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Development of a CFRP system to provide continuity in existing reinforced concrete buildings vulnerable to progressive collapseOrton, Sarah Lynn, January 1900 (has links)
Thesis (Ph. D.)--University of Texas at Austin, 2007. / Vita. Includes bibliographical references.
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Optimum shear strengthening of reinforced concrete beamsYapa, Hiran Deshantha January 2011 (has links)
External prestressed carbon fibre reinforced polymer (CFRP) straps can be used to strengthen shear deficient reinforced concrete (RC) structures. The strengthening system is associated with a number of parameters including the number of straps, strap locations, strap stiffness, and strap prestress. The initial goal of this research was to identify the optimum values for these parameters in order to design an efficient and effective shear retrofitting system. The shear friction theory (SFT) and modified compression field theory (MCFT) were identified as potential predictive theories to model the shear behaviour of RC beams retrofitted with CFRP straps. Possible modifications to the theories to reflect CFRP prestressed straps were investigated. Two popular optimisation algorithms namely the genetic algorithm (GA) and particle swarm optimisation (PSO) were coded and tested with six test functions. These algorithms were used to find the optimum shear retrofitting configurations and also to reduce the computational cost associated with the SFT and MCFT evaluations. An experimental investigation was carried out to validate the SFT and MCFT predictions for various CFRP strap configurations. The investigation consisted of an unstrengthened control beam and five CFRP strengthened beams. The shear behaviour of the beams was significantly influenced by the CFRP strap configurations. A critical load level where the beam stiffness started to deteriorate significantly was identified. It was found that there was a correlation between this load level and the yielding of the internal shear links and a rapid increase in crack openmg. The SFT and MCFT were validated using the experimental results. The peak shear capacities predicted using the SFT were more consistent with the stiffness deteriorating loads identified in the experimental investigation than with the ultimate loads of the beams. The reinforcement forces and crack opening values found from the SFT were consistent with the experimental results. The MCFT predicted the total shear response, ultimate shear capacity, crack opening, and internal and external reinforcement forces in the beams. The accuracy of the MCFT predictions reduced slightly when either the strap configuration was highly nonuniforrn or the initial prestress level in the straps was relatively low. The shear link yielding load levels predicted by the MCFT were found to be similar to the SFT predictions. By using the coded optimisation algorithms in combination with the SFT or MCFT, the optimum CFRP strap configurations were found for a selected case study. Both theories predicted an offset for the optimum strap locations from the locations associated with equal spacings along the shear span. A reasonable agreement between the SFT and MCFT predictions for the optimum shear strengths and strap locations was observed. A parametric study demonstrated that the concrete strength, internal shear link locations, beam depth, and shear span to depth ratio of the beam do not significantly influence the optimum strengthening configurations for the CFRP strap system. External prestressed carbon fibre reinforced polymer (CFRP) straps can be used to strengthen shear deficient reinforced concrete (RC) structures. The strengthening system is associated with a number of parameters including the number of straps, strap locations, strap stiffness, and strap prestress. The initial goal of this research was to identify the optimum values for these parameters in order to design an efficient and effective shear retrofitting system. The shear friction theory (SFT) and modified compression field theory (MCFT) were identified as potential predictive theories to model the shear behaviour ofRC beams retrofitted with CFRP straps. Possible modifications to the theories to reflect CFRP prestressed straps were investigated. Two popular optimisation algorithms namely the genetic algorithm (GA) and particle swarm optimisation (PSO) were coded and tested with six test functions. These algorithms were used to find the optimum shear retrofitting configurations and also to reduce the computational cost associated with the SFT and MCFT evaluations. An experimental investigation was ca1Tied out to validate the SFT and MCFT predictions for various CFRP strap configurations. The investigation consisted of an unstrengthened control beam and five CFRP strengthened beams. The shear behaviour of the beams was significantly influenced by the CFRP strap configurations. A critical load level where the beam stiffness started to deteriorate significantly was identified. It was found that there was a correlation between this load level and the yielding of the internal shear links and a rapid increase in crack opening. The SFT and MCFT were validated using the experimental results. The peak shear capacities predicted using the SFT were more consistent with the stiffness deteriorating loads identified in the experimental investigation than with the ultimate loads of the beams. The reinforcement forces and crack opening values found from the SFT were consistent with the experimental results. The MCFT predicted the total shear response, ultimate shear capacity, crack opening, and internal and external reinforcement forces in the beams. The accuracy of the MCFT predictions reduced slightly when either the strap configuration was highly nonuniform or the initial prestress level in the straps was relatively low. The shear link yielding load levels predicted by the MCFT were found to be similar to the SFT predictions. By using the coded optimisation algorithms in combination with the SFT or MCFT, the optimum CFRP strap configurations were found for a selected case study. Both theories predicted an offset for the optimum strap locations from the locations associated with equal spacings along the shear span. A reasonable agreement between the SFT and MCFT predictions for the optimum shear strengths and strap locations was observed. A parametric study demonstrated that the concrete strength, internal shear link locations, beam depth, and shear span to depth ratio of the beam do not significantly influence the optimum strengthening configurations for the CFRP strap system.
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Non-linear behavior of unbraced two-bay reinforced concrete framesShadyab, Mehdi 01 January 1980 (has links)
In this investigation, the primary objective was to study the nonlinear behavior of unbraced two-bay concrete frames and to determine the extent to which ultimate load theory or limit design can be applied to these structures. The frame behavior was investigated analytically by two methods. In the first method the frame stability equation was derived assuming that members of the frame possess an elasto-plastic moment-curvature relationship. This stability analysis was also carried out by another model consisting of a column attached to a linear spring and carrying the total frame load. The second method was through a computer program which took material and geometric nonlinearities of concrete frames into account. A model concrete frame, with a scale factor of approximately one-third was considered. Variable parameters were loading condition, column reinforcement ratio, and beam to column load ratio. For each frame, the gravity loads were increased proportionally until 75% of the frame ultimate capacity under gravity loads was reached. Then; while these gravity loads were held constant, lateral load was applied and increased to failure. The overall geometry, 21-in high columns and 84-in long beam, were kept the same for all of model frames investigated. The computer study and the stability model analysis indicated that all frames remained stable until four plastic hinges (two in each bay) formed, thus producing a combined sway mechanism. Based on the scope of this study, it appears that limit design may be employed for unbraced reinforced concrete structures.
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A Computer Program to Design Reinforcement for Concrete Beams Subjected to TorsionSchwarz, James E. 01 January 1985 (has links) (PDF)
A concrete beam is rarely subjected to pure torsion loading. However, in many design applications a beam is subjected to torsional loads in addition to bending and shear loading. The American Concrete Institute has developed a specification for the design of beams subjected to torsion. These specifications are found in ACI 318-83. In this research report, a computer program is presented, using these specifications, which will aid engineers in the design of reinforcement for concrete beams subjected to torsional loading. The provisions of the ACI 318-83 specification and their implementation into the computer program are presented. A sample problem is solved to compare the results of normal hand calculations to the results of the computer program. A listing of the computer program, written in Microsoft's GW BASIC, is provided. The designer enters information pertaining to the beams cross sectional properties, material properties and loading conditions. The program computes the concrete and reinforcement strength requirements and determines the amount of reinforcement required. The stirrup spacing and longitudinal reinforcement required are then determined and output to the designer.
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Yield-line analysis and experimental study of reinforced concrete slabs containing openingsAhart, Stephen Gregory January 1986 (has links)
Four rectangular, isotropically reinforced concrete slabs were constructed and loaded until collapse. All slabs were fixed on three edges with the fourth edge free. Three slabs contained openings at various locations while the fourth remained solid. The magnitudes of deflections were measured during loading and the final yield pattern and ultimate load were compared to those predicted by simple and advanced yield-line theory.
An analytical computer program was developed and is presented for quick evaluation of the ultimate load and collapse mode of many types of uniformly loaded slabs by simple yield-line theory. Short specialized programs were also formulated to analyze the experimental slabs, considering the presence of simple corner levers and edge loads around the openings. This resulted in more accurate theoretical predictions and produced estimates of the percent difference between simple and advanced theory predictions. Analysis of the results showed excellent agreement between the advanced theory predictions and the experimental results. / M.S.
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Redistribution of bending moment in continous structures of reinforced concreteHsu, Ko-chi 09 November 2012 (has links)
Generalized moment-curvature relations of reinforced concrete members for various cases have been developed. For a limited range of parameters, graphs have been prepared. With these graphs, and within the range of the parameters given, is possible to solve statically indeterminate structures of reinforced concrete with accuracy taking account of the effects of creep in the concrete. / Master of Science
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The development of a field procedure for determining the chloride content of concrete and an analysis in the variability of the effective diffusion constantHerald, Stephen Estel January 1989 (has links)
During the initial phase of the investigation, four methods were selected for investigation from a review of literature sources,the specific ion probe, spectrophotometer, digital titrator, and Quantab titrator strips.
The initial results from the laboratory testing procedure and evaluation based on cost, speed, accuracy, and level of expertise required indicated the specific ion probe was more suitable for use in the field when compared to the remaining methods selected.
Effects of cement content and reaction temperature on the results obtained for the specific ion probe were also investigated. Results of the tests for the effects of cement content were somewhat inconclusive, but indicated more variability in the results as the amount of chloride present in the specimens increased. However, correlation between the increase in variability and i cement content was not indicated. The specific ion probe is affected by differences in temperature and the appropriate correction factor for the variation was determined.
Field validation of the procedure was undertaken to substantiate the findings from the laboratory investigation. This was accomplished by subjecting the specific ion probe to testing specimens from bridges located in different exposure groups within the United States. Four bridges were tested for chloride content in Pennsylvania. Following this initial phase, three bridges were tested in Virginia, Florida, and Wisconsin respectively.
An analysis of the variability in the effective diffusion constant for the bridges tested was also performed to determine any relationships which exist between different exposure groups and to determine effects of time. / Master of Science
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Assessment of the behaviour factor for the seismic design of reinforced concrete structural walls according to SANS 10160 : part 4Spathelf, Christian Alexander 12 1900 (has links)
Thesis (MScEng (Civil Engineering))--Stellenbosch University, 2008. / The South African code for the design loading of building structures, namely SABS
0160 (1989), was revised with the requirements for seismic design prescribed in SANS
10160: Part 4: Seismic actions and general requirements for buildings. SANS 10160:
Part 4 incorporates the seismic design provisions of several seismic codes of practice,
however, the influence of the value prescribed for the behaviour factor has not been
established with regard to South African conditions.
The behaviour factor is used by most seismic design codes to account for the energy
dissipating effects of plastification in structural systems when subjected to earthquake
ground motion, to reduce the elastically determined forces to be designed for. However,
a considerable difference is observed in the values of the behaviour factor prescribed for
the design of reinforced concrete walls between the leading international seismic codes.
The aim of this study is to assess the value of the behaviour factor prescribed in SANS
10160: Part 4 for reinforced concrete structural walls under the influence of South
African seismic conditions and code requirements.
A method of quantifying the value of the behaviour factor was developed and
implemented in the study by Ceccotti (2008). This method entails estimation of the
maximum analytical behaviour factor as the ratio of seismic intensity at failure of the
structure to the seismic intensity prescribed by the design code. Such a method is
adopted for this study where the lateral force resisting systems of six-, eight- and tenstorey
buildings are investigated with nonlinear static analysis to quantify the maximum
computationally-determined value of the behaviour factor.
Firstly, it is observed that it is possible to quantify the value of the behaviour factor
through the use of a computational study. The nonlinear static method of analysis is
shown to provide reliable results in the estimation of the behaviour factor for a sixstorey
building, however, does not perform well for taller buildings. Further investigation with the use of dynamic time-history analysis is proposed to evaluate the
influence of the factors identified in this study.
The behaviour of structural walls, designed for reduced forces with the prescribed
behaviour factor of 5.0, exhibits high yield strengths and resists the design seismic
action entirely elastically. This high strength is found to be due to the
reliability/redundancy factor prescribed by SANS 10160: Part 4 and because of the high
values of structural overstrength. Similar studies observed high values of structural
overstrength for buildings designed for low seismic intensity, which were shown to
result from the fact that the resistance required to gravity loading became more critical
than the seismic loads in the design of the structural system.
This study identifies several factors that influence the value of the behaviour factor,
such as the number of walls in the lateral force resisting system; the number of storeys
of the buildings; available displacement ductility of the structural system; and the
ground type designed for.
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Deflections of reinforced concrete flat slabsEigelaar, Estee M. 03 1900 (has links)
Thesis (MScEng (Civil Engineering))--University of Stellenbosch, 2010. / ENGLISH SUMMARY: It is found that the serviceability limit state often governs the design of slender reinforced concrete
members. Slender flexural members often have a percentage tension reinforcement less than 1.0%
and an applied bending moment just above the point of first cracking. For such members, the
available methods to evaluate the serviceability conditions produce inadequate and unrealistic
results. The evaluation of the serviceability of a slender member includes the calculation of the
predicted deflection, either by empirical hand-calculation or analysing a finite element model, and
the verification using the span-to-effective-depth ratio.
The focus of the study is on flat slab structures. It investigates the different deflection prediction
methods and the span-to-effective-depth ratio verifications from various design standards. These
design standards include the ACI 318 (2002), the SABS 0100-1 (2000), the EC2 (2004) and the BS
8110 (1997). The background to the methods, as well as the parameters which influences the
deflection development for lightly reinforced members, are investigated in order to define the
limitations of the methods. As a result of the investigation of the deflection calculation methods, an
Alternative Approach is suggested and included in the comparisons of the various methods.
The deflection prediction methods and the span/effective depth verification procedures are
accurately formulated to predict the serviceability behaviour of beams. Additional approaches had
to be used to apply these methods to a two-dimensional plane such as that of a flat slab structure.
The different deflection prediction methods and the span/effective depth verification methods are
calculated and compared to the recorded data of seven experimental flat slab specimens as
performed by others. A study by Gilbert and Guo (2005) accurately recorded the flexural behaviour
of flat slab specimens under uniformly distributed loads for test periods up to 750 days. The
methods to evaluate the serviceability of a slender member were also applied to slab examples
designed using South African standards.
The study concludes by suggesting a suitable deflection prediction method for different parameter
(limitation) categories with which a slender member can comply to. The typical span/effective depth
ratio trend is also presented as the percentage tension reinforcement for a slender member changes. It is observed that the empirical hand-calculation methods present more reliable results
than those of the finite element models. The empirical hand-calculation methods are accurate
depending on the precision to which the slab was constructed relative to the actual slab design.
The comparison of the deflection methods with South African case studies identified the role played
by construction procedures, material parameters and loading history on slab behaviour. / AFRIKAANSE OPSOMMING: Die diensbaarheidstoestand is in baie gevalle die bepalende faktor vir die ontwerp van slank
gewapende beton elemente bepaal. Slank elemente, soos lig bewapende buigbare beton elemente,
het gewoonlik ‘n persentasie trekbewapening van minder as 1.0% en ‘n aangewende buigmoment
net wat net groter is as die punt waar kraking voorkom. Die metodes beskikbaar om die
diensbaarheid van sulke elemente te evalueer gee onvoldoende en onrealistiese resultate. Die
evaluering van die elemente in die diensbaarheidstoestand sluit in die bepaling van defleksies deur
berekening of die analise van ‘n eindige element model, en die gebruik van die span/effektiewe
diepte metode.
Die fokus van die studie is platbladstrukture. Die doel van die studie is om die verskillende metodes
vir die bereking van defleksie asook die verifikasie volgens span/effektiewe diepte metodes van die
verskillende ontwerp standaarde te ondersoek. Die ontwerp standaarde sluit die ACI 318 (2002),
SABS 0100-1 (2000), EC2 (2004) en die BS 8110 (1997) in. Die agtergrond van hierdie metodes is
ondersoek asook die parameters wat ‘n rol speel, sodat die beperkings van die metodes
geidentifiseer kan word. As ‘n gevolg van die ondersoek na die beperkings van die metodes, is ‘n
Alternatiewe Benadering voorgestel. Die Alternatiewe Benadering is saam met die metodes van die
ontwerpstandaarde gebruik om die verskille tussen die metodes te evalueer.
Die defleksievoorspelling en die span/effektiewe diepte verifikasie metodes is korrek geformuleer
om die diensbaarheid van balke te evalueer. Ander benaderings was nodig om die diensbaarheid van
blad blaaie te toets.
Die onderskeie defleksievoorspelling en span/effektiewe diepte metodes is bereken vir sewe
eksperimentele plat blaaie soos uitgevoer deur ander navorsers. Gilbert and Guo (2005) het ‘n studie
uitgevoer waar die buigingsgedrag van die sewe plat blaaie, met ‘n uniforme verspreide las vir ‘n
toetsperiode van tot 750 dae, akkuraat genoteer is. Die metodes om die diensbaarheid van ‘n slank
element te toets, was ook op Suid-Afrikaanse blad voorbeelde getoets. Dit was gedoen om die Suid-
Afrikaanse ontwerp van ligte bewapende beton elemente te evalueer. Die gevolgetrekkings stel ‘n gepaste defleksie metode vir ‘n slank element vir verskillende beperking
kategorië voor. Dit is ook verduidelik hoe die tipiese span/effektiewe diepte verhouding met die
persentasie trek bewapening vir ‘n slank element verander. Dit is bevind dat die imperiese
handmetodes om defleksies te bereken, meer betroubaar as die eindige element modelle se
resultate is. Die imperiese handberekening metodes is akkuraat relatief tot hoe akkuraat die blad
konstruksie tot die blad ontwerp voltooi is.
‘n Vergelyking van defleksieberekening met Suid-Afrikaanse gevallestudies het die belangrikheid van
konstruksieprosedures, materiallparamteres and belastingsgeskiedenis geïdentifiseer.
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The effect of seismic activity on reinforced concrete frame structures with infill masonry panelsJarvis, Wesley James 04 1900 (has links)
Thesis (MEng)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: Certain regions within the Western Cape Province are at risk of a moderate intensity
earthquake. It is therefore crucial that infrastructure in these areas be
designed to resist its devastating effect. Numerous types of structural buildings
exist in these seismic prone areas. The most common types are either reinforced
concrete framed buildings with masonry infill or unreinforced masonry
buildings. Many of these buildings predate the existence of the first loading
code of 1989 which provided regulations for seismic design. The previous code
was superseded in 2010 with a code dedicated to providing guidelines for seismic
design of infrastructure. A concern was raised whether these buildings
meet the requirements of the new code. A numerical investigation was performed
on a representative reinforced concrete framed building with masonry
infill to determine whether the building meets the new code’s requirements.
The results from the investigation show that the stresses at critical points in
the columns exceed the codified requirements, thus leading to local failure.
After careful review it was discovered that these local failures in the columns
will most likely lead to global failure of the building. / AFRIKAANSE OPSOMMING: In sekere streke in die Wes-Kaap bestaan daar risiko van matige intensiteit
aardbewings. Dit is dus noodsaaklik dat die infrastruktuur in hierdie gebiede
ontwerp word om die vernietigende uitwerking te weerstaan. Gebous
met verskillende tipes strukturele uitlegte kom in hierdie gebied voor. Die
mees algemene struktuur tipe is gewapende beton-raam geboue met baksteen
invol panele sowel as ongewapende baksteen geboue. Baie van hierdie geboue
is gebou voor die eerste las-kode van 1989 wat regulasies vir seismiese ontwerp
voorsien in gebruik geneem is. Die vorige kode is vervang in 2010 met ’n
kode toegewy tot die verskaffing van riglyne vir seismiese ontwerp van infrastruktuur.
Kommer het ontstaan of hierdie geboue voldoen aan die vereistes
van die nuwe kode. ’n Numeriese ondersoek is uitgevoer op ’n verteenwoordigende
gewapende beton geraamde gebou met baksteen panele om te bepaal
of die gebou voldoen aan die nuwe kode vereistes rakende sismiese ontwerp.
Die resultate van die ondersoek toon dat die spanning op kritieke punte in
die kolomme die gekodifiseerde vereistes oorskry, wat tot plaaslike faling lei.
Na verdere onderssoek is dit bepaal dat die plaaslike faling in die kolomme
waarskynlik tot globale faling van die gebou sal lei.
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