1 Introduction
Modern Chinese architecture had experienced a significant transition from traditional to modern construction techniques (
Li, 2004). This process can be divided into two distinct phases. The first phase, spanning from the First Opium War in 1840 to the outbreak of the War of Resistance Against Japanese Aggression in 1931, saw the lower reaches of the Yangtze River, epitomized by Shanghai and Nanjing, emerge as the vanguard of modern Chinese construction. Under the influence of Western civilization, these regions extensively adopted construction types and techniques from Europe and America (
Cody, 2003;
Bracken, 2013). With the outbreak of the war and the relocation of the Nationalist Government’s capital to Chongqing, the center of Chinese construction shifted to the inland upper reaches, marking its second phase. The development of construction techniques in the downstream Yangtze River cities before the war was primarily characterized by “transplantation,” focusing on the introduction and absorption of advanced foreign techniques. In contrast, during the war, Chongqing emphasized “grafting,” placing a higher value on the improvement of local traditional crafts (
Peng, 2023).
In Chongqing, where Western influence was not dominant, the interaction between downstream technical diffusion and local construction traditions was the main driving force for architectural production. The relocation of the wartime capital greatly accelerated the technical interaction between the upper and lower reaches of the Yangtze River. However, at the same time, material shortages, population expansion, and bombing destruction profoundly constrained the development of construction (
Han and Rong, 2023), resulting in a modernization path distinctly different from that of the pre-war downstream cities. During the war, steel and cement were war materials that required military approval for purchase and use. Therefore, in the civilian sector, the expensive and scarce reinforced concrete structure was mostly used for important air-raid shelters. Brick-timber structure was widely used in civilian buildings in the downtown, while timber (bamboo) structure was mostly found in suburban areas. In wartime Chongqing, due to the huge demand for construction, brick supply was insufficient, and although local stone resource was abundant, the difficulty of mining and processing limited its use (
Li, 2013). Therefore, in ordinary civilian buildings, it was a natural choice to save bricks and stones and widely use locally abundant renewable materials such as wood and bamboo.
The practices of the Kwan, Chu and Yang Architects & Engineers (Kitai) in wartime Chongqing were excellent models for studying Chinese constructions at this stage. Kitai was the largest, most widely distributed, and most well-known architectural institute in modern China (
Han and Rong, 2023). During the war, Kitai relocated its headquarters from Nanjing to Chongqing and completed over 50 construction projects there, involving three common construction types: brick-timber structure, timber (bamboo) structure, and reinforced concrete structure. In practice, it explored principles such as “adapting to local conditions, using local materials, designing and constructing according to the materials” (
Zhang, 2007), achieving architectural production under extremely constrained conditions and becoming typical examples of wartime Chongqing construction techniques, with characteristics of both “transplantation” and “grafting".
Current research predominantly focuses on the modernization of construction practices in China’s coastal cities, encompassing the transformation of materials, techniques, and structures (
Cody, 2003;
Pan and Campbell, 2017, 2018;
Shu 2018;
Han et al., 2020;
Han and Wang 2023). In contrast, studies on inland regions remain scarce (
Li and Jing, 2019), obscuring the diversity of China’s architectural modernization pathways. This study examines three wartime construction types in Chongqing―brick-timber structures, timber (bamboo) structures, and reinforced concrete structures―to reveal their technical strategies, patterns, and driving mechanisms under extreme conditions. It further argues that these practices represent an alternative modernization trajectory distinct from that of the eastern coastal regions. This research thus broadens the scope of studies on modern Chinese architecture.
2 Theoretical framework
2.1 Characteristics of modern Chinese construction techniques
Existing literature indicates that construction knowledge and techniques in China’s coastal regions were extensively transplanted from European and American countries. Cody (2023) documented the profound imprint of American architectural knowledge and techniques on Eastern Chinese cities. Pan and James (
2017,
2018) traced the introduction of Western brick-timber construction system and tools to China, elucidating the adaptive characteristics of this construction knowledge through comparative analyses of Chinese and British texts (Pan and Campbell,
2017,
2018).
Shu (2018) unveiled the influence of British techniques on Shanghai’s architecture by juxtaposing bricklaying methods in modern Shanghai and the UK. Han delineated the adaptive features of construction techniques in Nanjing by juxtaposing them with Western techniques (
Han et al., 2020;
Han and Wang 2023).
Compared with coastal areas, research on construction techniques in modern inland areas only recently gained traction.
Li (2023) summarized the technical characteristics of Chongqing’s brick-timber construction system,
Li and Jing (2019) identified the hybrid Chinese-Western strategies employed in timber frameworks in wartime Chongqing through classified surveys and mechanical analyses. Based on the above literature, this paper analyzes the construction strategies of Kitai’s three construction types in wartime Chongqing, revealing their economic and practical characteristics.
2.2 The mode and driving mechanism of Chinese modern construction techniques
John Fairbank conceptualized modern Chinese history through the “impact-response” framework, positing that the incursion of Western forces and China’s subsequent reactions constituted the primary drivers of historical development (
Fairbank, 1982). This model broadly accounted for the architecture in China’s coastal cities from 1840 to 1937. Based on this,
Xu (2020) attributed the architectural development in coastal areas to the result of the complex interaction between colonialism and nationalism. Paul Cohen, however, highlighted the vast disparities within China―its uneven development and varied degrees of Western impact―and introduced the “China-centered perspective.” This approach underscored the role of internal Chinese factors in propelling modernization.
Cohen (1984) emphasized regional studies, noting that coastal areas, as China’s outermost layer, experienced the most intense Western impact and exhibited the most profound reactions, aligning with Fairbank’s model. In contrast, the inland regions, shielded from direct Western influence, retained a stronger traditional dominance.
Peng’s (2023) research demonstrates that modern China’s textile industry exhibited a distinct dualistic pattern. One pattern, represented by coastal cities, was characterized by a rapid industrialization process involving the comprehensive transplantation of Western-style production lines. The other, represented by wartime Chongqing, involved a grafting model that utilized Western knowledge to improve traditional handicrafts. At that time, due to wartime blockades, limited mechanized mass production was far from sufficient to meet the textile demands. Consequently, the government dispatched experts to improve traditional textile machinery and train female workers. With the participation of 500,000 women, the acute shortage of textiles was significantly alleviated. Compared with the transplantation model, the grafting model featured lower investment and was more friendly to traditional practitioners, representing a gradual industrialization process.
Drawing on the above discussions, this paper argues that the technical strategies exhibited by Kitai’s three construction types in wartime Chongqing were designed to address the real issues in architectural production under the specific conditions. These strategies represented corresponding technological patterns, characterized by a combination of transplantation and grafting. The driving mechanisms primarily stemmed from the interactions among different regions within China, rather than external Western impacts, as Western forces never established a dominant presence in Chongqing.
3 Research methods
3.1 Case classification analysis
Kitai’s extensive and diverse constructions, characterized by distinct features, served as quintessential examples of architecture produced in wartime Chongqing. This study focuses on three construction types from Kitai’s Chongqing projects: brick-timber structures, timber (bamboo) structures, and reinforced concrete air-raid shelters. Based on both case representativeness and documentation completeness, the cases outlined in the below were selected for detailed study.
Brick-Timber Structures: the US Embassy News Office building (1943—1944), Shangqingsi Branch of Meifeng Bank (1939), Beibei Branch of Meifeng Bank (1939), Minquan Road Branch of Juxingcheng Bank (1941), and the Farmers Bank (1942). All exhibited significantly modified brick-timber systems with structures, enclosures, and appearances of the wartime characteristics.
Timber (Bamboo) Structures: buildings on the Jiangjin Campus of National Women’s Normal College (1941) exemplified this type. They encompassed small-span buildings (the medical room, bathroom and toilet, storage room, and dormitory), medium-span buildings (the classrooms, libraries, and primary school classrooms), and large-span buildings (the auditorium and dining hall). These structures departed from traditional Chinese forms, incorporating improvements based on Western structural principles.
Reinforced Concrete Air-Raid Shelters: the air-raid shelter for the International Broadcasting Station of the Central Broadcasting Administration (1941) and the combined air-raid shelter for the Bank of Communications and the Farmers’ Bank (1939). The former represented a small-scale facility, while the latter was a large-scale shelter. Each adopted distinct construction strategies to meet their specific structural and spatial demands.
Through a detailed analysis of these three case categories, the paper examines the adaptive strategies employed in wartime Chongqing and identifies their technical development patterns.
3.2 Archival retrieval and historical contextual analysis
Although Chongqing preserves China’s largest concentration of wartime architectural heritage, many of these structures had undergone significant alterations over the past 80 years. A substantial number had been demolished and subsequently reconstructed using modern techniques, preserving only the original appearance. This makes recognizing historical construction methods through physical artifacts highly challenging. Archives provide a crucial remedy for this gap. This study retrieved nearly 3000 historical documents, including architectural drawings, construction details, contracts, estimates, tender documents, construction schedules, permit applications, and correspondence, documenting the full architectural production process. These documents reveal not only technical construction details but also the decision-making processes underpinning the adoption of specific techniques.
By situating construction techniques within wartime Chongqing’s unique historical context―marked by material shortages, population influx, and bombing damage―this research reconstructs the strategies architects used to achieve production goals amidst actual constraints, identifies corresponding technical patterns. Consequently, the paper addresses these core questions:
· How did the brick-timber system achieve cost-effective and aesthetically pleasing buildings despite shortages of bricks?
· How did the vernacular Chuandou style trusses, common in suburban areas, achieve structural stability while enabling larger, column-free interior spaces?
· How did the reinforced concrete air-raid shelter reconcile structural robustness with spatial usability requirements?
It should be noted that the original archive files featured inherently limited precision, and digitization further degraded detail resolution, rendering many elements indiscernible (Fig. 1). Therefore, the paper employs redrawn archive illustrations, using both 2D and 3D reconstructions of key technical details to enhance clarity and visualization.
4 Analysis and discussions
4.1 Cost-effective construction and decent appearance of brick-timber “pseudo Western buildings"
The brick-timber system began to emerge in the concessions of Chinese coastal cities in the 1840s and was the earliest Western-style construction type transplanted in modern China. The brick-timber structure used timber trusses to transfer the roof load to brick walls, which then transmitted it to the ground through strip foundations. Due to its simple construction and controllable cost, the brick-timber structure was quickly mastered by Chinese craftsmen, becoming the most common architectural structure in coastal cities before 1937 (
Han et al., 2020). After the port opening in Chongqing (1890), most of the constructed foreign firms also adopted this structure. “Western building” referred to Western-style buildings, which in modern China were often associated with decent appearance, clear functions, spacious spaces, and advanced facilities. “Pseudo-Western building” was a term that emerged in the wartime to describe Western-style buildings that appeared decent but were actually cheaply constructed. The “Western” aspect lay in their decent appearance, while the “pseudo” aspect lay in their cost-effective construction. How to achieve decent architectural appearances through cheap materials and construction measures was the key issue that needs to be addressed in the production of “pseudo-Western buildings.” The “pseudo-Western buildings” designed by Kitai made significant modifications to the brick-timber system, achieving cost-effective construction through structural reduction and enclosure grafting, and meeting the demand for decency through appearance simulation.
4.1.1 Structural reduction: framework transformation of bricks
Structural reduction referred to replacing the common “brick wall—timber truss” with “brick column—timber truss,” which transformed the wall load-bearing structure into a column load-bearing structure, achieving the framework use of bricks and the goal of saving bricks. This transformation was inspired by the reinforced concrete structure that entered China’s coastal areas in the early 20th century. Although the advantage of reinforced concrete lay in its framework structure, in the nearly 30 years after its introduction to China, pure framework structure was not the mainstream of reinforced concrete buildings. In order to seek large spans while saving costs, many buildings combined brick-timber structure with reinforced concrete framework, such as combining peripheral brick walls, internal reinforced concrete frameworks, timber beams, timber floors, and timber trusses in one building (
Han and Wang 2023) (Fig. 2). It was the combination of brick wall and concrete framework that inspired the framework transformation of bricks. Although such structural modifications had been carried out in a few cases before 1937, their widespread popularity emerged in wartime Chongqing. Among Kitai’s 14 brick-timber structure projects with detailed archives, 13 projects were modified to the “brick columns‒timber trusses” combination, accounting for about 93%, involving various functional types such as banks, offices, residences, theaters, and factories, indicating high recognition of this structure by architects, construction companies, and owners.
The practice of structural reduction was to retain the timber trusses, but replace the entire brick wall with brick columns that only support the nodes of the timber trusses. Compared with the common “brick wall‒timber truss”, the stiffness and earthquake resistance of the “brick column‒timber truss” was significantly weakened. If used in buildings of two stories or more, it needed to add a ring beam. Taking the bank buildings in wartime Chongqing designed by Kitai as examples, these banks, mostly three-story buildings, all adopted the “brick column‒timber truss” structure (
Kiai, 1942). The section of the column was about 51 cm (20 inches), and the span was about 3—4 m, which was roughly half of the reinforced concrete structure. If no brick walls were filled in between, it could save nearly 70% of the bricks compared with the “brick wall‒timber truss.” The brick columns of these banks were connected by reinforced concrete ring beams, with timber beams laid on the ring beams for general floors and timber trusses laid on the top floor, then with Chinese grey tiles laid (Fig. 3).
4.1.2 Enclosure grafting: revival of local crafts
Enclosure grafting was mainly reflected in the replacement of solid brick walls with local materials and crafts, which effectively reduced costs and achieved rapid construction. Enclosure grafting was obviously inspired by traditional residences; it started in the lower Yangtze River area and was promoted in wartime Chongqing. In the brick-timber construction in Nanjing during the 1920s, the use of hollow brick wall (Fig. 4(a)) to replace solid brick wall had already appeared in ancillary buildings (
Han et al., 2020). This hollow masonry could save 30%—40% of bricks compared with solid brick walls of the same thickness. In Nanjing’s residential buildings, lathed and plastered timber partition (Fig. 4(b)) was widely used to make internal non-loadbearing wall. The method was to nail timber laths on timber frames and then plaster with linen lime mortar, with the advantages of being lightweight, simple in craftsmanship, and inexpensive.
After 1937, for the purpose of saving costs and rapid construction, buildings in wartime Chongqing placed greater emphasis on simple and cheap local materials and crafts. Hollow brick wall was already considered a luxury and only used in the exterior wall of financially strong bank buildings; the application of lathed and plastered partition was more widespread than in the pre-war downstream areas. In addition, the wartime brick-timber construction system in Chongqing also grafted the commonly used plastered bamboo mat wall (Fig. 4(c)) in vernacular buildings. Its method was similar to lathed and plastered partitions, nailing woven bamboo fences on timber frames, and then plastering with linen lime mortar. Since the southwest region was rich in bamboo, its price was cheaper than wood, and the craftsmanship was simpler, so plastered bamboo mat wall was the most popular in wartime Chongqing. In the “brick column‒timber truss” buildings designed by Kitai, ordinary civilian buildings such as office buildings, residences, dormitories, theaters, and factories all used lathed and plastered timber partitions or plastered bamboo mat partitions for internal and external non-load-bearing walls. Even banks also greatly reduced their construction standards, with non-load-bearing interior wall using lathed and plastered timber partition, and external enclosure using hollow brick wall. Through the grafting of vernacular enclosures such as hollow brick wall, lathed and plastered timber partition, and plastered bamboo mat wall, the wartime brick-timber construction system achieved multiple effects of saving bricks, reducing cost, and rapid construction.
4.1.3 Appearance simulation: acquisition of decency
Appearance simulation referred to the practice of simulating expensive materials through surface construction or using formal composition to simulate specific styles, with the aim of masking cheap construction methods to achieve a decent appearance. In the Beaux-Arts system, the “character” of a building was crucial, and the appearance of a building should be consistent with its function. For example, bank buildings needed to create a solid and luxurious atmosphere to demonstrate their strength and enhance the trust of depositors; administrative buildings needed to be dignified to demonstrate their authority and seriousness. In buildings such as residences and dormitories, lathed and plastered timber partition and plastered bamboo mat wall could simulate the appearance of plastered brick wall, which was also one of the reasons for their widespread application. In bank buildings, wet pebble dashing and artificial stone coating were used to simulate the appearance of granite (
Han et al., 2020). These two methods were also widely used in the pre-war lower Yangtze River cities before 1937, but in wartime Chongqing, they were high-grade construction methods and were only applied in buildings with financially strong owners. Wet pebble dashing used a mixture of stone particles and cement mortar as the surface layer, and the stone particles were exposed by rinsing with water before it solidified; artificial stone coating used a mixture of stone powder and stone chips with cement mortar as the surface layer, and it was chiseled after it had initially solidified (Fig. 5). Since both of these finishes required operation on a cement mortar base, it was the hollow brick wall that could minimally meet the requirements for cement mortar adhesion.
In addition to material simulation, style simulation was also an important way to obtain a decent appearance. Generally speaking, a specific architectural style often corresponded to a specific character and function. For example, Western classical style was elegant and solemn, commonly seen in government and educational buildings; Art deco style had smooth lines and a prosperous atmosphere, often used in commercial buildings. The US Embassy News Office building (1943—1944) designed by Kitai also adopted the “brick column‒timber truss” structure, with internal and external walls all using plastered bamboo mat, and the roof covered with Chinese grey tiles but its appearance adopted the Greek Revival classical style (
Liuhe et al., 1943). Since it was difficult to make complex moldings of this style with plastered bamboo mat walls, the building greatly simplified the decoration, only protruding the ring beams from the outer wall to form a decorative waistline (Fig. 6). Although the Chinese grey tiles and the bare outer surface appeared a bit shabby, the application of the Greek Revival style still gave the building an overall solemn and elegant temperament. The wartime banks designed by Kitai generally imitated the pre-war bank appearance, adopting the modern Art-deco style with vertical lines to present the bank’s strong financial strength and prosperous upward temperament as much as possible (Fig. 7).
4.2 Stable structure and column-free interior space of timber (bamboo) system
The Chuandou-style timber structure was a widely used traditional structural form in southwestern residences. Compared with the Tailiang-style commonly seen in official architecture and northern residences, the Chuandou-style used fewer large timber materials, had slender column diameters, and the dense arrangement of columns facilitated the installation of enclosure structures. Using this structure in suburban areas in wartime Chongqing was not only economically advantageous in terms of low cost, but also maximized the local craftsmen’s skills to ensure the quality of the project. However, the Chuandou-style timber structure belonged to the purlin frame―the roof was borne by the purlins and columns and then transmitted downward. The tie beams played the role of connecting the columns. If they bore the load of the short columns, they would be subjected to compression and bending, leading to stress concentration. Therefore,
The Chongqing Building Regulations (1941) stipulated that the spacing of the ground columns should not exceed three steps, that is, no more than two consecutive short columns (
Wu, 1941). Taking the Chuandou-style timber structure with a column diameter of 15 cm as an example, the span between the ground columns did not exceed 3 m, which was not sufficient to cover medium and large spaces such as classrooms and auditoriums that emerged in modern times. In addition, the Chuandou-style timber trusses were connected to each other by purlins, and the lack of diagonal members made them prone to deformation under lateral forces. How to improve the traditional Chuandou-style timber structure so that it could achieve structural stability and cover larger spaces was a key issue.
Western-style timber truss spread to Chinese coastal cities in along with the brick-timber construction system in the 1840s and had undergone nearly a century before the war, architects and construction companies in coastal cities had fully grasped its principles. Western timber truss was bowstring truss with triangles. The weight of the roof was borne by the arch composed of two oblique sides and transmitted along the oblique axis to the beam. The vertical columns inside the triangle were designed to hold the beam and mainly bore tension rather than pressure, which did not affect the overall span (
Liu, 2022). A triangular timber truss with a cross-section of about 15 cm could span about 6 m. In addition, there were various forms of connections between the triangular trusses, such as horizontal, diagonal, and scissors braces, forming a composite force-bearing framework with better overall mechanical properties.
Therefore, using the principles of Western timber trusses to improve the Chuandou-style timber structure became a natural construction strategy in wartime Chongqing. In the Jiangjin campus of National Women’s Normal College (1941) designed by
Kitai (1941), small-span buildings used improved Chuandou-style timber trusses with Western components; medium-span buildings used a hybrid strategy of Chuandou-style and Western trusses; and large-span buildings mainly used Western timber (bamboo) trusses. By grafting Western structural principles onto local crafts, the building complex achieved structural stability and met various span requirements under the premise of cost-effective construction and controllable quality.
4.2.1 Improvement of the chuandou-style timber structure: improved column-and-tie timber trusses in small-span buildings
The improvement of the Chuandou-style timber structure referred to the practice of using the Western truss principles to improve the Chuandou-style truss or the connections between the Chuandou-style trusses. In the Women’s Normal College, small buildings such as medical room, storage room, student dormitory, bathroom and toilet all used the Chuandou-style timber structure trusses with short columns. The span between the ground columns of a single truss was about 1.8—2.7 m, all located at the partition walls. Inspired by Western structural principles, most of these buildings added scissors braces as connecting components between trusses to enhance the overall structure.
The medical room used 7-purlin Chuandou style trusses. After column cutting, only 3 columns of the gable wall truss were landed, and the middle truss had 4 ground columns, with a span of about 1.2—2.7 m between columns. The trusses were connected by scissors braces (Fig. 8). The bathroom and toilet used a 5-purlin Chuandou style trusses. After column cutting, only 3 columns landed, with a span of about 1.8 m between columns, and the middle column was located at the partition. The trusses were connected by scissors bracing (Fig. 9). The storage room and dormitory jointly enclosed a courtyard, but their structures were set separately. The storage room used 4-purlin Chuandou style trusses. After column cutting, 3 columns of the gable wall truss landed, and two columns close together provided convenience for door openings. One truss in the middle has 2 columns landing, forming a column-free indoor space for convenient storage (Fig. 10).
The dormitory had a slightly larger span, but its partitions were dense, so it still used the Chuandou style trusses (9 purlins). After column cutting, only 4 columns landed, with a span of 1.8—2.7 m between columns, all located at the partitions. Its special feature was the addition of diagonal bracing components at the eaves to disperse the concentrated stress at the connection between the tie beams and the columns, increasing the stability of the eaves. Trusses are connected with scissors braces (Fig. 10).
Through the strengthening of the connections between trusses (medical room, student dormitory, bathroom and toilet) and the improvement of the truss itself (student dormitory), the Chuandou style timber structure could be more stable in small buildings.
4.2.2 Combination of Chinese and Western: two types of trusses in medium-span buildings
The combination of Chinese and Western referred to the situation where the Chuandou style truss and Western truss appeared in the same building, which was another way of using Western structural principles to improve local timber truss. It was commonly seen in medium-span buildings, where the Chuandou style trusses were used at partitions, and Western trusses were used indoors to create column-free indoor spaces. For example, in the reading room and large classrooms of the Women’s Normal College, which required column-free spaces, Western truss was used, while other parts still used the Chuandou style truss.
In the classroom, the interior of the large classroom used Western trusses with a span of about 5.5 m to create a column-free indoor space. The rest of the parts used 9-purlin Chuandou style trusses, all with 4 columns landed at the partitions. The outer corridor used diagonal braces to support the protruding eaves. The two Western trusses in the large classroom had their web members connected by a horizontal brace, and the rest of the Chuandou style trusses were connected by two sets of scissors braces (Fig. 11).
The interior of library used Western trusses with a span of about 4.8 m to create a column-free indoor space. The gable wall used a 7-purlin Chuandou style truss with column cutting, with 3 columns landed and a span of about 2.4 m between columns. The outer corridor used the method of adding new column to support a one-step beam (1.2 m). In addition to purlins, trusses were connected by two horizontal braces (Fig. 12).
By using Western trusses to cover medium-span column-free indoor spaces and the Chuandou style trusses to cover small spaces, both types of space requirements were met. The strengthening of the connections between trusses helped to enhance the overall structure.
4.2.3 Comprehensive optimization: bamboo and timber trusses in large-span buildings
Comprehensive optimization referred to the improvement of truss form, material strength, and roof load to achieve larger span indoor spaces. This exploration was the result of the improvement of local crafts based on material and structural mechanics. The truss form of this type of was mainly Western, the main structural material was bamboo, and the roof load was reduced by replacing Chinese grey tiles with thatched roofs.
Bamboo had better mechanical properties in tensile strength, compression resistance, shear resistance, and bending resistance than timber (about twice that of timber), and also had the advantages of short growth cycle and low price. However, bamboo’s performance was not as stable as timber, it was easy to deform when damp, prone to cracking and rotting, and difficult to repair. Therefore, bamboo was mostly used in temporary buildings as structural material. The actual service life of the Jiangjin campus was about 5 years, which was suitable for exploring the bamboo structures.
At first, Kitai used bamboo structure in primary school classrooms to explore its application in medium-span buildings. The trusses at the inner partitions of this building combined the dense slender columns of the Chuandou style with the Western trusses. The columns were bound and reinforced with diagonal braces, and all 5 columns were landed, with a span of 1.4 m between each other. When encountering a door at the inner partition, the middle two diagonal braces were removed. The trusses inside the classroom cancelled the middle 3 vertical columns and 2 diagonal braces to create a 6.4-m column-free indoor space. The trusses at the gable wall cancelled the upper diagonal braces to open high windows for ventilation. The eaves were supported by a combination of horizontal braces, diagonal braces, and roof truss components. Trusses in the building was connected by two sets of scissors braces and horizontal braces to form an overall structure (Fig. 13).
In the design of the auditorium and dining hall, Kitai further enlarged the indoor space. The building was about 26 m long and 12 m wide. In auditorium mode, it could accommodate 550 people, and in dining hall mode, it could accommodate 368 people. Its indoor trusses were composed of timber columns, bamboo diagonal columns, and triangular bamboo trusses, forming a trapezoidal indoor space with a span of about 12 m. The trusses at the gable wall combined the dense slender columns of the Chuandou style truss with the characteristics of Western bowstring truss, with 6 columns landed (the middle column did not land to facilitate door opening), and the columns were reinforced with diagonal braces. Adjacent trusses were connected by 5 cross braces and 2 scissors braces indoors. Scissors braces were set on the upper part of the outer wall between adjacent trusses, while was set every other truss on the lower part of the outer wall. The roof used bamboo rafters and thatched roofs to reduce the load, and the walls were covered with bamboo fences (Fig. 14).
By using bamboo trusses and reducing the roof load, the structural span was greatly increased, the dense diagonal braces and horizontal braces further enhanced the overall structure. It could be seen that this bamboo and timber truss system had achieved multiple goals of cost-effectiveness, structural stability, and large span.
4.3 Solid structure and spacious interior of air-raid shelters
Air-raid shelter was protective building constructed to withstand bomb attacks; it was originated in Europe during World War I. China’s air-raid shelter knowledge was transplanted from Europe. In 1928, shortly after its establishment, the Nanjing Nationalist Government sent officials to Europe to investigate air-raid defense construction. The Mukden Incident in 1931 and the Battle of Shanghai in 1932 heightened the awareness of the urgency of air-raid defense across the society. Subsequently, under the government’s leadership, the establishment of air-raid defense school in 1933 and the formation of military air-raid defense department in 1934 marked the beginning of the systematic development of China’s air-raid engineering. By the end of 1937, just before the Nationalist Government relocated to Chongqing, several books on air-raid defense architecture had been published in China’s coastal regions, and a small number of air-raid defense projects had been completed (
Yu and Li, 2017). The pre-war air-raid construction knowledge research and engineering practice mainly took place in the lower Yangtze River areas of Nanjing, Shanghai, and Hangzhou, as well as Guangzhou in South China. During the war, air-raid institutions and personnel passed through Hankou and finally settled in Chongqing, achieving large-scale construction practice of air-raid shelters in wartime Chongqing. From the principle of air-raid engineering, good air-raid effect required a solid building structure. The more solid the structure, the thicker the components such as the roof and walls, and the narrower the building space. This contradiction was not prominent in small air-raid facilities, but in large air-raid project, how to use relatively thin wall and roof to achieve structural solidness while ensuring a certain degree of spaciousness was the key issue that needs to be solved. Kitai met the structural requirements of small air-raid shelters by contracting the span in its design, achieving cost-effective and practical purposes. In the design of large air-raid shelters, it closely tracked European cutting-edge results and successfully balanced the solidness and spaciousness of air-raid shelters through reinforced steel placement.
4.3.1 Span contraction: cost-effective and practical small air-raid shelters
Span contraction referred to the practice of reducing the span of air-raid building to achieve a solid structure with less and cheaper materials, which inevitably led to cramped indoor space, so it was only suitable for small air-raid shelters. Since the number of users was small and the protection level was not high, convenience and economy were the main demands. Therefore, it was a natural choice to build small protective spaces with relatively cheap materials.
In 1940, Kitai designed the air-raid shelter for the International Broadcasting Station of the Central Broadcasting Administration (1940), which was built against the mountain (
Kitai, 1940). The front part was an office, using rammed earth walls and timber trusses, and the rear part was the air-raid shelter hidden in the mountain. The shelter was divided into two parts. The wider part was connected to the office, with a span of about 2.1 m and a height of about 3.2 m. The wall was built of stone, with the thickest part about 1.8 m, gradually tapered from bottom to top to 0.9 m, and the roof used a 30-cm-thick cement slab. Extending deeper into the mountain was the narrower part, using a stone arch structure, with a span of only 90 cm and a height of about 2.7 m, with a height-to-width ratio of 3/1, and the top was a 90-cm-thick stone arch roof. The air-raid shelter was covered with three layers of protection, from inside to outside were 90-cm-thick soil, 90-cm-thick sand, and 60-cm-thick soil respectively (Fig. 15). According to the standards for air-raid shelter covering thickness derived from bomb penetration depth, destruction thickness, and power radius in “
Air-Raid Architecture” (
Zheng, 1937), this type of roof could roughly resist small bombs, as well as napalm bombs and Koffing gas bombs.
The close connection with the front building ensured that staff could take shelter in time in emergencies. The narrow span reduced the use of materials. Although the project met the requirements of convenience, economy, and basic air-raid protection, the accompanying space was extremely cramped. Fortunately, this project was only for the radio station staff, with a small number of people.
4.3.2 Reinforcement optimization: comprehensive balance of large air-raid shelters
Large air-raid facility needed to accommodate a large number of people and important materials, requiring a higher protection level and sufficient spacious interior space. The contradiction between solid structure and spacious space was very prominent. The first issue to solve this contradiction was the choice of structural materials. To withstand a one-ton heavy bomb, the safe thickness of soil was 20 m, rock layer was 4—5 m, ordinary concrete was 3 m, and reinforced concrete was 2 m (Table 1). It could be seen that reinforced concrete was the best choice for large air-raid shelters. The second issue was the balance between structure and space. If the span was too large, it would lead to too thick structure and high cost; on the contrary, if the structure was weak and economical, it would lead to too narrow space.
In the combined air-raid shelter designed by Kitai for the Bank of Communications and the Farmers’ Bank (1939), which could accommodate 550 people and important items, reinforced concrete structure was selected (
Kitai, 1937). In the sketch design stage (June 1939), the air-raid shelter was a reinforced concrete arch structure buried 27 m underground. Its main wall thickness was 60 cm, the net width was 6.7 m, the net height was about 4 m, and the length was 93 m. The civil defense part had a 30-cm-thick reinforced concrete cavity inside the main body, with a net width of 3.7 m and a net height of 2.7 m. This meant that the structural layer of the civil defense part reached a thickness of 90 cm. However, in the blueprint design of the following month (July 1939), the double-layer cavity structure was canceled, the span was reduced, and the air-raid shelter became a single-layer reinforced concrete cavity buried 30 m underground. Its net width adopted the 3.7 m of the civil defense part in the sketch, the net height was increased to 4.9 m, making the space more spacious, and the structural thickness was reduced to 46 cm (Figs. 16 and 17).
There were three reasons for the reduction of structural thickness in the blueprint. Firstly, the burial depth was deep enough. The mountain depth of 27—30 m was sufficient to withstand heavy bomb attacks, so it was no need for a double-layer cavity structure. Secondly, the span was shortened. With the cancellation of the double-layer cavity, the net width of the shelter was reduced by 45%, which reduced the demand for structural thickness. Finally, the optimization of steel reinforcement layout. The sketch did not mention the layout of steel reinforcement, but this point was particularly emphasized in the blueprint. The blueprint showed that the reinforced concrete structure used a double-layer steel mesh, dividing each part into steel grids with unequal side lengths of 18—36 cm. The two layers of mesh were connected by steel bars to form a cross-grid, thereby enhancing the structural performance and reducing the structural thickness.
In summary, the blueprint design of this large air-raid shelter reflected the dual optimization of structure and space. While ensuring structural safety, the design improved the efficiency and comfort of space use. The increase in space use efficiency led to a reduction in structural span, and the optimization of reinforcement layout further reduced the structural thickness, thereby greatly saving cement usage (although increasing steel usage). Notably, this type of reinforcement layout was first seen in the air-raid regulations of France and Switzerland, and was not mentioned in the pre-war Chinese air-raid publications until it was included in “
Air-Raid Architecture” (
Lu, 1942). It meant that the air-raid engineering in wartime Chongqing, while applying the knowledge and experience of the middle and lower reaches of the Yangtze River, closely tracked the international cutting-edge, alleviated the contradiction between solid structure and spacious space in local practice, and in turn promoted the accumulation of technical knowledge.
4.4 The technical development patterns in wartime chongqing
The above three construction types in wartime Chongqing all underwent varying degrees of change and represented typical technical development patterns. The first pattern was the combination of transplantation and grafting, mainly reflected in the construction of brick-timber “pseudo-Western buildings”. Initially transplanted from the West in the 1840s, brick-timber structure underwent minor adaptive modifications in the lower Yangtze River region before 1937. However, in wartime Chongqing, it experienced fundamental localization. To save bricks, wartime Chongqing developed the “pseudo-Western building” in the brick-timber system. The common “brick wall - timber truss” structure was modified into “brick column - timber truss,” and the brick-based enclosure structure was replaced by local crafts such as plastered bamboo mat wall. Through structural reduction and enclosure grafting, it adapted to the shortage of bricks in the wartime Chongqing. At the same time, “pseudo-Western buildings” used material simulation and specific styles to minimize the sense of simplicity, achieving a balance between cheap construction and decent appearance.
The second was the “grafting‒integration” pattern, mainly reflected in the construction of single-story timber (bamboo) structures. Traditional Chinese timber structures, which had gradually declined under the impact of Western brick-timber structure, regained popularity in remote suburbs due to their cheap and easy-to-build characteristics during the war. To enhance its structural performance and obtain larger column-free interior spaces, architects educated in the West improved the local craftsmen’s Chuandou-style timber structure, integrating the mechanical properties of bamboo and the stability of diagonal components to form hybrid trusses capable of spanning larger areas (
Zhu et al., 2023). This represented an optimized method that achieved both structural stability and larger spans.
The third was the “transplantation‒tracking” pattern, mainly reflected in the construction of reinforced concrete air-raid shelters. Reinforced concrete air-raid shelters, transplanted from Europe in the 1930s (Yu and Li, 2023), gained prominence in wartime Chongqing after a brief period of dissemination in the middle and lower reaches of the Yangtze River. In the practice of air-raid engineering, the architects continuously tracked international advancements, designing shelters that balanced structural solidness with spacious interiors. This, in turn, fostered the development of air-raid knowledge in China, achieving a synchronized accumulation of knowledge and practice.
The above three construction types and their development patterns presented a modernization path whose driving mechanism mainly came from the interaction between regions within China, rather than external Western impact. This indicated that by the wartime period, China’s construction techniques had already developed the ability to sustain and evolve on its own. Architects represented by Kitai were the key forces in shaping this endogenous technical development.
5 Conclusion
5.1 Theoretical contributions
The narrative of China’s architectural modernization has long been dominated by a coastal perspective. However, this paper, through its study of the three construction types in wartime Chongqing led by Kitai, provides an inland perspective and a unique case for China’s architectural modernization, revealing an alternative path to modernization.
Modern Chongqing experienced a shift from the periphery to the center. Before the war, Shanghai and Nanjing in the lower Yangtze River region became the national economic, political, and cultural centers due to their prosperous economy and capital status, and their influence continued to spread inland through Hankou in the middle reaches. The upstream Chongqing was long politically unstable and economically backward, on the periphery of modernization. However, with the outbreak of the war, the middle and lower reaches of the Yangtze River were successively occupied, and a large number of educational and industrial departments moved inland with the Nationalist Government, and Chongqing’s status rapidly rose to become the wartime military, political, economic, and cultural center. If the prosperity of the pre-war lower Yangtze River cities was due to the accumulation of nearly a century of semi-colonial economy, then the wartime prosperity of Chongqing was the result of the forced inland migration of human and material resources from the middle and lower reaches under the “trading space for time” war policy, presenting a characteristic of short-term outbreak.
Practitioners like Kitai from the lower Yangtze River region demonstrated the mutual adaptation between the advanced knowledge and experience of the coastal areas and the underdeveloped production conditions of the inland regions. Through the flexible application of various structural systems, including brick-timber, timber (bamboo), and reinforced concrete, as well as related internal and external construction measures, they developed unique construction strategies specific to wartime Chongqing. In this process, imported techniques were transplanted, and local elements were preserved. The interaction and integration of these two aspects generated a new local technical tradition, revealing an alternative path to modernization. This path, based on the interaction between the upper and lower reaches of the Yangtze River, integrating local resources, expanded the construction strategies under wartime circumstances. It demonstrated the adjustment and innovation of Chinese construction techniques under specific historical conditions and also reflected the endogenous characteristics of the modernization development of Chinese architecture.
5.2 Limitations and future research directions
The construction techniques of wartime Chongqing was an important part of modern Chinese architectural heritage, reflecting the architectural development status and phased results of the inland areas during the war.
Regrettably, the vast majority of Kitai’s wartime architectural works in Chongqing had been demolished. Surviving structures had predominantly been rebuilt using modern techniques to replicate original appearances. Future conservation efforts for Chongqing’s wartime architectural heritage must prioritize the specific preservation of these technical characteristics. They constitute not only material historical evidence but also a testament to the modernization of Chinese construction technology.
The developmental trajectory of wartime Chongqing’s construction techniques offers key insights for future research on architectural production in developing regions. The near-30-year globalization period following the Cold War accelerated the transregional flow of techniques. Fundamental challenges for architectural production in these regions include adapting imported techniques to local production conditions and enabling indigenous techniques to meet contemporary demands. Under conditions of resource scarcity and environmental constraint, wartime Chongqing successfully sustained local architectural production by integrating imported techniques with local craft traditions. This practice extended beyond simple technical layering to create a culturally distinctive, composite technical system. This experience vividly illustrates Appadurai’s concept of the “technoscape”: transregionally mobile technical elements, reinterpreted by local practitioners, avoid the homogenizing tendencies of technological universalism while overcoming the limitations of traditional nostalgia (
Appadurai 1996). Consequently, the technical development model of wartime Chongqing retains significant relevance for contemporary architectural production in developing regions.
2095-2635/2025 The Authors. Publishing services by Elsevier B.V. on behalf of KeAi Communications Co. Ltd.
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