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id stringlengths 40 40	title stringlengths 15 120	text stringlengths 41 3.14k	source stringclasses 2 values
ab8bdf3f058abbb146538084b7286071e7e168c5	sir charles edward saunders, frsc (february 2, 1867	sir charles edward saunders, frsc (february 2, 1867 – july 25, 1937) was a canadian agronomist. he was the inventor of the 'marquis' wheat cultivar. saunders secondary school in london, ontario is named for him and other members of his prominent family, including his father, agriculturist william saunders and naturalis...	wikipedia
64ae222fc3073db8776fd664d12fb42e9e5ae2e8	creep and shrinkage of concrete are two physical	creep and shrinkage of concrete are two physical properties of concrete. the creep of concrete, which originates from the calcium silicate hydrates (c-s-h) in the hardened portland cement paste (which is the binder of mineral aggregates), is fundamentally different from the creep of metals and polymers. unlike the cree...	wikipedia
9ae18c9e46be39d453a6e12d87679928f95ca589	creep and shrinkage of concrete are two physical	initial elastic strain. when a deformation is suddenly imposed and held constant, creep causes relaxation of critically produced elastic stress. after unloading, creep recovery takes place, but it is partial, because of aging. in practice, creep during drying is inseparable from shrinkage. the rate of creep increases ...	wikipedia
92040eeb3fef4cf11b2dd23a5f77fc006e94ea92	creep and shrinkage of concrete are two physical	portland cement paste. it is caused by slips due to bond ruptures, with bond restorations at adjacent sites. the c-s-h is strongly hydrophilic, and has a colloidal microstructure disordered from a few nanometers up. the paste has a porosity of about 0.4 to 0.55 and an enormous specific surface area, roughly 500 m2/cm3...	wikipedia
6403d3802501fcdc087c98f8710cb2bc8f3d7e06	the best approach to computer creep analysis of	the best approach to computer creep analysis of sensitive structures is to convert the creep law to an incremental elastic stress–strain relation with an eigenstrain. eq. (1) can be used but in that form the variations of humidity and temperature with time cannot be introduced and the need to store the entire stress hi...	wikipedia
7d0a9f40a5f8ddce2d45c8d3a2e54febf92e752a	in preliminary design of structures, simplified calculations may	in preliminary design of structures, simplified calculations may conveniently use the dimensionless creep coefficient φ (t, t ′) = e (t ′) j (t, t ′) − 1 {\displaystyle \varphi (t,t')=e(t')j(t,t')-1} = ϵ creep / ϵ initial {\displaystyle \epsilon _{\mbox{creep}}/\epsilon _{\mbox{initial}}}. the change of structure state...	wikipedia
4038d9d2c369e0a2bbd3450160caf5cb63391132	the creep effects are particularly important for prestressed	the creep effects are particularly important for prestressed concrete structures (because of their slenderness and high flexibility), and are paramount in safety analysis of nuclear reactor containments and vessels. at high temperature exposure, as in fire or postulated nuclear reactor accidents, creep is very large an...	wikipedia
054703ffcd8fe26ea7bd4fc73544310226cd0054	creep and shrinkage can cause a major loss	creep and shrinkage can cause a major loss of prestress. underestimation of multi-decade creep has caused excessive deflections, often with cracking, in many of large-span prestressed segmentally erected box girder bridges (over 60 cases documented). creep may cause excessive stress and cracking in cable-stayed or arch...	wikipedia
46d9a8101efa998dada34cf1804347aaaf919bce	the foregoing form of functions j (t, t	the foregoing form of functions j (t, t ′) {\displaystyle j(t,t')} and ϵ s h (t) {\displaystyle \epsilon _{sh}(t)} has been used in the design of structures of high creep sensitivity. other forms have been introduced into the design codes and standard recommendations of engineering societies. they are simpler though le...	wikipedia
30e2cbb6b57b092c3cae97c8fd7112ac69636c2a	empirical formulae have been developed for predicting the	empirical formulae have been developed for predicting the parameter values in the foregoing equations on the basis of concrete strength and some parameters of the concrete mix. however, they are very crude, leading to prediction errors with the coefficients of variation of about 23% for creep and 34% for drying shrinka...	wikipedia
21aceebf9bd6a61abff15d2162d50cd340ca4041	where f (t) = exp { − 8	where f (t) = exp { − 8 } {\displaystyle f(t)=\exp\{-8\}} and t 0 ′ = max (t ′, t 0) {\displaystyle t'_{0}=\max(t',t_{0})}. the form of the expression for shrinkage halftime τ s h {\displaystyle \tau _{sh}} is based on the diffusion theory. function 'tanh' in eq. 8 is the simplest function satisfying two asymptotic con...	wikipedia
64c1f064a916fec0df60516577b67cfd33527454	where d = 2 v / s {\displaystyle	where d = 2 v / s {\displaystyle d=2v/s} = effective thickness, v / s {\displaystyle v/s} = volume-to-surface ratio, k t {\displaystyle k_{t}} = 1 for normal (type i) cement; k s {\displaystyle k_{s}} = shape factor (e.g., 1.0 for a slab, 1.15 for a cylinder); and ϵ s h ∞ ≈ ϵ s ∞ e (607) / (e (t 0 + τ s h) {\displaysty...	wikipedia
5e570fe33c7a046c4376e5aba14da2b9ecef4ba0	although multidimensional finite element calculations of creep and	although multidimensional finite element calculations of creep and moisturediffusion are nowadays feasible, simplified one-dimensional analysis of concrete beams or girders based on the assumption of planar cross sections remaining planar still reigns in practice. although (in box girder bridges) it involves deflection...	wikipedia
42509748c811eb676066e13d51c788a1a882e865	conversion to a rate-type form is also necessary	conversion to a rate-type form is also necessary for introducing the effect of variable temperature, which affects (according to the arrhenius law) both the kelvin chain viscosities and the rate of hydration, as captured by t e {\displaystyle t_{e}}. the former accelerates creep if the temperature is increased, and the...	wikipedia
bb052d733137947a49a60ae3a9125a37e7a2d95c	for finite element structural analysis in time steps,	for finite element structural analysis in time steps, it is advantageous to convert the constitutive law to a rate-type form. this may be achieved by approximating c g (θ) {\displaystyle c_{g}(\theta)} with a kelvin chain model (or the associated relaxation function with a maxwell chain model). the history integrals su...	wikipedia
f88b18e3329bf039c68762de74bc3b299ecd3a2b	where k s h {\displaystyle k_{sh}} = shrinkage	where k s h {\displaystyle k_{sh}} = shrinkage coefficient. since the ϵ ˙ s h {\displaystyle {\dot {\epsilon }}_{sh}} -values at various points are incompatible, the calculation of the overall shrinkage of structures as well as test specimens is a stress analysis problem, in which creep and cracking must be taken into ...	wikipedia
89a109f99df6281f95cd045983a6df1c82efbb1c	the evolution of humidity profiles h (x, t)	the evolution of humidity profiles h (x, t) {\displaystyle h(\mathbf {x},t)} (x {\displaystyle \mathbf {x} } = coordinate vector) may be approximately considered as uncoupled from the stress and deformation problem and may be solved numerically from the diffusion equation h ˙ = {\displaystyle {\rm {{\dot {h}}=}}} div +...	wikipedia
304f21df1869227ceca072fb14fef8bfe3cc576a	at variable environment, time t {\displaystyle t} in	at variable environment, time t {\displaystyle t} in eq. (3) must be replaced by equivalent hydration time t e = ∫ β h β t d t {\displaystyle t_{e}=\int \beta _{h}\beta _{t}{\mbox{d}}t} where β h {\displaystyle \beta _{h}} = decreasing function of h {\displaystyle h} (0 if h < {\displaystyle h<} about 0.8) and β h ∝ e ...	wikipedia
1c1181deb980b47b2fcc6895dd41eb7703c1ed7d	the concept of microprestress is also needed to	the concept of microprestress is also needed to explain the stiffening due to aging. one physical cause of aging is that the hydration products gradually fill the pores of hardened cement paste, as reflected in function v (t) {\displaystyle v(t)} in eq. (3). but hydration ceases after about one year, yet the effect of ...	wikipedia
57ff09346f14e4c3de39cd1762e4eb546ba211d1	where c 0, c 1 {\displaystyle c_{0},c_{1}} =	where c 0, c 1 {\displaystyle c_{0},c_{1}} = positive constants (the absolute value ensures that s {\displaystyle s} could never become negative). the microprestress can model the fact that drying and cooling, as well as wetting and heating, accelerate creep. the fact that changes of w {\displaystyle w} or h {\displays...	wikipedia
405a609bdb0594bbe08401f14d95cfbd93e4ae69	a crucial property is that the microprestress is	a crucial property is that the microprestress is not appreciably affected by the applied load (since pore water is much more compressible than the solid skeleton and behaves like a soft spring coupled in parallel with a stiff framework). the microprestress relaxes in time and its evolution at each point of a concrete s...	wikipedia
c429c77571ca0af5587f8e145da50112cbd8d0d1	at variable mass w {\displaystyle w} of evaporable	at variable mass w {\displaystyle w} of evaporable (i.e., not chemically bound) water per unit volume of concrete, a physically realistic constitutive relation may be based on the idea of microprestress s {\displaystyle s}, considered to be a dimensionless measure of the stress peaks at the creep sites in the microstru...	wikipedia
d1125ff8f79702aaa49cffbe96d5381a6966f4a3	equations (3) and (4) are the simplest formulae	equations (3) and (4) are the simplest formulae satisfying three requirements: 1) asymptotically for both short and long times θ {\displaystyle \theta }, j ˙ (t, t ′) {\displaystyle {\dot {j}}(t,t')}, should be a power function of time; and 2) so should the aging rate, given by d v − 1 (t) / d t {\displaystyle {\rm {{\...	wikipedia
717a4202737a74274969d926a8d22444073a900e	where x ˙ = ∂ x / ∂	where x ˙ = ∂ x / ∂ t {\displaystyle {\dot {x}}=\partial x/\partial t}; η f {\displaystyle \eta _{f}} = flow viscosity, which dominates multi-decade creep; θ {\displaystyle \theta } = load duration; λ 0 {\displaystyle \lambda _{0}} = 1 day, m = 0.5 {\displaystyle m=0.5}, n = 0.1 {\displaystyle n=0.1}; v (t) m p a − 1 {...	wikipedia
b971245097274ae0bdd384cfef7c964ee18ef1eb	in measurements, young's elastic modulus e {\displaystyle e}	in measurements, young's elastic modulus e {\displaystyle e} depends not only on concrete age t ′ {\displaystyle t'} but also on the test duration because the curve of compliance j (t, t ′) {\displaystyle j(t,t')} versus load duration t − t ′ {\displaystyle t-t'} has a significant slope for all durations beginning with...	wikipedia
6627e1dc19f8eb101376c4e29898270f847e6f3d	in measurements, young's elastic modulus e {\displaystyle e}	t')=\lim _{\delta \to 0}j(t'+\delta,t')} happens to be approximately age-independent, which makes q 1 {\displaystyle q_{1}} a convenient parameter for defining j (t, t ′) {\displaystyle j(t,t')}.	wikipedia
5153c006d7592124fbe2d62323644eef155e29ef	at high stress, the creep law appears to	at high stress, the creep law appears to be nonlinear (fig. 2) but eq. (1) remains applicable if the inelastic strain due to cracking with its time-dependent growth is included in ϵ 0 (t) {\displaystyle \epsilon ^{0}(t)}. a viscoplastic strain needs to be added to ϵ 0 (t) {\displaystyle \epsilon ^{0}(t)} only in the ca...	wikipedia
ee8f717fccbb3b485f4a863a3b77672525186a41	to generalize eq. (1) to a triaxial stress–strain	to generalize eq. (1) to a triaxial stress–strain relation, one may assume the material to be isotropic, with an approximately constant creep poisson ratio, ν ≈ 0.18 {\displaystyle \nu \approx 0.18}. this yields volumetric and deviatoric stress–strain relations similar to eq. (1) in which j (t, t ′) {\displaystyle j(t,...	wikipedia
77e5957b735df088aeb6cc17fa540eaaadbe3fa8	here ϵ 0 {\displaystyle \epsilon ^{0}} denotes shrinkage	here ϵ 0 {\displaystyle \epsilon ^{0}} denotes shrinkage strain ϵ s h {\displaystyle \epsilon _{sh}} augmented by thermal expansion, if any. the integral is the stieltjes integral, which admits histories σ (t) {\displaystyle \sigma (t)} with jumps; for time intervals with no jumps, one may set d σ (t ′) = d t ′ {\displ...	wikipedia
423d7a386250e00cb6a9c65d2210b1808dd71f8f	in service, the stresses in structures are <	in service, the stresses in structures are < 50% of concrete strength, in which case the stress–strain relation is linear, except for corrections due to microcracking when the pore humidity changes. the creep may thus be characterized by the compliance function j (t, t ′) {\displaystyle j(t,t')} (fig. 2). as t ′ {\disp...	wikipedia
72e161d8d72c527fbefe72bb19478c2ba1dd04b3	the creep originates in the calcium silicate hydrates	the creep originates in the calcium silicate hydrates (c-s-h) of hardened portland cement paste. it is caused by slips due to bond ruptures, with bond restorations at adjacent sites. the c-s-h is strongly hydrophilic, and has a colloidal microstructure disordered from a few nanometers up. the paste has a porosity of ab...	wikipedia
107ba797ff19aa0eb9730f4de96ad285265330d5	the chemical processes of portland cement hydration lead	the chemical processes of portland cement hydration lead to another type of shrinkage, called the autogeneous shrinkage, which is observed in sealed specimens, i.e., at no moisture loss. it is caused partly by chemical volume changes, but mainly by self-desiccation due to loss of water consumed by the hydration reactio...	wikipedia
209498d339f0f7d16e31634121219fb7f0111726	drying shrinkage at high humidities (fig. 1 top	drying shrinkage at high humidities (fig. 1 top and middle) is caused mainly by compressive stresses in the solid microstructure which balance the increase in capillary tension and surface tension on the pore walls. at low pore humidities (<75%), shrinkage is caused by a decrease of the disjoining pressure across nano-...	wikipedia
dd1af806c5334463ad8b08f8d071718bb29d3898	in practice, creep during drying is inseparable from	in practice, creep during drying is inseparable from shrinkage. the rate of creep increases with the rate of change of pore humidity (i.e., relative vapor pressure in the pores). for small specimen thickness, the creep during drying greatly exceeds the sum of the drying shrinkage at no load and the creep of a loaded se...	wikipedia
b5bf5a7543dda6f3ebabc2802a3a407c19229783	the multi-year creep evolves logarithmically in time (with	the multi-year creep evolves logarithmically in time (with no final asymptotic value), and over the typical structural lifetimes it may attain values 3 to 6 times larger than the initial elastic strain. when a deformation is suddenly imposed and held constant, creep causes relaxation of critically produced elastic stre...	wikipedia
3242da1760b8164f680f7344ae7b45a41ed6db69	changes of pore water content due to drying	changes of pore water content due to drying or wetting processes cause significant volume changes of concrete in load-free specimens. they are called the shrinkage (typically causing strains between 0.0002 and 0.0005, and in low strength concretes even 0.0012) or swelling (< 0.00005 in normal concretes, < 0.00020 in hi...	wikipedia
79ba3da287da8c49e1d87e2a4dcb23c18c064e40	creep and shrinkage of concrete are two physical	creep and shrinkage of concrete are two physical properties of concrete. the creep of concrete, which originates from the calcium silicate hydrates (c-s-h) in the hardened portland cement paste (which is the binder of mineral aggregates), is fundamentally different from the creep of metals and polymers. unlike the cree...	wikipedia
db54ec4242c141472db50f24c0dab45f724e8daa	in geometry, the conchoid of dürer, also called	in geometry, the conchoid of dürer, also called dürer's shell curve, is a plane, algebraic curve, named after albrecht dürer and introduced in 1525. it is not a true conchoid.	wikipedia
3f6ce7d08e9647905cd0399c460a184cd44a3e9a	it was first described by the german painter	it was first described by the german painter and mathematician albrecht dürer (1471–1528) in his book underweysung der messung (instruction in measurement with compass and straightedge p. 38), calling it ein muschellini (conchoid or shell). dürer only drew one branch of the curve.	wikipedia
178a49492a61a4bcddac1bfbadb336e23b196977	the envelope of straight lines used in the	the envelope of straight lines used in the construction form a parabola (as seen in durer's original diagram above) and therefore the curve is a point- glissette formed by a line and one of its points sliding respectively against a parabola and one of its tangents.	wikipedia