Anant R. Kukreti

End-plate connection moment-rotation relationship

Abstract A methodology, based on finite element modeling, is presented to analytically develop the moment-rotation relationship for a bolted steel end-plate connection. The methodology is demonstrated for a flush end-plate connection. Experimental testing of a few selected specimens was conducted to verify the finite element modeling and associated computer analysis procedure. The finite element model was used to conduct a parametric study to determined the effect of various geometric and force related variables on the prediction of maximum end-plate separation. Sufficient cases were then analyzed, which cover the variation of these variables within practical ranges. The analyses data collected were regressed to develop a predicton equation characterizing the general behavior of the connection.

Hysteresis behavior of semi-rigid double web angle steel connections

Abstract This study presents the cyclic behavior of two types of semi-rigid double web angle connections: bolted-bolted (angles bolted to the beam web and column flange) and welded-bolted (angles welded to beam web and bolted to column flange), with their bolts pretensioned to the proof load. Twenty test specimens were prepared and cyclic load was applied to each test specimen using load control at the beginning cycles, which was converted to displacement control in subsequent cycles upon yielding of angles or bolts materials. The moment–rotation hysteresis loops and the failure modes for all the test cases are presented. The failure modes for bolted-bolted test specimens, depending on angle thickness, were either excessive rotation or beam web bearing, and for the welded-bolted specimens were excessive rotation or bolt fracture. The stiffness, strength, and ductility of the tested connections are compared to those of flush end-plate moment connections reported in literature.

Dynamic analysis of nonlinear structures by pseudo-normal mode superposition method

Abstract An algorithm is developed for dynamic response analysis of nonlinear structural systems by using the pseudo-normal mode superposition technique. The analytical formulation is based on finite element theory for spatial dependence and both geometric and material nonlinearities are considered. Lagrangian concept is used to describe the motion of the discrete system. An “assumed linear” stiffness is used throughout the response solution and the nonlinearities are grouped together with the external dynamic loads acting on the system and called as pseudo-loads. The discrete coordinates are transformed to modal coordinates based on the “assumed linear” stiffness for the whole system. The pseudo-loads are then approximated by a quadratic polynomial of time on increments (or subintervals) which can be made sufficiently small to ensure convergence in the limit. This approximation is performed iteratively by fitting a unique quadratic curve through three points over each subinterval. It was found that selecting these points at the beginning, at the middle, and at the end of the increment gives the most efficient and accurate solution. Two iterative techniques are presented: a direct iteration about the pseudo-loads, and an iteration about the incremental displacements. The second one proves to be more efficient for a multi degrees-of-freedom problem. For a geometrically nonlinear beam problem, comparison of results with a linear approximation of pseudo-load and the Park Stiffly-Stable method, show the algorithm presented gives more accurate, efficient and stable solutions.

Finite element modeling of large capacity stiffened steel tee-hanger connections

Abstract This paper presents the development of a mathematical model describing the behavior of a stiffened steel tee-hanger connection. The particular tee-hanger connection has two rows of pretensioned high-strength bolts on either side of the tee-stem (eight bolts total). This geometric configuration results in a highly indeterminate problem as the bolt forces cannot be determined directly. Thus, an analytical study with modeling of the connection as an assemblage of finite elements was conducted. Only one-quarter of a symmetric section of the tee-hanger was analysed with eight-noded isoparametric brick elements used for the tee-flange plate elements. Bi-linear stress-strain behavior is considered for both the bolt and plate material. To consider the inelastic steel behavior in each cycle, the elastic moduli of the yielded elements are reset to their secant values. Analytical results are compared with results from tee-hanger connection tests. Based on comparison of experimental and analytical results, it is concluded that the model developed adequately explains the connection behavior. The study is restricted to A36 steel and A325 bolts with maximum diameter of 1 1 2 inches.

Analysis of eccentrically stiffened plates with mixed boundary conditions using differential quadrature method

Abstract Differential quadrature solution for the flexural analysis of eccentrically stiffened plates subjected to transverse uniform loads is presented. In-plane forces in the plate are considered to take into account the axial stiffness of the plate and the interaction between the beams and the plate due to the eccentricity. Torsional and shear stiffnesses of the beams are also considered. The analysis procedure presented can be used for: point loads applied at the corners of the plate segments; roller point supports at the corners of the plate segments; and outer edges having different combinations of boundary conditions, which includes, free, simply supported, clamped, or resting on beams. The method gives the same accuracy for the moments and shears as that for the deflections and is computationally efficient and simple to program. The results for single panels with complicated boundary conditions are compared with the available exact results. Two examples, one with central eccentric stiffener, and the other with two central mutually perpendicular stiffeners are analyzed and compared with the available results. An example of a plate with no stiffeners but with mixed boundary conditions is also analyzed and compared with the finite element results. All the results are close to the published results.

Stress-dependent permeability measurement using the oscillating pulse technique

Abstract Permeability of Indiana Limestone samples undergoing deformation in a triaxial cell along several stress paths such as triaxial compression, hydrostatic compression and uniaxial strain was measured using the oscillating pulse technique. This technique consists of applying a sinusoidal pressure wave at the upstream end of the sample and recording the pressure—time behavior at the downstream end. The solution to the general one-dimensional diffusivity equation can be obtained by applying the appropriate boundary conditions to give a method of evaluating diffusivity and permeability in a relatively short time. The process of sending a pulse to evaluate permeability has been programmed in Visual Basic which can be incorporated into any regular triaxial testing automated routines to measure permeability at different stages of loading until failure. Stored waveforms of the upstream and downstream pressure responses with time are analyzed to evaluate the attenuation and phase shift in the waveform. For comparison purposes, permeability was also measured using steady-state methods for samples subjected to a hydrostatic compression stress path and good correlations were observed. During triaxial compression failure tests, in most tests the permeability decreased continuously until the end of the test. Permeability also decreased with increasing confining pressure, while under uniaxial strain (i.e. one-dimensional compaction ( k 0 ) tests), there was a sudden reduction of permeability at a particular stress level.

Fundamental frequency analysis of single specially orthotropic, generally orthotropic and anisotropic rectangular layered plates by the differential quadrature method

Abstract A differential quadrature method is presented for computation of the fundamental frequency of a thin single-layer specially orthotropic and anisotropic rectangular plate. The partial differential equations of motion for free vibration are solved for the boundary conditions by approximating them by substituting weighted polynomial functions for the differential operators. By doing this, the uncoupled and coupled partial differential equations of motion are reduced to sets of homogeneous algebraic equations. These sets of homogeneous algebraic equations are combined to give a set of general eigenvalue equations. The results for the eigenvalue (or fundamental frequency) for all the cases analyzed are compared with solutions obtained by another numerical method. Effects of level of discretization, boundary conditions, aspect ratio and taper ratio on the accuracy and rate of convergence of the results are also discussed. The method presented gives accurate results and is found to use much less computer time.

Analysis of circular plate-elastic half-space interaction using an energy approach

Abstract An analytical formulation is developed, based on an energy approach, to predict the flexural behavior of uniformly loaded thin flexible circular plates resting in smooth and continuous contact with an isotropic elastic half-space. In this development, the deflected shape of the plate is approximated by an even power series expansion in terms of the radial coordinate. Any number of terms in the series can be considered. The coefficients associated with the series are evaluated by making use of the principle of minimum potential energy. Analytical expressions are derived for the contact stress distribution, the plate deflection, and the plate radial moment. The results obtained from the proposed procedure compare very well with the existing solutions of similar problems.

Finite element analysis to predict the cyclic hysteretic behavior and failure of end-plate connections

Abstract In this paper, the development of a computer program to analyze the moment-rotation behavior of end-plate connections subjected to seismic loading is presented. A three-dimensional finite element procedure has been developed for the analysis. Only half of a symmetric section, including both the tension and compression portions of the connection have been modeled. Idealized bilinear stress-strain curves have been considered for the end-plate (A36) and bolt (A325) materials. The inelastic behavior of the materials has been modeled using incremental plasticity theory described by the von Mises yield criterion and Mrozs kinematic hardening model. The computer program developed has the capability of applying pretention loads to bolts in the connection model. It can also evaluate the boundary conditions at the back of the end-plate to account for the end-plate separation and computes the relative end-plate rotation. The program also identifies fractured elements and redistributes the strain energy from these fractured elements to the unfractured continuum before the external load is incremented. Failure of the connection is identified in the program when unstable crack growth occurs or when the connection experiences a loss in moment capacity. The results predicted by the automated analysis procedure were verified by comparison with experimental results obtained for three connection geometries in which only the end-plate thickness was varied. Based on the comparison of analytical and experimental results it was concluded that the finite element computer program gave sufficiently accurate results.

Integrated Urban Evacuation Planning Framework for Responding to Human-Caused Disasters over a Surface Transportation Network

The purpose of emergency evacuation is to move people away from a dangerous place because of a threat or an occurrence of a natural or a human-caused disastrous event. Although research has investigated emergency evacuations during hurricanes and nuclear power plant disasters, there is a lack of comprehensive, interdisciplinary research on urban evacuation planning by the use of surface transportation networks, especially for terrorist-induced emergencies. Recent disasters reveal how different factors hinder emergency evacuations in urban areas. Therefore, it is imperative to investigate how these factors should be taken into account in establishing an urban evacuation strategy. To achieve this goal, a framework for an integrated urban emergency evacuation contingency plan (IUE2CP) was developed to provide a basis for creating an emergency evaluation preparedness system. Such a system can raise public awareness of the evacuation procedures and provide guidelines for municipal governments. First, the paper presents the components of the IUE2CP framework, including the novel concept of the emergency evacuation backbone network. The Beijing Olympic Green serves as a case study of the IUE2CP initiative. Second, evacuation network planning objective models are structured, including harm zone and buffer zone traffic control planning objective models. Third, the primary requirements for emergency evacuation communication systems are discussed. Finally, to include human behavior factors in IUE2CP, the concepts of situation awareness and distributed situation awareness are introduced, and the framework for their application in the feed-forward and feedback control mechanisms during evacuation is presented.