Beijing Phoenix Center, as the new media headquarters of Phoenix Group in Beijing, is not only a comprehensive building that integrates television program production, office, and commercial functions but also carries numerous innovations in technology and art. The project was carefully designed by the BIAD_UFo studio, led by Shao Weiping, and took over six years from the start of design in June 2007 to completion in July 2013. It covers an area of approximately 1.88 hectares, with a total construction area of 72,478 square meters and a building height of 54 meters, showcasing a perfect blend of grandeur and modernity.

By cleverly utilizing the design concept of the Möbius strip, the high-rise office area and media studio harmoniously integrate, providing a comprehensive program production venue and supporting service facilities while creating a smooth and dynamic spatial volume. Its unique architectural form beautifully complements the natural landscape of Chaoyang Park, forming a picturesque tapestry of harmonious coexistence between humanity and nature. Meanwhile, the ingenious application of parametric and digital construction technologies made the design and construction process of the entire project appear effortless, fully demonstrating the remarkable achievements of contemporary steel structure technology.

Gao Jiling, as the Deputy General Manager, Chief Engineer, and Senior Engineer Researcher of ZHM Huawu Steel Structure, not only possesses a profound industry background and academic accomplishments but is also the overall leader for the deepening design and manufacturing of the steel structure for the Phoenix Center. In an exclusive interview with AC "Architectural Creation" magazine, he shared many insights and reflections regarding the Phoenix Center project. When discussing the "Phoenix Center" project, Gao Jiling particularly emphasized the four major technical challenges in the deepening detailing design and manufacturing of the steel structure: the deepening detailing design technology for the transmission of three-dimensional architectural form information, the processing technology for primary and secondary ribs, the processing technology for steel arch bridges, and the installation technology for steel structures. The successful application of these technologies not only highlights China's excellence and innovative capability in the field of steel structure manufacturing but also provides valuable experience and inspiration for future architectural creations.

The first challenge faced is the massive information processing challenge brought by the three-dimensional complex architectural form. In this project, traditional paper-based two-dimensional construction drawings could no longer meet the needs for conveying design information. By the time we got involved, Chief Architect Shao Weiping had already begun constructing the CATIA model, and the steel structure framework had taken initial shape. Although the details still needed refinement, the overall framework laid the foundation for subsequent work. The key was how to convert the CATIA model into two-dimensional drawings. It is worth noting that the construction drawings provided by the structural professionals at that time (i.e., traditional two-dimensional construction drawings) were relatively brief; relying solely on these for processing design would make it difficult to achieve the required precision due to insufficient information contained in the drawings.

The steel structure part of this project includes six core components: steel structure canopies, circular ramps, sky ladders, arch bridges, platforms, and horse paths(overhead walkways), with the total steel usage expected to reach approximately 7,000 tons.

At the beginning of this project, our primary task was to develop a set of construction drawings to guide manufacturing and processing. However, faced with the challenge of how to use CATIA software for steel structure processing, we engaged in in-depth communication with the structural designers. After two discussions, we made two key decisions: first, the steel structure construction drawings would follow the traditional drawing method, mainly serving as a basis for program execution but not directly used for deepening design and manufacturing; second, to fully utilize the CATIA software model already constructed by Chief Architect Shao Weiping's team, we would closely collaborate with their team for the deepening design and manufacturing of the steel structure.

In subsequent operations, we gradually uncovered challenges in the application of the CATIA model. Due to our team's lack of professionals proficient in CATIA software, while Shao's team had software operational capabilities, they were largely unfamiliar with the technical conditions and requirements for steel structure processing. Although we attempted to combine the strengths of both parties by having the design team's CATIA operators input the necessary information for steel structure manufacturing into the model, practice proved this method unfeasible. The main reason was that the software operators lacked an understanding of the requirements for steel structures, making it difficult to accurately convey information; moreover, the details and volume of information involved in deepening design and manufacturing of steel structures were immense. If all were reflected in a single model, it would lead to excessively large model data that could not effectively operate within the software.

This experience aligns with our understanding within the BIM system: each discipline should establish its own model, while the overall integration model often needs to omit a large amount of detailed information. If there is too much detailed information, the overall model will become too large to be usable in practical operations. The same problem also appeared in our subsequent application in CATIA software.

Single Discipline Model of Steel Structure in Rhino Software

In addressing the challenges of using CATIA software, we attempted another approach. Given Rhino's excellent performance in handling steel structures, we decided to explore the application of its single discipline model. This attempt not only improved work efficiency but also brought new possibilities for the detailing deepening design and processing of steel structures. Through Rhino software, we were able to convey the information required for steel structure manufacturing more accurately, thus optimizing the entire manufacturing process. This practice proved that establishing a single discipline model for specific professions is an efficient and practical method.

The left image shows the reference surface provided by the original design, while the right image illustrates the concept of the curved path. We fitted the reference surface to derive the curved path. Based on this, we changed our working method to extract key information from the CATIA model, such as building layers, skins, main ribs, secondary rib centerlines, and profile lines. Next, we integrated the Rhino software with the CATIA model and constructed a deepening model of the steel structure in Rhino. This model focused on the steel structure, omitting other parts of the building, thus forming a typical "single discipline" 3D model that contains all information about the steel structure. Practice has shown that this method is highly effective. Although Rhino is not as strong as CATIA in terms of parametric capabilities, its performance in surface modeling is not significantly different, fully meeting our technical needs. Moreover, due to Rhino's non-vector characteristics, it can accommodate more information. After completing the Rhino model, we imported it into CAD software for plan drawing. Thus, we successfully completed the entire process from CATIA to Rhino to CAD with high efficiency.

Method for Creating Trajectory Curves: We fitted the reference surface to generate trapezoidal cross-section trajectory curves that align with the original design line.

Reference Cross-section: Ensure that one edge of the reference cross-section is entirely located on the reference surface, and any position of the reference cross-section must remain perpendicular to the trajectory curve. To determine the reference cross-section, we need to calculate the line segments located within the reference plane and perpendicular to the trajectory curve, while also identifying the line segments that pass through the trajectory curve and are perpendicular to it. The plane containing these two line segments is the required reference cross-section.

Arrangement of Reference Cross-sections: The spacing of fixed position points directly affects the processing accuracy of components. If the fixed position points are too sparse, the precision of the components will not meet the requirements, and the alignment with the original design line will also be affected, damaging the architectural effect and overall appearance. However, if the fixed position points are too dense, although more information can be collected, it will significantly increase the workload for deepening detailing design and factory processing, reducing work efficiency. After comprehensive consideration, we ultimately determined the spacing of fixed position points to be 500 millimeters, which can control the processing error within 2 millimeters, ensuring both precision and efficiency.

Arrangement of Reference Cross-sections for Twisted Components: Using the trajectory curve method, we fitted all reference surfaces to generate trapezoidal cross-section trajectory curves that align with the original design line.
Based on the arrangement of reference cross-sections, we can further determine the numbering of positioning control points on each surface. This allows us to clearly grasp the bending and twisting states and positional information of each panel.

Through the analysis of reference cross-sections, we can further clarify the numbering of positioning control points on the bending and twisting panels. This step enables us to better understand the bending and twisting states of each panel and their precise positions in space.

After clarifying the numbering of positioning control points on the bending and twisting panels, the next step is to measure the spatial coordinates of each control point. This process is crucial as it directly relates to the accuracy of subsequent processing.

Through this approach, we successfully integrated the three steps of "precise expression of design intent - production processing layout - drawing of planar processing diagrams," achieving efficient and seamless transmission of architectural three-dimensional data. This innovative model not only improved design efficiency but also brought great convenience to production processing. Later, this model was widely applied in handling three-dimensional complex architectural components, such as the complex curved surface structures of Kunming Airport, where we easily solved processing challenges. We explored an effective way to transform the complex forms of architectural design concepts into concrete, manufacturable practical operations.

Spatial Unfolding of the Twisted Panel

After determining the spatial coordinates of each positioning control point on the twisted panel, the next step is to unfold the panel into a plane based on these control points. This process involves converting three-dimensional surface data into two-dimensional plane data, which is a key link to ensure the accuracy of subsequent processing. Through precise spatial unfolding, we can simplify complex three-dimensional forms into manufacturable two-dimensional drawings, thereby providing clear guidance for production processing.

Control Point Numbering for the Unfolded Twisted Panel

In the process of converting the spatial data of the twisted panel into plane data, we need to number each control point on the unfolded plane. These numbers not only help us track and locate each control point but also ensure that each step can be executed accurately during subsequent processing and assembly. Through this step, we can further simplify complex spatial forms, providing clearer and more specific guidance for production processing.

Coordinate Table of Control Points for the Unfolded Twisted Panel

In the "Phoenix Center" project, we faced enormous challenges, as this project is unique nationwide. It was precisely because of this project that we were able to address the issues of a large amount of spatial twisted steel structures and explore the innovative design information transmission technology that combines CATIA, Rhino, and CAD. This technological breakthrough has enabled "ZHM Huawu Steel Structure" to achieve a unique technological leadership position nationwide. This exploration of technology from scratch has not only greatly tested our technical capabilities but also brought us a continuous competitive advantage.

Steel Structure Canopy Design

In the "Phoenix Center" project, we created a steel structure canopy with a total weight of approximately 5200 tons, featuring a unique design that consists of inner and outer layers. Both layers utilize twisted components with variable cross-section trapezoidal shapes, cleverly interwoven with spatially curved steel pipes, forming a stable and aesthetically pleasing architectural appearance. This innovative design not only showcases our profound expertise in steel structure technology but also brings a distinctive visual effect to the entire project.

Axonometric Analysis of a Single Twisted Main Ribs

In the design of the steel structure canopy for the "Phoenix Center" project, the single twisted main rib exhibits significant spatial twisting characteristics. Its twist amplitude is quite large, with an average twisting angle of up to 5 degrees per meter of component, indicating a considerable relative deflection angle at the ends. Meanwhile, the bending radius of the component in the longitudinal direction is relatively small, with a minimum bending radius of only about 6 meters. Additionally, the wall thickness of the box varies greatly, ranging from 16 millimeters to 115 millimeters, which undoubtedly poses significant challenges for processing and welding.

Enlarged View of the Double-layer Diagonal Circular Frame

In the design of the steel structure canopy for the "Phoenix Center" project, the double-layer diagonal circular frame is one of its unique structural features. This design element is thoroughly showcased in the enlarged view, making its intricate construction and complex spatial relationships clear at a glance. The design of this double-layer diagonal circular frame not only reflects the stability of the structure but also brings a unique aesthetic effect to the entire canopy.

Axonometric View of the Connection Between the Twisted Main Ribs and Secondary Ribs

In the design of the steel structure canopy for the "Phoenix Center" project, the clever connection between the twisted main ribs and secondary ribs is an indispensable part. Each segment of the structure is meticulously designed with main ribs, secondary ribs, and curtain wall connection components, presenting a complex twisted form in space, with varying intersection angles between the main and secondary ribs, ensuring both stability and aesthetics of the structure.

Composition of Twisted Main and Secondary Ribs

In the design of the steel structure canopy for the "Phoenix Center" project, the composition of the twisted main ribs and secondary ribs is quite sophisticated. The main rib structure integrates various components, including main rib splicing boxes, secondary rib round tube brackets, box-shaped brackets, and curtain wall round tubes, working together to present the complexity and stability of the structure.

Comparison of the torsional component parameters of the "Phoenix Center" with the National Stadium and Kunming Airport

When discussing the design of the steel structure canopy for the "Phoenix Center" project, it is worthwhile to compare the composition of its main and secondary torsional ribs with similar components from the National Stadium and Kunming Airport. Such a comparison will help us gain a deeper understanding of the design concepts and implementation details of torsional components in different architectural projects.

After understanding the processing flow you introduced, I realized how workers obtain information from two-dimensional drawings to process the steel. However, I am still curious about the forming process of the hyperbolic structural ribs. How are these complex structural ribs ensured to perfectly fit the design shape during the process of welding steel strips into quadrilateral steel structural ribs?

Gao Jiling: Indeed, this is a significant challenge we faced in the "Phoenix Center" project. Although workers process according to two-dimensional drawings, what ultimately presents itself is a hyperbolic steel structure beam. This is where our carefully developed "processing and forming technology for spatial torsional components" comes into play.

The "Phoenix Center" project can be considered the most complex challenge our company has faced to date. Aside from the trusses of the entrance canopy and a few concrete structural support members, all other components are curved, whether in planar torsion or spatial torsion, with almost no horizontal or vertical components. Among them, the main ribs of the building's outer wall are particularly tricky, with a trapezoidal cross-section that is small in size, 750 mm in height and 330 to 500 mm in width, and formed by the splicing of four steel plates, creating a spatial three-dimensional torsional structure, with a plate thickness of up to 115 mm, making the processing difficulty unprecedented. Although the bending of the secondary ribs is relatively simple, the complexity of the main ribs is still beyond imagination. In addition, the two indoor ring slope structures resembling "bridges," though not large in size, present unprecedented complexity: both the planar and vertical dimensions are curved, and the cross-section is crescent-shaped, resulting in a unique "saddle surface" at the bottom.

The final processing technology for the main ribs is not entirely innovative but draws on traditional shipbuilding techniques. The bow and stern of the ship's hull adopt three-dimensional spatial bending shapes, a technology that has been maturely applied in shipbuilding. However, the main ribs of the "Phoenix Center" consist of four steel "strips," which require precise splicing, undoubtedly increasing the complexity of processing. Although we employed similar technology in the "Bird's Nest" project, the number of curved components at that time was limited, and the cross-sections were larger. In contrast, the steel structure cross-section of the "Phoenix Center" is smaller, with thicker steel plates, and the total length of the torsional plates exceeds 30,000 meters. This means that to complete the processing of all main ribs, we must splice over 30,000 meters of plates accurately and efficiently. Therefore, our main challenges focus on precision and progress.

In facing the complex challenges of the "Phoenix Center" project, we cleverly applied "shipbuilding" technology and created a "sample box," or "inner mold." This inner mold was made according to the profile of the trapezoidal cross-section main ribs, removing the plate thickness to form a hollow structure. In this way, we can visually check the forming accuracy of the steel plates without complex measuring tools.

Traditional measuring methods, such as steel tapes and total stations, are inadequate when facing three-dimensional spatial torsional structures. However, with the "sample box" inner mold, we only need to compare the formed steel plates with it to quickly assess their accuracy. If the steel plate closely fits the inner mold, it indicates high processing accuracy; if there are gaps, reshaping is required.

This method of checking accuracy is not only simple and intuitive but also reduces the requirement for specialized skills. Ordinary workers can efficiently complete this task, significantly improving production efficiency.

For the accuracy check after the torsional plate forming, we rely on the carefully crafted "sample box inner mold." So how does this inner mold ensure that the outer skin's curvature strictly follows the design and avoids "deformation"? How does it accurately reflect the three-dimensional data in the design?

Gao Jiling explained that torsional ribs have a normal surface, meaning that the cross-section perpendicular to the normal is always a standard cross-section. These normal surfaces have clear dimensions; for example, the trapezoidal cross-section dimensions are (700 - 750) × 350 mm. As long as cutting is done on the normal surface, a standard cross-section can be obtained. If cutting deviates from the normal surface, even a slight deviation will result in an irregular cross-section.

When processing long main ribs, we find a normal surface every 500 or 800 millimeters, which makes the cross-section very convenient to produce. We create normal surface frames using small wooden strips, and these frames are twisted relative to each other, forming multiple normal surfaces. Although the twisting angle is easy to control in theoretical models, caution is still required in practical operations. After completing the twisting angle production, we connect the four corner points to form the desired twisted surface. It is worth noting that the frames of the normal surfaces are very sturdy, while the plywood connecting them is softer, so we nail the plywood according to the twisting of the normal surface frames, allowing for the natural formation of an accurate twisted surface.

Sample Box Production Process

In the accuracy inspection process of the twisted board, we not only rely on the carefully crafted "sample box liner," but also need to go through a series of complex sample box production processes. These processes ensure that the curvature of the outer skin strictly follows the design, thus avoiding the occurrence of "deformation." By precisely reflecting the three-dimensional data in the design, the sample box becomes an important basis for verifying the accuracy of the twisted board after shaping.

Steel Plate Welding Sequence

In the previous "shipbuilding" process, we employed a similar technique. However, the forming of the ship's wall steel plates is relatively simple, completed by rolling and pressing using an oil press or three-roll bending machine. However, accurately inspecting the forming effect remains a challenge. Without proper methods, construction supervision may struggle to assess the accuracy of the steel plate forming. With the tool of the "sample box," we can intuitively inspect the forming effect of each steel plate, ensuring that every bend and twist meets design requirements.

For the complex bends and twists in construction, we do need to create a "sample box" for each steel beam. During the steel structure production process of the "Phoenix Center," we used both wooden and steel "sample boxes" for inspection. This way, regardless of the total length of the main rib, we can ensure that every bend and twist is precise through the "sample box."

Additionally, our "woodworking workshop" plays a key role in this process. Although the cost of high-level carpentry is relatively high, it is their exquisite skills that ensure the reliability of the process. This unique craftsmanship not only reflects our commitment to tradition and manual techniques but also demonstrates significant advantages in actual engineering. During the splicing of multiple steel plates, we can achieve smooth, gapless welds, ensuring high precision and quality of the overall structure.

This process, while seemingly traditional, exhibits efficiency and precision in practical applications. Compared to some "advanced" technologies that rely on high-tech equipment, it may not have an advantage in initial investment, but its uniqueness lies in its dependence on the skilled craftsmanship of each worker. It is this "traditional" manual craftsmanship that allows us to achieve smooth, gapless welds, ensuring high precision and quality of the overall structure.

The steel plate welding process includes: first setting up the frame, then positioning the bottom plate of the main body, followed by the positioning of internal partitions and side plates. After that, the positioning of the cover plate and welding of the internal partitions are carried out. Once these steps are completed, the side sealing plates are positioned and the main welds of the box body are welded. Next, the installation positioning of components and welding of the steel plates are performed. Finally, integrity acceptance and pre-assembly are conducted.

In the bridge manufacturing process, we adopted a "reverse construction" method. Due to the difficulty in positioning the saddle surface at the bottom of the bridge, we observed that the "unidirectional" arc surface on the upper side is simpler, so we decided to "flip" the bridge over for production. This way, with the bottom surface facing up and the top surface facing down, positioning during production becomes simpler. We first created transverse and longitudinal "hard blocks," which serve as internal supporting wooden ribs of the sample box. By precisely designing the arc lines on the upper surfaces of these wooden ribs, we can easily create tangents that intersect with the saddle surface perpendicularly. Then, we tightly nailed flexible plywood onto the hard blocks, forming a very precise hyperbolic arc surface.

The steel arch bridge presents a "saddle-shaped" box structure, characterized by its unique cross-sectional design and parabolic arch shape along its length. The cross-section is a gradient crescent shape, varying in width from 6 to 11 meters, while the height in the middle of the cross-section remains at 0.9 meters. Additionally, the projections of the bridge surface inside and outside present irregular arcs, making the overall design of the bridge both aesthetically pleasing and practical. The total weight of a single steel arch bridge is approximately 300 tons, with a length of 42 meters; its top plate approximates a slanted conical surface, while the bottom plate presents a saddle-shaped surface, together forming this unique steel arch bridge.

Segmented Processing

The manufacturing of steel arch bridges adopts a segmented processing approach. This method makes the construction of the entire bridge more flexible and efficient. During the processing, various parts of the bridge are divided into different segments, and then fine processing and production are carried out on each segment. This approach not only simplifies the manufacturing process but also improves the quality and stability of the bridge.

Comparison with Other Projects

The use of segmented processing for manufacturing steel arch bridges shows significant advantages compared to other projects. This flexible and efficient processing strategy makes the construction process of the bridge smoother, while simplifying the manufacturing process and further enhancing the quality and stability of the bridge.

Pre-assembly Plan

In the manufacturing process of the steel arch bridge, we adopted an innovative pre-assembly plan. The application of this plan not only optimized the structural design of the bridge but also effectively reduced adjustments and corrections during on-site construction, greatly improving construction efficiency and precision. Through careful pre-assembly, we ensured that all components of the bridge could be precisely connected and fixed, laying a solid foundation for the overall quality and stability of the bridge.

Construction Process

In the manufacturing process of the steel arch bridge, we first set up a stable framework to provide a solid foundation for subsequent construction. Next, we performed precise positioning and installation of the top plate to ensure the stability of the bridge structure. Finally, we completed the assembly and welding of the bottom plate, further strengthening the overall stability of the bridge. Through this series of construction processes, we successfully manufactured a high-quality and stable steel arch bridge.

On-site Installation of Steel Structure Arch Bridge

After the completion of the steel arch bridge manufacturing, we carried out on-site installation work. This step is crucial for ensuring the safety and stability of the bridge. We strictly followed the design drawings, accurately positioning and installing each component to ensure that every connection is solid and reliable. Through meticulous construction and rigorous operation, we successfully completed the on-site installation of the steel structure arch bridge, laying a solid foundation for the safe operation of the bridge.

Construction Challenges and Breakthroughs of Steel Structure Arch Bridge

During the construction of the steel structure arch bridge, we faced numerous challenges. Among them, how to cleverly apply traditional shipbuilding techniques to the processing and manufacturing of spatially curved components became a key issue. Through continuous exploration and practice, we successfully overcame this challenge, providing valuable experience for similar projects. In addition, we developed a comprehensive and mature operational system for "spatial twisting" steel structures, enabling us to easily handle subsequent large projects, such as "Kunming Airport," showcasing our exceptional professional ability.

October 27, 2010, Official Start of Steel Structure Construction

On this day, we welcomed the crucial starting point of steel structure construction. This not only marked the project entering a new phase but also indicated that we would face more challenges and opportunities. From this day forward, we began our journey of racing against time and fighting against difficulties, aiming to create an even more outstanding steel structure arch bridge.

Revealing the Steel Structure Construction Process

After October 27, 2010, we delved into every aspect of the steel structure construction process. This journey was not only filled with technical challenges but also showcased our professionalism and perseverance. From the initial preparation of steel materials to precise cutting, welding, and the assembly and reinforcement of the structure, every step embodied our wisdom and effort. Every detail of this process laid a solid foundation for us to create a high-quality steel structure arch bridge.

Successful Completion of Steel Structure Construction

On May 21, 2011, the steel structure construction was successfully completed. Looking back on those days, we collectively experienced the summary meeting of the Phoenix Center project, gathering with the client, Mr. Gu Deyu, the chief architect, Mr. Shao Weiping, and representatives from the curtain wall manufacturer to share in the joy of success. Mr. Shao's hands-on involvement in the project and his selfless guidance deeply moved us. In facing technical challenges, we not only achieved significant technical progress but also established a unique competitive advantage in the industry. During those days, whenever we talked about the "Phoenix Center," our hearts were filled with pride and a sense of accomplishment.

Today, in the lobby of the "ZHM Huawu Steel Structure" headquarters, the model of the "Phoenix Center" still occupies the most prominent position. It not only attracts countless visitors but has also become a truly original work, providing endless shock and imagination to people. Although we have undertaken many large projects, the model of the "Phoenix Center" always stands out among these models, showcasing its extraordinary charm.

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