Effect Of Gravity Load Research Articles

Test of High-Rise Core Wall: Effective Stiffness for Seismic Analysis

A test was conducted on a large-scale model of a concrete shearwall from the core of a high-rise building. The wall was slender (height-to-length ratio of 7.2), had a flanged cross section, a low percentage of vertical reinforcement (0.45%), and was subjected to a constant axial compression of 0.1f c ' A g to simulate the effect of gravity loads. Approximately 70% of the flexural resistance of the wall was due to the applied axial compression. The main emphasis of the test was to investigate the influence of cracking on effective stiffness for seismic analysis. Of particular interest was recovery of uncracked-section stiffness due to axial compression from gravity loads closing flexural cracks in walls with a low percentage of vertical reinforcement. Extensive measurements were made of concrete strains over the cracked region of the wall, and these were used to calibrate a nonlinear flexural stiffness model for high-rise concrete shearwalls. The final failure mode was buckling of an unsupported vertical reinforcing bar leading to concrete spalling and bar fracture after a few post-buckling cycles. The maximum global drift of the wall was 2.4%.

Artificial gravity loading increases the effects of the glutamate transporter inhibitors on the glutamate release and uptake in rat brain nerve terminals

The present study evaluated the effect of artificial gravity loading on transporter-mediated uptake and release of L-glutamate using the inhibitors of glutamate transporters as tools. The competitive nontransportable, DL-threo-beta-benzyloxyaspartate (DL-TBOA), and transportable, DL-threo-beta-hydroxyaspartate (DL-THA), inhibitors were demonstrated to better inhibit the L-[14C]glutamate uptake under centrifuge-induced hypergravity compared with the normal gravity control. The effect of DL-TBOA on depolarization-induced carrier-mediated L-[14C]glutamate release also increased after hypergravity loading in Na+- and low [Na+] NMDG- supplemented media. 10 µM DL-TBOA-induced decrease in L-[14C]glutamate release in Na+ — supplemented medium was 15.2±2.2 % in the control experiments and 26.2±3.9 % after centrifuge-induced loading (P≤0,05) and in low [Na+] medium was 37.0±2.5 % and 45.0±3.4 %, respectively.

Effect of Prefertilization Gravity Load to Mouse Secondary Oocytes on In Vitro Fertilization

ABSTRACT In our previous study, we observed decreases in the rate of fertilization and increases in the rate of polyspermy when mouse ova were exposed to hypergravity during in vitro fertilization. Moreover, the structures in mouse ova were changed by hypergravity. However, it was not determined whether the change in the rate of fertilization was caused by gravitational force acting directly on a process during fertilization or by structural changes in the ovum caused by hypergravity. We investigated the effect of prefertilization hypergravity, which excluded the direct acts on a process during fertilization, on in vitro fertilization. The rates of monospermy, polyspermy, and non-fertilization were investigated under various gravity loading conditions: Pre-G group, 3G-load (centrifugal force) for 2 h before insemination; During-G group, 3G-load for 6 h during fertilization; PreD Non-G group, 3G-load was not performed. The rat...

Rainwater rivulets on a cable subject to wind

Rainwater rivulets appear on inclined cables of cable-stayed bridges when wind and rain occur simultaneously. In a restricted range of parameters this is known to cause vibrations of high amplitudes on the cable. The mechanism underlying this effect is still under debate but the role of rainwater rivulets is certain. We use a standard lubrication model to analyse the dynamics of a water film on a cylinder under the effect of gravity and wind load. A simple criterion is then proposed for the appearance and position of rivulets, where the Froude number is the control parameter. Experiments with several geometries of cylinder covered with water in a wind tunnel show the evolution of the rivulets with the Froude number. Comparison of the prediction by the model with these experimental data shows that the main mechanism of rivulet formation and positioning is captured. To cite this article: C. Lemaitre et al., C. R. Mecanique 334 (2006).

Diurnal atmospheric tide and induced gravity variations

Abstract The gravity loading effects induced by the diurnal (S 1 ) air tide are investigated. We compare worldwide superconducting gravimeter records belonging to the GGP (Global Geodynamics Project) network with loading predictions computed from recent air and oceanic tidal models. Although discrepancies between the observations and models are large, the global tidal models allow a significant reduction of gravity residuals compared with the classical and empirical local pressure correction as well as with the loading computed with surface pressure provided by meteorological centers under the assumption of an inverted barometer response of the ocean to pressure forcing.

Effect of artificial gravity and exercise load on cardiovascular deconditioning, myatrophy, and osteoporosis in young men before and after bedrest.

Effect of artificial gravity and exercise load on cardiovascular deconditioning, myatrophy, and osteoporosis in young men before and after bedrest.

Design of Single Angles Bent About the Major Principal Axis

Hot rolled steel angles are frequently used in applications wherein their flexural strength must be quantified. While flexural applications of angle members frequently involves bending within the plane of one of the angle legs, other bending scenarios can arise. One other similar scenario involves bending a single angle member about its major principal centroidal axis as shown in Figure 1. A practical example of when this type of bending may occur involves the case of sign and billboard structures in which an equal leg single angle member may be specified for the girts that support the face of the sign. The effects of gravity loading from the face of the sign result in major axis bending of the girts. In such instances it is obviously important to understand the major axis strength characteristics of the single angle members. \Nonlinear finite element modeling techniques have been employed herein for the study of equal-leg, hot-rolled steel single angle members bent about the major principal centroidal axis. Results from the modeling indicate that a lower bound design approach can be encapsulated in the form of two, linear, nominal moment predictive equations that depend on the angle leg slenderness and the angle beam overall slenderness.

Size Effect Hidden in Excessive Dead Load Factor

The paper shows that the excessive value of the dead load factor in the ultimate load requirements of the current structural design code implies a size effect. The size effect implied, however, does not have a rational form; it cannot distinguish among various types of failure in which very different size effects apply. This size effect partly compensates for the absence of the actual size effect, primarily the size effect due to energy release, from the current code specifications. Therefore, it would be dangerous to reduce the dead load factor without simultaneously introducing size effect provisions into the code. The question of a possible reduction in the dead load factor cannot be separated from the question of size effect, and so the fracture experts and reliability experts must collaborate. Further it is shown that a possible size effect is hidden in a reliability-based code due to the fact that the reliability implied in the code increases with the contribution of the dead load effect to the overall gravity load effect. The overreliability ratio defined in this study may be used to quantify the additional size effect that can be hidden in a reliability-based code.

Behavior and design of single plate shear connections

Steel shear connections are primarily used to transfer the reaction of a simply supported beam to its support, normally a column or a beam. Currently, the most common shear connection in North America is a single plate connection consisting of a plate fillet welded to a supporting column or girder and bolted to the web of a simply supported beam. A shear connection should be strong enough to be able to transfer the shear force, yet, it should be sufficiently flexible and ductile to allow the end of simply supported beam to rotate with ease and accommodate the rotation demand of the beam. This paper summarizes a number of research and development projects conducted at the University of California, Berkeley to study behavior of single plate shear (shear tab) connections and to develop design procedures and guidelines, both for gravity and lateral load (seismic and wind) effects. The connections were sufficiently ductile to accommodate end rotation demands of simply supported beams under gravity load and drift rotations under lateral load effects. Design procedures developed and proposed and currently used in design of single plate connections are strength-based procedures that ensure occurrence of ductile and more desirable failure modes, such as yielding of the steel plate prior to occurrence of brittle and less desirable failure modes such as fracture of bolts and welds.

An evaluation ofP-Δ amplification factors in multistorey steel moment resisting frames

Three different amplification factors that have been proposed to account for P-Δ effects in the seismic design of multistorey building structures are described and compared. Nonlinear dynamic analyses of a typical 20-storey steel moment resisting frame are carried out under earthquake ground motions typical of eastern and western Canada to evaluate the gravity load effects and to assess the effectiveness of each type of amplification factor in accounting for these effects. All three approaches maintain the ductility demand within the level computed without P-Δ effects, but lateral deformations are generally larger than those obtained neglecting the gravity loads. Nonlinear dynamic analyses are also performed on a shear-beam (stick) model of the same building to examine the possibility of using such simple models for studying the dynamic stability of buildings subjected to ground motions. The shear-beam model does not predict adequately the seismic behaviour of steel moment resisting frames for which P-Δ effects are significant.Key words: ductility, earthquake, ground motion, lateral deformation, moment resisting frame, P-Δ effects, push-over analysis, seismic, shear-beam model, stability coefficient, amplification factor.

Effect of Gravity Load on Cortical Granule Distribution in the Mouse Oocyte.

In this study we investigated the effects of gravity over 1 G on the distribution of cortical granules (CGs) in mouse oocytes. We had found eggs incubated in a centrifuge culture medium showing a high rate of polyspermy, but there had been no difference between 2 G and 3 G loads in the incidence of polyspermy. We focused on cortical granules (CGs) which are known to act as a protection against polyspermy. The CG-free area of mouse oocytes subjected to increased G, when compared to that of control oocytes, was found to be significantly larger. Therefore, it can be assumed that the increased G caused an abnormal CG distribution which resulted in a high incidence of polyspermy in oocytes subjected to increased G. Further, as the centrifugation force was increased, the CGs free area of oocytes did not tend to expand. Observation was facilitated by using FITC-LCA fluorescent dye and TEM.

Experimental Study of Small Scale Dam Models

An experimental study of a small-scale model of a concrete gravity dam was conducted. Tests were carried out to simulate the hydrostatic, hydrodynamic, and seismic loads. The dynamic loads were estimated using the simplified method of analysis in concrete gravity dams. A loading mechanism with two actuators was designed to apply four concentrated loads at the upstream face of the dam model. The static load that represents the hydrostatic pressure was kept constant. The dynamic load was applied cyclically by an actuator to represent the dynamic effects of the earthquake loading. An existing concrete gravity dam monolith was modeled. The material properties of the model were maintained in the same manner as for the prototype. The gravity load effect of the dam was accounted for analytically. Results of the experiments show that it is possible to simulate the hydrodynamic load on a dam model using a finite number of concentrated mechanical loads. Measured strains in the dam model were found to be similar to the strains in the prototype predicted using available finite element analysis techniques.

Probabilistic‐Based Structural Specifications

The construction industry is both the largest civilian industry and the most unique in terms of fragmentation and its approach to controlling risk. Structural specifications establish nominal safety factors and design criteria for engineered structures such as buildings, bridges, dams, and power facilities. The goal is satisfactory strength capacity to safely and economically meet the demands of structural performance. Structures must resist the highly uncertain effects of combined gravity, earthquakes, wind, and snow loads supported by natural and human‐made materials. The public's expectation is that structures should last a long time and have low lifetime risk of structural failure. Historically, specifications have contained safety factors which evolved from past experiences and provided adequate safety or low risk. Due to pressures of economy and the need to optimize structural performance, structural specifications have recently been developed and accepted by industry based on structural reliability and risk‐assessment principles. This paper reviews developments of probabilistic applications in structural specifications including specification format, database, implementation examples, target risk levels, present research activities, and future goals for establishing optimal risk‐design procedures.

Effect of gravity load on seismic response of steel-framed structures

The effect of gravity load on inelastic seismic response of steel framed structures is investigated in this study. For this purpose, a new plastic hinge model is developed to represent inelastic behavior of beams in a structure considering the gravity load effects. From seismic analysis on an idealized frame structure using the layer model, it has been found that the hysteresis curve for the inelastic moment-rotation relationship is shifted toward the positive moment direction due to the gravity load moments. The properties of the plastic hinge model are derived from the results of the inelastic analysis on the one-story structure using the layer model. Then inelastic analyses on various multi-story steel frames are performed using the proposed plastic hinge model. The results indicate that seismic responses such as ductility demand, damage index and interstory drift may be underestimated, particularly on the lower stories of structures, if the gravity load moments are not considered in the analysis.

Tidal loading in south western Europe: A test area

The gravity attraction and loading effects computed on the basis of recent ocean tide models still present non negligible discrepancies for the principal tidal lunar wave M2. The installation of new tidal gravity stations in these regions would be useful to assess the accuracy of these new ocean tide models, in particular for the Atlantic ocean. This investigation clearly proves that there is a real scientific interest to set up a new Earth tides gravity profile along the coasts from Belgium to Portugal.

Advanced Finite Element Modeling of Rotor Blade Aeroelasticity

An advanced beam finite element has been developed for modeling rotor blade dynamics and aeroelasticity. This element is part of the Element Library of the Second Generation Comprehensive Helicopter Analysis System (2GCHAS). The element allows modeling of arbitrary rotor systems, including bearingless rotors. It accounts for moderately large elastic deflections, anisotropic properties, large frame motion for maneuver simulation, and allows for variable order shape functions. The effects of gravity, mechanically applied and aerodynamic loads are included. All kinematic quantities required to compute airloads are provided. In this paper, the fundamental assumptions and derivation of the element matrices are presented. Numerical results are shown to verify the formulation and illustrate several features of the element.

Effects of gravity load on seismic response of multistorey buildings

This paper includes analytical studies for an investigation of the redistribution of the gravity load moment for strong earthquakes and an evaluation of the effect of gravity load on the seismic response of building structures. In the earlier stage of strong earthquakes, gravity load results in different plastic rotations and bending moments at both ends of beams in multistorey building structures. After some significant inelastic excursions, the gravity load moments in beams are redistributed, so that the gravity load moments at both ends of the beams are significantly reduced. Reduction of gravity load moments at the beam ends changes the distribution of bending moment demands over the height of multistorey building structures. Therefore, beams in lower floors of the building structure continue to experience inelastic deformations while beams in the upper floors behave within elastic limits after the component of the gravity load moment disappears. As a result, excessive structural damage may occur in the lower floors of multistorey building structures subjected to a strong earthquake. The implications of the effect of gravity load moment for earthquake resistant design are that it is desirable to reduce the contributions of gravity load and to increase seismic load in determining the design moment.

Gravity Load Effect on Seismic Behavior of Interior Slab-Column Connections

The effect of superimposed slab loading on the behavior of exterior slab-column connections was studied by testing 2-bay slab-column subassemblies. Each subassembly consisted of an interior and two exterior connections. Three identical slab-column subassemblies were subjected to the same cyclic lateral-displacement history while each supported a different superimposed slab load. The tests show that increased slab load substantially reduces the lateral drift capacity of the connections. A limiting shear stress is suggested to insure adequate drift capacity for exterior slab-connectiions. A rational method to calculate the moment capacity of exterior connections is developed. The test results are compared with present ACI 318-83 Building Code provisions and ACI Committee 352's recommendations for design of slab-column connections.

Suppression Method of Disturbance Torque Due to System Drift via an Observer in the Robot Control System

The degradation of performances in the robot manipulator control system results from disturbance torques due to the system drift, frictions in the gears, Coriolis, gravity loading, and centrifugal effects of the link. The torque due to the system drift is closely related to the difference between ground levels and the variation of characteristics of the control system, while the others depend on the manipulator's physical parameters, instantaneous joint configuration, joint velocity and acceleration, and the load it is carrying. In this paper, an estimation algorithm of the system drift in the robot manipulator control system is proposed, which is based on the gradient search method. This algorithm is executed in the steady state for the elimination of the system drift because the variation of the characteristic of the control system due to the change in temperature, supply voltage, and etc. are slow compared with the motion of the robot manipulator. The proposed algorithm is implemented on the control system for a robot manipulator with six degrees of freedom, which has an 80386/80387 as a main processor and a TMS 320C30 as a processor for motion control. Experimental results show that the proposed suppression method of the system drift via an observer can be effectively used in controlling robot manipulators with high dynamic performance at both the transient and steady states.

Gravity Load Effect on Seismic Behavior of Exterior Slab-Column Connections

Gravity Load Effect on Seismic Behavior of Exterior Slab-Column Connections