Comparative Assessment of the Strengths of Solid and Glued Laminated Timber
CHAPTER ONE
Aimย andย Objectives
Aimย
Theย aimย ofย thisย study isย toย assessย theย strengthย propertiesย ofย glueย laminatedย Ireย (Funtumia,ย Africana)ย Oriro(Antiaristoxicaria)ย andย Awunย (Alstoniacongensis)ย species using polyvinylย acetate (PVA) glueย with a view to presenting the capabilityย ofย glulam elements madeย fromย the selectedย timberย species.
Objectives
Theย specificย objectivesย are;
- To determine the glueability of Ire (Funtumia,ย Africana),Oriroย (Antiarisย Toxicaria) andย Awunย (Alstoniaย Congensis).
- To evaluate the effects of varied temperature on strength performance of polyvinyl acetate glue and the mechanical properties of the glue laminated compression
- To determine the mechanical properties such as static bending strength, compression parallel and perpendicular to grain of solid wood and glulam beams specimen of the species studied.
- To compare the mechanical properties of solid and glued laminated timber
CHAPTERย TWO
ย Literatureย review
Structuralย Glueย Laminatedย Timber
Accordingย toย theย gluedย laminatedย timberย associationย (GLTA)ย ofย theย Unitedย Kingdom, glulam beams account for 50% of total glued laminated timber sales forย structural application in the United Kingdom making it one of the fastest growingย structural materials today; its consumption is reported to have doubled between 1985ย and 1995 in Britain alone.ย Glued laminated timber has gained wide application andย demand because of the standard sizes and availability of glued laminated structuralย elements such as beams and columns. This trend has made architects and specifies toย giveย preferenceย toย glulamย overย otherย materialsย forย aย wideย rangeย ofย structuralย applicationย in building.
Structural glued laminated timber is obtained by gluing up suitably selected andย prepared pieces of stress graded wood in straight or curved form with the grain of allย pieces running parallel to the longitudinal axis of the member (APA, 1996; Moodyย and Hernandez 1997). This technology allows the flexibility in the formation ofย structural elements with a wide variety of sizes, profiles, and lengths having superiorย strength, serviceability, and appearance to sawn timber. Structural elements such asย beams, columns, floor joist and purlins can be produced as glulam elements.ย Gluedย laminatedย timberย beamsย areย manufacturedย withย theย strongestย laminationsย onย theย bottomย andย topย ofย theย beam,ย whereย greatestย tensionย andย compressionย stressesย occurย so as to optimizeย the useย ofย the material (Wan, 2011).
Depending on the intended use, glued laminated timber members can be manufactured using single or multiple grade of timber, similarly any specie can be used for glulam timber, provided its mechanical and physical properties are compatible and ย the specie ย glueable (APA, 1996; Zhiyong & Robert, 2007).
CHAPTERย THREE
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ย Experimental Procedure
Preamble
This research set out to determine and compare the strength properties and failure mode of solid wood and glued laminated elements of three timber species in Nigeria, namely; Ire (Funtumiaย Africana),ย Oriroย (Antiaristoxicaria)ย andย Awunย (Alstoniacongensis). The glueability of the said species was investigated using Polyvinyl Acetate glue. Effects of varied temperature on strength properties and failure characteristics of both solid wood and glue laminated element were investigated. Details of materials and methods are as follows.
CHAPTERย FOUR
PRESENTATIONOFย RESULTย ANALYSISย ANDย DISCUSSION
Preamble
Three strength properties were investigated for the timber species as summarized on tables 4.1 to table 4.9. Solid and glue laminated timber elements were produced from Ire (Funtumiaย Africana),Awunย (Alstoniaย congensis)ย andย Oriroย (Antiarisย toxicaria). The structural elements included solid and glue laminated beams and short columns. Results were analyzed, examined and discussed.
CHAPTERย FIVE
Summary,ย Conclusionย andย Recommendation
Summary ofย Researchย Findingsย
Laboratory experiments were conducted to determine the physical and mechanicalย properties of three Nigerian timber species, namely:ย Ire (Funtumia african), Awunย (Alstonia congensis) and Oriro (Antiaris toxicaria,) in accordance with ASTM D193, EN 13183-1 (2002), EN 408 (2003) and EN 384(2004). The mechanical properties were determined using three points loading for bending strength. The characteristic values of the material property were calculated and tabulated on table 4.7: Characteristicย materialย properties.ย Theย strengthย propertiesย wereย adjustedย toย 18%ย moisture content relevant to the equilibrium moisture content for structural use ofย timber in Nigeria as shown on table 4.8: Adjusted characteristic bending strength toย 150mmย depth.ย Theย Nigerianย standardย codeย ofย practiceย (NCPย 2:1975)ย hasย sevenstrengthย classesย rangingย fromย N1-ย N7ย withย theย highestย strengthย inย N1ย andย theย lowestย beingย N7.ย From theย results of laboratoryย test the following wereย found:
- From the results of Characteristic properties it was shown that solid wood hadhigher strength properties than glue laminated timber with Ire offering theย highest bending strength of 62.15 N/mm2ย to 43.3 N/mm2ย followed by Awunย withย 9N/mm2toย 30.6N/mm2ย andย Oriroย offeringย 15.92N/mm2toย 22.44N/mm2ย for solid and glulam beams respectively. This fact is recognizedย inย literatureย byย Zhiyongย and Ross, (2006)ย Thelandersson andย Larsen,ย (2003).
- The glulam elements developed significant clear solid wood strength of 55%95%ย andย 143%ย inย edgewiseย bendinginย Ire,ย Awunย andย Oriroย respectivelyย whichย could beย improvedย uponย with moreย efficient pressing
- Failure generally occurred in wood fiber and not along the glue line for theglulamย elements as shown in Platesย V, VII,ย IXย and XII.
- The results of bending strength and compression parallel and perpendicular tograin in the both solid and glulam elements were of structural significance asย containedย in table 4.7:Characteristic material properties.
- For Compressive strength parallel to grain, at varied temperature, the effects of heat on glulam elements showed a progressive loss of strength with increasing temperature and thus strength and temperature were negatively correlated as shown in Fig.5: Effects of temperature variation on compressiveย
Conclusion
Givingย theย above,ย theย followingย conclusionsย wereย reached:
- The said species are glueable using polyvinyl acetate glue
- Polyvinylacetateย gluedย jointsย performedย reasonablyย wellย withinย temperatureย variationย fromย 00C to 1000
- Thestrengthย ofย glulamย wasย notย alwaysย higherย thanย solidย woodย howeverย theย strengthย ofย glulamย elementsย wasย ofย structuralย significanceย withย Ireย offeringย theย highest bending strength of 62.15 N/mm2ย , 43.3 N/mm2ย followed by Awun withย 9N/mm2ย and 30.6N/mm2ย andย Oriro offeringย 15.92N/mm2ย , 22.44N/mm2ย forย solidย and glulam beams respectively.
- Solid and glulam beams were more flexible in flat wise bending with higher MOEFor classification according to density and strength class of NCP 2 (1973) theย speciesย all fall toย groupย N7.
- Timber classified into the least strength class of N7ย could be used for structuralย purposeย in tandemย with thoseย fromย higher strength classesย as woodย composite.
Recommendation
- Based on the strength developed, the glulam elements of the said species are useful as structural elements using polyvinyl acetate
- Giving the extent of strength developed the species show useful potential for structural application as glulam elements with higher strength properties than solid wood over greater depths and span
- The use of polyvinyl acetate glued elements should be restricted to temperatures at and close to room temperature.
- Ire (Funtumia Africana) and Oriro (Antiaris Toxicaria) are timbers harvested andsold in the local timber market without information on their properties. These timbersย fall in the same class as Awun (Alstonia Congensis) andย should be included inย reviewedย editions of NCP 2.
- According to NCP 2(1973) all Nigerian timber species are hardwood i.e. harvested from broad leaf trees regarded as deciduous trees on the bases of which the timber species especially Awun and Oriro are hard wood while Ire is a
Recommendation forย Furtherย Studies
Furtherย studiesย couldย assess;
- The glueability of other timber species as contained in NCP2 with the view to establish their glueability.
- Suitability of other types of synthetic glues on local timber species for structural The mechanical properties of structural sized beams and columns of the species used in the study
- The relationship between the quantity of glue and the strength of the glue line as well as the effect of species on the
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