Parallel Strand Lumber

By Mrinal Dugar and Reeva TeotiaB.Arch 4th Year.

Section A120695043120695058

What is a Lumber?• Lumber is wood in any stage from the time it is cut from a tree

through its use in construction or paper. • Lumber is cut from a tree through a process called felling. After it is

cut and shipped, it is supplied either "rough" or "finished".• Finished lumber is cut to standard sizes, (2x4, 2x6, etc) and is

primarily used in the construction industry. Most finished lumber is cut from softwood trees such as pine, fir, or cedar. Some rough lumber includes hardwoods for use in high-grade wood floors.

• Rough lumber is raw and uncut to standardized measurements. It is used for furniture or specialty manufacturing where custom cutting and shaping is required. Usually rough lumber is cut from trees such as oak, and may be available in a variety of sizes for shipping. In many instances, rough lumber will also have the bark still attached.

Rough cut lumber.

Finish cut lumber.

What exactly is PSL?• Parallel strand lumber (PSL) is a high strength structural composite lumber product

manufactured by gluing strands of wood together under pressure.Because it is a glued-manufactured product, PSL can be made in long lengths but it is usually limited to 20m (66 ft.) by transportation constraints.the strand elements with wood fibres are primarily oriented length wise.

AVAILABLE SIZES IN THE MARKET:-• least dia. of the strands must not exceed 6.4 mm. and the avegare length is 150 times the

dia. (min.).• The product is manufactured as a 12" x 12" or 12" x 18" billet in a rectangular cross-

section, which is then typically sawn and trimmed to smaller cross-sectional sizes• Typical thicknesses are 3½", 5¼” or 7"; typical depths are 9½", 11⅞" 14", 16" & 18". Typically

the beams are made to a maximum length of 60 feet.

PSL Manufacturing Process.• PSLs are made of long, thin strips of wood (usually Douglas fir or hemlock)

that are coated with high-strength waterproof resin glue; aligned so that the strips are parallel; formed into large billets that are pressed to their proper thickness; and heated to cure the glue. One manufacturer uses microwaves to cure the PSL instead of heat from conventional fuel. The billets of PSL are then sawn to form beams in the same dimensions as those sawn from logs. The result is straight, stable beams that can be purchased in lengths as long as 44 feet. These are of uniform strength and density throughout. The manufacturing process reduces the waste from each log to less than 1/3 of its volume.

• Manufactured at a moisture content of 11 percent, which is approximately the equilibrium moisture content of wood in most service conditions, PSL is less prone to shrinking, warping , cupping, bowing or splitting.

• It is made from southern pine from wood strands from which the growth imperfections have been removed. This results in a product having consistent properties and high load carrying ability.

• Douglas Fir (DF) and Southern Yellow Pine (SYP) are the most commonly used wood species

• If boards or beams can be found that are longer than 16 feet, they are often not straight enough or strong enough to use for floor joists, rafters, or load-bearing studs. The formation

of strands and then being parallel glued over each other.

Uses of PSL.• PSL is well suited for use as beams and columns for post and beam construction, and

for beams, headers, and lintels for light framing construction.• It is commonly used for heavily loaded columns, and beam and header

applications where high bending strength is needed.• PSL is suited to applications where finished appearance is important. It is also suited

to concealed structural applications where appearance is not a factor.• PSL readily accepts preservative treatment and a very high degree of penetration and

therefore protection is possible. Treated PSL should be specified for members which will be directly exposed to high humidity conditions.

• Beams, purlins/rafters, columns• - Timber-frame constructions

Pepsico factory rooftop

load bearer.

Outer fascade

glass glazing support.

Australia expo mart

glass support.

Load distributi

ng connecting joints

Column nad beam

joints

Uses in different forms and structures.

Types of defects in PSL.• Defects occurring in lumber are grouped into the following four divisions• ConversionDuring the process of converting timber to commercial form the following defects may occur:• Chip mark this defect is indicated by the marks or signs placed by chips on the finished surface of timber• Diagonal grain improper sawing of timber• Torn grainwhen a small depression is made on the finished surface due to falling of some tool• Wanpresence of original rounded surface in the finished product

Defects due to fungus

• Fungi attack timber when these conditions are all present:• The timber moisture content is above 25% on a dry-

weight basis.• Wood with less than 25% moisture (dry weight basis) can

remain free of decay for centuries. Similarly, wood submerged in water may not be attacked by fungi if the amount of oxygen is inadequate.

BLUE STAIN DEFECT

DRY ROT DEFECTBROWN ROT DEFECT

HEART ROT DEFECT

SAP STAIN DEFECT WET ROT DEFECT WHITE ROT DEFECT SEASONING DEFECT

FUNGAL DEFECTS

Advantages of using PSL.• The advantages of SCL are high

strength, flexibility of sizes and shapes, stiffness, and excellent treatability with preservatives.

• High stress• More consistency for strength

performance and stability, due to lamination.

• It satisfies environmental concerns.

Psl core

Adhesives used and available in market.

The types of adhesives used in engineered wood include:• Urea-formaldehyde resins (UF) most common, cheapest, and not waterproof.• Phenol formaldehyde resins (PF) yellow/brown, and commonly used for

exterior exposure products.• Melamine-formaldehyde resins (MF) white, heat and water resistant, and

often used in exposed surfaces in more costly designs.• Methylene diphenyl diisocyanate (MDI) or polyurethane (PU) resins• expensive, generally waterproof, and does not contain formaldehyde.

Uses of PSL in column and beams according to span and load distribution.