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Primary cracks (Figure 1) form when the tensile stress at the outer surface of the concrete reaches the tensile strength of concrete. When a primary crack forms, the concrete in the vicinity of the crack is relieved of any tension, resulting in a stress free zone near the crack.
Anchors, experimentally show a lower load-bearing capacity when installed in a cracked concrete member. The reduction is up to 40% with respect to the un-cracked condition, depending on the crack width. [7] The reduction is due to the impossibility to transfer both normal and tangential stresses at the crack plane.
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 high strength concretes).
Concrete has a very low coefficient of thermal expansion, and as it matures concrete shrinks. All concrete structures will crack to some extent, due to shrinkage and tension. Concrete which is subjected to long-duration forces is prone to creep. The density of concrete varies, but is around 2,400 kilograms per cubic metre (150 lb/cu ft). [1]
Example of flat piece of concrete having dislodged with corroded rebar underneath, Welland River bridge across Queen Elizabeth Way in Niagara Falls, Ontario. The expansion of the corrosion products (iron oxides) of carbon steel reinforcement structures may induce internal mechanical stress (tensile stress) that cause the formation of cracks and disrupt the concrete structure.
The derivation of the maximum arching moment of resistance of laterally restrained concrete bridge deck slabs utilised Rankin's [21] idealised elastic-plastic stress-strain criterion for concrete, valid for concrete cylinder strengths up to at least 70N/mm 2, which he had derived on the basis of Hognestad, Hanson and McHenry's [23] ultimate ...
For symmetrical configurations, the length of the crack from the line of symmetry is defined as and is half of the total crack length . Crack growth equations of the form d a / d N {\displaystyle da/dN} are not a true differential equation as they do not model the process of crack growth in a continuous manner throughout the loading cycle.
Typically concrete slabs perform better than implied by their R-value. [5] The R-value does not consider thermal mass, since it is tested under constant temperature conditions. Thus, when a concrete slab is subjected to fluctuating temperatures, it will respond more slowly to these changes and in many cases increase the efficiency of a building ...