The design practice of the roof structure of the old library of early architecture in Wuhan University

ABSTRACT The Old Library of Wuhan University is located at the core of the early architectural complex of Wuhan University. The main structure of the octagonal hill-style roof adopts the steel-truss bearing structure, which creates a traditional form of Chinese roof that stretches like bird wings. It is a standard for the integration of modern structural technology and regional culture. This paper analyzes the application of steel truss in the roof of Early Architecture of Wuhan University. Through the in-depth interpretation of the current authentic historical materials, for example, the roof structure drawings of the Old Library, this paper explores the practice of designers to create the roof curve form of Chinese traditional buildings, and expounds the significance and historical value of the roof structure design of the Old Library to the modernization of Chinese traditional buildings in the modern era.


Introduction
The early architectural complex of Wuhan University was built from 1928 to 1937. It was planned and designed by the American architect Kales. 1 It is an important and practical exploration in the process of modern universities' campus planning and modernization of traditional buildings in China. There are 15 buildings and 26 blocks in the early stage, with a building area of about 50,000 m 2 . It covers an area of about 2 km 2 (more than 3,000mu). In 2001, the Early Architecture of Wuhan University was listed as the fifth batch of national key cultural relics' protection units. The Old Library of Wuhan University (Figure 1), built in 1935, is located on the top of the lion mountain, adjacent to the former Boys' Dormitory in the south, the former Law School of Wuhan University in the west and the former Liberal Arts School of Wuhan University in the east. The Old Library of Wuhan University is an important part of the early architectural complex of Wuhan University. It is the landmark building and spiritual symbol of Wuhan University. It is in the shape of "I" on the plane, which is composed of the main building of the center and four auxiliary buildings on the front and rear wings. It is designed according to the scale of 1,500 2 students (Zhongqing). Its (useable) floor area reaches 6,234 3 square meters (Luohua and Sheng 2005).The building structure adopts new reinforced concrete frame structure and the steel truss structure, and the roof of the main building adopts the higher-grade octagonal hill style 4 because of its core position, with a structural span of 18 meters. The roof of the annex building is of single eaves and mountain style, with the green glazed tiles and a seven-ring tripod on it. The architectural image is powerful and solemn; the design idea is advanced, which is the pioneer of Chinese Universities' campus architecture. It is the essence of the combination of Chinese and western historical buildings on the campus of Wuhan University. Now, its function has been transformed into the History Museum of Wuhan University.
Since the official completion of the Old Library building in January 1935, it has been repaired and rectified for many times due to human-made function upgrading and natural disasters. In this process, however, the detailed original drawings and data of the Old Library have not been sorted out. Especially, the detailed drawings of the roof can not be found. In 2015, we carried out the detailed mapping of the Old Library, and the architectural drawings of the Old Library kept in the archives of Wuhan University and the early architectural structure drawings of Wuhan University donated by Octave Levenspiel 5 in 2005 were comprehensively scanned, sorted and read. Through the drawings and documents, We can gain deeper insights into the original roof structure design of the old library as well as fully explain the engineers' understanding and integration of the modern construction technologies and the characteristics of Chinese traditional roofs. The engineers' successful combination of the modern steel-truss structure technologies and the traditional roof forms featuring regional culture is of great significance and historical value to the modernization of Chinese modern traditional architecture.

Steel truss of the early building roofs in Wuhan University
The roofs of the early buildings of Wuhan University are novel, unique, rich and diverse. They are the most distinctive and historical part of the campus landscape of Wuhan University. There are many forms, such as Chinese traditional Xieshan roof, four-slope glass roof, dome and so on. In the construction process, the designer adopts the combination of the new structural system and the Chinese traditional building roof, which reflects the interaction between Chinese and western modern architectural technologies and cultural cognition.
Steel truss is a widely used structural form in the roof structure of the early buildings of Wuhan University. The steel structure technology was introduced into modern China from the West. At first, its development was mainly concentrated in coastal cities. Around 1930, the steeltruss structure system was introduced into the field of industrial architecture as a long-span building technology, and then popularized to civil architecture. For example, for the Capital Cinema built in 1936, the roof steeltruss structure has a span of 24 meters. For the Eurasian Airlines Longhua hangar built in Shanghai in the same year, architect Xi Fuquan chose the trapezoidal steel truss as the large-span space roof structure of the hangar, with a span of 32 meters, setting the largest record of steel truss span in modern China (Fuquan 1937) 6 The rapid development of the steel-truss technology in modern Chinese architecture has laid a technical and material foundation for the application of steel truss technology in the early buildings of Wuhan University. The steel-truss technology is used in a series of buildings, such as the roof steel truss of the Old Library of Wuhan University, the glass roof carried by the steel truss of the Institute of Technology (Figure 2), the steel-truss roof of Central China Institute of Hydraulic Engineering ( Figure 3) and the triangular arch roof steel truss of Songqing Gymnasium (Figure 4, Table 1).
The earliest application of the steel-truss system in the early buildings of Wuhan University was the Old Library, which was built in October 1933 and completed in September 1935. It was built by Cathay Land Co., Ltd. 7 Engineers Shanghai. The span of the main structure has reached 18 meters. The main structure of the reading room's ceiling structure uses the parallel chord steeltruss system to cover the top floor, and the roof truss uses the composite steel-truss system to bear the roof structure. Its complex form and structure system are very rare in the modern campus libraries. The construction of the Institute of technology began in November 1934 and was completed in January 1936. Its atrium adopts steel truss to bear the glass roof, and the roof combined with glass, steel truss and glazed tile with traditional architectural characteristics is bold and novel, which is reflected incisively and vividly by the combination of Chinese and western techniques. Chinachem Real Estate Co., Ltd. is also responsible for the structural design of the Institute of technology, with a structural span of 15.54 meters. The construction of the Hydraulic Institute began in August 1935 and was completed in April 1936. The roof truss adopts the triangular steel truss, which is composed of 16 steel trusses. The roof is arranged with triple eaves and high windows with the three-hinged arch radian. A. Levenspiel, Engineer Shanghai is responsible for the structural design. It is the exploration of the truss structure system from industrial plants to civil buildings. The design scheme has undergone three adjustments (Qiaohui et al. 2020) 8 The span of the actually completed building structure reached 21.8 m. The construction of Songqing Gymnasium began in October 1935 and was completed in July 1936. The roof truss structure of Songqing Gymnasium uses six triangular arch steel trusses, and Shanghai Chinachem Real Estate Co., Ltd. is responsible for the structural design, with a structural span of 21.9 m.

Structural design drawings of the old library
Among the early buildings of Wuhan University that applied steel truss, the Old Library was the first. Its building structure was completed by Cathay Land Co,LTD. Engineers Shanghai and the reviewer of structural engineering was Polish engineer Arabhan Levinsbil. Levinsbil graduated from East London College in electrical engineering. In 1917, he came to Hong Kong, China to engage in construction engineering and participated in the design of some hotels and bridges. In 1919, he came to Shanghai as a chief construction engineer and worked for the Bank of Amway, 9 a British enterprise and Cathay Land Co.,LTD. Engineers Shanghai. He participated in the Chinachem Apartments projects, 10 etc. Cathay Land Co.,   In the 1930s, British Amway foreign bank officially transferred the company to new Sassoon foreign bank in 1935 due to poor management. 10 In 1926, Chinachem real estate company invested in the construction of two ordinary apartments. In 1928, another 3.3 million yuan was invested to build Chinachem apartment, which is now the North Building of Jinjiang hotel. Chinachem apartment adopts reinforced concrete frame structure, with a total of 14 floors, a height of 57 meters and a construction area of 21,202 square meters. The "one" shape plane is not segmented, and the whole body is up and down. It adopts brown face bricks, white mortar lines, stone window frames and vertical lines, striving to highlight the towering effect. There are 7 elevators up and down the stairs. The first to tenth floors are guest rooms, with separate cooling, heating and sanitary equipment. The top floor is a kitchen with good lighting and ventilation, which was prominent in high-rise buildings in Shanghai at that time. It is an excellent historical building in Shanghai.
LTD. Engineers Shanghai contracted the structural design of the second phase of the early buildings of Wuhan University, such as Gymnasium, School of Engineering, School of Law, and Library. After the outbreak of the Anti-Japanese war in 1937, the early buildings of Wuhan University were occupied by the Japanese army, and the architectural drawings collected were lost due to the relocation of the University. In 2005 OTF Levinsbil, the son of Arabhan Levinsbil, the academician of the American Academy of Engineering, donated more than 150 early architectural engineering drawings left by his father to Wuhan University. These drawings went through the baptism of war with Levinsbil, accompanying him for the second half of his life, and then collected by his son. From the fully-preserved drawings, we can see that Levinsbil attaches importance to and cherishes these drawings. These drawings are the design drawings of five buildings of Wuhan University's School of Technology, School of Science, Old Library, School of Law and Songqing Gymnasium. They were identified as the national first-class cultural relics by Hubei Provincial Cultural Relics Management Department in 2014 (Yinqin 2020). They were now stored in the archives of Wuhan University.
In these drawing files, 33 architectural structure design drawings of the Old Library are drawn on three types of drawings, including blueprints, kraft paper drawings and sketches. Among them, 21 structural drawings of roof steel truss of the main structure are shown on three kinds of drawings (7 blueprints, kraft paper drawings and sketches respectively). The roof steel-truss structure system in the main structure drawing of Wuhan University Library is drawn in detail. There are 12 drawings of foundation structure and pier column (10 sulfuric acid paper drawings and 2 sketches). In the main structure drawing of the Old Library, only the drawing tab of the roof steel truss structure drawing is marked with the name of Shanghai Sinochem Real Estate Co., Ltd., Draftsman H.S.WANG or L. C.CHEN. 11 The names of relevant drawing reviewers are not filled in the signatures of other infrastructure drawings. Through consulting the drawings, we know that Levinsbil participated in the architectural structure design of the Old Library as the reviewer of the structural drawings of Chinachem Real Estate Co., Ltd. (Figures 5 and 6) 12 These drawings have high quality. They are all European drawings marked in English, and their drawing scales are different. The main plane drawing scale is 1/ 8" = 1'-0', 13 which is about 1:100, and the local detail drawings are mostly 1:50 and 1:25. The drawing time is concentrated between September 1933 and December 1934 ( Table 2). The dimensions of the drawing are very detailed (Figure 7); the drawing scale (Figure 8), component size ( Figure 9) and spacing length are unified in English units, and the drawing quality is very different from that of modern construction drawings. It is like drawing on the sulfuric acid paper with pencils, and  The draftsman of the structural drawings of the old library, due to the limited historical data related to these engineers, the specific origin needs to be further studied. 12 The study on the signature of the early architectural drawings designed by Levins bill found that its signature was the same as that of the reviewer of the structural drawings of the old library, which can infer Levins Bill's identity and role in the library structural design project. 13 The drawing scale on the drawing is marked 1/8'' = 1''-0'', which is about 1:100 now. then copying it on the blueprint and the kraft paper, so as to save for a longer time.
The historical materials of the structural drawings of modern architecture are of great importance for the study of modern architectural heritage .These case studies are of pioneering significance as the introduction of western advanced structural technology, the establishment and development of modern "architectural industrial system", and the integration of modern structural technologies and regional culture (Tian 2017) 14 These precious original structural drawings of the Old Library intuitively express the main structure and roof truss construction practices of Wuhan University Library. Through careful study of the drawings, we can clearly analyze how the foreign structural designers solve the problem of "like" the appearance form of Chinese architectural roof, and understand their practical exploration in the combination of modern architectural technologies and the form of the Chinese traditional architectural roof. These historical maps provide a large number of credible and important historical materials for the study of the construction of early buildings in Wuhan University. Through these structural drawing files, we can see the innovative practice and exploration of the designers in the structural design of the Old Library of Wuhan University, which is the epitome of architectural development in this historical period. These drawings and archives are full of valuable cultural abundance. They are not only a file about specific buildings, but also a true record of the activities of architects and engineers in modern China.

Structural design of a flat concave roof
The broad and protruding concave curved roof of Chinese architecture is one of the biggest characteristics of Chinese traditional architecture, which has the most profound visual impact on westerners. For the roofs of Chinese traditional buildings, many scholars have done special research on the Chinese wooden structures. For example, Liang Sicheng's research on the Ying-zao Fa-shi and the engineering practice of the Ministry of works of the Qing Dynasty (Ying-zao Fa-shi 2001) is more inclined to the artistic tendency and the  qualitative analysis on the style of the wooden structure. (Yunsu 2005) interpreted the Chinese traditional wooden structure from the perspective of design thinking, which serves as reference for exploring the standards and practices of Chinese traditional architecture. (Yan 2011) 15 comprehensively combed the ideas of foreign scholars about the curved roofs in China over the past century, and expounded that the main concern of the scholars is the cognition of the Chinesestyle curved roofs. (Haiqing 2002)conducted relatively mature research 16 on the development of the modern architectural technologies, paid attention to the progress of modern technological history, and summarized how to imitate the roof structure design characterized by curved roofs of Chinese traditional architecture in appearance . When western architects engaged in modern campus architectural design in China, in order to comply with the revival of Chinese tradition, they built new buildings in this aspect. As one of the most characteristic parts of Chinese traditional architecture, the roof is not only an important problem to be solved, but also a difficulty of architectural structure. This has also experienced the evolution of form selection, and the overall trend is from the localization of local tradition to the standardization of official architecture. Church architects engaged in church work in China follow the principle of object-oriented and wide dissemination, and follow the "territorial principle of taking the parish as the object, that is, carrying out the corresponding design based on local architecture" (Changxin 2011)  Most of the roof truss structures of these buildings use the light roof truss system and the wood frame structure, and the roof curve method is not unified, which is the exploration of Chinese large roof by early western architects. The Old Library of Wuhan University is located at the commanding height of the campus. The roof of the main building is gabled octagonal hip style with glazed tiles (Figure 10). These practices indicate the core position of the Old Library in the campus complex of Wuhan University. The roof structure of Wuhan University Library is similar to those roof structures designed by western architects, and it is innovative. The roof truss load-bearing structure system of the Old Library adopts the steel truss structure. The roof is poured with concrete, and the cornices, rafters, cornice heads, bucket arches, exotic animals and other decorations are prefabricated with concrete for installation.  The roof curve is controlled by the steel truss curved rod, which is novel. The roof slope is closer to that of the buildings in the Qing Dynasty, and the overall building is solemn and majestic (Figure 11). These practices completely replace the traditional loadbearing form and roof practice of roof structure by columns, beams, bucket arches and roof trusses, and the curved-roof practice embodies the idea of "lifting and folding", which is regarded as beneficial exploration and progress in new structure, new materials and new technologies in the expression of traditional architectural form.

New roof truss structure system
The roof of the main building of the Old Library adopts the Chinese traditional gabled octagonal hip roof with a high level of Chinese traditional architecture. Its structural form is relatively complicated, which is a challenge for foreign engineers to support the complex traditional roof form with a new structural system. The cases of Chinese concave curved roofs designed and built earlier by western architects mostly use the wood trusses. For example, the trapezoidal wood truss structure is used in the roof truss of the sage chapel designed by Perkins in 1917, and the combination of the local triangular trusses and the light roof truss system is used in the West Science Building of Jinling University in 1924 (Jiayao 2019) 19 In terms of the selection of structural materials used for the Old Library, the structural engineers use new steel and concrete materials, with high strength and light weight. It has the characteristics of good overall rigidity, strong deformation capacity, high concrete strength, easy plasticity and simple production process. According to the different stress characteristics and spatial characteristics of the building, different main structure systems are selected, which gets rid of the traditional Chinese wooden structure form and reflects the progress of modern structure technologies.
The reading space in the hall on the first floor of the main building of the Old Library has a span of 18 meters and a net height of 9.6 meters. Therefore, the main structure and roof structure of the whole building are the most challenging. In order to ensure the integrity of the space, the structural designer uses the reinforced concrete frame structure for the main body, and the steel-truss structure is adopted for the ceiling and roof truss of the hall (Figure 12). In order to create a light and rich roof, the structural engineer adopts the reinforced concrete structure and uses steel truss as the main load-bearing member to support the roof. The steel roof truss is imported and customized in Shanghai, which is spliced with rivets as well as lifted and assembled with electric winch (Figure 13). These new structural systems create a wide indoor space of the Old Library, realize the application of modern architectural technologies combined with western technologies, and reflect the integration of Chinese and western architectural forms. They are novel practices in the process of modernization of Chinese traditional architectural forms.

Roof construction method
By studying the historical drawings, we can see that the large roof and its bottom beam pillar structure of the Old Library adopt the form of integral cast-in-situ. According to the literature records, the construction process of the the Old Library of Wuhan University is: the wall and cement reinforced column to the roof truss beam, the installation of the roof truss, the laying of iron reinforcement cement on the roof truss, and the capping of green glazed tiles. 20 It can be seen from the drawing that the specific method is used to install the steel roof truss structure after pouring the reinforced concrete column  to the roof truss beam and placing it on the beam, 21 and then the reinforcement of the roof's concrete slab structure is arranged through the support of the steel-truss structure. The horizontal reinforcement of roof concrete slab and longitudinal reinforcement of beam structure can be clearly seen in the drawing. 22 They are connected together to facilitate the integral cast-in-place of roof and beam structure.
At the same time, in order to reduce the load of the roof structure and create a gentle concave image, the structural designer adjusted the thickness of the roof reinforced concrete slab. From the drawings, we can see that the thickness of the roof concrete slab structure changed from the roof 3" slab (70 mm) to the eaves connecting the main load-bearing structure 6½" (165 mm) (Figure 14). These practices have important meanings. First, they ensure the integrity of roof structure, steel roof truss structure and main loadbearing column structure, reduce the weight of roof structure, and make the whole roof structure more stable and firm. Second, the construction process is simplified; the construction speed is accelerated; the construction cost is reduced ( Figure 15). Third, the roof slope is more gentle, and an artistic style of stretching like bird wings flying around is created.

Adding curved and straight bars
In the whole roof structure system, the curve design of roof is the most difficult part for structural engineers. The steel truss structure of the roof of the Old Library is in a well shape on the plane, and there are two through main trusses in the vertical direction. In addition to the main truss, there are five forms of auxiliary trusses in the space. The overall steel roof truss adopts the form of combined triangular steel truss, which is composed of five forms of trusses: Truss A, Truss B, Truss C, Truss D and Truss E (Figure 16). Among them, Truss A is a triangular truss system supporting the slope of the main roof, with four horizontal rows and two vertical middle rows in the whole roof structure. Truss B is mainly arranged in two vertical rows to connect the parallel chord truss of the truss system. Truss C and Truss D are truss systems supporting the roof cornices, and Truss D is arranged along four diagonal corners, a total of four. Truss C is a frame supporting the warping of octagonal Xieshan roof. It is symmetrically arranged along the diagonal of four corners, with a total of eight. Truss E is a common structure of Fink-typed 23 steel truss supporting the top of roof truss, which is arranged vertically in the middle two rows. Truss A, Truss C and Truss D all create a roof curve while supporting the concrete roof by adding curved and linear members. Among these members, member 1, member 2 and member 3 are straight lines, and member 4 is a gentle curve (Figure 17), which provides technical support for the practice and exploration of the traditional Chinese roof form in the Old Library. In the 1920s and 1930s, when western architects completed the curve style of Chinese traditional roof, they mostly adjusted the height of the wooden column of the roof truss to form multiple broken lines, and added more linear rods to obtain the curve appearance of the roof. Not only linear rods but also curved rods were added to the roof truss of the Old Library, which made the curve of the roof more gentle and natural. It reflects the technical maturity of the integration of modern structure and traditional form.

Roof slope and curve control
"Today's house lifting system is divided into four parts: one point is lifted from the back of the eaves to the back of the ridge. Although there is a slight increase in halls and corridor houses, it is mostly based on one point in four, which is consistent with the classics." 24 The roof slope of early buildings with mature development of Chinese ancient architecture was small and gradually increased later. For example, the ratio of the roof height of the East Hall of Foguang Temple to the Square Center distance between the front and rear eaves was 1/4. Most buildings in the Song, Liao, Jin and Yuan Dynasties were 1/4-1/3, and it was stipulated to be 1/3 in the Qing Dynasty. 25 Compared with the steep roof slope of foreign architects in early modern times, the roof slope of the Old Library is closer to the roof slope proportion of traditional Chinese buildings. The roof truss height H is about 21ʹ0" and the Square Center distance between the front and rear eaves B is about 58ʹ0", which is about 1/3, and the slope is closer to the proportion specified in the Qing Dynasty ( Figure 18). For the roof curve of the Old Library, the curve and linear members (Table 3) are added to the triangular roof steel truss structure to form a gentle curve  at the lower 2/5 part of the steel truss structure, and then the roof is poured with concrete to form a sloping roof. The curvature of the curved members of Truss A and Truss D is the same. 26 Truss C is divided into 7 parts horizontally, and the right roof curve is formed by 8 different heights (Figure 19). Truss D It is divided into 11 parts horizontally, forming a relaxed and narrow wing angle curve from 12 different heights.This curve-control method is not common in the recorded modern Chinese campus buildings designed by foreign architects. This is an innovative method of structural designers, which makes the Old Library a model of the integration of China and the west in the development of modern Chinese architectural history.

Conclusion
The roof with novel and diverse forms is one of the most distinctive part in the early building complex of Wuhan University. The designer has built a unique, novel, solid and beautiful campus building complex by integrating advanced design concepts, new materials, new structures and new technologies with traditional building forms. The application of the steel truss structure in the roof of early buildings of Wuhan University is successful. The Old Library is the earliest case of the application of steel truss in the early building complex of Wuhan University. According to the characteristics of new materials, the structural engineers adopted the long-span steel-truss structure system and the related construction technologies by casting the roof, steel truss and main beam structure as a whole. These practices such as adding straight and curved bars, carrying out the innovative curve control and so on make the roof slope of the Old Library closer to the Qing-style roof of traditional Chinese buildings, creating a gentle and beautiful roof curve. These innovative structural design practices fit the traditional Chinese roof form; also, the roof structure of the whole building is very strong. This makes the Old Library of Wuhan University a model of the successful combination of modern structural technologies and regional culture in modern campus architecture, fully reflects the integration of eastern and western architectural culture and technologies, and is an innovative and practical exploration of modern architects, engineers and craftsmen.

Disclosure statement
No potential conflict of interest was reported by the author(s).

Funding
This work was supported by the National Natural Science Foundation of China [51808408].

Notes on contributors
Akbar Askar is specialised in the history and theory of architecture, focusing on architectural and construction history in Modern China (19th and early 20th centuries). He is postgraduate students of Qiaohui Tong in School of Urban Design at Wuhan University.
Qiaohui Tong is a doctoral supervisor in School of Urban Design at Wuhan University. She research focuses on the history and theory of architecture, Architectural Cultural Heritage Protection and Development and Protection and Renewal of Urban Context.
Qiguo Li is a Master's supervisor at the School of Architecture and Art, Hefei University of Technology. He research focuses on the history and theory of architecture, Architectural Cultural Heritage Protection, and spatial evolution and development of industrial and mining towns.
Yiyao Tang is specialised in the history and theory of architecture, focusing on architectural and construction history in Modern China (19th and early 20th centuries). She is a doctoral student of Qiaohui Tong in School of Urban Design at Wuhan University.