Gelžbetoninių Konstrukcijų Normalinių Plyšių Pločio Skaičiavimo Metodų Analizė

Abstract

The width of normal cracks at the level of tensile reinforcement was calculated according to various methods using the data obtained from experimental tests on reinforced concrete beams (without reinforcement pre-stress), pre-cast reinforced concrete slabs and ribbed roof slabs. Th e numerical results were compared to actual crack widths measured during the experimental tests. Also, the crack widths of pre-stressed reinforced concrete beams were calculated according to various methods and compared with each other. Th e following conclusions were reached based on the analysis of numerical and experimental results: 1) Design stresses in tensile reinforcement calculated according to [STR] and [EC] design codes are very similar, although the calculation of such stresses is more logical and simple according to [EC]. Design stresses calculated according to [RU] are greater due to the estimation of the plastic deformations of concrete in the compressive zone. Th e method proposed by Rozenbliumas (Розенблюмас 1966) estimates tensile concrete above the crack peak, and thus allows a more accurate calculation of stresses in tensile reinforcement (Fig 3). Therefore, the latter stresses in pre-stressed RC beams may be decreased by 10–12 %, when height hct ≠ 0 (Fig 1, c) and ratio M/MRd varies between 0,65 and 0,75; 2) The widths of normal cracks in conventional RC beams (subjected to load that corresponds approx. 70 % of their carrying capacity) calculated according to [STR] and [EC] design codes are almost equal to the experimentally obtained crack widths. When beams and slabs are loaded by approximately 52 % of their carrying capacity, design crack widths wk [EC] are approximately 12 % less than wk [STR], although the design crack width wk [RU] is signifi cantly greater. Here, ratio β in the beams and slabs is equal to 2 and 3.3 respectively. Th erefore, the design code [RU] ensures higher probability that the crack width will not reach the limit value (for environmental class XO and XC1) equal in all design codes mentioned in this article; 3) In case of loaded prestressed reinforced concrete beams, the calculated increases of crack widths wk [EC], wk [RU] and w [5] are greater if compared to wk [STR] (Fig 6). Th e increased reinforcement ratio ρ has more signifi cant infl uence on the increases of crack widths calculated according to other design codes if compared to wk [STR]. Tensile concrete above the crack peak has signifi cant infl uence on the design crack width when pre-stressed RC beams are lightly reinforced (ρ ≤ 0,008); 4) During the evaluation of the state of fl exural RC members, expression (5) could be used for calculating the crack width or a position of the neutral axis when the heights of the crack and the tensile zone above the crack are known (calculated or measured experimentally). Design crack widths w (5) are very similar to the experimentally obtained results.

Crack Width and Load-Carrying Capacity of RC Elements Strengthened with FRP

“…A wide range of experimental research was conducted by Jokūbaitis et al [23][24][25][26][27][28], and the empirical expression of the critical width of a normal crack tip was derived for flexural RC elements:…”

Flexural behaviour of reinforced concrete members strengthened with prestressed CFRP laminate

“…Different approach was proposed by Jokūbaitis et al (Jokūbaitis and Kamaitis, 2000, Jokūbaitis, 2001, Jokūbaitis, 2009, Jokūbaitis and Juknevičius, 2009, Jokūbaitis et al 2013, Jokūbaitis and Juknevičius, 2013 based fracture mechanics of solids. In accordance with his crack development model for RC structures, the flexural RC element crack has two peaks, one leads to the crack spread toward the beam neutral axis, and the other refers to the tensile reinforcement.…”

“…where h cr and h ct are the crack depth and the depth of the tensile zone above it, respectively; w cr and δ cr.0 are the crack width and the critical width of a normal crack tip respectively. Wide range of experimental research were conducted by Jokūbaitis et al (Jokūbaitis and Kamaitis, 2000, Jokūbaitis, 2001, Jokūbaitis, 2009, Jokūbaitis and Juknevičius, 2009, Jokūbaitis et al 2013, Jokūbaitis and Juknevičius, 2013 and the empirical expression of the critical width of a normal crack tip was derived for flexural RC elements:…”

The Analysis Of Reinforced Concrete Box Girder Viaduct Defects and Their Estimation

“…Having compared the widths of flexural cracks calculated by the above mentioned methods, it was noticed that w k (STR 2.05.05:2005) and w k (ENV 1992(ENV -2:1996 calculating values differ up to 1.4 times, whereas the calculated stresses s s (STR 2.05.05:2005) and s s (ENV 1992(ENV -2:1996 are not different. Jokūbaitis and Juknevičius (2009), when analyzing the calculation of flexural crack widths of prestressed reinforced concrete beams according to the methods of STR 2. 05.05:200505.05: and ENV 199205.05: -2:1996, obtained similar results as in our calculations.…”