Stress-graded lumber good alternative to steel trusses

LOS BAÑOS, Laguna – Stress-graded lumber has the potential as alternative material to steel trusses for buildings.

In fact, construction engineers can opt to use stress-graded lumber as alternative in the next two to three years, it was projected by the Department of Science and Technology-Forest Products Research and Development Institute (DOST-FPRDI) based here.

Stress-graded lumber trusses are attractive construction materials at par with steel and concrete because it is as durable as 10 times cheaper, pointed out Dr. Florentino O. Tesoro, FPRDI director.

Stress grading is a method of sorting lumber into groups, with each group having a set of predetermined structural design properties. Although lumber producers and traders adhere to some sort of visual sorting, there exists no common system of assigning quality to lumber for construction.

Stress grading allows for species substitution. A contractor, for instance, does not have to worry if the commonly used timber species needed for this project (i.e., guijo, tanguile, or yakal) is out of stock. He can always use a lesser known species as long as it belongs to the same stress group as the one required.

This, pointed out FPRDI researcher Dr. Florence P. Soriano, is one of the biggest benefits of stress-grading.

"It relieves pressure on over-exploited species by increasing the use of substitute lesser-known species," she said. "Also, it enables timber producers to improve their profit by pricing their products according to strength and not some unrealiable criterion like color."

Dr. Soriano averred that stress grading reduces material waste and boost builders’ confidence by allowing engineers to design structural components with just the right amount of material required for stiffness and strength. It also provides quality control on imported lumber so that consumers get their money’s worth.

Recently, FPRDI teamed up with the Japan-based International Tropical Timber Organization (ITTO) to develop a scientific system that would grade lumber for structural use in the Philippines.

In a two-and-half year project, an FPDI-ITTO team hopes to establish stress grades by conducting nondestructive and destructive tests on full-size lumber available in the Philippines.

"Our plan," said Dr. Soriano, who is head of the project, "is to promote the use of stress-graded lumber in constructing public buildings. The Department of Education has estimated that the need for public school classrooms would rise from 36,000 to 88,000 in the next 10 years. Assuming that one classroom would need 1,307 board feet of lumber, 16,000 to 20,000 cubic meters of stress-graded lumber are needed each year."

It will not be easy pushing for the use of stress-graded lumber in the country, she admitted.

She stated: "The first thing people ask is, where do we get all the lumber we need? These days, the campaign to save our forests has become so popular that it sounds almost indecent to advocate the use of wood in construction. But we need to realize that there are other options. We do not have to rely on our forests alone to meet our timber needs."

Soriano recalled that in 1998, about 639,000 hectares of tree farms were established in the country through the Industrial Tree Plantation and Industrial Tree Farm Management Agreements program of the Department of Environment and Natural Resources (DENR). These farms were planted to such short-rotation species as falcata, gubas, and bagras.

In 1999, about 511,000 cubic meters of wood were produced by these plantation species while only 95,440 cu m came from native species.

"Of course, we can also depend on imported logs," she said. "In 1999, as much as three-fourths of our construction lumber was imported, importation being a convenient and relatively inexpensive means of acquiring lumber."

Most buildings also gend to avoid using wood as much as they can because it is often perceived as an inferior material – not durable, flammable, and has limited use.

Fact is, Dr. Soriano explained, wood, considering its strength to weight ratio, is one of the strongest and stiffest of all materials. When properly used and cared for, it will last indefinitely as long as it is permanently dried or permanently saturated and treated with the right preservatives."