Donald W. White

Refined 3D finite element modeling of partially-restrained connections including slip

This study presents an approach for refined parametric three-dimensional (3D) analysis of partially-restrained (PR) bolted steel beam-column connections. The models include the effects of slip by utilizing a general contact scheme. Non-linear 3D continuum elements are used for all parts of the connection and the contact conditions between all the components are explicitly recognized. A method for applying pretension in the bolts is introduced and verified. The effect of several geometrical and material parameters on the overall moment–rotation response of two connection configurations subject to static loading is studied. Models with parameters drawn from a previous experimental study of top and bottom seat angle connections are generated in order to compare the analyses with test results, with good prediction shown by the 3D refined models. The proposed 3D modeling approach is general and can be applied for accurate modeling of a wide range of other types of PR connections. A pronounced effect of slip and friction, between the connection components is shown with connections having thicker (stiffer) seat angles. This study demonstrates the effects of clamping through the bolts and contact between the components on the overall non-linear moment–rotation response. Equivalent moment–rotation responses of pull-test simulations are compared to FE model responses of full connections without web angles. The moment–rotation from the pull test is shown to be equivalent to that of the full FE model for small rotations. As the rotation increases a softer response is shown by the pull tests.  2002 Elsevier Science Ltd. All rights reserved.

Plastic-Hinge methods for advanced analysis of steel frames

Abstract A number of recent research efforts have focused on the development of advanced analysis techniques and their possible application in limit-states design of steel structures. The new Australian Standard AS4100-1990 allows the use of this type of analysis for the design of frames in which the members are of compact section and are sufficiently restrained against lateral-torsional buckling to develop the systems in-plane capacity. The term ‘advanced’ is intended to indicate any method of analysis that sufficiently captures the limit states encompassed by specification equations for member proportioning such that the checking of such equations is not required. The first part of this paper presents a detailed investigation of the adequacy of two second-order plastic-hinge based approaches for use as advanced analysis techniques. This is followed by a discussion of one possible approach for consideration of geometric imperfection effects in advanced analysis/design. The paper closes with a look at some of the issues regarding consideration of out-of-plane strength and rotation capacity in frames designed based on two-dimensional advanced inelastic procedures.

Limit states design of semi-rigid frames using advanced analysis: Part 1: Connection modeling and classification

Abstract This paper presents a method for modeling connection moment-rotation curves which are essential for proportioning two-dimensional semi-rigid steel frame structures analyzed based on a second-order inelastic analysis. Procedures for calculating the key parameters used to describe the moment-rotation curves of various types of angle connections are presented. Design aids are generated in which salient size parameters that affect the moment-rotation behavior of the connection can be identified. Two schemes by which connections can be classified in terms of strength, stiffness and rotation capacity are presented, and their design implications are discussed. Analysis and design methodologies are provided in Part 2, a companion paper in which the ultimate strength and serviceability limit state behavior of a semi-rigid frame example are studied using an advanced analysis. The aim of these two-part papers is to advance the use of second-order plastic hinge based analysis for proportioning two-dimensional semi-rigid frames without the need of separate specification equation checks.

Buckling models and stability design of steel frames: a unified approach

Abstract This paper presents a unified approach to elastic analysis and frame stability design within the context of the AISC LRFD Specification. The advantages, proper usage, and limitations of isolated subassembly, story, and system-based buckling models for calculation of column design strengths are addressed. Based on an understanding of the fundamental characteristics of these elastic/inelastic buckling (i.e. effective length) models, significant simplifications are suggested in the calculations necessary for design. This is followed by a discussion of certain anomalies that can occur in the calculation of column strengths, and an explanation of how these anomalies should be avoided. The paper closes with a study of specific equations and fundamental assumptions behind two story-buckling models suggested in the current AISC LRFD Commentary. Example calculations and detailed comparisons to alternative approaches are provided in a companion paper.

Limit states design of semi-rigid frames using advanced analysis: Part 2: Analysis and design

Abstract This paper presents an integrated advanced inelastic analysis method for proportioning semi-rigid steel frame structures in which the beam-to-column connections are composed of angles. The modeling of connection moment-rotation curves and their classifications have been presented and discussed in a companion paper. An approach called the second-order refined plastic hinge analysis is introduced. The method is validated by comparing the results with those obtained based on a more exact plastic zone analysis. It is shown that the refined plastic hinge analysis provides a good representation of inelastic behavior, and that it enables the full assessment of system and member inelastic behavior up to the limit state of strength. This analysis method is used to assess the adequacy of a two-dimensional semi-rigid frame, and its members and connections in resisting the factored load effects. The design is evaluated with respect to the systems strength and serviceability limit states, including conformance with the code requirements for strength and stability of individual members, and rotation capacity of connections. The inclusions of connection nonlinear effects in advanced inelastic analysis provide a straightforward task for proportioning of frame members and connections, thus avoiding the complexity of having to perform specification member capacity checks for individual frame members.

Beam-column design in steel frameworks— insights on current methods and trends

Abstract The first part of the paper describes the background behind the development of the current AISC-LRFD beam-column interaction equations. This is followed by a rigorous evaluation of the LRFD procedures with a specific focus on the use of effective length factors for beam-column design. Various methods of computing effective length factors are reviewed, and characteristic values obtained from the different methods are demonstrated. Comparisons are made between ultimate strength curves represented by the LRFD beam-column equations and strength curves computed by second-order inelastic analysis. Lastly, the procedure in the current Canadian Standard CSA-S16.1-M89, which does not involve the use of effective length factors, is posed in LRFD format and compared to the current LRFD method, which requires the use of K factors. The goal is to illustrate the qualities and limitations of both types of design approaches.

Strength and ductility of compact-flange I-girders in negative bending

Abstract This paper reviews available experimental and finite element test data pertaining to the negative moment-plastic rotation behavior of continuous-span steel I-girders with compact or ultra-compact flanges. Current American specification formulas for the pier-section strength of these types of members and a moment-plastic rotation model recently developed by the authors are examined against the experimental and finite element test results. Several weaknesses in current specification provisions are observed. The new M-θp model avoids these weaknesses and provides a lower-bound approximation of the complete moment-plastic rotation response at the pier section.

Negative bending resistance of HPS70W girders

Abstract This paper investigates the influence of material and geometric parameters on the flexural behavior of I-girders fabricated from Grade 70W high performance steel. Three cross-section geometric parameters are considered: compression flange slenderness ( b fc /2 t fc ), web slenderness (2 D cp / t w ), and the ratio of the web depth to the compression flange width ( D / b fc ). Also, three material parameters are studied: the yield ratio ( F y / F u ), the ratio of the strain-hardening and yield strains ( ϵ st / ϵ y ), and the strain-hardening modulus ( E st ). The parametric studies are conducted using full non-linear shell finite element models of the hypothetical physical girders. The resulting moment–rotation curves obtained from these simulated experiments are compared with simplified moment–plastic rotation equations that have been developed in previous research, and with current AASHTO specification strength equations.

Stability of steel frames: the cases for simple elastic and rigorous inelastic analysis/design procedures

In this paper, two stability design approaches that are alternatives to traditional buckling-solution based procedures are outlined and their merits are discussed. The first approach, which is commonly referred to as a notional load type procedure, is effectively a modified first plastic hinge technique. This approach provides a simple elastic analysis based solution for the stability design of steel frames. The second approach, termed an advanced analysis design procedure, involves the use of a rigorous second-order inelastic analysis as part of the design assessment. Several examples are provided to illustrate the implications of these alternative procedures relative to the use of traditional buckling solution based design equations.

A matrix class library in C++ for structural engineering computing

Abstract Matrix computations are traditionally performed using procedural languages such as FORTRAN. This paper describes the object-oriented design and implementation of a matrix class library in C++. A wide range of abstractions and algorithms such as symmetric matrices, profile matrices, banded matrices, column vectors, and LU decompositions are presented which address a variety of time/ space demands in structural engineering computing. The object-oriented design presented here applies encapsulation, inheritance, composition, and type parameterization. Consistent semantics and uniform syntax of the interface is a major focus of the design for the matrix class library. Careful design to take advantage of the type system of C++, a strongly typed object-oriented programming language, allows potential misuses of abstractions to be detected at compile time. The proposed object-oriented matrix library not only improves the clarity and expressiveness of the client code, but also enhances its reliability.