Thesis (Ph. D.)--University of Texas at Austin, 2006. / Vita. Includes bibliographical references.

This thesis presents the results obtained from a preliminary investigation into the potential application of the friction damping concept to wood structures to improve their seismic response. Sliding friction devices which contain heavy duty brake lining pads have been proposed in order to enhance a wood structure's seismic performance. The devices are mounted onto a structure's shearwalls to dissipate seismic energy input during the wall's deformation in an earthquake. Prototypes of the four friction damping devices were tested to examine their hysteretic behaviour. Conventional full scale, 2.44 x 2.44 m (8 x 8 ft) timber shearwalls, typical of ones used in residential and light-commercial building applications, and ones retrofitted with the friction damping devices were tested on a shake table. Three set of tests were conducted. They involved loading the walls under unidirectional racking, static-cyclic and simulated earthquake loads. Test results from the two types of shearwalls were compared against each other and against the findings from the computer programs SADT and FRICWALL. SADT is a finite elements program which computes the load-deformation behaviour of shearwalls. FRICWALL is an inelastic time-history dynamic model which computes the response time-history of a shearwall under a simulated seismic event. The cyclic tests of the friction damping devices showed that they exhibited very stable and non-deteriorating hysteretic behaviour. The shake table tests of the full scale timber shearwalls showed that the friction damped walls were stiffer, can sustain an average of 23.7 % higher racking load and dissipate an average of 42.9 % more energy than the conventional ones before a ductile failure. Failure in the conventional walls was brittle. These results were in agreement with the SADT findings. Under slow cyclic loads, they dissipated more energy, but because their overall hysteretic behaviour was still pinched, they were just as inefficient as the conventional walls at dissipating energy. On the average, their seismic performance was only marginally better than that of the conventional wall, with an average drop of 9.6 % in peak wall deflection. This is far short of the average of 29.5 % computed by FRICWALL. Detailed analysis of the results show that due to bending in the framing members of the shearwall, the load necessary to cause slippage of the friction devices was not achieved until wall deflections in the order of 25.4 mm (1.0 in) was reached. Since only at the peak or near-peak excitation levels of an earthquake did shearwall deflections surpass this magnitude, the devices were not able to contribute to the energy dissipation of the shearwalls during the majority portion of a seismic event. / Applied Science, Faculty of / Civil Engineering, Department of / Graduate

Investigations into the behaviour of precast buildings under earthquake loading have shown that the connections are likely to be the weakest link in a pre-cast structure, and the stability of the structure under earthquake loading depends upon the strength & stability of these connections. A 2-dimensional non-linear dynamic analysis of a one storey box-type pre-cast buildings is presented. The shear walls in the buildings are modelled by linear springs, the properties of which depend upon the connections connecting the rigid panels of the shear walls. To check the effectiveness of the NBCC code design, computer studies have been made on a box-type building statically designed for different eccentricities. The strength of the shear walls was calculated assuming that each panel was a cantilever fixed at the base with dowel bars providing the flexural steel. To make the building survive a major earthquake, we need dowel connections that can take 5mm to 6mm elongation which can be easily accommodated. Studies have also shown that under the action of an earthquake, the response of a highly unsymmetrical building will not be very different from that of a symmetric building as long as the building is properly designed using the NBCC code provisions for earthquake loading. It has also been shown that the NBCC code design eccentricity equation is somewhat conservative in calculating the design eccentricity and that a small change in the stiffness of walls perpendicular to the direction of earthquake has little effect on the response of the structures. / Applied Science, Faculty of / Civil Engineering, Department of / Graduate

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Civil Engineering, 1982. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING / Bibliography: leaves 140-141. / by Chin Pang Wong. / M.S.

No description available.

The available earthquake records are classified into five groups according to their site stiffness and epicentral distance as the grouping parameters. For the groups thus defined, normalized response spectra are obtained for single-degree-of-freedom and massless oscillators. The effectiveness of the grouping scheme is examined by studying the variance of response quantities within each group. The implicit parameters of average frequency and significant duration are obtained for each group and their effect on the response spectra is studied. Correlation analyses between various ground motion characteristics such as peak displacement, velocity, acceleration and root mean square acceleration are carried out for each group. Smoothed design spectra for relative and pseudo velocities and relative acceleration responses of single degree of freedom oscillators and the velocity and acceleration responses of massless oscillators are proposed for each group. Methods to predict relative velocity and relative acceleration spectra directly from the pseudo velocity spectra are presented. It is shown that the relative spectra can be reliably estimated from the pseudo spectra. The site dependent design spectra are defined for a wide range of oscillator periods and damping ratios. / Master of Science

New modal synthesis methods are developed for calculating the exact eigenproperties of structures divided into two substructures. Unlike the conventional mode synthesis techniques, here the synthesis of modes is carried out by solving a second eigenvalue problem by nontraditional means: the eigenvalues of the combined structure are obtained by solving simple characteristic equations which,in the proposed approach, can be defined in closed-form. These equations can be easily solved by a simple Newton-Raphson iterative scheme, especially when good initial estimates of the roots are available. Herein, explicit expressions are provided to calculate these initial values; these expressions are obtained via a second order matrix perturbation analysis of the algebraic eigenvalue problems. Once the eigenvalues are known, the eigenvectors can be calculated with closed-form expressions without solving any simultaneous equations. Several variants of the methods are developed to consider various damping cases which can be encountered in practice. Furthermore, for each damping case, two parallel approaches are developed that allow one to utilize two different types of modes - free and fixed attachment modes - of one of the substructures to be synthesized with the free attachment modes of the other structure. The eigenproperties of the combined system, once calculated, can be utilized in a mode superposition approach for the calculation of the system response for any forcing function . For seismic analysis of combined primary and secondary structures, such as a main structure supporting piping or other auxiliary system, the combined structure is divided into two substructures. The eigenproperties of these two substructures are then synthesized to obtain the eigenproperties of the combined system. To obtain response for seismic design motions defined in terms of ground response spectra, response spectrum approaches are presented which utilize the eigenproperties of the combined system. Closed-form formulas are presented to obtain any displacement-related response quantity of interest for the seismic input defined in terms of ground response spectra. The seismic response calculated by the proposed procedure accounts for the dynamic interaction effects between the primary and secondary structures and the nonclassically damped characteristics of the combined system in an analytically exact way. Numerical results showing the performance of the modal synthesis methods are presented. The applicability of the response spectrum approaches is verified by numerical simulation studies. The approach is applicable to light as well as heavy secondary structures equally effectively. It can also be used for seismic analysis of tertiary systems in industrial units. The potential application of the approach for efficient and accurate vibration analysis of aerospace and aircraft structures should also be of interest. / Ph. D.

An analytical formulation for seismic analysis of multiply supported secondary systems is developed. The formulation is based on the random vibration theory of structural systems subjected to correlated inputs at several points. The response of the secondary systems is expressed as a combination of the dynamic, pseudo-static and cross response components. The dynamic part is associated with the inertial effect induced by the support accelerations. The pseudo-static part is due to the relative displacement between supports, and the cross part takes into account the correlation between these two parts of the response. The seismic input in this approach is defined in terms of the auto and cross pseudo-acceleration and relative velocity floor spectra. The information about floor displacements and velocities as well as their correlations is required for calculating the pseudo-static and cross response components. These inputs can be directly obtained from the ground response spectra. The interaction effect between the primary and secondary systems is studied. This effect is specially significant when the modes of the secondary system are tuned or nearly tuned to the modes of the primary system. The floor spectral inputs are appropriately modified to take into account this interaction effect. The design response of the secondary system when computed with these modified floor inputs will incorporate the interaction effect. The applicability of the proposed methods is demonstrated by several numerical examples. / Ph. D. / incomplete_metadata

Structures built next to each other in congested cities are likely to pound on each other during strong ground shaking caused by earthquakes. The main objective of this study is to examine the problem of mutual structural pounding to identify its effect on structures and then propose solutions to mitigate its effects. Mutual pounding of structural systems with varying mass, stiffness, and seismic joint gaps, subjected to several different input motions are examined. To evaluate the effects of pounding, the numerical results with and without pounding have been considered. The resilience between two impacting masses is represented by linear springs and also nonlinear Hertz model contact stiffness. Pounding causes a large increase in the shear force in the stories higher than the top pounding story, a large increase in the accelerations of the pounding floors and also large overturning effects on both structures. The parametric study of pounding of structures in series showed that in most cases the corner structures are penalized more than the interior structures. The study of the effect of foundation flexibility on the structural pounding response showed that a proper consideration of this parameter must be included in the analysis. To alleviate the pounding effects to avoid damage to structural elements and supported secondary equipment, it was found necessary to join the structures by rigid links and brace all the stories of at least the taller structure. Joining of the floors is required to reduce the excessive floor accelerations caused by impact, whereas the story bracings are required to reduce the excessive story shears or bending moments in the higher stories caused by pounding of the lower floors. It is observed that except for very soft soils, the proposed pounding mitigation scheme will increase the shear force transmitted to the foundation, thus requiring a strengthening of the foundation as well. Since the forces in the rigid links connecting the two structures were observed to be reasonable, the joining of the two structures does not pose any special problem; it can be easily accomplished by using large-size steel rods hooked properly with both structures. In the case of column pounding where the floors of one structure pound on the columns of the other structure, the pounding mitigation strategy is to provide K-bracings on all pounding columns and diagonal bracing in the other stories to reduce high bending moment in the column, and to rigidly join them to avoid high pounding acceleration. / Ph. D.

published_or_final_version / Civil Engineering / Master / Master of Philosophy