An Engineering Study for Improving Safety and …...An Engineering Study for Improving Safety and Reliability of Bamboo Scaffoldings Final Report Submitted to Occupational Safety &

An Engineering Study for Improving Safety and

Reliability of Bamboo Scaffoldings

Final Report

Submitted to

Occupational Safety & Health Council

Prepared by

Dr. Chih-Chen Chang

Department of Civil Engineering

The Hong Kong University of Science & Technology

Prof. Tong-Xi Yu

Department of Mechanical Engineering

The Hong Kong University of Science & Technology

14th

June 2002

Tables of contents

i

Tables of contents

CHAPTER 1: INTRODUCTION .................................................................................... 1

1.1 USE OF BAMBOO SCAFFOLDING IN HK ................................................................. 1

1.2 ADVANTAGES AND DISADVANTAGES OF BAMBOO SCAFFOLDING ........................ 1

1.3 ENGINEERING PROBLEMS ...................................................................................... 4

1.4 RESEARCH PLAN AND METHODOLOGY .................................................................. 4

CHAPTER 2: MATERIAL PROPERTIES OF BAMBOO ......................................... 7

2.1 NORMAL COMPRESSIVE TESTS .............................................................................. 7

2.2 COMPRESSIVE TESTS UNDER DIFFERENT HUMIDITY ............................................... 9

2.3 COMPRESSIVE TEST UNDER AGING EFFECT .......................................................... 10

2.3.1 Indoor aging condition .............................................................................. 10

2.3.2 Outdoor aging condition ........................................................................... 11

2.4 THREE-POINT LOADING TEST ............................................................................... 12

2.5 BUCKLING TEST .................................................................................................. 13

CHAPTER 3: MATERIAL PROPERTIES OF THE FASTENING TIE AND

SCAFFOLD INTERSECTION .......................................................... 25

3.1 TENSILE TESTS FOR THE FASTENING TIE .............................................................. 25

3.2 CREEP EFFECT OF THE FASTENING TIE ................................................................. 26

3.3 TENSILE TESTS FOR THE FASTENING TIE DURING FIXING THE JOINT ..................... 27

3.4 SCAFFOLD INTERSECTION TESTS ......................................................................... 28

CHAPTER 4: EXPERIMENT ON THE FULL-SCALE SCAFFOLDING .............. 32

4.1 AIM OF THE FULL-SCALE SCAFFOLDING EXPERIMENT ......................................... 32

4.2 DESCRIPTION OF THE FULL-SCALE SCAFFOLDING ................................................ 32

4.3 TEST EQUIPMENT ................................................................................................ 32

4.4 UNIFORM DISTRIBUTED LOAD TESTS ................................................................... 33

4.4.1 Test setup .................................................................................................. 33

4.4.2 Results of uniform distributed load tests .................................................. 34

Tables of contents

ii

4.5 DROP TESTS ........................................................................................................ 35

4.5.1 Test setup .................................................................................................. 35

4.5.2 Results of the drop tests ............................................................................ 36

CHAPTER 5: COMPARISON OF THE EXPERIMENT AND THE FINITE

ELEMENT MODELING .................................................................... 56

5.1 DESCRIPTION OF THE FINITE ELEMENT MODELING OF SCAFFOLDING ................... 56

5.2 COMPARISON OF THE RESULTS BETWEEN THE EXPERIMENT AND THE FINITE

ELEMENT MODEL ................................................................................................. 57

5.2.1 Comparison of the uniform distributed load tests ..................................... 57

5.2.2 Comparison of the drop tests .................................................................... 57

5.3 RELIABILITY ANALYSIS OF THE FULL-SCALE SCAFFOLDING ................................ 59

5.3.1 Analysis of the uniform distributed load .................................................. 59

5.3.2 Analysis of the drop load .......................................................................... 61

CHAPTER 6: COMPUTER ANALYSIS ON SOME TYPICAL BAMBOO

SCAFFOLDINGS ................................................................................ 70

6.1 BAMBOO SCAFFOLDING AT CONSTRUCTION SITES ............................................... 70



6.2 BAMBOO SCAFFOLDING USED FOR MAINTENANCE WORK .................................... 74



CHAPTER 7: CONCLUSIONS AND RECOMMENDATIONS ............................... 84

REFERENCES ........................................................................................................... 86

Lists of tables

iii

Lists of tables

TABLE 2.1: TEST CASES FOR THE COMPRESSIVE STRENGTH OF BP AND PP ........................ 14

TABLE 2.2: MECHANICAL PROPERTIES FOR BP UNDER NORMAL COMPRESSIVE TEST ......... 14

TABLE 2.3: MECHANICAL PROPERTIES FOR PP UNDER NORMAL COMPRESSIVE TEST ......... 14

TABLE 2.4: MECHANICAL PROPERTIES FOR FIR UNDER NORMAL COMPRESSIVE TEST ........ 14

TABLE 2.5: TEST CASES FOR THE COMPRESSIVE STRENGTHS OF BAMBOO UNDER 4

DIFFERENT HUMIDITY LEVELS .......................................................................... 14

TABLE 2.6(A): MECHANICAL PROPERTIES UNDER HUMIDITY LEVEL 60% .......................... 15

TABLE 2.6(B): MECHANICAL PROPERTIES UNDER HUMIDITY LEVEL 75% ........................... 15

TABLE 2.6(C): MECHANICAL PROPERTIES UNDER HUMIDITY LEVEL 90% ........................... 15

TABLE 2.6(D): MECHANICAL PROPERTIES UNDER HUMIDITY LEVEL 98% .......................... 15

TABLE 2.7: PROCEDURES OF ASTM D1037-96 AND GB13124-91 .................................... 15

TABLE 2.8: SUMMARY OF COMPRESSIVE TESTS RESULT UNDER INDOOR AGING EFFECT ..... 16

TABLE 2.9: MECHANICAL PROPERTIES OF SPECIMENS UNDER THREE POINTS LOADING TEST

......................................................................................................................... 16

TABLE 2.10: RESULTS OF THE BUCKLING TESTS ................................................................. 16

TABLE 3.1: SUMMARY OF TENSILE TEST FOR FASTENING TIE ............................................. 29

TABLE 3.2: SUMMARY OF THE INTERSECTION TESTS .......................................................... 29

TABLE 4.1(A): RESULTS OF THE TESTS UNDER 5 KN LOAD ACT AT THE BOTTOM PLATFORM

................................................................................................................... 37

TABLE 4.1(B): RESULTS OF THE TESTS UNDER 10 KN LOAD ACT AT THE BOTTOM PLATFORM

................................................................................................................... 37

TABLE 4.1(C): RESULTS OF THE TESTS UNDER 15 KN LOAD ACT AT THE BOTTOM PLATFORM

................................................................................................................... 38

TABLE 4.1(D): RESULTS OF THE TESTS UNDER 5 KN LOAD ACT AT THE UPPER PLATFORM

................................................................................................................ 38

TABLE 4.1(E): RESULTS OF THE TESTS UNDER 10 KN LOAD ACT AT THE UPPER PLATFORM

................................................................................................................ 39

TABLE 4.1(F): RESULTS OF THE TESTS UNDER 5 KN LOADS ACT AT BOTH PLATFORMS ....... 39

TABLE 4.1(G): RESULTS OF THE TESTS UNDER 10 KN LOADS ACT AT BOTH PLATFORMS .... 40

Lists of tables

iv

TABLE 4.2: NUMBER OF TESTS AT EACH LOCATION ............................................................ 40

TABLE 4.3(A): BENDING STRAIN (X10-6

) UNDER THE IMPACT OF THE 20 KG SAND BAG

WITHOUT UDL ........................................................................................... 41

TABLE 4.3(B): BENDING STRESS (N/MM2) UNDER THE IMPACT OF THE 20 KG SAND BAG

WITHOUT UDL ........................................................................................... 41

TABLE 4.4(A): BENDING STRAIN (X10-6

) UNDER THE IMPACT OF THE 20 KG SAND BAG WITH

UDL OF 3 KN/M2 ....................................................................................... 42

TABLE 4.4(B): BENDING STRESS (N/MM2) UNDER THE IMPACT OF THE 20 KG SAND BAG

WITH UDL OF 3 KN/M2 .............................................................................. 42

TABLE 5.1: COMPARISON BETWEEN THE FINITE ELEMENT AND THE EXPERIMENT RESULTS

(UDL = 8.02 KN/M2) ........................................................................................ 64

TABLE 5.2: MAXIMUM DROP FORCE DUE TO FREE FALL OF SAND BAGS .............................. 64

TABLE 5.3(A): RESULTS OF THE DROP TEST AT LOCATION 3 ............................................... 64

TABLE 5.3(B): RESULTS OF THE DROP TEST AT LOCATION 4 ............................................... 64

TABLE 5.4: RELIABILITY OF THE TRANSOM UNDER UDL ................................................... 65

TABLE 5.5: LOADING OF THE STANDARD UNDER A UDL 3 KN/M2 APPLIED AT THE BOTTOM

PLATFORM ........................................................................................................ 65

TABLE 5.6: RELIABILITY OF THE LEDGER UNDER DROP FORCE (SIMPLY SUPPORT) ............. 65

TABLE 5.7: RELIABILITY OF THE LEDGER UNDER DROP FORCE (CLAMPED SUPPORT) .......... 65

TABLE 5.8: RELIABILITY OF THE STANDARD UNDER 60 KG FREE DROP AT LOCATION 10 .... 66

TABLE 6.1: RELIABILITY OF THE TRANSOM UNDER UDL ................................................... 77

TABLE 6.2: LOADING AT THE STANDARDS UNDER A UDL 3 KN/M2 APPLIED AT THE BOTTOM

PLATFORM FOR THE CONSTRUCTION SITE MODEL ............................................. 77

TABLE 6.3: RELIABILITY OF THE STANDARD UNDER A 5 KN DROP FORCE FOR THE

CONSTRUCTION SITE MODEL............................................................................. 77

TABLE 6.4: LOADING OF THE STANDARD UNDER A UDL 3 KN/M2 APPLIED AT THE BOTTOM

PLATFORM FOR THE MAINTENANCE MODEL ...................................................... 77

TABLE 6.5: RELIABILITY OF THE STANDARD UNDER A 5 KN DROP FORCE FOR THE

MAINTENANCE SITE MODEL .............................................................................. 78

Lists of figures

v

Lists of figures

FIGURE 2.1(A): RELATIONSHIP BETWEEN MECHANICAL PROPERTIES AND AREA OF BP ...... 17

FIGURE 2.1(B): RELATIONSHIP BETWEEN MECHANICAL PROPERTIES AND DIAMETER OF BP

................................................................................................................ 17

FIGURE 2.1(C): RELATIONSHIP BETWEEN AREA AND DIAMETER OF BP .............................. 18

FIGURE 2.1(D): RELATIONSHIP BETWEEN YOUNG’S MODULUS AND DIAMETER OF BP ........ 18

FIGURE 2.2(A): RELATIONSHIP BETWEEN MECHANICAL PROPERTIES AND AREA OF PP ...... 19

FIGURE 2.2(B): RELATIONSHIP BETWEEN MECHANICAL PROPERTIES AND DIAMETER OF PP 19

FIGURE 2.2(C): RELATIONSHIP BETWEEN AREA AND DIAMETER OF PP ............................... 20

FIGURE 2.2(D): RELATIONSHIP BETWEEN YOUNG’S MODULUS AND DIAMETER OF PP ........ 20

FIGURE 2.3(A): STRENGTH OF BAMBOOS UNDER DIFFERENT RELATIVE HUMIDITY LEVELS 21

FIGURE 2.3(B): YOUNG’S MODULUS OF BAMBOOS UNDER DIFFERENT RELATIVE HUMIDITY

LEVELS ....................................................................................................... 21

FIGURE 2.4(A): REDUCTION OF STRENGTH OF PP DURING THE AGING PROCESS ................. 22

FIGURE 2.4(B): REDUCTION OF STRENGTH OF BP DURING THE AGING PROCESS ................. 22

FIGURE 2.5: SET UP FOR THE FLEXURE TEST ...................................................................... 23

FIGURE 2.6(A): SET UP FOR THE BUCKLING TEST ................................................................ 23

FIGURE 2.6(B): SPECIMEN DURING LOADING ...................................................................... 23

FIGURE 2.6(C): END CONDITION BEFORE TESTING .............................................................. 24

FIGURE 2.6(D): END CONDITION AFTER TESTING ................................................................ 24

FIGURE 3.1: RESULTS OF THE CREEP EFFECT OF THE FASTENING TIE .................................. 30

FIGURE 3.2: SINGLE CHANNEL PORTABLE DATA LOGGER ................................................... 30

FIGURE 3.3: SET-UP OF INTERSECTION TESTS ..................................................................... 31

FIGURE 3.4: DETERMINING IMPENDING FRICTION FORCE OF A BP-BP JOINT ...................... 31

FIGURE 4.1: FRONT VIEW OF THE SCAFFOLD ...................................................................... 43

FIGURE 4.2: SIDE VIEW OF THE SCAFFOLD .......................................................................... 43

FIGURE 4.3: DIMENSIONS OF THE SCAFFOLD ...................................................................... 44

FIGURE 4.4(A): STRAIN GAUGE .......................................................................................... 44

FIGURE 4.4(B): TENSILE JACKS .......................................................................................... 44

FIGURE 4.4(C): DATA LOGGER AND COMPUTER ................................................................. 45

Lists of figures

vi

FIGURE 4.4(D): LOAD CELL ................................................................................................ 45

FIGURE 4.5: STRAIN GAUGE ATTACH ON PP ....................................................................... 45

FIGURE 4.6(A): LOCATIONS OF STRAIN GAUGES ATTACHED ON THE STANDARD AT THE

FRONT SIDE ................................................................................................ 46

FIGURE 4.6(B): THE LOCATION OF SENSORS ATTACHED ON THE STANDARD AT THE BACK

SIDE ........................................................................................................... 47

FIGURE 4.7(A): FRONT VIEW OF THE LOADING SETUP ......................................................... 48

FIGURE 4.7(B): SIDE VIEW OF LOADING SETUP ................................................................... 48

FIGURE 4.7(C): THE LOADING SETUP ................................................................................. 48

FIGURE 4.8: LOADING THE TENSILE JACK DURING THE TESTS............................................. 49

FIGURE 4.9: RESULTS OF UNIFORM DISTRIBUTED LOAD TESTS ........................................... 49

FIGURE 4.10: MEMBER FORCES OF THE CENTER MEMBER AT THE FRONT FACE UNDER UDL

................................................................................................................... 50

FIGURE 4.11: DROP TEST LOCATIONS ................................................................................. 50

FIGURE 4.12: BEFORE THE SAND BAG DROPPED ................................................................. 51

FIGURE 4.13: RECORDED STRAINS OF THE DROP TEST ........................................................ 51

FIGURE 4.14: BEFORE THE DROP OF THE 40 KG SAND BAG ................................................. 52

FIGURE 4.15: AFTER THE DROP OF THE 40 KG SAND BAG ................................................... 52

FIGURE 4.16: JOINT CONDITION OF LOCATION 9 BEFORE THE DROP OF 40 KG SAND BAG AT

CENTER ...................................................................................................... 53

FIGURE 4.17: JOINT CONDITION OF LOCATION 9 AFTER THE DROP OF 40 KG SAND BAG AT

CENTER ...................................................................................................... 53

FIGURE 4.18: THE MEMBER WAS FAILED AT THE LOCATION 9 ............................................ 54

FIGURE 4.19: ANOTHER VIEW TO SEE THE FAILURE AT THE LOCATION 9 ............................ 54

FIGURE 4.20: THE SAFETY BELT FIX AT THE LOCATION 10 ................................................. 55

FIGURE 4.21: MEMBER FAILURE DURING THE DROP OF 60 KG SAND BAG AT LOCATION 10 55

FIGURE 5.1: FEM MODEL OF THE SCAFFOLD ...................................................................... 67

FIGURE 5.2: LOADING OF THE UDL TESTING ..................................................................... 67

FIGURE 5.3(A): SETUP OF THE FREE DROP TESTS ................................................................ 68

FIGURE 5.3(B): THE FREE DROP TESTS ................................................................................ 68

FIGURE 5.4: THE RESULTING DROP FORCE OF DIFFERENT DROP WEIGHT ............................ 69

Lists of figures

vii

FIGURE 5.5: A SIMPLE MODEL TO SIMULATE A TRANSOM UNDER UDL .............................. 69

FIGURE 5.6: A SIMPLE MODEL TO SIMULATE A LEDGER UNDER DROP FORCE ...................... 69

FIGURE 6.1: BAMBOO SCAFFOLDING AT SHAM TSENG ....................................................... 79

FIGURE 6.2: THE CATCH FAN WITH STRUCTURAL SUPPORTS ............................................... 79

FIGURE 6.3: CLOSE SHOT OF THE SCAFFOLDING ................................................................. 80

FIGURE 6.4: THE FEM MODEL OF THE SCAFFOLDING AT SHAM TSENG .............................. 80

FIGURE 6.5: LOADING AT THE BOTTOM PLATFORM ............................................................ 81

FIGURE 6.6: LOADING AT EACH PLATFORM ........................................................................ 81

FIGURE 6.7: SCAFFOLDING FOR MAINTENANCE WORK AT HKUST .................................... 82

FIGURE 6.8: BOTTOM OF THE SCAFFOLDING AT HKUST ................................................... 82

FIGURE 6.9: CLOSE SHOT OF THE SCAFFOLDING AT HKUST .............................................. 83

FIGURE 6.10: THE FEM MODEL OF THE SCAFFOLDING AT HKUST .................................... 83

Chapter 1

1

Chapter 1: Introduction

1.1 Use of Bamboo Scaffolding in HK

Bamboo scaffolding is a popular temporary structure for supporting working platforms in

Hong Kong. It is used widely in building construction, building facade and wall repairs,

decoration and sign erection, slope maintenance, etc. Fu [1] concluded in 1993 that over

two-thirds of bamboo scaffoldings are for building construction. The market share of the

bamboo scaffolding in Hong Kong was first summarized and documented by So and

Wong [2]. They concluded that the bamboo scaffolding has 100% and 95% of the market

share for the construction work in the private section in the 1980s and in the 1990s,

respectively. Also for the public sector, the bamboo scaffolding grasps 100% of the

market share in the work issued by the Housing Society and in the new building work

issued by the Building Authority.

1.2 Advantages and Disadvantages of Bamboo Scaffolding

The reasons why the bamboo scaffolding prevails in Hong Kong can be attributed to the

following factors:

1) Economy

So and Wong [2] reported that the average cost of a piece of 6 m long bamboo was

about HK$ 10 in 1998, while the cost of a 6 m, 48mm steel tube was about HK$ 80

and that of a 2 m aluminum ally tube was about HK$ 250. Although the usable life of

metal tubes is about 15 to 20 years, which is far superior to that of bamboo which

normally can not be re-used, the storage of these metal tubes makes them even less

appearing to the industry in Hong Kong due to extremely high storage cost.

2) Efficiency

Erecting and dismantling bamboo scaffolding are relatively easy and can be very fast.

The weight of a typical bamboo is about 1.1 to 1.3 kg/m [3]. Constructing and

dismantling bamboo scaffolding do not require special tools. On the average, a skilled

Chapter 1

2

bamboo scaffold worker can erect about 600 to 700 m2 or dismantle 2,000 m

2 per day.

As a comparison, a skilled metal scaffold worker can erect about 300 to 400 m2 or

dismantle 500 to 600 m2 per day.

3) Flexibility

Bamboo scaffolding can be very flexible and adaptable to different construction

requirements in terms of shape, height, and working space. Bamboo can be cut,

without significant adverse effect to its mechanical properties, to suit the shape of a

building with special shapes, contours, or corners.

However, the bamboo scaffolding does not come without disadvantages, some of which

can be severe and result in potential hazards to the workers. These disadvantages include:

1) Variation in Mechanical Properties

Bamboo is a natural material that does not possess uniform mechanical properties. Its

mechanical properties depend on species, years and locations of growth, and moisture

contents. To make the condition even more complicate, even for one piece of bamboo,

its cross sectional areas, moisture contents, rigidities and strengths all vary from

location to location. Zhou [4] reported some properties of 61 species of bamboo,

including volume weight, percentage of swelling, density of vascular bundle,

compressive and tensile strengths, etc. A total of 9,000 samples of 311 culms were

collected from 26 districts in 11 provinces of China from 1963 to 1978. Jansseu [5]

collected and summarized reports on the properties of bamboo in 1991. Bamboo’s

properties varying with its thermal expansion, moisture content, elasticity, bending,

compression, shear and torsion were reported. Bamboo also corrodes and degrades

easily under normal weather variation. It cracks when the humidity is low and its

strength reduces when the humidity is high. Under Hong Kong’s warm and humid

environment, the bamboo’s life span is expected to be less than one year [4].

2) Quality Control and Human Dependency

Erecting and dismantling of bamboo scaffolding depend highly on the skill and the

experience of workers. In the Construction Sites (Safety) Regulations, Regulation

38E states “This regulation requires that only trained workmen with adequate

Chapter 1

3

experience and under the supervision of a competent person shall erect, alter or

dismantle scaffolds”. A competent person is referred to who has completed

satisfactorily a formal training in bamboo scaffolding work such as the 3-year

Bamboo Scaffolder Apprenticeship Scheme operated by the Vocational Training

Council, the 1-year full-time training course in Bamboo Scaffolding of the

Construction Industry training Authority (CITA), other similar bamboo scaffolding

training courses/programs, or has satisfactorily passed the Trade Test on Bamboo

Scaffolding of the CITA; and who has passed an experience of 10 years or more in

bamboo scaffolding work. A trained workman is referred to a scaffolder who has

satisfactorily completed a formal training in bamboo scaffolding work equivalent to

any of those mentioned for a competent person and possessed at least 3 years of

experience in bamboo scaffolding work. The relatively stringent training requirement

for the bamboo scaffolders is a good measure to ensure the quality and the safety of

the bamboo scaffolding. The requirement is also a good indication on how the skill

and the experience of the scaffolders affect the quality of the bamboo scaffolding.

3) Maintenance and management

Regular inspection of bamboo scaffolding is absolutely necessary due to at least the

following reasons:

(i) The significant variation and the environmental degradability of bamboo’s

mechanical properties;

(ii) The potential creep and fatigue behavior of the nylon strips used as joint

fixture for bamboos;

(iii) The ease of accidental damage and dismantlement by other workers.

In the Construction Sites (Safety) Regulations, Regulation 38F states “A scaffold shall

not be used unless it (a) has been inspected by a competent person before being taken into

use for the first time; (b) has been inspected by a competent person after any substantial

addition, partial dismantling or other alteration; (c) has been inspected by a competent

person after any exposure to weather conditions likely to have affected its strength or

stability or to have displaced any part; (d) has been inspected by a competent person at

regular intervals not exceeding 14 days immediately preceding each use of the scaffold”.

Chapter 1

4

1.3 Engineering Problems

Bamboo scaffolding has not been a popular subject for study in universities and not too

many articles on systematic engineering studies of the bamboo scaffolding can be found

in the literature. Chen, et al. [6] presented a computerized methodology for analysis and

design of bamboo scaffolding systems. A full-scale scaffolding system with double layers

was tested to failure for verification of the computer approach. Yu and Chung [7]

performed a statistical analysis on over 500 compression and 200 bending tests of two

bamboo species, Kao Jue and Mao Jue. They found that moisture content was the most

important physical property in defining the mechanical properties of both species of

bamboo. Practical design data and formulas were also presented.

The bamboo scaffolding’s high popularity in the construction industry unfortunately is

accompanied by its relatively high accident rate. The Labor Department summarized a

total of 31 fatal accidents related to bamboo scaffold between 1994 and 1998 [8]. This

number suggests that a detailed and thorough engineering study aiming toward improving

the safety of bamboo scaffolding is urgently needed.

1.4 Research plan and methodology

This proposal aims at conducting a systematic and detailed engineering analysis on the

safety and reliability of the bamboo scaffolding using combination of laboratory tests and

computer calculations. Detail steps for the realization of the proposal consist of four

items which are discussed in the following.

1) Material properties of bamboo

The material properties of bamboo, such as elasticity, tensile strength, compressive

strength, bending strength, shear strength, torsion and thermal expansion, are the

foundation for the engineering analysis to be conducted in this proposal. These

properties are well-known to be functions of the species of bamboo, the number of

Chapter 1

5

nodes, the moisture content, the weather condition, the inherent defects, etc. These

properties will be obtained from a series of laboratory tests under a well-controlled

environment using some typical bamboo members.

2) Material properties of fastening tie and scaffold intersection

The bamboo components are joined together using nylon strip lashings, the properties

and the strength of typical lashing fixtures (or bamboo scaffold intersections) should

be experimentally determined before incorporated into the analysis. The test would

include the effects of the fastening method of bamboo members, the type and

mechanical properties of nylon strips, the method of installation of ties, and the

number and the overlapping length of bamboo members.

3) Computer modeling and analysis

After determining the mechanical properties of the bamboo and the intersection, we

will then develop finite element models to analyze some typical scaffolding

configurations, such as single-row bamboo scaffolding system, double-row bamboo

scaffolding system, truss-out bamboo scaffolding system, cantilever type bamboo

scaffolding system, and scaffolding system for slope works. These bamboo

scaffolding systems will be designed following the Code of Practice for Bamboo

Scaffolding Safety published by the Labour Department in 2001 [9]. The material

properties obtained in the previous stages will be used to establish the finite element

models. Specifically, the following studies will be conducted:

(a) Maximum stresses and deformations at some critical locations of the

scaffoldings under different combinations of dead and live loads. These load

combinations should emulate various stages of working condition.

(b) Maximum stresses and deformations at some critical locations of the

scaffoldings under different combinations of dead and live loads plus an impact

load applied at some intersections. The impact load is to emulate the accidental

fall of a person from the scaffoldings.

(c) The ultimate load-carry capacity of the scaffoldings under different

combinations of dead loads, live loads and impact loads.

Chapter 1

6

4) Full-scale tests

A typical bamboo scaffolding will be built and used as a test bed to verify some of the

analysis results obtained. The bamboo scaffolding should conform to the technical

requirements outlined in Section 4 of the Code of Practice for Bamboo Scaffolding

Safety [9]. The methodology used for testing should follow as close as possible some

recognized international standards. Some strain gauges and accelerometers will be

attached at some critical locations of the scaffolding to measure deformation and

acceleration under various load combinations that emulate different working

scenarios. The scaffold intersections or the nylon lashings should be carefully

inspected and documented for each test.

Chapter 2

7

Chapter 2: Material properties of bamboo

Three types of materials are usually used in the bamboo scaffolding in Hong Kong. They

are Bambusa Pervariabius Grade A (BP, 篙竹 or Kao Jue), Phyllostachys Pubescens (PP,

毛竹 or Mao Jue) and Fir (木杉). Their material properties are obtained through the

following experiments.

2.1 Normal compressive tests

The aim of these tests is to measure the compressive strength and the young’s modulus of

the specimens under the normal laboratory condition. A total of 44 BP specimens, 18 PP

specimens and 10 Fir specimens were tested under normal condition.

The specimens of BP and PP were divided into three cases. For case one, the specimens

had a node near their quarter locations. For case two, the specimens had a node near their

middle locations. For case three, the specimens had no node. Table 2.1 shows the number

of specimens in each case for BP and PP. The reason for having three different cases is to

found out the effect of node on the material properties.

The length for all specimens was 200 mm. This length was used to prevent buckling

effect of the specimens during the tests. The test equipment 815 MTS was used to carry

out the experiment.

Table 2.2-2.4 show the means and the standard deviation (std) of the diameter (D), the

cross section area (A), the compressive strength (S) and the Young’s modulus (E) for the

three types of bamboo tested. The strength was obtained from dividing the recorded

ultimate load by the measured cross section area. Also shown in the tables is the lower

bound of strength with 95% probability of occurrence. The following observations can be

concluded from these tables:

Chapter 2

8

(1) For the same type of material (BP and PP), the presence and the location of node

do not significantly affect both the strength and the Young’s modulus.

(2) While the strengths of BP and PP are about the same, the Young’s modulus of BP

is higher than that of PP.

(3) The compressive strengths and the Young’s moduli of Fir are significantly lower

than those of BP and PP.

Detailed analyses on the test results of BP and presented in Figure 2.1. Some

observations are summarized as follows:

(1) The strength of BP decreases linearly and quadratically as the area and the

diameter increases, respectively.

(2) The ultimate load of BP increases linearly and quadratically as the area and the

diameter increases, respectively.

(3) The young’s modulus of BP in general decreases as the diameter increases.

Detailed analyses on the test results of PP area presented in Figure 2.2. It is noted that the

properties of PP have a similar behavior as those of BP.

Chapter 2

9

2.2 Compressive tests under different humidity

The aim of these tests is to measure the compressive strength and the young’s modulus of

the specimens under four different relative humidity, 60%, 75%, 90% and 98%,

respectively. A total of 44 BP specimens, 49 PP specimens and 12 Fir specimens were

tested under the four humidity levels. The specimens were placed in the environmental

chamber for two days with temperature kept constant at 26C. After two days, the

specimens were tested using the MTS 815 and the displacement and the loading were

recorded during the tests.

At each humidity level, a few samples were selected from the same bamboo component.

An additional sample was also selected from the same component and tested at the room

condition. This additional sample was used as a reference to quantity the humidity effect

on bamboo. The test results indicated that both the ultimate strengths and young’s

modulus of BP, PP and Fir all decrease as the relative humidity level increases. It is

because specimens with different moisture contents have different failure modes. When

the moisture content in the specimens is high, the failure mode is end bearing while the

moisture content in the specimens is low, the failure mode become splitting. A similar

result was shown in [5] and [8].

Figure 2.3 (a) & (b) showed this decreasing trend graphically. It showed that PP and Fir

had similar decreasing rate with the increasing relative humidity. BP was influenced by

the relative humidity in a greater amount. As BP’s wall thickness is thinner than the

others’, the moisture is easier to get into the whole cross section. So, the moisture content

in BP is higher than that in the other materials and BP showed a greatest decreasing trend

than the other two materials.

Chapter 2

10

2.3 Compressive test under aging effect

The compressive test under aging effect divided into two sections, one is under indoor

aging condition and the other is under outdoor aging condition.

2.3.1 Indoor aging condition

For the indoor aging condition, the procedures outlined in the ASTM D1037-96 and

GB13124-91 were followed. ASTM D1037-96 is the standard test methods for evaluating

properties of wood base and particle panel materials and GB13124-91 is the methods of

testing bamboo-mat plywood. These procedures were summarized in Table 2.7.

Table 2.8 summarizes the test results under the indoor aging condition. The asterisks “*”

in the table indicate cases that significant cracks were seen in the bamboo specimens such

that compressive tests could not be performed.

Based on these test results, the following conclusions can be made:

(1) The compressive strengths of all three types of bamboo all reduce to the

neighborhoods their respective lower 95% probability of occurrence values as

shown in Tables 2.2 to 2.4 under the ASTM D1037-96 procedure.

(2) Similar trends can be observed for the compressive strengths under the

GB13124-91 procedure.

Chapter 2

11

2.3.2 Outdoor aging condition

The specimens were placed outdoors and water was sprayed on the specimens once a day

to accelerate the aging process. Compressive tests of at least two specimens were carried

out every week for 12 weeks to investigate the change of the material properties.

The compressive strengths of similar sizes of bamboo specimens without any aging effect

obtained in section 2.1 were used as a reference for comparison. Figure 2.4 show the

reduction of the compressive strengths of PP and BP as a function of times in weeks for

the outdoor aging effect. Although the data are quite fluctuating, it is seen that the

bamboo compressive strengths become smaller under outdoor aging condition by about

20% as compared to these similar sizes of bamboo specimens without subjecting to any

aging effect.

Chapter 2

12

2.4 Three-point loading test

Three-point loading tests are used to evaluate the flexure modulus of the bamboo

specimens. Specimens were placed in the Dartec loading machine with round pin

supports at both ends and the loading was added at the middle of the specimens (see

Figure 2.5). Loading and the displacement at the loading location were recorded to find

out the flexure properties of the specimens.

The ultimate strengths found in the three-point loading test are higher than those found in

the compressive test. It can be concluded that the flexural failure might not be a dominant

factor for the bamboo failure.

Chapter 2

13

2.5 Buckling test

The buckling tests are to evaluate the buckling strength of long bamboo members.

Typical length of the specimens was 2500 mm. Figure 2.6(a) shows the set-up of the

buckling tests.

Table 2.10 show the experimental buckling loads obtained from the tests. For comparison,

the theoretical buckling loads for simple-simple support and for clamp-clamp support

condition are also shown in the table. It can be see that the experimental buckling loads

pretty much fall between these two theoretical buckling loads. This is reasonable since

the end conditions for the specimens were not simple support nor clamp support. In fact,

when the initial curvature is small, the end condition behaves more like a clamp support

and when the initial curvature is large, the end condition behaves more like a simple

support. The results show that using the clamp-clamp condition to determine the buckling

load of a long bamboo leads to a higher estimate which is non-conservative and unsafe.

On the other hand, the simply-simply support condition with curvature provides lower

bound estimates of the buckling loads of long bamboos. In the case that no obvious

curving is seen, the buckling loads of the simply-simply support condition without

curvature can be used. Figure 2.6(c) and (d) show the end conditions before and after

testing for one of the specimens.

Chapter 2

14

Table 2.1: Test cases for the compressive strength of BP and PP

Material Case 1 Case 2 Case 3

BP 12 11 21

PP 5 5 8

Table 2.2: Mechanical properties for BP under normal compressive test

NL D (mm) A (mm2) S (N/mm

2) E (kN/mm

2)

mean std mean Std mean std 95% prob. mean std

1/4 53.2 6.8 969.5 365.5 58.6 7.7 45.9 7.9 1.3

1/2 53.4 6.8 969.8 355.4 56.6 6.0 46.7 7.9 1.6

none 54.6 5.5 989.5 295.8 56.0 9.7 40.1 7.6 2.1

Table 2.3: Mechanical properties for PP under normal compressive test

NL D (mm) A (mm2) S (N/mm

2) E (kN/mm

2)

mean std mean Std mean std 95% prob. mean std

1/4 77.8 18.8 1875.7 1002.1 60.1 12.9 38.9 6.7 1.9

1/2 77.4 18.5 1814.1 883.1 61.7 9.8 45.5 6.5 2.1

none 77.8 9.5 1739.6 427.9 60.4 7.8 47.5 6.1 1.2

Table 2.4: Mechanical properties for Fir under normal compressive test

D (mm) A (mm2) S (N/mm

2) E (kN/mm

2)

mean std mean std mean std 95% prob. mean std

92.6 7.0 6763.4 1044.7 25.8 6.4 15.3 3.9 1.2

Index: D = Diameter

NL = Node Location

A = Area

S = Strength

E = Young's modulus

Table 2.5: Test cases for the compressive strengths of bamboo under 4 different humidity

levels

Relative humidity

Material 60% 75% 90% 98%

BP 10 13 10 11

PP 11 14 12 12

Fir 4 3 3 3

Chapter 2

15

Table 2.6(a): Mechanical properties under humidity level 60%


2) E (kN/mm

2)

mean std mean std mean std mean std

BP 52.3 5.1 826.6 144.5 63.5 6.7 8.8 1.2

PP 73.5 5.9 1612.0 217.4 61.1 3.3 6.3 1.0

Fir 88.3 1.5 6118.1 208.3 32.3 3.8 4.3 0.8

Table 2.6(b): Mechanical properties under humidity level 75%


2) E (kN/mm

2)


BP 52.5 5.5 968.4 198.5 48.5 7.1 6.7 1.6

PP 82.2 10.2 1924.7 521.3 60.7 5.9 6.3 1.5

Fir 88.0 2.6 6085.8 368.4 29.5 1.1 4.1 0.8

Table 2.6(c): Mechanical properties under humidity level 90%


2) E (kN/mm

2)


BP 55.1 1.1 891.3 56.2 50.7 5.1 6.2 1.3

PP 63.4 5.3 1154.1 178.9 62.9 4.6 6.6 1.6

Fir 89.3 5.7 6284.8 787.8 24.2 10.6 2.6 0.7

Table 2.6(d): Mechanical properties under humidity level 98%


2) E (kN/mm

2)


BP 53.1 2.4 884.6 146.2 41.9 6.4 5.9 1.0

PP 82.2 5.1 1811.2 278.5 57.0 7.4 5.9 1.3

Fir 89.0 6.1 6240.5 834.1 23.5 8.6 2.6 0.5

Table 2.7: Procedures of ASTM D1037-96 and GB13124-91

ASTM D1037-96 GB13124-91

1. Soaked in 49± 2°C water for 1 hour

2. Put in 93± 3°C water stream for 3 hours

3. Placed in -20± 2°C environmental for 20 hours

4. Dried up in 99± 2°C for 3 hours

5. Put in 93± 3°C water stream for 3 hours

6. Dried in 99± 2°C for 8 hours

7. Repeat steps 1 – 6 for 6 circles

8. Placed in room environment for 48 hours

(20°C and humidity 65± 1%)

1. Soaked in 63± 2°C water for 6

hours

2. Stored in -20°C for 6 hours

3. Dried in 63± 2°C for 6 hours

4. Stored in room temperature for

48 hours

Chapter 2

16

Table 2.8: Summary of compressive tests result under indoor aging effect

Condition Material Node location S (N/mm2) E (kN/mm

2)

ASTM D1037-

96

BP ¼ 44.2 9.2

BP ½ * *

BP None 42.2 5.1

PP ¼ 46.8 7.2

PP ½ * *

PP None * *

Fir None 16.7 0.8

GB13124-91

BP ¼ 50.4 11.3

BP ½ 40.7 6.9

BP None * *

PP ¼ 54.8 6.2

PP ½ 50.4 6.9

PP None 55.7 12.5

Fir None 14.8 0.8

*: Specimens failed during the aging process

Table 2.9: Mechanical properties of specimens under three points loading test

Material E (kN/mm2) S (N/mm

2)

Fir 6.3 44.6

PP 11.8 78.7

BP 20.0 80.7

Table 2.10: Results of the buckling tests

Sample

number Type

Initial

curvature

(x10-6

mm-1

)

Buckling

loading

(kN)

Theoretical buckling load (kN)

Simple - simple

support with

curvature

Simple - simple

support without

curvature

Clamp - clamp

support without

curvature

1 BP 5.3 11.4 3.6 3.9 15.4

2 BP 19 7.8 3.9 5 20.1

3 BP 20 15.6 5.3 6.3 25.4

4 BP 27 5.4 4.2 5.7 23

5 BP 46 9.4 5.7 8.8 35.1

6 BP 48 4.9 2.6 4.3 17

7 PP 24 36.7 12.6 17.3 69.2

8 PP 40 29.8 20.6 34.9 139.7

9 Fir 1.6 69.7 36.4 37 147.9

10 Fir 11 59.3 54.7 62.7 250.9

Chapter 2

17

20

30

40

50

60

70

80

90

400 600 800 1000 1200 1400 1600 1800 2000

Area (mm2)

Ultimate Load (kN)

Strength (N/mm2)

Figure 2.1(a): Relationship between mechanical properties and area of BP

30

35

40

45

50

55

60

65

70

75

80

40 45 50 55 60 65

Diameter (mm)

Ultimate Load (kN)

Strength (N/mm2)

Figure 2.1(b): Relationship between mechanical properties and diameter of BP

Chapter 2

18

0

200

400

600

800

1000

1200

1400

1600

1800

2000

40 45 50 55 60 65

Diameter (mm)

Are

a (m

m2)

Figure 2.1(c): Relationship between area and diameter of BP

0

2

4

6

8

10

12

40 45 50 55 60 65

Diameter (mm)

Youn

g's

modul

us

(kN

/mm

2)

Figure 2.1(d): Relationship between young’s modulus and diameter of BP

Chapter 2

19

30

50

70

90

110

130

150

170

500 1000 1500 2000 2500 3000 3500 4000

Area (mm2)

Ultimate Load (kN)

Strength (N/mm2)

Figure 2.2(a): Relationship between mechanical properties and area of PP

20

40

60

80

100

120

140

160

40 50 60 70 80 90 100 110

Diameter (mm)

Ultimate Loading (kN)

Strength (N/mm2)

Figure 2.2(b): Relationship between mechanical properties and diameter of PP

Chapter 2

20

500

1000

1500

2000

2500

3000

3500

4000

40 50 60 70 80 90 100 110

Diameter (mm)

Are

a (m

m2)

Figure 2.2(c): Relationship between area and diameter of PP

Relationship between Young's modulus and diameter of PP

0

1

2

3

4

5

6

7

8

9

10

40 50 60 70 80 90 100 110

Diameter (mm)

Young's

modulu

s (k

N/m

m 2

)

Figure 2.2(d): Relationship between young’s modulus and diameter of PP

Chapter 2

21

Strength of specimens under T=26oC

20

25

30

35

40

45

50

55

60

65

70

55% 60% 65% 70% 75% 80% 85% 90% 95% 100%

Relative Humidity (%)

Mea

n s

tren

gth

(N

/mm

2)

BP

PP

Fir

Figure 2.3(a): Strength of bamboos under different relative humidity levels

Young's modulus of specimens under T=26oC

2.00

3.00

4.00

5.00

6.00

7.00

8.00

9.00

55% 60% 65% 70% 75% 80% 85% 90% 95% 100%

Relative Humidity (%)

Young's

modulu

s

(kN

/mm

2)

BP

PP

Fir

Figure 2.3(b): Young’s modulus of bamboos under different relative humidity levels

Chapter 2

22

Reduction of strength of PP

0

10

20

30

40

50

60

70

80

90

100

0 2 4 6 8 10 12

Week

Red

ucti

on

%

Figure 2.4(a): Reduction of strength of PP during the aging process

Reduction of strength of BP

0

10

20

30

40

50

60

70

80

90

100

0 2 4 6 8 10 12

Week

Red

ucti

on

%

Figure 2.4(b): Reduction of strength of BP during the aging process

Chapter 2

23

Figure 2.5: Set up for the flexure Test

Figure 2.6(a): Set up for the buckling test

Figure 2.6(b): Specimen during loading

Chapter 2

24

Figure 2.6(c): End condition before testing

Figure 2.6(d): End condition after testing

Chapter 3

25

Chapter 3: Material properties of the fastening tie and scaffold intersection

3.1 Tensile tests for the fastening tie

The tensile strength of the fastening tie was tested using the MTS Universal Testing

machine 858. The most common type of lashings was used for the tests. The dimension

of the specimens was width = 6 mm, thickness = 1 mm and length = 100 mm. Two

pulling rates 8 mm/min and 80 mm/min were tested. Six specimens were tested for each

pulling rate to determine the Young’s modulus, the ultimate load and the strength of the

fastening tie. The test results are shown in Table 3.1. It is seen that a higher loading rate

tends to produce higher values for all properties. It is note that the strength of the

fastening tie is about three times of that of that of the bamboo, while its Young’s modulus

is about one third of that of the bamboo.

Chapter 3

26

3.2 Creep effect of the fastening tie

This experiment was to determine the creeping effect on the fastening tie. The machine

applied a load (50 N or 100 N) to the fastening tie within 5 sec and then kept the load

constant. The extension of the specimens was recorded to evaluate the creeping effect of

the fastening tie. Each test was carried out for a time duration of 30 hours to observe the

behavior of the fastening tie under tensile loading condition.

The results were shown in Figure 3.1. For a constant tensile load of 50 N applied on the

fastening tie, the initial elongation of the fastening tie is about 0.5 mm and steadily

reaches 3 mm after 15 hours. The creep strain induced by the 50 N load is about 3%. On

the other hand, for a constant tensile load of 100 N, the initial elongation is about 1 mm

and steadily reaches 4.7 mm after 25 hours. The creep strain induced by the 100 N load is

about 5%.

Chapter 3

27

3.3 Tensile tests for the fastening tie during fixing the joint

This test was to evaluate the tensile force inside the fastening tie during fixing the joints.

Strain gauge was attached to the tie before fixing the joint and the single channel portal

data logger took the reading before and after fixing the joint. The tensile force can be

obtained by multiply the strain with the axial rigidity (EA). A few tests were conducted

and the strains incurred due to the fastening were recorded.

It is found that the mean tensile force in the fastening tie during fixing the joints is about

23 N. This force is much less than the ultimate tensile force of 1135 N obtained in section

3.1, which indicates that fracture of fastening tie during fixing the joint is not likely. The

mean tensile force developed in the fastening tie however is expected to induce the creep

behavior with a creep strain between to be about 2 %. This creep strain is expected to

loosen the bamboo joint as time progresses.

Chapter 3

28

3.4 Scaffold intersection tests

The objective of the scaffold intersection tests was to obtain the impending friction

between the two bamboo components of a joint. The impending friction is defined as the

maximum friction before the two components slide relative to each other. This impending

friction will be used as an indicator for local instability/failure of a scaffold intersection.

Also obtained from the tests are the relative rotational stiffness for the two components of

the joint. This rotational stiffness will be used in the numerical finite element analysis

presented in Chapter 5. The most common type of joint is a single-side joint (see Figure

3.3). This type of joint possesses zero rotational stiffness if the two components rotate

toward the direction which is perpendicular to the direction of the fastening tie. Due to

this zero rotational stiffness, it is difficult to perform the intersection tests. It was decided

to use a cross type of joint as shown in Figure 3.3 for the test. The set-up to the two types

of test are shown in Figure 3.3. The impending friction forces obtained were divided by

two to approximate the impending friction forces of single-side joints. A total of four

types of intersection were tested: BP-PP, PP-Fir, BP-Fir and BP-BP. Four tests were

conducted for each type of intersection.

Table 3.2 summarizes the results of these intersection tests. It is seen that the impending

friction forces for these four types of intersection are in the order of 100 – 200 N and the

rotational stiffness are in the order of 200 – 300 N-m/rad. These results would be useful

in the safety analysis of the bamboo scaffoldings.

Chapter 3

29

Table 3.1: Summary of tensile test for fastening tie

Creep rate (mm/min)

E (kN/mm2) Ultimate loading (N) Strength (N/mm

2)

mean std mean std mean std

8 1.80 0.08 1135.0 36.1 189.2 6.0

80 2.28 0.14 1162.0 98.6 193.7 16.4

Table 3.2: Summary of the intersection tests

Impending friction (N)

Rotational stiffness (N m/rad)

Mean std mean std

BP-PP 170 11.3 262.6 6.3

PP-Fir 277 49 305.8 35.5

BP-Fir 94.7 27.2 200.3 34.8

BP-BP 151.3 35.6 220.1 25.4

Chapter 3

30

Creep effect under different loads

0

1

2

3

4

5

6

0 5 10 15 20 25 30

Time (hours)

Elo

ngat

ion (

mm

)

.

50N load

100N load

Figure 3.1: Results of the creep effect of the fastening tie

Figure 3.2: Single channel portable data logger

Chapter 3

31

k = 0

Single-side joint Cross joint

clamped

Load cell force

LVDT

force

Determination of impending friction Determination of rotational stiffness

Figure 3.3: Set-up of intersection tests

Figure 3.4: Determining impending friction force of a BP-BP joint

Chapter 4

32

Chapter 4: Experiment on the full-scale scaffolding

4.1 Aim of the full-scale scaffolding experiment

The objective of the full-scale scaffolding tests is to experimentally validate the safety of

scaffoldings under uniform distributed loads and drop loads.

4.2 Description of the full-scale scaffolding

The scaffolding that was used for testing was a double-layer scaffolding with dimensions

4.98 m x 3.6 m x 0.6 m (height x length x width). Each layer had seven standards, two of

which at the outmost were PP, the middle standard was Fir and the remaining four

standards were BP. The scaffolding had two board platforms at the height of 1.3 m and 4

m, respectively. It was X-braced by two PP bamboos at the back side and two BP

bamboos at the front sides and connected to a rigid steel frame at one side. Photos

showing the scaffolding can be found in Figure 4.1-4.3. This scaffolding was constructed

by Mr. B.Y. Poon who has over 25 years experience in bamboo construction and is a

certified bamboo scaffolding worker.

4.3 Test equipment

The equipment used in the tests included strain gauges (see Figure 4.4(a)), tensile jack

(see Figure 4.4(b)), data logger and computer (see Figure 4.4(c)) and load cell (Figure

4.4(d)). A total of 49 strain gauges were installed at various locations of the standards as

shown in Figure 4.5 and 4.6(a)-(b).

Chapter 4

33

4.4 Uniform distributed load tests

4.4.1 Test setup

In the Code of Practice for Bamboo Scaffolding Safety issued by the Labour Department,

bamboo scaffolding should be designed to withstand a uniform distributed load (UDL) of

3 kN/m2 in masonry or special duty. To create the UDL condition in the laboratory, a

loading setup as shown in Figure 4.6 was used. The load generated by the tensile jack

was applied on two I-beams which were roller-supported on four I-beams. Two rigid U

beams were placed underneath these four I-beams and transmitted the force to the

platform of scaffolding. The tests were separated into the following seven cases:

(1) Loads applied at the bottom platform

a. 5 kN jack force (UDL = 2.67 kN/m2)

b. 10 kN jack force (UDL = 5.35 kN/m2)

c. 15 kN jack force (UDL = 8.02 kN/m2)

(2) Loads applied at the upper platform



(3) Loads applied at both platforms



For each case, at least 5 independent tests were conducted. The mean values and the

standard deviations of the column strains close to the bottom platform were computed

based on the measured strains. The mean values and the standard deviations of the

standard forces were then calculated by multiplying the strain valves with the averaged

bamboo cross sectional rigidities obtained in Chapter 2.

Chapter 4

34

4.4.2 Results of uniform distributed load tests

Table 4.1(a)-(g) show the results of these UDL tests, where the results of UDL acting at

the bottom platform, upper platform and both platforms are shown in Table 4.1(a)-(c),

4.1(d)-(e) and 4.1(f)-(g), respectively. From these results, the following observations can

be seen.

(1) The forces carried by the PP (standards 1 and 7) and the Fir (standard 4) are

larger than those carried by the BP (standards 2,3,5 and 6).

(2) For the UDL acting at the same platform, the standard forces are

approximately linearly proportional to the magnitudes of the UDL.

(3) For the UDL acting at both platforms, the standard forces are approximately

equal to the superposition of the standard forces obtained from the UDL acting

at the bottom and at the upper platform respectively.

(4) The standard deviations of the measured strain are quite small which suggests

that the test results are quite consistent.

(5) There does not appear to be any notable deformation nor any sign of damage in

any part of the scaffolding for UDL up to 5.35 kN/m2 (or jack force up to 10

kN). When the 15 kN jack force (or UDL = 8.02 kN/m2) was applied at the

bottom platform, some noises were heard from the scaffolding which however

did not produce any notable deformation nor damage once the force was

released.

(6) The compressive stress caused by the standard forces is much less than the

compressive strength found in Section 2.1. It indicated that the member would

not fail in compressive failure under this loading.

(7) The simple-simple support condition of a long member provided a lower

bound value of the buckling load which has shown in Section 2.5. The

calculated buckling load for a PP bamboo with 0.6 m long is 241 kN which is

much greater than the force carried by the standards.

Chapter 4

35

4.5 Drop tests

4.5.1 Test setup

The tests were divided into two parts: 1) Drop without any load on the scaffold and 2)

Drop with an UDL of 3 kN/m2 on each of the two platforms. Table 4.2 summarizes the

number and the location of tests conducted.

1) Drop without any other load on the scaffold

A sand bag was used to simulate a person falling from a height. The test procedure

followed the BS EN 364:1993 standard [10]. The sand bag was attached to a safety belt

with length of 1.2 m. The other end of the safety belt was attached to several locations on

the scaffoldings (see Figure 4.11). At each location, five drop tests were performed in

order to obtain the mean and the standard deviation of the standard forces. During the

tests, the sand bag was lifted up by a rope to 1.2 m above the test location before released.

The maximum clearance between the sand bag and the scaffold is 300 mm. The record

rate of the data logger was set to be 50 Hz to ensure the sudden change of strain due to

the drop could be recorded. Two sand bags with weight of 20 kg and 40 kg respectively

were used for the tests.

2) Drop with an UDL of 3 kN/m2 on each of the two platforms.

The test procedure was similar to the previous one except that an UDL of 3 kN/m2 was

applied on each of the two platforms. It was used to simulate the worse situation that a

person fell from a height when the scaffold was under the design load. A sand bag with

weight of 20kg was used for the tests.

Chapter 4

36

4.5.2 Results of the drop tests

Table 4.3-4.4 show the results of these drop tests, where the results of drop tests of 20 kg

sand bag without UDL is shown in Table 4.3(a)-(b) and the results of drop tests of 20 kg

sand bag with UDL of 3 kN/m2 is shown in Table 4.4(a)-(b). From these results, the

following observations can be seen.

(1) The bending stresses of all the bamboos are much lower than the flexural

strength found in Section 2.4. The flexural strength is nearly a hundred times

larger than the bending stresses found in the drop tests.

(2) The axial forces of the standard in the drop tests are not significant. Most of

the standard are carried almost zero axial forces.

(3) In Table 4.3(b), it can be seen that the bending stress are usually concentrated

at the dropped location and the neighborhood locations in the drop tests

without UDL. The dropped location was usually occurred the highest bending

stress.

(4) The drop of the 40 kg sand bag at the location 8 causes a great deflection at the

joint. Figure 4.14 and 4.15 showed the difference of the joint allocation before

and after one drop. The displacement before and after the drop is nearly 25 mm.

Other than the tied location, the neighborhood joint has recorded displacement.

Figure 4.16 and 4.17 showed the displacement of the joint at location 9. The

difference of the displacement is 20 mm.

(5) When the 40kg sand bag was dropped at location 9, the ledger was failure near

the joint (see Figure 4.18). It showed that the ledgers are probably cannot

afford such an impact load.

(6) A sand bag with 60 kg was tested. The sand bag was dropped at the location 10.

The member is bent significantly after the drop (see Figure 4.21). It showed

that the ledgers are not suitable for fixing the safety belt.

Chapter 4

37

Table 4.1(a): Results of the tests under 5 kN load act at the bottom platform

Strain (x10-6

) Force (kN)

standard Mean Std Mean Std

front

1 (PP) -19.58 0.38 -0.26 0.01

2 (BP) -24.42 1.28 -0.12 0.01

3 (BP) -16.58 0.80 -0.08 0.00

4 (Fir) -24.67 0.76 -0.37 0.01

5 (BP) -5.08 1.28 -0.03 0.01

6 (BP) -21.50 3.97 -0.11 0.02

7 (PP) -20.00 2.10 -0.31 0.03

back

1 (PP) -46.83 2.02 -0.62 0.03

2 (BP) -17.67 1.15 -0.17 0.15

3 (BP) -11.58 1.01 -0.13 0.12

4 (Fir) -26.42 5.14 -0.17 0.47

5 (BP) 1.92 0.80 0.02 0.01

6 (BP) -5.00 2.65 -0.02 0.01

7 (PP) -28.08 2.18 -0.37 0.03

Table 4.1(b): Results of the tests under 10 kN load act at the bottom platform

Strain (x10-6

) Force (kN)


front

1 (PP) -36.17 2.25 -0.48 0.03

2 (BP) -58.17 7.77 -0.29 0.04

3 (BP) -35.50 2.78 -0.18 0.01

4 (Fir) -47.83 2.25 -0.72 0.03

5 (BP) -13.33 6.21 -0.07 0.03

6 (BP) -48.67 2.93 -0.24 0.01

7 (PP) -43.00 3.17 -0.57 0.04

back

1 (PP) -86.67 3.51 -1.15 0.05

2 (BP) -37.17 1.04 -0.18 0.01

3 (BP) -21.67 5.48 -0.11 0.03

4 (Fir) -63.00 5.63 -0.95 0.09

5 (BP) 6.83 2.08 0.03 0.01

6 (BP) -10.17 2.57 -0.05 0.01

7 (PP) -47.17 6.45 -0.62 0.09

Chapter 4

38

Table 4.1(c): Results of the tests under 15 kN load act at the bottom platform

Strain (x10-6

) Force (kN)


front

1 (PP) -59 2.9 -0.78 0.04

2 (BP) -85.2 6.2 -0.42 0.03

3 (BP) -39 5.4 -0.19 0.03

4 (Fir) -66.2 4.3 -1.00 0.07

5 (BP) -20.4 7.2 -0.10 0.04

6 (BP) -74.3 3.8 -0.37 0.02

7 (PP) -64 4.9 -0.84 0.07

back

1 (PP) -124 8.4 -1.64 0.11

2 (BP) -57 4.0 -0.28 0.02

3 (BP) -32.7 4.8 -0.16 0.02

4 (Fir) -83.2 10.6 -1.25 0.16

5 (BP) 7.3 4.9 0.04 0.02

6 (BP) -12.2 4.6 -0.06 0.02

7 (PP) -72 8.1 -0.95 0.11

Table 4.1(d): Results of the tests under 5 kN load act at the upper platform

Strain (x10-6

) Force (kN)


front

1 (PP) -13.50 2.0 -0.18 0.03

2 (BP) -23.83 5.7 -0.12 0.03

3 (BP) -22.00 3.5 -0.18 0.11

4 (Fir) -21.17 1.0 -0.32 0.02

5 (BP) -13.17 1.5 -0.07 0.01

6 (BP) -23.00 4.3 -0.11 0.02

7 (PP) -12.40 1.2 -0.15 0.02

back

1 (PP) -19.17 5.0 -0.25 0.07

2 (BP) -11.67 4.5 -0.06 0.02

3 (BP) -9.17 3.5 -0.05 0.02

4 (Fir) -34.00 2.3 -0.51 0.03

5 (BP) -31.17 2.3 -0.15 0.01

6 (BP) -98.67 3.5 -0.49 0.02

7 (PP) -7.50 5.3 -0.10 0.07

Chapter 4

39

Table 4.1(e): Results of the tests under 10 kN load act at the upper platform

Strain (x10-6

) Force (kN)


front

1 (PP) -25.50 2.0 -0.34 0.03

2 (BP) -49.83 3.7 -0.25 0.02

3 (BP) -42.83 2.3 -0.26 0.07

4 (Fir) -44.33 2.8 -0.67 0.04

5 (BP) -24.50 0.5 -0.12 0.00

6 (BP) -44.33 5.8 -0.22 0.03

7 (PP) -25.04 4.1 -0.35 0.04

back

1 (PP) -13.50 31.7 -0.18 0.42

2 (BP) -33.00 3.9 -0.16 0.02

3 (BP) -29.83 2.3 -0.15 0.01

4 (Fir) -66.50 7.3 -1.00 0.11

5 (BP) -58.67 3.2 -0.29 0.02

6 (BP) -166.83 3.5 -0.83 0.02

7 (PP) -18.33 10.6 -0.24 0.14

Table 4.1(f): Results of the tests under 5 kN loads act at both platforms

Strain (x10-6

) Force (kN)


front

1 (PP) -38.17 3.06 -0.50 0.04

2 (BP) -54.83 3.06 -0.27 0.02

3 (BP) -43.50 4.58 -0.22 0.02

4 (Fir) -44.33 1.04 -0.67 0.02

5 (BP) -21.50 0.87 -0.11 0.00

6 (BP) -44.00 6.14 -0.23 0.00

7 (PP) -33.33 2.71 -0.43 0.03

back

1 (PP) -43.33 17.90 -0.81 0.03

2 (BP) -38.00 3.97 -0.20 0.04

3 (BP) -26.00 3.00 -0.13 0.03

4 (Fir) -35.00 15.55 -0.63 0.10

5 (BP) -36.33 1.76 -0.18 0.01

6 (BP) -69.33 19.81 -0.51 0.11

7 (PP) -34.33 3.79 -0.45 0.05

Chapter 4

40

Table 4.1(g): Results of the tests under 10 kN loads act at both platforms

Strain (x10-6

) Force (kN)


front

1 (PP) -71.00 2.18 -0.94 0.03

2 (BP) -113.17 6.29 -0.56 0.03

3 (BP) -78.83 7.52 -0.39 0.04

4 (Fir) -86.00 5.68 -1.30 0.09

5 (BP) -40.83 2.02 -0.20 0.01

6 (BP) -86.00 10.48 -0.46 0.00

7 (PP) -65.1 2.37 -0.89 0.03

back

1 (PP) -43.33 17.90 -1.57 0.08

2 (BP) -38.00 3.97 -0.39 0.03

3 (BP) -26.00 3.00 -0.31 0.02

4 (Fir) -35.00 15.55 -1.25 0.20

5 (BP) -36.33 1.76 -0.32 0.02

6 (BP) -69.33 19.81 -0.83 0.07

7 (PP) -34.33 3.79 -0.92 0.03

Table 4.2: Number of tests at each location

Location

Tests

20kg sand bag

without UDL

20kg sand bag

with UDL 3kN/m2

40kg sand bag

without UDL

60kg sand bag

without UDL

1 5 times 5 times

2 5 times 5 times

3 5 times 5 times

4 5 times 5 times

5 5 times 5 times

6 5 times 5 times

7 5 times 5 times

8 5 times

9 1 times (Member

failed)

10 1 times (Member

failed)

Chapter 4

41

Table 4.3(a): Bending strain (x10-6

) under the impact of the 20 kg sand bag without UDL

standard Location 1 Location 2 Location 3 Location 4 Location 5 Location 6 Location 7

front

1 (PP) 18.42 36.85 18.43 0.00 36.85 0.00 27.64

2 (BP) 27.64 36.85 9.21 9.21 27.64 18.43 27.64

3 (BP) 27.64 46.06 18.43 9.21 46.06 9.21 18.43

4 (Fir) 0.00 0.00 9.21 92.13 27.64 0.00 27.64

5 (BP) 9.21 9.21 9.21 27.64 9.21 0.00 18.42

6 (BP) 0.00 55.28 18.43 18.43 9.21 9.21 9.21

7 (PP) 9.21 0.00 0.00 18.43 18.43 0.00 9.21

back

1 (PP) 36.85 36.85 0.00 9.21 0.00 0.00 9.21

2 (BP) 9.21 36.85 9.21 18.43 18.42 9.21 9.21

3 (BP) 18.42 9.21 55.28 9.21 46.06 9.21 18.43

4 (Fir) 9.21 18.43 73.71 175.05 9.21 0.00 9.21

5 (BP) 9.21 0.00 0.00 0.00 27.64 36.85 9.21

6 (BP) 9.21 9.21 9.21 18.43 27.64 110.59 36.85

7 (PP) 36.86 9.22 18.43 9.21 46.06 9.21 46.06

Table 4.3(b): Bending stress (N/mm2) under the impact of the 20 kg sand bag without

UDL


Front

1 (PP) 0.11 0.22 -0.11 0.00 -0.22 0.00 -0.17

2 (BP) 0.19 0.26 -0.06 0.06 -0.19 0.13 -0.19

3 (BP) -0.19 -0.32 0.13 0.06 0.32 0.06 0.13

4 (Fir) 0.00 0.00 0.03 0.28 -0.08 0.00 0.08

5 (BP) -0.06 0.06 -0.06 0.19 -0.06 0.00 -0.13

6 (BP) 0.00 -0.39 -0.13 0.13 0.06 0.06 -0.06

7 (PP) 0.06 0.00 0.00 0.11 -0.11 0.00 -0.06

Back

1 (PP) 0.22 0.22 0.00 0.06 0.00 0.00 0.06

2 (BP) 0.06 0.26 0.06 0.13 0.13 0.06 0.06

3 (BP) -0.13 -0.06 0.39 0.06 0.32 0.06 0.13

4 (Fir) 0.03 0.06 0.22 0.53 -0.03 0.00 0.03

5 (BP) -0.06 0.00 0.00 0.00 -0.19 -0.26 0.06

6 (BP) -0.06 0.06 -0.06 0.13 0.19 -0.77 -0.26

7 (PP) 0.22 0.06 -0.11 0.06 -0.28 0.06 -0.28

Chapter 4

42

Table 4.4(a): Bending strain (x10-6

) under the impact of the 20 kg sand bag with UDL

of 3 kN/m2


Front

1 (PP) -4.22 9.21 -51.07 0.00 -73.69 -32.64 -50.28

2 (BP) 0.21 18.42 -18.64 0.00 -73.69 9.00 -55.07

3 (BP) 3.00 -18.42 43.07 -27.63 -92.12 33.85 49.07

4 (Fir) -32.64 -27.64 -13.43 -9.21 9.21 -22.64 -5.00

5 (BP) -46.28 -36.85 -64.28 9.22 9.21 -55.07 -55.49

6 (BP) -25.03 -82.91 -48.66 18.43 27.64 -21.02 -34.25

7 (PP) 21.43 9.21 6.21 0.00 -9.21 6.21 3.00

Back

1 (PP) 67.89 64.49 24.24 18.43 -9.21 24.24 40.25

2 (BP) 68.29 92.12 60.69 9.21 -36.85 60.69 68.29

3 (BP) 31.84 36.86 97.14 27.64 -64.48 51.08 68.69

4 (Fir) 4.60 9.21 59.90 9.24 9.21 -13.81 4.60

5 (BP) -31.85 -27.64 -32.64 46.07 36.85 -69.49 -13.43

6 (BP) -68.32 -55.29 -79.11 -46.06 -9.21 -180.50 -95.95

7 (PP) 15.02 -18.42 -51.86 18.43 101.36 -24.22 -67.90

Table 4.4(b): Bending stress (N/mm2) under the impact of the 20 kg sand bag with UDL

of 3 kN/m2


front

1 (PP) -0.03 0.06 -0.31 0.00 -0.44 -0.20 -0.30

2 (BP) 0.00 0.13 -0.13 0.00 -0.52 0.06 -0.39

3 (BP) 0.02 -0.13 0.30 -0.19 -0.64 0.24 0.34

4 (Fir) -0.10 -0.08 -0.04 -0.03 0.03 -0.07 -0.02

5 (BP) -0.32 -0.26 -0.45 0.06 0.06 -0.39 -0.39

6 (BP) -0.18 -0.58 -0.34 0.13 0.19 -0.15 -0.24

7 (PP) 0.13 0.06 0.04 0.00 -0.06 0.04 0.02

back

1 (PP) 0.41 0.39 0.15 0.11 -0.06 0.15 0.24

2 (BP) 0.48 0.64 0.42 0.06 -0.26 0.42 0.48

3 (BP) 0.22 0.26 0.68 0.19 -0.45 0.36 0.48

4 (Fir) 0.01 0.03 0.18 0.03 0.03 -0.04 0.01

5 (BP) -0.22 -0.19 -0.23 0.32 0.26 -0.49 -0.09

6 (BP) -0.48 -0.39 -0.55 -0.32 -0.06 -1.26 -0.67

7 (PP) 0.09 -0.11 -0.31 0.11 0.61 -0.15 -0.41

Chapter 4

43

Figure 4.1: Front view of the scaffold

Figure 4.2: Side view of the scaffold

Chapter 4

44

Figure 4.3: Dimensions of the scaffold

Figure 4.4(a): Strain gauge

Figure 4.4(b): Tensile jacks

Chapter 4

45

Figure 4.4(c): Data logger and computer Figure 4.4(d): Load cell

Figure 4.5: Strain gauge attach on PP

Chapter 4

46

Figure 4.6(a): Locations of strain gauges attached on the standard at the front side

Chapter 4

47

Figure 4.6(b): The location of sensors attached on the standard at the back side

Chapter 4

48

Figure 4.7(a): Front view of the loading setup

I-beams

U-beams

Loading

Figure 4.7(b): Side view of loading setup

Figure 4.7(c): The loading Setup

U-beam

I-beam

Loading

Chapter 4

49

Figure 4.8: Loading the tensile jack during the tests

Force distribution of the column under load 15kN

-1.8

-1.6

-1.4

-1.2

-1.0

-0.8

-0.6

-0.4

-0.2

0.0

0.2

1 2 3 4 5 6 7

Column

Forc

e (k

N)

Front layer

Back layer

Figure 4.9: Results of uniform distributed load tests

Chapter 4

50

Force carried by the center member at the front face

-1.8

-1.6

-1.4

-1.2

-1

-0.8

-0.6

-0.4

-0.2

0

0.2

-2 0 2 4 6 8 10 12 14 16

Applied loading (kN)

Me

mb

er

forc

es

(k

N)

Loading at bottom platform

Loading at upper platform

Loading at both platforms

Figure 4.10: Member forces of the center member at the front face under UDL

Figure 4.11: Drop test locations

platform

Chapter 4

51

Figure 4.12: Before the sand bag dropped

Recorded strains during the drop at the location 7

-150

-100

-50

0

50

100

150

0 1 2 3 4 5 6 7 8 9 10

Time (sec)

Str

ain

(x10-6

)

Figure 4.13: Recorded strains of the drop test

Chapter 4

52

Figure 4.14: Before the drop of the 40 kg sand bag

Figure 4.15: After the drop of the 40 kg sand bag

Chapter 4

53

Figure 4.16: Joint condition of location 9 before the drop of 40 kg sand bag at center

Figure 4.17: Joint condition of location 9 after the drop of 40 kg sand bag at center

Chapter 4

54

Figure 4.18: The member was failed at the location 9

Figure 4.19: Another view to see the failure at the location 9

Chapter 4

55

Figure 4.20: The safety belt fix at the location 10

Figure 4.21: Member failure during the drop of 60 kg sand bag at location 10

Chapter 5

56

Chapter 5: Comparison of the experiment and the finite element modeling

5.1 Description of the finite element modeling of scaffolding

In this section, the finite element program SAP2000 was used to model the structural

behavior of bamboo scaffoldings under the UDL and the drop loads. In the previous

chapter, it was found that the standard forces were approximately linear to the magnitude

of the applied UDL. This is a good indication that the structural behavior of bamboo

scaffolding is approximately linear and thus linear elements can be used to model the

scaffolding. In the analysis, we used linear orthotropic frame elements to model the

bamboo components. Nonlinear hook elements were however used to model the bamboo

intersections due to the apparent bilinear stiffness behavior of the joints. The dimensions

of the finite element model were set to meet as accurately as possible with those

measured from the scaffolding model in the laboratory. The mean material properties that

obtained from Chapter 2 were used in the analysis. The support conditions for all the

standards were assumed to be clamped. The finite element model is illustrated in Figure

5.1.

Chapter 5

57

5.2 Comparison of the results between the experiment and the finite

element model

5.2.1 Comparison of the uniform distributed load tests

Figure 5.2 shows how the UDL are added onto the finite element model. Since the

behavior of scaffolding is approximately linear, so only one loading case is shown here.

The UDL was assumed to act at the bottom platform only with a magnitude of 7.14

kN/m2 (corresponding to a jack force of 15 kN). Table 5.1 shows the standard force

comparison between the finite element analysis results and those obtained from the

measurement. Based on the comparison, the following observations can be made:

(1) Both results indicate that the PP and the Fir carry more loads than the BP.

(2) The force difference between the finite element analysis and the experiment is

smaller for the PP and the Fir. Roughly, the difference ranges between 10 to

20%.

(3) Both results indicate that the standards of the scaffolding would not fail even

when the UDL exceeds two times of the design value.

5.2.2 Comparison of the drop tests

To compare the results of drop tests, the forces produced by the free drop of 20 kg, 40 kg

and 60 kg sand bags were first measured in the laboratory. The safety belt was attached to

an aluminum plate which was attached with two strain gauges for strain measurement

during the free drop. The set up of is shown in Figure 5.3(a). The cable force was then

obtained by multiplying the strain values by axial rigidity of the aluminum plates. Table

5.2 and Figure 5.4 shows the resulting force caused by the free drop of 20 kg, 40 kg and

60 kg sand bag. It is seen that the maximum drop force can reach as high as 6000 N for a

60 kg drop weight. Note that the mean drop force of 2550 N caused by a 20 kg drop

weight is already higher than the impending friction forces obtained in Chapter 3

(between 100 to 300 N). This suggests that slippage of the bamboo joint where the safety

belt attached is almost unavoidable. This explains the joint slippage that we observed

during the drop tests.

Chapter 5

58

In the finite element analysis, the mean drop force found in the free drop tests was

assumed to act on the model in a static fashion. The bending moments at the strain gauge

locations were calculated and compared with these obtained from the experiments. Table

5.3(a) and (b) show two of these comparisons where the 20 kg sand bag would drop from

location 3 and 4, respectively. From these results, the following observations can be seen:

(1) Although differences between the two results are seen, the magnitudes of

bending moments are in the same order.

(2) It is again seen that the moments exerted on the PP and Fir are higher than

those on the BP, except for the BP where the sand bag is directly attached to.

(3) These bending moments do not appear to damage these standards, nor to the

overall integrity of the scaffolding.

(4) The damaging effect due to the free fall of a sand bag appears to be more of a

local nature, which might result in the slippage of joints and/or fracture of

horizon ledger. This ledger fracture was seen in the laboratory when the weight

of the sand bag increases beyond 40 kg.

More detailed analyses on the reliability and safety of scaffolding are carried out in the

next session.

Chapter 5

59

5.3 Reliability analysis of the full-scale scaffolding

In this study, the safety and reliability of a bamboo scaffolding is determined by a

quantitative number called “safety index”. This safety index is defined as,

valueanalyzedor Measured

bamboo of strength sticCharacteri index Safety

When the safety index is smaller than 1, which means the measured or analyzed value

exceeds the characteristic strength of bamboo and hence implies that the scaffolding is

damaged. On the hand, a larger safety index (larger than 1) represents a safer scaffolding.

5.3.1 Analysis of the uniform distributed load

Under a uniform distributed load, the load would first be transferred from the working

platform to the horizontal transoms and ledgers, and finally to the vertical standards. To

analyze the reliability of the scaffolding under a uniform distributed load, two failure

cases were studied. For case one, the scaffold was assumed to fail at one of the transoms.

For case two, the scaffold was assumed to fail at one of the standards.

Case 1 (failure at the transom):

Transoms are connected to the ledgers by the fastening ties. The fastening tie

fixes the position of the transoms relative to the ledgers but could not provide

enough resistance to rotation at the ends of the transoms. As a result, the transom

can be modeled approximately as a simply-supported beam as shown in Figure

5.5.

To study the reliability of the transoms, it is necessary to calculate the loads

carried by these transoms. These loads can be modeled as distributed loads with

magnitudes of the UDL times their corresponding tributary widths. For examples

in Figure 4.3, the transom that carries the maximum load is the one that connected

to the 3rd

standard. The distributed load that acts on their transom is 0.65 x UDL.

Chapter 5

60

The mean flexural strength of transoms (usually BP) is 80.7 N/mm2 and its

standard deviation is 19.3 N/mm2 as obtained in Chapter 2. The lower bound of

the flexural strength with 95% probability of occurrence is computed to be 49

N/mm2 based on the gaussian assumption. Table 5.4 shows the reliability of the

3rd

transom under different magnitudes of UDL. It is seen that under the design

UDL (3 kN/m2), the safety indexes are 7 and 4 if the mean strength and the lower

95% strength are used respectively.

Chapter 5

61

Case 2 (failure at the standard):

Table 5.5 shows the standard forces induced by the design UDL of 3 kN/m2

acting at the lower platform. Two types of failure are possible: buckling failure

and compressive strength failure. The theoretical buckling loads for the BP, PP

and Fir with a length of 0.65 m and under simply support condition without initial

curvature are: 29.6 kN, 154.7 kN and 108.8 kN respectively (from Section 2.5).

The safety indexes for the standards under buckling condition are computed and

listed in Table 5.5. It is seen that the smallest safety index is 68.8 which occurs at

the 2nd

and 3rd

BP standards. On the other hand, the compressive strengths for the

BP, PP and Fir are 57 N/mm2, 61 N/mm

2 and 26 N/mm

2, respectively. The safety

indexes for the standards under compressive strength condition are again

computed and listed in Table 5.5. It is seen that the smallest safety index is 93.7

which again occurs at the 2nd

and the 3rd

BP standards.

5.3.2 Analysis of the drop load

When an object is attached the bamboo joint, the load induced by the free fall of the

object is first carried mostly by the ledger at the joint. The force is then transmitted to the

standards via the fastening ties. To analyze the reliability of the scaffolding under a drop

load, two failure cases were studied. For case one, the scaffold was assumed to fail at the

ledger. For case two, the scaffold was assumed to fail at the standard.

Case 1 (failure at the ledger):

As obtained in Chapter 3, the impending friction forces for the joints range

between 100 to 300 N. These values are much smaller than the maximum drop

force caused by a 20 kg weight (or more). So it can be concluded that slippage of

the fastening tie at the joints would occur. The slippage of the fastening tie would

then provide a kinetic friction force that reduces some amount of drop force

acting on the ledger. As a conservative measure, assume that the kinetic friction

force is ignored in the following analysis. Figure 5.6 shows a simple model to

simulate a ledger under drop force. It is expected that the support conditions of

Chapter 5

62

the ledger would be between simply support and clamped support (but more close

to the clamped support). The mean flexural strength of ledger (usually BP) is 80.7

N/mm2 and its standard deviation is 19.3 N/mm

2 as obtained in Chapter 2. The

lower bound of the flexural strength with 95% probability of occurrence is

computed to be 49 N/mm2 based on the gaussian assumption. The length between

two standards is 0.6 m. Tables 5.6 and 5.7 show the reliability of the ledger under

different drop weights for the simply support and for the clamped support,

respectively. It is seen that the ledger would fail even under the free drop of a 20

kg weight if the boundary condition is simply supported. On the other hand, if the

boundary condition is clamped supported, the ledger would fail on the average

when the drop weight reaches 60 kg. Since the actual boundary condition of the

ledger is closer to the clamped condition, so it can be concluded that the ledger

could fail when the drop weight exceeds 40 kg.


For the drop test, the weight is always drops at the backside. Table 5.8 shows the

standard forces induced by free drop of a 60 kg weight (maximum drop force = 5

kN). Two types of failure are possible: buckling failure and compressive strength

failure. The theoretical buckling loads for the BP, PP and Fir with a length of

0.65m and under simply support condition without initial curvature are 29.6 kN,

154.7 kN and 108.8 kN, respectively (from Section 2.5). The safety indexes for

the standards under buckling condition are computed and listed in Table 5.8. It is

seen that the smallest safety index is 27.7 which occurs at the 3rd

BP standard. On

the other hand, the compressive strengths for the BP, PP and Fir are 57 N/mm2, 61

N/mm2 and 26 N/mm

2, respectively. The safety indexes for the standards under

compressive strength condition are again computed and listed in Table 5.8. It is

seen that the smallest safety index is 37.7 which again occurs at the 3rd

BP

standard.

Based on the UDL and the drop load analyses, the following conclusion can be made:

Chapter 5

63

(1) Under the design UDL, both the transoms and standards are not expected to

fail. Their safety indexes are between 4 to 7 for the transoms and between 70

to 90 for the standards.

(2) Under the drop force, the fastening tie, that joints the horizontal ledger to the

vertical standard, is expected to slip even under the free drop of a 20 kg weight.

Also the horizontal ledger is expected to fail under the drop force caused by an

object weights between 40 to 60 kg.

(3) The damage caused by the drop force is quite local. Although the ledger may

fail under the drop force, the standards on the other hand appear to be quite

safe even under a 60 kg free drop.

Chapter 5

64

Table 5.1: Comparison between the finite element and the experiment results (UDL =

8.02 kN/m2)

Back FEM

model (kN)

Experiment (kN)

Difference Front FEM

model (kN)

Experiment (kN)

Difference

1 (PP) -1.23 -1.64 0.41 1 (PP) -0.73 -0.78 0.05

2 (BP) -0.75 -0.28 -0.47 2 (BP) -0.71 -0.42 -0.29

3 (BP) -0.74 -0.16 -0.58 3 (BP) -0.68 -0.19 -0.49

4 (Fir) -1.38 -1.25 -0.13 4 (Fir) -1.22 -1.00 -0.22

5 (BP) -0.57 0.04 -0.61 5 (BP) -0.48 -0.10 -0.38

6 (BP) -0.51 -0.06 -0.45 6 (BP) -0.47 -0.37 -0.1

7 (PP) -0.97 -0.95 -0.02 7 (PP) -1.09 -0.84 -0.25

Table 5.2: Maximum drop force due to free fall of sand bags

Weight (kg) Number of

tests

Drop force (kN)

Mean std

20 11 2.55 0.32

40 7 3.85 0.85

60 9 4.90 0.72

Table 5.3(a): Results of the drop test at location 3

Back FEM

model (N-m)

Experiment (N-m)


model (N-m)

Experiment (N-m)

Difference

1 (PP) 2.32 0.00 2.32 1 (PP) 1.74 3.80 -2.06

2 (BP) 1.41 0.47 0.94 2 (BP) 0.92 0.47 0.45

3 (BP) 5.19 2.80 2.39 3 (BP) 1.11 0.93 0.18

4 (Fir) 10.05 11.12 -1.07 4 (Fir) 4.11 1.39 2.72

5 (BP) 1.05 0.00 1.05 5 (BP) 0.84 0.47 0.37

6 (BP) 0.91 0.47 0.44 6 (BP) 0.73 0.93 -0.20

7 (PP) 1.85 3.80 -1.95 7 (PP) 1.65 0.00 1.65

Table 5.3(b): Results of the drop test at location 4

Back FEM

model (N-m)

Experiment (N-m)


model (N-m)

Experiment (N-m)

Difference

1 (PP) 1.70 1.90 -0.20 1 (PP) 1.50 0.00 1.50

2 (BP) 1.09 0.93 0.16 2 (BP) 0.91 0.47 0.44

3 (BP) 1.20 0.47 0.73 3 (BP) 0.95 0.47 0.48

4 (Fir) 18.30 26.40 -8.10 4 (Fir) 9.21 13.89 -4.68

5 (BP) 1.16 0.00 1.16 5 (BP) 1.04 1.40 -0.36

6 (BP) 1.12 0.93 0.19 6 (BP) 1.05 0.93 0.12

7 (PP) 2.10 1.90 0.20 7 (PP) 1.80 3.80 -2.00

Chapter 5

65

Table 5.4: Reliability of the transom under UDL

UDL (kN/m

2)

Maximum stress in the

transom (N/mm

2)

Mean strength = 80.7N/mm

2

Lower 95% strength = 49N/mm

2

> mean Safety index > 95% Safety index

3 12.1 No 7.0 No 4.0

6 24.2 No 3.5 No 2.0

9 36.3 No 2.3 No 1.3

12 48.4 No 1.8 No 1.0

15 60.6 No 1.4 Yes < 1.0

18 72.7 No 1.2 Yes < 1.0

21 84.8 Yes < 1.0 Yes < 1.0

Table 5.5: Loading of the standard under a UDL 3 kN/m2 applied at the bottom platform

Standard force (kN)

Safety index

Buckling Compressive

strength

Front standard

1 (PP) 0.41 377.3 303.8

2 (BP) 0.41 72.2 98.3

3 (BP) 0.39 75.9 103.3

4 (Fir) 0.70 155.4 162.8

5 (BP) 0.37 80.0 108.9

6 (BP) 0.33 89.7 122.1

7 (PP) 0.63 245.6 197.7

Back standard

1 (PP) 0.70 221.0 177.9

2 (BP) 0.43 68.8 93.7

3 (BP) 0.43 68.8 93.7

4 (Fir) 0.79 137.7 144.3

5 (BP) 0.28 105.7 143.9

6 (BP) 0.27 109.6 149.2

7 (PP) 0.55 281.3 226.5

Table 5.6: Reliability of the ledger under drop force (simply support)

Drop weight

(kg)


ledger (N/mm2)

Mean strength = 80.7 N/mm

2

Lower 95% strength = 49 N/mm

2

> mean Safety index

> 95% Safety index

20 105.6 Yes <1.0 Yes <1.0

40 159.4 Yes <1.0 Yes <1.0

60 202.9 Yes <1.0 Yes <1.0

Table 5.7: Reliability of the ledger under drop force (clamped support)

Drop weight

(kg)


ledger (N/mm2)


2


2

> mean Safety index

> 95% Safety index

20 52.8 No 1.5 Yes <1.0

40 79.7 No 1.0 Yes <1.0

60 101.5 Yes <1.0 Yes <1.0

Chapter 5

66

Table 5.8: Reliability of the standard under 60 kg free drop at location 10

Standard force (kN)

Safety index


strength

Back standard

1 (PP) 0.39 396.7 319.4

2 (BP) 0.79 37.5 51.0

3 (BP) 1.07 27.7 37.7

4 (Fir) 1.42 76.6 80.3

5 (BP) 0.19 155.8 212.1

6 (BP) 0.05 592.0 805.8

7 (PP) 0.04 3867.5 3114.1

Chapter 5

67

Figure 5.1: FEM model of the scaffold

Figure 5.2: Loading of the UDL testing

Chapter 5

68

Figure 5.3(a): Setup of the free drop tests

Figure 5.3(b): The free drop tests

Chapter 5

69

Force

Length

Drop force vs weight

0

1

2

3

4

5

6

20 30 40 50 60

Weight (kg)

Dro

p f

orc

e (

kN

)

Figure 5.4: The resulting drop force of different drop weight

Figure 5.5: A simple model to simulate a transom under UDL

Figure 5.6: A simple model to simulate a ledger under drop force

UDL x tributary width

Length

Chapter 6

70

Chapter 6: Computer analysis on some typical bamboo scaffoldings

6.1 Bamboo scaffolding at construction sites

One of the main functions of the bamboo scaffolding is to provide working platform at

the construction site. The bamboo scaffolding at the construction site is usually very tall.

Normally, there is a catch fan installed with triangular supports every several floor (see

Figure 6.1). The triangular supports are used to transfer the load from the scaffold to the

permanent structure. As a result, it is sufficient to analyze only a typical part of the

scaffolding instead of the whole scaffolding.

The bamboo scaffolding in a construction site near Sham Tseng was investigated in this

study (see Figure 6.2). A part of the scaffolding was simulated using an FEM model. The

scaffolding between two catch fans was chosen as it was assumed that the load above the

catch fan was transferred to the building by the triangular supports. The model was

shown in Figure 6.4. The size of the model is 9.6 m x 12 m x 0.6 m (length x height x

width).


Similar to the Section 5.3.1, two failure cases were studied.




magnitudes of the UDL times their corresponding tributary widths. The tributary

width in this model is 0.6 m. The distributed load that acts on their transom is 0.6

x UDL. The mean flexural strength of transoms (usually BP) is 80.7 N/mm2 and

its standard deviation is 19.3 N/mm2 as obtained in Chapter 2. The lower bound of


Chapter 6

71

N/mm2 based on the gaussian assumption. The reliability of the transom shows in

Table 6.1. It is seen that under the design UDL (3 kN/m2), the safety indexes are

7.2 and 4.4 if the mean strength and the lower 95% strength are used respectively.


Table 6.2 shows the backside standard forces induced by the design UDL of 3

kN/m2 acting at the lower platform. Two types of failure are possible: buckling

failure and compressive strength failure. The theoretical buckling loads for the PP

with a length of 1.8 m and under simply support condition without initial

curvature is 21.5 kN (from Section 2.5). The safety indexes for the standards

under buckling condition are computed and listed in Table 6.2. It is seen that the

smallest safety index is 12 which occurs at the 3rd

PP standards. On the other hand,

the compressive strength for the PP is 61 N/mm2 respectively. The safety indexes

for the standards under compressive strength condition are again computed and

listed in Table 6.2. It is seen that the smallest safety index is 69.2 which again

occurs at the 3rd

PP standards. The results show that the overall failure of this

model is dominated by buckling. If the UDL 3 kN/m2 is applied at each floor

(total six floors), the maximum load is also occurred at the 3rd

PP member at the

backside, which is equal to 11.2 kN. The safety index for the buckling failure is

around 1.9.


Similar to the Section of 5.3.2, tow failure cases were studied.





the fastening tie at the joints would occur. It is expected that the support

conditions of the ledger would be between simply support and clamped support

(but more close to the clamped support). The mean flexural strength of ledger

Chapter 6

72

(usually BP) is 80.7 N/mm2 and its standard deviation is 19.3 N/mm

2 as obtained

in Chapter 2. The lower bound of the flexural strength with 95% probability of

occurrence is computed to be 49 N/mm2 based on the gaussian assumption. As the

distance between two standards is 0.6 m which is the same as the model in

Section 5, the results in Table 5.6 and 5.7 can be used for this case. A similar

conclusion can be made that the ledger could fail when the drop weight exceeds

40 kg.


For the drop test, the weight is always drops at the front side. Table 6.3 shows the

standard forces induced by a drop force equal to 5 kN (which is similar to the

maximum drop force provide by a 60 kg weight) drops at the 7th

standard count

from left of the 1st floor. Two types of failure are studied: buckling failure and

compressive strength failure. The theoretical buckling loads for the BP and PP

with a length of 0.6 m and under simply support condition without initial

curvature are 34.8 kN and 193.7 kN, respectively (from Section 2.5). The safety

indexes for the standards under buckling condition are computed and listed in

Table 6.3. It is seen that the smallest safety index is 26.5 which occurs at the 7th

BP standard. On the other hand, the compressive strengths for the BP and PP are

57 N/mm2 and 61 N/mm

2, respectively. The safety indexes for the standards under

compressive strength condition are again computed and listed in Table 6.3. It is

seen that the smallest safety index is 30.8 which again occurs at the 7th

BP

standard.



fail. Their safety indexes are between 4.4 to 7.2 for the transoms and between

12 to 69.2 for the standards.



Chapter 6

73






Chapter 6

74

6.2 Bamboo scaffolding used for maintenance work

The bamboo scaffolding is also frequently used for the maintenance works. It may be

used as a working platform for the surface finishing or for the drainage repair outside the

buildings. The shape of these scaffoldings could be quite different, as they need to fit the

shape of the building or the slope.

One bamboo scaffolding at the Hong Kong University of Science and Technology was

chosen for investigation. Figure 6.7 shows the overview of the scaffolding. The distance

from the bottom of its standards to the first ledger was around 2 m (see Figure 6.8).


Similar to the Section 5.3.1, two failure cases were studied.




magnitudes of the UDL times their corresponding tributary widths. The tributary

width in this model is 0.6 m. The distributed load that acts on their transom is 0.6

x UDL. The mean flexural strength of transoms (usually BP) is 80.7 N/mm2 and

its standard deviation is 19.3 N/mm2 as obtained in Chapter 2. The lower bound of


N/mm2 based on the gaussian assumption. The reliability of the transom shows in

Table 6.1. It is seen that under the design UDL (3 kN/m2), the safety indexes are

7.2 and 4.4 if the mean strength and the lower 95% strength are used respectively.


Table 6.4 shows the standard forces induced by the design UDL of 3 kN/m2

acting at the lower platform. Two types of failure are studied: buckling failure and

compressive strength failure. The theoretical buckling loads for the PP with a

length of 2 m and under simply support condition without initial curvature is 17.4

Chapter 6

75

kN (from Section 2.5). The safety indexes for the standards under buckling

condition are computed and listed in Table 6.4. It is seen that the smallest safety

index is 10.9 which occurs at the 3rd

PP standards. On the other hand, the

compressive strength for the PP is 61 N/mm2. The safety indexes for the standards

under compressive strength condition are again computed and listed in Table 5.5.

It is seen that the smallest safety index is 77.9 which again occurs at the 3rd

BP

standards. If the design UDL (3kN/m2) is applied at each floor (total six floors),

the maximum load is also occurred at the 3rd

PP member at the backside, which is

equal to 10.3 kN. The safety index for the buckling failure is around 1.7.


Similar to the Section of 5.3.2, tow failure cases were studied.





the fastening tie at the joints would occur. The slippage of the fastening tie would

then provide a kinetic friction force that reduces some amount of drop force

acting on the ledger. As a conservative measure, assume that the kinetic friction

force is ignored in the following analysis. Figure 5.6 shows a simple model to

simulate a ledger under drop force. It is expected that the support conditions of

the ledger would be between simply support and clamped support (but more close

to the clamped support). The mean flexural strength of ledger (usually BP) is 80.7

N/mm2 and its standard deviation is 19.3 N/mm

2 as obtained in Chapter 2. The

lower bound of the flexural strength with 95% probability of occurrence is

computed to be 49 N/mm2 based on the gaussian assumption. As the distance

between two standards is 600mm which is the same as the model in Section 5, the

results in Table 5.6 and 5.7 can again be used. A similar conclusion can be made

that the ledger could fail when the drop weight exceeds 40kg.

Chapter 6

76


For the drop test, the weight is always drops at the front side. Table 6.5 shows the

standard forces induced by a drop force equal to 5 kN (which is similar to a drop

force provide by a 60 kg weight) drops at the 4th

standard count from right of the

1st floor. Two types of failure are studied: buckling failure and compressive

strength failure. The theoretical buckling loads for the BP and PP with a length of

0.6m and under simply support condition without initial curvature are 34.8kN and

193.7kN, respectively (from Section 2.5). The safety indexes for the standards

under buckling condition are computed and listed in Table 6.5. It is seen that the

smallest safety index is 37 which occurs at the 4th

BP standard. On the other hand,

the compressive strengths for the BP and PP are 57 N/mm2 and 61 N/mm

2,

respectively. The safety indexes for the standards under compressive strength

condition are again computed and listed in Table 6.5. It is seen that the smallest

safety index is 42.9 which again occurs at the 4th

BP standard.



fail. Their safety indexes are between 4.4 to 7.2 for the transoms and between

10.9 to 77.9 for the standards.








Chapter 6

77

Table 6.1: Reliability of the transom under UDL

UDL (kN/m

2)


transom (N/mm

2)


2


2

> mean Safety index

> 95% Safety index

3 11.2 No 7.2 no 4.4

6 22.4 No 3.6 no 2.2

9 33.5 No 2.4 no 1.5

12 44.7 No 1.8 no 1.1

15 55.9 No 1.4 yes < 1.0

18 67.1 No 1.2 yes < 1.0

21 78.3 No 1.0 yes < 1.0

24 89.4 Yes < 1.0 yes < 1.0

Table 6.2: Loading at the standards under a UDL 3 kN/m2 applied at the bottom platform

for the construction site model

Standard force (kN)

Safety index


strength

Back standard

1 (PP) 0.9 23.9 138.4

2 (PP) 1.7 12.7 73.3

3 (PP) 1.8 12.0 69.2

4 (PP) 1.7 12.7 73.3

5 (PP) 0.8 26.9 155.7

Table 6.3: Reliability of the standard under a 5 kN drop force for the construction site

model

Standard force (kN)

Safety index


strength

Front standard

5 (PP) 0.6 302.7 194.6

6 (BP) 0.9 40.4 46.8

7 (BP) 1.3 26.5 30.8

8 (BP) 0.8 44.0 51.0

9 (PP) 0.6 345.9 222.4

Table 6.4: Loading of the standard under a UDL 3 kN/m2 applied at the bottom platform

for the maintenance model

Standard force (kN)

Safety index


strength

Back standard

1 (PP) 0.5 34.9 249.1

2 (PP) 1.1 15.8 113.2

3 (PP) 1.0 17.4 124.6

4 (PP) 1.6 10.9 77.9

5 (PP) 1.3 13.4 95.8

6 (PP) 1.1 15.7 112.2

7 (PP) 1.1 16.6 118.6

8 (PP) 1.1 15.4 110.2

9 (PP) 1.0 17.1 122.1

10 (PP) 0.6 31.7 226.5

Chapter 6

78

Table 6.5: Reliability of the standard under a 5 kN drop force for the maintenance site

model

Standard force (kN)

Safety index


strength

Front standard

5 (PP) 0.2 144.8 167.9

6 (BP) 1.1 177.7 114.3

7 (BP) 0.9 37.0 42.9

8 (BP) 1.2 168.4 108.3

9 (PP) 0.3 112.1 130.0

Chapter 6

79

Figure 6.1: Bamboo scaffolding at Sham Tseng

Figure 6.2: The catch fan with structural supports

Chapter 6

80

Figure 6.3: Close shot of the scaffolding

Figure 6.4: The FEM model of the scaffolding at Sham Tseng

Chapter 6

81

Figure 6.5: Loading at the bottom platform

Figure 6.6: Loading at each platform

Chapter 6

82

Figure 6.7: Scaffolding for maintenance work at HKUST

Figure 6.8: Bottom of the scaffolding at HKUST

Chapter 6

83

Figure 6.9: Close shot of the scaffolding at HKUST

Figure 6.10: The FEM model of the scaffolding at HKUST

Chapter 7

84

Chapter 7: Conclusions and recommendations

Conclusions and recommendations obtained from this study are itemized as follows.

(1) The material properties of commonly used bamboos, including BP, PP and Fir,

exhibit large variations as shown in chapter 2. The standard deviation is about

30% of the mean values for the Young’s modulus and about 20% of the mean

values for the compressive strength. The sizes of bamboos also have large

variations. The standard deviations of bamboo diameter range from about

10% of the mean value for the BP, about 20% of the mean value for the PP, to

about 7% of the mean value for the Fir.

(2) The material properties of bamboos would decrease as the relative humidity

increases. The trend is approximately linear. The reduction appears to be more

pronounced for the BP. Also a 12-week aging test shows that the bamboos’

properties would reduce linearly as a function of time. Again, the reduction of

BP’s properties is more pronounced than that of PP’s.

(3) The results of the buckling tests show that the buckling loads of bamboo

components are lower than those obtained by assuming clamped support

conditions for both ends. The buckling loads for assuming simply support

conditions at both ends appear to provide good estimates on the lower bounds

of the buckling loads.

(4) The full-scale test results show that, even under an UDL with a magnitude

twice as large as the design value (3 kN/m2), the scaffolding does not appear

to have any sign of damage. It can be concluded that the scaffolding is quite

safe under the design UDL.

(5) The drop test results indicate that the standard forces produced by the free

drop of a 20 kg sand bag are all smaller than their strengths. Under the linear

assumption, the failure of standards is not expected even when the mass of the

sand bag increased by triple. It is however observed that the horizontal ledger,

where the sand bag is attached to, suffers from significant settlement. When a

40 kg and a 60 kg sand bag are used for the drop test, fracture of the

horizontal ledger is seen. Analysis shows that the maximum dynamic force

Chapter 7

85

generated during the free drop of a 20 kg sand bag exceeds the impending

friction forces of the bamboo intersection, which causes slippage of the

horizontal ledger. Also the maximum force exceeds the bending strength of

the bamboos and results in fracture of the ledger. These results conclude that

the bamboo scaffold intersection is not a suitable anchorage for the safety belt

and harness. To ensure the safety of workers, it might be necessary to attach

the safety belt to a more strong and permanent structure or an independent

lifeline.

(6) There are some differences between the experimental results and the FEM

results. However, the differences in the major components that carry most of

the loads are within 30%. So even though the FEM model cannot estimate

accurately all the forces in the scaffolding, it can be used as a preliminary tool

for analyzing the behavior and the safety of the scaffold.

(7) Some typical scaffoldings were simulated in Chapter 6 using the finite

element analysis program. When the design UDL is applied only on one

platform, the safety indexes for the ledger and the standard are larger than 4

and 12, respectively. This means that both ledger and standard would not fail

under this condition. Further analysis indicates that the safety index reduces to

about 2 under the worst possible loading condition when the design UDL is

applied at all platforms. Note that it might be necessary to study how the

variation of bamboo properties, the humidity and the degradation of properties

due to aging would further affect this safety index.

(8) It is commonly known that bamboo scaffoldings can be damaged under strong

wind condition. This phenomenon was not studied in this research. To ensure

the safety and the reliability of scaffoldings under strong wind condition, it is

necessary to have a further detailed study that requires the use of wind tunnel

tests for validation.

References

86

References

1. Fu, W.Y. (1993). “Bamboo scaffolding in Hong Kong,” The Structural Engineer,

71 (11), June 1993, 202-204.

2. So, F.Y.S. and Wong, F.K.W. (1998). “Bamboo scaffolding development in Hong

Kong – a critical review,” Proceedings of the Symposium on Bamboo and Metal

Scaffolding, 23 Oct. 1998, 63-75.

3. Comparative study on safety and application of bamboo and metal scaffolding in

Hong Kong, Report by the (Tsinghua-Gammon) Construction safety Research

Center, 2001.

4. Zhou, F.C. (1981). “Studies on Physical and Mechanical Properties of Bamboo

Woods,” Journal of Nanjing Technological college of Forest Products, Volume 2,

June 1981, 1-32.

5. Janssen, J.J.A. (1991). Mechanical Properties of Bamboo, Kluwer Academic

Publishers.

6. Chan, S.L., Wong, F.K.W., So, F.Y.S. and Poon, S.W. (1998). “Empirical design

and structural performance of bamboo scaffolding,” Proceedings of the

Symposium on Bamboo and Metal Scaffolding, 23 Oct. 1998, 5-21.

7. Yu, W.K. and Chung, K.F. (2001). “ Mechanical properties of bamboo for

scaffolding in building construction,” Proceeding of the International Conference

on Construction, Volume 2, 19-21 June 2001, 266-272.

8. Summary of causes of the 31 total accidents related to bamboo scaffolds in 1994-

1998, Internal summary of the Labor Department.

9. Code of Practice for Bamboo Scaffolding Safety, Occupational Safety and Health

Branch, Labor Department, March 2001.

10. BS EN 364: 1993. Personal protective equipment against falls from a height –

Test methods. British Standard

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