I Английский язык для студентов строительных специальностей

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limitations, practitioners have developed many connection details over the years. Lashing poles with soaked bamboo strips was the preferred method for a long time, but the strips decayed and needed constant attention and replacement.

By the late 1970s, nylon strips had replaced bamboo strips. The new strips made erection faster and they also lasted longer, but connections still tended to weaken over time due to weathering. This led to Hong Kong researchers specifying engineered connections through experimental investigation. The recommended value for basic characteristic resistance for each lashing is 1.1 kN with a partial safety factor of 1.1-1.25.

The nylon strips are well-specified, with a minimum ultimate strength of 0.5 kN, a width of 5.5 — 6 mm and a thickness of 0.85 —

1 mm. The overlap of two lashed bamboo poles should be 1.5—

2 m, and the distance between the lashings should not be greater than 300 mm.

Other materials such as putlogs, anchor bolts and steel brackets are specified in the Buildings Department guidelines. The established specifications for bamboo poles, however, were given in the Labour Department's earlier codes. The poles should be 3—5 years old and air-dried in vertical positions under indoor conditions for at least

3 months before use; they should be free from cracks, irregular
knots and worm-eaten spots.

Despite bamboo and lashing materials having been specified, the effort of codifying the design data is still ongoing.

Engineering characteristics.

One of the disadvantages in designing bamboo structures is the lack of structural design data and established mechanical properties. Building codes over the globe have yet to embrace bamboo, though a draft code on bamboo structural design is under review. Basic mechanical properties have been dealt with by many authors but, unlike timber, bamboo properties do not relate to species because of the dependency on other factors such as geographical location and age.

More recent research on bamboo scaffolding carried out at Hong Kong Polytechnic University with the support of the International Network for Bamboo and Rattan has thus concentrated on the locally

available kao jue and mao jue varieties. The studies indicated that despite large variations in diameter, wall thickness and moisture content, representative values of mechanical properties could be arrived at. Two failure modes, namely end bearing and splitting, were identified in compression tests. End-bearing failures were mainly due to high moisture content. For bending tests, splitting and local crashing were identified as reasons for failure.

Based on a systematic experimental investigation on column-buckling behaviour of bamboo members, researchers found that load reduction due to column buckling is significant and accordingly developed a limit-state design method. Two failure modes, namely overall buckling and local buckling, were identified respectively in mao jue (long column-wet) and kao jue (short column-wet) members in most of the cases.

The engineering characteristics of structural bamboos are similar to those of timber and codification along similar lines to timber should be the next logical step. If the Hong Kong Buildings Department publishes a code of practice for bamboo scaffold as it has suggested, this would lead to promotion and wider acceptance of bamboo as a building material worldwide. Training and safety.

In the past, the skills required for erecting bamboo scaffolding were taught by a master scaffolder through a traditional apprentice system that would last for 3 years. However, apprentices can now pick up the skill within a year through on-job training or by attending a Construction Industry Training Authority training

course.

After working in industry for at least 4 years, a scaffolder can take the CITA trade test, which consists of a 0.5 h written examination followed by a 6 h practical test in which the candidate

is required to:

- inspect an erected scaffold and rectify the defects;

- dismantle the scaffold safely;

- re-erect the scaffold.

In 2006, 268 candidates applied for the test and 62% passed. Apart from the extent of workcompleted and quality of workmanship, candidates are also assessed on their safety-consciousness.

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324 Английский язык для студентов строительных специальностей