Showing papers on "Bending moment published in 2007"

Experimental and Analytical Progressive Collapse Evaluation of Actual Reinforced Concrete Structure

Abstract: One approach to evaluate progressive collapse of structures is to study the effects of instantaneous removal of a load-bearing element such as a column. In this paper, using experimental and analytical results, potential progressive collapse of an actual 10-story reinforced concrete (RC) structure following the explosion of an exterior column is evaluated. Development of Vierendeel action is identified as the dominant mechanism in redistribution of loads in this structure. The concrete modulus of rupture is identified as an important parameter in limiting the maximum recorded vertical deformation of the system to only 0.25 in. (6.4 mm). The changes in the directions of bending moments in the vicinity of the removed column and their effects such as potential reinforcing bar pullout (bond failure) are studied. Potential failure modes and their consequences are studied. Some shortcomings of integrity requirements in current codes are pointed out and effects of beam reinforcement detail on the development of catenary action are discussed.

Gust Loads Alleviation Using Special Control Surfaces

Abstract: Control laws are designed for the alleviation of dynamic gust loads on a wind-tunnel model of a transport aircraft using wing-mounted control surfaces. Three different control surfaces are used: the symmetrically actuated main ailerons, special underwing forward-positioned control surfaces at about 0.8 of the wingspan, and special wing-tip forward-positioned control surfaces. The 5.3-m-span cable-mounted wind-tunnel model was constructed at the TsAGI laboratories and is being tested as there part of the 3AS 5th Framework European Commission research project. The length of one-minus-cosine vertical gust velocity profile is tuned to yield maximal wing-root bending moment All the control laws are based on simple low-pass filters for easy and robust application in the wind tunnel. Each is based on single input of a wing-tip accelerometer, which is shown to react sufficiently before the peak of the wing-root bending moment

An artificial muscle actuator for biomimetic underwater propulsors.

Abstract: In this paper, we introduce the analytical framework of the modeling dynamic characteristics of a soft artificial muscle actuator for aquatic propulsor applications. The artificial muscle used for this underwater application is an ionic polymer–metal composite (IPMC) which can generate bending motion in aquatic environments. The inputs of the model are the voltages applied to multiple IPMCs, and the output can be either the shape of the actuators or the thrust force generated from the interaction between dynamic actuator motions and surrounding water. In order to determine the relationship between the input voltages and the bending moments, the simplified RC model is used, and the mechanical beam theory is used for the bending motion of IPMC actuators. Also, the hydrodynamic forces exerted on an actuator as it moves relative to the surrounding medium or water are added to the equations of motion to study the effect of actuator bending on the thrust force generation. The proposed method can be used for modeling the general bending type artificial muscle actuator in a single or segmented form operating in the water. The segmented design has more flexibility in controlling the shape of the actuator when compared with the single form, especially in generating undulatory waves. Considering an inherent nature of large deformations in the IPMC actuator, a large deflection beam model has been developed and integrated with the electrical RC model and hydrodynamic forces to develop the state space model of the actuator system. The model was validated against existing experimental data.

Finite element modeling of self-loosening of bolted joints

Abstract: A three-dimensional finite element (FE) model with the consideration of the helix angle of the threads was developed to simulate the second stage self-loosening of a bolted joint. The second stage self-loosening refers to the gradual reduction in clamping force due to the back-off of the nut. The simulations were conducted for two plates jointed by a bolt and a nut and the joint was subjected to transverse or shear loading. An M12 X 1.75 bolt was used. The application of the preload was simulated by using an orthogonal temperature expansion method. FE simulations were conducted for several loading conditions with different preloads and relative displacements between the two clamped plates. It was found that due to the application of the cyclic transverse load, microslip occurred between the contacting surfaces of the engaged threads of the bolt and the nut. In addition, a cyclic bending moment was introduced on the bolted joint. The cyclic bending moment resulted in an oscillation of the contact pressure on the contacting surfaces of the engaged threads. The microslip between the engaged threads and the variation of the contact pressure were identified to be the major mechanisms responsible for the self-loosening of a bolted joint. Simplified finite element models were developed that confirmed the mechanisms discovered. The major self-loosening behavior of a bolted joint can be properly reproduced with the FE model developed. The results obtained agree quantitatively with the experimental observations.

Closed-Form Solutions for Flexural Response of Fiber-Reinforced Concrete Beams

Abstract: A constitutive law for fiber-reinforced concrete materials consisting of an elastic perfectly plastic model for compression and an elastic-constant postpeak response for tension is presented. The material parameters are described by using Young's modulus and first cracking strain in addition to four nondimensional parameters to define postpeak tensile strength, compressive strength, and ultimate strain levels in tension and compression. The closed-form solutions for moment-curvature response are derived and normalized with respect to their values at the cracking moment. Further simplification of the moment-curvature response to a bilinear model, and the use of the moment-area method results in another set of closed-form solutions to calculate midspan deflection of a beam under three- and four-point bending tests. Model simulations are correlated with a variety of test results available in literature. The simulation of a three- and four-point bending test reveals that the direct use of uniaxial tensile response underpredicts the flexural response.

Influence of Skew Angle on Reinforced Concrete Slab Bridges

Abstract: The effect of a skew angle on simple-span reinforced concrete bridges is presented in this paper using the finite-element method. The parameters investigated in this analytical study were the span length, slab width, and skew angle. The finite-element analysis (FEA) results for skewed bridges were compared to the reference straight bridges as well as the American Association for State Highway and Transportation Officials (AASHTO) Standard Specifications and LRFD procedures. A total of 96 case study bridges were analyzed and subjected to AASHTO HS-20 design trucks positioned close to one edge on each bridge to produce maximum bending in the slab. The AASHTO Standard Specifications procedure gave similar results to the FEA maximum longitudinal bending moment for a skew angle less than or equal to 20°. As the skew angle increased, AASHTO Standard Specifications overestimated the maximum moment by 20% for 30°, 50% for 40°, and 100% for 50°. The AASHTO LRFD Design Specifications procedure overestimated the FEA maximum longitudinal bending moment. This overestimate increased with the increase in the skew angle, and decreased when the number of lanes increased; AASHTO LRFD overestimated the longitudinal bending moment by up to 40% for skew angles less than 30° and reaching 50% for 50°. The ratio between the three-dimensional FEA longitudinal moments for skewed and straight bridges was almost one for bridges with skew angle less than 20°. This ratio decreased to 0.75 for bridges with skew angles between 30 and 40°, and further decreased to 0.5 as the skew angle of the bridge increased to 50°. This decrease in the longitudinal moment ratio is offset by an increase of up to 75% in the maximum transverse moment ratio as the skew angle increases from 0 to 50°. The ratio between the FEA maximum live-load deflection for skewed bridges and straight bridges decreases in a pattern consistent with that of the longitudinal moment. This ratio decreased from one for skew angles less than 10° to 0.6 for skew angles between 40 and 50°.

Calibration of the Hull Girder Ultimate Capacity Criterion for Double Hull Tankers

Abstract: This paper presents the background for the Hull Girder Ultimate Strength Capacity criterion in the IACS Common Structural Rules (CSR) for Double Hull Tankers, 2006. This new Rule criterion represents an explicit control of the most critical structural failure mode-- sagging failure of a loaded tanker in severe weather. The criterion is based on a partial safety factor (PSF) approach, where the characteristic values and magnitudes of the corresponding partial safety factors have been specified and calibrated by the use of structural reliability analysis (SRA) techniques. The approach to the ultimate strength assessment is presented together with supporting background information. A simplified method is used based on the ultimate capacity of the deck structure as this is effectively the limiting structural component in assessing the ultimate sagging bending capacity. The calculation of the extreme wave bending moment is based on ship motion analysis taking due account of the extreme value issues. A review of the uncertainties in deriving the ultimate strength capacity and the extreme wave bending moment is given. Five test ships, ranging from a Product Tanker to VLCC's, have been used as reference ships for the calibration. The employed SRA method uses a design modification factor based on the area of plates and stiffeners of the main deck in order to modify the ultimate capacity so that the hull girder ultimate strength meets a selected safety level. With this approach it is possible to illustrate how the partial safety factors change as a function of safety level. The net thickness approach, as given in the Rules, is used. However, the effect on safety of gross versus net scantlings is quantified and discussed. Finally, the target safety level is selected based on experience, comparison with existing ships and engineering judgement.

Comfort enhancement by an active vibration reduction system for a flexible railway car body

Abstract: In order to improve the ride comfort of lightweight railway vehicles, an active vibration reduction system using piezo-stack actuators is proposed and studied in simulations. The system consists of actuators and sensors mounted on the vehicle car body. Via a feedback control loop, the output signals of the sensors which are measuring the flexible deformation of the car body generate a bending moment, which is directly applied to the car body by the actuators. This bending moment reduces the structural vibration of the vehicle car body. Simulations have shown that a significant reduction in the vibration level is achieved.

Evaluation of minimum reinforcement ratio in FRC members and application to tunnel linings

Abstract: In lightly reinforced concrete (RC) structures, the area of steel cannot be lower than a minimum value, so that the ultimate limit state can be reached under a yielding moment higher than the cracking moment. Also in the serviceability stage, a minimum amount of reinforcement should be provided in tensile zones, in order to reduce crack widths. In fiber-reinforced concrete (FRC) members, due to the presence of structural fibers in the cementitious matrix, the minimum amount of steel area can be significantly reduced. Fiber can guarantee tensile stresses in a cement-based matrix even in the presence of wide cracks. Therefore, for the same cross-section of steel, a reinforced FRC member in bending can show higher bending moments, and reduced crack widths, than those measured in classical RC beams. This is particularly true in case of massive members, like the structures of tunnel linings. For such elements, and starting from the constitutive relationships recommended by Rilem TC 162-TDF, a new approach for the evaluation of minimum reinforcement area is proposed in this paper. By means of this nonlinear model, it is possible to calculate a reinforcement area lower than that calculated according to Eurocode 2 and Rilem TC 162-TDF prescriptions.

Transient deformation of elastic capsules in shear flow: effect of membrane bending stiffness.

Abstract: The transient deformation of liquid capsules enclosed by elastic membranes with bending rigidity in shear flow has been studied numerically, using an improved immersed boundary-lattice Boltzmann method. The purpose of the present study is to investigate the effect of interfacial bending stiffness on the deformation of such capsules. Bending moments, accompanied by transverse shear tensions, usually develop due to a preferred membrane configuration or its nonzero thickness. The present model can simulate flow induced deformation of capsules with arbitrary resting shapes (concerning the in-plane tension) and arbitrary configurations at which the bending energy has a global minimum (minimum bending-energy configurations). The deformation of capsules with initially circular, elliptical, and biconcave resting shapes was studied; the capsules' minimum bending-energy configurations were considered as either uniform-curvature shapes (like circle or flat plate) or their initially resting shapes. The results show that for capsules with minimum bending-energy configurations having uniform curvature (circle or flat plate), the membrane carries out tank-treading motion, and the steady deformed shapes become more rounded if the bending stiffness is increased. For elliptical and biconcave capsules with resting shapes as minimum bending-energy configurations, it is quite interesting to find that with the bending stiffness increasing, the capsules' motion changes from tank-treading mode to flipping mode, and resembles Jeffery's flipping mode at large bending stiffness.

Elastic analysis of laterally loaded pile in multi-layered soil

Abstract: An analysis is developed to determine the response of laterally loaded piles in layered elastic media. The differential equations governing pile deflections in different layers due to a concentrated static force and/or moment acting at the pile head are obtained using the principle of minimum potential energy and calculus of variations. The differential equations are solved analytically using the method of initial parameters. Pile deflection, slope of the deformed axis of the pile, bending moment and shear force can be reliably obtained by this method for the entire pile length. The input parameters needed for the analysis are the pile geometry and the elastic constants of the soil and pile. It is observed that soil layering has a definite impact on pile response and must be taken into account for proper analysis and design. The analysis forms the basis for future formulations that can consider stress–strain nonlinearity.

Characterization and modeling of extensional and bending actuation in ionomeric polymer transducers

Abstract: Ionomeric polymer transducers have received considerable attention in the past ten years due to their ability to generate large bending strain and moderate stress at low applied voltages. Bending transducers made of an ionomeric polymer membrane sandwiched between two flexible electrodes deform through the expansion of one electrode and contraction of the opposite electrode due to cation displacement. This is similar to a bimorph-type actuation. In this study we report actuation through the thickness of the membrane, leading to the potential of a new actuation mechanism for ionomeric polymer materials. Several experiments are performed to compare bending actuation with extensional actuation. A novel fabrication process previously developed by the authors, called the direct assembly process, is used to fabricate ionic polymer transducers with controlled electrode dimensions and morphology. In the first experiment, the actuators are cut in a beam shape and are allowed to bend in a cantilever configuration. In the second set of experiments, bending is constrained by sandwiching the membranes between two solid metal plates and force is measured across the thickness of the actuator. A bimorph model is used to assess the effect of electrode thickness on the strain. In the bimorph model, the electrode is assumed to be the 'active area' that generates strain due to charge displacement. An electromechanical coupling model that relates strain to charge is assumed. This model contains a linear and a quadratic term that acts at the active area and produces volumetric strain. The quadratic term in the strain generates a zero net bending moment for ionic polymer transducers with symmetric electrodes, while the linear term is canceled in extensional actuation for symmetric electrodes. The model successfully predicts the bending response from parameters computed using experimental thickness results. The prediction is particularly precise in estimating the trends of nonlinearity as a function of the amount of asymmetry between the two electrodes.

Riesz basis property of serially connected Timoshenko beams

Abstract: In this paper we study the Riesz basis property of serially connected Timoshenko beams with joint and boundary feedback controls. Suppose that the left end of the whole beam is clamped and the right end is free. At intermediate nodes, the displacement and rotational angle of beams are continuous but the shearing force and bending moment could be discontinuous. The collocated velocity feedback of the beams at intermediate nodes and the right end are used to stabilize the system. We prove that the operator determined by the closed loop system has compact resolvent and generates a C 0 semigroup in an appropriate Hilbert space. We also show that there is a sequence of the generalized eigenvectors of the operator that forms a Riesz basis with parentheses. Hence the spectrum determined growth condition holds. Therefore if the imaginary axis is not an asymptote of the spectrum, then the closed loop system is exponentially stable. Finally, we give a conclusion remark to explain that our result can be applied not ...

Simulating Seismic Response of Cantilever Retaining Walls

Abstract: Many failures of retaining walls during earthquakes occurred near waterfront. A reasonably accurate evaluation of earthquake effects under such circumstance requires proven analytical models for dynamic earth pressure, hydrodynamic pressure, and excess pore pressure. However, such analytical procedures, especially for excess pore pressure, are not available and hence comprehensive numerical procedures are needed. This paper presents the results of a finite-element simulation of a flexible, cantilever retaining wall with dry and saturated backfill under earthquake loading, and the results are compared with that of a centrifuge test. It is found that bending moments in the wall increased significantly during earthquakes both when backfill is dry or saturated. After base shaking, the residual moment on the wall was also significantly higher than the moment under static loading. Liquefaction of backfill soil contributed to the failure of the wall, which had large outward movement and uneven subsidence in the backfill. The numerical simulation was able to model quite well the main characteristics of acceleration, bending moment, displacement, and excess pore pressure recorded in the centrifuge test in most cases with the simulation for dry backfill slightly better than that for saturated backfill.

Analysis of dowelled timber to timber moment-resisting joints

Abstract: Dowelled joints, widely used in timber structures, are designed to transfer shear forces and bending moments between timber members. The anisotropic non-linear behaviour of the timber beneath the fasteners controls the stiffness of these joints. At the ultimate load-carrying capacity, the failure modes result from the shear stresses induced by the load distribution among the fasteners. The paper presents the experimental results obtained for beam to column joint with or without reinforcement using glued plywood plates. Based on these results, a two-dimensional finite element model was developed in two stages to describe the three-dimensional behaviour of the joint. At the single fastener scale, the model considers the non-linearity induced by the timber embedding and the fastener bending. At the structural scale, the modelling approach considers the timber as an elastic orthotropic material whereas each fastener is modelled by two non-linear springs. The elastic-plastic behaviour of each spring element is defined by the local scale model defined in two perpendicular directions. The load distribution among the fasteners is compared to the analytical results according to design rules. Considering the global load displacement curves, the results show that the modelling approach provides a good estimation of the structural response.

Evaluation of dynamic loads on a skew box girder continuous bridge - Part I : Field test and modal analysis

Abstract: Field measurements were carried out to evaluate dynamic loads on an existing skew box girder continuous bridge. This paper presents the experimental procedure, the data acquisition system, the calibration test, the modal analysis and the load distribution in a transversal direction. A three-axle heavy truck was hired for use in the test to calibrate the field measurements. The static and dynamic bending moments of the tested bridge induced by the calibration truck were obtained. The relationship between the measured strain and bending moment were determined. Information on the dynamic behaviours of the bridge were obtained from an experimental and theoretical modal analysis. The influence of skewness on the static and dynamic behaviours of the bridge as well as on the load distribution in the transversal direction for the calibration truck and in-service vehicles was investigated. It was found that the influence of skew in both the static and dynamic behaviours of the bridge within the skew angle range of 0 degrees-30 degrees is very small.