The Texas Department of Transportation (TxDOT) uses precast, prestressed concrete panels (PCPs) as stay-in-place formwork for most bridges built in Texas. The PCPs are placed on the top flanges of adjacent girders and topped with a 4-in. cast-in-place (CIP) slab. This thesis is directed towards identifying and quantifying the serviceability implications of reducing the deck reinforcement across the interior spans of CIP-PCP decks. The goal of this research is to understand how the PCPs influence cracking and crack control in the CIP slab and to make recommendations to optimize the top mat reinforcement accordingly. Several tests were conducted to evaluate the performance of different top mat reinforcement arrangements for ability to control crack widths across PCP joints. The longitudinal reinforcement was tested using a constant bending moment test, a point load test, and several direct tension tests. Because of difficulty with the CIP-PCP interface during the longitudinal tests, direct tension tests of the CIP slab only were used to compare the transverse reinforcement alternatives. Prior to testing, various top mat design alternatives were evaluated through pre-test calculations for crack widths. Standard reinforcing bars and welded wire reinforcement were considered for the design alternatives. During this study, it was found that the tensile strength of the CIP slab is critical to controlling transverse crack widths. The CIP-PCP interface is difficult to simulate in the laboratory because of inherent eccentricities that result from the test specimen geometry and loading conditions. Furthermore, the constraint and boundary conditions of CIP-PCP bridge decks are difficult to simulate in the laboratory. Based on the results of this testing program, it seems imprudent to reduce the longitudinal reinforcement across the interior spans of CIP-PCP decks. The transverse reinforcement, however, may be reduced using welded wire reinforcement across the interior spans of CIP-PCP decks without compromising longitudinal crack width control. A reduced standard reinforcing bar option may also be considered, but a slight increase in longitudinal crack widths should be expected. / text

Structural engineering is facing an extraordinarily challenging era. These challenges are driven by the increasing expectations of modern society to provide low-cost, architecturally appealing structures which can withstand large earthquakes. However, being able to avoid collapse in a large earthquake is no longer enough. A building must now be able to withstand a major seismic event with negligible damage so that it is immediately occupiable following such an event. As recent earthquakes have shown, the economic consequences of not achieving this level of performance are not acceptable. Technological solutions for low-damage structural systems are emerging. However, the goal of developing a low-damage building requires improving the performance of both the structural skeleton and the non-structural components. These non-structural components include items such as the claddings, partitions, ceilings and contents. Previous research has shown that damage to such items contributes a disproportionate amount to the overall economic losses in an earthquake. One such non-structural element that has a history of poor performance is the external cladding system, and this forms the focus of this research. Cladding systems are invariably complicated and provide a number of architectural functions. Therefore, it is important than when seeking to improve their seismic performance that these functions are not neglected. The seismic vulnerability of cladding systems are determined in this research through a desktop background study, literature review, and postearthquake reconnaissance survey of their performance in the 2010 – 2011 Canterbury earthquake sequence. This study identified that precast concrete claddings present a significant life-safety risk to pedestrians, and that the effect they have upon the primary structure is not well understood. The main objective of this research is consequently to better understand the performance of precast concrete cladding systems in earthquakes. This is achieved through an experimental campaign and numerical modelling of a range of precast concrete cladding systems. The experimental campaign consists of uni-directional, quasi static cyclic earthquake simulation on a test frame which represents a single-storey, single-bay portion of a reinforced concrete building. The test frame is clad with various precast concrete cladding panel configurations. A major focus is placed upon the influence the connection between the cladding panel and structural frame has upon seismic performance. A combination of experimental component testing, finite element modelling and analytical derivation is used to develop cladding models of the cladding systems investigated. The cyclic responses of the models are compared with the experimental data to evaluate their accuracy and validity. The comparison shows that the cladding models developed provide an excellent representation of real-world cladding behaviour. The cladding models are subsequently applied to a ten-storey case-study building. The expected seismic performance is examined with and without the cladding taken into consideration. The numerical analyses of the case-study building include modal analyses, nonlinear adaptive pushover analyses, and non-linear dynamic seismic response (time history) analyses to different levels of seismic hazard. The clad frame models are compared to the bare frame model to investigate the effect the cladding has upon the structural behaviour. Both the structural performance and cladding performance are also assessed using qualitative damage states. The results show a poor performance of precast concrete cladding systems is expected when traditional connection typologies are used. This result confirms the misalignment of structural and cladding damage observed in recent earthquake events. Consequently, this research explores the potential of an innovative cladding connection. The outcomes from this research shows that the innovative cladding connection proposed here is able to achieve low-damage performance whilst also being cost comparable to a traditional cladding connection. It is also theoretically possible that the connection can provide a positive value to the seismic performance of the structure by adding addition strength, stiffness and damping. Finally, the losses associated with both the traditional and innovative cladding systems are compared in terms of tangible outcomes, namely: repair costs, repair time and casualties. The results confirm that the use of innovative cladding technology can substantially reduce the overall losses that result from cladding damage.

Este trabalho aborda o estudo da instabilidade lateral das vigas pré-moldadas durante o regime de serviço e durante a fase transitória. Na fase de serviço inclui os casos de apoios indeformáveis e deformáveis à torção. Para a fase transitória, o cálculo da carga crítica é desenvolvido para as diversas disposições dos cabos de içamento. O estudo do equilíbrio no espaço é realizado a partir da resolução das equações diferenciais regentes da instabilidade elástica. A resolução do sistema diferencial composto pelas equações acopladas da flexão lateral e da torção é realizada por vários métodos, incluindo o desenvolvimento e automatização do método numérico de Runge-Kutta, para algumas seções típicas. Apresentam-se ainda os procedimentos empíricos encontrados na literatura técnica, baseados em ensaios experimentais, para o cálculo dos fatores de segurança. Os resultados dos exemplos numéricos mostram que as situações de serviço não são, em geral críticas, ao contrário da fase transitória. Os exemplos mostram ainda que a suspensão com balanços é uma forma de diminuir os problemas de instabilidade lateral desta fase. / This work deals with the lateral stability of precast beams on service and during intermediate phase - handling and transportation. At service phase it is considered rigid and semi-rigid connections with torsion deformation. At handling phase, the critical load is evaluated for several positions of lifting cables. The study of the equilibrium conditions is done with the solution of the differential equation of elastic instability problem. The solution of flexural and torsional coupled equation is gotten by use of some methods, including the one developed and authomatized from the application of Runge-Kutta method, for certain sections. Empirical procedures are presented based on experimental tests, found in technical papers to compute fators of safety. The results of numerical examples show that the service situations are not generally critical, unlike the intermediate situations. The results show also that a possible way to avoid this problem is with the use of lifting points with a distance from the ends.

Este trabalho aborda o estudo da instabilidade lateral das vigas pré-moldadas durante o regime de serviço e durante a fase transitória. Na fase de serviço inclui os casos de apoios indeformáveis e deformáveis à torção. Para a fase transitória, o cálculo da carga crítica é desenvolvido para as diversas disposições dos cabos de içamento. O estudo do equilíbrio no espaço é realizado a partir da resolução das equações diferenciais regentes da instabilidade elástica. A resolução do sistema diferencial composto pelas equações acopladas da flexão lateral e da torção é realizada por vários métodos, incluindo o desenvolvimento e automatização do método numérico de Runge-Kutta, para algumas seções típicas. Apresentam-se ainda os procedimentos empíricos encontrados na literatura técnica, baseados em ensaios experimentais, para o cálculo dos fatores de segurança. Os resultados dos exemplos numéricos mostram que as situações de serviço não são, em geral críticas, ao contrário da fase transitória. Os exemplos mostram ainda que a suspensão com balanços é uma forma de diminuir os problemas de instabilidade lateral desta fase. / This work deals with the lateral stability of precast beams on service and during intermediate phase - handling and transportation. At service phase it is considered rigid and semi-rigid connections with torsion deformation. At handling phase, the critical load is evaluated for several positions of lifting cables. The study of the equilibrium conditions is done with the solution of the differential equation of elastic instability problem. The solution of flexural and torsional coupled equation is gotten by use of some methods, including the one developed and authomatized from the application of Runge-Kutta method, for certain sections. Empirical procedures are presented based on experimental tests, found in technical papers to compute fators of safety. The results of numerical examples show that the service situations are not generally critical, unlike the intermediate situations. The results show also that a possible way to avoid this problem is with the use of lifting points with a distance from the ends.

Typescript (photocopy). / Digitized by Kansas Correctional Industries

Thesis. 1977. M.Arch.A.S.--Massachusetts Institute of Technology. Dept. of Architecture. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ROTCH. / Bibliography : p. 103. / by Loren Ahles. / M.Arch.A.S.

Thesis. 1975. M.S.--Massachusetts Institute of Technology. Dept. of Civil Engineering. / Bibliography: leaves 70-72. / M.S.

Over the last two decades, sustainability has matured to become a societal imperative and is at the forefront of UK government policy and industry strategy. For example, the Strategy for Sustainable Construction (BERR, 2008) and Low Carbon Construction (BIS, 2012) reports have focused on encouraging more sustainable construction through reductions in energy, water and resource use. In response to such demands, the UK precast concrete industry developed a sector sustainability strategy and subsequently chose to continue activities in this area through an Engineering Doctorate (EngD) research project. The project focused on the scope for applying the principles of product stewardship (PS) as a means to mitigate environmental impacts associated with precast products, throughout the entire life-cycle of their use. Numerous PS schemes have been adopted in other industrial sectors, such as chemicals, electronics and product manufacture. One of the distinguishing features of PS is that multiple stakeholders need to take responsibility for their ‘share' of environmental impacts, and that life-cycle thinking should pervade the value chain. Hence, through PS, the precast industry might be able to address not only the impacts within cradle-to-gate phases, but also develop a framework to positively act on broader, cradle-to-grave impacts. The aim of this research was to develop a framework for embedding the principles of PS more deeply into the precast industry, creating a novel pathway towards more sustainable construction. The research commenced with a literature review to understand the key sustainability issues affecting the industry, followed by an analysis and synthesis of industry key performance indicator (KPI) data from 2006–2012. Industry participation in the research was facilitated through a questionnaire survey and interviews with senior staff within UK precast businesses. Evidence of PS practices was found to exist within the industry through responsible sourcing schemes, implementation of Environmental Management Systems and through the mitigation of various specific impacts. However, the coordinated communication of such initiatives was found to be lacking and with the advent of new European standards around Environmental Product Declarations (EPD) for construction, it was decided that the precast industry would benefit from a sector-specific EPD framework to capture and communicate its PS credentials. An EPD framework and tool was therefore developed and validated through a focus group, to establish whether an EPD can be used successfully to deliver environmental information and refine an approach such that it would accord with the principles of PS. Further research and development arising from this research could focus on implementation and evaluation of the industry-specific EPD scheme, a mechanism to communicate and share life-cycle information amongst upstream and downstream stakeholders and a means through which stakeholder responsibility can be attributed and managed effectively. The key findings of this research have been presented in four peer–reviewed papers (one of which is in draft) which are presented in the Appendices.

Sector sustainability strategies can provide industry sectors with a way of managing risks and opportunities, and contributing to sustainable development. The UK Government has encouraged their development in the construction industry. British Precast, as the trade association for the precast concrete industry in the UK, had undertaken to develop a sector sustainability strategy for that industry. However, the development of such strategies is a departure from the traditional role of the trade association and presented British Precast with a number of challenges. This EngD research programme was therefore established in order to address those challenges and facilitate progress towards a more sustainable precast industry. The research programme has followed a mixed method strategy of inquiry based on action research methodology, that is, a series of research cycles have been undertaken with the findings from each cycle being used to inform and guide subsequent cycles; archival analysis, survey and case study were the main research methods used. The requirement of the EngD programme to publish elements of the work in refereed journal and conference papers as the research progresses has allowed the research to be validated as scientifically satisfactory. The strategy development process combined best practice, current and emerging theory, original research, stakeholder engagement, and experience from other sectors and industries. The strategy was produced in the form of an action plan for British Precast. This plan differs from the sustainability strategies produced for other sectors of the construction products industry in that rather than simply promoting action on specific objectives, it provides British Precast with a means of engaging with the industry and its stakeholders, and facilitating progress towards a more sustainable precast industry. The action plan has been well received by the industry and its stakeholders, and there is clear evidence that it is helping to guide the business decisions of companies in the industry, and that progress towards a more sustainable precast industry is being achieved as a result. The research supporting the strategy development process has added to current knowledge and guidance on the development of sector sustainability strategies, but shown that there are limits to the influence trade associations can have over their members' actions. It has also been shown that the development of management systems, particularly environmental management systems to ISO 14001, and continuous performance improvement cultures can assist companies in managing for sustainability, supporting the findings of other studies. However, further work is needed to build support for the action plan within the precast industry, particularly amongst SMEs, to support the downstream supply chain in using precast products to deliver more sustainable construction, and to assist companies in achieving progress towards corporate sustainability. Recommendations are made for this work.

A precast concrete structural system offers many advantages over in-situ casting. For example, greater control over the quality of materials and workmanship, improved health and safety (with casting carried out at ground level rather than at height) and cost efficiency (with standard forms continually re-used) are all realised through the off-site production of structural elements. As a result, a large body of research has been conducted into their performance, with many national codes of practice also devoting specific sections to design and detailing. However, contemporary design practice has been shown to not always correctly reflect the findings of published experimental studies. Concrete technology is continually evolving, as is the industry s knowledge of how to model and predict the behaviour of the resulting structural components. Using such understanding to design and justify the more efficient, cost-effective or flexible manufacture of precast components can offer a key commercial advantage to a precast manufacturer. In this context, the numerical and experimental investigations undertaken as part of this study have been specifically focussed on quantifying the advantages of utilising beneficial alternatives. Specifically the research has looked at improvements in concrete mixes, lightweight aggregates and reinforcing strategies, for precast structural elements required to transfer loads both vertically and horizontally. However, because of the non-standard solutions considered, different approaches have been used to demonstrate their suitability. Towards this goal, an alternative assessment strategy was devised for slender precast concrete panels with central reinforcement. The procedure was found to lead to design capacities that are in good agreement with actual experimental findings and should thus result in future manufacturing efficiency. The method can also be used for alternative concrete types and reinforcement layouts. Fresh and early-age material characteristics of self-compacting concrete mixes with a partial or complete replacement of traditional gravel and sand constituents with lightweight alternatives were investigated. This was done to demonstrate the feasibility of their use for the manufacture of large scale structural components, with clear benefits in terms of lifting and transportation. A computational push-down procedure was utilised to demonstrate the potential unsuitability of current tying regulations for avoiding a progressive collapse event in precast framed structures. The findings are considered to be of particular significance for these structures due to the segmental nature of the construction and the associated inherent lack of structural continuity.