Theodore V. Galambos

Probability-based criteria for structural design

Abstract Probability-based loading and resistance criteria are presented that are suitable for routine safety checking in design. The criteria are based on a comprehensive analysis of statistical data on structural loads and resistances and an examination of levels of reliability implied by the use of current design standards and specifications. The criteria are intended to be used in specifications that are oriented towards limit states design.

Nonlinear Finite-Element Analysis of Critical Gusset Plates in the I-35W Bridge in Minnesota

Reported evidence suggests that failure of gusset plates initiated the collapse of the I-35W Bridge in Minneapolis, Minnesota. The particular gusset plates were at a panel point designated as U10. Therefore, an analytical investigation was conducted on the condition of the U10 gusset plates at the time of bridge collapse. The forces delivered to panel point U10 were reproduced using available information of the bridge. These forces were introduced to detailed nonlinear three-dimensional finite-element models to calculate stress and strain states of the gusset plates. The results indicate that substantial portions of the U10 gusset plates were yielded at the time of collapse, confirming earlier findings from federal and state investigations. Weight increase due to past deck reconstruction and construction material and equipment staged on the day of collapse, along with insufficient thickness of the gusset plate, were identified as the main contributing factors to the substantial yielding. The results also suggest that the interaction of compression and shear played an important role in the gusset plate failure.

Recent research and design developments in steel and composite steel–concrete structures in USA

Abstract A brief review of the status of structural steel research in the US at the end of the Twentieth Century is presented in this paper to show that while many problems are being solved, there are new and challenging problems remaining. The chief impetus for continued research is that provided by natural disasters, such as earthquakes, tropical storms, tornadoes and floods occurring in densely populated urban areas. New materials and new experimental and computational technologies also give rise to new and exciting research problems.

Design recommendations for equal leg single angle flexural members

Abstract Current design specifications do not address issues of compactness and bracing requirements for use in the plastic analysis and design of single angle flexural members. The research described herein employs experimentally verified nonlinear finite element analysis techniques, implemented on super-computer hardware platforms, for the development of equal leg single angle compactness and bracing requirements. Four common flexural orientations are investigated. Geometric and material nonlinearities are considered in the models, as are the effects of residual stresses.

Load and resistance factor design of composite columns

Test capacities of composite concrete-encased steel profile and concrete-filled tube columns and beam-columns are compared with predictions of the design model of the American Institute of Steel Construction Load and Resistance Factor Design criteria. Some 300 tests were examined. It was found that the design model is conservative, but that the scatter of the tests with respect to the AISC design model is also high. A first-order second-moment reliability study revealed that the concrete-encased members exceeded the target reliability index in the design specification, but that the concrete-filled tubes had an inadequate reliability index when compared to the target value. It is recommended that both a better design model and further tests are needed to arrive at satisfactory design criteria.

Systems reliability and structural design

Abstract It is demonstrated that current limit state structural design standards do not explicitly account for systems reliability. An improvement is suggested, using systems factors, which accounts for the different levels of damage implied by the various limit states.

Guidelines for Analysis Methods and Construction Engineering of Curved and Skewed Steel Girder Bridges

This report contains guidelines on the appropriate level of analysis needed to determine the constructability and constructed geometry of curved and skewed steel girder bridges. Required plan details and submittals are included in the guidelines. When appropriate in lieu of a 3D analysis, the guidelines also introduce improvements to 1D and 2D analyses that require little additional computational costs. The report will be of immediate interest to bridge and construction engineers.

Evaluation of web buckling test results on welded beams and plate girders subjected to shear

The limit state design requirements for welded beams and plate girders in shear, and combined bending and shear, are analysed and criteria for two codes (AISC and Eurocode 3) are compared. As the differences in the design requirements are substantial, a comparison of the achieved reliability indices is made in order to find which model is closer to the target reliability level. The statistical parameters of the experimental results are evaluated and the first order-second moment method is used for the calibration. The results vary for these two models and it is necessary to achieve target values of reliability by correcting the models by the resistance factors.

The effect of lateral bracing on the stability of steel trusses

Abstract Results of two analytical studies on three-dimensional rigid space trusses are reported and compared to experimental results. Single trusses as well as two and three braced truss systems were investigated by finite element analysis for the elastic buckling strength of the system. The effects of the following parameters were investigated: axial and flexural stiffness of the bracing, the brace end-conditions, the number of trusses, and the effect of bracing only the top chord.

Reliability of axially loaded columns

Abstract The reliability of current and proposed design formulae for axially loaded columns is determined by the first-order second-moment probabilistic method. Computed reliability indices are compared to target values, and the consequences of changing the resistance factor are examined. The basic behavioural model includes the effects of residual stress, initial crookedness and small end-restraint.