How To Do Detailed Design Drawings of "Portal Frame" Building?

What is "Portal Frame" building?

Portal frame light-weight steel structure is a structural system composed of beams, columns and other components. It has the characteristics of light weight, large use space, and strong earthquake resistance. It is widely used in factories, warehouses, supermarkets, entertainment and sports facilities, station and other public buildings.

How to do detailed design drawings of "Portal Frame" building?

There is an intermediate process between the structural design and the manufacturing and installation of the steel structure of light-weight building with gabled-frame-the detailed design.

As the link carrier of structural design and on-site construction, detailed design generally needs to be divided into three stages to make a portal frame building from a simple structural design to a building entity manufactured in a factory and installed on site: detailed design preparation stage,detailed design stage and the output stage of results.

Stage 1: Preparation for detailed design

The first thing needs to do is to have an in-depth familiarity with the drawings, and then carry out a preliminary three-dimensional construction in his own brain. During the process, the engineer needs to point out the conflicting parts in the drawings and the aspects that need to be optimized in design and construction, so as to prepare for communication and find the best solution.

Stage 2: Detailed Drawing

1. Pre-embedded Foundation Construction

The first and most important step in model building is the construction of the foundation. If the pre-embedded foundation is not built correctly, it will affect whether the building can be installed successfully, and even affect the safety of the structure. Therefore, the foundation parts must pay attention to:

1. The size, material and positioning of the embedded anchor bolts shall be in accordance with the requirements of the embedded layout diagram in the structural drawing, and at the same time, whether the anchor bolts meet the requirements of the anchorage length shall be considered.

2. The positioning of the pre-embedded anchor bolts should be consistent with the position between the foundation and the short columns of the foundation. Generally, the center should be aligned. If the positioning is eccentric, it will affect the structural force. If the design requires eccentricity, it should be deepened according to the design requirements.

3. When the number of rebar in the foundation short column is small and it is not convenient to install and fix the pre-embedded anchor bolts, pre-embedded brackets should be provided to ensure that the pre-embedded anchor bolts do not shift during foundation concrete pouring.

4. When positioning the pre-embedded anchor bolt units, a pre-embedded positioning steel plate for installation and positioning should be provided. The thickness of the positioning steel plate should be determined according to the size and quantity of the anchor bolts. Generally, a 6-10mm steel plate is used. Concrete pouring holes should be opened in the center of the positioning plate, and the hole diameter of the anchor bolt on the positioning plate is 2mm larger than the diameter of the anchor bolt.

5. The top of the embedded anchor should be threaded to fix the steel column. The length of the thread wire should be determined according to the thickness of the base plate of the column foot, the thickness of the washer plate and the thickness of the nut, and should usually be 20~50mm higher than the top nut.

2. Beams and Columns Construction

The main load-bearing components of the portal frame are steel columns and steel beams. The steel columns are divided into rigid frame columns, wind-resistant columns and mezzanine columns. The steel beams are divided into roof beams, mezzanine beams and crane beams.

It should be noted that: when crane beams should be installed when there is over headed crane, and sub-columns and beams should be installed at locations with mezzanines.

1) The cross-sectional size, plate thickness, and materials grade of steel columns and beams shall comply with the requirements of the steel frame diagram in the structural drawing.

2) The positioning dimension of the anchor bolt hole at the foot of the steel column should be consistent with the positioning dimension of the embedded anchor bolt. In order to eliminate the installation error of the steel frame, the hole diameter should be 5~10mm larger than that of the embedded anchor bolt. The steel column foot should be determined according to the structural design whether to set the shear key. When the column foot is protected by wrapped concrete, it should be noted that the size of the column foot stiffener does not exceed the concrete protective layer.

3) When there is no specific requirement in the design of the steel column top, it is usually made flat to facilitate the installation of the column top gutter. The setting and size of the stiffening plate at the top of the column should consider the influence on the installation of the gutter at the top of the column, so as to prevent the gutter from being unable to be placed because the stiffening plate is too large.

4) It should be considered the requirements of the structural design on the roof slope during making detailed drawing of steel beams, and the roof slope is generally 5%~10%.

5) The spacing between high-strength bolts at the joints between steel columns and beams, and beams and beams is generally 70-250 mm. In order to prevent the connection plates from being loosely joined and affecting the friction coefficient between the plates when the spacing is too large, stiffeners should be provided.

6) The section size, plate thickness and material of the steel crane girder shall be in accordance with the requirements of the crane girder layout drawing and the details drawing.

7) The length of the end plate of the steel crane girder should consider the height of weld at the connection with upper flange in the design requirements, and the top of the end plate is generally 5~10mm from the upper surface of the upper flange.

In the whole process, in addition to the construction of the main components, the node detailed modeling is also crucial. The detailed design has always emphasized: strong columns and weak beams, strong nodes and weak components.

The most important thing to pay attention to in the joint deepening modeling is the bolt size, specification, grade, spacing, thickness of the connecting plate, and the grade and size of the weld should meet the design requirements.

3. Support System Construction

The support system of the portal frame generally includes tie bar, horizontal supports, and column vertical supports. There are flexible and rigid supports. Flexible supports generally use round steel, and rigid supports generally use angle steel or round tubes. The support is mainly used to transmit the lateral horizontal force and connect the structural members as a whole.

In this part: the section size, plate thickness, and material grade of the steel support should be in accordance with the requirements of the structural drawing; the connection nodes at the end of the tie bar should not extend into the inner side of the steel column or steel beam flange, so as to prevent the length of the tie bar from exceeding the steel column and steel beam. The setting of tie bar at the eave position should consider the installation of the gutter & down pipe; the specification and grade of the bolt connecting should be connected according to the design requirements, and high-strength bolts should be used as far as possible to reduce the welding workload;

The horizontal support of the roof should be set at a position about 150mm below the upper flange of steel beam, and the flexible horizontal support of round steel should be provided with turnbuckle bolts for easy tensioning.

4. Cladding System Construction

The envelope structure is relatively simple, which includes purlins, knee bracing, bracing bar, sleeve pipe, etc. During the deepening process, the section size, plate thickness and material shall be in accordance with the requirements of the structural drawing.

The common purlin are: C type, H type and Z type.

The C-shaped purlins are connected by hinge joints, and a gap of 10~15mm should be left between purlins.

The Z-shaped purlins are connected by lap joints, and the length of the lap joints is according to the design requirements.

High-frequency welded H-shaped steel purlins are connected by hinge joints, and a gap of 10~15mm should be left between purlins, and the lower flange at the end of the purlins needs to be cut off.

C and Z-type purlins should be drilled 18~25mm oblong holes. In order to eliminate installation errors, the high-frequency welded H-shaped steel purlins should be enlarged round holes, and the hole diameter is 4~5mm larger than that of bolts or braces.

The holes for connecting bolts at both ends of knee bracing should be 18~25mm oblong holes. The setting position should avoid collision with the horizontal support.

5. Parapet Wall Post, Roof Montior, Steel Staircase and Steel Canopy

6. Model Number

After the model is built, the next step is to number the model parts as a whole. After the numbering is completed, the system will automatically assign a unique number to each component, which is convenient for on-site installation and identification.

Stage 3: Output of Results

After the completion of the detailed design drawing, the results need to be transformed into various drawings and lists that can be used for factory manufacturing and on-site installation.