Eric M. Lui

Analysis and behaviour of flexibly-jointed frames

Abstract A method for analysing the behaviour of flexibly-connected plane steel frames is presented. Two types of elements are used in the analysis procedure: the beam-column (frame) element and the connection element. The beam-column element formulation is based on an updated Lagrangian approach. Allowance for the coupling effect of axial force and bending moments, as well as for the formation of plastic hinges in the member, is made for this beam-column element. The nonlinear behaviour of the connection is modelled by an exponential function. Both loading and unloading responses of the connections are taken into consideration in the formulation. The monotonic load-deflection response of frames with flexible connections is traced using an incremental load control Newton-Raphson iterative technique. Based on sub-assemblage and frame analyses, it is concluded that connection flexibility has an important influence on frame behaviour.

Behavior of braced and unbraced semi-rigid frames

Abstract The state-of-the-art limit states specification for structural steel buildings explicitly acknowledges the semi-rigid nature of most connections by allowing for the construction of semirigid frames under its Type PR (Partially Restrained) Construction provision. The construction of semi-rigid frames differs from that of rigid frames in that connection behavior must be taken into consideration in the analysis and design process. This paper attempts to shed light on the subject by outlining a methodology for semi-rigid frame analysis. Analytical studies of both braced and unbraced semi-rigid frames are presented. It is found that the use of bracings not only increases the strength and stiffness of semi-rigid frames, but it drastically reduces the sensitivity of the frames to differences in connection behavior. It is further demonstrated that for design application the assumption of linear connection behavior is quite adequate for braced semi-rigid frames.

Steel frame analysis with flexible joints

Abstract The first papt of the paper discusses various mathematical models that have been proposed to represent the nonlinear moment-rotation behavior of the semi-rigid steel beam-to-column connections. This is followed by a brief description of two simplified and a rigorous analysis capable of dealing with these models in flexibly-connected steel frames. Numerical studies of frames made-using these simplified and rigorous analysis methods are presented. Observations regarding the effects of flexible connections on the strength, deflection and internal force distribution of steel framed structures are discussed.

Effects of joint flexibility on the behavior of steel frames

Abstract The first part of this paper presents an analytical procedure for the analysis of framed structures considering the flexibility of steel beam-to-column connections. This is followed by a presentation of several numerical examples to enumerate the behavior of these frames. Finally, some phenomena that are associated with flexibly connected frames are discussed.

Seismic analysis and assessment of a skew highway bridge

Abstract The seismic response of a skew reinforced concrete box girder bridge—the Foothill Boulevard Undercrossing—is analyzed and studied using finite element models. The effects of superstructure flexibility, substructure boundary conditions, structural skewness and stiffness eccentricity are assessed using spectral analyses. The results show that the internal forces and displacements of the supporting columns as well as the displacement of the deck will be underestimated if one neglects the flexibility of the bridge deck. The study also demonstrates that the seismic response of the bridge is affected quite noticeably by the boundary conditions of the bridge columns and the overall skewness of the bridge. Based on this study, a theory to explain the failure of this bridge is presented.

A parallel frontal solver on the Alliant FX/80

Abstract A methodology for large-scale structural analysis using a parallel frontal solution algorithm is presented. The algorithm is well suited for concurrent processing by a multiple instructions, multiple data (MIMD) machine. The method is very adaptive to a parallel environment because of the inherent parallelism of the approach, which does not require the formation of the global structure stiffness matrix. Thus large memory and storage space are not required. The method can be applied to large-scale structures which normally cannot be analyzed efficiently by a conventional serial computer. Numerical studies using the Alliant FX/80 multiprocessor computer at the Northeast Parallel Architectures Center (NPAC) of Syracuse University indicate that significant speed-up can be achieved by applying the method to large-scale problems. The method is general and can be extended to enhance its applicability and versatility.

DYNAMIC RESPONSE OF SKEW HIGHWAY BRIDGES

A simplified bridge model suitable for use in a parametric study of short-span skew highway bridges and bridges with stiffness eccentricity is presented. The proposed model is simple, yet it captures all essential features that affect the dynamic response of these bridges. Using this simplified model, formulas for computing earthquake response of the bridges are developed and parameters that significantly influence the dynamic response of the bridges are identified. The study indicates that the response of a given skew bridge depends not only on its deck aspect ratio, the stiffness eccentricity ratio, the skew angles, its natural frequencies, but also on the frequency ratio. In particular, the rotational to translational frequency ratio has a pronounced influence on the dynamic response of the bridge. It is found that skew bridges with high rotational to translational frequency ratios often exhibit less dependence on such parameters as deck aspect ratios, stiffness eccentricity ratios and skew angles.

Frame analysis with panel zone deformation

Abstract Conventional analyses of frameworks are usually carried out without considering the effect of panel zone deformation on frame behavior. As a result, center-to-center distances rather than clear spans are used for the lengths of the members. As is evident from experimental studies, the effect of panel zone deformation has a pronounced influence on frame behavior. In particular, the strength and drift of the frame will be affected if panel zone deformation is taken into consideration in the analysis. In this paper, various deformation modes of the panel zone are identified. A simple model which can be used to represent all these modes is then presented. The validity of this model is established by comparison with experiments on joint subassemblages. Finally, a two-bar frame with different behavioral joint models is analyzed numerically to demonstrate the importance of using realistic models in frame analysis.

Stability design criteria for steel members and frames in the United States

Abstract This paper attempts to give designers an insight into the beam-column problem. The important parameters such as (i) the ultimate strength of columns and beams which are special cases of beam-columns and (ii) secondary effects (P-δ and P-Δ), that should be considered in the ultimate strength design of beam-columns, are identified and discussed. Ultimate strength design interaction equations recommended and proposed in the United States for different categories of beam-columns are then presented. Important features of these equations are summarized. Directions of further research are indicated.

Torsional effects on short-span highway bridges

Abstract The torsional effects on short-span highway bridges are investigated for two situations: post-design asymmetric bridges and nominally symmetric bridges subject to seismically induced torque. The study indicates that for post-design asymmetric bridges the presence of accidental post-design asymmetric factors significantly influences the dynamic response of bridges having a small rotational to translational frequency ratio. For nominally symmetric bridges, the seismically induced torque often triggers rotational motions, which tend to aggravate the bridge deck displacements and magnify the shear forces of the supporting columns. If necessary, this torsional effect should be considered in the seismic design of bridges.