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The first set of building regulations for reinforced concrete were drafted under the leadership of professor Morsch of the university of Stuttgart and were issued in Prussia in 1904. Design regulations were issued in Britain, France, Austria, and Switzerland between 1907 and 1909.
5. Crack causes
Reinforced concrete beam appears crack of causes is complex, main has material or climate factors, and construction improper, and design and construction errors, and change using features or using does not reasonable,, usually can summed up for following several:
1, Concrete is not full hardened State Shi, as drying had fast, is produced shrink crack, usually occurred in surface Shang, crack does not rules, width small.
2, When cement hydration and hardening cracks. Cement hydration and hardening process, distributing a lot of heat, makes concrete internal and external temperature, exceeds a certain value, the inconsistent due to the shrinkage of concrete and cracks.
3, Temperature cracks. During cement hardening, concrete surface and internal temperature is large, leading to concrete surface temperatures and larger temperature changes dramatically shrink, bound by concrete and cracks.
4, Design and incomplete. Inadequate cross-section of reinforced concrete beams, height beam span is too large, too small, or because of a calculation error, effective bar section is small, reinforced improperly, nodes are not reasonable causes structural cracks of concrete beam.
5, Construction quality resulting in cracks. Due to the low concrete grade, effective bar section is small, sectional dimensions do not conform to the design led to the concrete beam cracks. Due to improper construction, formwork support sink, or premature demolition of bottom mold and supporting the formation of cracks. Construction of lax controls, overload load on the beam, which could cause a crack.
6, Prefabricated reinforced concrete beams in the course of transport, lifting, because the support is not reasonable, the hang point location, and vibration or shock loadings and larger, can also cause cracks of reinforced concrete beams.
7, Used in the procedure, alter function, change offices to warehouses, roofing and floor, improper use, increasing the load on the beam, all of them you get cracks.
6. Cause of cracks
According to crack, cracks can be pided into two types: one is the General due to materials, climate, plastic shrinkage cracking and shrinkage cracks. Such cracks on bearing small, General or do not deal with cracks in another clear influence of beam's carrying capacity, with the expansion and extension of crack, reach yield strength of reinforcement and concrete compression zone variable increases stiffness greatly reducing, component damage. This type of cracks in reinforcement must be taken as soon as possible, to meet the structural safety requirements. For crack dealing, first pay attention to the investigation and analysis on cracks, determine the type, extent, damage and reinforcement of cracks based on. Survey from the crack width, length, whether through location, whether the elasticity limit stress, there is no moisture or water leakage, site environmental design and construction drawings, many start with analysis of nature of the causes of cracks, to take the appropriate measures.
(A) After investigation analysis, confirmed crack in does not reduced hosted force of situation Xia, take surface processing law, and filling law, and injected law, simple of processing method:
1,Surface patch law: the law applies Yu sewing more narrow, to recovery widget surface beautiful and improve durability Shi by used, common of is along concrete crack surface laying film material, General available ring oxygen class resin or resin impregnated glass cloth. Construction of concrete surfaces with a wire brush before damage, washed and dry.
2, Filling method: when the crack is wider, along cracks of concrete surface cut into a v-shaped or u-shaped Groove, resin mortar material to fill, you can also use materials such as cement mortar or asphalt. Construction, debris cleared in the first slot and, if necessary, Prime Binder, filled filling full hardening, surface polished with grinding or polishing machines.