New methods for calculating the stochastic and seismic design response of linear and nonlinear structures are presented. For linear structures, two approaches are developed: (1) the modified mode displacement approach for classically as well as non-classically damped structures, and (2) the generalized force derivative approach for classically damped structures. Both techniques improve the calculation of the pseudostatic contribution of the truncated modes without including them in the analysis. In particular, the modified mode displacement approach is a useful tool for the calculation of seismic design responses affected by the contributions or higher modes. It properly considers the modal correlations as well as the correlation between retained and truncated modes. It is as fast as the mode acceleration method of structural dynamics and it only requires the commonly used ground response spectra employed by the classical mode displacement approach. On the other hand, the generalized force derivative approach requires the input to be defined in terms of its power spectral density function, but it improves even further the estimation of the missing mass effect due to the trucation of modes. For nonlinear structures, the stochastic equivalent linearization technique is employed to develop response spectrum approaches for hysteretic shear buildings and for two dimensional frames with plastic hinges. For this purpose, a generalized modal analysis technique is successfully employed. The proposed response spectrum approaches require the input be defined in terms of the response spectrum of first order oscillators as well as in terms of the commonly used ground response spectra. For shear buildings, the work is extended to include the calculation of floor response spectra. A simulation study is performed to compare the results obtained by the proposed approach. / Ph. D.

No description available.

No description available.

Cohesionless sands are known to be susceptible to failure by liquefaction when they are saturated and subjected to earthquake shaking. Considerable study has been directed towards this subject over the past 20 years in recognition of the possibility of large-scale property damage or loss of life due to this type of failure. Recent evidence has shown that small degrees of cementation in a sand significantly reduce the likelihood of liquefication. However, the work to date has been limited to studies with conventional testing devices and simple loading paths. These devices are suspected of inducing premature failure in cemented soils, and are not capable of modeling the effects of multiaxial loading. In this investigation, there were two major objectives. The first involved the development and fabrication of a new three~dimensional shear device with the capability of applying load to cemented sands with a minimum of stress concentration effects, and of using load paths which are more representative of the true effects of an earthquake than is possible in conventional equipment. The second concerned performance of a series of production tests to investigate the behavior of cemented sands under a range of earthquake loading paths. The production tests were largely performed using the new three—dimensional shear device. The test results showed that cemented soils have more resistance to earthquake loading than previously thought since stress concentration effects in conventional testing do induce premature failure through the effects of stress concentrations. On the other hand, it was found that either cemented or uncemented sands show less resistance to earthquake loadings if multiaxial stress conditions are applied to the sample as opposed to uniaxial loadings. This is important in explaining the fact that sites with seemingly similar conditions often show different behavior, since slightly different earthquake loading pattems can cause different responses. One factor explaining differences in response is found to be the mean normal stress, which is not the same for all loadings, and plays an important role in the pore pressures developed in the soil. / Ph. D. / incomplete_metadata

Thesis (MScIng)--Stellenbosch University, 2005. / Some digitised pages may appear illegible due to the condition of the original hard copy. / ENGLISH ABSTRACT: Reinforced concrete (RC) frames with unreinforced masonry infill form the structural system of many buildings and this is also true for South Africa. It is common practice to consider the masonry infill as a non-structural component and therefore it does not contribute to the performance of the Re frame buildings under lateral loading such as earthquake loading. This is done by leaving a sufficient gap between the Re frame and the infill. This ensures that there is no contact between the frame and the infill during an earthquake event. However, it has been suggested that masonry infill can play a significant role in the performance of a Re frame building under lateral loading. The first part of the study focuses on the South African situation. The relevance of shear walls in these Re frame buildings as well as the size of the gap (between frame and infill) left in practice, are investigated. This is done by finite element analysis. The second part of the study focuses on the effects that the infill can have on the global performance of the structure when there is full contact between the Re frames and infill. The effect of openings in the infill to the response of the frame is also investigated. Finite element models of single span Re frames with infill is built and analyzed in order to investigate possible damage to the infill, frame infill interaction and to obtain the non linear stiffness of the frame with infill as a whole. This obtained non linear stiffness can be modelled in Diana as a non linear spring that will be used in the development of a simplified analysis method. The simplified method developed consists of a frame and two such non linear springs, placed diagonally, and which have the same force versus displacement behaviour as the original frame with infill. These single span frames can be added together to model a whole frame. In a first step to generalise the simplified method, various geometries of infills are considered, varying span and height, as well as opening percentage, representing windows and doors of varying total area and positioning. However, in this study a single masonry type, namely solid baked clay bricks set in a general mortar, is considered. To generalise the approach further, other masonry types can be considered in the same way. The use of these springs in a simplified model saves computational time and this means that larger structures can be modelled in Diana to investigate response of'Rf' frame buildings with infill. The work reported in this thesis considers only in-plane action. Out-of-plane-action of the masonry infill has been reported in the literature to be considerable, under the condition that it is sufficiently tied to the frame to prevent mere toppling over, causing life risking hazards in earthquake events. This matter should be studied in continuation of the current research to generalise the simple approach to three dimensions. / AFRIKAANSE OPSOMMING: Gewapende betonrame (GBR-e) met ongewapende messelwerk invulpanele (invul) vorm die strukturele ruggraat van vele geboue en dit geld ook vir geboue in Suid-Afrika. Dit is algemene praktyk om die invulpaneel in sulke geboue as 'n nie-strukturele komponent te beskou. Daarvolgens dra dit nie by tot die gedrag van 'n GBR gebou onderhewig aan 'n aarbewing nie. Dit word bereik deur 'n groot genoeg gaping tussen die betonraam en die invul te los. Die gevolg is dat daar geen kontak tussen die betonraam en die invul plaasvind indien daar 'n aardbewing sou voorkom nie. Dit is egter voorgestel dat invul 'n noemenswaardige rol kan speel in die gedrag van 'n GBR gebou onderwerp aan 'n horisontale las. Die eerste deel van die studie fokus op die Suid-Afrikaanse situasie. Die relavansie van skuifmure in GBR geboue asook die grootte van die gaping (tussen die raam en invul) wat in die praktyk gebruik word, word ondersoek. Dit word gedoen met behulp van eindige element analises. Die tweede deel van die studie fokus op die effek wat invul kan hê op die globale gedrag van 'n struktuur wanneer daar volle kontak tussen die GBR en die invul is. Die effek wat die teenwoordigheid van openinge in die invul kan hê op die gedrag van 'n GBR is ook ondersoek. Eindige element modelle van enkelspan GBR met invul is gemodelleer en geanaliseer om die moontlike skade aan die invul, die interaksie tussen die GBR en die invul asook die nie-lineêre styfheid van die raam en invul as 'n geheel, te ondersoek. Hierdie nielineêre styfheid kan in Diana as 'n nie-lineêre veer gemodelleer word en word gebruik in die ontwikkeling van 'n vereenvoudigde metode. Hierdie vereenvoudigde metode wat ontwikkel is, bestaan uit 'n raam en twee sulke nielineêre vere (diagonaal geplaas). Die raam met vere het dieselfde krag teenoor verplasingsgedrag as die van die oorspronklike raam met invul wat dit voorstel. Hierdie rame kan saamgevoeg word om 'n raam uit 'n gebou as 'n geheel te modelleer. Verskeie invul geometrieë word gebruik in die analises in 'n eerste stap om die vereenvoudigde metode te veralgemeen. Die span en hoogte asook opening persentasie van die invul word gevariëer om vensters en deure van veskeie grootte en posisie voor te stel. In die studie, 'n enkel messelwerk tipe, naamlik solied klei bakstene geset in algemene mortar, word gebruik. Ander messelwerk tipes kan gebruik word om die metode verder te veralgemeen. Die gebruik van die vere in die vereenvoudigde metode spaar berekenings tyd en dit beteken dat groter strukture in Diana gemodelleer kan word om die gedrag van GBR geboue met invul te ondersoek. Die werk gedoen in die tesis neem slegs in-vlak aksie in ag. Literatuurstudie dui daarop dat goeie uit-vlak-aksie van messelwerk invul bestaan, mits dit goed geanker is aan die raam om te verseker dat dit nie kan omval en 'n gevaar vir lewens in 'n aardbewing inhou nie. Dit behoort verder bestudeer te vord in die vervolging van die huidige ondersoek om die vereenvoudige metode na drie dimensies te veralgemeen.

Thesis (M.S.)--University of Nevada, Reno, 2004. / "December 2004." Includes bibliographical references (leaves 57-61). Online version available on the World Wide Web.

Recent experience demonstrates that waterfront structures are vulnerable to earthquake damage. The poor seismic performance of these facilities has been primarily due to liquefaction of backfill and/or foundation soils and the lack of seismic design standards for waterfront structures. The seismic performance of waterfront structures is a key issue in the evaluation of the unimpeded operations of the port system and affiliated facilities following earthquakes. The widespread economic consequences of earthquake-induced damage to waterfront structures and required serviceability of port components after earthquakes highlight the need for improved performance-based design methods. The weak foundation soils and high water tables that are common at ports result in a high vulnerability to seismically-induced ground failures and corresponding damage to adjacent structures. Liquefaction of backfill and foundation soils next to waterfront structures contributes to an increase in active lateral earth pressures against walls, loss of stability of rock dike, excessive ground settlements, and lateral soil movements. Current pseudostatic methods are not well suited to account for the influence of excess pore pressure generation as well as amplification of acceleration. In order to limit earthquake-induced deformations of waterfront structures, various ground treatment strategies have been used to mitigate liquefaction hazards at numerous ports. However, very few guidelines exist for specifying the extent of remedial soil treatment required to insure the serviceability of the waterfront components after a design-level earthquake. This research has investigated the seismic response of waterfront structures, specifically concrete caissons and pile-supported wharves, during past earthquakes. A numerical model was validated by comparing the computed response to field performance. A series of parametric studies were conducted for waterfront structures in improved soils. The effectiveness of soil improvement in controlling permanent seismically-induced deformations of the waterfront structures is evaluated as functions of wall geometry, the density of backfill soils, the stiffness of piles, the extent of the improved soil, and the characteristics of the strong ground motions. The results were synthesized into simplified, practice-oriented design charts for deformation-based analysis, and preliminary guidelines for estimating the extent of ground treatment that is required given allowable deformation limits for the caissons and pile-supported systems. / Graduation date: 1999

Thesis (Ph. D.)--University of Texas at Austin, 2000. / Vita. Includes bibliographical references (leaves 191-194). Available also in a digital version from Dissertation Abstracts.

Thesis (Ph. D.)--Lehigh University, 2003. / Includes vita. In two parts. Includes bibliographical references (leaves 598-603).

Timber has been a widely used construction material throughout the history of human development and it is still popular to this day. Timber frames are a common structural form used in historical and modern day structures. An effective means to connect timber members together is via bolts or dowels due to their high strength, ductile behaviour and flexibility in application. Such joints are, however, vulnerable and prone to damage especially during seismic attacks. In order to improve the performance and longevity of timber framed structures, it is necessary to develop simple but effective strengthening schemes for dowel-type timber joints. Additionally, strategies to repair and reinstate damaged joints are also required. The main objectives of this program of doctoral research are to (1) develop strengthening and repair schemes for bolted timber joints using advanced composite materials (i.e. carbon fibre reinforced polymer, CFRP) as well as traditional materials (i.e. steel plates, epoxies and mortars), and (2) investigate the effectiveness of the schemes in improving the seismic performance of timber frames. The strengthening and repair schemes are applied to single-bolt joints and tested under monotonic load. Optimal strengthening and repair schemes are then applied to moment resisting joints and the joints are subjected to monotonic and cyclic loading. Finite element models are then assembled for the latter joint tests. The calibrated joint models are then used in finite element models of timber frames with varying number of storeys and support conditions. The seismic performances of the timber frames are investigated by conducting both nonlinear static and nonlinear time history analyses. The results of the experimental investigations and the finite element analyses show that the strengthening schemes can enhance the strength and stiffness of joints. Optimum strengthening schemes can also improve the seismic performance of timber frames. Based on the work arising from the program of research, future research needs are finally identified. / published_or_final_version / Civil Engineering / Doctoral / Doctor of Philosophy