Nonlinear Progressive Collapse Analysis Research Articles

Nonlinear Progressive Collapse Analysis Including Distributed Plasticity

This paper demonstrates the effect of incorporating distributed plasticity in nonlinear analytical models used to assess the potential for progressive collapse of steel framed regular building structures. Emphasis on this paper is on the deformation response under the notionally removed column, in a typical Alternate Path (AP) method. The AP method employed in this paper is based on the provisions of the Unified Facilities Criteria – Design of Buildings to Resist Progressive Collapse , developed and updated by the U.S. Department of Defense [1]. The AP method is often used for to assess the potential for progressive collapse of building structures that fall under Occupancy Category III or IV. A case study steel building is used to examine the effect of incorporating distributed plasticity, where moment frames were used on perimeter as well as the interior of the three dimensional structural system. It is concluded that the use of moment resisting frames within the structural system will enhance resistance to progressive collapse through ductile deformation response and that it is conserative to ignore the effects of distributed plasticity in determining peak displacement response under the notionally removed column.

Reliability of fixed offshore jacket platform against earthquake collapse

In this study, an approach for the reliability assessment of a fixed offshore jacket platform against earthquake collapse is presented. The platform is modelled using a nonlinear finite-element model taking into account the effect of pile–soil interaction. The platform ultimate base shear resistance is first computed by using a nonlinear progressive collapse analysis and used as a resistance variable for reliability assessment. The seismic-induced dynamic base shear, acting on the platform base, due to seismic loads is then computed. The probability of platform collapse under seismic loading is computed using a finite-element reliability code. The first-order/second-order reliability methods are used for computation of safety indices. These values are then compared with target safety levels as set in offshore platform design codes. A case study for a fixed jacket platform located in the Gulf of Suez offshore of Egypt is analysed using the proposed approach. Results show that computed safety levels are within the target values. The proposed approach can be a valuable tool for platform designers/operators for assessment of platform safety and reliability in seismically active areas.

Parallel Axial-Flexural Hinge Model for Nonlinear Dynamic Progressive Collapse Analysis of Welded Steel Moment Frames

In this study, a parallel axial-flexural hinge model capable of representing postyield flexural behavior and considering interaction effects of axial force and moment is proposed for a simplified nonlinear progressive collapse analysis of welded steel moment frames. To this end, the load-resisting mechanism of the column-removed double-span beams was investigated based on the material and geometric nonlinear parametric finite-element analysis. A multilinear parallel point hinge model which captures the moment-axial tension interaction was then proposed. The emphasis was to develop a reliable and computationally efficient macromodel for practical progressive collapse analysis. The application of the proposed hinge model to nonlinear dynamic progressive collapse analysis was illustrated by using OpenSEES program. The accuracy as well as the efficiency of the proposed model was verified based on inelastic dynamic finite-element analysis results. The importance of including catenary action effects for proper progressive collapse resistant analysis and design was also emphasized.

Simplified nonlinear progressive collapse analysis of welded steel moment frames

In this study, two nonlinear analysis methods are proposed that can be used for a simplified but accurate evaluation of progressive collapse potential in welded steel moment frames. To this end, the load-resisting mechanism of the column-removed double-span beams in welded steel moment frames was first investigated based on material and geometric nonlinear parametric finite element analysis. A simplified tri-linear model for the vertical resistance versus chord rotation relationship of the double-span beams was developed. The application of the developed model to energy-based nonlinear static progressive collapse analysis was then proposed. The relationship between the gravity loading and the maximum dynamic chord rotation or the concept of collapse spectrum was also established for a quick assessment of the maximum deformation demands.

Submarine Impact With the Oseberg Jacket

The Oseberg jacket was installed at the Oseberg field in the North Sea during the summer of 1987 and the production started on December 1, 1988. On March 6, 1988, a submarine accidentally impacted with the Oseberg jacket. This paper presents results from the evaluation of the importance of the damage to the overall structural safety. A nonlinear progressive collapse analysis is applied for the safety check. The theoretical computations are verified through evaluation of strain and acceleration time series recorded during the submarine impact. The reduction in the overall structural capacity of the jacket was in the order of 10 percent. However, the local member capacity was significantly reduced and it was necessary to remove the damaged member in order to obtain the initial level of safety.

Elastic-plastic-fracture analysis of concrete structures

The paper presents a computer implementation technique for an elastic-plastic-fracture analysis of concrete structures. To this end, the finite element formulation for a fractured concrete element as well as the relevant redistribution procedure of released stresses are described. Further, it is discussed how the finite element method may be applied effectively in the analysis of concrete structures subjected to different types of loading conditions. In particular, in order to avoid the structure-load system interaction during an unstable process of material fracturing, two extreme loading conditions are considered: (1) dead load, and (2) the load applied by a rigid testing machine. This leads in turn to a pure load and a pure displacement-control analysis. Based on the computer program developed, two typical computational examples are presented involving nonlinear progressive collapse analysis of split-cylinder test, and implosion analysis of a concrete cylindrical hull.