W.F. Chen

On the computer-based design analysis for the flexibly jointed frames

Abstract The paper presents a computer-based method that can be easily applied to design practice for steel building frames with flexible joints using small computers. In this development, special attention is paid to the efficient use of computer capacity, and to the simplicity in formulation of the analytical procedures without losing the numerical stability and accuracy of a rigorous solution.

Advanced inelastic analysis of frame structures

Abstract This paper provides a state-of-the-art summary of recent advances in inelastic analysis of space frame structures. Particular attentions are devoted to inelastic modelling of framework components for accurate representation of frame behaviour and the applications of plastic hinge analysis for large-scale framework. Issues related to inelastic buckling and post-buckling unloading of struts, modelling of gradual yielding in steel beam-columns, inelastic modelling of composite floor beams subject to sagging and hogging moments, modelling of building core walls and semi-rigid beam-to-column connections in three-dimensional frameworks are discussed. Numerical examples are provided to illustrate the acceptability of the use of the inelastic models in predicting the ultimate strength and inelastic behaviour of spatial frameworks.

Constitutive models for concrete

Abstract In a recent work, the strain-hardening theory of plasticity has been utilized to formulate a complete stress-strain relationship for concrete material under general three-dimensional stress states up to the ultimate stress condition. No attempt has been made to model more accurately the behavior of fractured concrete, once the ultimate condition or fracture criterion is exceeded. Herein, an extended formulation which includes the constitutive relationships of fractured concrete is described. The extension considers both the kinematics of crack development under a tensile type of failure and the limited plastic flow before crush under a compressive type of failure. The dual representation of concrete behavior in terms of stresses as well as strains at the ultimate or fracture state along with a sudden stress drop which results in local stress redistribution after cracking or crushing are the essential features of this continued development.

Effective elastic moduli of concrete with interface layer

Abstract In this paper, the effective elastic moduli E ∗ and μ ∗ of concrete are obtained from the analytical solution of a two-dimensional microstructural model, and the relationships between E ∗ , μ ∗ and the elastic moduli of each constituent of concrete are studied. Engineering formulas of the effective elastic moduli on the basis of engineering mechanics are also derived and their advantages and limitations are assessed. The variation of E ∗ and μ ∗ values with the basic elastic moduli E1, E2 and E3 of sand (or aggregate), interface and cement paste is given. It is found that the E ∗ and μ ∗ values are affected significantly by the interface layer. The results provide a deeper understanding of the influences of each constituent of the microstructure on the overall behavior of concrete, and an analytical relationship between the nonlinear behavior of concrete and the properties of its constituent. They are also helpful for developing new high-strength concrete materials with an improved strength and stiffness.

Effective length factor of columns in flexibly jointed and braced frames

Abstract In order to rationally evaluate the stability of columns in flexibly jointed and braced frames, the governing equations for determining the effective length factor ( K -factor) of columns are derived considering the effects of the non-linear moment–rotation characteristics of beam-to-column connections. In this study, to derive the equations, the alignment chart approach is used and a recent study on the stability of flexibly jointed frames and the concept of the Shanleys inelastic column buckling theory are applied. With a proper evaluation of the tangent connection stiffness for semi-rigid beam-to-column connections at buckling state and with the introduction of the modified relative stiffness factors, the alignment chart in the present AISC-LRFD specification can be used to find the corresponding column K -factor in flexibly jointed frames. This is described in this paper. Furthermore, using two flexibly jointed and braced portal and one-bay two-story frame examples, the effects of the non-linear moment–rotation characteristics of connections on the K -factor are numerically studied and the K -factors obtained by two simplified methods are compared with the present method.

3-D nonlinear analysis of R/C slender columns

Abstract A numerical technique for the analysis of reinforced concrete slender columns subjected to end loadings is presented. Both material and geometric nonlinearities are accounted for in the present analysis. The incremental deflection approach is applied to calculate the load corresponding to a specified deflection. In this way, the complete load-deflection curve can be traced including the post-peak softening branch. The analysis procedure is applicable to any engineering material and for columns with arbitrary end conditions. However, numerical results presented in this paper are given for isolated columns only.

Behavior of tall buildings with mixed use of rigid and semi-rigid connections

Abstract Semi-rigid connections are rarely used in tall building frames. In this paper, the mixed use of rigid connections with semi-rigid connections for tall building frames as a way to reduce costs is investigated. Using the three-parameter power model for semi-rigid connections, a four-bay eight-story frame is numerically analyzed with four combinations of mixed use of rigid and semi-rigid connections. It is shown that normalized building drift Δ H can be kept under 1 400 by properly selecting the combination of rigid and semi-rigid connections.

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.

Nonlinear analysis of concrete cylinder structures under hydrostatic loading

Abstract The paper reports the recent results of four aspects of nonlinear analysis of concrete cylinder structures under hydrostatic loading—(1) further development of concrete constitutive relationships based on a plasticity formulation; (2) kinematics of failure mode for crushing and cracking concrete; (3) implementing the results in the form of a subroutine suitable for incorporation in a large finite-element analysis computer code (NONSAP program); and (4) studying the behaviour and strength of concrete cylindrical shell structures under hydrostatic pressure. The computer model developed includes the nonlinear displacement and material behaviour which is capable of performing parametric studies on the influence of geometric imperfections, variable restrained end supports, nonlinear nature of stress-strain-fracture response, and the non-conservative nature of hydrostatic loading. Using this computer model, comparisons have been made with the results of tests on actual cylinders, providing the needed confirmation of the validity of the model.

Cap models for clay strata to footing loads

Abstract Plasticity cap models are applied to obtain progressive failure solutions of flexible and smooth strip footings as well as rigid and rough strip footings on an overconsolidated stratum of clay. The comparative study of the elastic-plastic small deformation response of clay to footing loads is made within the framework of finite element analysis with different plasticity models based on a non-associated and the associated flow rule. More specifically, the analyses include the following features: (i) Drucker-Prager perfect plastic model with different methods in determining the material constants using the associated flow rule, (ii) Drucker-Prager perfect plastic model with the associated flow rule and a non-associated flow rule, and (iii) Drucker-Prager perfect plastic yield surface with a work-hardening plane cap and a work-hardening elliptic cap and their associated flow rules.