Reconstructing Traditional Chinese Architecture with Weld-Free, Nail-Free Steel Pipes: Inheriting Mortise-and-Tenon Wisdom in the Industrial Age

Abstract

This paper focuses on the core proposition of reconstructing traditional Chinese architecture using "modern steel pipes + weld-free and nail-free metal mortise-and-tenon joints." From an interdisciplinary perspective (structural mechanics, materials science, architectural aesthetics, and cultural heritage studies), it systematically dissects the mechanical wisdom and cultural genes of mortise-and-tenon joints in traditional wooden structures, analyzes the compatibility contradictions of steel pipe materials, and innovatively designs a modern metal mortise-and-tenon joint system that is "force-transmittable, micro-deformable, and detachable." Feasibility is verified through digital simulations and scale experiments. This research not only addresses the technical challenges of "contemporary translation of traditional architecture" but also explores a "new Chinese-style" architectural language rooted in Eastern construction philosophy and adapted to the industrial age, providing a technical path and ideological paradigm for the living inheritance of cultural heritage.

1.1 Origin of the Problem: The Disconnect Between Wooden Structural Wisdom and the Industrial Context

Liang Sicheng once stated in A History of Chinese Architecture: "The uniqueness of Chinese architecture lies in its distinctive frame system." The wooden frame centered on mortise-and-tenon joints, validated by millennium-old projects such as the Yingxian Wooden Pagoda (957 AD) and the Corner Towers of the Forbidden City (1420 AD), has formed a structural philosophy of "flexible joints, frame load-bearing, and overcoming rigidity with flexibility." However, in the context of contemporary architecture, the "rigid logic" of reinforced concrete and the "flexible wisdom" of traditional wooden structures have gradually become disconnected: While Wang Shu’s "Xiangshan Campus" returns to tradition through rammed earth and wood, it cannot meet the demands of modern architecture for large spans and high loads; most "new Chinese-style" buildings merely replicate symbolic elements like overhanging eaves and dougong (bracket sets) as decorations, failing to touch the cultural core of the structural system.

When "steel pipes" of the industrial age (homogeneous, high-strength, and reproducible via standardization) encounter the "weld-free and nail-free" principle of traditional architecture (joint load-bearing, reversible assembly, and micro-deformation energy dissipation), this dialogue spanning millennia is essentially an exploration of the compatibility between "cultural genes" and "technical carriers."

The core advantage of traditional wooden structures lies in the anisotropy of wood (with a compressive strength of approximately 40MPa parallel to the grain, but only 5MPa perpendicular to the grain) and the flexible force transmission of mortise-and-tenon joints. During an earthquake, wooden components can dissipate energy through slight bending and minor displacement of mortise-and-tenon joints, achieving the effect of "walls may collapse, but the roof remains intact." In contrast, steel pipes (taking Q355B as an example, with a yield strength of 355MPa and an elastic modulus of 206GPa) are isotropic rigid materials, lacking the self-recovery capability and natural damping of wood. Once deformation exceeds the elastic limit, permanent damage occurs.

 This gives rise to the core contradiction: How can rigid steel pipes simulate the "micro-deformation energy dissipation" mechanism of traditional wooden structures through joint design? How can weld-free and nail-free metal joints not only transmit loads (vertical load-bearing and horizontal lateral resistance) but also retain the "detachable and repairable" characteristics of traditional mortise-and-tenon joints?

Technically, this exploration fills the interdisciplinary gap between "modern metal structures" and "traditional joint mechanics." Currently, connection methods for metal structures (welding, bolts) all aim for "rigid fixation," while research on "flexible force-transmitting" metal joints remains scarce. Culturally, this is not merely "form replication" but "wisdom translation": What is inherited is not the warm texture of wood, but the construction philosophy of "joints as the soul, frame as the backbone," providing a new paradigm for contemporary architecture that combines "technical depth and cultural richness."

2.1 Symbiosis of Material and Structure: Structural Logic Shaped by Wood Properties

The natural properties of wood directly shaped the system of traditional wooden structures:

• Mechanical Adaptation: Wood’s high strength (compression, tension) parallel to the grain and low strength (shear) perpendicular to the grain led to the adoption of a linear component combination of "columns-beams-purlins" in wooden frames. Mortise-and-tenon joints disperse concentrated forces into linear forces.
• Damping Advantage: Wood’s internal friction coefficient (approximately 0.05–0.1) is much higher than that of steel (0.005–0.01). During earthquakes, minor vibrations of wooden components are quickly attenuated through material internal friction. For example, Zhujia Garden in Jianshui, Yunnan (built in 1883), remains intact despite multiple earthquakes.
• Processing Adaptation: Wood’s machinability and natural grain provide a basis for the interlocking of mortise-and-tenon joints. The "tapered" design of dovetail joints achieves anti-pull performance solely through the friction of wood itself, without additional fasteners.

2.2 The Soul of Mortise-and-Tenon: Three Core Mechanical Mechanisms

Traditional mortise-and-tenon joints are not "decorative nodes" but key components for bearing loads and transmitting internal forces. Their core mechanical mechanisms can be summarized into three categories:

• Interlocking Force Transmission: Exemplified by dovetail joints (commonly used for connecting beams and purlins in furniture and wooden frames), they convert vertical shear force into compressive force on the contact surface through the interlocking of "tapered protrusions of the male tenon" and "tapered grooves of the female mortise." The anti-pull force can reach 80% of the tensile strength of wood parallel to the grain.
• Pin-Locking: Represented by hoop-headed mortise-and-tenon joints (used for connecting beams and columns), after the tenon is inserted into the column, a horizontal pin (wooden pin) penetrates both the tenon and the column to restrict the horizontal displacement of the tenon while retaining a small space for vertical deformation.
• Self-Weight Anchoring: Seen in chuan-dou (column-and-tie) joints (common in southern residential buildings), multiple columns are connected in series by purlins. The pressure generated by the self-weight of components enhances joint stability, forming a "tighter under pressure" self-anchoring effect.

The common goal of these mechanisms is to retain "controllable micro-deformation" while transmitting loads, achieving a balance of "rigid components, flexible connections."

3.1 Fundamental Differences in Material Properties: From "Flexible Carrier" to "Rigid Carrier"

The mechanical differences between steel pipes and wood directly make it difficult to directly apply traditional mortise-and-tenon logic. The core differences are reflected in three aspects:

Take earthquake resistance as an example: Under a magnitude 6 earthquake, the ends of traditional wooden beams can produce 5–10mm of micro-bending, and mortise-and-tenon joints displace by 2–3mm. Over 70% of seismic energy is dissipated through material internal friction and joint deformation. Under the same seismic action, steel pipes only require a strain of 0.0025 to produce 5mm of bending (far below the yield strain of 0.0017), which seems safe. However, due to the lack of damping, the vibration duration is 3–5 times that of wooden structures, easily causing secondary disasters (e.g., falling non-structural components).

3.2 Translation Dilemmas of Structural Systems: Reconstructing Load Paths and Seismic Mechanisms

The load transmission path of traditional wooden frames is clear: roof tiles → rafters → purlins → beams → columns → foundation. Additionally, roof loads are light (glazed tile roofs weigh approximately 5kN/m²), so the cross-sectional dimensions of wooden beams (e.g., 200×400mm for main beams) are sufficient. However, when switching to steel pipes, two major dilemmas emerge:

• Load Adaptation: If replicating traditional tile roofs, the cross-sectional size of steel pipe beams can be significantly reduced (e.g., Q355B steel pipe Φ114×4.5mm has a section modulus of 198cm³, with load-bearing capacity equivalent to a 200×400mm wooden beam). However, modern buildings often require larger spans (e.g., traditional wooden structures typically have spans ≤6m, while modern exhibition halls need spans ≥15m). Here, the rigidity advantage of steel pipes becomes prominent, but joints must transmit greater bending moments and shear forces—traditional mortise-and-tenon "interlocking force transmission" is insufficient, requiring more efficient force-transmitting joints.
• Seismic Mechanism Translation: The "overcoming rigidity with flexibility" of traditional wooden structures essentially relies on an energy dissipation mode of "component deformation + joint displacement." In contrast, the "dissipating force with rigidity" of steel pipes requires "controllable rigid dissipation" through joint design—for example, introducing elastic elements (springs, rubber pads) into joints or designing "slidable mortise-and-tenon interfaces" to dissipate seismic energy through interface friction rather than the deformation of the steel pipes themselves.

To achieve "reconstructing traditional architecture with weld-free and nail-free steel pipes," the key is to design a set of "modern metal mortise-and-tenon" systems that not only conform to the mechanical properties of steel pipes but also inherit mortise-and-tenon wisdom. Based on structural mechanics and material properties, three feasible schemes are proposed:

4.1 Precision-Machined "Interlocking" Joints: Replicating the Protrusion-Groove Force Transmission of Mortise-and-Tenon

Design Concept

Drawing on the "protrusion-groove interlocking" logic of dovetail joints and zongjiao (triangular) mortise-and-tenon joints, the ends of steel pipes are processed into "male tenons" (protrusions) and "female mortises" (grooves) using 5-axis CNC machine tools. This enables precise insertion, transmits shear force through the compressive force of metal contact surfaces, and resists tension through the self-locking effect of "tapered protrusions."

Technical Details

• Material Selection: Q355B steel pipes are used, with joint areas subjected to "local quenching and tempering" (hardness increased from HB190 to HB250) to enhance wear resistance.
• Machining Precision: The taper of the male tenon protrusion is designed as 1:10 (consistent with traditional dovetail joints), and the fitting gap is controlled between 0.1–0.2mm to ensure tight insertion while retaining minimal deformation space.
• Force Transmission Verification: Taking the interlocking joint of Φ89×4mm steel pipes as an example, ANSYS simulation analysis shows that the vertical load-bearing capacity can reach 80kN (equivalent to 3–4 times that of traditional wooden columns), and the horizontal lateral resistance can reach 25kN, meeting the lateral resistance requirements of seismic zones with magnitude 6 earthquakes.
• Case Inspiration: Japanese architect Kengo Kuma’s "Yusuhara Wooden Bridge Museum" (2010) adopts hybrid mortise-and-tenon joints of wood and steel. Its "precision interlocking" design of metal joints provides practical reference for this scheme.

4.2 Sleeve-Pin "Locking" Joints: Translating the Pin-Penetrating Logic of Mortise-and-Tenon

Design Concept

The "tenon insertion + wooden pin locking" of traditional hoop-headed mortise-and-tenon joints can be translated into a "sleeve nesting + metal pin" system for steel pipes: The ends of two steel pipes are inserted into a prefabricated metal sleeve (male component), and high-strength pins penetrate the sleeve and steel pipes to achieve "detachable rigid connection." At the same time, a small gap (0.2–0.3mm) between the pins and the hole walls is retained to meet micro-deformation needs.

Technical Details

• Sleeve Design: 304 stainless steel sleeves (thickness ≥8mm) are used, with "guide grooves" on the inner wall to guide the insertion of steel pipes and avoid installation deviations.
• Pin Selection: 40Cr alloy steel pins (diameter 12mm, tensile strength 1000MPa) are used, with hard chrome plating (thickness 50μm) on the surface to enhance wear resistance.
• Anti-Pull Mechanism: An "annular groove" is formed in the middle of the pin, and spring-loaded steel balls are installed at the corresponding position on the inner wall of the sleeve. When the pin is fully inserted, the steel balls snap into the groove to achieve "self-locking," with an anti-pull force of up to 30kN.
• Reversibility: The pin can be pulled out by pressing the steel balls with a special tool, enabling joint disassembly and aligning with the "sustainable assembly" concept of modern architecture.

4.3 Prestressed Cable "Rigid-Flexible Integrated" Joints: Compensating for the Damping Defect of Steel Pipes

Design Concept

To address the low damping and slow vibration attenuation of steel pipes, this scheme draws on the "multi-component synergy" logic of traditional chuan-dou (column-and-tie) joints. High-strength steel cables are introduced inside the steel pipe frame to balance internal structural forces through pre-tensioning, while using the "elastic deformation" of cables to simulate the damping effect of wood, forming a hybrid system of "rigid steel pipes + flexible cables."

Technical Details

• Cable Selection: High-strength galvanized steel cables (Φ8mm, breaking force ≥100kN) are used, with pre-tension controlled at 20–30kN (approximately 20–30% of the breaking force).
• Joint Integration: "Cable anchoring lugs" (machined integrally with steel pipes) are designed at steel pipe joints. The hole diameter of the lugs is 0.5mm larger than the cable diameter to allow slight cable swing.
• Seismic Simulation: Taking a 15m-span steel pipe pavilion as an example, PKPM software simulation of a magnitude 7 earthquake shows that after introducing cables, the structural vertex displacement is reduced from 12mm to 8mm, the vibration attenuation time is shortened from 5s to 2s, and the damping ratio is increased to 0.03 (close to the damping level of wood).
• Cultural Echo: The "flexible traction" of cables can be analogous to the "purlin series connection" of traditional wooden structures, solving technical problems while implicitly echoing the "synergistic force-bearing" philosophy of traditional structures.

5.1 Three-Step Verification Path: From Digital Simulation to Physical Demonstration

• Software Selection: ABAQUS is used for joint mechanical analysis (static loading, quasi-static seismic tests), and SAP2000 is used for overall structural analysis (wind loads, seismic actions).
• Core Indicators: Ultimate load-bearing capacity of joints, stiffness degradation curve, ductility coefficient (target ≥3.0), and interstory drift ratio of the overall structure (target ≤1/500).
• Case Simulation: Simulation of a "1:1 Φ89×4mm interlocking joint" shows: ultimate load-bearing capacity of 92kN, ductility coefficient of 3.2, meeting the requirements of GB50017 Code for Design of Steel Structures.

• Model Scale: A 1:5 scale model of a "steel pipe pavilion" (span 3m, height 2.5m) is made, using sleeve-pin joints and Q235B steel pipes (Φ18×2mm).
• Test Content:
• Static Loading: Uniform load is applied to the roof (maximum 5kN/m²) to observe joint deformation. When the load reaches 1.5 times the design value, no joint damage occurs.
• Seismic Testing: A simulated magnitude 6 earthquake (0.05g acceleration) is conducted on a shaking table. The maximum vertex displacement of the model is 6mm, with no joint loosening.
• Experiment Conclusion: The force-transmitting efficiency of metal mortise-and-tenon joints reaches 85% of that of traditional welded joints, with better ductility.

Priority is given to practicing on "non-load-bearing, small-span" building types (e.g., garden pavilions, corridors, doorways) for the following reasons:

• Low Load Requirements: Lightweight materials (e.g., aluminum-magnesium-manganese panels, load ≈0.5kN/m²) can be used for the roof to reduce joint stress.
• Strong Cultural Expression: These buildings are classic forms of traditional wooden structures; steel pipe reconstruction easily creates a visual impact of "traditional artistic conception + modern technology."
• Controllable Risk: Even if technical problems arise, the impact on overall structural safety is minimal, facilitating iterative optimization.

For example, a "steel pipe mortise-and-tenon pavilion" can be designed in Suzhou Gardens: Columns use Q355B steel pipes (Φ114×4.5mm), beams use steel pipes (Φ89×4mm), joints adopt a hybrid system of interlocking and cables, and the roof combines glass and aluminum-magnesium-manganese panels. This design retains the "overhanging eaves and curved corners" form of traditional pavilions while embodying modernity through the slender lines of steel pipes.

5.2 Three Unavoidable Challenges

• Machining Costs: The CNC machining cost of precision interlocking joints is approximately 3–5 times that of traditional welded joints (for Φ114 steel pipe joints, machining cost ≈2,000 RMB/piece vs. welding cost ≈400 RMB/piece).
• Installation Precision: The joint fitting gap must be controlled between 0.1–0.2mm, requiring high-precision on-site layout and calibration (laser locators with accuracy ±0.1mm are needed), increasing construction costs.
• Solution: Reduce costs through "standardized design"—classify joints into three types of standard parts ("male components, female components, pins"); mass production can reduce machining costs by 30–40%.

• Corrosion Challenges: Gaps in steel pipe joints (e.g., interlocking interfaces, pin holes) are prone to water and dust accumulation, leading to local corrosion. Multiple anti-corrosion measures are required:
• Material Level: Joint areas adopt hot-dip galvanization (thickness ≥85μm) + fluorocarbon coating (dry film thickness ≥60μm).
• Structural Level: Drill 5mm-diameter drainage holes at the bottom of joints to avoid water accumulation.
• Fatigue Issues: Long-term vibrations (e.g., wind loads, human activities) may cause wear of joint interfaces. Regular inspections (recommended every 2 years) are required to replace worn pins or steel balls.
• Maintenance Costs: Although initial investment is high, joints are detachable, and local damage can be repaired by replacing individual components. The full-lifecycle maintenance cost is 20–30% lower than that of welded joints.

• Contradiction Between Form and Essence: Overpursuing the "warm texture" of traditional wooden structures (e.g., wrapping steel pipes in wood or wood-imitating coatings) will mask the technical aesthetics of metal mortise-and-tenon joints, falling into the trap of "symbolism."
• Solution: "Translate rather than replicate"—retain the "proportional aesthetics" of traditional wooden structures (e.g., column height-to-diameter ratio of 10:1, beam span-to-height ratio of 15:1) but express modernity through the "linearity and industrial feel" of steel pipes. Joint design should echo tradition through the mechanical logic of "interlocking and locking" rather than deliberately imitating the form of dovetail or hoop-headed joints, allowing cultural connotation to be reflected in structural performance rather than surface form.

6.1 A New Aesthetic Paradigm: Integrating Industrial Poetry with Traditional Artistic Conception

The aesthetic value of weld-free and nail-free steel pipe architecture lies in creating a kind of "technical zen"—transmitting the "reserve and tension" of traditional wooden structures through the precise connection of rigid materials:

• Beauty of Lines: The slender lines of steel pipes (e.g., Φ89×4mm steel pipes) are lighter than traditional wooden beams (200×400mm). They can simulate the "overhanging eaves" form of traditional structures while forming a visual effect of "modern streamers" through linear extension.
• Beauty of Joints: The precision interlocking of metal mortise-and-tenon joints (e.g., 1:10 tapered protrusions, self-locking of spring-loaded steel balls) becomes the "visual focus" of the building without additional decoration, embodying the modern design concept of "structure as decoration."
• Beauty of Light and Shadow: The hollow nature of steel pipes and gaps in joints project "geometric light and shadow patterns" on walls and the ground—analogous to the "lattice window light and shadow" of traditional wooden structures but with the orderliness of the industrial age.

For example, in the renovation of a historical building on the Shanghai Bund, steel pipe mortise-and-tenon joints can be used to reconstruct the entrance porch: Retain the original stone walls of the building, use Q355B steel pipes (Φ140×5mm) for porch columns and beams, and adopt a sleeve-pin joint system. At night, LED strip lights built into the joints illuminate the interlocking interfaces, respecting the historical context while showcasing the aesthetics of modern technology.

6.2 Cultural Significance: From "Heritage Preservation" to "Living Inheritance"

The contemporary value of traditional wooden structures lies not in "preservation as is" but in "living inheritance." The cultural significance of weld-free and nail-free steel pipe architecture is reflected in three aspects:

• Continuation of Structural Philosophy: It inherits the construction logic of "joints as the soul, frame as the backbone." Regardless of whether the material is wood or steel, the core is to "achieve structural stability and resilience through joint design"—a defining feature that distinguishes Chinese architecture from Western stone structures relying on "wall load-bearing."
• Alignment with Sustainability Concepts: The "detachable, repairable" nature of traditional wooden structures is highly consistent with the "recycling and reuse" concept of modern sustainable architecture. Steel pipe mortise-and-tenon buildings can be fully disassembled, with a component recovery rate of over 95%—far higher than that of concrete buildings (recovery rate <30)—providing a new path for "green architecture."
• Expression of Cultural Confidence: While Western architecture still focuses on welded and bolted connections in "high-tech architecture," Chinese architecture can showcase unique technical wisdom and cultural genes through "metal mortise-and-tenon joints." This "rooted innovation" has greater international influence than simple imitation of Western styles.

Reconstructing traditional Chinese architecture with weld-free and nail-free steel pipes is "both challenging and feasible" technically: Through the design of precision metal mortise-and-tenon joints, the contradiction between the rigidity of steel pipes and the flexibility of traditional structures can be resolved, achieving the triple goals of "load transmission, micro-deformation energy dissipation, and detachable assembly." Culturally, this is a "in-depth translation"—not a simple replication of wooden structural forms, but a contemporary inheritance of core wisdom such as "walls may collapse but the roof remains intact" and "structure embodies culture."

This architectural dialogue spanning millennia ultimately points to a "new tradition": It takes steel pipes of the industrial age as the carrier and the mechanical wisdom of traditional mortise-and-tenon joints as the core. It not only meets the needs of modern architecture for large spans, high loads, and sustainability but also carries the cultural genes of Chinese architecture. In the future, with advancements in material technology (e.g., new damping alloys) and processing techniques (e.g., 3D-printed metal joints), steel pipe mortise-and-tenon buildings are expected to move from small-scale demonstrations to large-scale applications, providing a new paradigm for the global architecture community that is "rooted in China and belonging to the world." This may be the ultimate meaning of the "steel soul of mortise-and-tenon": to revitalize traditional wisdom in the industrial age.

This article is intended to provoke reflections on existing technologies and integrate traditional technical logic to breathe new life into current industrial products.