Looking back at the century-old industrial history of Yangpu Riverside through modern wooden architecture

Looking back at the century-old industrial history of Yangpu Riverside through modern wooden architecture

Project Location: East side of Yangshupu Port, Yangpu Riverside, Shanghai

Completion date: July 2018

Project area: 72 square meters

Architectural Design: Tongji Original Design Studio (Zhang Ming/Zhang Zi)

Structural Design and Construction: Jimu Construction Technology Engineering (Shanghai) Co., Ltd., Shanghai Construction Machinery Engineering Co., Ltd.

Photography: Zhang Yong

Origin of the plan

Located on the former site of Xiangtai Timber Company (established in 1902) on the Yangpu Riverside in Shanghai, a region with a century-long industrial history, the project was designed from the outset by the architects using a steel-timber composite structure. The project's primary function is to provide citizens with warm shelters for rest, daily services, and medical assistance; therefore, the architects proposed a spatial structure system formed by stacked A-frame structural units, named "Renrenwu" (Everyone's House).

Structural system establishment

Steel-wood combination, herringbone spatial structure units, and small cross-sectional components are the main requirements of architects for structural design. In the early stages of the project, engineers actively explored more reasonable combined structural systems, more beautiful and exquisite spatial connection nodes, and component sizes that can fully and effectively exert stress.

The steel-wood composite structure comprises combinations at the structural system level, load-bearing component level, and node connection level. From an architectural perspective, the building uses 800mm as its basic module, with a height of 4.6m, a length of 13.6m, and a width of 6.4m. The exterior consists of a spatial structure formed by eight diagonal wooden members, four of which are directly supported by the ground, while the other four are suspended in the air. The interior is a spatial steel frame structure with a glass curtain wall. Based on this, a steel-wood composite structural form was established at the system level, effectively connecting the four suspended diagonal wooden members to the inner spatial steel frame structure through steel node connectors, thus forming an integrated steel-wood load-bearing spatial structural system.

Figure: Structural System Composition Analysis Diagram

Figure: Cross-sectional view of the steel-wood integral load-bearing spatial structure system

Study of the force process

After the structural system is formed, the next step is to analyze and study the stress process of the system.

The force distribution of the outer wooden diagonal bracing spatial structure system is as follows: Under vertical and wind loads, the diagonal bracing in the ground-supported area is mainly subjected to axial force with relatively small bending moments, while the diagonal bracing in the non-ground-supported area is mainly subjected to bending moments with relatively small axial forces. This demonstrates the distinct spatial force characteristics and clear force division of this structural system. After review, European spruce glued laminated timber with good load-bearing capacity was selected, and the diagonal bracing cross-section was made to 60mm x 60mm. Furthermore, considering that the horizontal support rods are purely axially loaded members used to improve the lateral stiffness of the structure, their cross-section was made to 40mm x 40mm.

Figure: Internal force diagram of the outer wooden diagonal bracing spatial structure system under vertical load.

(b) Bending moment diagram (vertical load)

Figure: Internal force diagram of the outer wooden diagonal bracing spatial structure system under wind load.

(a) Axial force diagram (wind load)

Figure: Internal force diagram of the outer wooden diagonal bracing spatial structure system under wind load.

(b) Bending moment diagram (wind load effect)

For the internal hollow steel frame structure system, its lateral stiffness is the weak point. The design cleverly utilizes the door openings at both ends to form spatial trusses, and adds a small truss near the end span. The stress analysis results show that after adding this spatial truss, the lateral deformation of the structure is reduced from 20mm to 10mm, which is a significant effect. In addition, to achieve a lightweight architectural experience, the cross-sectional dimensions of the steel frame members are minimized to 50mm wide square steel tubes.

Figure: Side-resisting trusses added to the internal space steel frame

The stress process of the steel-wood integral load-bearing spatial structure system is as follows: Under vertical load, the internal steel frame structure provides vertical support to the ungrounded part of the outer wooden space structure; under wind load, the lightweight aluminum alloy roof is subjected to upward wind suction, and the wooden structure directly connected to it transmits the pull force to the internal steel frame and moves upward synchronously, thereby reducing its deformation.

Connection node processing

As a prefabricated building, the most crucial aspect of steel-wood structure in achieving complete factory prefabrication and on-site assembly is the ingenious design of connection nodes. The node design must comprehensively consider factors such as meeting load-bearing requirements, aesthetic architectural effect, and ease of assembly.

1. Wooden cross-bracing column base node

The wooden cross bracing is designed as a hinged joint at the column base. To facilitate connection with the foundation concrete, a steel embedded plate with anchor bars is first embedded in the concrete foundation. Then, the cross bracing is fixed to the semi-circular steel plate with through bolts and double nuts are provided to prevent loosening.

Figure: Timber crossbeam post base node

2. T-shaped steel connectors at the junction of the wooden cross bracing and the horizontal support rod.

A typical connection point in this project is the connection between the wooden cross brace and the horizontal support rod. Here, a clever T-shaped steel connector is used: First, a large-headed screw is driven into the center of the cross brace node from the outside; then, four self-tapping screws are used to connect the flange of the T-shaped steel node plate to the cross brace on the inside of the cross brace node; finally, the web of the T-shaped steel node plate is inserted into the slotted horizontal support rod and fixed in place with four screws. This T-shaped steel connector method integrates with the entire timber structure assembly process, not only meeting the load-bearing requirements but also facilitating on-site installation, resulting in a simple and aesthetically pleasing appearance. It also enhances the rigidity of the connection node, achieving the design concept of "strong node, weak component".

Figure: T-shaped steel connector node

3. Extended T-shaped steel connectors at the connection points between the longitudinal connecting rods and the horizontal support rods on the roof.

Because a longitudinal connecting rod is provided at the connection between the wooden cross bracing and the horizontal support rod at the roof, the flanges on both sides of the T-shaped steel connector are lengthened in the design of the steel connection node, and the longitudinal connecting rod is fixed to the extended flanges of the T-shaped steel connector with 6 screws.

Image: Extended T-shaped steel connector node

For steel-wood composite structures, a well-organized construction and assembly process is crucial. In this project, construction proceeded from the inside out and from bottom to top. First, the internal steel frame structure was installed. Then, the spatial structure composed of the diagonal wooden members on the periphery was installed symmetrically one by one. Next, the horizontal wooden support rods were fixed, and the four central wooden frames were connected to the steel frame. Finally, the aluminum alloy roof was installed, with an internal glass curtain wall.

The on-site construction and installation of the main structure of Renrenwu took only one month. It withstood multiple tests from Shanghai's rainy season and summer typhoons. The design combined the characteristics of different materials, used a reasonable steel-wood composite structural load-bearing system, cleverly handled the connection nodes, and gave full play to the advantages of prefabricated buildings, ultimately achieving a combination of architectural art and modern industrial construction.