K.M. Abdalla

Expanded database of semi-rigid steel connections

This paper expands the existing database of semi-rigid steel connections at Purdue University by including additional test data on header-plate and seat-angle, and double-web and seat-angle connections. The experimental moment rotation curves are also compared with several analytical models describing these curves.

Steel column-to-column connections under combined load: A quadratic programming approach

Abstract The aim of this paper is the investigation of the mechanical behaviour of bolted steel column-to-column connections under moment and axial loads by means of a method that takes into account the possibility of the appearance of detachment phenomena between the splice plates. As is well known, regions of detachment (called nonactive contact regions below), due to the appearance of the prying-action phenomenon, do appear on the adjacent fronts of such steel splice plates, greatly affecting the mechanical response of steel connections of this type. The significance of the problem under investigation arises from the fact that column-to-column splices are extensively applied in any possible combination to the design and construction of steel structures. It is therefore obvious that, since local failure phenomena on such connections due to undesirable—and not a priori defined—detachment between the splice plates (as consequence of the development of the prying-action phenomenon) may cause a total destruction of the whole steel structure. For this reason, it is important for such a behaviour to be accurately predicted and the previously mentioned nonactive contact regions on the splice plates to be defined. In this sense, such an investigation leads to an amelioration of the design principles for bolted steel column-to-column splices and to a refinement of the respective steel construction standards.

Sensitivity analysis results on the separation problem of bolted steel column-to-column connections

Abstract The present paper deals with the sensitivity analysis of bolted steel column-to-column connections, by taking into account the development of separation phenomena on the joint endplates. A variational inequality and quadratic programming approach is first proposed to the investigation of the separation problem on such bolted steel connections. Applying the classical unilateral contact law to describe in a quasi-static way the separation process along the surface between the splice plates, the continuous problem can be formulated either as a variational inequality or equivalently as a quadratic programming problem. Then, by means of an appropriate finite element discretization scheme, the discrete problem is formulated as a quadratic optimization problem with inequality constraints. In order to investigate the variation of the structural response of the connection under consideration due to the variation of critical design parameters, the sensitivity analysis problem is formulated; the latter is a quadratic programming problem where design parameters appear only in the quadratic term. This problem can be effectively treated numerically by means of an appropriate quadratic optimization algorithm. The applicability and the effectiveness of the method are illustrated by means of two numerical applications.

A Neural Network Approach to the Modelling, Calculation and Identification of Semi-Rigid Connections in Steel Structures

Abstract A two-stage neural network approach is proposed for the elastoplastic analysis of steel structures with semi-rigid connections. At the first stage, the moment-rotation law of the connection is obtained from experimental results by the use of a neural network based on the perceptron model. At the second stage, the elastoplastic analysis problem is formulated for the given moment-rotation law as a Quadratic Programming Problem and solved by a neural network based on the Hopfield model.

A variational inequality and quadratic programming approach to the separation problem of steel bolted brackets

Abstract A variational inequality and quadratic programming approach is herein proposed for the investigation of the separation problem of steel bolted brackets. By applying the classic unilateral contact law to describe the separation process along the contact surfaces between the bracket and the column flange, the continuous problem is formulated as a variationa! inequality or as a quadratic programming problem. By applying an appropriate finite element discretization scheme, the discrete problem is formulated as a quadratic optimization problem with inequality constraints which, in turn, can be effectively treated numerically by means of an appropriate quadratic optimization algorithm. The applicability and the effectiveness of the method is illustrated by means of a numerical application.

Failure Behavior of a Top and Seat Angle Bolted Steel Connection with Double Web Angles

AbstractThe article presents a three-dimensional nonlinear finite-element model that was developed for the study of a top and seat angle bolted steel connection with double web angles. Unilateral contact and friction laws were used to simulate the interaction among the connected parts. Large displacements as well as the von Mises failure criterion were also considered for the steel parts and bolts. Numerical results were compared with the experimental research conducted on the same steel joint. This study finds yielding of the top angle as well as shear failure of the bolts connecting the beam bottom flange with the seat angle to be very important for the overall response of the structure. For this reason, a parametric investigation of the influence of the top angle on the behavior of the structure and the study of the prying forces developed at the top angle were conducted.

Review and Classification of Semi-Rigid Connections

Most design engineers assume the behavior of their building connections either as perfectly pinned or as completely fixed elements. This simplification results in an inaccurate prediction of frame behavior. Full-scale experiments are generally necessary to describe actual behavior of these connections. At the University of Illinois, Young [1], (1917) Wilson, and Moore [2], (1917), performed the first experiment to assess the rigidity of steel frame connections. Since then, experimental testing has been continued.

Analysis and design of mushroom slabs with a strut-tie model

The strut-tie model developed in recent years is applied here to study the problem of mushroom slabs. This method gives a clear physical picture of the effect of the increase in slab depth at column on the slab design, as compared to the case of conventional uniform depth. In fact, drop panel and capital constitute a perfect section, consistent with the distribution of negative moment in the column strip. A maximum depth is available at the point of maximum moment and as the depth decreases from the column, negative moment also decreases. This paper describes the application of the strut-tie model to the actual analysis and design of the subject problem with an illustrative example.

A numerical approach to the dynamic unilateral contact problem of soil-pile interaction under instabilizing and environmental effects

The paper deals with a numerical approach for the dynamic soil-pile interaction, considered as an inequality problem of structural engineering. So, the unilateral contact conditions due to tensionless and elastoplastic softening/fracturing behavior of the soil as well as due to gapping caused by earthquake excitations are taken into account. Moreover, second-order geometric effects for the pile behavior due to preexisting compressive loads and environmental soil effects causing instabilization are taken also into account. The numerical approach is based on a double discretization and on mathematical programming. First, in space the finite element method (FEM) is used for the simulation of the pipeline and the unilateral contact interface, in combination with the boundary element method (BEM) for the soil simulation. Next, with the aid of Laplace transform, the problem conditions are transformed to convolutional ones involving as unknowns the unilateral quantities only. So the number of unknowns is significantly reduced. Then a marching-time approach is applied and finally a nonconvex linear complementarity problem is solved in each time-step.

Neural Processing in Semi-Rigid Connections of Steel Structures

The problem of classifying measured one-dimensional relations (e.g. stress-strain laws, moment-rotation laws, etc.) into a predetermined family of laws is considered for semi-rigid steel connections. Experimentally measured data have been loaded in back-propagation neural networks and have been used in structural analysis tasks. A second application concerns the use of Hopfield neural networks for the solution of the nonlinear computational mechanics problem. The structural analysis problem of a structure with semi-rigid joints has been written as an inequality constrained optimization problem, or an equivalent linear complementarity problem. Both formulations are amenable to neural network computations by a Hopfield network.