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Английский язык для студентов строительных специальностей
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SUPPLEMENTARY READING | 319
Hong Kong continues its long-standing tradition of using bamboo scaffolding for new construction, renovation, repair work and signage. The city stands alone from the rest of the world in recognizing the sustainability of bamboo over steel and aluminium and has progressively raised training and safety standards of bamboo scaffolders. Bamboo scaffolding had previously been used in many parts of southeast Asia and mainland China but has mostly now been replaced by metal scaffolding. Except, that is, in Hong Kong, home to five of the world's 25 tallest buildings. Its bamboo scaffblders remain unperturbed by the ever-increasing heights at which they weave their bamboo webs. Working with giant grass.
According to Chinese legend the craft dates back 5000 years, when Yau Chao-Shi, a mythological character whose birthday is still celebrated, taught his people how to construct nest-like bamboo shelters in trees. Bamboo grows up to 30 m tall. It reaches its full height in one year and persists for several years without growing taller or wider, making it technically a grass rather than a tree. It is nevertheless the world's fastest growing woody plant and, as such, is particularly useful for stabilising riverbanks and preventing slope erosion. Bamboo stems can be harvested after three years and are self-renewing, with new shoots produced from the roots without replanting. The circular hollow stems make light and, when seasoned, tough construction poles that can be used without further processing or finishing.
Some 1250 species and 150 traditional applications have been identified for bamboo. Millions of people live in houses made of bamboo in parts of central and north America and Asia. It provides floor decking, wall panels, rafters, ceilings, roofs, doors and windows. Bamboo is also used for building fences and light traffic bridges in south Asia. Traces of bamboo scaffolding are still seen in south China, but in Hong Kong it continues to be extensively used, researched and improved.
The traditional art of bamboo scaffolding has been passed on from one generation to the next with little written information. However, with increasing interest from the construction industry, educational institutions, statutory departments and promoters of
sustainable resources, there has been a steady growth in the number of written regulations, guidelines, codes, conferences and publications on the subject. The focus in Hong Kong is on the locally available bamboo types, namely kao jue and mao jue, the nominal external diameters of which at base are 40 mm and 75 mm respectively.
The Code of Practice for Scaffolding Safely was first published in 1995 by the Hong Kong Labour Department. The code provided practical guidelines to the construction and maintenance of both bamboo and metal scaffolds. It gave broad material specification and minimum requirements for the configuration of commonly used scaffold types. Loads on working platforms supported by the scaffolds, however, were provided only for metal scaffolds. A separate code for bamboos, entitled Code of Practice for Bamboo Scaffolding Safety, was published in 2001. This included the minimum imposed loads on working platforms and a performance specification.
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In 2006, the Hong Kong Buildings Department published Guidelines on the design and construction of bamboo scaffolds to supplement the Labour Department code. The guidelines provide recommended practice for the design, erection, maintenance and dismantling of bamboo scaffolds. If scaffold layouts need to deviate from the guidelines, the Buildings Department recommends a performance-based design by a corporate civil or structural member of the Hong Kong Institution of Engineers. After gauging industry reaction, the Buildings Department will consider publishing a code of practice in the future.
Forms of bamboo scaffolding.
Bamboo scaffolding is used in its various forms according to the utility. Double-layered bamboo scaffolds are most commonly used in new construction and also in major renovation. External works such as rendering, painting, wall tiles and plumbing are carried out from a continuous working platform laid between the inner and outer scaffolds. The inner layer is erected at about 200 mm from the building edge, and the outer layer at about 600 mm from the inner layer. There are many variations to form, articulation, types of bamboos and spacing based on specific site requirements and the craftsmen's training and preference.
Английский язык для студентов строительных специальностей
SUPPLEMENTARY READING 321
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For the outer layer, large-diameter (75 mm) mao jue poles are used as the main vertical posts spaced at about 1 — 3 m centres. They rest on firm ground at ground level and on steel brackets securely fixed to the structural members of the building at higher levels. Buildings Department guidelines require these steel brackets to be provided at 15 m vertical intervals or every fifth floor. Each post should rest on one steel bracket, and the horizontal spacing between the brackets should not exceed 1—3 m. Smaller 40 mm diameter kao jue poles are fixed as standards (uprights) between each pair of mao jue posts.
The posts and standards are connected by mao jue ledgers (horizontals), with a vertical spacing of about 600-750 mm. The scaffolders sit and put their leg over the ledgers and fix the tier above it. The upright standards and posts are also lapped by them sitting in this position. The 600—750 mm gap spacing is just convenient working distance which is the height between the scaffolder's hip and shoulder. This way, the joints and members are load-tested during the erection stage itself by the scaffolder's own weight. Cross-bracing is provided by using kao jue poles inclined at an angle of 45—60°. For the inner layer, kao jue poles are used for main posts and ledgers; the intermediate standards are generally not necessary. The main posts of both layers are supported by the same set of triangular steel brackets.
Scaffolds are tied to buildings using 6 mm diameter horizontal mild-steel wires at vertical and horizontal spacings not exceeding 6.6 m and 3 m respectively. These are referred to as "putlogs" though, unlike putlogs in metal scaffolding systems, which transmit vertical platform loads into the building wall, putlogs in bamboo scaffolding provide lateral restraint and wind resistance. They are provided at closer spacing higher up, where wind forces can be significant.
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Working platforms for carrying out external works are normally vertically spaced at 2 m. The maximum imposed load on working platforms varies between 0—75 kPa (very light duty) to 3 kPa (very heavy duty) in the Labour Department's code. The code requires that no more than two working platforms in the former case and no more than one working platform in the latter case should be in use in any bay, that is the space between two adjacent standards along
the face of the scaffold. In the double-layered system, kao jue transom, poles spanning between the ledgers are used to support the working platforms, and are therefore provided at every platform level and with a maximum horizontal spacing of about 1.5—2.4 m.
Single-layered bamboo scaffolding is generally used to provide protective cover to renovation works on existing buildings where working platforms are not necessary. It is also used for some new construction, for example where external curtain glass walls are designed to be installed as large panels. Such scaffolds are also used in demolition, where all demolition works are carried out from inside the building including removal of external features. It is mandatory to fit tarpaulin sheets to contain demolition dust and debris, but these need to be removed during typhoons. Fixed external rather than internal ledgers facilitate the removal of tarpaulins.
However, single-layered scaffolds are less safe than double-layered scaffolds and usage is discouraged. They are not included in either the Labour Department's code or the Buildings Department guidelines. For minor repair works, including external plumbing, air-conditioning unit replacements and concrete or rendering repair, truss-out bamboo scaffolds are commonly used. This is light-duty, short-duration work and small-diameter kao jue poles are used. The standards, ledgers and raking poles are all supported by triangular steel brackets, which in turn are securely fixed to the structural elements of the building. Putlog ties restrain the top of the standards.
Bamboo scaffolding is also used to erect many of the large cantilevered advertising signs frequently seen over Chinese streets. In Hong Kong, the maximum allowed length to height ratio is 4:3 and the scaffold should be erected in a manner not to obstruct the traffic flow below. Such scaffolds are usually supported by steel wires or hang-poles securely fixed to the structural elements of the building. The lower level is usually decked out with wooden planks to act as a working platform.
Lashing connections.
Joints in bamboo construction have always been tricky. The poles are neither perfectly straight nor round, they have nodes at irregular spacings and their thickness varies. Despite such
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