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- Persson, Bertil
(författare)
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Quasi-instantaneous and Long-term Deformations of High-Performance Concrete with Some Related Properties
- 1998
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This report outlines an experimental and numerical study on quasi-instantaneous and long-term deformations of High-Performance Concrete, HPC, with some related properties. For this purpose about two hundred small cylinders and about one thousand cubes of eight types of HPC were cast. The age at loading varied between 18h and 28 days. Other principal properties of HPC were studied up to 4 years' age. Creep deformations of the HPC were studied from 0.01 s of loading time until 5 years' age. The work also includes observations of recovery at unloading and transversal deformations (Poisson's ratio). Elastic modulus and dynamic modulus of elasticity were studied on both young and mature concrete. Parallel studies were performed on shrinkage, strength, hydration, carbonation and on internal relative humidity of HPC. Supplementary dimensional studies were performed on twenty larger cylinders. Field studies were carried out on almost thirty prestressed beams. The results show good correlation between maturity and the quantity of creep of HPC. The results also show good correlation between, on one hand, the stress level and the mix design of the HPC and, on the other hand, the creep properties of HPC given a constant loading time. The phenomenon named autogenous shrinkage was observed during the study. The autogenous shrinkage was related to the self-desiccation and chemical shrinkage in HPC. Also the elastic properties of HPC were dependent on the moisture state at testing. The field studies on beams confirmed the findings in the laboratory. The short-term studies indicated that the creep rate (related to unit stress) of mature HPC was fairly independent of the compressive strength. The short-term basic creep rate (related to unit stress) of HPC after heat curing was observed to be twice as large at -1°C as at other temperatures. Besides loading time, the long-term compliance of HPC was mainly dependent on the maturity and the compressive strength both when loading the HPC and at 28 days' age. The creep was slightly reduced by use of 10% silica fume instead of 5%. The calculated long-term total compliance of the present study coincided reasonably well with previous research, taking into account that the exact HPC mix was unknown. However, the observed creep compliance was slightly larger than previously seen. The initial compliance calculated according to the previous studies was more affected by the strength than were the results of the present study. The following principal results were obtained: · Elastic modulus was related to compressive strength and porosity as demonstrated in normal strength concrete, NSC. · The creep rate (related to unit stress) was dependent on both the duration of loading and the maturity of the HPC. · Creep properties of the HPCs obtained by the quasi-instantaneous loading were applicable to the long-term studies performed with a much lower loading rate. · Specific creep was shown to be reduced with increase in silica fume content. Autogenous shrinkage was reduced by the use of granulated silica fume instead of silica fume slurry due to the greater fineness.
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| 2. |
- Persson, Bertil
(författare)
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Migrän : Genetiskt inflytande, uppväxtförhållanden och personlighet i migränfamiljen
- 1994
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The monograph consists of an extensive survey of psychological and behavioral genetic research on migraine, reports of three empirical studies in this area and an extensive English summary. Study 1 indicated persons with migraine (n=28) drawn from a neurological clinic to have experienced negative psychosocial events to a significantly greater extent during their development than persons free of migraine in general population (n=28) had. In study 2, part 1 involving 30 subjects with migraine 87% reported stress as a major migraine trigger (the headache often appeared after stress). Study 2, part 2, a family history study showed there to be a significantly greater prevalence of migraine (27%) among the siblings of the same 30 migraine subjects than among the siblings of 30 migraine-free controls drawn from the general population (10%). This result suggests the heritability of migraine, although the high discordance found also points to the importance of the within-family environment. Study 3, part 1, involving 30 sibling pair in which the one had migraine (migraine sibling) and the other was migraine-free and use of various personality instruments (Eysenck Personality Inventory, EPI; Coulour Word Test, CWT; Visual Aftereffects, VAE; Meta Contrast Technigue, MCT; and Ceasarec-Markes Personality Schedule, CMPS) showed the migraine siblings to score significantly higer on neuroticism (EPI), to be more sensitive (MCT; EPI) to disply signs of greater anxiety (VAE; CWT) and to report greater scarcity of friends during childhood and less verbal as well as nonverbal encouragement from their parents, than the migraine-free siblings. Neuroticism was found to correlate significantly with migraine, but not with headache frequency or severity in the migraine group. It is argued that, due to the high neuroticism of migrainics, psychotherapy should be considered as an alternative to other prophylactic treatments such as use of beta-adrenoceptor blockers, although the acute onset should be pharmacologically treated. Study 3, part 2, employed a special developed Sibling Behavioral Genetic Method (SBM) involving participants of 30 full sibling pairs, one sibling with and the other without migraine, and also a new pairing of the same subjects so as to produce genetically unrelated pairs (again one with and the other without migraine). Both groups were approximately similar on factors such as SES, age, gender, grade and sixe of the maily. A certain model was applied to test an additive genetic hypothesis. Out of 21 personality factors sensitivity (MCT), achievement (CMPS), extraversion-introversion (EPI), aggression (CMPS), anxiety (CWT), guilt-feelings, exhibition and succorance (CMPS) fit the model assuming additive genetic influences. However, within family environment appeared to be the major source of variance for most of the traits. Neuroticism (EPI), anxiety (MCT) and defense of status (CMPS) could be accounted for socioeconomic status (SES). The results also supported the assumption thatgenetically related siblings reared together experience quite different envoronments, as different in fact as the genetically unrelated controls.
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