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NEWSLETTEROF THE NATIONAL TIMBERBRIDGEINITIATIVE ~~~~~Editor - Tinathan Coger August 1994

Red Maple and Yellow PoplarGlulam Timber Beams

n ed Maple and Yellow Poplar- are rapidly becoming pre-dominant hardwood species in the for-ests of the northeastern United States.

cRED MAPLEIAcer ,ull,um)

Because these two specieshave not beenconsidered for structural applications,there has been little interest in devel-

opment of red maple or yellow poplarlumber products.

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Issue 17

Second National Timber Bridge DesignCompetitiona he winners of the 1994 National Timber Bridge

Design Competition Awards have been selected.This is the second national student competition orga-nized by the Southwest Mississippi Resource Conserva-tion and Development Incorporation's Executive Board.

The award selections were made by a panel of judgeswhich included N. Montgomery Dodson, ConsultingEngineer; James Brohaw, Engineer - Applied ResearchAssociates; and Stephen C. Quintana, Program Director c

of the Timber Bridge Information Resource Center.

The Timber Bridge Student Design Competition is in-tended to familiarize engineering and forestry studentswith the structural capabilities of wood and its potentialas a principal material for highway bridges and relatedtransportation structures. The competition is open tostudents of civil engineering, agricultural engineering,and forestry throughout the United States.

The 1994 national student competition received favor-able responses from various colleges and forest productsgroups. A total of twenty colleges sent notices of intentto participate. Fourteen submitted design and test resultsfor final competition. Many other colleges were unableto participate.

The Southwest Mississippi Resource Conservation andDevelopment, Inc., with assistance from the Departmentof Civil Engineering at Mississippi State University (thehost university), coordinated the competition.

Continued on page 4Continuedonpage 2

Red Maple and Yellow Poplar ...continued from page 1

Recently, two separate research programs werecarried out that studied the performance of glued-laminated (glulam) timber beams manufacturedwith red maple and yellow poplar lumber (seenote at the end of this article for references).

The objective of these studies was to develophardwood lamination combinations with designstrength and stiffness properties comparable tothose of the more commonly used softwoodcombinations.

Tabulated design values for strength and stiff-ness of several species of hardwood glulammembers and for several lamination layup com-binations are published in AITC 119-85 (AITC,1985).

Current hardwood glulam specifications are pub-lished only for layup combinations of uniformgrade laminations and for selected species. Forthe more commonly used softwood glulam tim-ber, tabulated design values are published inAITC 117-87 for several softwood species andfor a wide variety of lamination combinations(AITC, 1987). Because the performance ofglulam timber manufactured with softwood lami-nation lumber is better understood than hard-

wood glulam, a wider variety of efficient com-binations of softwood glulam timber are foundin the AITC 117 standard.

In developing the new combinations of hard-wood glulam timber, existing standards werefollowed. The tabulated design values for glulamtimbers were calculated using the industry stan-dard ASTM D3737 procedures (ASTM, 1992).The calculation procedures require that the gradeand species of all the laminations in the layup bespecified and known.

The ASTM D3737 calculation procedures arewell established and verified for softwood glulamtimbers, and are used to predict the tabulateddesign values for the softwood lamination layupcombinations published in AITC 117. TheASTMD3737 procedures have not been used to generatedesign values for strength and stiffness ofpracti-cal hardwood lamination layup combinations.To determine the lamination lumber informationfor the hardwood species, preliminary tests wereconducted on several lumber specimens to obtaininformation needed by the ASTM D3737 proce-dures.

:J

:JUsing the information on the hardwood speciesof lumber, and the ASTM D3737 procedures, itwas determined that the layup combination shownin Figure 1could achieve adesign bending strength(Fb) of 2400 Ib/in2 and a design modulus ofelasticity (MOE) of 1.8 (10)6 Ib/in2; commonlyreferred to as 2400F - 1.8E. This combinationofstrength and stiffness is the most common speci-fication used in softwood glulam manufacture.Note in Figure 1 that the combination consists ofE-rated lumber on the top compression and bot-tom tension laminations; No.2 grade lumber isused in the core laminations. The E-rating no-menclature refers to the MOE level of thelumber and to the maximum allowed edge-knot.

.JContinued on page 3

cRed Maple and Yellow Poplar ...continuedfrom page 2

For example, the 2.0-1/6 grade shown in Figure1 indicates that the lamination grade must havean average MOE of 2.0 (10)6 Ib/in2 and edge-knot characteristics cannot exceed 1/6 the areaof the cross-section. Another important note isthat 15% of the combination is made from 1/6

edge-knot lumber, and the remaining 85% of thecombination is made from 1/3 edge-knot andNo.2 grade lumber. Thus, a 2400F - 1.8Ehardwood glulam combination was designedwhile utilizing a large percentage oflow-qualitylumber.

15% 2.0-113

10% 1.8-113

c 50% No.2

10% 1.8-113

15% 2.0-113

Figure 1. Layup configuration for 2400F -1.8E hardwood glulam timber.

For each of the studies (red maple and yellowpoplar), approximately 45 beams were manu-factured in 3 different sizes (15 beams in eachsize group). The varying sizes allowed theresearchers to study the decrease in calculatedbending stress as beam size increased; com-monly referred to as the volume effect.

cAll beams were tested to failure to determine theultimate modulus of rupture, and the MOE wasdetermined using the load-deflection informa-tion up to the design load (the applied load thatcorresponds to the 2400 Ib/in2 design bendingstress).

The results of these two studies showed that

efficient combinations of hardwood glulam tim-ber can be manufactured to achieve the common

design specification of2400F - 1.8E. It was alsodetermined that the ASTM D3737 calculationprocedures, which have historically been basedon softwood timber, are applicable for the designof hardwood glulam timber. Finally, it wasobserved that the volume effect in hardwood

glulam timber was similar to that observed inpast research for softwood glulam timber.

NOTE: The two research studies discussed in thisarticle are the Forest Products Laboratory ResearchPaper No. 519 (FPL-RP-519) for the red mapleglulam timber research, and FPL-RP-520 for theyellow poplar glulam timber research. For copies ofthese papers, contact USDA Forest Service, ForestProducts Laboratory, One Gifford Pinchot Drive,

Madison, WI 53705-2398.

Second National Competition ...continued from page 1

Awards:

First Place and $750.00 - University ofOkla-homa - The timber bridge consisted of twostress laminated, double bulb-tee stringers us-ing No.3 southern pine and utility douglas fir(2X4, IXI2, IX8) for materials.

Second Place and $500. 00 - West Virginia Uni-versity, Entry A - The timber bridge consistedof 4 box beam stringers using yellow pine andll2-inch plywood decking for materials.

Third Place and $250.00 - Mississippi StateUniversity ~ The timber bridge consisted oftwo main trusses with three secondary stringersusing southern pine for materials.

Special Award A and $300.00 - University ofMissouri at Kansas City. Most economical andcost-competitive timber bridge.

Special Award Band $200.00 - Princeton Uni-versity. Most aesthetic timber bridge.

The remaining top ten colleges and universitiesnot selected for awards received $100.00 iftheirentry passed all the requirements. These col-leges included: Oregon State University, Mil-waukee School of Engineering, Ohio State Uni-versity, University of New Hampshire, WestVirginia University -Entry B, Washington Uni-versity, Virginia Polytechnical Institute and StateUniversity, and California State University atFresno.

Also participating was the University of BritishColumbia, Canada.

National Sponsors :)The second National Timber Bridge DesignCompetition was sponsored by the SouthwestMississippi Resource Conservation and Devel-opment, Inc.; Mississippi State University, De-partment of Civil Engineering; and the USDAForest Service Timber Bridge Information Re-source Center. The competition received theendorsement of the American Forest and PaperAssociation's Timber Bridge Task Force. Thestaff of the Southern Forest Products Association

provided valuable input in planning the competi-tion.

If you are interested in the 1994 fall competi-tion or wish to be a sponsor, please contact:Southwest Mississippi Resource Conservationand Development, Inc.; 114 Industrial ParkDrive;Brookhaven,MS 39601-2148;Phone:(601) 833-5539.

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* u.s.GOVERNMENTPRINTINGOFFICE:1994-507-110