shear strength of concrete filled glass fiber reinforced gypsum walls

ORIGINAL ARTICLE

Shear strength of concrete filled glass fiber reinforcedgypsum walls

Kang Liu Æ Yu-Fei Wu Æ Xin-Liang Jiang

Received: 26 January 2007 / Accepted: 21 May 2007 / Published online: 20 July 2007

� RILEM 2007

Abstract Glass fiber reinforced gypsum (GFRG)

walls, known as a green product that helps to save

energy and protect the environment, are promising

new building materials developed in Australia in the

early 1990s. Driven by the wide-spread interest from

the construction industry and the research commu-

nity, substantial research has been carried out in

Australia and a few Asian countries such as China,

Malaysia and India to investigate its performance,

including the structural behavior for building con-

struction. This paper investigates the shear strength of

GFRG walls fully or partially filled with concrete in

the hollow cores. Eight full scale GFRG walls were

tested under cyclic loadings. The shear performance

of the tested walls, including the shear failure mode,

hysteresis responses, the ultimate shear strength and

the axial load effect, were studied in the paper. With

the aid of nonlinear finite element analyses, a design

procedure for the shear strength of the concrete filled

GFRG walls is developed.

Keywords GFRG � Wall � Shear strength � Axial

load effect � Tests

1 Introduction

Known as Rapidwall in the building industry, glass

fiber reinforced gypsum (GFRG) walls are new

building materials developed in Australia in the early

1990s. GFRG walls are machine-made panels with

hollow cores and are made of modified gypsum

plaster and reinforced with cut glass fibers. A typical

cross-section of a standard panel is shown in Fig. 1.

During the manufacturing process, glass fibers of

about 300–350 mm in length are randomly distributed

inside the panel skins and in the ribs. The fiber

volume in the panel is 0.8 kg per square meter of wall

surface area. The physical properties of the current

standard GFRG panels are listed in Table 1.

In building construction, the standard large panels

are cut in the factory into building components that

may have window and door openings. These compo-

nents are then transported to the construction site and

erected in a similar way to the construction of precast

concrete panels. The cavities (hollow cores) inside the

panel can be filled with various materials, such as

concrete or insulation materials, to serve different

purposes, such as to increase the strength or improve

the thermal and sound insulation of the walls. In a

Rapidwall building, most or all the building compo-

nents are constructed with GFRG panels. Therefore,

the GFRG walls serve as both architectural partitions

and structural walls. More details of the GFRG panels

and the structural system of Rapidwall buildings can be

found in the work of Wu [1] and Wu and Dare [2, 3].

K. Liu � Y.-F. Wu (&)

Department of Building and Construction, City University

of Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong

e-mail: [email protected]

X.-L. Jiang

Department of Civil Engineering, Tianjin University,

Tianjin, China

Materials and Structures (2008) 41:649–662

DOI 10.1617/s11527-007-9271-8

Research works have shown that GFRG building

assemblies have a much smaller embodied energy

(EE) coefficient and CO2 gas emission (from the

manufacturing of panels to the completion of build-

ing construction) compared with other traditional

building construction with bricks, reinforced concrete

and precast concrete panels [4]. Therefore, GFRG

panels are considered as a green product that helps to

save energy and protect the environment.

Since concrete can be placed into the hollow cores

of the GFRG panels, these composite walls can be

very strong and have significant axial and shear

strength, and are therefore suitable for use with multi-

story buildings. In the Australian construction

practice, all or most of the hollow cores are filled

with concrete. Significant investigations have been

undertaken to study the behaviors of the fully filled

GFRG walls under both axial and shear loads [5–7].

Design guidelines are available for the design of

these fully filled GFRP walls [5].

However, filling all the hollow cores with concrete

may not be necessary especially for walls in low-rise

buildings, or for upper storey walls in high-rise

buildings. To save construction cost, Chinese builders

recommended filling as few of the cores in the GFRG

walls with concrete as possible. The percentage of

cores to be filled with concrete depends on the

loading conditions of the wall. In order to understand

the structural performance of the partially filled

GFRG walls, significant and large scale experimental

Fig. 1 Standard details of

GFRG panel

Table 1 Physical

properties of GFRG panelsProperty name Value Note

Unit weight 40 kg/m2

Thermal expansion

coefficient

12 · 10–6 mm/mm/8C

Water absorption <5% By weight after 24 h immersion

Thermal resistance 0.36 m2 K/W Unfilled panel

1.63 m2 K/W With 35 kg/m3 and R2.5 rockwool

batts infill and standard texture finishing

Sound transmission

coefficient (STC)

28 Unfilled panel

45 Concrete filled panel

Fire resistance level (FRL) >3 h For structural adequacy

650 Materials and Structures (2008) 41:649–662

investigations were undertaken at Tianjin University,

PRC [6]. The experimental work reported in this

paper was part of that experimental program.

This work reports the experimental investigation

of the shear strength of fully and partially filled

GFRG walls. Particular attention is paid to the effect

of axial load on the shear strength of these walls, and

the mechanism of the axial load effect. Interesting

conclusions are drawn from this study, which may

also be applicable to other kinds of structural walls.

2 Test specimens

Due to the composite nature of concrete filled GFRG

walls and the additional composite action between

the concrete infill cores and the GFRG wall panel, the

structural behavior of these walls is extremely

complicated. Experimental testing is the best way to

investigate the problem. In this investigation, eight

GFRG wall specimens were constructed for testing.

Details of the test specimens are given in Table 2 and

Fig. 2. All the specimens were 2.75 m high with

different widths.

These specimens were divided into four different

batches. The first batch was 1,520 mm wide panels

with all cores filled with concrete. The second batch

was 1,270 mm wide panels with every other core

filled with concrete. The third batch was 1,770 mm

wide panels with every third core filled with concrete.

The fourth batch was 2,270 mm wide with every

fourth core filled with concrete.

The GFRG panels for the test specimens were cut

from randomly selected sample panels. A reinforced

concrete beam of 250 mm wide and 500 mm high

was used as a fixed base under each test specimen,

and was cast monolithically with the infill concrete of

a test panel. Each specimen had also a reinforced

concrete beam, 120 mm wide and 240 mm high at its

top to represent the wall-to-floor connection. In the

construction of a wall specimen, the GFRG panel was

erected vertically on top of the bottom beam form,

and self-compacting concrete was filled into the

hollow cores from the top of the wall; a procedure

that is identical to the practice in the construction

industry. Concrete cubes were made for each batch of

wall specimens and were tested at the same time as

the specimens to identify the concrete strength. The

concrete strengths and the elastic modulus for the

specimens are given in Table 2.

Table 2 Details of the test

specimenBatches Specimen

No.

Dimensions

b · h (mm)

Concrete elastic

modulus (MPa)

Concrete compressive

strength (MPa)

Vertical load

(kN/m)

B1 S1 1520 · 2750 3.33 · 104 32.42 184

S2 1520 · 2750 3.33 · 104 32.42 312

B2 S3 1270 · 2750 3.33 · 104 32.42 112

S4 1270 · 2750 3.39 · 104 43.78 172

B3 S5 1770 · 2750 3.33 · 104 32.42 53

S6 1770 · 2750 3.39 · 104 43.78 110

B4 S7 2270 · 2750 3.33 · 104 32.42 49

S8 2270 · 2750 3.39 · 104 43.78 104

(a)

(c)

(d)

(b)

Fig. 2 Shear test specimens. (a) B1, (b) B2, (c) B3, (d) B4

Materials and Structures (2008) 41:649–662 651

A 16 mm diameter high-yield strength steel

reinforcing bar was inserted into the centre of each

concrete filled core, which was bent into the top and

bottom beams. The material properties of the rein-

forcement are given in Table 3.

3 Test setup and instrumentation

All specimens were tested under cyclic lateral load

and a fixed axial load. The test setup is shown in

Fig. 3. The vertical loading system consisted of five

main parts: two test frames, two reaction steel beams

perpendicular to each other, six hydraulic jacks, one

spreader steel beam and a few rollers. To simulate the

real loading condition, the vertical load was applied

on the test panels before the lateral force, through six

hydraulic jacks that were fixed on the reaction steel

beam. The displacement of these hydraulic jacks was

maintained during the tests which prevented the free

rotation of the test panel at the top. Under the

spreader steel beam, steel rollers were used to reduce

the friction between the spreader steel beam and the

top RC beam of the test panel.

The lateral loading system comprised five main

parts: the reaction wall, one pulling and pushing

hydraulic jack, four tensile steel bars bolted to two

end steel plates, two steel beams to prevent the

rotation of the bottom RC beam of the test panel, and

other two steel beams to prevent the lateral displace-

ment of the bottom RC beam.

The lateral force and the vertical load were

measured by Load Cell 1 and Load Cell 2 respec-

tively. The horizontal displacement was measured by

linear variable differential transformers LVDT1, 2

and 3, as shown in Fig. 3. LVDT1 was used to

measure the top lateral displacement of the test panel.

LVDT2 and 3 were used to measure the base

displacement. Both an automatic data acquisition

system and manual recordings were adopted to record

the test results.

The most important feature of this setup was that

the vertical loading system prevented the test spec-

imens from end rotations. Specimens were forced to

deform in a shear-dominant way, which ensured a

shear failure mode instead of a flexural failure mode.

Table 3 Material properties

Materials E (MPa) fc (MPa) ft (MPa) fy (MPa)

Concrete 3.33 · 104 32.42 3.05 –

GFRG 1.14 · 103 5.00 1.00 –

Reinforcement 2.06 · 105 – – 402

Front view Side view

Fig. 3 Test setup


4 Test procedure and loading history

According to Specification of Testing Methods for

Earthquake Resistant Building (JGJ101–96) [8], the

testing was conducted under a force-displacement

mixed control mode, as shown in Fig. 4. The force

and displacement cycles were achieved simply by

pushing and pulling the hydraulic jack. All the

responses, including loads, displacements and strains,

were automatically recorded by the automatic data

acquisition system. The loads and displacements

were also manually recorded at the peak points of

each cycle. After recording the data at each displace-

ment increment, the test panel was visually inspected,

and all cracks were marked. When all the information

had been obtained for a force or displacement step, a

new force or displacement increment was applied to

the test panel, and so on.

5 Observation and test results

All eight specimens went through a similar failure

process. First, a weak cracking sound was heard when

the shear resistance was about 50–60% of the peak

strength. The first batch of visible diagonal shear

cracks was then observed. The reversal of load

produced diagonal cracks that were symmetrical to

the cracks that had already occurred. The cracks in

both directions formed a cracking pattern like a net,

as shown in Fig. 5. Diagonal shear cracking devel-

oped gradually with increasing lateral load. Extensive

diagonal cracks occurred before the peak load was

reached. The test panels reached the peak load when

a visible longitudinal shear crack developed in the

panel, as shown in Fig. 6. After the development of

the first longitudinal crack, the shear resistance

started to drop, and other longitudinal cracks formed

one by one when the lateral displacement further

increased. All these longitudinal cracks were formed

near the ribs of the test panels. This indicated that the

friction between the infill concrete cores and the

GFRG panel was overcome and relative slip between

them took place. This resulted in the over-stressing

and longitudinal tearing off of the two 13 mm thick

panel skins. The trace of the relative slip at the

interface was clearly seen when the concrete cores

were exposed after the tests [2].

The above observation indicated that the shear

failure mode of the concrete filled GFRG panels was

very different from that of the conventional rein-

forced concrete walls. The typical shear failure

modes of reinforced concrete shear walls are diagonal

tension failure, diagonal compression failure and

shear sliding failure [9]. However, due to the relative

weak nature of the two skins of the GFRG panels

compared to the concrete cores and the ribs of the

panel, the only possible shear failure mode in the

body of the walls was the longitudinal interface shear

failure (or interface shear slipping failure), although

diagonal shear cracking was developed to a large

extent before a interface shear failure occurred. This

observation was identical to that of the previous tests

[2].

The hysteresis responses of the eight specimens

are given in Fig. 7. It can be seen from the response

curves that the shear responses of these walls are

more ductile than that of the conventional RC walls.

This is caused by the glass fibers inside the panel that

prevented the brittle tensile failure of the materials,

and the unique longitudinal shear failure mode that

poses a more ductile nature.

6 Development of shear strength model

It was concluded in Reference [2] that the shear

strength of concrete filled GFRG walls is proportional

to their length. Therefore, the shear strength of a

concrete filled GFRG wall is simply equal to the unit

shear strength, which was derived from experimental

tests, multiplied by the length of the wall. However,

the previous works and the corresponding design

guidelines were only applicable to fully filled GFRG

walls and without the top and bottom RC beams. TheFig. 4 Loading history


top and bottom RC beams form a RC frame with the

internal concrete cores. As a result, the lateral or

shear resistance of the walls with the top and bottom

beams must be greater than that derived from the

previous works.

To calculate the shear strength, the envelope

curves of the positive part of the hysteresis responses

are produced and provided in Fig. 8. The peak

resistances of the specimens are the strengths of the

walls that are summarized in Table 4. These strength

values are used as the bases for deriving shear

strength model. The bending resistances in the table

are calculated from the internal RC frame that

consists of the top and the bottom RC beams and

the internal RC cores. Figure 9 shows a typical

response curve of the internal RC frame without the

presence of a GFRG panel. This response curve is

calculated by non-linear finite element analysis as

described in the following section. Alternatively, the

resistance of the internal RC frame can also be

calculated using the conventional RC theory.

The lateral resistance of the concrete filled GFRG

walls comes from two different actions: (1) the shear

resistance of the GFRG panel and (2) the lateral

Fig. 5 Cracking patterns.

(a) S1, (b) S2, (c) S3, (d)

S4, (e) S5, (f) S6, (g) S7, (h)

S8


resistance of the internal RC frame due to the bending

of the internal reinforced concrete cores. The super-

position law applies in this case. In other words, the

total shear strength of the wall equals to the shear

resistance of the GFRG panel plus the lateral

resistance of the internal RC frame. This is because

the peak lateral resistance of the internal RC frame

occurs at or near the peak of the total shear strength

of the wall, due to the ductile longitudinal shear

failure mode. This concurrence has been observed in

all the eight test walls.

Taking away the frame bending strength from the

peak strength in Table 4 gives the net panel shear

strengths of the walls as given in column 5 of

Table 4. It can be seen in the table that the net panel

shear strength is proportional to the length of the

wall. Therefore, the unit shear strengths that are the

panel shear strengths divided by the length of the wall

are essentially a constant for all the walls. This

conclusion is identical to that of the previous work by

Wu and Dare [2], although the previous tests did not

include the internal RC frames. The unit shear

strength derived in this work (see Table 4) is slightly

larger than that derived from the previous work [2].

This is because the GFRG panels used in this work

were made from the new production line that used a

more advanced technology for fiber distribution.

Therefore, the strength of panel used in this work

was greater than that used in the previous work.

Based on the above study, the design procedure for

the shear strength of concrete filled GFRG walls with

top and bottom RC beams is proposed as follows: (1)

calculating the lateral resistance of the internal RC

frame without GFRG panel by the conventional RC

theory (2) calculating the shear strength of the panel

by multiplying the unit shear strength with the length

of the wall and (3) adding the results of (1) and (2) to

give the total lateral resistance of the wall.

7 Axial load effect

The test results (shown in Table 4) indicated that

unlike reinforced concrete shear wall, vertical loads

have no significant effect on the shear strength of

concrete filled GFRG walls. This contradicts the

conventional RC theory. It also differs from the

results of the previous shear tests of fully filled GFRG

walls conducted by Wu and Dare [2], where it was

concluded that the axial load increases the shear

strength of the walls. This unusual phenomenon on

axial load effect not only puzzled the investigators

but also caused serious concern on the consistency of

these test results. In order to better understand the

structural behaviors of concrete filled GFRG walls,

finite element analyses are carried out that are

described in the following section.

7.1 Finite element modeling

The cross-section of GFRG walls is complex, see

Fig. 1. As mentioned in the test part, the bond

interfaces between the concrete cores and the ribs of

the GFRG panel are relatively weak. This weakness

is one of the most important characteristics that

govern the response and failure mode of these walls.

Therefore, relative movements or slips between them

must be adequately modeled. As a result, three

dimensional nonlinear modeling of the concrete filled

GFRG walls is extremely complicated and difficult.

Trial run of the 3D model resulted in non-conver-

gence of the solution. Therefore, 2D modeling is

adopted in this work. The 2D FEM model is shown in

Fig. 10. This 2D model not only greatly simplifies the

problem but also captures the essential feature of the

Fig. 6 Longitudinal cracks


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Fig. 7 Hysteresis responses. (a) S1, (b) S2, (c) S3, (d) S4, (e) S5, (f) S6, (g) S7, (h) S8


problem: allowing slips at the interfaces between the

concrete cores and the gypsum panel. The eight-node

2D plane-stress elements are used to model the

concrete and the GFRG panel. The reinforcement

bars are embedded in the concrete elements, and the

so called embedded reinforcement element is em-

ployed in the model, which means perfect bonding

between the reinforcement and the surrounding

concrete. The top and bottom RC beams are much

stiffer and stronger than the wall itself. Therefore,

these beams are simply modeled with elastic plain

concrete elements.

Ideally, the interfaces should be modeled as

contact elements. Unfortunately, adding contact ele-

ments to the 2D model results in very poor conver-

gence of the analyses, and practically no complete

response curve can be obtained. Therefore, an

alternative method is used in this work to model the

interface: adding a thin layer of interface elements

between the concrete core and the rib of the GFRG

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Fig. 8 Envelope curves. (a) S1 & S2, (b) S3 & S4, (c) S5 & S6, (d) S7 & S8

Table 4 Strength of

specimensBatches Specimen

No.

Peak

strength

(kN)

Frame bending

strength (kN)

Panel shear

strength (kN)

Unit shear

strength (kN/

m)

Vertical

loading (kN/

m)

B1 S1 157 67.86 89.14 58.64 184

S2 147 69.68 77.32 50.90 312

B2 S3 110 33.66 76.34 60.11 112

S4 112 34.69 77.31 60.87 172

B3 S5 145 31.89 113.11 63.90 53

S6 143 33.36 109.64 61.94 110

B4 S7 173 32.65 140.35 61.83 49

S8 167 33.88 133.12 58.64 104


panel. A nonlinear relation of the shear stress vs.

shear slip was used in modeling the interface

elements, as shown in Fig. 11. This interface layers

can adequately model the frictional slips at the

interfaces and also solve the problem of non-conver-

gence.

7.2 FEM analyses

To compare to the test results, specimens S1 and S2

are analyzed using the finite element program

ANSYS. The material properties of concrete, i.e.

the compressive strength fc and the elastic modulus E,

were obtained from the compression tests of concrete

cubes. The tensile strength ft is calculated from the

compressive strength fc according to CEB-FIP Model

Code [10], or

ft ¼ 0:3ðfcÞ2=3 ð1Þ

The three material properties of the GFRG panel, i.e.

the compressive strength fc, the tensile strength ft and

the elastic modulus E, are determined from Reference

[5]. The elastic-perfectly-plastic model is used for the

reinforcement bars and the yield strength was deter-

mined from tensile tests of reinforcement bars. It is

found in the FEM analyses that the reinforcement

does not have significant effect on the results. The

material properties of concrete, reinforcing bar and

the GFRG panel used in this finite element analysis

are summarized in Table 3.

The force-displacement curves from the FEM

analyses for specimens S1 and S2 are compared with

the test envelope curves in Fig. 12(a) and (b),

respectively. These comparisons indicate that both

the peak strength and the variation of stiffness of the

walls are well captured and matched with the test

results, which validates the FEM model. This FEM

model is then used to study the effect of the axial load

on the shear strength of GFRG walls in the next

section.

7.3 Effect of interface roughness

In order to find the reason that caused the contradic-

tory results of this work compared with that of the

previous work of Wu and Dare [2], various factors

that may affect the shear strength of the walls are

analyzed with the above FEM model. The material

properties of concrete and steel bar, which might be

different between the two investigations, are found to

have little effect on the shear strength of the walls.

The material properties of the GFRG panel are found

to have more effect on the results. However, within

the possible range of variation of the properties of the

GFRG panel, it is not likely to cause a great

difference. There were also differences in the details

of test specimens and the test setup. However, it is

believed that those differences are not the key factor

that causes the problem. Now the only remaining

factor is the interface properties. The response curves

of wall S1 with an axial load of 184 kN/m and two

different interface properties are shown in Fig. 13. It

can be clearly seen from the figure that it is the

interface properties that cause the difference in the

shear strength.

Figure 14 further gives the FEM results of wall S1

with a small interfacial friction under different axial

loads. Figure 15 shows the results of the same wall

and the same axial loads but with a greater interfacial

friction. It is clear from these two figures that the

axial load has no effect on the shear strength of

concrete filled GFRG walls when the interfaces are

smooth, and the axial load effect exists for walls with

rough interfaces.

7.4 Mechanism of axial load effect

The axial load effect can be explained physically.

According to Priestley et al. [11], the axial load effect

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Fig. 9 Typical response curve of the internal RC frame


on a conventional concrete shear wall can be

explained using a strut model, as shown in Fig. 16.

The strut angle a, in Priestley et al.’s model, is

affected by the depth of the compression zone. The

additional shear strength due to the axial load can be

expressed as

DF ¼ tan a� DN ð2Þ

However, the strut cannot be formed if a concrete

wall is cut into several longitudinal strips and the

contact surfaces between these strips are smooth. The

concrete inside a GFRG wall is divided into longi-

tudinal strips by the ribs of the panel. The bond and

friction between the gypsum panel and the concrete

Fig. 10 Finite element model

Fig. 11 Shear slip–stress relation of interface elements


cores provide certain longitudinal shear force to form

the diagonal strut. It must be the difference of the

interfacial bond properties between the walls in this

work and that in the previous work that caused the

difference of the test results, and this is evident in

Fig. 17. Exposure of the concrete cores from the wall

specimens tested in the previous work [2] found that

the interfaces were rough, see Fig. 17(a). However,

the interfaces were found to be much smoother for

the walls tested in this work, as shown in Fig. 17(b).

Information provided by the manufacturer shows that

the GFRG panels for the previous work were

manufactured using the old technology in the old

(a)

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50

100

150

2000 10 20 30 40 50 60 70 80

0

50

100

150

200

e (k

N)

cro

F

Displacement (mm)

Analysis Test

(b)

0 10 20 30 40 50 60 70 80

0

50

100

150

2000 10 20 30 40 50 60 70 80

0

50

100

150

200

e (k

N)

cro

F

Displacement (mm)

Analysis Test

Fig. 12 Comparison of response curves between FEM and test

results. (a) specimen S1, (b) specimen S2

0 10 20 30 40 50 600

50

100

150

200

2500 10 20 30 40 50 60

0

50

100

150

200

250

e (k

N)

cro

F

Displacement (mm)

Large friction Small friction

Fig. 13 Response curves of wall S1 with different interface

properties

0 10 20 30 40 50 60 70 80

0

50

100

150

2000 10 20 30 40 50 60 70 80

0

50

100

150

200

Vertical load=184kN Vertical load=312kN

e (k

N)

cro

F

Displacement (mm)

Fig. 14 Comparison of response curves of wall S1 with little

interfacial friction

0 4 8 12 16 200

50

100

150

200

2500 4 8 12 16 20

0

50

100

150

200

250e

(kN

)cr

oF

Displacement (mm)

Vertical load = 312 kN/mVertical load = 184 kN/m

Fig. 15 Comparison of response curves of wall S1 with a

greater interfacial friction


production line in Adelaide, Australia. The wall

panels used in this work were produced with a new

technology in the new production line at Jinan,

China.

The above analyses explained the importance of

the interfacial roughness in the shear strength of the

concrete filled GFRG walls. Therefore, it is important

for designers to understand that the design guidelines

developed from the previous experimental investiga-

tions are only applicable to GFRG panels that are

made from the old production lines. For panels made

with the new technology in the new production lines,

the results and conclusions derived from this work

shall be applicable. To be conservative, the axial load

effect on the shear strength can be omitted in designs.

8 Conclusions

This work investigates the shear strength of the

concrete-filled GFRG walls. The structural system of

these walls includes a top and a bottom RC beam.

Partial concrete filling to the hollow cores of the

GFRG panels was considered in the investigation.

Full scale experimental testing was undertaken to

evaluate the lateral resistance of the walls. Nonlinear

finite element analyses are utilized to study the

various factors that may affect the shear strength of

the walls. Based on the test results and the FEM

analyses, the shear design model for the walls is

developed. From this study, the following conclu-

sions are drawn:

1. The longitudinal shear failure is typical in both

the fully and the partially concrete filled GFRG

walls;

2. The lateral resistance of the walls with a top and

a bottom beam consists of two parts: (a) the

flexural resistance of the internal RC frame

formed by the top and the bottom beams and

the infill concrete cores; and (b) the shear

strength of the GFRG panel that equals to the

length of the panel multiplied by the unit shear

strength that depends on the strength of the

panel;

3. The internal surface roughness of the panel or the

frictional bond at the interfaces between the

concrete cores and the GFRG panel significantly

affects the axial load effect on the shear strength

of the walls. When the interfaces are smooth,

Fig. 16 Vertical load effect

Fig. 17 Surface of concrete

core. (a) Reference [2], (b)

this test


which was the case tested in this work, the axial

load has no effect on the shear strength of the

walls; and

4. The above conclusion on the axial load effect is

general and applicable to other kinds of walls. It

is generally accepted in the conventional RC

theory that the axial load increases the shear

strength of a wall. The results from this study

reveal that this axial load effect may not exist

when longitudinal joints or weaknesses that

affect the transfer of longitudinal shear stress

present in a wall.

Acknowledgement The work described in this paper was

fully supported by a grant from the Research Grant Council of

the Hong Kong Special Administrative Region, China [Project

No. CityU 1113/04E].

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shear strength of concrete filled glass fiber reinforced gypsum walls

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