I. Determination of a reasonable span:
Different production process processes and use functions determine the span of the plant to a large extent. Some enterprises even require to design it into a more economic span according to their own use functions.A reasonable span shall be determined according to the height of the warehouse.
Under general circumstances, when the column is high and the load is certain, the span is increased appropriately, and the amount of steel used in the steel frame increases is not very obvious, but the space is saved, the basic cost is low, and the comprehensive benefit is considerable.It found that when the eaves height is 7.5m,, the steel amount of steel frame span between 18-30m is 10-15kg/m2, when the steel span between 21-48m is 12-24kg/m2, and 12m, span exceeds 48m (intermediate design swing column), the steel amount saving more than 40%, so the portal steel frame should be selected according to the specific requirements, and should not blindly pursue a large span.

Second, the choice of building length and width
Generally speaking, the principle of length is greater than the width, which can reduce the amount of steel used, and also reduce the air load between the column support, thus reducing the amount of steel used in the support system.
For example: 1: Building size 60 × 50m,, the plant shall be 60m as length and 50m as span direction, i. e.: 60 (L) × 50 (W) instead of 50 (L) × 60 (W).
III. Selection of floor slope
The floor slope shall be determined according to the comprehensive factors of the building panel structure, drainage slope length and column structure height, generally taking 1 / 10~1 / 30. The amount of steel used for different floor slopes has a greater impact.

We give examples of this example:
The results are calculated by analyzing the amount of steel at different floor breaks with a single span of 42m, cornice height of 6m:
When the floor break is 0.5:10, a frame weight is 3,682 Kg
When the floor break is 1.0:10, a frame weight is 3,466 Kg
When the floor break is 1.5:10, a frame weight is 3,328 Kg
When the floor break is 2.0:10, a frame weight is 3,240 Kg

As can be seen from the above, for a single span steel frame, a better way to reduce the weight of the steel frame is to increase the floor slope, the greater the slope, the more the steel saving.
However, for some multicross frames, the large slope will instead increase the amount of steel for the frame, due to the large break degree will result in the increase of the inner column length.When the building span is large, the breaking degree increase can reduce the deflection of roof steel dyeing.
After the research calculation, the more economic slope is:
Multi-span buildings: 1:20
Single span, with a span of less than 45m:0.5:10
Single span, with a span of less than 60m:1.5:10
Single span, with a span greater than 60m:2.0:10
In fact, the selection of floor slope is also related to whether the building parawall, the increase of slope will lead to the increase of parawall cost.
IV. Choose the cornice height
The cornice height has a great impact on the cost, mainly manifested in the following aspects

Increase in 1, cornice height will result in increased wall panel area, increased wall purlins, and increased steel use of columns;
2, If the steel column has no lateral support (e. g., or side column can not set corner support), the cornice height impact on the frame weight will be more prominent;
Increasing the height of the 3, cornice will result in an increased wind load acting on the frame.If the cornice height, building width is> 0.8, to control the lateral displacement, sometimes even need to change the column foot from hinge to steel.
V. Em height is determined by the following factors:
Net high requirements at the 1, cornice;
2, has the net height and beam height;
3, has a crane, crane beam and crane hook height.