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The use of metal-organic frameworks (MOFs) so far has largely relied on nonspecific binding interactions to host small molecular guests. We used long organic struts (~2 nanometers) incorporating 34- and 36-membered macrocyclic polyethers as recognition modules in the construction of several crystalline primitive cubic frameworks that engage in specific binding in a way not observed in passive, open reticulated geometries. MOF-1001 is capable of docking paraquat dication ([PQT.sup.2+]) guests within the macrocycles in a stereoelectronically controlled fashion. This act of specific complexation yields quantitatively the corresponding MOF-1001 pseudorotaxanes, as confirmed by x-ray diffraction and by solid- and solution-state nuclear magnetic resonance spectroscopic studies performed on MOF-1001, its pseudorotaxanes, and their molecular strut precursors. A control experiment involving the attempted inclusion of [PQT.sup.2+] inside a framework (MOF-177) devoid of polyether struts showed negligible uptake of [PQT.sup.2+], indicating the importance of the macrocyclic polyether in [PQT.sup.2+] docking.

In order to meet the emerging trend of performance-based design of structural systems, attempts have been made to develop a multiobjective optimization technique that incorporates the performance-based seismic design methodology of concrete building structures. Specifically, the life-cycle cost of a reinforced concrete building frame is minimized subject to multiple levels of seismic performance design criteria. In formulating the total life-cycle cost, the initial material cost can be expressed in terms of the design variables, and the expected damage loss can be stated as a function of seismic performance levels and their associated failure probability by the means of a statistical model. Explicit formulation of design constraints involving inelastic drift response performance caused by pushover loading is expressed with the consideration of the occurrence of reinforced concrete plasticity and the formation of plastic hinges. Due to the fact that the initial material cost and the expected damage loss are conflicting by nature, the life-cycle cost of a building structure can be posed as a multiobjective optimization problem and solved by the [epsilon]-constraint method to produce a Pareto optimal set, from which the best compromise solution can be selected. The methodology for each Pareto optimal solution is fundamentally based on the Optimality Criteria approach. A ten-story planar framework example is presented to illustrate the effectiveness of the proposed optimal design method. DOI: 10.1061/(ASCE)0733-9445(2007)133:10(1462) CE Database subject headings: Frames; Concrete, reinforced; Optimization; Life cycles; Plastic hinges; Inelasticity; Drift.

A companion paper has described the analytical development of a panel zone dissipator modular node (PZ-MN) prototype for use in seismic-resistant steel moment frames. The PZ-MN dissipates energy through stable yielding of its panel zone, an objective accomplished by mitigating the effects of panel zone distortion on the surrounding members. The PZ-MN is configured directly for this purpose through a casting process. This paper presents experimental verification of the PZ-MN prototype. This process relied heavily on interaction with industry partners to create a castable and constructible shape. The PZ-MN prototype was cast at full scale, fabricated and subjected to FEMA-350 qualification testing with and without gravity load. The PZ-MN prototype exhibited remarkable performance, greatly exceeding qualifying drift angles and possessing exceptional hysteretic characteristics. Using models based on these characteristics, frame performance is evaluated. Design guidelines are given on the basis of the analytical and experimental results. DOI: 10.1061/(ASCE)0733-9445(2007)133:10(1404) CE Database subject headings: Seismic design; Steel frames; Welds; Connection; Full-scale tests; Dynamic analysis.

A panel zone dissipator modular node (PZ-MN) has been developed for use in seismic-resistant steel moment frames. The PZ-MN is configured directly for optimal seismic performance through a casting process. The PZ-MN dissipates energy through stable yielding of the panel zone. This objective is accomplished by mitigating the effects of panel zone distortion on surrounding members and connections. Field welds are removed from critical cross sections and demands are redirected in noncritical paths. A cast piece easily accommodates the geometries and features to meet this objective. The PZ-MN was developed through a comprehensive analytical research program and verified through full-scale experimentation. This paper describes the analytical development stage. Investigation of trial configurations, key parameters, and enhancements resulted in a prototype design for the PZ-MN. The PZ-MN prototype shows the potential for excellent seismic performance, including under the combined effects of lateral and gravity load. This performance is experimentally verified in a companion paper. DOI: 10.1061/(ASCE)0733-9445(2007)133:10(1393) CE Database subject headings: Seismic design; Steel frames; Welds; Connections; Nonlinear analysis; Modular structures.

A computational analysis method is presented to investigate the potential energy of fully nonlinear framed structures and other energy characteristics due to earthquake ground motions. The overall potential energy is directly related to the stiffness of the structure, and it consists of three components in a fully nonlinear system: (1) strain energy representing the storing energy that is associated with the linear elastic portion of the structural response; (2) higher-order energy representing the energy associated with the geometric nonlinear effect of the overall structural response, which is derived from finite element method; and (3) plastic energy representing the energy dissipated by material inelasticity of the structure, and it is being derived analytically. The merit of proposed analysis method lies in the uncoupling of geometric nonlinearity and material inelasticity effects before solving for the equation of motion, and this leads directly to the analytical representations of each energy form. Both plastic energy and higher-order energy based on single-degree-of-freedom system are studied in detail to demonstrate the beauty of the proposed analysis method. In addition, a method of generating energy density spectra is also proposed, which is useful to enhance the understanding energy characteristics in seismic analysis. Finally, a five-story frame is used as a numerical example to illustrate the effectiveness and robustness of the proposed method. DOI: 10.1061/(ASCE)0733-9399(2007)133:10(1061) CE Database subject headings: Energy dissipation; Inelasticity; Framed structures; Seismic analysis.

A novel approach for seismic nonlinear analysis of inelastic framed structures is presented in this paper. The nonlinear analysis refers to the evaluation of structural response considering P-delta effect, which is in the form of geometric nonlinearity, and inelastic behavior refers to material nonlinearity. This novel approach uses finite element formulation to derive the elemental stiffness matrices, particularly to derive the geometric stiffness matrix in a general form. At the same time, this approach separates the inelastic displacement from total deflection of the structure by applying two additional constant matrices, namely, the force-recovery matrix and the moment-restoring matrix in the force analogy method. The benefit behind this treatment is explicitly locating and calculating the inelastic response, together with strategically separating the coupling effect between the material nonlinearity and geometric nonlinearity, during the time history analysis. Comparison with the traditional incremental methods shows that the proposed method is very time efficient as well as straight-forward. One portal frame and one five-story frame are used as numerical examples to illustrate and verify the robustness of current approach. DOI: 10.1061/(ASCE)0733-9399(2006)132:9(959) CE Database subject headings: Dynamic analysis; Material properties; Inelastic action; Framed structures; Seismic effects; Nonlinear analysis.

This article presents a newly developed modal strain energy decomposition method for damage localization that is capable of identifying damage to individual members of three-dimensional (3D) frame structures. This method is based on decomposing the modal strain energy of each structural member (or element) into two parts, one associated with the element's axial coordinates and the other with its transverse coordinates. In turn, two damage indicators are calculated for each member to perform the damage localization analysis. Implementing this method requires only a small number of mode shapes identified from both the damaged and baseline structures. Numerical studies are conducted of a 3D five-story frame structure and also a complicated offshore template platform, based on synthetic data generated from finite-element models. In addition to providing theoretical insights to illustrate the advantages of using this newly developed method, this article also demonstrates numerically that the new method is capable of localizing various kinds of damaged elements (a vertical pile, horizontal beam, or slanted brace) at a template offshore structure. DOI: 10.1061/(ASCE)0733-9399(2006)132:9(941) CE Database subject headings: damage; decomposition; framed structures; localization; modal analysis; strain energy.

The passive mega-subcontrolled structure proposed recently is a new form of structure associated with the design and construction of supertall buildings. However, a shortcoming still exists in its structural configuration. In this paper, a new configuration of the passive mega-subcontrolled frame is proposed. A more realistic analytical model of this structure subjected to random wind loads is presented, in which the substructures are treated as a multi-degree-of-freedom (MDOF) system and a nonwhite stochastic process in time and space is used. The dynamic equations and the response spectrum expressions, as well as the mean square response expressions, are derived on the basis of complex modal-analysis theory. A practical steel passive mega-subcontrolled frame is investigated; it is designed with reference to the conventional mega-subframe used in the Tokyo City Hall. The influence of the relative mass ratio and the relative stiffness ratio on the controlling effectiveness is investigated: and a proposed relative stiffness region, which is very useful in practical engineering design, is first presented. The corresponding computing results demonstrate that the structural configuration proposed here has extraordinary effectiveness in controlling displacement responses and acceleration responses, and the shortcoming that existed in the previously presented configuration can be overcome effectively. DOI: 10.1061/(ASCE)0733-9399(2005) 131 : 10(1046) CE Database subject headings: Frames; Wind loads; Buildings, high-rise; Vibration; Japan; Control systems.

A robust finite element procedure for large deflection and inelastic analysis of imperfect steel frames with semirigid base is proposed and the nonlinear behavior of semirigid frames with various modes of initial imperfection is studied. Special consideration to the method of simulating the frame initial imperfections is given. The refined plastic hinge method is used for modeling of the section plastification and both the notional force and the initially imperfect geometry of the frames obtained by an eigenvalue buckling analysis are used for modeling the geometrical imperfections. The difference between the notional force and the eigenbuckling mode models and of semirigid base connections are studied. From the examples reported in this paper, the effective length is not required to be assumed and the advanced analysis is noted to be applicable to practical design of this type of steel frames. CE Database subject headings: Imperfection; Connections, semi-rigid; Hinges; Frames; Finite element method; Inelastic action.

Design and detailing requirements of seismic provisions for concentrically braced frames (CBF) were specified based on the premise that bracing members with low KL/r and b/t will have superior seismic performance. However, relatively few tests investigate the cyclic behavior of CBF. It is legitimate to question whether the compression member of CBF plays as significant a role as what has been typically assumed explicitly by the design provisions. In this paper, the existing experimental data are reviewed to quantify the extent of hysteretic energy achieved by bracing members in compression in past tests, and the extent of degradation of the compression force upon repeated cycling loading. Although it is recognized that many parameters have an influence on the behavior of braced frames, the focus of this paper is mostly on quantifying energy dissipation in compression and its effectiveness on seismic performance. Based on the experimental data review from previous tests, it is found that the normalized energy dissipation of braces having moderate KL/r (80-120) do not have significantly more normalized energy dissipation in compression than those having a slenderness in excess of 120. The normalized degradation of the compression force envelope depends on KL/r and is particularly severe for W-shaped braces. DOI: 10.1061/(ASCE)0733-9445(2005)131:4(552) CE Database subject headings: Building frames; Slenderness ratio; Energy dissipation; Compression; Bracing; Seismic response.

In this paper, a nonlinear three-dimensional finite element (FE) model of light frame buildings capable of static and dynamic analysis is presented. The model can accommodate various material and structural configurations, including multilevel structures. A customizable commercial general purpose FE code is used in the analytical investigation of the model formulation. The model as presented is capable of predicting the hierarchical response of the structure from the global, such as the maximum displacement, down to the individual demand placed on substructures such as a nailed joint connection. This capability is provided by replacing individual substructure responses, e.g., in-plane responses of shear walls, with energetically equivalent and more computationally efficient nonlinear springs. The predictive ability of the model is experimentally validated, in Part II, based on global and local response comparisons, considering measures of energy dissipation, displacement, and load. Validated, this model provides the analyst a powerful tool to investigate various aspects of light frame building behavior under static and dynamic loading. DOI: 10.1061/(ASCE)0733-9445(2005)131:4(676) CE Database subject headings: Three-dimensional models; Framed structures; Building frames; Finite elements; Hysteretic systems; Nonlinear analysis.

In this paper, a nonlinear three-dimensional finite element model, presented in Part I, capable of static and dynamic analysis is compared with the results of an experiment on a full-scale asymmetric light frame building. The predictive ability of the model is experimentally validated based on global and local response comparisons, using measures of energy dissipation, displacement, and load. Comparison of modeling and experimental test results show that the energy dissipation, hysteretic response, the load sharing between the walls, and the torsional response are estimated reasonably well. The model predicts higher order response parameters such as energy dissipation more accurately than load or displacement. Validated, this model provides a tool to investigate various aspects of light frame building behavior under static and dynamic loading. DOI: 10.1061/(ASCE)0733-9445(2005)131:4(684) CE Database subject headings: Framed structures: Building frames; Model verification; Wooden structures; Nonlinear analysis; Three-dimensional models; Finite elements; Hysteretic systems.

A post-tensioned friction damped connection (PFDC) for earthquake resistant steel moment resisting frames (MRFs) is introduced. The connection includes friction devices on the beam flanges with post-tensioned high strength strands running parallel to the beam. The connection minimizes inelastic deformation to the components of the connection as well as the beams and columns, and requires no field welding. Inelastic analyses were performed on a six-story, four-bay steel MRF with PFDCs to study its response to strong ground motions. The PFDC--MRF was designed using a performance based design approach. Results show the MRF with PFDCs has good energy dissipation, self-centering capability, and strength. Variability in the maximum friction forces that develop in the friction devices was determined not to have a significant effect on the MRF performance. The analyses indicate that the seismic performance of a MRF with PFDCs can exceed that of a MRF with conventional moment resisting connections. DOI: 10.106l/(ASCE)0733-9445(2005)131:4(529) CE Database subject headings: Post tensioning; Steel; Friction; Building frames; Connections; Seismic response.

Reliability analysis of structural systems often requires finite element (FE)-based simulation to estimate failure probabilities. Common simulation methods, even those incorporating variation reduction techniques, usually involve a very large number of FE analyses to achieve acceptable accuracy. A recently developed directional approach significantly improves the efficiency of directional simulation by utilizing deterministic point sets to preserve the underlying joint probability distribution of the random vector describing the structure and by employing neural networks to focus the simulation effort in the significant regions. This paper investigates the application of this method to structural system reliability analysis. The method is illustrated using deformation-based system limit states, proposed for performance-based engineering, for two plane steel frames. CE Database subject headings: Computation; Finite element method; Probability; Structural reliability; Simulation: Steel frames; Structural engineering.

In an attempt to trace the collapse of structures in seismic events, this paper discusses an alternative approach to the formulation and solution of the large deformation inelastic problem in planar frame structures. A beam-column element that includes the effect of geometric and material nonlinearities is developed using the flexibility approach. The formulation uses force interpolation functions and the principle of virtual forces in rate form. It is formulated in the context of the state space approach, where the global system of conservation equations and the local constitutive equations are solved simultaneously. The differential-algebraic system solver is used to solve the resulting system of equations. Numerical examples are presented to illustrate the functionality of the analysis using the newly formulated approach. DOI: 10.1061/(ASCE)0733-9445(2002)128:12(1575) CE Database keywords: Collapse; Deformation; Framed structures; Inelastic action.

Building structures subjected to fire will generally experience complex force-temperature paths. In this paper, these paths are expressed simply by two basic paths: the path of constant forces but subjected to elevated temperature (FT path), and the path of constant temperature but subjected to applying forces (TF path). A total of 13 beam specimens subjected to two such basic paths were tested. The results show that the fire resistance for the FT path is different from that for the TF path; the former is always greater than the latter, and the two are similar only when the temperature exceeds 525 [degrees] C or thereabout. However, there are always great differences between their deformations. Therefore, the behaviors of reinforced concrete flexural members subjected to fire are closely dependent on the force-temperature paths they experience. Thus, in fire-resistant design, especially for statically indeterminate structures, to more accurately ascertain their fire resistances the force-temperature path factor cannot be neglected. DOI: 10.1061/(ASCE)0733-9445(2002) 128:3(365) CE Database keywords: Concrete reinforced; Fire resistance; Temperature effects; Structural members.

This is the second of two papers discussing the theories and applications of three reinforced concrete (RC) frame elements with bond slip between the reinforcing bars and the concrete. This paper presents the element state determinations for the displacement-based, the force-based, and the Hellinger-Reissner mixed formulations. The convergence, accuracy, and computational times of the three elements are compared through two numerical examples. The distinctive element characteristics in terms of force and deformation discontinuities between adjacent elements are discussed for the three proposed formulations. The ability of these formulations to detect the overall softening response of RC members due to the pullout failure of the rebars in the anchorage zone is also tested. The elements are all able to capture the drop in member stiffness due to the rebar slip and the failure due to bar pullout. The force-based and the mixed elements are, however, much more precise than the displacement-based element. The force-based element is slightly more precise, but the mixed element is numerically more stable. DOI: 10.1061/(ASCE)0733-9445(2002)128:3(356) CE Database keywords: Concrete; Reinforced; Frames; Bonding; Beams; Finite elements; Nonlinear analysis.

Open cross-section, thin-walled, cold-formed steel columns have at least three competing buckling modes: local, distortional, and Euler (i.e., flexural or flexural-torsional) buckling. Closed-form prediction of the buckling stress in the local mode, including interaction of the connected elements, and the distortional mode, including consideration of the elastic and geometric stiffness at the web/flange juncture, are provided and shown to agree well with numerical methods. Numerical analyses and experiments indicate postbuckling capacity in the distortional mode is lower than in the local mode. Current North American design specifications for cold-formed steel columns ignore local buckling interaction and do not provide an explicit check for distortional buckling. Existing experiments on cold-formed channel, zed, and rack columns indicate inconsistency and systematic error in current design methods and provide validation for alternative methods. A new method is proposed for design that explicitly incorporates local, distortional and Euler buckling, does not require calculations of effective width and/or effective properties, gives reliable predictions devoid of systematic error, and provides a means to introduce rational analysis for elastic buckling prediction into the design of thin-walled columns. DOI: 10.1061/(ASCE)0733-9445(2002)128:3(289) CE Database keywords: Thin-wall structures; Columns; Buckling; Cold-formed steel.

This paper outlines the development of a finite element for use in the inelastic second-order analysis of partially (PR) and fully (FR) restrained planar steel frames. The finite element considers spread of plastification within the cross section and along the member length; centroidal shift of the elastic core; a variety of residual stress distributions; and P-[Delta] effects. Nonlinear spring elements are used in modeling beam-end connections. An arc-length technique (with iteration) is used in the analysis of individual beam-columns, while constant-work simple Euler stepping (no iteration) is used in the nonlinear analysis of frameworks. Full nonlinear load-deformation response of planar beam-columns and frames is computed. Accuracy is demonstrated through comparison with previously published analytical results. It is shown that concentrated plasticity models may lead to an overestimation of connection rotation in PR frameworks. A companion paper discusses the inelastic ultimate load analysis of large steel PR frameworks and evaluation of connection classification systems.

A new procedure for determining eigenvector derivatives of a complex structural system has been developed. The novel scheme uses the dynamic flexibility method and is based on the practical complete modal space approach. It can be used on systems with or without repeated eigenvalues while the numerical results obtained are precise. There is also a reduction in computer processing time while engineers would find that it is easier to do theoretical computations using the proposed method.

In this paper, the results of static and cyclic lateral load tests on the wooden frames that constitute an ancient Korean commoner's house are presented. The typical form of beam-column joint used for this type of house is a tenon. Full-scale models of two types of frames are used for testing. The effects of joint type and wooden lattice on the lateral loading capacity and the failure modes of frames are investigated. The tests show a significant nonlinearity and inelasticity in the load-displacement curve. The general failure modes of joints are either shear or bending failure at the mortise branches of a tenon. The nonlinear hysteretic characteristics of the frame are identified and modeled by the so-called modified Double Target model.

Several bidirectional tests were performed on structural clay tile infilled steel frames to assess the interaction of in-plane and out-of-plane forces and to understand the behavior of damaged infills. Tests consisted of in-plane and out-of-plane uniform lateral load tests, out-of-plane drift tests, sequential tests (in-plane damage followed by out-of-plane loading, and out-of-plane damage followed by in-plane loading), one combined in-plane and out-of-plane test, and a seismic shake table test. Infill panels had sufficient out-of-plane stability under both inertial (uniform) loads and imposed drift loads. This stability was due to arching, or the development of in-plane membrane forces. The interaction of in-plane and out-of-plane forces was not significant, particularly at moderate levels of loading. The primary effect of sequential loading was loss of in-plane stiffness due to elimination of the diagonal cracking limit state. Under combined in-plane and out-of-plane loading, the infill remained remarkably stable, even after much damage to the masonry panel.

The relationship between axial load and end-rotational stiffness is derived. Reliable postelastic performance of concentrically braced frames requires that braces be designed for predictable buckling behavior. For cross-braced frames, restraint provided by the complementary brace (including both translational and rotational stiffness) can have a significant effect on buckling strength; this effect is complicated by the tension in the complementary brace, which increases its stiffness. Differential equations of stability are employed to determine upper and lower bounds of buckling strength, as well as to formulate the relationship between axial load and rotational stiffness. Given current detailing practices, it is desirable to control the plane of buckling so that the ductility of end-gussets is utilized; values of the effective length factor are provided to allow the design of braces for predictable buckling behavior. Out-of-plane buckling of systems with crossed torsionally stiff braces may place severe torsional demands on the end-gussets of the brace in tension; in-plane buckling is a viable alternative if it can be shown that it occurs at a lower load than out-of-plane buckling.

The American Institute of Steel Construction load and resistance factor design (AISC-LRFD) Specification states that second-order effects should be considered in the design of frames; however, most designers are experienced only in first-order analysis. To accomplish the second-order design requirement, the AISC-LRFD Specification provides an approximate method to account for the second-order effect bases on first-order analysis, where moment amplification factors [B.sub.1] and [B.sub.2] are introduced to account for the P-[Delta] effect (member instability) and P-[Delta] effect (frame instability), respectively. However, the [B.sub.1] factor of the AISC-LRFD Specification may vary greatly from the exact solution, especially when the member is under a high axial load. In this paper, a new moment amplification factor [Mathematical Expression Omitted] is proposed for calculating the P-[Delta] effect in the design of steel beam-columns. Parametric studies were performed to examine the accuracy of the proposed moment amplification factor and to compare it with that from theoretical analysis and from current design specification. It was found that the proposed method is simpler and more accurate than that given in the current design specification.

The effective length factor, K, of a column is dependent on the lateral restraint imposed on it. The sway and no-sway alignment chart K-factors are special cases when the lateral restraint is zero and infinite, respectively. Therefore, they are not directly applicable to practical columns. A general formula is derived that is applicable to columns in fully braced, partially braced, and unbraced frames, i.e., to cases in which the lateral restraint can vary from minus infinity to plus infinity. The advantage of using the formula is demonstrated by comparing it with other methods. For example, the AISC LRFD Specification Commentary does not allow K-factors less than the limit imposed by Eq. C-C2-4b to be used when calculated by means of Eq. C-C2-4a. With the proposed formula this restriction is removed, thereby increasing the design range. It also shows that K-factor formulas based on the stiffness concept become increasingly unconservative as the lateral restraint becomes very large.

The traditional building practices used for the construction of residential buildings in Kuwait proved to be extremely effective in resisting fire and enduring severe structural damage from shelling during the 1990 Iraqi invasion of Kuwait. This paper describes and illustrates how infill walls acted as wail-bearing elements to keep a building standing, even after the loss of supporting members. Two reinforced concrete (RC) frame structures, both of which were subjected to direct shelling and lost main supporting elements, are presented. The first frame does not have infill walls, while the second has them. The difference in behavior between the two cases shows the effectiveness of infill walls in preventing progressive collapse under such abnormal loading. A finite-element technique using the modified interface friction element, which represents the interface between the frame and the infill, is presented herein to explain the behavior of frames with infill walls before and after shelling. The finite-element method gave a good correlation with the actual behavior of the cases investigated.

This paper reports the test results from a study investigating the influence of openings on the lateral resistance of wood-based shear walls built with both standard and oversize oriented strand board panels under monotonic and cyclic loading conditions. Test results showed that the application of nonstandard oversize panels significantly improved the performance of the perforated shear wails compared with standard 1.2 x 2.4 m panels. Door and window openings caused a significant decrease in the strength and stiffness of the walls and precipitated a change in failure mode, especially for wails with oversize panels. Although nail failure modes were commonly observed in walls without openings, a combination of nail and panel failures were observed in shear walls with openings. A newly proposed cyclic test protocol was used that consisted of fewer but more severe displacement excursions, compared with many other test protocols. This was believed to better reflect typical earthquake excitation and avoid low cycle nail fatigue failures, which were observed previously with long sequence cyclic test protocols.

This paper presents a detailed investigation into the contribution of plasterboard to the lateral resistance of cold-formed steel-framed residential structures. It details the development of a finite-element model for laterally loaded plasterboard-lined cold-formed steel wall frames for residential construction. The model utilizes nonlinear element properties and three-dimensional geometrical configurations and is capable of simulating the influence of boundary conditions such as corner return walls and ceiling cornices. The analytical results from the finite-element model were successfully verified against experimental racking test results. A sensitivity analysis was conducted using the model to study the influence of return walls, ceiling cornices, and wall length on the lateral capacity of the wall system. It is concluded that a wall with corner return walls, ceiling cornices, and skirting boards has more than three times the lateral capacity of an identical isolated wall panel. The relationship between the wall length and the ultimate lateral load-carrying capacity of the wall system is dependent on the presence of these boundary conditions.

Traditional timber connections with wood pegs are encountered in the renovation and rehabilitation of historic wood structures and in the construction of new structures where rustic appearance and traditional methods are desired. This study examined four types of traditional connections: mortise and tenon, mortise and tenon with a shoulder, mortise and tenon with a shoulder and a knee brace, and fork and tongue. A total of 60 specimens, primarily white oak and Douglas fir, were tested. About a quarter of the specimens were assembled and allowed to season under simulated in-service load. All specimens were tested under simulated gravity load up to failure or to about five times typical design load. Some knee-braced specimens were retested to simulate lateral loads. Test results showed that joint behavior is primarily linear. A tightly fitting joint carries load with less peg damage than a loose joint allows. A mortise and tenon with a shoulder performs better than a mortise and tenon or a fork and tongue. At typical occupancy sustained live plus dead load levels, the effects of warping and checking caused by drying shrinkage overshadow any damage caused by the sustained load. Analysis of structures employing these connections requires that the behavior of the wood-pegged joints be included in a reasonable manner. In frames without knee braces, the joints can be modeled as pinned connections. In frames with knee braces, the post-to-beam and knee-brace connections can be modeled as pinned, although the reduction in effective axial stiffness of the knee brace caused by the wood pegs must be included. The effects of shear deformations should be incorporated into the analysis.

A study was conducted to determine the feasibility of two different approaches for reliability estimation of spacecraft structures and their components. The first approach uses Monte Carlo simulation techniques to analyze the structure, while the other uses the stochastic finite element method to calculate failure probabilities. These approaches were tested using examples in spacecraft design. Results showed that both methods are viable.

Static and dynamic tests were conducted on wood frame shear walls to (1) determine the wall resistance to lateral loading; (2) examine the wall performance under fully reversed cycles of dynamic loading; and (3) compare the static and dynamic performance as measured using the same test facility. Tests were conducted on standard 2.44 by 2.44 m (8 by 8 ft) walls, constructed of plywood or oriented strand board sheathing. Four specimens were tested statically using the traditional ASTM E-564 test procedure: three half-cycles, loading monotonically to failure. Eight specimens were tested dynamically, using a proposed test standard that was recently developed by the Structural Engineers Association of Southern California. A comparison of the static and dynamic test results demonstrates several key differences. The ultimate loads measured in the dynamic tests are slightly less than those measured in the static tests; however, the ductility of the wall, when measured dynamically, is between 34 and 42% less than the corresponding static ductility. Furthermore, damage in the static tests is characterized by the pulling away of the sheathing from the frame, extraction of the sheathing nails, and splitting of the bottom plate. Damage in the dynamic tests is generally confined to pullout and fatiguing of the sheathing nails, which eventually break off. The dynamic tests show a reduction in load and stiffness and pinched hysteresis with continued cycling at a given displacement. The results of this study suggest that the actual load factors for a shear wall subjected to an earthquake will be significantly lower than the intended design.

Discrete ground structure topology optimization design methods have to date received considerable attention in structural engineering. An alternative class of structural topology optimization methods, which have not yet received much attention in structural engineering, but which have undergone considerable development in the past decade, are the so-called continuum formulations. In this work, a continuum structural topology optimization formulation is presented and applied to the concept design optimization of structural bracing systems that are needed to stiffen tall structures against sidesway under lateral-wind and seismic-type loading. Although demonstrated here in the context of these specific design examples, continuum structural topology optimization methods are believed to hold potential as a design tool for a wide range of civil engineering type structures. A variety of continuum topology design formulations, including static compliance minimization and eigenvalue optimization, are explored, and solution parameters are varied to show that a number of design possibilities can be realized as solutions.

Identical mathematical expressions for viscoelastic and viscous damper-brace components are derived as the function of two fundamental nondimensional parameters. These two parameters are used to investigate the properties of viscoelastic (VE) and viscous (VS) systems by conducting parameter analysis. Usually both VS and VE damper-brace components provide added stiffness and damping to the whole system. The magnitude of the added stiffness and damping depends not only on the damper, but also on the interaction of the damper with other members of the frame. Under conditions of low frequency and stiff brace, the added stiffness provided by a VS damper-brace component is negligible. based on harmonic theory, closed-form solutions for seismic response prediction are presented and are used to determine the optimal design. As an example, the seismic performance of a 10-story steel frame incorporated with VE and VS dampers is studied.

The seismic damage analysis of steel frames based on the use of global evaluation indices is addressed, A general procedure is proposed aimed at estimating the degree of damage induced by severe earthquakes in structures not supplied with monitoring systems. Special reference is made to the Park-Ang, McCabe-Hall, and plastic fatigue indices. The procedure is characterized by a form of automatic calibration of the free coefficients contained in the expressions of these indices. This allows one to constrain the arbitrariness in the coefficient choices, representing the greatest source of uncertainties for practical damage field assessment. Story stiffness degradation and permanent interstory displacements are assumed as the a posteriori measurable quantities upon which the reliability of the computational predictions supporting damage estimation are checked. The suitability of this procedure as well as of the considered indices for seismic damage characterization are discussed with reference to two case studies, represented by one shear-type and one concentrically braced, two-story plane steel frame, experimentally tested to failure.

Hollow sections are generally either circular-to-circular (CCHS) or rectangular-to-rectangular (RRHS). Structures with circular braces and rectangular chords (CRHS) may have advantages in certain applications, combining a simple joint geometry for fabrication and relatively lower stress concentration factors (SCFs). Seven different CRHS joints were fatigue tested in constant amplitude axial loading. SCFs were measured experimentally and compared with various parametric formulas. The SCF values for CRHS joints were found to be between those of CCHS and RRHS joints. On the basis of measured SCF values for CRHS joints, the fatigue strength was in good agreement with current fatigue design codes. Parametric formulas for RRHS joints were in all cases found to give conservative prediction of SCF. Lacking more rational prediction methods, these formulas in combination with the DEn T curve/AWS X2 curves for tubular joints may be used in fatigue design of CRHS joints.

This paper describes the behavior of profiled concrete shear panels that may be used as core walls in framed construction. This research developed as a part of a larger program of work on a novel form of composite walling system that utilizes double skins of profiled steel sheeting to form a sandwich construction. The work reported here involves the profiled concrete alone and provides information on the behavior of concrete walls that may be formed with a profiled surface. Model tests of 1/6 scale using micro-concrete confirmed that the diagonal tension limit state should be the design criterion and the shear resistance of the profiled panels can be derived from its equivalent plain concrete panel. Compared to plain concrete panels, the state of stress within the panel and its boundaries is changed due to profile geometry. It has been found that a reduction factor may be introduced in the design equation to take into account the effect of hysteretic application of load. Finite-element simulation of the profiled panels was found to be good enough to predict the precracking behavior.

The nonlinear static and dynamic responses of individual steel braces under cyclic end displacement are studied in this paper using a fiber-type beam-column model that employs a realistic hysteretic stress-strain law and includes the effect of large displacement, strain hardening, gradual spread of yielding, and proper coupling of the axial and flexural yielding. The study considers square tube braces of different sizes and end conditions, and focuses on the effect of internal inertia as well as the magnitude and distribution of the fiber strain in the members. It is found that the importance of inertia depends on the slenderness of the members and the frequency of the end displacement input. Under certain conditions, the effect of inertia can be very significant and its inclusion can lead to deformation modes fundamentally different from those predicted by quasi-static analysis. The inelastic deformation in the braces is highly concentrated and is affected by factors including member size, end conditions, and the number of load cycles.

The subject matter of this paper is essentially an extension of the moment distribution method of analysis and with the aim of offering a simple approach to the construction of influence line diagrams for continuous structures, the members of which can be either of constant or of variable cross section. The distributions of the fixed-end moments are similar to the Hardy-Cross approach except that they are performed algebraically rather than by successive arithmetical approximations. The results are a series of simple equations with only one unknown, which can be easily evaluated with the aid of a desk calculator or by elementary programming for the computer. These simple equations can be expanded to include the effects of sway. They also include the effects of degrees of end fixation.

Members of a plane-frame structure may be subjected to a combination of lateral loads, end moments, and axial forces. Analysis of such a structure may be classified as elementary, first-order or second-order, depending on the load conditions, magnitude of displacements, and method of solution. A numerical procedure is presented in this paper for the solution of geometrically nonlinear problems considering second-order effects. After a brief literature review, the paper presents the assumptions pertinent to the research; the relationship between the engineering strain and Green strain tensor considering small strain and moderate to large rotations; finite-element consideration in the derivation of the incremental stiffness matrices using increments of total potential energy and the concepts of a variational method; a procedure for the solution of the nonlinear problems and its algorithm; numerical examples and comparison of the numerical results with published literature; and conclusions and results. The algorithm that is presented in this paper is useful in identifying the differences between the first- and second-order analysis of structural systems.

The paper is intended to present a numerical and experimental study on the local-overall interactive buckling behavior and ultimate load of I-section steel columns. The numerical method, named the finite strip plasticity coefficient increment initial stress method, is proposed to trace up the interactive buckling ultimate load-carrying capacity of thin-walled plate structures involved in elastic-plastic and large deflection. The detailed solution procedures based on the amended Newton-Raphson iteration technique are presented. The structure discretization degree is reduced by the finite strip method and the computing quantity of elastic plasticity is significantly decreased by means of the section plasticity coefficient concept. Parameters such as column slenderness, web and flange plate width-thickness ratio, welded residual stress, and load eccentricity are considered in this paper. The experimental results of 11 welded I-section steel columns with relatively large plate width-thickness ratio have been found to agree reasonably with the numerical predictions. The results have shown that the column failure brought about by local buckling, overall buckling, or local-overall interactive buckling, and the local buckling of component plates does not mean a complete loss of the load-carrying capacity of the column at once.

A new method for the preparation of inorganic cyanides structure was prepared for Ga(CN)3. The structure is stabilized in most transition metal compounds, though large alkali metals form an ordered array similar to that of the K2MFe(CN)6 family with M = Ni, Co, and Cu. Results show that Ga(CN)3 can be combined to form framework structures MGa(CN)4(M = Li or Cu) and inclusion compounds such that CCl4 substitutes one of the networks in a manner similar to the situation in N(CH3)4-MZn(CN)4 (M = Cu2a or Li2b) [MGa(CN)4 and MZn(CN)4- are isoelectronic].

In recent years nonlinear dynamic analysis of three-dimensional structural models is used more and more in the assessment of existing structures in zones of high seismic risk and in the development of appropriate retrofit strategies. In this framework beam finite-element models of various degrees of sophistication are used in the description of the hysteretic behavior of structural components under a predominantly uniaxial state of strain and stress. These models are commonly derived with the displacement method of analysis, but recent studies have highlighted the benefits of frame models that are based on force interpolation functions (flexibility approach). These benefits derive from the fact that models with force interpolation functions that reproduce the variation of internal element forces in a strict sense yield the exact solution of the governing equations in the absence of geometric nonlinearity. While the numerical implementation of force-based models at first appears cumbersome, simple examples of nonlinear analysis in this paper offer conclusive proof of the numerical and computational superiority of these models on account of the smaller number of model degrees of freedom for the same degree of accuracy in the global and local response. A numerical implementation that bypasses the iterative nature of the element state determination in recent force-based elements is also introduced, thus further expanding the benefits of flexibility-based nonlinear frame models.

A new design model is presented to derive expressions for the elastic effective length factors for columns in unbraced multistory frames. This model takes into account the effects of boundary conditions at the far ends of the columns above and below the column in question. According to the relative bending stiffness of the girders and columns framing at the far ends, the far end conditions can be modeled as rigid, hinged, or fixed. Because the alignment chart model is based on rigid-far-end conditions, it is not applicable in designing columns with either hinged or fixed-far-end conditions. This refined model rectifies inherent problems associated with currently available solutions caused by both the invalid assumption of constant story drift angles and the errors in mathematical formulation. Using the background of extensive numerical studies, a modified design procedure based on the alignment chart is suggested. The proposed design procedure is characterized by both simplicity and accuracy.

Conventional design does not exclude risk of local damage to a structure due to accidental events. Safety of the structure can be improved by ensuring that failure of any of its components does not cause, within an appropriate level of reliability, collapse of the whole structure or a major part of it. In this paper reliability of multistory framed structures subjected to column failure is investigated using a probabilistic method. The method is based on a combination of a nonlinear finite-element structural model and a first-order reliability method. Uncertainties in material properties, geometry, loads, and the structural model itself are taken into account, and their influence on frame reliability is considered. The uncertain parameters appropriate to the strength of reinforcing steel, live load, and the model uncertainty are found to have a major influence on the frame reliability. For three-span frames with different numbers of stories and span-length ratios, critical cases of column failures are identified. As a result it is possible to restrict the number of examined structures. Finally, a simplified probabilistic method is proposed for the reliability assessment of damaged frame structures.

This paper describes an analytical study to investigate the behavior of subassemblages with a range of semirigid connections under different test conditions and loading arrangements. The [[Alpha].sub.plan] concept, which gives an indication of the benefit of the restraint from the beam-to-column connection after incorporating the potentially disadvantageous influence of moment through the connection, is validated. It is noted that the M-[Phi] response is of fundamental importance and the success or failure of semirigid design methods rests on it. However, it is the most difficult parameter to determine accurately. The results in this study have shown that significant variations of the M-[Phi] response have a negligible effect on the load carrying of the column and the behavior of the subassemblage. This implies the precise form of the M-[Phi] response is not important for the column capacity of braced frames. Due to the boundary condition of the model, these results only translate into the braced frame behavior.

There have been controversy and uncertainties surrounding the rotational behavior of conservative internal bending moments in three-dimensional frames. The two contesting representations of conservative internal bending moments are the quasi-tangential and the semitangential moments, each of which has its own shortcoming from the purely physical point of view. This situation must be rectified, as the correct identification of the nature of internal moments is indispensable for reliable buckling and large displacement analysis of three-dimensional structures. This paper presents a new type of conservative moment that has hitherto never been considered in the literature, and demonstrates that the proposed representation of conservative internal moments can be justified on both physical and rigorous mathematical grounds. Various issues relating to finite rotations and the work done by conservative moments in space are also addressed.

Modal reduction methods are a useful alternative to fully discrete matrix models for the efficient simulation of large dynamic response problems in frame analysis. The primary advantage of modal methods is computational efficiency, since they require less memory and fewer floating-point operations relative to conventional dynamic analyses of frames. The most important limitation of modal schemes is the difficulty in capturing strong nonlinear effects while retaining the simplicity of standard modal analysis algorithms. Modal methods obtained from inverse Lanczos iteration constitute a particularly elegant protocol for obtaining approximate time histories of response for nonlinear analyses of large frames and similar flexible structures. Examples underlining the strengths and weaknesses of Lanczos approximations are presented, and conclusions as to the utility of such modal reduction schemes for nonlinear dynamic analysis are drawn.

This paper analyzes dynamic localization of damage in structures with softening inelastic hinges and studies implications for the seismic response of reinforced concrete or steel frames of buildings or bridges. First, the theory of limit points and bifurcation of the symmetric equilibrium path due to localization of softening damage is reviewed. It is proven that, near the state of static bifurcation or near the static limit point, the primary (symmetric) path of dynamic response or periodic response temporarily develops Liapunov-type dynamic instability such that imperfections representing deviations from the primary path grow exponentially or linearly while damage in the frame localizes into fewer softening hinges. The implication for seismic loading is that the kinetic energy of the structure must be absorbed by fewer hinges, which means faster collapse. The dynamic localizations are demonstrated by exact analytical solutions of torsional rotation of the floor of a symmetric and symmetrically excited frame, and of horizontal shear excitation of a building column. Static bifurcations with localization are also demonstrated for a portal frame, a multibay frame, and a multibay-multistory frame. The widely used simplification of a structure as a single-degree-of-freedom oscillator becomes invalid after the static bifurcation state is passed.