Dynamic Instability of Soil-SDOF Structure Systems under Far-Fault Earthquakes

2015 ◽  
Vol 31 (4) ◽  
pp. 2419-2441 ◽  
Author(s):  
Faramarz Khoshnoudian ◽  
Ehsan Ahmadi ◽  
Mahdi Kiani ◽  
Mohammad Hadikhan Tehrani
Keyword(s):  
Soil Structure ◽  
Dynamic Instability ◽  
Reduction Factor ◽  
Strength Reduction ◽  
Strength Reduction Factor ◽  
Vibration Period ◽  
Collapse Strength ◽  
Fixed Base ◽  
Far Fault ◽  
Reduction Factors

A parametric study is devoted to investigating the dynamic instability of soil-structure systems under far-fault earthquakes. The superstructure and soil are simulated as a bilinear single-degree-of-freedom (SDOF) oscillator and based on the cone model concept, respectively. The results show that soil flexibility makes the system dynamically more unstable and that as the non-dimensional frequency increases, the collapse strength-reduction factor highly decreases. Moreover, increasing the aspect ratio leads to a lower collapse strength-reduction factor. However, its effect is found to be negligible. The effects of vibration period and post-yield slope on the collapse strength-reduction factor are the same as on the fixed-base condition. Additionally, comparison of collapse strength-reduction factors resulting from exact time history analyses with those proposed in FEMA 440 for the fixed-base condition shows a great underestimation with errors larger than 20% at approximately all cases and 60% at extreme cases. Finally, a formulation is calibrated using nonlinear regression analysis in order to estimate collapse strength-reduction factors of soil-structure systems.

Strength reduction factor of self-centering structures under near-fault pulse-like ground motions

2020 ◽  
Vol 24 (1) ◽  
pp. 119-133
Author(s):  
Huihui Dong ◽  
Qiang Han ◽  
Xiuli Du ◽  
Canxing Qiu
Keyword(s):  
Ground Motions ◽  
Time History ◽  
Reduction Factor ◽  
Strength Reduction ◽  
The Self ◽  
Hysteretic Behavior ◽  
Hysteretic Model ◽  
Strength Reduction Factor ◽  
Vibration Period ◽  
Near Fault

Many studies on the strength reduction factor mainly focused on structures with the conventional hysteretic models. However, for the self-centering structure with the typical flag-shaped hysteretic behavior, the corresponding study is limited. The main purpose of this study is to investigate the strength reduction factor of the self-centering structure with flag-shaped hysteretic behavior subjected to near-fault pulse-like ground motions by the time history analysis. For this purpose, the smooth flag-shaped model based on Bouc-Wen model which can show flag-shaped hysteretic behavior is first described. The strength reduction factor spectra of the flag-shaped model are then calculated under 85 near-fault pulse-like ground motions. The influences of the ductility level, vibration period, site condition, hysteretic parameter, and hysteretic model are investigated statistically. For comparison, the strength reduction factors under ordinary ground motions are also analyzed. The results show that the strength reduction factor from near-fault pulse-like ground motions is smaller. Finally, a predictive model is proposed to estimate the strength reduction factor for the self-centering structure with the flag-shaped model under near-fault pulse-like ground motions.

The Effect of Multiaxiality on the Evaluation of Weldment Strength Reduction Factors in High-Temperature Creep

1994 ◽  
Vol 116 (1) ◽  
pp. 76-80 ◽  
Author(s):  
R. Sandstro¨m ◽  
S.-T. Tu
Keyword(s):  
Transfer Function ◽  
Weld Metal ◽  
Creep Strength ◽  
Rupture Strength ◽  
Reduction Factor ◽  
Strength Reduction ◽  
Strength Reduction Factor ◽  
Welded Tube ◽  
Metal Creep ◽  
Reduction Factors

The conventional way to define the weldment creep strength reduction factor is usually based on uniaxial creep data of weld metals and parent metals. In order to take the multiaxial effect into consideration, this paper has defined a structural transfer function which can be evaluated from general creep stress analysis. An analytical model is then proposed in the light of the function. Two numerical examples of typical weld properties show that the transfer function has a load-independent feature, which allows one to obtain multiaxial stress components in a weldment through minimal computation effort. Fairly good estimation of the stress level in the weld metal is achieved. On the basis of the present semi-analytical procedure, the weldment creep strength reduction factors are evaluated. For a 0.5Cr0.5Mo0.25V butt-welded tube under internal pressure, which has a higher weld metal creep-rupture strength, and lower weld metal creep strain rate, the reduction factors range from 0.9 to 0.95. For the AISI 316 butt-welded tube of cold-worked parent metal and creep soft weld metal, lower strength reduction factors are found, but they may still be nonconservative due to stress enhancement in the heat-affected zone.

scholarly journals Shear Strength Reduction Factor of Prestressed Hollow-Core Slab Units Based on the Reliability Approach

2017 ◽  
Vol 2017 ◽  
pp. 1-11 ◽  
Author(s):  
Hae-Chang Cho ◽  
Min-Kook Park ◽  
Hyunjin Ju ◽  
Jae-Yuel Oh ◽  
Young-Hun Oh ◽  
...  
Keyword(s):  
Shear Strength ◽  
Reliability Index ◽  
Structural Reliability ◽  
Reduction Factor ◽  
Strength Reduction ◽  
Hollow Core ◽  
Strength Reduction Factor ◽  
Target Reliability Index ◽  
Hollow Core Slab ◽  
Reduction Factors

This study investigated the shear design equations for prestressed hollow-core (PHC) slabs and examined the suitability of strength reduction factors based on the structural reliability theory. The reliability indexes were calculated for the shear strength equations of PHC slabs specified in several national design codes and those proposed in previous studies. In addition, the appropriate strength reduction factors for the shear strength equations to ensure the target reliability index were calculated. The results of the reliability index analysis on the ACI318-08 equation showed that the shear strengths of the members with the heights of more than 315 mm were evaluated to be excessively safe, whereas some members with low depths did not satisfy the target reliability index.

Plastic Collapse Behaviors of Tubulars With Recess Patterns

2015 ◽  
Author(s):  
Haifeng Zhao ◽  
David Iblings ◽  
Aleksey Barykin ◽  
Mohamed Mehdi
Keyword(s):  
Empirical Relationship ◽  
External Pressure ◽  
Reduction Factor ◽  
Strength Reduction ◽  
Plastic Collapse ◽  
Strength Reduction Factor ◽  
Periodic Distribution ◽  
Collapse Strength ◽  
Post Buckling ◽  
Collapse Behavior

The collapse strength of tubulars with recess patterns machined into their walls is an important topic for oilfield downhole tools as it applies to perforating guns, prepacked sand screens, and perforated and slotted liners. This paper presents a study of the plastic collapse behavior of thick-walled tubulars (those with an outside diameter to thickness ratio of approximately 10) having different patterns of circular recesses (blind holes partially machined into the tubing wall) that are subjected to external pressure. An empirical relationship between the reduction in collapse strength and the periodic distribution of recesses was constructed to account for the weakening effects of recess diameter, recess depth, axial spacing, angular phasing, etc. This strength reduction factor was introduced into the Tamano formula to predict collapse strength of recessed tubulars. Applicability of this empirical formula was validated with the aid of nonlinear, post-buckling Finite Element Analyses (FEA). The modeling approach was verified by full-scale physical tests. However, results of the physical testing are not presented in this paper. The strength reduction factor in combination with the Tamano formula provides a simple way of parametrically predicting the collapse strength of tubulars having circular recess patterns.

scholarly journals Laboratory and Numerical Investigation on Strength Performance of Inclined Pillars

Energies ◽  
2018 ◽  
Vol 11 (11) ◽  
pp. 3229 ◽  
Author(s):  
Kashi Jessu ◽  
Anthony Spearing ◽  
Mostafa Sharifzadeh
Keyword(s):  
Numerical Models ◽  
Critical Role ◽  
Economic Loss ◽  
Shear Loading ◽  
Reduction Factor ◽  
Strength Reduction ◽  
Strength Reduction Factor ◽  
Pillar Design ◽  
Strength Performance ◽  
Reduction Factors

Pillars play a critical role in an underground mine, as an inadequate pillar design could lead to pillar failure, which may result in catastrophic damage, while an over-designed pillar would lead to ore loss, causing economic loss. Pillar design is dictated by the inclination of the ore body. Depending on the orientation of the pillars, loading can be axial (compression) in horizontal pillars and oblique (compression as well as shear loading) in inclined pillars. Empirical and numerical approaches are the two most commonly used methods for pillar design. Current empirical approaches are mostly based on horizontal pillars, and the inclination of the pillars in the dataset is not taken into consideration. Laboratory and numerical studies were conducted with different width-to-height ratios and at different inclinations to understand the reduction in strength due to inclined loading and to observe the failure mechanisms. The specimens’ strength reduced consistently over all the width-to-height ratios at a given inclination. The strength reduction factors for gypsum were found to be 0.78 and 0.56, and for sandstone were 0.71 and 0.43 at 10° and 20° inclinations, respectively. The strength reduction factors from numerical models were found to be 0.94 for 10° inclination, 0.87 for 20° inclination, 0.78 for 30° inclination, and 0.67 for 40° inclination, and a fitting equation was proposed for the strength reduction factor with respect to inclination. The achieved results could be used at preliminary design stages and can be verified during real mining practice.

Plastic Collapse Behaviors of Tubulars with Recess Patterns—Application in Hollow Carrier Perforating Guns

2016 ◽  
Vol 3 (1) ◽  
Author(s):  
Haifeng Zhao ◽  
David Iblings ◽  
Aleksey Barykin ◽  
Mohamed Mehdi
Keyword(s):  
Empirical Relationship ◽  
External Pressure ◽  
Reduction Factor ◽  
Strength Reduction ◽  
Oil Field ◽  
Plastic Collapse ◽  
Strength Reduction Factor ◽  
Periodic Distribution ◽  
Collapse Strength ◽  
Collapse Behavior

The collapse strength of tubulars with recess patterns machined into their walls is an important topic for oil field downhole tools, especially in hollow carrier perforating gun systems. This paper presents a study of the plastic collapse behavior of thick-walled tubulars (those with an outside diameter to thickness ratio of approximately ten) having different patterns of circular recesses (blind holes partially machined into the tubing wall) that are subjected to external pressure. An empirical relationship between the reduction in collapse strength and the periodic distribution of recesses was constructed to account for the weakening effects of recess diameter, recess depth, axial spacing, angular phasing, etc. This strength reduction factor was introduced into the Tamano formula to predict collapse strength of recessed tubulars. Applicability of this empirical formula was validated with the aid of nonlinear, postbuckling finite element analyses (FEA). The strength reduction factor in combination with the Tamano formula provides a simple way of parametrically predicting the collapse strength of tubulars having circular recess patterns.

scholarly journals Evaluation of Weldment Creep and Fatigue Strength-Reduction Factors for Elevated-Temperature Design

1990 ◽  
Vol 112 (4) ◽  
pp. 333-339 ◽  
Author(s):  
J. M. Corum
Keyword(s):  
Elevated Temperature ◽  
Fatigue Strength ◽  
The United States ◽  
Fatigue Tests ◽  
Reduction Factor ◽  
Strength Reduction ◽  
Strength Reduction Factor ◽  
Nuclear Component ◽  
American Society ◽  
Reduction Factors

New explicit weldment strength criteria in the form of creep and fatigue strength-reduction factors were recently introduced into the American Society of Mechanical Engineers Code Case N-47, which governs the design of elevated-temperature nuclear plant components in the United States. This paper provides some of the background and logic for these factors and their use, and it describes the results of a series of confirmatory creep-rupture and fatigue tests of simple welded structures. The structures (welded plates and tubes) were made of 316 stainless steel base metal and 16-8-2 weld filler metal. Overall, the results provide further substantiation of the validity of the strength-reduction factor approach for ensuring adequate life in elevated-temperature nuclear component weldments.

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