Early attempts to achieve this effect were hampered both by the limited steel strengths available and by shrinkage and creep of the concrete under sustained compression, coupled with relaxation of the steel. This meant that the steel lost a large part of its initial pretension and as a result residual stresses were so small as to be useless. It is now possible, however, to produce stronger concretes which have good creep properties, and very high strength steels which can he stressed up to a high percentage of their 0.2 per cent proof stress are also available, for example, hard-drawn wires may carry stresses up to about three times those possible in grade 500 reinforcing steel. This not only results in savings of steel quantity, but also the effects of shrinkage and creep become relatively smaller and may typically amount to the loss of only about 25 per cent of the initial applied force. Thus, modern materials mean that the prestressing of concrete is a practical proposition, with...
The classification limits provided in Table. 5.2 assume that the cross-section is stressed to Clause 5.5.2(9) yield, though where this is not the case, clauses 5.5.2(9) and 5.5.2(10) may allow some Clause 5.5.2( 10) relaxation of the Class 3 limits. For cross-sectional checks and when buckling resistances are Clause 5.3 determined by means of a second-order analysis, using the member imperfections of clause
(4) Relaxation at temperatures of the structure over 20 C will be higher than given in Figure 4.8. This may affect building structures in hot climates, power plants, etc. If necessary the producer should be asked to include relevant information in the certificate see 3.3.2(2) . (5) Short-term relaxation losses at a temperature of the structure exceeding 60 C can be 2 to 3 times those at 20 C. However, in general, heat curing, over a short period, may be considered to have no effect on long term relaxation results (see 188.8.131.52.5). Figure 4.8 Relaxation losses after 1 000 h at 20 C Figure 4.8 Relaxation losses after 1 000 h at 20 C where APc, and APu(x) are defined in 184.108.40.206 and APir is the short-term relaxation loss. (7) The short-term relaxation loss (APir), which occurs in pre-tensioning between stressing the tendons and transferring the stress to the concrete, should be estimated using the data in 220.127.116.11.1.
The finite difference (relaxation) method90 has had a long-established use in civil engineering. Partial differential equations that define material behaviour and boundary conditions are replaced by finite-difference approximations at a number of discrete points throughout the rock mass. The resulting set of simultaneous equations is then solved. A finite difference computer program is available specifically designed for modelling The distinct element method or dynamic relaxation method101 allows a problem to be formulated assuming rock blocks to be rigid, with deformation and movement occurring only at the joints and fissures so that for this type of analysis in its simplest form no information is needed on the deformability and strength of intact rock. The method is a discontinuum modelling approach which is suitable in cases where the behaviour of the rock mass is dominated by the properties of joints or other discontinuities. In such cases the discontinuity stiffness (i.e. force...
He location of the earthquake is specified by the location of the focus or hypocentre, hich is the point on the fault here the rupture initiates and from where the first seismic waves are generated. This point is specified by the geographical coordinates of the epicentre, which is the projection of the hypocentre on the Earth's surface, and the focal depth, which is the distance of the hypocentre below the Earth's surface, measured in kilometres. Although for the purposes of observatory seismology, using recordings obtained on sensitive instruments at distances of hundreds or thousands of kilometres from the earthquake, the source can be approximated as a point, it is important to emphasise that in reality the earthquake source can be very large. The source is ultimately the part of the crust that experiences relaxation as a result of the fault slip the dimensions of the earthquake source are controlled by the length of the fault rupture and, to a lesser extent, the amount of slip on...
Limit states for anchorages typically involve structural failure of the anchor tendon or anchor head corrosion or distortion of the anchor head failure at the interface of the grout with the tendon or the surrounding ground instability of the ground containing the anchor and associated structures or loss of anchorage force owing to creep, relaxation, or excessive displacement of the anchor head. en 1997-1 8.3(1)P
Is the variation of stress in the tendons due to creep, shrinkage and relaxation at location x, at time t. is the variation of stress in the tendons at section x due to relaxation. This may be derived from Figure 4.8, for a ratio of initial stress characteristic tensile stress, (Bp fpk) calculated from
Ii) Class, indicating the relaxation behaviour P(6) In this Code, three classes of relaxation are defined (see 18.104.22.168) Class 1 for wires and strands, high relaxation Class 2 for wires and strands, low relaxation Class 3 for bars. 22.214.171.124 Relaxation P(1) The products shall be classified for relaxation purposes, according to the maximum percentages of loss of stress.
Relaxation Audio Sounds Babbling Brook
This is an audio all about guiding you to relaxation. This is a Relaxation Audio Sounds with sounds from the Babbling Brooks.