How to Optimize the Design of Steel Structure Portal Frame

Optimum design of steel structures is not only to reduce the amount of steel used, but to grasp the overall concept, which involves factors such as load taking, building structural form, force transmission path, material properties and so on.

Steel amount of portal frame is related to with structural style, loading, size of buildings, quality of steel and others. The building size mainly including the span of frame, distance of column, height of eave, and Slop of roof, When initial condition confirm of the steel structure project, should find economic and resonable condition in the variable condition.

1. Crane and live load are factors of column space, When big loading, the column space should small, 6-7.5m is suitable, generally is 6m, Small loading the column space used 8-10m, general 9m, increase the column space should comprehensive consider the influence Girts and Purlins for the price.

2. The span of frame has the optimal size, mainly influence factor is loading, small loading, 24-36m span is suitable, big span, economic span is 18-24m.

3. The stress control of steel frame, structural calculation of steel structure generally used computer program analysis, the steel frame on the condition of stable, the stress control of steel parts in the range 0.90-0.95, The Steel Structural such as cross section of beam height should more high , decrease the thickness of web plate, that can decrease the steel quantity. When steel frame a little high, general control by stability stress, now can add strong tie bar on the middle of column, decrease calculate height of column. 

4. Flange brace can decrease the length of rigid frame, when cross section of beam more high, stability stress is control factor, flange brace can stop the instable because beam pressed. The space between two flange brace is twice as the space of purlin. 

5. Frame structural better used one kind of steel, consider from the economic, when the strength is major factor, used Q345B, when stable is major factor, used Q235B, Q345 can more save 15%-25% than the Q235.

6. There are two connection methods of steel column: knuckle joint and rigid connection, when generally no crane, the steel column used rigid connection. When the workshop have complex requirements, the column used knuckle joint.