Crack Control of Reinforced Concrete Beams Reflections - Education Industry
Crack Control of Reinforced Concrete Beams Reflections - Education Industry
Abstract: reinforced concrete beam outside the direct stress and load times under stress, causing structural deformation and cracks. This paper analyzes the reinforced concrete beam crack causes and the corresponding control measures.
Keywords: reinforced concrete beam cracks Component in the course of the long-term effect by the annual range of temperature, when the temperature difference of expansion and contraction stress when the ultimate tensile strength greater than the component will crack. Crack by many factors, including structural design, foundation settlement differences, the construction quality, materials quality, environmental impact, regardless of cause of the cracks which will impact to the building body structure.
One, the reasons for crack formation. 1, the site of fracture. (A) the tensile cracks in beams. When pouring concrete construction because of poor management, poor use of steel, resulting in insufficient strength tensile steel beams. Construction, the early form removal, construction loads exceeding the design load or strength less than the design requirements, and the use of improper use of load greatly exceeds the original design load, the beam cracks in tension zone. Beam generated by the tensile cracks commonly used slurry closed, to prevent corrosion, and then do under the circumstances reinforcement processing. (B) of the beam near the diagonal crack in the bearing. Beam intensity lower than the design concrete strength, shear steel shortage, stirrups did not increase, some due to overload, early form removal strength when the concrete strength less than the standard value, resulting in a low and produce shear capacity of shear cracks. Should first deal with the bonding slurry hydraulic injection, further reinforcement, to ensure the safe use of beams. (C) of the beam compression zone cracks. Beam height is small, and some checking beam without crack, not compacting concrete vibrators, long beam on temperature and diurnal temperature deformation under the action of temperature and long-term environment in the dry state shrinkage deformation, beam temperature and shrinkage The comprehensive Cooperation With the next crack. Under the wide and narrow slit, a cross-cutting, not through the. Crack length for the high beam 3 / 5 4 / 5, not crack the bottom beam, which cracks can be pressure cement injection, bonding and sealing cracks and reinforced.
2, Analysis. Reinforced concrete beam cracks are complex, including: material or climatic factors, inappropriate construction, design and construction errors, change the function or use of unreasonable. Can generally be summarized as follows: shrinkage cracks. Concrete is still in the not fully hardened state, such as excessive drying, the shrinkage cracks, usually on the surface, irregular cracks, width small. When the hydration and hardening of cement cracks. Cement hydration and hardening process, distributed a lot of heat generated inside and outside the concrete temperature above a certain value, due to inconsistencies resulting from concrete shrinkage cracks. Temperature change cracks. During the hardening of cement, concrete, larger temperature difference between surface and interior, leading to rapid temperature changes of concrete surfaces have a greater cooling and contraction, are bound within the concrete, and cracks. Inadequate design. If enough cross section of reinforced concrete beams, beam span is too large, a high degree of small, or because of calculation error, the reinforced section is too small, improper location of reinforcement, the node is unreasonable, will be led to the structural cracks in concrete beams.
Second, control measures. Occurrence and composition of concrete cracks of concrete cement, net sand, gravel, mixing agent of raw materials, but also with concrete after pouring the insulation moisture conservation measures relevant. (A) the quality control of raw materials. Cement: In the concrete pavement and massive concrete facilities in the higher temperature rise caused by hydration heat, temperature range, the temperature easily cause cracks. To this end, should be used in the construction of the lower heat of hydration of cement, cement used to minimize the amount of units. Coarse aggregate: in reinforced concrete construction, the maximum size of coarse aggregate and reinforcement of structures, concrete water craft, larger aggregate size to reduce water consumption, concrete shrinkage and bleeding of the consequent reduction However, increasing the size of aggregate concrete segregation prone, therefore, must adjust grading design, and strengthen the vibration during the construction. For the size of 5 ~ 40mm stones require fewer needle sheet, ultra-low regulation, particle size distribution curves meet screening requirements, so to avoid blocking the pump, reduce the rate of sand, cement consumption, increasing concrete strength. The results showed that: The stone size 5-40mm 5 ~ 25mm diameter than the use of gravel to reduce water consumption per cubic meter of concrete around l5kg: cement ratio in the same circumstances, to reduce the amount of cement per cubic meter of concrete around 20kg (water-cement ratio 0.709), while reducing the temperature of concrete; when the particle size of 50mm gravel to meet the screening curve requirements, the sand rate control can be met in 42% of the pumping requirements.
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