1. Structural control of deflection is designed according to the normal use of the limit state.For steel structure, too much deflection will easily affect the roof drainage and create a sense of fear for people, and for concrete structure, too much deflection will cause local damage of durability (including concrete cracks).In my opinion, the above damages caused by excessive deflection of building structure can be solved by arching.

2. Some structures are easy to arch, such as double-slope portal girder, if the absolute deflection exceeds the limit, it can be adjusted by increasing the slope of the roof during fabrication.Some structure arching is not easy, such as for large span beams, if the relative deflection exceeds the limit, then each section of the beam has to be arching, due to the arching of the beam spliced for the folded line, and the deflection deformation for the curve, it is difficult to coincide with the two lines, which will result in the unevenness of the roof.For the frame flat beam is more difficult to arch, can not make the flat beam into a curved line.

3, if you are ready to arch, to reduce the amount of steel used by the deflection control of the structure, deflection control provisions to be reduced, then you must control the deflection of the live load, the deflection generated by the constant load with the arch to ensure that the deflection.