III. Read one more text on the problem and do the tasks. Laminated Veneer Lumber and Other Structural Sections

A. The strength of timber is determined by the weakest cross-sections having defects than by clear straight grain wood itself, which normally has two to four times higher strength than commercial sawn timber. Large defects can be avoided when logs are first cut into thin sections and then glued to a reconstituted product. Especially the tensile strength is increased.

Glued laminated timber has a higher strength than its raw material. Still more benefit of the redistribution of large defects into several small ones is obtained in the fabrication of plywood, in which logs are peeled to veneers with thicknesses of 1 to 5 mm. Plywood veneers are glued usually in right angles to each other.

B. Laminated veneer lumber (LVL) is a product close to plywood, except that veneers are parallel and larger dimensions are available. The idea of LVL came from the 1960s and the production has expanded in the 1980s. Today LVL is produced commercially in the USA by seven companies, in Finland, Japan, New Zealand and Australia. The biggest LVL producer in the US markets LVL under the trade mark Micro=Lam LVL. In Finland the product is called Kerto-LVL. The 1993 production of LVL was 440000 m³ in America, 51000 m³ in Europe and 40000 m³ in other parts of the world and showed a rising trend.

Parallel strand lumber (Parallam) is a beam-like product made of long

wood strands, which was developed in Canada in the 1970’s and 1980’s. It is now fabricated also in the USA. Another new American structural wood product is Intrallam, which is made from large parallel chips. Kerto-LVL is produced as a standard product when all veneers are parallel (Kerto-S) and also as Kero-Q in which about every fifth veneer is in the perpendicular direction.

C. Parallam is made from Douglas fir and Southern yellow pine. As in the manufacture of LVL, logs are peeled into veneers. The sheets of veneer are then clipped into strands up to 2400 mm in length and 2-3 mm in thickness. The adhesive is applied to the oriented strands which are fed into a rotary belt press and cured under pressure by microwave heating. The process is monitored by programmable logic controllers. Parallum emerges from the process as a continuous billet that can be factory-cut and trimmed to standard sizes up to 20 m in length. Maximum depth of beam is 480 mm and width 285 mm. Square cross-sections up to 180x180 mm are commonly produced for columns.

Intrallum is made from large chips up to 300 mm in length and 70 mm in width. After drying a polyurethane adhesive is applied and chips are organized to a direction parallel to the panel length. The fabricated product is a large panel which is cut to the required dimensions.

D. LVL is being used as beams, plates, members of trusses and shells. This is done in new buildings as well as in renovation for beams, joists, truss chords, vehicle-decking, concrete formwork and prefabricated housing. The largest structure made of LVL in Europe is Oulu-done with a diameter of 115 m.

The uses of Intrallam are similar to those of LVL. Parallam is used for beams, headers and columns. In residential building construction in America it is often used in beams when a material with higher strength is needed. Both LVL and Parallam are competing with steel in large span structures. The advantages of the wood-based alternatives are good architectural appearance, longer resistance in case of fire and the easy techniques for fastening of the secondary structure.

Task 1.

Define which of the statements are:

A- true B- false C- not mentioned in the text

1. A reconstituted product allows to avoid the large defects of sawn timber.

2. Glued laminated timber is not stronger than the raw material.

3. Parallel strand lumber (Parallam) was developed in France.

4. LVL is being used in aircraft industry.

Task 2.

Which paragraphs (A,B,C,D) express the following ideas?

1. The production of LVL has spread all over the world.

2. LVL and parallam have a wide variety of application.

Task 3.

Answer the question. Make the right choice.

Where was the largest structure made of LVL constructed?

It was constructed _____.

A. in Australia

B. in Africa

C. in Europe

D. in America

Task 4.

Finish the sentence in accordance with the text.

Laminated veneer lumber is a product close to _____.

A. chipboard

B. fiberboard

C. particle board

D. plywood

Task 5.

Answer the question:

What are thin sheets of logs glued to a reconstituted product for?

A. They are glued to avoid large defects and to increase strength.

B. They are glued to decrease the strength.

C. They are glued to reduce the dimensions.

D. They are glued to increase moisture content.

Task 6.

What is the main idea of the text?

A. Laminated products haven’t found wide markets in the world.

B. Laminated products have got better qualities and properties than solid wood.

C. Laminated products are of no value for structural use.

D. Laminated products have lower qualities and properties in comparison

with other wood products.