽  
Arterial Stiffness ◽  
Ace Inhibitors ◽  
Antihypertensive Treatment ◽  
Left Ventricular ◽  
Torsional Deformation ◽  
Flow Reserve ◽  
Stiffness Reduction ◽  
Arterial Blood ◽  
Lv Mass

Abstract Background We investigated the effects of antihypertensive treatment on vascular function, longitudinal and torsional deformation in hypertensives. Methods In 200 untreated patients with arterial hypertension (age 52.5±11.6 years, 56% females), we measured at baseline and after a 3-year of antihypertensive treatment (160 received ACEi± diuretics and 40 CCBs± diuretics): a) 24h ambulatory blood pressure b) Carotid-femoral pulse wave velocity (PWV) b) Coronary flow reserve (CFR), LV mass index (LVMI), the global longitudinal strain (GLS) and diastolic (LongSRSE) strain rate, peak twisting (Tw-deg) and untwisting at mitral valve opening (UtwMVO), at peak E (UtwE) and at the end of the E wave (UtwendE) of the mitral inflow as well as twisting (TwVel-deg/sec) velocity using speckle tracking imaging. We calculated the % change of LV untwisting as difference between peakTw and UtwMVO, UtwpeakE and UtwendE. Results Compared to baseline, there was an improvement of GLS (−19.9±3.4 vs. −18.7±3.1%), LongSRS (−1.08±0.22 vs. −0.98±0.26 1/s), LongSRE (1.09±0.36 vs. 0.99±0.31 1/s), peak Tw (16.2±5.1 vs. 18.7±5.9 deg), Tw velocity, and the %LV untwisting (31.04±19.28 vs 26.02±15.69% at MVO, 60.04±19.78 vs 53.96±19.76% at peakE and 79.98±14.24 vs 75.90±17.01% at endE) post-treatment. In parallel, CFR (2.72±0.61 vs. 2.55±0.64), PWV (10.34±1.93 vs. 11.2±2.08 m/s) and LVMI were improved (p<0.01 for all comparisons). By ANOVA, the interaction term between changes of all the above parameters and antihypertensive treatment (ACE inhibitors vs calcium channel blockers) was not significant (p>0.05). By multivariate analysis, the reduction of 24h meanBP and PWV independently determined the respective improvement of GLS (b=0.478 and b=0.248 respectively), LongS (b=0.428 and b=0.201 respectively) as well as Twisting (b=0.449 and b=0.294 respectively) after adjusting for changes in LV mass, CFR and atherosclerotic risk factors (p<0.05). Conclusions Long-term optimal blood pressure control with ACE inhibitors and CCBs improves LV longitudinal and torsional mechanics in hypertensives in parallel with arterial stiffness and blood pressure. This improvement in LV deformation and twisting was independently related to changes in arterial blood pressure and arterial stiffness. Funding Acknowledgement Type of funding source: None

An Approach to Determine the Stiffness Reduction Factor of Tunnel Lining

2011 ◽  
Vol 243-249 ◽  
pp. 3659-3662
Author(s):  
Hai Ying Zhou ◽  
Li Xin Li ◽  
Ting Guo Chen
Keyword(s):  
Numerical Analysis ◽  
Flexural Rigidity ◽  
Resistance Coefficient ◽  
Reduction Factor ◽  
Tunnel Lining ◽  
Soil Resistance ◽  
Stiffness Reduction ◽  
Simplified Method

Based on the segmental joint tests, it was found that the practical range of joint flexural rigidity was in range of 8500-29000kN•m/rad. A simplified method for determining the stiffness reduction factor of tunnel lining() was proposed using results from the segmental joint tests in which some parameters were obtained by calibration against a 3D Numerical analysis. The influence of joint flexural rigidity, soil resistance coefficient, thickness of tunnel lining and tunnel calculation radius on the stiffness reduction factor of tunnel lining was examined. The stiffness reduction factor can be simply expressed as a function of joint flexural rigidity ratio, soil resistance coefficient, thickness of tunnel lining and tunnel calculation radius for the typical tunnel lining.

Vehicle’s New Anti-Roll System for Suspension Parasitic Stiffness Reduction and Non-Linear Roll Stiffness Characteristic

2013 ◽  
Author(s):  
Bo Min Kim ◽  
Dae Sik Ko ◽  
Jong Min Kim
Keyword(s):  
Ride Comfort ◽  
Torsional Stiffness ◽  
Operating Efficiency ◽  
Leaf Spring ◽  
Roll Motion ◽  
Stiffness Reduction ◽  
Stiffness Characteristic ◽  
Non Linear ◽  
Roll System ◽  
Vehicle Dynamic Simulation

In general, vehicle uses torsional stiffness of a stabilizer bar to control the roll motion. But this stabilizer bar system has problems with degradation for ride comfort and vehicle’s NVH characteristic due to the suspension parasitic stiffness caused by deformation and wear of the stabilizer bar rubber bush. In addition, it is difficult to control the vehicle’s roll motion effectively in case of excessive vehicle roll behavior when it is designed to satisfy ride comfort simultaneously because of the stabilizer bar’s linear roll stiffness characteristic. In this paper, the new anti-roll system is suggested which consists of connecting link, push rod, laminated leaf spring, and rotational bearing. This new concept anti-roll system can minimize the suspension parasitic stiffness by using rotational bearing structure and give the vehicle non-linear roll stiffness by using the laminated leaf spring structure which are composed of main spring and auxiliary one. Reduction of suspension parasitic stiffness and realization of non-linear roll stiffness in this anti-roll system were verified with both vehicle dynamic simulation and vehicle test. Also, this study includes improvement of the system operating efficiency through material change and shape optimization of the leaf spring, and optimal configuration of the force transfer system.

Investigation of Sensitivity Effect Based on Mass and Stiffness Modification in Automobile Crankshaft

2015 ◽  
Vol 752-753 ◽  
pp. 839-844
Author(s):  
R.M.S. Zetty ◽  
B.A. Aminudin ◽  
L.M. Aung ◽  
M.K. Khalid ◽  
H.M.Y. Norfazrina ◽  
...  
Keyword(s):  
Sensitivity Analysis ◽  
Natural Frequency ◽  
Dynamic Characteristics ◽  
Differential Analysis ◽  
Partial Differential ◽  
Mechanical Parts ◽  
Stiffness Reduction ◽  
Experiment And Simulation ◽  
Good Agreement

A modeling through sensitivity analysis is one of the promising methods to investigate the dynamic characteristics of complex mechanical parts. This study aimed to investigate the effect of sensitivity based on mass and stiffness modification in automobile crankshaft as a function of natural frequency. Verification for the crankshaft model that is used in the experiment and simulation was done and both results showed good agreement and small errors percentage. The modification was also done by reducing the different percentage of crankshaft’s mass and stiffness. Partial differential analysis was used in the sensitivity analysis in order to figure out the natural frequency after every set of modification. According to the results, we also found that there were changes of sensitivity value by changes in mass value but the stiffness value remains unchanged. However, there is no significant effect of stiffness reduction on vibration was found in this research.

scholarly journals Low-rise structures in reinforced concrete: approximation of material nonlinearity for global stability analysis

2018 ◽  
Vol 11 (1) ◽  
pp. 1-25
Author(s):  
L. M. MOREIRA ◽  
C. H. MARTINS
Keyword(s):  
Global Stability ◽  
Iterative Process ◽  
Global Analysis ◽  
Second Order ◽  
Material Nonlinearity ◽  
Flexural Stiffness ◽  
Analysis Model ◽  
Structural Element ◽  
Global Stability Analysis ◽  
Stiffness Reduction

Abstract In the analysis of the second-order global effects, the material nonlinearity (NLF) can be considered in an approximate way, defining for the set of each structural element a mean flexural stiffness. However, there is less research concerning low-rise buildings in the analysis of global stability in contrast to high buildings, because these have a greater sensitivity to this phenomenon and they are more studied. In this way, the paper objective is to determine the flexural stiffness values, of beams and columns, for buildings with less than four floors, to approximate consideration of the NLF in the global analysis. The idealized examples to buildings with 1, 2 and 3 floors, being simulated through the software CAD/TQS and an analysis model based in an iterative process. The simulations results defined the stiffness values of the set of beams and columns in each example, followed by a statistical analysis to define general values of application in the buildings. Finally, a proposal is suggested of stiffness reduction coefficients for beams and columns to be adopted in the approximation the NLF (EIsec = αv/p ∙ Eci Ic), as follows: buildings with 1 floor (αv = 0,17 and αp = 0,66), buildings with 2 floors (αv = 0,15 and αv = 0,71) and buildings with 3 floors (αv = 0,14 and αv = 0,72). The results obtained can be used for the analysis of low-rise structures to consider the second order global effects with more safely.

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