Thesis (MScFor)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: South Africa is a timber scarce country that will most probably experience a shortage of structural
timber in the near future. In this study the concept of using young finger‐jointed Eucalyptus grandis
timber was evaluated for possible application in roof truss structures while the timber is still in the
green, unseasoned state. 220 finger‐jointed boards of cross‐sectional dimension 48 x 73 mm and 36 x
111 mm timber, cut from 5‐18 year old Eucalyptus grandis trees were obtained from Limpopo province,
South Africa. The boards were manufactured using a polyurethane (PU) adhesive at moisture content
levels above fibre saturation point and no drying was performed. The objectives of this study were to
determine various mechanical and physical properties of this finger‐jointed product. More specifically
(1) to determine the strength and stiffness potential of the product in the wet and the dry condition, (2)
to evaluate physical properties such as density, warp, checking and splitting, (3) to evaluate potential
indicator properties to be used as structural grading parameters, and (4) to compare the flexural
properties to the current SA pine resource and SANS structural grade requirements.
The boards were divided into two groups of the same size, which constituted the wet and the dry
samples. Each sample was further separated into six different groups for testing the different strength
and stiffness properties. The dry group was stacked in a green‐house for nine weeks until equilibrium
moisture content was reached. Afterwards selected physical properties such as warp, checking and
splitting were assessed. Destructive testing was conducted on the boards and the results were used to
determine various mechanical properties. Finally, each board was assessed for density and moisture
content (MC) values.
The study showed that the young finger‐jointed Eucalyptus grandis timber had very good flexural
properties. Both mean modulus of elasticity (MOE) and modulus of rupture (MOR) 5th percentile
strength values for wet and dry boards complied with the current SANS 10163‐1 (2003) requirements for
grade S7.The values of tensile perpendicular to grain and compression perpendicular to grain strength
did not conform to SANS requirements for grade S5. The other strength properties for the wet and dry
groups complied with one of the three SANS structural grades. The 5 year old (48 x 73 mm) boards’
showed significantly higher levels of twist and checking compared to 11 year old boards of the same
dimension. Only 46.3% of the finger‐jointed products conformed to the density requirements in SANS
1783‐2 (2004) for grade S7. There was a significant difference in density between the three age groups (5, 11 and 18 years) presented in this study. The variation in both MOE and MOR values of the fingerjointed
product proved to be significantly lower in comparison to currently used SA pine sources.
Based on the results from this study the concept of producing roof trusses from wet, unseasoned and
finger‐jointed young Eucalyptus grandis timber has potential. However, additional research on a number
of issues not covered in this study is still required for this product including full scale truss evaluations,
proof grading, PU adhesive evaluation at elevated temperatures, nail plate load capacity, and the
possible need for chemical treatment of the product against Lyctus beetles. / AFRIKAANSE OPSOMMING: Suid Afrika is ‘n land wat waarskynlik ‘n tekort aan strukturele hout sal ervaar in die nabye toekoms. In
hierdie studie word die gebruik van jong gevingerlasde Eucalyptus grandis hout vir die moontlike gebruik
in dakstrukture, terwyl nat en ongedroog, ondersoek. 220 gevingerlasde planke van deursnit 48 x 73 mm
en 36 x 111 mm gesaag van 5‐18 jaar‐oue Eucalyptus grandis bome en afkomstig van die Limpopo
provinsie in Suid Afrika, is gebruik. Die produk is vervaardig met poli‐uretaan (PU) lym uit planke met
vog inhouds vlakke bo veselversadigingspunt. Die doelwit van hierdie studie was om verskeie meganiese
en fisiese eienskappe van die vingerlas produk vas te stel. Meer spesifiek (1) om die sterkte en modulus
van elastisiteit (MOE) potensiaal van die vingerlas produk in die nat en droë toestand te analiseer, (2)
om die fisiese eienskappe soos digtheid, vervorming, oppervlakbarse en spleting te ondersoek, (3) om
potensiële graderingsparameters te evalueer, en (4) om die buigeienskappe van die produk te vergelyk
met SA dennehout asook die SANS strukturele graad vereistes.
Die planke is verdeel in twee groepe, ‘n nat groep en ‘n droë groep. Elke groep is verder verdeel in ses
kleiner groepe soos buig, trek en drukmonsters. Die droë groep was in ‘n kweekhuis geplaas vir nege
weke totdat veselversadigingspunt bereik is. Daarna is geselekteerde fisiese eienskappe soos
vervorming, oppervlak barse en spleting gemeet. Destruktiewe toetsing is uitgevoer op die planke en die
resultate was gebruik om verskeie meganiese eienskappe vas te stel. Laastens is elke plank se digtheid
en voggehalte gemeet.
Die studie het getoon dat die jong gevingerlasde Eucalyptus grandis hout goeie buigeienskappe het.
Beide die gemiddelde MOE en buig sterkte 5de persentiel waardes van die nat en droë groep het
voldoen aan die huidige SANS 10163‐1 (2003) vereistes vir graad S7. Die sterkte‐eienskappe van
loodregte trekkrag en loodregte druk het nie die vereistes vir SANS graad S5 gemaak nie. Die ander
sterkte‐eienskappe van die nat en droë groep het voldoen aan een van die drie SANS strukturele
graadvereistes. Die 5 jaar‐oue (48 x 73 mm ) planke het beduidend hoër vlakke van draai‐trek en
oppervlakbarste getoon as die 11 jaar‐oue planke van dieselfe dimensie. Slegs 46.3% van die vingerlas
produk het voldoen aan digtheidsvereistes vir SANS graad S7. Daar was ‘n beduidende verskil in
dightheid tussen die drie ouderdomsgroepe (5, 11 en 18 jaar). Die MOE en buigsterkte‐waardes van die
Biligom produk het beduidend laer variasie as huidige SA denne houtbronne getoon. Die resultate verkry in die studie toon dat die konsep om dakkappe te vervaardig van nat, gevingerlasde
jong Eucalyptus grandis hout die potensiaal het om suksesvol toegepas te word. Bykomende navorsing
oor ‘n aantal faktore wat nie in hierdie studie ingesluit is nie word steeds benodig. Dit sluit in ‘n
volskaalse dakkap evaluasie, proefgradering, PU lym evaluasie by hoë temperature, spykerplaat
ladingskapasiteit en die moontlike noodsaaklikheid van chemiese behandeling van die produk teen
Lyctus kewers, insluit.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/80072 |
| Date | 03 1900 |
| Creators | Crafford, Philippus Lodewicus |
| Contributors | Wessels, Brand, Stellenbosch University. Faculty of AgriSciences. Dept. of Forest and Wood Science. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
| Format | 87 p. : ill. |
| Rights | Stellenbosch University |
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