Detailed 3D Finite Element Model Research Articles

Bridge–embankment interaction under transverse ground excitation

AbstractSeismic performance and dynamic response of bridge–embankments during strong or moderate ground excitations are investigated through finite element (FE) modelling and detailed dynamic analysis. Previous research studies have established that bridge–embankments exhibit increasingly flexible performance under high‐shear deformation levels and that soil displacements at bridge abutment supports may be significant particularly in the transverse direction. The 2D equation of motion is solved for the embankment, in order to evaluate the dynamic characteristics and to describe explicitly the seismic performance and dynamic response under transverse excitations accounting for soil nonlinearities, soil–structure interaction and imposed boundary conditions (BCs). Using the proposed model, equivalent elastic analysis was performed so as to evaluate the dynamic response of approach embankments while accounting for soil–structure interaction. The analytical procedures were applied in the case of a well‐documented bridge with monolithic supports (Painter Street Overcrossing, PSO) which had been instrumented and embankment participation was identified from its response records after the 1971 San Fernando earthquake. The dynamic characteristics and dynamic response of the PSO embankments were evaluated for alternative BCs accounting for soil–structure interaction. Explicit expressions for the evaluation of the critical embankment length Lc are provided in order to quantify soil contribution to the overall bridge system under strong intensity ground excitations. The dynamic response of the entire bridge system (deck–abutments–embankments) was also evaluated through simplified models that considered soil–structure interaction. Results obtained from this analysis are correlated with those of detailed 3D FE models and field data with good agreement. Copyright © 2007 John Wiley & Sons, Ltd.

Retrofit of a Three-Span Slab Bridge with Fiber Reinforced Polymer Systems—Testing and Rating

A 45-year old, three-span reinforced concrete slab bridge with insufficient capacity was retrofitted with 76.2- and 127-mm wide bonded carbon fiber-reinforced polymer (FRP) plates, 102-mm wide bonded carbon FRP plates with mechanical anchors at the ends, and bonded carbon FRP fabrics. The use of four systems in one bridge provided a unique opportunity to evaluate field installation issues and to examine the long-term performance of each system under identical traffic and environmental conditions. Using controlled truckload tests, the response of the bridge before retrofitting, shortly after retrofitting, and after one year of service was measured. The stiffness of the FRP systems was small in comparison to the stiffness of the bridge deck, and accordingly the measured deflections did not change noticeably after retrofitting. The measured strains suggest participation of the FRP systems, and more importantly, the strength of the retrofitted bridge was increased. A detailed 3D finite-element model of the original and retrofitted bridge was developed and calibrated based on the measured deflections. The model was used to predict more accurately the demands for computing the rating factors. The addition of FRP plates and fabrics led to a 22% increase in the rating factor and corresponding load limits. During a one-year period, traffic loading and environmental exposure did not apparently affect the performance of the FRP systems. The increased capacity and acceptable performance of the FRP systems enabled the engineers to remove the load limits in order to resume normal traffic. Future tests are necessary to monitor the long-term behavior of the FRP systems.

Shear-lag versus finite element models for stress transfer in fiber-reinforced composites

The stress transfer from broken to unbroken fibers in fiber-reinforced polymer-matrix (PMC) and aluminum-matrix (AMC) composites is studied using a detailed 3D finite element model (FEM) and using the standard shear-lag model (SLM). The stress transfer predicted by the SLM is in good agreement with the FEM results for the PMC at high fiber volume fractions but not at low volume fractions. For the AMC with an elastic/plastic matrix, the FEM results depend on whether the fiber is broken initially (pre-break) or after loading (post-break), while the SLM is independent of the fiber break load. Compared to the pre-break FEM, the stress transfer in the SLM is too low at high volume fractions and fairly accurate at low volume fractions while the reverse trend obtains when the SLM is compared to the post-break FEM. These results suggest that the SLM is generally accurate for high fiber/matrix stiffness ratios and high fiber volume fractions, and/or when global matrix yielding proceeds fiber breaking such that the tangent stiffness of the matrix is small. At low volume fractions, matrix load carrying capacity accounts for much of the discrepancy between the SLM and the FEM, which can be rectified by more sophisticated SLMs. A simple elastic model demonstrates that neglect of the finite fiber dimensions and fiber shear deformation in the SLM can also affect the stress transfer. It is concluded that although the standard SLM cannot generally be used for simulations of composite deformation and failure, it is reasonably accurate for an important range of composite constituent material properties.

3D Finite Element Analysis of Temperature‐Induced Stresses in Dowel Jointed Concrete Pavements

ABSTRACT A detailed 3D finite element (3DFE) model is developed to investigate the applicability of Westergaard's curling stress equations to doweled jointed concrete pavements. The model does not rely on any of Westergaard's assumptions and is capable of handling nonlinear and/or time-dependent temperature profiles. However, only linear gradient is applied to facilitate the comparison with Westergaard's results. The transverse stress calculated using Westergaard's formula was found to be within 10% of that computed using 3DFE. Westergaard's longitudinal stress equation required a correction. The 3DFE results confirm Westergaard's finding that the slab curling stresses are independent of slab length. Thus, curling stress does not explain the field-observed dependency of mid-slab cracking on the slab length. Through the examination of the mechanism of dowel-concrete interaction, it is shown that uniform temperature changes play the major role in mid-slab transverse cracking of relatively long slabs. Due to...

A {l-2}-order Thermoelastic Theory For Composite And Sandwich Plates And Its Validation

A {l,2}-order theory originally proposed by Tessler et al. [1] has been extended by Annett [2] to include the structural response of laminated and sandwich plates subjected to thermal gradients. The theory takes into account the effect of transverse shear and normal deformations. In this paper, approximations for the components of the displacement vector, transverse shear strains and transverse normal stress are reviewed in details. Results corresponding to a symmetric laminated plate and a symmetric sandwich panel are validated against those of a detailed 3D finite element model.

Closed loop finite-element modeling of active/passive damping in structural vibration control

A three-dimensional (3D) finite-element closed loop model has been developed to predict the effects of active/passive damping on a vibrating structure. The example used is a cantilever structure containing a viscoelastic material (VEM) layer sandwiched between a piezoelectric actuator and the base structure. This hybrid arrangement is called an active constrained layer damper (ACLD). A piezoelectric sensor is also embedded in the structure. The finite-element analysis includes a control algorithm to close the loop between the sensor and the actuator. The parametric study considers different types of control as well as geometric parameters related to the ACLD. Comparisons are made between active constrained layer and passive constrained layer, and active damping only. The results obtained here reiterate that ACLD is better for vibration suppression than either the purely passive or active system and provides higher structural damping with less control gain when compared to the purely active system. This is the first attempt at a detailed 3D finite-element model that makes no approximations about the piezoelectric devices and includes closed loop modeling.

Fracture mechanics analyses including constraint investigations on reactor pressure vessels under pressurized thermal shock loading

In the integrity assessment of reactor pressure vessels the emergency core cooling system injection is one of the main load cases to be analysed. For a more generic assessment, parametric analyses are done concerning the load pattern, the postulated crack geometry and the material properties. With detailed axisymmetric and 3D-finite element (FE) models of reactor pressure vessels, temperature distributions in the structures and the deformations are calculated by elastic-plastic FE analyses for axisymmetric and asymmetric strip-like cooling assumptions. With it, boundary conditions for FE detail models with partly and 360° circumferential cracks are determined. Different material properties for the circumferential weld near the core mid-height, the cladding and the base metal with estimated influence of neutron irradiation are considered. Crack loading based on the J-integral is calculated for different crack geometries, and different parameters describing the constraint on the crack ligament with proposals for a fracture assessment concept are discussed. Furthermore, simplified methods based on analytical formulas to calculate the stress distribution in the wall and the stress intensity factor are applied and compared with FE results.

Elastic Constants for Z‐Core Sandwich Panels

The computational effort to analyze a sandwich panel can be greatly reduced if an equivalent 2D thick-plate bending model is used instead of a detailed 3D finite-element model. The success of the transformation from a sandwich panel to a 2D thick-plate bending model depends on the equivalent elastic constants used. In this note, these elastic constants for Z-core sandwich panels are summarized. The elastic constant for the shear stiffness in the weaker direction for Z-core sandwich panels is derived. To ascertain the validity of the elastic constants, the results obtained from the 2D thick-plate bending model with different boundary conditions are compared with a detailed 3D finite-element model. From the results, it is shown that excellent agreement is obtained between the two models.