Thesis (MEng)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: Precast concrete has been used for decades in the construction industry, locally as well as internationally. Rapid urban development and the need for shorter construction periods for building and infrastructure projects have however encouraged more use of precast concrete construction. The improved speed of construction, high quality and less labour requirements that precast offers makes it an effective type of construction method for modern development. The utilization of various precast concrete systems has been frequently used in the international construction industry, making it a very popular construction method. It was however found that one of the major drawbacks or concerns with the use of precast concrete is the connections between the precast elements. In-situ construction does not have this problem, because it is designed to a monolithic structure or building. It was identified that if the connections in precast buildings or structures are designed or constructed in an insufficient way, it can lead to severe structural problems and even failure. This highlights the importance the design and construction of precast concrete connections have on the overall stability, strength and robustness of the structure. Precast concrete buildings are not merely separate precast elements, connected together to eventually form the same principals of in-situ construction. Precast concrete and connection design is considered to be a specialist field and requires the sufficient expertise and knowledge to understand the structural system and all its different aspects. The precast connection’s function is not merely to transfer loads, but also to develop continuity and ensure monolithic behaviour of the entire precast concrete structure (Englekirk 2003). The most important or desirable structural functions of precast connections are; (i) direct transfer of loads (load paths and flow or forces), (ii) develop structural continuity and integrity, (iii) distribution of concentrated loads, (iv) allow for movements and unintended restraints and lastly to (v) ensure efficient rigidity and robustness for the connection. It can be seen that there is many factors that contribute to the overall design and construction phases of precast concrete connections. The aim of this study is to identify and investigate aspects that influence the design and construction of precast concrete connections. This study will mainly focus on precast concrete and precast connection preferences of participants in the South African construction industry. During this study, industry participants (contractors and consultants) were asked to identify certain aspects and concerns associated with precast concrete and precast connection construction. These answers were used to develop guidelines and preferences that can be used by industry participants to improvise and effectively manage the precast construction, mainly focussing on the connections between the precast elements. / AFRIKAANSE OPSOMMING: Voorafvervaardigde beton word al vir dekades gebruik in die konstruksiebedryf, plaaslik sowel as internasionaal. Vinnige stedelike ontwikkeling en die behoefte vir korter konstruksie tydperke vir die struktuur en infrastruktuur projekte het egter die gebruik en implementasie van voorafvervaardigde beton konstruksie laat toeneem. Die verbeterde spoed van die konstruksie proses, 'n hoë gehalte produk en minder arbeid vereistes wat voorafvervaardiging bied maak dit dus 'n effektiewe tipe konstruksie metode vir moderne ontwikkelings. Die benutting van verskeie voorafvervaardigde beton sisteme en elemente word reeds herhaaldelik gebruik in die internasionale konstruksiebedryf, wat dit vervolglik ʼn baie populêre en effektiewe sisteem maak. Dit is egter bevind dat een van die groot struikelblokke of probleme met die gebruik van voorafvervaardigde beton is die verbindings tussen die voorafvervaardigde elemente. In-situ beton konstruksie het dus nie hierdie probleem nie, want dit word ontwerp om 'n monolitiese beton struktuur of gebou te vorm. Dit was immers geïdentifiseer dat as die verbindings in ʼn voorafvervaardigde gebou of struktuur, ontwerp word deur ʼn ontoereikende manier, dit kan lei tot ernstige strukturele probleme en selfs strukturele faling. Dit beklemtoon dus die belangrikheid wat die ontwerp en konstruksie proses van voorafvervaardigde beton verbindings het op die algehele stabiliteit, sterkte en robuustheid van die struktuur. Voorafvervaardigde beton geboue en strukture kan nie slegs beskou word as aparte voorafvervaardigde elemente wat met mekaar verbind word om eventueel dieselfde beginsels van insitu konstruksie te vorm nie. Voorafvervaardigde beton en verbinding ontwerp word beskou as 'n spesialis veld en vereis dat die ontwerper die nodige kundigheid en kennis van die strukturele stelsel en al sy verskillende aspekte verstaan. Voorafvervaardigde beton verbindings se funksie is nie net om toegepaste kragte oor te dra nie, maar ook om strukturele kontinuïteit te ontwikkel en te verseker dat monolitiese gedrag gehandhaaf word vir die hele voorafvervaardigde beton struktuur (Englekirk 2003). Die mees belangrike strukturele funksies van voorafvervaardigde beton verbindings sluit die volgende in; (i) verseker direkte oordrag van toegepaste kragte (vloei van kragte), (ii) ontwikkeling van strukturele kontinuïteit en integriteit, (iii) die verspreiding van puntbelastings, (iv) moet voorsiening maak vir die bewegings in die voorafvervaardigde element en konneksie self en laastens (v) verskaf doeltreffende rigiditeit en robuustheid vir die konneksie sone. Dus kan daar afgelei word dat daar baie faktore is wat bydra tot die algehele ontwerp en konstruksie fases van voorafvervaardigde beton verbindings. Die doel van hierdie studie is om aspekte te identifiseer en te ondersoek wat die ontwerp en konstruksie van aspekte beton verbindings wel beïnvloed. Die studie sal hoofsaaklik fokus op voorafvervaardigde beton en verbindings voorkeure van persone in die Suid-Afrikaanse konstruksiebedryf. Tydens die studie was persone in die industrie (kontrakteurs en konsultante) ook gevra om sekere aspekte en kwellings wat verband hou met voorafvervaardigde beton asook die verbindings te identifiseer. Die antwoorde wat verkry was uit die industrie deelnemers kan toepaslik gebruik om word riglyne en voorkeure op te stel wat vervolglik gebruik en toegepas kan word in die konstruksie bedryf van Suid Afrika. Die riglyne kan effektief gebruik word om voorafvervaardigde beton asook die verbindings te verbeter en persone in die konstruksie bedryf in te lig oor voorkeure en toepassings van hierdie metode.

Thesis. 1975. M.Arch.A.S.--Massachusetts Institute of Technology. Dept. of Architecture. / Includes bibliographical references. / M.Arch.A.S.

Thesis (Ph. D.)--University of Texas at Austin, 2000. / Vita. Includes bibliographical references (leaves 397-401). Available also in a digital version from Dissertation Abstracts.

Title from PDF of title page (University of Missouri--Columbia, viewed on Feb 18, 2010). The entire thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file; a non-technical public abstract appears in the public.pdf file. Thesis advisor: Dr. Vellore S. Gopalaratnam. Includes bibliographical references.

Multi-span precast concrete segmental bridges are commonly constructed using the balanced cantilever method, which essentially involves sequentially extending precast segments outwards from each pier in a balanced manner. A gap of 100 to 200 mm wide is usually provided around the mid-span location between the last two approaching segments to facilitate erection. In-situ concrete is then cast to ‘stitch’ the segments together, thus making the bridge deck continuous. In the current practice, the in-situ concrete stitches are usually designed to be capable of sustaining considerable sagging moment but only minimal hogging moment. Failure of stitches may occur under exceptional circumstances that may potentially trigger a progressive collapse. However, relatively little research in this area has been carried out. In view of this, the author is motivated to undertake an extensive study of the behaviour of in-situ concrete stitches and the effects of their performance on the robustness of typical segmental bridges. Experimental study is carried out to examine the behaviour of in-situ stitches under different combinations of internal forces. Series of stitch specimens of different configurations are tested. Subsequent parametric studies are conducted numerically to examine the effects of various parameters on the load-displacement characteristics of the stitches. Formulae for strength estimation are proposed based on the results. A study of robustness involves analyzing the collapse behaviour of a structure in an extreme event and the analysis should be carried out up to and then well beyond the state of peak strength of structural members. A finite element programme for post-peak analysis is therefore developed for the present study. As the ability of a member section to sustain large inelastic deformation can ultimately affect the robustness of a structure, an investigation is conducted to examine the effects of steel content, yield strength and prestressing level on the ductility and deformability of prestressed concrete sections. Using the programme developed, the formation of collapsing mechanisms of a multi-span segmental bridge deck in an extreme event is examined. A typical bridge deck is subject to prescribed accidental load on its span in order to analyze the sequence of failure. Substantial redistribution of internal forces along the deck is observed as failures initiate, thus causing subsequent failures of other deck sections even though they have been designed to resist the internal forces at the ultimate limit state. The results indicate that any span of a multispan bridge may become a temporary end-span in the event of collapse of an adjacent span and the strength of the sections must be designed accordingly to prevent progressive failure. As a span becomes a temporary end-span, the in-situ concrete stitches may experience substantial moment and shear, and their failure could potentially trigger progressive collapse of the entire bridge deck. Towards the end of the thesis, important design considerations that can enhance the performance of in-situ concrete stitches and robustness of precast concrete segmental bridges are presented. / published_or_final_version / Civil Engineering / Doctoral / Doctor of Philosophy

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The primary objective of the dissertation research is to establish the seismic demands of precast concrete floor diaphragms designed with an emerging design methodology. To accomplish this, three-dimensional (3D) finite element (FE) models of diaphragm-sensitive precast concrete structures have been developed by extending two-dimensional (2D) diaphragm model developed previously for nonlinear static "pushover" analyses. Using these models, diaphragm seismic demands under expected hazard are evaluated through the nonlinear transient dynamic analyses (NLTDA).The research work is composed of four major parts:(1) Developing 3D NLTDA analytical model for diaphragm-sensitive precast concrete structures: The 3D structure model is extended from a 2D FE diaphragm model developed by a previous researcher. This process involves properly handling comparability conditions in 3D, incorporating proper hysteresis behavior for the diaphragm reinforcement, and developing appropriate lateral force resisting system (LFRS) models. A sensitivity analysis is performed for 3D NLTDA modeling to assist in creating an appropriate model.(2) Application of the model in integrated analysis-driven physical testing: These experiments occurred at Lehigh University (LU) with project collaborators. The loading in these tests were controlled by NLTDA of the 3D analytical model. The tests were used to examine the seismic response of key joints (critical flexure and shear joints) in the diaphragm under realistic demands and to further calibrate the analytical model.(3) Analytical modeling in support of shake table testing: The shake table test was performed at University of California San Diego (UCSD). The test involved a half scale three-story diaphragm-sensitive precast concrete structure. NLTDA using the 3D analytical model is used to assist in design and performance prediction of the test specimen. The test results are being used to calibrate/verify the analytical model.(4) Calibrating design factors for the emerging diaphragm design methodology: In the last research step, the 3D analytical model is used to calibrate trial design factors for the emerging diaphragm design methodology. These factors are established based on a parametric study of NLDTA at different seismic hazard levels using simple structure configurations. These factors will be evaluated on models of realistic structures to determine design factors for the final design procedure.

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