Toward A Better Estimation Of Shear Capacity And Structural Reliability Of Prestressed Concrete Girders

The main objectives of this study are to evaluate the adequacy of the current AASHTO methods for shear design of prestressed concrete (PC) bridge girders, determine the reliability of PC bridge girders in shear based on the current LRFD General Procedure, determine the most accurate and consistent method for predicting the shear capacity of AASHTO “I” shape PC bridge girders, and recalibrate the AASHTO LRFD code for shear as necessary. These objectives were achieved through lab testing of two full scale Type II girders, finite element modeling for more than 330 PC girders, parametric analysis, regression analysis, and structural reliability analysis for more than 200 PC bridge cases. As a result of this study, a regression equation and a modification to the current LRFD General Procedure were proposed, and rating factors based on MI live load traffic data were computed and discussed

Implementation of Fortran finite element analysis source code with application : particle deposition in a 90 degree duct bend

Two FORTRAN 77 finite element analysis source codes, by 1.N. Reddy, were input into a PC, debugged, executed, and tested successfully. These programs are available to students interested in implementing a good finite element analysis source code on a PC or on a workstation in one or two dimensions. The programs can solve problems relating to heat transfer, stresses, beam analysis, frames, trusses, plane elasticity, plate bending, and laminar viscous incompressible fluids with various node and element combinations. The two-dimensional program was used to obtain the velocity distributions in a 90 degree duct bend with incoming and exiting fully developed flows so that particle deposition analysis could be studied varying the inertia parameter, S. It was found that at values of S below 1.0, the maximum particle deposition occurred at the point where the 90 degree duct bend met the exit vertical section; for S=1.0, deposition was even throughout the duct; finally, for S greater than 1.0, maximum particle deposition occurred at the center of the 90 degree turn of the duct. All particles were deposited on the upper wall of the duct. Extra anti-corrosive agents should be placed in the area of maximum particle deposition when the particulate matter is harmful to the duct material

A substructure based parallel dynamic solution of large systems on homogeneous PC clusters

This study focuses on developing a parallel solution framework for the linear dynamic analysis of large structural models on homogeneous PC clusters. The framework consists of two separate stages where the former is preparing data for the parallel solution that involves partitioning. The latter is a fully parallel finite element analysis that utilizes substructure based solution approach with direct solvers to perform implicit integration. The linear dynamic analysis of a large scale model was performed on a homogeneous PC cluster and the number of computers was varied in order to demonstrate the performance and the efficiency of the overall solution framework. The performance of the implemented framework was also compared with the widely acknowledged parallel direct solver, MUMPS

Efficient single-step time-dependent analysis of PC structures

This paper describes an efficient single-step method to predict the time-dependent behaviour of prestressed concrete (PC) structures due to concrete creep, concrete shrinkage and cable relaxation. A versatile tendon sub-element is first developed to model prestressing cables of arbitrary profiles. To enable accurate estimation of losses of cable forces, a new relaxation model is formulated based on the equivalent creep coefficient, which is verified to work not only in the case of intrinsic relaxation but also under various boundary conditions. An efficient single-step finite-element method is then devised for time-dependent analysis of PC structures considering creep, shrinkage and relaxation based on the age-adjusted elasticity modulus, shrinkage-adjusted elasticity modulus and relaxation-adjusted elasticity modulus respectively. The effects of creep, shrinkage and relaxation on the long-term performance of PC structures are investigated. The numerical results obtained indicate not only the accuracy of the method but also the significance of considering the interaction among various time-varying factors.published_or_final_versio

Faults and unbalance forces in the switched reluctance machine

The paper identifies and analyzes a number of severe fault conditions that can occur in the switched reluctance machine, from the electrical and mechanical points of view. It is shown how the currents, torques, and forces may be estimated, and examples are included showing the possibility of large lateral forces on the rotor. The methods used for analysis include finite-element analysis, magnetic circuit models, and experiments on a small machine specially modified for the measurement of forces and magnetization characteristics when the rotor is off-center. Also described is a computer program (PC-SRD dynamic) which is used for simulating operation under fault conditions as well as normal conditions. The paper discusses various electrical configurations of windings and controller circuits, along with methods of fault detection and protective relaying. The paper attempts to cover several analytical and experimental aspects as well as methods of detection and protection

Distributed Finite Element Analysis Using a Transputer Network

The principal objective of this research effort was to demonstrate the extraordinarily cost effective acceleration of finite element structural analysis problems using a transputer-based parallel processing network. This objective was accomplished in the form of a commercially viable parallel processing workstation. The workstation is a desktop size, low-maintenance computing unit capable of supercomputer performance yet costs two orders of magnitude less. To achieve the principal research objective, a transputer based structural analysis workstation termed XPFEM was implemented with linear static structural analysis capabilities resembling commercially available NASTRAN. Finite element model files, generated using the on-line preprocessing module or external preprocessing packages, are downloaded to a network of 32 transputers for accelerated solution. The system currently executes at about one third Cray X-MP24 speed but additional acceleration appears likely. For the NASA selected demonstration problem of a Space Shuttle main engine turbine blade model with about 1500 nodes and 4500 independent degrees of freedom, the Cray X-MP24 required 23.9 seconds to obtain a solution while the transputer network, operated from an IBM PC-AT compatible host computer, required 71.7 seconds. Consequently, the $80,000 transputer network demonstrated a cost-performance ratio about 60 times better than the$15,000,000 Cray X-MP24 system

Long-Term Performance Evaluation Of NUdeck In Kearney East Bypass

The Kearney East Bypass bridge is the first project that implements the newly developed precast concrete deck system (known as 2nd generation NUDECK). The new system consists of full-depth full-width precast prestressed concrete deck panels that are 12 ft (3.66 m) long each. The panels have covered shear pockets at 4 ft (1.22 m) spacing on each girder line to host clustered shear connectors that are adjustable in height. Narrow unreinforced transverse joints are used to eliminate the need for deck overlay. Also, deck panels are post-tensioned in the longitudinal direction using a new post-tensioning system that eliminates the need for post- tensioning ducts, strand threading, and grouting operations. The project has twin bridges: a southbound bridge with cast-in-place (CIP) concrete deck, and northbound bridge with the new precast concrete (PC) deck system. The two bridges were completed in the fall of 2015 and opened to traffic in the fall of 2016. Due to the unique features of the new PC deck system, this research project was initiated to monitor short-term performance using live load test and long-term performance under traffic loads to evaluate the system performance. Both CIP concrete deck and PC deck bridges were instrumented and tested during the summer of 2016 to compare the performance of their superstructures. Also, finite element analysis (FEA) was conducted to predict the performance of the new PC deck system. The results of both analytical and experimental investigations indicated that the PC deck system performs as predicted and very comparable to the conventional CIP concrete deck

STUDY ON SPATIAL STRESS EFFECT OF PC CONTINUOUS THIN-WALLED BOX GIRDER BRIDGE

In order to study the influence of spatial stress effect and shear lag effect on the cracking of PC continuous thin-walled box girder bridge, a spatial model was established by using ANSYS finite element software to analyze the internal stress distribution of the bridge. The test results are compared with the analysis results of spatial model and plane link system model through the load test of real bridge. The results show that the longitudinal stress is evenly distributed along the width direction, which means that the spatial stress effect and the shear lag effect have little influence on the downdeflection of the bridge. The shear lag coefficient at the longitudinal axis of midspan bottom plate and the intersection of bottom plate and web are larger than other positions, which is most likely to produce cracks caused by stress concentration, and should be strengthened here in practical engineering. The results of load test show that the results of spatial finite element analysis are more reliable than those of plane link system calculation, and the design and construction based on the results of spatial finite element analysis is safer

Mathematical formulation of the space curvature of the tendon in the PC structures

This paper presents the mathematical formulation of the space curvature of the prestressing tendon in the nonlinear analysis of prestressed concrete (PC) structures. The nonlinear behaviour of prestressed tendons is described by the one dimensional elasto-viscoplastic model. The tendon element geometry is described by the second order space function which is determined by its projections. These elements make it possible to model arbitrarily curved prestressing tendons in space, thus they can be determined independently of the three-dimensional (3D) finite element mesh. This is very important in the case when the prestressing tendon can not be located in a plane. The transfer of prestressing force on the concrete was modelled numerically. The developed model makes it possible to compute prestressing structures in phases: before prestressing, during prestressing and after prestressing. The described models are implemented in the computer programme for a 3D analysis of the prestressed concrete structures where the structures are discretized by three-dimensional finite elements with an embedded one-dimensional element of prestressed tendons