The object of this thesis is twinfold. Firstly, to study and check the effective width requirements recommended by different committees¹ for the design of ribbed precast concrete load bearing walls. Secondly, to rationalize the practice of the designing of the precast prefabricated components of any general polygonal shape. The recommendations regarding the minimum thickness of a thin wall, the effective width, etc., have been specified for some cases in code books and other tentative specification books², in the form of rules of thumb. In these rules of thumb, several parameters which may be of significance, such as dimensions of the rib itself, are not taken into account. A finite element approach has been adopted to investigate various combinations of these parameters, as well as the effects of different boundary conditions. Similar problems arise also in the cases of T-beams, L-beams and design of aircraft structures, in which a stressed skin is mounted on ribs, which are assembled in the form of a space frame. So far interaction curves have been made available in some design books only for the prestressed concrete member having rectangular cross-sections and for any other shape, approximations are made, such as making a rectangular section having an equivalent area or having the same moment of inertia or section modulii, etc. But this practice seems very irrational especially in the case of precast components which are always produced in a factory on a mass scale. A computer program has been written which can give the interaction curve for the member of any polygonal shape. 1. DRAFT 3: Of PCI Committee, 'Recommendations for Prestressed Bearing Wall Design.' 2. 'Symposium on Precast Concrete Wall Panels.' Publications ACI, SP-11, Second Printing 1966, pp. 39-44. / Applied Science, Faculty of / Civil Engineering, Department of / Graduate

The research on headed stud connections described in this thesis forms a part of a larger program with the objective of predicting the behaviour of precast concrete panel buildings under earthquake loads. The first objective of this research is to produce experimentally a concrete failure of the connection and to compare the actual failure load to the one predicted by the PCI design handbook. The tests show that the PCI shear-tension interaction equation for single headed studs can be used for the prediction of a concrete failure for a connection of the type tested. This method yields conservative results if a special equilibrium model for the determination of the stud tension force is used, and the bearing capacity of the structural steel angle on the concrete is neglected. The second objective of this research is to determine the bearing capacity of a reversed angle connection. Experiments show that this bearing capacity is equivalent to a force resulting from a stress equal to the concrete strength uniformly distributed over the concrete area enclosed by the structural steel angle 2" x2". Furthermore, the location of this force can be assumed in the center of gravity of the structural steel angle shape, regardless of whether or not there is an endplate present. / Applied Science, Faculty of / Civil Engineering, Department of / Graduate

No description available.

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.

Traditional seismic design philosophy for reinforced concrete seismic frame structures localises damage and inelastic deformation to regions of significant plasticity within the beam (plastic hinge zones) during a severe earthquake event. Collapse prevention of the frame is applied through capacity design methods, requiring the maximum expected flexural strength of the beam plastic hinges to be reliably assessed in order to design for, and ensure, the predominantly elastic flexural response of the columns in the frame. Previous experimental and numerical investigations have shown that significant and detrimental damage to the frame and floor system occurs due to the formation and elongation of ductile beam plastic hinges; requiring extensive post-earthquake repair or demolition with likely loss of function of the building. This poses significant economic consequences to occupiers of the building, as the time required to reinstate the integrity of the structural and non-structural building components is often lengthy. More importantly, it has been highlighted that the interaction between elongating ductile plastic hinges and the accompanying floor system enhances the flexural strength of the beam hinges, altering the distribution of forces in the seismic frame compared to that assumed during capacity design. Research has shown that the consideration of frame-floor interaction in current New Zealand design codes significantly underestimates the flexural strength enhancement of beam plastic hinges, threatening the hierarchy of strength and collapse prevention mechanisms employed in capacity design. Recent research has introduced change in the design philosophy of precast concrete seismic frames. Rather than designing for localised damage in the frame, unique Non-tearing (of the floor) connection details have been developed which provide a gap or slot between the end of the beam and column face and force connection rotation to occur about a shallow hinge located at the top of the beam, thereby avoiding the formation of plastic hinges and associated beam elongation effects altogether. Research investigations have shown that Non-tearing connections successfully minimise damage to the structural frame and floor, while providing seismic energy dissipation characteristics at least comparable to that of traditional reinforced concrete connections. In this research, the mechanics of different non-tearing connection arrangements were investigated and original theory introduced for the aspects of connection behaviour which diverged from fundamental reinforced concrete design. A variety of precast concrete non-tearing connection details were developed, with the design focus placed on economic and construction efficiency in order to encourage the rapid implementation of non-tearing connection technology into New Zealand construction industry. The performance of the developed connection details were explored and assessed experimentally and analytically. A two bay precast concrete frame with precast floor system was tested under a demanding reversed cyclic, quasi-static loading protocol using displacement control. The seismic response of the non-tearing connection details employed in the test frame successfully minimised damage to the frame and floor systems. Only minor repair of one primary crack at each connection between the floor diaphragm and supporting beam would be required after a design level earthquake. Issues encountered with buckling of the longitudinal reinforcement in the bottom of the beam reduced the connection performance at high levels of drift. However, detailing measures were successfully employed in successive tests which improved the drift capacity of the connections. Detailing improvements to enhance the seismic response of the developed non-tearing connections were recommended based observations from the frame test. Numerical analysis of the non-tearing connection details was performed using simple rotational and compound spring models, with the key features of the experimental response captured with excellent accuracy. The analytical models were constructed using engineering theory, rather than by calibration with experimental observations. The modelling assumptions and principles adopted in the analysis have been presented for use in design offices or future research programmes when designing and analysing seismic frames using non-tearing connections. This research successfully contributed to the development and progression of non-tearing frame technology. With further research and the refinement of construction details, non-tearing floor connections exhibit impressive potential for providing superior seismic safety, performance and efficiency in precast concrete seismic frame buildings.

In predicting the likely behaviour of precast prestressed concrete flooring systems in fire using advanced finite element methods, an improved numerical model using the non-linear finite element program SAFIR has been developed in order to investigate the effects and the interaction of the surrounding structures and has been used extensively throughout this thesis. Note that fire induced spalling is not included in the analysis. In the numerical investigation of the new model, the reinforced concrete topping is modelled as part of the beam elements in order to predict the behaviour of single hollowcore concrete slabs, with various support conditions, under a Standard ISO fire. It is shown that the current approach using tendons that are anchored into the supporting beams leads to a major problem for precast prestressed flooring systems. In order to resolve this problem, a multi-spring connection model has been developed to include the old and new connection systems corresponding to the New Zealand Concrete Standard NZS 3101. The connection model with hollowcore slabs is validated against a published fire test. The investigation on restrained hollowcore floors is performed with various parameters and boundary support conditions. Numerical studies on various boundary support conditions show that the behaviour of hollowcore floors in fire is very sensitive to the existence of side beams. Further investigations on the effects of fire emergency beams, which reduce the transverse curvature of floors to improve fire resistance, are made on 4x1 multi-bay hollowcore floors with different arrangements of theses beams. The numerical studies show that fire emergency beams significantly increase the fire resistance. Code based equations which can calculate the shear resistance and splitting resistance are then introduced. The Eurocode equation can be modified with high temperature material properties to estimate the shear capacity of a hollowcore slab. The modified Eurocode equation which is fit to fire situations validated against the published literature with respect to shear tests in fire. The structural behaviour of single tee slabs having different axial restraint stiffness as well as the variation of axial thrust in fire is then studied. SAFIR analyses of single tee slabs show that fire performance can increase when a web support type is used that has high axial restraint stiffness. A series of test results on prestressed flat slabs conducted in United States are used to validate a simply supported numerical model. The application of multi-spring connection elements is also investigated in order to examine the feasibility of continuity.

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