Enlarged cross section method is a method used to increase the components of the structure or increase the components of the reinforcement area , not only enhance the bearing capacity, but also can increase its cross section stiffness and change the natural frequency of vibration, the normal use of stage performance is improved, the reinforcement method is widely used in reinforced concrete structure of the beam, slab, column, etc.

（Section-enlarging Reinforcing Method for Concrete）

The application scope of enlarged section reinforcement method

Enlarged cross section method is suitable for the reinforcement of reinforced concrete bending and compression member. When beam, slab, column's load is different from eac other, and its stiffness can't meet the requirements, choose the section reinforcement is more effective.The concrete strength level of the original component is not lower than C10 according to the test results.Construction is the focal point of this method is to ensure that new and old concrete interface treatment and the quality of the bond, only when the processing interface and its bonding quality conforms to the specification requirements, can consider new concrete and existing concrete work together, the whole cross section to calculate.

The basic principle of reinforcement calculation for bending member

(1) when the strengthening flexural member only in compressive zone, the bearing capacity, crack resistance, steel bar stress, crack width and deflection calculation and checking, according to the current national standard specifications for design of concrete structures GB50010 provisions on composite type flexural member.If the calculation results show that the concrete laminated layer can meet the requirement of bearing capacity, the compression reinforcement and distribution reinforcement should be arranged according to the construction requirements.

(2) when the bending member is strengthened in the tensile zone, the new tensile reinforcement is considered, and the strength of the newly added reinforcement is reduced.

The construction requirement of increasing section reinforcement method

Enlarged cross section method in the aspect of structure design must solve the problem,"how to work with new added parts and the original part of the overall?". Test research shows that the reinforced structure will appearthe tensile, bending, shear etc all kinds of complex stress strength in the process of mechanical joint surface. The key is the shear and tension.In the elastic stage, the shear stress and normal stress mainly by combining surface on both sides of the new and old concrete bonding strength, under the cracking and limit state, mainly through the anchoring reinforcement or passive shear friction produced by anchor bolts.Due to the combination of surface concrete bonding shear strength and tensile strength is much lower than concrete strength, the combination surface is the weak link of reinforced arear, and the failure always occurs in combination .Therefore, combining with the surface must be treated, necessary configuration from the design structure of the combined surface enough through combining the shear friction reinforcement or anchorage connects two parts, is to ensure that the joint surface force effectively, whole work between old and new parts.

The construction points of enlarged section reinforcement method

1.Unloading before reinforcement

2.Connection surface treatment

3.The construction of new layer