Existing large span roof space frame structure reinforcement and renovation (part 1)

For the current standard and the original standard by the safety assessment for the space frame is not safe, should be a comprehensive study of the feasibility of reinforcement and renovation, including: the evaluation of the use value of this existing building reinforcement and renovation,feasibility of reinforcement technology implementation program(including reinforcement design and reinforcement construction), economic cost of reinforcement and renovation inputs, etc. For the project use value is not large, the implementation of reinforcement and transformation when the technical safety risks, the cost of large investment in the project, it is recommended to include the demolition of renewal and reconstruction; For reinforcement and renovation of high use value, reinforcement technology implementation program is basically feasible, reinforcement and renovation of the economic cost of the project is not too much, should focus on the consideration of reinforcement and renovation. For buildings with important historical value, should be considered to strengthen the transformation and protection, strengthening and transformation should maintain the shape of the building and as far as possible to keep the structural system unchanged, such as structural system changes should ensure the restorability of the original structural system. For buildings with important historical value, should be considered to strengthen the transformation and protection, strengthening and transformation should maintain the shape of the building and as far as possible to keep the structural system unchanged. If the structural system is altered, the recoverability of the original structural system should be ensured.

The reinforcement and renovation of the structure must be based on the actual project to carry out a multi-program comparison, under the premise of ensuring structural safety, with the principle of minimal interference with the original structural force system. For reinforcement and transformation projects, the roof and indoor hanging loads should be taken according to the actual situation, and the rod specifications and cross-section should be taken according to the actual measurement results, the combination of load conditions, structural calculation analysis, structural ultimate load capacity design, normal use limit state and structural seismic performance testing must meet the requirements of the current code.

1、Reduce the roof load indirect reinforcement method

The existing large-span space frame roof structure, its roof load is relatively large, for the use of wooden board + 2 layers of felt & 3 coats of bitumastic waterproof layer+ galvanized iron, its roof self-weight generally reaches 0.4kN/m2 ~ 0.5kN/m2; For the use of wooden board + slag wool insulation + 2 layers of felt & 3 coats of bitumastic waterproof layer + galvanized iron, the self-weight reaches 0.8kN/m2 ~ 0.9kN/m2; And the use of ribbed concrete slab + inorganic insulation materials + 2 layers of felt & 3 coats of bitumastic waterproof layer of heavy roofing, its roof load will reach 1.5N/m2 ~ 2.0kN/m2. Therefore, for these two types of roofs should be used metal pressure composite panels (with enclosure, insulation and waterproofing), its roof load will be significantly reduced. The roof load is greatly reduced, firstly, the internal force of the roof structure rods is reduced, so that the safety requirements can be met without reinforcement of the roof structure and rods; Secondly, the deflection of the structure can be greatly reduced, and the sensory and use performance can be better; Thirdly, the insulation and waterproof performance of the roof can be greatly improved; Finally, the main thing is that the self-weight of the roof is greatly reduced, which can effectively reduce the seismic effect on the lower supporting structure and ensure the safety of the lower supporting structure under the earthquake.

Beijing Airport Expressway Tianzhu Toll Station was built in 1992, the roof was ribbed concrete field plate, and its self-weight was 1.20kN/m2. After the completion of the project, due to aesthetic requirements, a layer of decorative glazed tile eaves was added in the middle span on the basis of the original layer of decorative glazed tile eaves, which increased the roof load, and the measured deflection in the middle span was 1/211 of the span, slightly exceeding the allowable deflection of 1/250 as required by the specification, and a very small amount of rod stress slightly exceeded the design allowable stress. In 2005, at the request of the owner, the roof was modified to ensure that the performance of the space frame structure met the requirements of the regulations. After comparing multiple options, the method of partial unloading of the roof in the mid-span area was finally adopted to reduce the mid-span deflection and meet the deflection requirements of the code, which ensured the safety of the structure. During construction, the roof waterproofing layer was removed first, and then a total of 30 prefabricated ribbed concrete field plates were removed from 5 rows and 6 columns in the mid-span, at which time the deflection of the space frame was reduced, and the concrete ribbed plates were removed and replaced with composite sandwich color steel plates, and then the waterproofing was redone on the roof. The space structure is not reinforced again, so that the stress and mid-span deflection of the space frame meet the requirements of the regulations and achieve the purpose of indirect reinforcement by reducing the roof load.

By reducing the structural mass of the roof, the occurrence of overall collapse damage under strong earthquakes can also be significantly reduced. The Dongfang Steam Turbine Plant in Hanwang Town, Deyang, which was hardest hit by the “5-12” Wenchuan earthquake, had a ground crack of 9 degrees, and a large number of single-story plants with large concrete roof panels + prefabricated concrete roof frames in a row-frame structure, which collapsed extensively; And there are some plants with large concrete roof panels replaced by pressed steel sheet roofs due to previous roof leaks, and these plants are basically intact. Also, the gymnasium of Dongfang Steam Turbine Plant in Hanwang Town adopts the space frame structure roofing of colorful pressed steel composite panels, and the structure is intact. Therefore, reducing the self-weight of the roof is also extremely effective in improving the overall seismic performance of the structure.