Christopher M. Foley

Formulation for Reliable Analysis of Structural Frames

Structural engineers use design codes formulated to consider uncertainty for both reinforced concrete and structural steel design. For a simple one-bay structural steel frame, we survey typical uncertainties and compute an interval solution for displacements and forces. The naive solutions have large over-estimations, so we explore the Mullen-Muhanna assembly strategy, scaling, and constraint propagation to achieve tight enclosures of the true ranges for displacements and forces in a fraction of the CPU time typically used for simulations. That we compute tight enclosures, even for large parameter uncertainties used in practice, suggests the promise of interval methods for much larger structures.

Risk-Based Seismic Design for Optimal Structural and Nonstructural System Performance

An automated performance-based design methodology to optimize structural and nonstructural system performance is outlined and it is shown that it can be used to enhance understanding of structural steel system design for minimum life-cycle costs. Performance is assessed using loss probability with direct economic loss expressed as a percentage of the building replacement cost. Time-based performance assessment is used to compute the expected annual loss of a given steel framing system assuming exposure to three seismic hazard levels. Damage to the structural system, nonstructural displacement-sensitive components, and nonstructural acceleration-sensitive components is characterized using fragility functions. A steel building with three-story, four-bay topology taken from the literature is used to demonstrate application of the algorithm with subsequent comparison of designs obtained using the proposed methodology and others found in the literature.

Performance-Based Optimization Considering Both Structural and Nonstructural Components

Development of performance-based design (PBD) methodologies for buildings and a better understanding of the performance and damage to nonstructural components during ground motion events give rise to design problems that involve structural and nonstructural component performance. The current research effort is geared toward development of an automated PBD environment to optimize structural system performance. FEMA-350 and HAZUS procedures are used to evaluate confidence levels associated with the probability of a structure not meeting targeted performance levels. A genetic algorithm (GA) is used to solve this complex optimization problem where confidence levels are incorporated into a GA fitness function along with initial construction cost in a series of optimal design scenarios. Inelastic time-history analysis is used to evaluate the designs under different levels of hazard during execution of the evolutionary algorithm. Different optimization formulations are studied in order to explore the symbiotic relationship between seismic hazard magnitude, initial construction cost, and confidence levels for damage exceedance for structural and nonstructural components.

ADVANCED ANALYSIS OF STEEL FRAMES USING PARALLEL PROCESSING AND VECTORIZATION

Advanced methods of analysis have shown promise in providing economical building structures through accurate evaluation of inelastic structural response. One method of advanced analysis is the plastic zone (distributed plasticity) method. Plastic zone analysis often has been deemed impractical due to computational expense. The purpose of this article is to illustrate applications of plastic zone analysis on large steel frames using advanced computational methods. To this end, a plastic zone analysis algorithm capable of using parallel processing and vector computation is discussed. Applicable measures for evaluating program speedup and efficiency on a Cray Y-MP C90 multiprocessor supercomputer are described. Program performance (speedup and efficiency) for parallel and vector processing is evaluated. Nonlinear response including postcritical branches of three large-scale fully restrained and partially restrained steel frameworks is computed using the proposed method. The results of the study indicate that advanced analysis of practical steel frames can be accomplished using plastic zone analysis methods and alternate computational strategies.

Inelastic analysis of partially restrained unbraced steel frames

The development of a finite element for use in the inelastic ultimate load analysis of steel frames is presented. The element is capable of modelling partial plastification within the cross-section, residual stresses, shift in the elastic neutral axis with plastification and partially restrained connections. The incremental equations of equilibrium are written and the constant work implementation of the simple Euler stepping algorithm is used to trace the full nonlinear load-deformation response of several structural steel frames with partially restrained connections. The effect of connection stiffness on the load-deflection behaviour and spread of plastification throughout the frames is quantified and discussed.

Toward design office moment-rotation curves for end-plate beam-to-column connections

Abstract A semi-analytic method to model moment-rotation curves for unstiffened extended end plate connections is presented. Two physically based parameters; connection initial stiffness and connection moment capacity, and one experimentally based parameter are used in a three-parameter power model. Good correlation between the proposed model and experimental results is shown. The proposed method is then simplified, resulting in moment-rotation curve modeling suitable for design office environments.

Benchmark Problems in Structural Design and Performance Optimization: Past, Present, and Future - Part I

In 1981, the Optimal Structural Design Committee of ASCE identified impediments preventing structural engineers from adopting widespread application of optimization techniques in design. Almost 30 years later, many of the structural optimization algorithms that have been developed are still being tested on simplistic models proposed in the 70s and 80s. There is a need for new realistic system benchmarks that could serve as testbed application and verification of novel methods of structural optimization. We discuss the advancements of the past and present a venue for development of future benchmark problems. This paper serves three purposes: it challenges developers of optimization techniques to tackle larger scale problems by posing new yet practical problems; it encourages practitioners to realize the strength of structural optimization techniques in developing safe and cost effective designs; and it seeks to persuade design professionals and academicians to efficiently utilize available computational power and paradigms in solving today’s engineering design and optimization problems. In an upcoming paper, review of performance of emerging design optimization techniques in handling the newly proposed optimization benchmarks will be studies. Future research and development needs will be discussed.

Parallel processing in the elastic nonlinear analysis of high-rise frameworks

Abstract The method of substructuring and the parallel processing technique of multitasking are applied in the analysis of high-rise structural frameworks. The performance of the proposed method is measured in both wall-clock time and connect time when run in a batch environment on a Cray Y-MP C90 supercomputer. An attempt is made to quantify the optimum number of processors that should be used in the analysis of rectangular frameworks based on the partitioning algorithm employed. Several high-rise planar structures are analyzed and the load-deformation response when subject to proportional and nonproportional loads is given.

Reliability-Based Inspection Protocols for Mast-Arm Sign Support Structures

AbstractThere have been numerous examples of poor in-service performance of welded, tube-to-transverse plate connections within mast-arm sign support structures in the last several decades. A considerable amount of research has been devoted to identifying structural response characteristics of these sign support systems and identifying how these connections may be repaired, retrofitted, or designed to facilitate longer service lives. Little attention has been given to using a systematic reliability-based approach to assess the probability of fatigue-induced crack initiation for in-service structures. The present research effort focuses on quantifying sources of uncertainty and formulating a reliability-based approach for prescribing inspection intervals corresponding to user-specified levels of probability of fatigue-induced crack initiation. The results indicate that implementation of reliability-based assessment procedures can be used to assign inspection intervals based on this probability, and the eng...

Modeling Error Uncertainty Characterization for Reliability-Based Fatigue Assessment in Sign Support Structures

Sign and luminaire support structures are prevalent throughout the transportation infrastructure network. Collapse and inspection of these signs pose hazards to the motoring public and the inspection personnel charged with their maintenance. There is a need to develop inspection protocols and understand variability in their performance to ensure public safety and to rationally disperse limited fiscal and personnel resources. This paper outlines a methodology that enables simulated and easured time histories of wind speed and resulting bending stress to be used in establishing parameters defining lognormal statistical models for modeling error that can be included in reliability-based assessment of structures subject to the tendency toward fatigue-induced crack initiation. Rainflow cycle counting is used to generate expected stress ranges from simulated and measured bending stress signals. The ratio of simulated expected stress range to measured expected stress range is defined as the modeling error bias factor. Statistical analysis of this factor at various magnitudes of wind speed is then used to formulate lognormal modeling error parameters suitable for implementation into a reliability-based assessment of fatigue-induced crack initiation risk for sign support structures.