The behavior of beam-to-column connections under earthquake-type loading has been studied in the past by testing isolated interior or exterior connections. In such tests, the beams are allowed to elongate freely when subjected to large deformation reversal. In a real building, however, the beams may be partially restrained against such elongation. The current design procedures which have been developed on the basis of tests on isolated connections, therefore, ignore the effects of continuity and beam elongation on the performance of connections. In this investigation, the behavior of connections was studied by testing indeterminate frame subassemblies under earthquake-type loading. Six half-scale multiple-connection subassemblies were tested. Each subassembly consisted of a two-bay frame isolated at the column mid-heights. Five single connection subassemblies were also treated to correlate the behavior of connections in multiple-connection subassemblies with the behavior of connections observed by testing isolated connections. Tests have shown that restriction to elongation of beams in indeterminate systems resulted in axial compression in beams which in turn had a significant effect on the performance of connections. The joint shear increased in both interior and exterior connections and the column-to-beam flexural strength ratio decreased. The energy dissipation was not affected by the continuity, but the lateral load resistance increased significantly. The stiffness degradation was more controlled and gradual in the indeterminate subassemblies compared to that observed in isolated connections. Based on the observed mechanism of lateral load resistance and the observed behavior of connections, a procedure is presented to account for the presence of axial compression in the main beams in the design of beam-to-column connections.

Tests on beam-to-column connections have shown that the presence of a slab significantly increased the flexural resistance of the beams under bending which caused tension in the slab. The presence of a slab in reinforced concrete buildings was studied both at the cross sectional and element modelling levels. At the cross sectional level, the experimentally observed progressive slab participation is recognized by a proposed strain distribution in the slab. The proposed strain distribution, along the flange width of a beam-slab section, accounts for the progressive increase in the slab participation with its changing pattern as a function of the strain level at the column face. The analytical prediction of the strain distribution in the slab agrees with the observed strain distribution in the slab of beam-column subassemblies. Furthermore, the increase in the yield curvature and hence a reduced postcracking stiffness of a beam-slab section resulting from the proposed strain distribution as compared with that of the uniform strain distribution is negligible. At the element level, the multi-spring model was modified to account for the recognition of different strength and stiffness in slab-in-tension and slab-in-compression directions of bending. Results from inelastic dynamic analyses of a typical multistory building with different slab participation suggest significant increases in story accelerations and base shears with increasing slab participation. The ductility requirements of the beams and columns are also significantly affected by the recognition of direction dependent stiffness in inelastic analyses. Due to a larger participation of the slab when in tension as compared with that in compression, the ductility requirement in slab-in-compression direction of the beams can get larger. Furthermore, the increased capacity of the beam-slab section affects the flexural and rotational ductility demands placed on the columns which can lead to a strong-beam and weak-column mechanism under lateral loading.

Response nonnormality is investigated for a yielding primary structure and a linear secondary system (P-S) subjected to a normally distributed ground acceleration. The nonlinearity considered is bilinear hysteretic (BLH) yielding in the primary structure. The coefficient of excess (COE), which is a normalized fourth cumulant function, is used as a measure of the nonnormality in the current study. An initial effort focuses on the nonnormality of primary absolute acceleration, since this is the base excitation of a light secondary system. Analytical and numerical results for a nonlinear but nonhysteretic substitute structure are shown to be in good agreement with those from simulation for both mean squared levels and COE of response. It is shown that the acceleration of the primary system can be significantly nonnormal in some situations. Linear substitute methods are used for analytically evaluating the nonnormality of secondary response. The basic concept is to use a linear model with nonnormal excitation to replace the nonlinear primary element with normal excitation, with the goal of matching the trispectrum for the acceleration of these two systems. The trispectrum is the frequency decomposition of the fourth cumulant function. Periodogram analysis (a special FFT technique for obtaining polyspectra) is developed for evaluating the trispectral function of BLH primary acceleration. A two filters model (with a more narrowband fourth cumulant filter) gives good approximations for the COE values of secondary response in most cases including both cascade and noncascade analysis. The probability of failure of secondary response affected by nonnormality due to nonlinearity in the primary is investigated. A nonnormality correction factor (NCF) which is equal to the ratio of the expected life for a Gaussian process to the expected life for the non-Gaussian process is used as an index of the nonnormality effect. Analytical approaches based on knowledge of the first four response cumulants are developed to approximate the NCF values. It is shown that the NCF for first-passage failure generally is more significant than for fatigue failure based on the cases in this study, and both failure modes can be significantly affected by the nonnormality in some situations.

Accuracy and efficiency are investigated for several different methods to obtain time histories of response of coupled linear or nonlinear systems subjected to seismic excitations. Solutions for the composite system of equations are considered, as well as iterative solutions of coupled equations for primary and secondary subsystems. Two new formulations involving stiffness coupling of the subsystems are introduced. For linear systems, the Newmark method for the composite system seems generally to give slightly better results than the primary-secondary methods. For nonlinear systems, the direct stiffness coupled subsystem approach is found to be more efficient than the other methods, especially if the nonlinearity is in one of the smaller subsystems. It is also shown that only Rayleigh damping can simultaneously lead to classical normal modes for the composite and for each subsystem without imposing any restrictions on the stiffness or mass matrices.

A mathematical closed-form solution is presented for steady-state lateral response of earth and rockfill dams in canyons subjected to asynchronous excitation consisting of SH waves incident at an arbitrary angle. The dam is idealized with a 2-dimensional shear beam model and the canyon is considered rectangular in shape and consisting of elastic rock. An extensive series of parametric studies is undertaken to investigate the influence of the main parameters on the steady-state response by considering the effects of the dam-canyon interaction. In particular the study focuses on the effects of: (a) the angle of incidence, (b) the impedance ratio, and (c) the canyon narrowness. The solution is extended for a transient arbitrary excitation consisting of inclined SH waves for use in equivalent linear seismic analysis. (Abstract shortened with permission of author.)

A two-part study of the dynamic response to horizontal base shaking of vertical, rigid and flexible walls retaining a uniform soil stratum is presented. The first part deals with available pseudostatic, limit-state methods of analysis; specifically, the Mononobe-Okabe method and its extension by Richards and Elms. Following a detailed review of these methods and of their underlying assumptions, comprehensive numerical data are presented that elucidate the effects and relative importance of the various parameters involved. Next, the design provisions for such systems recommended in different building codes are reviewed, and their interrelationship is discussed. Both unyielding and yielding walls are examined. In the second part of the study, the different experimental programs on retaining walls that have been carried out over the years are reviewed, and the results obtained for selected tests on walls with a non-deflecting base are compared with appropriate theoretical predictions. The agreement between the experimental results and analytical solutions that do provide for the flexibility of the wall is found to be reasonable.

Rice University's Department of Civil Engineering recently added an electro-hydraulic shaking table facility to their testing laboratory. The purpose of the shaking table is to evaluate the response of scaled model structures subjected to base excitation. Every component of the shaking table was carefully designed or sized to perform optimally at targeted levels. The performance curves for the shaking table which define the maximum load, velocity, and displacements that the table can attain were developed from the specifications of the hydraulic system. Interaction between the shaking table system and the foundation mass was analyzed. The dynamic characteristics of the slip plate and its interaction with model structures were studied to determine the optimum size of the slip plate. The transfer function between the command displacement signal sent to the table and the table displacement was developed analytically for the system, encompassing servovalve hydraulics and the PIDF control system.

One of the main challenges in structural design is to protect the structures from the damaging effects of destructive environmental forces such as wind loads and earthquakes. In this research, flexibility and energy dissipation capability are introduced into the base isolation interface by Magneto-Rheological (MR) Dampers and Semi-Active Independently Variable Stiffness Devices (SAIVS), which act as the connections between the ground and the building base. MR damper alters the damping coefficient and SAIVS switches the stiffness continuously and smoothly. The main objectives of this research are generation of nonlinear spectra of smart base isolated structures and development of new sliding mode control algorithm. To achieve these goals, analytical models of a two-story base isolated building and the corresponding computer program are developed to calculate the dynamic response of structures. The nonlinear spectra demonstrate the efficiency of two types of new dissipative mechanisms in reducing the dynamic response of the base isolated structures subjected to near fault ground motions. It is shown that a combination of MR dampers and SAIVS devices is most attractive in reducing the base displacements substantially without appreciably increasing base shear and superstructure accelerations. In the second part of this study, a new control algorithm based on sliding mode is developed for variable stiffness systems. The response of the structure to different earthquakes is computed using the new sliding mode controller. It is shown that the new sliding mode controller is effective in reducing base displacements and verified by comparing the simulated response with experimental results of the two-story 1:5 scale model tested on the shake table.

The prediction of the seismic behavior of waterfront structures has been considered as a challenging problem and attracted significant research interest, especially after the severe damage of such structures in Niigata, Japan, during the 1964 Niigata Earthquake. The objective of the present study is to improve our understanding of the effects of the backfill material and the wall-soil interface on the seismic behavior and safety performance of retaining walls. The nonlinear analyses are conducted by using an explicit finite-difference formulation for large-deformation analysis of soil-structure systems subjected to seismic excitation. The effects of separation at the wall-soil interface are investigated assuming a fix-based rigid wall and a linearly elastic backfill material. These effects are found to be significant, resulting to wall forces and moments that may be, respectively, 25 and 40% larger than those based on the assumption of no separation. The effects of nonlinearity of a typical saturated backfill soil in a waterfront structure are investigated by considering three different materials, namely, loose sand, medium sand and dense sand. The study examines the effects of relative density, intensity of base excitation, frequency of base excitation and number of cycles of loading on the wall pressures, forces, moments, displacements and rotations. The results show the dramatic effect of the excess pore-water pressure buildup that may lead to liquefaction or cyclic mobility.

The innovative methods proposed in this thesis provide effective and efficient solutions to the reliability problems of burst and collapse of tubes with random geometric imperfections under internal or external pressure. Steel tubes have broad applications in petroleum offshore engineering and must be designed to a safe but yet economical standard. The variation of imperfections from tube to tube necessitates a statistical characterization in which the burst and collapse pressures become random variables. In order to evaluate the burst and collapse pressure of a pipe with deterministic geometric imperfections, the finite element method is employed with a cylindrical shell element based on classical nonlinear shell theory. This element implements the return mapping algorithm for an elastic/plastic material and includes the effects of shell thinning and geometric imperfections. Incorporation of this finite element program into a reliability program developed for this study provides an effective numerical tool for the probabilistic analyses of the burst and collapse problems. For these analyses, the pipe thickness is modeled as an axially homogeneous and circumferentially inhomogeneous Gaussian random field based on measured data from two groups of pipes. Using the developed shell finite element program, Monte Carlo simulation (MCS) can be applied to the burst/collapse reliability problems. However, the enormous computational effort makes MCS infeasible except as a check for selected cases. Unfortunately, the system reliability method does not apply to the present problems because there are an infinite number of design points due to the special structure of the imperfections. Thus, a new approximate method is developed for the burst problem based on the correlations between the minimum thickness and burst pressure. The probability distribution of minimum thickness is obtained through an innovative homogenization procedure. Similarly, the collapse reliability problem is solved through introduction of a homogenized collapse function whose minimum correlates with the collapse pressure. The proposed reliability methods are applied to selected cases and verified by MCS. The effect of length on reliability in burst and collapse is investigated. Compared to MCS, the efficiency of the new methods makes them especially applicable to engineering problems, such as pipeline design and manufacturing quality control.