As part of the process for this recommendation, the magnitudeof the effect of using NME instead of ME factors was examined in relation toindividual foods and mixed diets. In the case of individual foods, thedifference between the use of NME and ME factors for the estimated energycontent is minimal for foods with low protein and fibre contents, but can bequite large for foods that are high in protein and/or fibre. (The maximumdifferences for protein and fibre supplements would be 24 and 27 percent,respectively.) The use of NME rather than ME factors has less effect on theestimation of energy content for most mixed diets than it has for individualfoods, because about 75 percent of the energy in mixed diets derives from fatand available carbohydrate, which have the same NME and ME factors (Table 3.3).Estimates of the energy provided by “representative” mixeddiets[11] showed that the use of NMEinstead of the Atwater general factors resulted in a decrease in estimatedenergy content of between 4 and 6 percent. As previously discussed, however,these differences can be greater in some diets (Table 3.5). The use of ME foodconversion factors conceals the fact that energy expenditure derived fromassessments of heat production varies with the composition of the diet that isbeing metabolized. For this reason, it may be necessary to make corrections tothe estimates of food energy requirements in circumstances where the diet hassubstantial amounts of protein or fibre. The factors outlined in Box III.1 ofAnnex III may be used to facilitate these corrections.
Benefits have been reported in men and women, although the majority of studies have been conducted on men and some studies suggest that women may not see as much gain in strength and/or muscle mass during training in response to creatine supplementation [20, 51, 64, 86,87,88,89,90]. However, as will be described below, a number of other applications in sport may benefit athletes involved in high intensity intermittent and endurance events as well. In terms of performance, the International Society of Sports Nutrition (ISSN) has previously concluded in its position stand on creatine supplementation that creatine monohydrate is the most effective ergogenic nutritional supplement currently available to athletes in terms of increasing high-intensity exercise capacity and lean body mass during training [5, 78]. Recent position stands by the American Dietetic Association, Dietitians of Canada, and the American College of Sports Medicine on nutrition for athletic performance all drew similar conclusions [91, 92]. Thus, a wide-spread consensus now exists in the scientific community that creatine supplementation can serve as an effective nutritional ergogenic aid that may benefit athletes involved in numerous sports as well as individuals involved in exercise training.
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Creatine monohydrate is the most effective ergogenic nutritional supplement currently available to athletes with the intent of increasing high-intensity exercise capacity and lean body mass during training.
One of the first studies of base-restrained members was conducted by Stoffers (1978) and analysed the influence of reinforcement, wall geometry and restraint conditions on the morphology of cracks, their spacing and their widths, which enabled the introduction of such factors in the mechanism of cracking which would enable the calculation of crack width depending on the diameter and spacing of the reinforcement. Subsequent studies of various authors focused on the formulation of the computational model, assuming such a relationship of height to length for which exceeding the tensile strength of concrete led to the formation of dilatation cracks. As a result of making significant progress in determining the development of the heat of hydration and its influence on the development of physical properties, as well as the formal description of these phenomena, further research studies enabled attempts to combine and expand the problem of the mechanics of cracking by taking the development of thermal stresses increased by restraints along the edges of the member into consideration: Van Breugel (1982, 1995), Emborg (1989), Rostásy and Onken (1994). As far as analyses using FEM (fine element method) are concerned, attention should be paid to the research studies of the team of Pettersson and Thelandesson (2001a, 2001b) and Pettersson et al. (2002). These studies present a wide parametric analysis of the influence of the properties of concrete, the amount of reinforcement and the boundary conditions on the maximum crack width. The issue was simplified to 2D, i.e., only average strains were considered on the wall thickness. The intensive development of numerical methods enabled further refinements to the models, as exemplified by research studies performed by the team of Flaga and Klemczak (2016), Flaga (2011), which contain the proposal of an advanced numerical model and an engineering model which, from the point of view of designers who do not have access to advanced computer programs, allowing both the size of the deformation and its effects to be determined. The problem of the mechanics of cracking under the influence of imposed deformations takes multiple forms. For example, Klemczak and Knoppik-Wróbel (2015) and Knoppik-Wróbel (2015) presented a significant influence of the support conditions on the degree of restraint. If wall rotation is considered, the degree of restraint in the structural joint increases, but it decreases in the upper part of the wall. This effect is more visible in the case of longer walls and it is almost imperceptible in the case of shorter walls.
In the performed tests, the influence of reinforcement was clearly visible for the models of Series I and II, with a degree of reinforcement exceeding 0.5%. For lower degrees of reinforcement, this effect was less visible or not noticeable at all. In addition, in all cases, the number of cracks in the vicinity of the steel beam was the highest. For the members of Series I and II, the average crack width increased with the distance from the steel beam. In the case of Series III, the largest average crack width occurred 0.20 m above the steel beam.
Beeby and Forth (2005) analysed a simplified case of the wall joined along the lower edge (Fig. 1). They assumed a lack of reinforcement and the fact that with the increase of distance to the crack, the stresses are increasingly transferred to the wall by shearing at the contact with the base, until at a certain distance Lo from the crack, stress distribution is constant. Such an assumption is fundamentally different if compared to a member restrained along the opposite edges, where the effect of cracking reduces stiffness globally. In this case, the formation of cracks causes the stiffness to change locally. Outside the Lo area, it is assumed that the stress state is undisturbed and that cracks do not affect the widths of other cracks. Similar assumptions were adopted by Bamforth et al. (2015). They found that a greater degree of restraint would result in wider cracks and that the formation of a new crack did not affect the width of the existing cracks.
Equation (31) is also included as a reference in ACI 207.2R-95 (1995) which, among many approaches describing crack width, adopted the equation developed by Gergely and Lutz (1968). The formula defining the crack width is based on statistical research, and in the case of massive structures, takes the following form:
In CIRIA C660 (2007), the method of calculation of crack width in imposed deformations is based on the relationship between standards EN 1992-1-1 (2004) and EN 1992-3 (2006). However, the difference is that in the case, where external restraint have their effect, the imposed deformation which determines the crack width is defined as
A completely different approach to the cracking of hardening concrete is presented in JCI (2008) and it concerns the period from casting a member to the structure reaching a temperature equal to the ambient temperature. During this period, the influence of drying shrinkage and non-linear temperature distributions on the thickness of the member that may cause surface cracks are neglected. It is assumed that these phenomena can be effectively eliminated through technology and water curing. The crack control model is based on the probability of crack formation:
The necessity of taking into account the total effect of external loads and imposed strains on the width of cracks was first discussed in DIN EN 1992-1-1/NA (2011). Research performed by Turner et al. (2017) proves that summing up the effects of imposed strains and external loads is the correct approach. Moreover, it was demonstrated that loads occurring later can double the width of the crack in relation to its width during the maturing of concrete.
where σrest,max is imposed deformations stress, Eeff is effective modulus of concrete elasticity, wck,lim is crack width limit, 1.1 is factor denoting a decrease in the width of the subsequent secondary cracks referred to the width of the primary crack, and n is value rounded up to the next integer.
The model takes into account the widening of the cracks in consecutive stages of the imposed restraint occurrence and self-stresses. Measurements of strains that were performed on cracked cross sections of semi-massive structures confirm this fact (Zych & Seruga, 2019). The width increase of cracks of Type I depends on, among other factors: the size and type of load (temperature, shrinkage, external load), current extent of wall cracking, changes of mechanical properties of concrete during the whole period of maturing. The crack width which occurs first is calculated with the following expression:
where tI is time immediately prior to cracking and tII is time immediately after cracking. Next, taking account of cracking, conditions of partial restraint and the effect of time the tensile force in the specimen was described after the formula: 2ff7e9595c
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