Cushion Stiffness Research Articles

Cushion Impact on Bearing Capacity Exerting Degree of Soil between Piles for Rammed Cement-Soil Pile Composite Foundation

Basing on filed loading test results, the influences of cushion stiffness to the playing process of pile head and soil surface pressure in composite foundation was analyzed. Cushion stiffness will affect bearing capacity and failure mode of composite foundation with rammed soil-cement pile, which is applied in a relatively good ground. It point out that the cushion stiffness must be considered when loading test used to determine the bearing capacity of composite foundation with rammed soil-cement pile.

A vehicle seat design concept for reducing whiplash injury risk in low-speed rear impact

To reduce whiplash injury risk in low-speed rear-impact accidents, a sliding mechanism of vehicle seat with crash energy-absorption (EA) function is proposed and analysed in this study. It can reduce relative motion between occupant head and torso under rear impact and lower values of neck injury related parameters such as neck injury criterion (NIC), neck displacement criterion (NDC) and neck forces and moment. A number of parameters of seat structure and countermeasures have great influence on occupant head–neck responses in rear impacts. They include head restraint position, seat recliner characteristic and seatback cushion stiffness, as well as the newly proposed seat sliding characteristic. A numerical model that includes a seat and a BIORID II dummy is used in a parametric study to evaluate effects of whiplash injury risk reduction. The analysis results show that proper combinations of the values of these parameters can mitigate the whiplash injuries and they form the basis of the existing countermeasures such as active head restraint and yielding seat as well as the newly proposed sliding seat. The simulations demonstrate the effectiveness of the sliding seat in whiplash injury reduction. Potential merits of the sliding seat, compared to the existing countermeasures, are also discussed. Furthermore, appropriate structural mechanisms for EA sliding of seat are designed through quasi-static tests and finite element simulations and an implementation is also preliminarily sketched.

Study on pile drivability with one dimensional wave propagation theory

Pile drivability is a key problem during the stage of design and construction installation of pile foundations. The solution to the one dimensional wave equation was used to determine the impact force at the top of a concrete pile for a given ram mass, cushion stiffness, and pile impedance. The kinematic equation of pile toe was established and solved based on wave equation theory. The movements of the pile top and pile toe were presented, which clearly showed the dynamic displacement, including rebound and penetration of pile top and toe. A parametric study was made with a full range of practical values of ram weight, cushion stiffness, dropheight, and pile impedance. Suggestions for optimizing the parameters were also presented. Comparisons between the results obtained by the present solution and in-situ measurements indicated the reliability and validity of the method.

Qualitative models of seat discomfort including static and dynamic factors

Judgements of overall seating comfort in dynamic conditions sometimes correlate better with the static characteristics of a seat than with measures of the dynamic environment. This study developed qualitative models of overall seat discomfort to include both static and dynamic seat characteristics. A dynamic factor that reflected how vibration discomfort increased as vibration magnitude increased was combined with a static seat factor which reflected seating comfort without vibration. The ability of the model to predict the relative and overall importance of dynamic and static seat characteristics on comfort was tested in two experiments. A paired comparison experiment, using four polyurethane foam cushions (50, 70, 100, 120 mm thick), provided different static and dynamic comfort when 12 subjects were exposed to one-third octave band random vertical vibration with centre frequencies of 2.5 and 5.5 Hz, at magnitudes of 0.00, 0.25 and 0.50 m.s-2 rms measured beneath the foam samples. Subject judgements of the relative discomfort of the different conditions depended on both static and dynamic characteristics in a manner consistent with the model. The effect of static and dynamic seat factors on overall seat discomfort was investigated by magnitude estimation using three foam cushions (of different hardness) and a rigid wooden seat at six vibration magnitudes with 20 subjects. Static seat factors (i.e. cushion stiffness) affected the manner in which vibration influenced the overall discomfort: cushions with lower stiffness were more comfortable and more sensitive to changes in vibration magnitude than those with higher stiffness. The experiments confirm that judgements of overall seat discomfort can be affected by both the static and dynamic characteristics of a seat, with the effect depending on vibration magnitude: when vibration magnitude was low, discomfort was dominated by static seat factors; as the vibration magnitude increased, discomfort became dominated by dynamic factors.

フィンガースカートを装着した小型ＡＣＶの傾斜時の静安定性について

The static pitch stability of small ACVs fitted with finger-type skirts is investigated. A simple method which predicts the static stability and the cushion stiffness is proposed. It yields rough approximations of quantities needed for the initial design. Numerical results of the analysis are presented. We consider two different operating conditions. In one case the skirt is in contact with the ground. In another case the contact does not occur. In both cases the pitch stability decreases with increasing distance of the center of gravity from the skirt hem line and with increasing hover height. However variation of the skirt inclination angle affects the pitch stability in opposite way in two different operating conditions.

Case Histories of Pile Driving in the Gulf of Mexico

This paper presents a series of case histories on pile driving in the Gulf of Mexico, demonstrating the value of a pile-drivability analysis to the engineer planning an offshore pile-driving operation. Actual pile-driving records are compared with the results of pile-drivability analyses. Introduction Considerable research has been done in the past concerning the dynamics of pile driving. Increasing demands of the present-day offshore oil industry have necessitated construction of larger platforms in deeper water requiring larger piles with greater penetrations. As this occurs, the driving of the penetrations. As this occurs, the driving of the piles becomes more critical to the overall design. piles becomes more critical to the overall design. Recent attention has been focused on pile driving in new exploration areas such as the North Sea, Gulf of Alaska, and offshore California. The older, more active producing areas in the Gulf of Mexico largely have been overlooked. One of the aims of this paper is to is to demonstrate the usefulness and accuracy of pile-drivability analyses in the Gulf of Mexico. pile-drivability analyses in the Gulf of Mexico. A pile-drivability analysis provides significant benefits during both the design and installation phases. Its primary purpose is to ensure proper and phases. Its primary purpose is to ensure proper and efficient pile installation in the field. The analysis accomplishes this by aiding in the selection of proper hammer-cushion combinations, pile wall thicknesses, and add-on lengths for the particular site. The predicted blow counts from the analysis may be quite predicted blow counts from the analysis may be quite useful during pile installation in assessing hammer performance and actual soil conditions. This performance and actual soil conditions. This assessment allows the field engineer to determine any changes in equipment necessary during the pile-driving operation. Background The method of analysis used for pile-drivability analyses is the one-dimensional wave equation, first proposed by Smith, and now generally used for proposed by Smith, and now generally used for dynamic analysis of pile driving. Later improvements were made by Samson et al., resulting in the Texas A and M U. Wave Equation Program. Further modifications in the last several years have resulted in more efficient versions of the program, but no analytical changes have been made in the program. The version of the program used for this study is the TIDYWAVE program (Aug. 1975). Basic Technique The model used for the one-dimensional wave equation idealizes the pile system as consisting of a ram, cushion, pile cap, pile, and surrounding soil. The physical and analytical model of a typical pile is shown in Fig. 1. The pile hammer and pile are modeled as a system of concentrated masses connected by springs representing the stiffness of the pile and cushion. The soil is modeled by a spring and dashpot in parallel, attached to each concentrated pile mass below the mudline and at the pile point. pile mass below the mudline and at the pile point. The hammer and cushion properties used in the study are given in Table 1. The values shown are based on those recommended by researchers at Texas A and M U. The factors of hammer efficiency and cushion stiffness have been found to be fairly typical. While the actual hammer used is noted on the driving record, the type of cushion usually is not known. JPT P. 580

Influence of cushion stiffness on the stability of cushion-loaded cylindrical shells

Influence of cushion stiffness on the stability of cushion-loaded cylindrical shells