Mechanical Properties of Structural Bamboo for Bamboo Scaffoldings

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Mechanical properties of structural bamboo for bamboo

Mechanical properties of structural bamboo for bamboo

scaffoldings

scaffoldings

K.F. Chung

K.F. Chung

**

, W.K. Yu

, W.K. Yu

 Department

 Department of of Civil Civil and and Structural Structural Engineering, Engineering, the the Hong Hong Kong Kong Polytechnic Polytechnic University, University, Hung Hung Hom,KowlooHom,Kowloon, n, Hong Hong Kong, Kong, ChinaChina Received 7 March 2001; received in revised form 14 September 2001; accepted 14 September 2001

Received 7 March 2001; received in revised form 14 September 2001; accepted 14 September 2001

Abstract Abstract

This paper presents an investigation on the mechanical properties of two bamboo species, namely

This paper presents an investigation on the mechanical properties of two bamboo species, namely Bambusa Pervariabilis Bambusa Pervariabilis (or(or Kao Jue) and

Kao Jue) and  Phyllostachys Pubescens  Phyllostachys Pubescens  (or Mao Jue), which are commonly used in access scaffoldings in the South East Asia, in  (or Mao Jue), which are commonly used in access scaffoldings in the South East Asia, in particular, in Hong Kong and the Southern China. A pilot study was carried out to examine the variation of compressive strength particular, in Hong Kong and the Southern China. A pilot study was carried out to examine the variation of compressive strength against various physical properties along the length of bamboo culms for both bamboo species. Moreover, systematic test series against various physical properties along the length of bamboo culms for both bamboo species. Moreover, systematic test series with a large number of compression and bending tests were executed to establish characteristic values of both the strengths and with a large number of compression and bending tests were executed to establish characteristic values of both the strengths and the Young’s moduli of each bamboo species for limit state structural design. It is shown that both Kao Jue and Mao Jue are good the Young’s moduli of each bamboo species for limit state structural design. It is shown that both Kao Jue and Mao Jue are good constructional materials with excellent mechanical properties against compression and bending. With a suitable choice of partial constructional materials with excellent mechanical properties against compression and bending. With a suitable choice of partial safety factors, structural engineers are able to design bamboo structures at a known level of confidence against failure.

safety factors, structural engineers are able to design bamboo structures at a known level of confidence against failure.

Structural engineers are thus encouraged to take the advantage offered by bamboo to build light and strong structures to achieve Structural engineers are thus encouraged to take the advantage offered by bamboo to build light and strong structures to achieve enhanced economy and buildability. The effective use of structural bamboo as a substitute to structural timber will mitigate the enhanced economy and buildability. The effective use of structural bamboo as a substitute to structural timber will mitigate the pressures on the ever-shrinking natural forests in developing countries, and thus, facilitate the conservation of the global environment. pressures on the ever-shrinking natural forests in developing countries, and thus, facilitate the conservation of the global environment. ©

© 2002 Elsevier Science Ltd. All rights reserved. 2002 Elsevier Science Ltd. All rights reserved.

Keywords:

Keywords:  Bamboo scaffoldings; Green construction; Structural bamboo; Qualification tests; Bamboo strength  Bamboo scaffoldings; Green construction; Structural bamboo; Qualification tests; Bamboo strength

1.

1. IntrodIntroductionuction

Timber is regarded as a good natural constructional Timber is regarded as a good natural constructional ma

mateteririalal, , anand d prprobobabablyly, , onone e of of ththe e ololdedest st knknowownn materials used in construction. A number of design materials used in construction. A number of design rec-ommendations [1–3] on structural timber are available, ommendations [1–3] on structural timber are available, and traditionally, most of them employ permissible stress and traditionally, most of them employ permissible stress design. In a modern structural timber code [4], ultimate design. In a modern structural timber code [4], ultimate limit state design philosophy is adopted and structural limit state design philosophy is adopted and structural adequacy is assessed with characteristic values of both adequacy is assessed with characteristic values of both loadi

loading ng and and resisresistance using tance using approappropriatpriate e partipartial al safetysafety factors. Among many physical properties that affect the factors. Among many physical properties that affect the stren

strength gth characharacteriscteristics tics of of strucstructural tural timbtimber, er, moismoistureture con

contentent, t, dendensitsity, y, sloslope pe of of gragrain in and defectand defects s are are con con--sidered as the most important ones.

sidered as the most important ones.

Bamboo is another natural constructional material and Bamboo is another natural constructional material and there are over 1500 different botanical species of there are over 1500 different botanical species of

bam-*

* Corresponding auCorresponding author. Tel.:thor. Tel.: ++852-23346389.852-23346389.

 E-mail

 E-mail address:address: cekchung@polyu.edcekchung@polyu.edu.hk u.hk (K.F. Chung).(K.F. Chung). 0141-0296/02/$ - see front matter

0141-0296/02/$ - see front matter©© 2002 Elsevier Science Ltd. All rights reserved. 2002 Elsevier Science Ltd. All rights reserved.

P I

P III: : S 0 1 4 1S 0 1 4 1 - 0 2 9 6- 0 2 9 6 ( 0 1 ) 0 0( 0 1 ) 0 0 1 1 0 - 91 1 0 - 9

boo in the world. Many of them have been used boo in the world. Many of them have been used tra-ditionally as structural members in low-rise houses, short ditionally as structural members in low-rise houses, short span foot bridges, long span roofs and construction span foot bridges, long span roofs and construction plat-for

forms ms in in coucountrntries ies witwith h pleplentintiful ful bambamboo boo resresourourcesces.. St

Stududieies s hahave ve shshowown n babambmboo oo to to be be an an idideaeal l anand d sasafefe structural material for many construction applications. In structural material for many construction applications. In general, it is believed that the mechanical properties of  general, it is believed that the mechanical properties of  bamboo are likely to be at least similar, if not superior, bamboo are likely to be at least similar, if not superior, to

to thosthose e of structural timberof structural timber. . FurthFurthermoreermore, , as as bambbamboooo grows very fast and usually takes 3–6 years to harvest, grows very fast and usually takes 3–6 years to harvest, depending on the species and the plantation, there is a depending on the species and the plantation, there is a growing global interest in developing bamboo as a growing global interest in developing bamboo as a sub-stitute of structural timber in construction. The effective stitute of structural timber in construction. The effective use of structural bamboo will mitigate the pressures on use of structural bamboo will mitigate the pressures on the

the ever-sever-shrinkhrinking ing naturnatural al forestforests s in in develdevelopinoping g coun coun--tries, and thus, facilitate the conservation of the global tries, and thus, facilitate the conservation of the global environment. However, a major constraint to the environment. However, a major constraint to the devel-opment of structural bamboo as a modern construction opment of structural bamboo as a modern construction material is the lack of design standards on both material is the lack of design standards on both mechan-ical properties and structural adequacy.

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Nomenclature Nomenclature  A

 Amm,, Z Z mm,, I I mm are measured cross-sectional area, section modulus and second moment of area, respectively, are measured cross-sectional area, section modulus and second moment of area, respectively,

F testtest,, F F designdesign are measured and design compressive force, respectively, are measured and design compressive force, respectively,

 M 

 M testtest,, M M designdesign are measured and design moment, respectively, are measured and design moment, respectively,

 f 

 f c,k c,k ,, f f c,dc,d are are characcharacteristeristic tic and and desigdesign n compcompressiressive ve strenstrengths, respectigths, respectively,vely,

 f 

 f b,k b,k ,, f f b,db,d are characteristic and design bending strengths, respectively, are characteristic and design bending strengths, respectively,

 E 

 E c,dc,d,, E E b,db,d  are average Young  are average Young’’s moduli under compression and bending, respectively,s moduli under compression and bending, respectively,

y cc,, y y bb are model factors for compressiare model factors for compression test and on test and bendbending test, respectiing test, respectively, andvely, and

g  

g  mm is is a paa partial rtial safety safety factor factor for for materimaterial al strenstrength.gth.

1.1.

1.1. BambBamboo oo scaffscaffoldioldingsngs

Bamboo scaffoldings have been used in building Bamboo scaffoldings have been used in building con-struction in China for over a few thousand years. It is struction in China for over a few thousand years. It is believed among Chinese that the

believed among Chinese that the fifirst bamboo scaffold-rst bamboo scaffold-ing was built some 5000 years ago while the basic ing was built some 5000 years ago while the basic fram-ing systems and the erection methods were established ing systems and the erection methods were established through practice about 2000 years ago. In Hong Kong through practice about 2000 years ago. In Hong Kong and other parts of the Southern China, bamboo and other parts of the Southern China, bamboo scaffold-ing

ings s are are oneones s of of the the few few tratraditditionional al bubuildilding systeing systemsms which

which survisurvive ve by by self-iself-improvmprovement ement throuthrough gh practpracticalical exp

experieriencences es of of scascaffoffoldilding ng prapractictitiotionerners s oveover r gengener- er-ati

ationsons. . NowNowadaadays, ys, in in spispite te of of opeopen n comcompetpetitiition on witwithh many metal scaffoldin

many metal scaffolding g systesystems imported all ms imported all over theover the world, bamboo scaffoldings remain to be one of the most world, bamboo scaffoldings remain to be one of the most prefer

preferred red accesaccess s scaffoscaffoldinlding g systsystems ems in in builbuilding con-ding con-struction in Hong Kong and the neighbouring areas. struction in Hong Kong and the neighbouring areas.

Bam

Bamboboo o scascaffoffoldildings ngs are are maimainly nly bubuilt ilt to to proprovidvidee workers access to different exposed locations to facilitate workers access to different exposed locations to facilitate various construction and maintenance activities. Owing various construction and maintenance activities. Owing to their high adaptability and low construction cost, to their high adaptability and low construction cost, bam-boo scaffoldings can be constructed in any layout to boo scaffoldings can be constructed in any layout to fol-low irregular architectural features of a building within low irregular architectural features of a building within a

a comcomparparatiativelvely y shoshort rt perperiod iod of of timtime. e. BesBesideides s widwidelyely erected on construction sites, they are also used in erected on construction sites, they are also used in sign-age

age ereerectictionon, , decdecoraoratiotion n worwork, k, demdemoliolitiotion n worwork k andand civil work.

civil work. Fig

Fig. . 1 1 illillustustratrates es the the typtypicaical l appappliclicatiation on of of bambambooboo scaffoldings in Hong Kong as a double layered bamboo scaffoldings in Hong Kong as a double layered bamboo acc

access ess scascaffoffoldildingngs s witwith h safsafe e worworkinking g plaplatfotforms rms forfor heavy duty work such as masonry work and installation heavy duty work such as masonry work and installation of curtain walls. Primary vertical members, or posts, are of curtain walls. Primary vertical members, or posts, are typically placed 1.8

typically placed 1.8––3 m apart with two to three second-3 m apart with two to three second-ary

ary ververtictical al memmemberbers, s, or or stastandandardsrds, , in in betbetweeween n whiwhilele horizontal members, or ledgers, are placed 0.6

horizontal members, or ledgers, are placed 0.6––0.75 m0.75 m apart. It is very important to provide suf 

apart. It is very important to provide suf fificient cient lateralaterall supp

supports to orts to the posts at the posts at regulregular ar interintervals for vals for strucstructuraltural adequacy of the bamboo scaffoldings. Moreover, adequacy of the bamboo scaffoldings. Moreover, diag-ona

onal l memmemberbers s are are alsalso o proprovidvided ed to to forform m tritriangangulaulatedted frameworks in order to increase the overall stability of  frameworks in order to increase the overall stability of  the

the scascaffoffoldildingsngs. . BamBamboo or boo or plaplastistic c strstrips ips are are useused d toto form connections between the vertical and the form connections between the vertical and the horizon-tal members.

tal members.

Ty

Typipicacal l ususagage e of of babambmboo oo scscafaffofoldldinings gs is is wiwidedelyly report

reported ed to the to the commcommunity of unity of strucstructural enginetural engineers [5],ers [5], and two complementary design guides [6,7] on erection and two complementary design guides [6,7] on erection and design of bamboo scaffoldings are compiled for the and design of bamboo scaffoldings are compiled for the building construction industry in the South East Asia, in building construction industry in the South East Asia, in partic

particular, Hong ular, Hong KongKong. . MoreoMoreover, industriaver, industrial l guideguides s onon safety of bamboo scaffolding are also available [8 safety of bamboo scaffolding are also available [8––10].10].

2.

2. RecenRecent research in structurt research in structural bambooal bamboo Str

Structucturaural l bambamboo boo havhave e beebeen n useused d tratraditditionionallally y inin China, Philippines, India, and Latin America for many China, Philippines, India, and Latin America for many hundred of years, but little research was reported in the hundred of years, but little research was reported in the past. Recent

past. Recent scienscientitifific c invinvestestigaigatiotions ns on on bambamboo as boo as aa construction material were reported by Au et al. in Hong construction material were reported by Au et al. in Hong Kong in 1978 [11] and also by Janssen in Holland in Kong in 1978 [11] and also by Janssen in Holland in 198

1981 1 [12[12]. ]. A A larlarge amounge amount t of of datdata a of of the mechthe mechanianicalcal properties for various bamboo species all over the world properties for various bamboo species all over the world were reported in 1991 [13]; however, only typical ranges were reported in 1991 [13]; however, only typical ranges of

of valvalues were ues were proprovidvided. More ed. More recerecentlntly, y, a a stustudy dy waswas reported in the literature [14] where bamboo was reported in the literature [14] where bamboo was

classi-fi

fied as a smart natural composite material with optimizeded as a smart natural composite material with optimized distribution of 

distribution of fifibers and matrices, not just across crossbers and matrices, not just across cross sec

sectiotions ns but but alsalso o aloalong ng memmember ber lenlengthgths, s, in in resresististinging environmental loads in nature.

environmental loads in nature.

A series of experimental studies on structural bamboo A series of experimental studies on structural bamboo were reported by Arce-Villalobos in 1993 [15] and were reported by Arce-Villalobos in 1993 [15] and prac-tical connection details for bamboo trusses and frames tical connection details for bamboo trusses and frames were also proposed and tested. Moreover, a recent study were also proposed and tested. Moreover, a recent study [16] on the traditional design and construction of [16] on the traditional design and construction of bam-boo in low-rise housing in Latin America is also boo in low-rise housing in Latin America is also avail-abl

able, e, and and inninnovovatiative ve appappliclicatiations ons of of bambamboo boo [17[17] ] inin building construction in India is also reported. building construction in India is also reported. Further-more, a theoretical study using advanced

more, a theoretical study using advanced fifinite elementnite element ana

analyslysis is of of one elemeone element nt per per memmember ber was was repreportorted ed byby Chan [18,19] to assess the load carrying capacities of  Chan [18,19] to assess the load carrying capacities of  bam

bamboo boo scascaffoffoldildingsngs. . MorMoreoveover, er, a a fulfull-sl-scalcale e bambambobooo scaffolding was built in a construction site and tested to scaffolding was built in a construction site and tested to fa

faililurure, e, prprovovididining g dadata ta fofor r cacalilibrbratatioion n of of ththee fifinitenite element model. Due to the slenderness of bamboo culms, element model. Due to the slenderness of bamboo culms, it was recommended that non-linear analysis was often it was recommended that non-linear analysis was often requi

required red to to predipredict ct the the buckbuckling behavioling behaviour ur of of bambbamboooo scaffoldings accurately.

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Fig. 1.

Fig. 1. BambBamboo scaffoldoo scaffoldings in Hong Kong. (a) ings in Hong Kong. (a) TypiTypical construcal constructionction. . (b) Diagram(b) Diagrammatimatic c illuillustratstration.ion.

3.

3. ScoScope of workpe of work

As

As naturnatural al non-non-homohomogenogenous us organorganic ic materimaterials, als, largelarge variations of physical properties along the length of variations of physical properties along the length of bam-boo culms are apparent: external and internal diameters, boo culms are apparent: external and internal diameters, dry density and moisture content. While engineers also dry density and moisture content. While engineers also expect variations in the mechanical properties of expect variations in the mechanical properties of bam-boo, they tend to accept that the mechanical properties boo, they tend to accept that the mechanical properties of bamboo are likely to be more consistent when of bamboo are likely to be more consistent when com-pared with those of concrete, probably similar to pared with those of concrete, probably similar to struc-tural timber. Consequently, the project aims to establish tural timber. Consequently, the project aims to establish characteristic values of the mechanical properties of two characteristic values of the mechanical properties of two bamboo species, namely,

bamboo species, namely, Bambusa Pervariabilis Bambusa Pervariabilis (or Kao (or Kao Jue) and

Jue) and   Phyllostachys Pubescens  Phyllostachys Pubescens   (or Mao Jue), which  (or Mao Jue), which are

are comcommomonly used nly used in in HonHong g KonKong g and the and the SouSouthethernrn China in bamboo scaffoldings. The project [20,21] may China in bamboo scaffoldings. The project [20,21] may be divided into the following parts of investigation: be divided into the following parts of investigation:

Part I Pilot study Part I Pilot study A pilot study is

A pilot study is fi first carried out to examine the vari-rst carried out to examine the vari-ation of compressive strength against a number of  ation of compressive strength against a number of  ph

physysicical al prpropoperertities es alalonong g ththe e lelengngth th of of babambmboooo culms of both bamboo species.

culms of both bamboo species. Part II Systematic tests

Part II Systematic tests

A number of test series are then carried out to A number of test series are then carried out to gener-ate test

ate test datdata a on on the comprthe compressessive and ive and the bendithe bendingng stren

strengths together gths together with with assocassociated iated YounYoungg’’s modulis moduli of both bamboo species. In each test series, a large of both bamboo species. In each test series, a large number of compression and bending tests on number of compression and bending tests on bam-bo

boo o cuculmlms s are carrare carrieied d ouout t ovover er a a wiwide de rarangnge e of of 

physical properties against natural occurrence. physical properties against natural occurrence. Stat-istical analysis on the test data is then performed to istical analysis on the test data is then performed to establish the characteristic values of the mechanical establish the characteristic values of the mechanical pro

properpertieties s of of botboth h bambamboo speciboo species es for for limlimit it stastatete structural design.

structural design.

The project forms part of a research and development The project forms part of a research and development pro

progragrammmme e to to propromotmote e the the effeffectective ive use use of of strstructucturaurall bamboo in building construction. The programme aims bamboo in building construction. The programme aims to

to genergenerate ate scienscientitifific design rules and data for the re-c design rules and data for the re-engineering of bamboo scaffoldings into modern green engineering of bamboo scaffoldings into modern green structures of high buildability through scienti

structures of high buildability through scientifific investi-c investi-gation and technology transfer. Other aspects of bamboo gation and technology transfer. Other aspects of bamboo scaffoldings such as column buckling and connections scaffoldings such as column buckling and connections will be reported separately.

will be reported separately.

4.

4. PilPilot studot studyy

The primary physical properties of bamboo culms are: The primary physical properties of bamboo culms are:

  External diameter,  External diameter, DD,, 

  Wall thickness,  Wall thickness, t t , (and cross-sectional area,, (and cross-sectional area, AA)) 

  Dry density,  Dry density, rr, and, and

  Moisture content, m.c.  Moisture content, m.c.

Som

Some e of of thethese se phyphysicsical al parparameameterters s varvary y sigsigninifificantlycantly alo

along ng the the lenlength of gth of bambamboo culmsboo culms, , depdependending ing on on thethe spe

speciecies. s. For For strstructucturaural l appappliclicatiationon, , it it is is impimportortant ant toto est

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culms, and also reliable co-relation between their culms, and also reliable co-relation between their physi-cal and mechaniphysi-cal properties.

cal and mechanical properties.

A preliminary study was carried out to examine the A preliminary study was carried out to examine the variation of the compressive strengths of both Kao Jue variation of the compressive strengths of both Kao Jue and Mao Jue along the length of bamboo culms against and Mao Jue along the length of bamboo culms against all

all the the priprimarmary y phyphysicsical al proproperpertieties. s. For For eaceach h spespeciecies,s, thr

three ee dry bambdry bamboo oo culculms ms werwere e testestedted, , and all and all of of thethemm were mature with an age of at least 3 years old with no were mature with an age of at least 3 years old with no visual defect. The test specimens were prepared as visual defect. The test specimens were prepared as fol-lows:

lows:

 A length of 750 mm from both the top and the bottom A length of 750 mm from both the top and the bottom

ends of each bamboo culm was discarded. ends of each bamboo culm was discarded.

  A number of test specimens were cut out from the  A number of test specimens were cut out from the

bamboo culms at regular intervals, each marked with bamboo culms at regular intervals, each marked with a label indicating its position from the bottom of the a label indicating its position from the bottom of the bamboo culm.

bamboo culm.

 The length of each test specimen was about twice the The length of each test specimen was about twice the

external diameter of the bamboo culms, but not larger external diameter of the bamboo culms, but not larger than 150 mm.

than 150 mm.

All

All the the phyphysicsical al proproperpertieties s of of the the testest t spespecimcimens ens werweree me

measasurured ed bebefofore re anand d afafteter r ththe e cocompmpreressssioion n teteststs s asas appropriate.

appropriate.

4.1.

4.1. Test proceTest proceduredure

Fig. 2 illustrates the general set-up of the compression Fig. 2 illustrates the general set-up of the compression tests, and both the applied loads and the axial shortening tests, and both the applied loads and the axial shortening of

of the the testest t spespecimcimens ens werwere e meameasursured ed durduring ing the teststhe tests.. Details of the compression tests may be found in [22,23] Details of the compression tests may be found in [22,23] wh

whilile e ththe e dadata ta ananalalysysis is prprococededurure e fofor r cocompmpreressssivivee strength and Young

strength and Young’’s modulus is given in Appendix A.s modulus is given in Appendix A. 4.2.

4.2. Test resuTest resultslts

Two failure modes, namely

Two failure modes, namely End bearing End bearing and and Splitting Splitting,, were identi

were identifified, as shown in Fig. 2. It was found thated, as shown in Fig. 2. It was found that mos

most t spespecimcimens ens faifailed led inin   End   End BeariBearingng, , espespecieciallally y inin tho

those se spespecimcimens ens witwith h highigh h momoististure ure concontentents. ts. As As thethe mois

moisture ture contcontent ent decredecreased, ased, crackcracks s alongalong fifiberbers s werweree often induced and caused

often induced and caused  Splitting Splitting. Typical load de. Typical load deflflec- ec-tion curves of test specimens associated with both failure tion curves of test specimens associated with both failure modes are also presented in Fig. 2.

modes are also presented in Fig. 2.

After data analysis, Fig. 3 presents the variations of  After data analysis, Fig. 3 presents the variations of  the physical properties along the length of the bamboo the physical properties along the length of the bamboo culms for both Kao Jue and Mao Jue. The failure loads, culms for both Kao Jue and Mao Jue. The failure loads, the ultimate compressive strengths and also the Young the ultimate compressive strengths and also the Young’’ss modulus against compression are presented in Fig. 4. modulus against compression are presented in Fig. 4.

4.3.

4.3. DiscuDiscussion on ssion on physphysical propertical propertiesies

(a) Kao Jue (a) Kao Jue

In general, the physical properties of all three culms In general, the physical properties of all three culms are found to be very similar among each other. It is are found to be very similar among each other. It is shown that while the external diameter is fair shown that while the external diameter is fair

uni-Fig. 2.

Fig. 2. CompCompressiression teston test. (a) Genera. (a) General test setl test set-up. (b-up. (b) Load de) Load deflflectionection curve

curves. s. (c) (c) TypiTypical failure cal failure modemode——end bearing. (d) end bearing. (d) TypiTypical cal failufailurere mode

mode——splitting.splitting.

form over the length of the bamboo culms with a form over the length of the bamboo culms with a typ

typicaical l valvalue ue of of 45 45 mm, the mm, the walwall l thithicknckness varieess variess from 8 mm at the bottom to 4 mm at the top of the from 8 mm at the bottom to 4 mm at the top of the culm. Consequently, the average cross-sectional area culm. Consequently, the average cross-sectional area is 750 mm

is 750 mm22 with a variation of 250 mmwith a variation of 250 mm22 along thealong the

whole member length. However, both the dry whole member length. However, both the dry den-sity and the

sity and the moismoisture content are ture content are fairly unifofairly uniform rm withwith a value of 700 kg/m

a value of 700 kg/m33 and 12.5%, respectively alongand 12.5%, respectively along

the whole member length. the whole member length. (b) Mao Jue

(b) Mao Jue

On the contrary to Kao Jue, the physical properties On the contrary to Kao Jue, the physical properties of the three culms of Mao Jue are found to be of the three culms of Mao Jue are found to be sig-ni

nifificantly different among each other. From the bot-cantly different among each other. From the bot-tom to the top of the culms, the external diameter is tom to the top of the culms, the external diameter is typically reduced from 80 mm to 50 mm. Moreover, typically reduced from 80 mm to 50 mm. Moreover,

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Fig. 3.

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Fig. 4.

Fig. 4. VariaVariation of mechation of mechanical pronical propertiperties along lenges along length of bamboo culmth of bamboo culms.s.

the wall thickness varies from 10 mm at the bottom the wall thickness varies from 10 mm at the bottom to 6 mm at the top of the culms. Consequently, the to 6 mm at the top of the culms. Consequently, the ave

averagrage e crocross-ss-secsectiotional nal arearea a is is foufound nd to to be be 17175050 mm

mm22 with a large variation of 1000 mmwith a large variation of 1000 mm22 along thealong the

whole member length. However, it is important to whole member length. However, it is important to note that the dry density is somehow uniform with note that the dry density is somehow uniform with

an average value of 700 kg/m

an average value of 700 kg/m33 and a variation of and a variation of 

100 kg/m

100 kg/m33 along the whole member length. More-along the whole member length.

More-over, large variation in the moisture content along over, large variation in the moisture content along the

the memmember ber lenlength gth is is alsalso o appapparenarent, t, ranranginging g frofromm 40% at the bottom to 20% at the top of the culms. 40% at the bottom to 20% at the top of the culms.

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4.4.

4.4. DiscuDiscussion on ssion on mechamechanicanical l proppropertieertiess

(a) Kao Jue (a) Kao Jue

Th

The e cocompmpreressssioion n cacapapacicity ty is is fofounund d to to be be at at ititss maximum of about 60 kN at the bottom of the culm maximum of about 60 kN at the bottom of the culm which is reduced steadily to about 30 kN at the top. which is reduced steadily to about 30 kN at the top. Aft

After er divdividiiding ng witwith h the the crocross-ss-secsectiotional nal areareas, as, thethe compressive strength is found to vary from 60 to 80 compressive strength is found to vary from 60 to 80 N/mm

N/mm22along the whole culm length. However, largealong the whole culm length. However, large

va

variriatatioion n in in ththe e YoYounungg’’s s momodudululus s agagaiainsnst t cocom- m-pre

pressission on is is appapparearent, nt, scascattetterinring g betbetweeween n 4 4 and and 1212 kN/mm

kN/mm22 along the whole culm length.along the whole culm length.

(b) Mao Jue (b) Mao Jue

Contrary to the physical properties, the mechanical Contrary to the physical properties, the mechanical properties of the three culms are found to be broadly properties of the three culms are found to be broadly similar. From the bottom to the top of the culms, the similar. From the bottom to the top of the culms, the compression capacity is reduced steadily from 100 compression capacity is reduced steadily from 100 kN at the bottom of the culms to 50 kN at the top. kN at the bottom of the culms to 50 kN at the top. Aft

After er divdividiiding ng witwith h the the crocross-ss-secsectiotional nal areareas, as, thethe compressive strength is found to be 50 N/mm

compressive strength is found to be 50 N/mm22at theat the

bottom of the culms which increases steadily to 70 bottom of the culms which increases steadily to 70 N/mm

N/mm22 at at ththe e totop. p. ThThe e YoYounungg’’s s modumodulus lus againagainstst

compression is found to vary steadily from 5 to 10 compression is found to vary steadily from 5 to 10 kN/mm

kN/mm22 from the bottom to the top of the culms.from the bottom to the top of the culms.

Consequently, it is shown that despite of the large Consequently, it is shown that despite of the large vari-ations in external diameter, wall thickness and dry ations in external diameter, wall thickness and dry den-sity, representative values of mechanical properties may sity, representative values of mechanical properties may be obtained for both Kao Jue and Mao Jue. Among all be obtained for both Kao Jue and Mao Jue. Among all the physical properties, it is found that moisture content the physical properties, it is found that moisture content is the most important one in governing the mechanical is the most important one in governing the mechanical properties of the bamboo. Moreover, it may be properties of the bamboo. Moreover, it may be accept-able to assume that all physical and mechanical able to assume that all physical and mechanical proper-ties are broadly constant along the culm lengths in Kao ties are broadly constant along the culm lengths in Kao Jue

Jue. . HowHoweveever, r, boboth th the the phyphysicsical al and and the the mecmechanhanicaicall prope

properties vary rties vary signisignifificantly along the culm lengths incantly along the culm lengths in Mao Jue, and thus, the non-uniformity should be Mao Jue, and thus, the non-uniformity should be incor-porated when assessing their structural behaviour. porated when assessing their structural behaviour.

5.

5. SystemSystematic testsatic tests

In order to establish characteristic values of the In order to establish characteristic values of the com-pressive and the bending strengths together with pressive and the bending strengths together with associa-ted Young

ted Young’’s moduli of each bamboo species, a set of s moduli of each bamboo species, a set of  systematic test series, or a quali

systematic test series, or a qualifification test programme,cation test programme, was executed. In each test programme, a large number was executed. In each test programme, a large number of compression and bending tests on bamboo specimens of compression and bending tests on bamboo specimens were carried out over a wide range of moisture contents were carried out over a wide range of moisture contents as follows:

as follows:

(a) Normal tests. The tests aimed to measure the (a) Normal tests. The tests aimed to measure the com-pressive and the bending strengths of the test pressive and the bending strengths of the test speci-mens in normal supply condition, i.e.

mens in normal supply condition, i.e.  Green Green ( (G0G0) and) and Green

Green++3 months3 months ( (G3G3). For each member position, six). For each member position, six

specimens were tested. specimens were tested.

(b) Wet tests. The tests aimed to measure the (b) Wet tests. The tests aimed to measure the com-pressive and the bending strengths of the test pressive and the bending strengths of the test speci-mens with high moisture contents. For each member mens with high moisture contents. For each member position, two specimens were immersed under water position, two specimens were immersed under water over different time periods.

over different time periods.

(c) Dry tests. The tests aimed to measure the (c) Dry tests. The tests aimed to measure the com-pressive and the bending strengths of the test pressive and the bending strengths of the test speci-mens with low moisture contents. For each member mens with low moisture contents. For each member position, two specimens were dried in oven at 105 position, two specimens were dried in oven at 105°°CC

over different time periods. over different time periods.

The designation system for the test specimens is de The designation system for the test specimens is defifinedned as follows:

as follows: Normal Tests

Normal Tests—— Wet Wet teststests——W W  Dry Dry teststests—— D D G0 G0 /  / G3G3



 A A  B  B C  C 



 X   X {1,2,3,4,5,6}{1,2,3,4,5,6}



 A  A  B  B C  C 



W {{aa,,bb,,cc,,d d ,,ee,, f  f ,,gg,,hh,,ii}}



1 1 2 2





 A  A  B  B C  C 



 D

 D{{aa,,bb,,cc,,d d ,,ee,, f  f ,,gg,,hh,,ii}}



1 1 2 2



N

Noo. . oof f tteesstts s NNoo. . oof f tteesstts s NNoo. . oof f tteessttss

=

= 33××66××22 ==33××99××22 ==33××99××22 =

=3636 ==5454 ==5454

where the time periods

where the time periods aa toto ii are de are defifined as follows:ned as follows: a

a bb cc dd ee ff gg hh ii 1

1 h h 2 2 h h 4 4 h h 8 8 h h 112 2 h h 1 1 d d 2 2 d d 3 3 d d 7 7 dd h

h== hour(s); d hour(s); d==day(s)day(s)

In general, the test specimens were selected and In general, the test specimens were selected and pre-pared as follows:

pared as follows:

 All bamboo culms were about 6 m in length and of  All bamboo culms were about 6 m in length and of 

3

3––6 years of age. They were air dry for at least 36 years of age. They were air dry for at least 3 months before testing.

months before testing.

 A length of 750 mm from both the top and the bottom A length of 750 mm from both the top and the bottom

ends of the bamboo culms was discarded. ends of the bamboo culms was discarded.

 ThThreree e spspececimimenens s wewere re cucut t ouout t frofrom m ththe e totop, p, ththee

mi

middddle le anand d ththe e bobottttom om poposisititionons s of of ththe e cuculm lm anandd marked with the letters

marked with the letters AA,, BB, and, and C C  respectively. respectively.

  Th  The e lenlength of gth of eaceach h spespecimcimen en was about 1200 mmwas about 1200 mm

wit

with h accaccepteptablable e outout-of-of-st-strairaightghtnesness s undunder er visvisualual inspection. The external diameters at the top and the inspection. The external diameters at the top and the bottom ends did not differ by more than 25 mm. bottom ends did not differ by more than 25 mm.

6.

6. Test procTest procedureeduress

Two tests were carried out in the quali

Two tests were carried out in the qualifification test pro-cation test pro-grammes as follows:

grammes as follows:

  Bending Tests  Bending Tests

Each bending test specimen was supported over a Each bending test specimen was supported over a clear span of 1000 mm. The specimens were tested clear span of 1000 mm. The specimens were tested under single point load at mid-span until failure as under single point load at mid-span until failure as shown in Fig. 5.

shown in Fig. 5.

(8)

Fig

Fig. . 5. 5. BenBendinding test. (a) g test. (a) GenGeneraeral test set-ul test set-up. (b) p. (b) LoaLoad d dedeflflectionection curves. (c) Typical failure mode

curves. (c) Typical failure mode——local crushing. (d) Typical failurelocal crushing. (d) Typical failure mode

mode——splitting.splitting.

After each bending test, two compression test After each bending test, two compression test speci-men

mens s werwere e taktaken en frofrom m the the benbendinding g testest t spespecimcimen.en. The height of the compression test specimens was The height of the compression test specimens was at least two times the external diameter of the at least two times the external diameter of the bam-boo culm, but not larger than 150 mm. The boo culm, but not larger than 150 mm. The speci-mens were tested under axial compression until mens were tested under axial compression until fail-ure as shown in Fig. 2, similar to those compression ure as shown in Fig. 2, similar to those compression tests in the pilot study.

tests in the pilot study.

Details of the compression and the bending tests may be Details of the compression and the bending tests may be found in [22,23] while the data analysis procedure for found in [22,23] while the data analysis procedure for both bending and

both bending and compcompressivressive e strenstrengths together withgths together with associated Young

associated Young’’s moduli is given in Appendix A. Its moduli is given in Appendix A. It should be noted that in bamboo scaffoldings, the should be noted that in bamboo scaffoldings, the hori-zontal distance between the primary vertical members, zontal distance between the primary vertical members, or posts, typically ranges from 1800 to 3000 mm. Thus, or posts, typically ranges from 1800 to 3000 mm. Thus,

the typical distance between points of in

the typical distance between points of inflflection along aection along a horizontal member, or a ledger, near internal supports is horizontal member, or a ledger, near internal supports is taken as 1000 mm. The bending tests are envisaged to taken as 1000 mm. The bending tests are envisaged to provide data on the

provide data on the flflexural behaviour of ledgers overexural behaviour of ledgers over internal supports under hogging moment.

internal supports under hogging moment. 6.1.

6.1. Test resuTest resultslts

  Compression tests  Compression tests

Two failure modes, namely

Two failure modes, namely  End bearing End bearing andand  Split-  Split-ting

ting, were identi, were identifified, as shown in Fig. 2. It was founded, as shown in Fig. 2. It was found th

that at mmoost st spspececimimenens s fafaililed ed inin   En  End d BeBearariningg,, esp

especieciallally y in in thothose se spespecimcimens ens witwith h highigh h moimoistusturere contents. As the moisture content decreased, cracks contents. As the moisture content decreased, cracks along

along fi fibers were often induced and causedbers were often induced and caused  Splitting Splitting.. Typ

Typicaical l loaload d dedeflflection ection curcurves ves of of testest t spespecimcimensens associated with both failure modes may be found in associated with both failure modes may be found in Fi

Fig. g. 2; 2; ththey ey arare e sisimimilalar r to to ththosose e obobtatainined ed in in ththee pilot study.

pilot study.

  Bending tests  Bending tests

Two

Two failfailure ure modmodes, es, namnamelyely,,   Splitting  Splitting andand   Local  Local crushing

crushing were identi were identifified, as shown in Fig. 5. Mosted, as shown in Fig. 5. Most sp

spececimimenens s wewere re fofounund d to to be be fafaililed ed inin   Splitting  Splitting,, esp

especieciallally y for for thothose se spespecimcimens ens witwith h low low moimoistusturere contents. For test specimens with high moisture contents. For test specimens with high moisture con-ten

tents, ts, the the spespecimcimens ens colcollaplapsed sed ununder der comcombinbineded bending and patch load, leading to

bending and patch load, leading to   Local crushing  Local crushing.. Typ

Typicaical l loaload d dedeflflection ection curcurves ves of of testest t spespecimcimensens associated with both failure modes may be found in associated with both failure modes may be found in Fig. 5.

Fig. 5.

A number of quali

A number of qualifification test programmes [13,14] forcation test programmes [13,14] for both Kao Jue and Mao Jue have been executed for both Kao Jue and Mao Jue have been executed for differ-ent

ent batchbatches es of of bambbamboo oo sampsamples. Statisticles. Statistical al analyanalysis onsis on all the test data was carried out to establish the all the test data was carried out to establish the character-istic values of the mechanical properties of the bamboo istic values of the mechanical properties of the bamboo species for limit state structural design. Tables 1 and 2 species for limit state structural design. Tables 1 and 2 sum

summarmarizeizes s the the ranranges ges of of the the meameasursured ed mecmechanhanicaicall pr

propoperertities es obobtatainined ed frofrom m ththe e ququalaliifificacatition on tetest st prpro- o-grammes. Moreover, the ranges of the physical grammes. Moreover, the ranges of the physical proper-ties covered in all the tests are also presented.

ties covered in all the tests are also presented. Ba

Basesed d on on a a tototatal l of of 36364 4 cocompmpreressssioion n teteststs s anand d 9191 bending tests, the variations of the compressive strength, bending tests, the variations of the compressive strength,  f 

 f cc, and the bending strength,, and the bending strength,  f  f bb, of Kao Jue against moist-, of Kao Jue against

moist-ure contents are presented in Fig. 6(a) and (b), ure contents are presented in Fig. 6(a) and (b), respect-ive

ively. ly. SimSimilailarlyrly, , basbased ed on on a a tottotal al of of 213 213 comcomprepressissionon tests and 128 bending tests, the variations of the tests and 128 bending tests, the variations of the com-pressive strength,

pressive strength, f  f cc, and the bending strength,, and the bending strength, f  f bb, of Mao, of Mao

Jue against moisture contents are presented in Fig. 7(a) Jue against moisture contents are presented in Fig. 7(a) and (b), respectively. The Young

and (b), respectively. The Young’’s moduli under com-s moduli under com-pression and bending for both Kao Jue and Mao Jue are pression and bending for both Kao Jue and Mao Jue are plotted in Figs. 8 and 9 respectively.

plotted in Figs. 8 and 9 respectively. It should be noted that

It should be noted that

  Kao Jue  Kao Jue

Both the compressive and the bending strengths are Both the compressive and the bending strengths are

(9)

Table 1 Table 1

Summary of physical and mechanical properties of 

Summary of physical and mechanical properties of  Bambusa pervariabilis Bambusa pervariabilis (Kao Jue) (Kao Jue) N

Nooss. . RRaanngge e MMaaxxiimmuum m MMiinniimmuum m AAvveerraagge e SSttaannddaarrd d CChhaarraacctteerriissttiicc d

deveviiatatiion on vavallue ue atat fififthfth percentile percentile External diameter

External diameter DD((mmmm) ) 33664 4 AAlll l ssppeecciimmeenns s 5577..6 6 2233..9 9 4400..7 7 55..9 9 3311..11 Internal diameter

Internal diameter d d ((mmmm) ) 33664 4 AAlll l ssppeecciimmeenns s 4455..2 2 1177..3 3 3300..4 4 44..5 5 2233..11 Wall thickness

Wall thickness t t  ((mmmm) ) 33664 4 AAlll l ssppeecciimmeenns s 1100..7 7 22..9 9 55..2 2 11..4 4 22..99 Cross-sectional area

Cross-sectional area A A (mm (mm22) ) 36364 4 AAlll l ssppeecciimmeenns s 1133775 5 22113 3 58589 9 220077

Second moment area

Second moment area I I  (mm (mm44) ) 33664 4 AAlll l ssppeecciimmeenns 3s 377..33××101044 1.161.16××101044 10.410.4××101044 6.016.01××101044

Dry density

Dry density rr (kg/m (kg/m33) ) 36364 4 AAlll l ssppeecciimmeenns s 11773311..6 6 552222..0 0 770088..8 8 8877..0022 ––

Moisture content Moisture content  m.c. m.c.((%%) ) 11003 3 mm..cc..5% 5% 55..0 0 00..2 2 11..8 8 11..44 –– 1 1336 6 mm..cc..==55––2200% % 1919..3 3 55..4 4 1133..4 4 22..33 1 1225 5 mm..cc..2020% % 111100..8 8 2200..2 2 4444..3 3 2222..11 –– Compressive strength Compressive strength  f  f cc (N/mm (N/mm22) ) 11003 3 mm..cc..5% 5% 11554 4 773 3 11003 3 115 5 7799 1 1336 6 mm..cc..==55––2200%% 9999 4444 6699 1122 4488 1 1225 5 mm..cc..2020%% 7575 3355 4488 88 3355 Young

Young’’s moduluss modulus E E cc (kN/mm (kN/mm22) ) 770 0 mm..cc..5% 5% 1155..8 8 44..9 9 1100..3 3 22..44 ––

1 1000 0 mm..cc..==55––2200% % 1616..1 1 22..5 5 99..3 3 22..99 9 90 0 mm..cc..2020% % 1144..2 2 22..2 2 66..8 8 22..22 –– Bending strength Bending strength f f bb (N/mm (N/mm22) ) 221 1 mm..cc..5% 5% 11444 4 884 4 10109 9 117 7 8800 5 53 3 mm..cc..==55––2200% % 11118 8 448 8 882 2 117 7 5544 1 17 7 mm..cc..2020%% 6666 3377 5522 99 3377 Young

Young’’s moduluss modulus E E bb (kN/mm (kN/mm22) ) 221 1 mm..cc..5% 5% 3355..3 3 1144..3 3 2222..0 0 55..00 ––

5 53 3 mm..cc..==55––2200% % 3399..3 3 1111..0 0 1188..5 5 44..33 1 17 7 mm..cc..2020% % 2288..5 5 1111..0 0 1166..4 4 44..77 –– Table 2 Table 2

Summary of physical and mechanical properties of 

Summary of physical and mechanical properties of  Phyllostachya Pubescens Phyllostachya Pubescens  (Mao Jue)  (Mao Jue) N

Nooss. . RRaanngge e MMaaxxiimmuum m MMiinniimmuum m AAvveerraagge e SSttaannddaarrd d CChhaarraacctteerriissttiicc d

deveviiatatiion on vavallue ue atatfififthfth percentile percentile External diameter

External diameter DD((mmmm) ) 22113 3 AAlll l ssppeecciimmeenns s 9955..4 4 3399..4 4 6688..6 6 1111..6 6 4499..55 Internal diameter

Internal diameter d d ((mmmm) ) 22113 3 AAlll l ssppeecciimmeenns s 7744..2 2 2277..6 6 5544..5 5 99..6 6 3388..77 Wall thickness

Wall thickness t t  ((mmmm) ) 22113 3 AAlll l ssppeecciimmeenns s 1111..0 0 44..7 7 77..1 1 11..3 3 55..00 Cross-sectional area

Cross-sectional area A A (mm (mm22) ) 21213 3 AAlll l ssppeecciimmeenns s 2288331 1 55778 8 1133997 7 446688

Second moment area

Second moment area I I  (mm (mm44) ) 22113 3 AAlll l ssppeecciimmeenns 2s 25588××101044 9.009.00××101044 76.176.1××101044 9.329.32××101044

Dry density

Dry density rr (kg/m (kg/m33) ) 21213 3 AAlll l ssppeecciimmeenns s 11228866..5 5 446633..5 5 779933..9 9 110088..33 ––

Moisture content Moisture content  m.c. m.c.((%%) ) 9 9 mm..cc..5% 5% 33..0 0 00..9 9 11..5 5 00..77 –– 4 41 1 mm..cc..==55––3300% % 2299..6 6 66..5 5 1188..3 3 77..88 1 1663 3 mm..cc..3030% % 5599..1 1 3300..1 1 4433..4 4 77..00 –– Compressive strength Compressive strength  f  f cc (N/mm (N/mm22) ) 9 9 mm..cc..5% 5% 11552 2 11222 2 13134 4 110 0 111177 4 41 1 mm..cc..==55––3300% % 11114 4 448 8 775 5 118 8 4466 1 1663 3 mm..cc..3030%% 8181 3377 5577 88 4444 Young

Young’’s moduluss modulus E E cc (kN/mm (kN/mm22) ) 9 9 mm..cc..5% 5% 1111..7 7 33..8 8 99..4 4 22..11 ––

4 41 1 mm..cc..==55––3300% % 1111..0 0 33..6 6 77..8 8 11..99 1 1663 3 mm..cc..3030% % 9..7 97 22..2 2 66..4 4 11..22 –– Bending strength Bending strength f f bb (N/mm (N/mm22) ) 115 5 mm..cc..5%5% 112244 5566 8855 2211 5511 3 32 2 mm..cc..==55––3300% % 550 0 11332 2 888 8 119 9 5566 8 81 1 mm..cc..3030% % 11118 8 449 9 776 6 113 3 5555 Young

Young’’s moduluss modulus E E bb (kN/mm (kN/mm22) ) 115 5 mm..cc..5% 5% 1199..7 7 1100..3 3 1133..2 2 22..44 ––

3

32 2 mm..cc..==55––3300% % 1188..2 2 77..1 1 1111..4 4 22..88

8

81 1 mm..cc..3030% % 1166..4 4 55..4 4 99..6 6 22..00 ––

about 80 N/mm

about 80 N/mm22 in dry condition, i.e. m.c.in dry condition, i.e. m.c.5%. In5%. In

wet

wet conconditditionion, , i.ei.e. . m.cm.c..20%, , bot20% both h strstrengengths ths areare reduced roughly by half to 35 N/mm

reduced roughly by half to 35 N/mm22..

The

The averaaverage ge YounYoungg’’s s modumoduli li againagainst st compcompressiressionon and bending are 10.3 and 22.0 kN/mm

and bending are 10.3 and 22.0 kN/mm22, respectively, respectively

in dry condition, and they are reduced roughly by in dry condition, and they are reduced roughly by one-third to 6.8 and 16.4 kN/mm

one-third to 6.8 and 16.4 kN/mm22 in wet conditions.in wet conditions.

  Mao Jue  Mao Jue

The compressive strength is 117 N/mm

The compressive strength is 117 N/mm22 in dry con-in dry

con-dition, i.e. m.c.

(10)

Fig. 6.

Fig. 6. VariaVariation of mechation of mechanical pronical propertiperties of Kao Jue against moises of Kao Jue against moisture conteture content.nt.

Fig. 7.

Fig. 7. VariaVariation of mechantion of mechanical propical propertieerties of s of Mao Jue againMao Jue against moistst moisture contenure content.t.

Fig. 8.

Fig. 8. VariaVariation of mechation of mechanical pronical propertiperties of Kao Jue against moises of Kao Jue against moisture conteture content.nt.

Fig. 9.

(11)

m.c.

m.c.30%, the strength is reduced roughly to one-30%, the strength is reduced roughly to one-third of its original value to 44 N/mm

third of its original value to 44 N/mm22. The bending. The bending

strength may be taken at 50 N/mm

strength may be taken at 50 N/mm22, irrespective to, irrespective to

the moisture content. the moisture content. The

The averaaverage ge YounYoungg’’s s modumoduli li againagainst st compcompressiressionon and bending are 9.4 and 13.2 kN/mm

and bending are 9.4 and 13.2 kN/mm22, respectively, respectively

in dry condition, and they are roughly reduced by in dry condition, and they are roughly reduced by on

one-te-thirhird d to to 6.4 and 6.4 and 9.6 kN/mm9.6 kN/mm22, , resrespecpectivtively ely inin

wet conditions. wet conditions.

7.

7. DesDesign data and ign data and desdesign ruleign ruless

In order to provide simple and effective design data, In order to provide simple and effective design data, sta

statististictical al anaanalyslysis is is is carcarrieried d out out oveover r thrthree ee difdifferferentent ran

ranges ges of of momoististure ure concontentents ts ((m.cm.c.) .) as as shshowown n in in ththee pilot study:

pilot study: Kao Jue Kao Jue (a) m.c.

(a) m.c.5%, (b) m.c.5%, (b) m.c.5520%, and (c) m.c.20%, and (c) m.c.20%.20%.

Mao Jue Mao Jue (a) m.c.

(a) m.c.5%, (b) m.c.5%, (b) m.c.5530%, and (c) m.c.30%, and (c) m.c.30%.30%.

Tab

Table le 3 3 sumsummarmarizeizes s the the proproposposed ed chacharacracterterististic ic com com--pression and bending strengths at

pression and bending strengths at fififth percentile valuesfth percentile values together with associated average Young

together with associated average Young’’s moduli. Thes moduli. The material partial safety factor for bamboo,

material partial safety factor for bamboo, g   g  mm, is proposed, is proposed

to be 1.5. It should be noted that the characteristic values to be 1.5. It should be noted that the characteristic values of the mechanical properties of both Kao Jue and Mao of the mechanical properties of both Kao Jue and Mao Jue are shown to be superior to common structural Jue are shown to be superior to common structural tim-ber, and probably also to concrete.

ber, and probably also to concrete.

Simple design rules for both compression and bending Simple design rules for both compression and bending capacities of Kao Jue and Mao Jue are proposed as capacities of Kao Jue and Mao Jue are proposed as fol-lows:

lows:

  Compression capacity:  Compression capacity: F F designdesign == f f c,dc,d ×× AAmm

  Bending capacity:  Bending capacity: M M designdesign == f f b,db,d ×× Z Z mm..

Table 3 Table 3

Proposed mechanical properties

Proposed mechanical propertiesaa forfor Bambusa pervariabilis Bambusa pervariabilis (Kao Jue) and (Kao Jue) and  Phyllostachya pubescens Phyllostachya pubescens  (Mao Jue)  (Mao Jue)

Characteristic strength (at

Characteristic strength (at  fi fifftth h DDeessiiggn n YYoouunngg’’s modulus (Averages modulus (Average B

Baammbbooo o ssppeecciiees s ppeerrcceennttiillee) ) DeessiigD gn n ssttrreennggtth h ((g  g  mm==1.5)1.5) vvaalluuee))

D

Drry y WWeet t DDrry y WWeet t DDrry y WWeett  Bambusa

 Bambusa pervariabilispervariabilis

Compression

Compression f f c,k c,k  (N/mm (N/mm22) ) 779 9 3355 f f c,dc,d (N/mm (N/mm22) ) 552 2 2233 E E c,dc,d (kN/mm (kN/mm22) 1) 100..3 3 66..88

(Kao Jue) (Kao Jue)

Bending

Bending f f b,k b,k  (N/mm (N/mm22) ) 880 0 3377 f f b,db,d (N/mm (N/mm22) ) 554 4 2244 E E b,db,d (kN/mm (kN/mm22) 2) 222..0 0 1166..44

Phyllostachya Phyllostachya

Compression

Compression f f c,k c,k  (N/mm (N/mm22) ) 11117 7 4444 f f c,dc,d (N/mm (N/mm22) ) 778 8 2299 E E c,dc,d (kN/mm (kN/mm22) ) 99..4 4 66..44

 pubescens

 pubescens (Mao Jue) (Mao Jue)

Bending

Bending f f b,k b,k  (N/mm (N/mm22) ) 551 1 5555 f f b,db,d (N/mm (N/mm22) ) 334 4 3366 E E b,db,d (kN/mm (kN/mm22) 1) 133..2 2 99..66 a

a Dry condition m.c.Dry condition m.c.5% for both Kao Jue and Mao Jue. Wet condition m.c.5% for both Kao Jue and Mao Jue. Wet condition m.c.20% for Kao Jue, and m.c.20% for Kao Jue, and m.c.30% for Mao Jue. Linear interpolation30% for Mao Jue. Linear interpolation

is permitted for mechanical properties with moisture contents between dry and wet conditions. is permitted for mechanical properties with moisture contents between dry and wet conditions.

In order to assess the structural adequacy of the design In order to assess the structural adequacy of the design rules, model factors

rules, model factors y y  are established which are de are established which are defifinedned

as follows: as follows:

  Compression capacity:  Compression capacity:

y  y cc== F  F testtest F  F designdesign 

  Bending capacity:  Bending capacity:

y  y bb==  M   M testtest  M   M designdesign ..

For the quali

For the qualifification test programmes, Figs. 10 and 11cation test programmes, Figs. 10 and 11 plot the model factors of the design rules for both plot the model factors of the design rules for both com-press

pression ion and and bendbending capacities against ing capacities against moismoisture con-ture con-tents for both Kao Jue and Mao Jue respectively. The tents for both Kao Jue and Mao Jue respectively. The average model factors for compression are found to be average model factors for compression are found to be 1.9

1.98 8 and 2.04 for and 2.04 for Kao Jue Kao Jue and Mao and Mao JueJue, , resrespecpectivtivelyely while the average model factors for bending are found to while the average model factors for bending are found to be 2.18 and 2.40 for Kao Jue and Mao Jue, respectively. be 2.18 and 2.40 for Kao Jue and Mao Jue, respectively. Cons

Consequenequently, the tly, the propoproposed design rules sed design rules are shown are shown toto be adequate over a wide range of physical properties. be adequate over a wide range of physical properties.

It should also be noted that the model factors of the It should also be noted that the model factors of the design rule for compression capacity against the position design rule for compression capacity against the position along the length of bamboo culms are presented in Fig. along the length of bamboo culms are presented in Fig. 4 for both Kao Jue and Mao Jue. The average model 4 for both Kao Jue and Mao Jue. The average model factors for compression are found to be 1.83 and 2.13 factors for compression are found to be 1.83 and 2.13 for Kao Jue and Mao Jue, respectively. Consequently, for Kao Jue and Mao Jue, respectively. Consequently, the proposed design rules are also shown to be adequate the proposed design rules are also shown to be adequate at any cross section along the length of bamboo culms. at any cross section along the length of bamboo culms.

8.

8. PractiPractical consideracal considerationstions

For structural design of bamboo scaffoldings in For structural design of bamboo scaffoldings in prac-tice, the following should be noted:

tice, the following should be noted:

(a) Moisture content (a) Moisture content

In general, the moisture contents at normal supply In general, the moisture contents at normal supply condition, i.e. air dry for three months after harvest, condition, i.e. air dry for three months after harvest, or

Figure

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References

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