H-beam is a new type of economic building steel.H-shaped steel has reasonable section shape, good mechanical properties, uniform extension of each point on the section and small internal stress during rolling. Compared with ordinary I-shaped steel, H-shaped steel has the advantages of large section modulus, light weight and metal saving, which can reduce 30-40% of the building structure; moreover, due to the flat inner and outer sides of the leg, the leg end is a right angle, and assembled into a component, which can save 25% of the welding and riveting work.It is often used in large-scale buildings (such as factory buildings, high-rise buildings, etc.) with large capacity and good section stability, as well as bridges, ships, hoisting and transportation machinery, equipment foundation, brackets, foundation piles, etc.

 H-beam is a kind of economic section steel with better section mechanical properties, which is developed by I-beam optimization. Especially, the section is named after the same letter “H”.Its characteristics are as follows:

       On the one hand, H-beam has wide flange and large lateral stiffness.It has strong bending resistance, about 5% – 10% higher than I-beam.The two surfaces of the flange are parallel to each other, which makes the connection, processing and installation simple.Compared with welded I-beam, it has the advantages of low cost, high precision, small residual stress, no need of expensive welding materials and weld inspection, and can save about 30% of the cost of steel structure fabrication.

       On the other hand, under the same section load, the weight of hot-rolled H steel structure is 15% – 20% less than that of traditional steel structure.Compared with the concrete structure, the hot rolled H steel structure can increase the use area by 6%, while the self weight of the structure can be reduced by 20% – 30%, and the design internal force of the structure can be reduced.H-shaped steel can be processed into T-shaped steel, and honeycomb beam can be combined to form various cross-section forms, which greatly meets the engineering design and production.

　   We all know that the steel structure engineering is systematic, and the room structure of each component needs precise calculation; if it is slightly beyond the scope of one error, it will affect the whole project; what is the problem in the steel structure construction that causes the steel structure deformation?

　　1.Arch camber of steel beam

The method of arching includes parabola arching and fold arching.For the portal frame, the arch is usually made up of broken line, that is to say, at the joint of steel beam, by controlling the angle of connecting end plate, the purpose of arch is achieved.

The purpose of steel beam arching is to offset some of the deformation after the roof steel beam is loaded and deformed, and the roof can still maintain a certain slope.If the camber of steel beam is too large, the roof slope near the ridge will be smaller, and if the deformation of steel beam is too large, the roof slope near the cornice will be smaller.

Too much slope change is not appropriate.Whether or not to arch, how big the arch, itself should be a design problem.When arch camber is not required in the design, the allowable deviation of camber is – 5 ~ 10 mm, that is to say, the construction party is not required to determine the amount of arch camber.

　　2.Improper installation of roof purlin leads to excessive deformation

In some projects, the connection plates of rigid tie bars and wind tie rods are set at different positions, which makes the horizontal support system not on the same plane, thus affecting the overall stability of the rigid frame.The rigid tie rod and the wind tie rod form a horizontal support system, and the setting height shall be consistent in the same slope direction.

In the installation of roof or wall purlin, some construction units increase and lengthen the bolt hole diameter of purlin or purlin support plate at will for the convenience of installation. Purlin is not only a component to support roof panel or hanging wall panel, but also a support set for corner braces of rigid frame beams and columns. Setting a certain number of corner braces can reduce the calculated length out of plane of rigid frame and effectively ensure the overall stability out of plane of rigid frame.If the diameter of purlin or purlin supporting plate is too large and too long, the corner brace will lose its proper function.

In addition, some units increase the roof load without authorization. In the original design, the suspended load such as suspended ceiling or equipment pipeline is not considered, while in the construction, the suspended load such as suspended ceiling is arbitrarily increased, resulting in excessive deflection or collapse of the steel beam.No unit shall increase the load beyond the design scope without authorization.In the process of construction or supervision, if such problems are found, it is required to send the increased load to the original design unit for review of structural bearing capacity, etc., and only when the structural safety and use requirements are met can roof lifting be carried out.

　　3.Crane beam deflection

Some industrial plants are designed with cranes.Crane beams and crane trusses shall not be deflected.But in the actual construction, including the construction and supervision units seldom check this index, so special attention should be paid!