Behaviour of high-strength concrete flexural walls

Proceedings of the Institution ofCivil EngineersStructures & Buildings 157April 2004 Issue SB2Pages 137–148

Paper 12709

Received 14/09/01Accepted 20/01/01

Keywords:buildings, structure & design/concrete structures/seismicengineering

Hyun-Do YunAssociate Professor,Department of ArchitecturalEngineering, ChungnamNational University, Daejeon,Korea

Chang-Sik ChoiAssociate Professor,Department of ArchitecturalEngineering, DaejinUniversity, Pouchon,Kyunggido, Korea

Li-Hyung LeeProfessor, Division ofArchitecture, HanyangUniversity, Seoul, Korea

Behaviour of high-strength concrete flexural walls

H.-D. Yun, C.-S. Choi and L.-H. Lee

This paper discusses the behaviour and strength of high-

strength (> 68·7 MPa) concrete structural walls. The

information will also enhance the current database for

the improvement of design recommendations. The

objectives of the present test were to investigate the

effect of parameters such as axial load and transverse

(horizontal) reinforcement on the behaviour of high-

strength concrete flexural walls, and to examine the

applicability of the ACI Building Code strength design

provision for predicting the strength of high-strength

concrete walls. To attain the objectives, five one-third

scale framed wall specimens were designed, constructed,

and tested. The walls tested were 1·20 m wide, 2·00 m

high and 85 mm thick with 180 mm 3 180 mm boundary

elements. The axial-load ratio was found to have a

significant effect on the flexural strength, failure mode

and ductility of high-strength concrete structural walls.

At a higher level of vertical load, lateral resistance of the

wall was improved, but ductility and deformability

decreased. The reduction of the horizontal web

reinforcement to almost half of the value specified by

the ACI Building Codes does not significantly affect the

failure load and the hysteretic behaviour.

NOTATION

Ag cross-sectional area of wall

Et cumulative dissipated energy

f 9c specified compressive strength of concrete in MPa

ki the secant stiffness corresponding to the first cycle in

each stage

ky the secant stiffness in the yielding

Vc the shear force contribution from the concrete

Vi the shear force corresponding to the first cycle in each

stage

Vy yielding shear force

Vu maximum shear force

Vs the shear force contribution from the horizontal

reinforcement

Vq shear strength of wall, defined in AIJ Guidelines

Vn the nominal shear strength of wall, defined in Appendix

A of ACI 318-99

�i the displacement corresponding to the first cycle in

each stage

�y yielding displacement

1. INTRODUCTION

Reinforced concrete structural walls are commonly used in

earthquake-resistant structures to satisfy the requirements for

lateral strength and stiffness against seismic forces, not only

for high-rise, but also for low-rise buildings in areas of high or

moderate seismic activity. In the event of a strong earthquake,

these walls generally behave beyond the elastic range and may

develop significant inelastic deformations. In designing

structural walls, a structural engineer must not only provide

adequate strength and stiffness, but should ensure that the wall

exhibits adequate ductility at severe earthquake conditions.

However, reinforced concrete walls are susceptible to brittle

failures when subjected to high axial loads due to gravity load

and seismic action. This tendency will become more

pronounced with increasing concrete strength.

Over the past two decades, major advances have been made in

the understanding of the behaviour of reinforced concrete

structural walls, particularly with regard to the role of the

variables improving seismic performance.1–5

However, little

experimental work has been done to assess the behaviour of

reinforced concrete shear walls subjected to high axial load,

partly because of the difficulty of applying high axial loads to

slender shear walls due to the inherent out-of-plane wall

instability problem. Lefas and Kotsovos6studied the effect of

axial load on strength, stiffness, and deformation

characteristics of rectangular walls under a constant axial load

and a monotonically increasing horizontal load. Zhang and

Wang7investigated the influence of axial-load ratio and shear

compression ratio on the behaviour of rectangular shear walls.

While little research has been carried out on framed walls

under high gravity load and seismic action, high-strength

concrete framed walls are becoming more frequently used as

the lateral resisting elements in wide-bay high-rise buildings.

This investigation is an exploratory phase of an experimental

programme of high-strength concrete framed walls subject to

the combined action of constant high axial load and reversed

cyclic horizontal loading.

2. EXPERIMENTAL PROGRAMME

The experiment described here involves the testing of five one-

third scale framed flexural walls with a height-to-width ratio

(hw=lw) of 1·80. Such walls, as shown in Fig. 1, are considered

to represent the three lower critical stories of a 60-storey

building structural wall system, six-bay by six-bay office,

assumed to be located in the Korean Seismic Design Code8

Structures & Buildings 157 Issue SB2 Yun et al. 137Behaviour of concrete flexural walls

seismic zone 2 (similar to the Uniform Building Code (UBC)9

seismic zone 2). The structural system consisted of six and four

walls in the E–W and N–S direction, respectively. The N–S

walls were selected for study.

The scope of the experiment was limited to tests on isolated

wall specimens. The test specimens were subjected to constant

axial load and reversed cyclic horizontal loading. All the

specimens were designed based on the philosophy that lateral

load capacity was controlled by flexure and, therefore, the

undesirable premature shear failure during the experiment

would be prevented. The overall dimensions of the test

specimens were kept constant.

2.1. Test specimen description

Many research projects10, 11

on size effect have shown that for

quasi-brittle materials the nominal stress at the ultimate load

exhibits a dependence on the specimen size. As size increases

300

300

500

150

500

150

700

400

207.585207.5500

A A

8-HD10

85

150 180 8401500

180 150

φ6@40

φ6@80

300

2000

400

2700

160

160

180

500

180

180

840

φ6@120

φ6@120

180

φ6@40

8D10(a)

180

180

840

φ6@120

φ6@60

180

φ6@40

8D10

(b)

180

180

840

φ6@120

φ6@240

180

φ6@40

8D10(c)

4-D10

4-D10

Fig. 1. Geometry and reinforcement details (section A–A) of wall specimens (dimensions in mm):(a) HW1, HW2 and HW3; (b) HW4; and (c) HW5

Structures & Buildings 157 Issue SB2 Yun et al.138 Behaviour of concrete flexural walls

there is a reduction in the nominal stress at ultimate load of

reinforced concrete members, with low amounts of shear and

flexural reinforcement. Although it is desirable to make full-

scale tests, due to limited resources it was only possible to test

at one-third scale in this project. On the basis of Pilakoutas’s

test results12

on geometrically similar walls with scales 1:2·5

and 1:5 and having aspect ratio 2·0, it was thought that

experiments at one-third scale will have little difference in

behaviour from a prototype structural wall.

Five isolated flexural walls, HW1 to HW5, as shown in Fig. 1,

were constructed and tested in this investigation. The

dimensions of the specimens correspond to one-third the

dimensions of the prototype. To scale down the prototype

structure to the specimens, two independent scale factors were

chosen for stress and length; all remaining scale factors were

either equal to unity or were functions of two factors. Each

wall was tested under combined action of constant axial load

and horizontal load reversals. All five wall specimens had

boundary elements. Boundary element transverse

reinforcement, 6 mm diameter hoops spaced at about 40 mm,

was selected in a way such that adequate confinement to core

concrete would be provided and longitudinal reinforcement

buckling in the post-yielding stage would also be prevented.

The geometry, dimensions, amount and arrangement of the

boundary elements of the walls were identical for all five

specimens. The main flexural reinforcement of each boundary

element consisted of eight 10 mm diameter high-tensile

deformed steel bars arranged in a rectangular manner.

All the specimens had the same geometry and were

monolithically connected to the top and foundation beam. A

heavily reinforced top beam (1·50 m long3300 mm deep 3

300 mm wide) functioned as both a uniform load transfer

through which axial and horizontal loads were applied to the

walls and as a cage for anchorage of the vertical bars. The

foundation beam (1·50 m long3400 mm deep 3 500 mm wide)

was utilised to clamp the specimens to the laboratory floor,

simulating a rigid foundation. A summary of the experimental

programme is presented in Table 1. The overall geometry and

dimensions of the wall specimens and reinforcement details are

shown in Fig. 1.

HW1 to HW3 were designed using 0·55% horizontal and 0·55%

vertical web reinforcement ratios. Vertical reinforcement

consisted of seven pairs of 6 mm diameter high-tensile round

steel bars, uniformly placed in two layers. The uniformly

distributed horizontal web steel consisted of two layers of

6 mm diameter high-tensile round steel bars. The bars were

spaced at 120 mm along the full height of the wall.

HW4 and HW5, with an axial-load ratio of 0·12, were designed

using 0·55% vertical web reinforcement ratios. Vertical

reinforcement consisted of seven pairs of high-tensile round

steel bars of 6 mm diameter, uniformly placed in two layers.

These bars were extended into the top beam and bottom-

footing slab by at least their development lengths. In an

attempt to test the validity of the shear (horizontal)

reinforcement for high-strength concrete flexural walls, HW4

and HW5 were designed using 1·10% and 0·25% horizontal

web reinforcement ratios, respectively. The horizontal bars

were anchored into the core of each boundary element using

908 hooks.

All reinforcing bars were provided with adequate anchorage

lengths at their ends. This was achieved by providing cogs at

the ends of the bars. All closed ties were terminated with 1358

hooks. In all specimens, the clear concrete cover to

reinforcement was 20 mm. Additional horizontal

reinforcement, four 10 mm diameter deformed bars, was

arranged at each floor slab level.

2.2. Material properties

Commercial ready-mixed concrete with replacement of 7·8%

(by weight) cement by silica fume was used and was made

using a selected ASTM Type I Portland cement. A high-range

water reducer (superplasticiser) and water-reducing retarder

were added to the mix to improve workability. The specified

28-day compressive strength of the mix was 68·7 MPa. The

maximum size of aggregate was 15 mm in order to ensure

good compaction of concrete in the test specimen. The slump

of the concrete was 150 mm. For each batch, 100 mm 3

200 mm cylinders were made to measure the compressive

strength and the splitting tensile strength of concrete. The

measured concrete strength and elastic modulus were tested by

the ASTM standard test method. The compressive strength and

the splitting tensile strength on the day of the wall test are

given in Table 2.

The reinforcing steel for all five walls was obtained from one

batch of steel for each bar diameter. Three samples were taken

and tested from each diameter of reinforcing used. Tension

tests were conducted on full-size bar samples in accordance

with ASTM A370 to determine yield strength, ultimate

strength, and total elongation. The physical properties of

reinforcing steel are given in Table 3. The test wall specimens

Wall Axial-load Storey beam Wall Boundary elementspecimen ratio reinforcement

ratio: % W3 H3 T:m3m3mm

rv:%

rh:%

B3 D:mm3mm

r f :%

rs:%

HW1 0·24 1·11 1·2 3 2·0 3 85 0·55 0·55 180 3 180 1·75 0·78HW2 0·12 1·11 1·2 3 2·0 3 85 0·55 0·55 180 3 180 1·75 0·78HW3 0·00 1·11 1·2 3 2·0 3 85 0·55 0·55 180 3 180 1·75 0·78HW4 0·12 1·11 1·2 3 2·0 3 85 0·55 1·10 180 3 180 1·75 0·78HW5 0·12 1·11 1·2 3 2·0 3 85 0·55 0·28 180 3 180 1·75 0·78

Table 1. Details of test specimens


were monolithically connected to foundation beams and cast

horizontally in timber moulds.

2.3. Testing apparatus

The testing apparatus is shown in Fig. 2. The wall footing is

rigidly connected to the strong floor using eight 32 mm

diameter high-tension bolts. A 980 kN MTS hydraulic actuator

attached to the reaction frame was used to apply a horizontal

force to the load transfer assembly mounted on the top of the

wall. To ensure out-of-plane stability and represent the

diaphragm effect of a floor slab, the wall is laterally guided by

low friction sliding ball bearings at the levels of the first and

second floor. Axial load was provided with a 980 kN MTS

hydraulic actuator on the top of the load transfer assembly and

maintained concentric to the test wall at all stages of loading.

2.4. Instrumentation and data acquisition

The data acquisition system consisted of 36 internal control

and recording channels. Instrumentation was provided to

measure loads, displacement, and strains at critical locations.

Lateral and axial load were measured using load cells capable

of maintaining linearity up to 980 kN. The load cells were

calibrated before and after each test in a test machine. As

shown in Fig. 3, the displacements of each specimen were

Compressive strength: MPa Slump: Elastic modulus: Poisson’smm MPa ratio

5-day 7-day 28-day 90-day�

42 63 65 69 150 33,150 0·11

� At the time of testing

Table 2. Average concrete compressive strengths

Type Yield strength, fsy: MPa Ultimate strength fsu: MPa

10 mm diameter deformed bar 413·9 664·06 mm diameter round bar 571·8 636·5

Table 3. Properties of reinforcement bars

Reaction wall

Strong frame

Loading beam

Ball jig

Reaction slab

Specimen

980 kN MTSActuator

Fig. 2. Test set-up

L11

L2

L3

L4

L5

L6

L1

L2

L3

L4

L5

L6

L1

L10

L9

L8

V13

V12

V11

V10

V1, V2V3

H2

HP1V7V6 V5 V4

H4H3

H6H5

V8, V9

H1

L7

Fig. 3. Instrumentation arrangement


measured using linear variable differential transducers (LVDTs).

Two LVDTs were installed at the top of the specimen to

monitor the top displacement. The horizontal displacement

profile of each specimen was measured using an LVDT at each

storey level (at three locations over the wall height). One LVDT

was installed at a distance of 100 mm from the wall base to

measure the sliding of the base. Twelve LVDTs were installed

close to the boundary elements to measure the curvatures

along the height of walls to obtain the flexural deflection. Steel

strain gauges were also provided on numerous hoops and

cross-ties within the boundary elements and on horizontal and

vertical reinforcement within the web. The foregoing system of

measurements made it possible to estimate the flexural, shear,

and sliding components of the wall deformation.

2.5. Testing procedure

A constant axial load was first applied through a spread beam

at the centres of the boundary elements of walls. HW1 to HW3

were subjected to three levels of axial-load ratio corresponding

to 0·24, 0·12, and 0·00 of the uniaxial compressive strength of

the wall cross-section that is equal to 0:97 f 9cAg. These levels of

axial load might be considered representative at the base of a

single-storey, medium-rise, and high-rise building,

respectively. During each test, the displacement at the top of

the wall was controlled.

A reverse cyclic loading was applied slowly to the top of the

specimens. The intended loading programme for all the walls is

shown in Fig. 4. Initially, the test specimen was exercised by

applying a 49 kN horizontal load in order to ensure that all

systems were working. The initial load was then released and

the zero reading was taken. The walls were cycled three times

at each of the incrementally increasing deflection levels until

failure. The deflection increments were based on yield

deflection. The yield deflection was determined by drawing a

straight line from the origin through the first yield load and its

intersection with a horizontal line drawn at the calculated

ultimate load level. The first yield load was obtained

experimentally when the strain gauges on the extreme tension

reinforcement at the boundary elements yielded.

3. EXPERIMENTAL RESULTS

3.1. Cracking process and failure mode

Flexural cracks initially appeared at the base of boundary

elements in the tensile zone during the first elastic loading, and

the cracks propagated from the wall boundary elements

towards the centre and from the bottom upwards. These cracks

were initially horizontal and confined within the length of the

boundary elements, but as the loading increased, they became

slightly inclined downwards and extended into the web (Fig. 5).

Eventually, these cracks formed a diagonal cracking pattern in

the web. The inclination increased along the wall height. At the

boundary elements, the density of the cracks increased, while

in the web the number of main cracks was limited to about

four or five on each side. In the lower part of the wall, flexural

cracks originating from one edge were intersected by inclined

shear or flexural-shear cracks originating from the opposite

edge, resulting in a characteristic criss-cross pattern, as shown

in Fig. 6. With cycling to increased deformations, the

rhomboidal pieces of concrete between the intersecting cracks

gradually deteriorated and spalling of cover concrete occurred.

The spalling zone extended further upwards in the case of

specimen HW3, which was subjected to horizontal load without

axial load (Fig. 7(c)). In the case of specimen HW4, which was

heavily reinforced (Fig. 7(d)) and had an axial-load ratio of

0·12, a major horizontal crack running through the entire base

of the wall formed but did not form in the other specimens. A

flexural plastic hinge region formed at the lower portion of the

wall; the height of the plastic hinge zone was approximately

half of the wall length. As loading continued, vertical cracks

appeared at the edge of the compression zone of the boundary

element bottom portion. The concrete cover at the toe in the

compression zone spalled off, while a number of closely spaced

vertical cracks developed inward and upward in the plastic

hinge zone.

�8

�6

�4

�2

0

2

4

6

8

Elasticcycle

1

4

7

10

13

16

Cycles

0 5 10 15 20 25 30 35 40

δy

δy

δy: Yield displacement

δi /δy

Fig. 4. Loading history


Significant loss of strength, leading to failure, was observed

when the concrete started to deteriorate in the most heavily

stressed parts of the boundary elements, and the web, hoops

and horizontal bars began to lose support and move away from

each other, as buckling and kinking of the longitudinal bars

occurred. The effects of axial-load ratio and the number of

horizontal bars on the cracking pattern and failure mode of the

specimens can be seen in Fig. 7. Because wall behaviour was

controlled by flexure, the cracking process was similar for all

specimens (see Fig. 5 and 6).

Figures 5 to 7 show the specimens after yielding and at failure.

It was observed that the high axial-load ratio restrained the

development of major inclined cracks in the web. This is

because increased axial load will reduce the principal tensile

stress in the web portion of the wall. The presence of higher

levels of constant axial load led to even less extensive crack

formation. Fewer flexural cracks were formed at the tensile

edge of the wall and diagonal cracking covered less of the web

of the wall. Nevertheless, higher axial-load levels only

managed to delay but not prevent the extension of the inclined

crack within the lower compressive edge of the boundary

elements.

3.2. Load–displacement response

Figure 8 shows the base shear force–top displacement

hysteresis loops for all the specimens. In the figure, the well-

known characteristics of reinforced concrete members

subjected to cyclic loading, such as unloading and reloading

stiffness reduction as the cyclic displacement amplitude

increases, and pinching of hysteresis loops, can be clearly seen.

The loops for the three specimens with a constant axial-load

ratio of 0·12 (Fig. 8(b), (d) and (e)) are generally similar,

exhibiting the characteristics of gradual stiffness and strength

degradation, and a significant degree of pinching; the latter is

much pronounced in the HW4 specimen with twice as much

Fig. 5. Cracking pattern at the yielding stage: (a) HW1; (b) HW2; (c) HW3; (d) HW4; and (e)HW5


horizontal reinforcement than that specified by the ACI

Building Code.13

Specimens HW2 and HW5 exhibited the

maximum degree of pinching although the amount of web

horizontal reinforcement in HW2 is double that in HW5; this is

a strong indication that pinching was controlled by bond-slip

and horizontal sliding, rather than by inclined shear crack

opening and web concrete crushing. Fig. 8(a) to (c) indicates

that even for high levels of constant axial load, some ductility

was observed and that as the axial load increases, load–

displacement response showed S-shaped hysteresis loops with

small residual displacement.

The strength of all specimens, except HW3, increased due to

the presence of the compression axial load, but the ductilities

Fig. 6. Cracking pattern at the ductility ratio of 3: (a) HW1; (b) HW2; (c) HW3; (d) HW4; and(e) HW5


were slightly inferior to that of HW3. Significant strength

degradation occurred at a displacement of 52 mm (2·65% drift)

following extensive concrete crushing and reinforcement

buckling at the boundary elements; further cycling led to

eventual fracture of some buckled bars. Hence, inelastic

performance of high-strength concrete structural walls

represented stable behaviour in flexural yielding and

maintaining horizontal load-carrying capacity. Despite the fact

that the HW4 and HW5 specimens incorporated twice and half

the amount of horizontal reinforcement used in the HW2

specimen, respectively, no significant difference in hysteretic

behaviour was observed.

3.3. Strength, stiffness and energy dissipation

characteristics

Table 4 summarises the prediction results of the ACI Building

Code and the Architectural Institution of Japan (AIJ)

Guideline14

and compares them with the experimentally

established load-carrying capacities of the walls. It is seen that

the predicted flexural strength of the specimen HW3, which

was not subjected to axial load, was almost the same as the

observed load-carrying capacity of the specimen. For

specimens HW1 and HW2 with axial-load ratio of 0·12 and

0·24 respectively, the measured strengths of these specimens

were larger than their predicted strengths by approximately

13%. This might be attributed to the enhanced concrete

strength due to confinement from surrounding concrete in high

axial-load ratio. The ACI 318-99 and AIJ Guideline therefore

seem to be slightly conservative.

The reduction of strength and stiffness of the reinforced

concrete, especially high-strength concrete, members subjected

to cyclic loading are significant for structures in seismic areas.

Therefore seismic-resistant members with significant

degradation of strength and stiffness due to the imposition of

severe cyclic loading must be avoided in seismic design. The

reductions of the shear load V i corresponding to the first cycle

in each stage plotted against displacement ductility ratio

(�i=�y) is shown in Fig. 9 for the positive and negative cycles.

The stiffness characteristics of high-strength concrete flexural

walls, which are a function of the slopes of the load–

deformation curves, were affected considerably under the

effects of the level of axial load. The stiffness characteristics of

the structural walls were dominated by a severe loss of stiffness

during and after yield as shown in Fig. 10(a). A principal cause

for loss of stiffness in walls was the diagonal shear crack and

crushing of wall web concrete. Fig. 10(a) indicates that all of

the specimens showed an increase in secant stiffness values as

the applied level of constant vertical stress increased. In the

early stages, the secant stiffness of HW1 was higher than that

for HW2 and HW3. However, with increasing loading cycles,

Fig. 7. Failure mode: (a) HW1; (b) HW2; (c) HW3; (d) HW4; and (e) HW5


the variation of secant stiffness for HW3 was less pronounced

than that for HW1 and HW2. It can be concluded that axial

load has a detrimental effect on stiffness variation in the post-

yielding stage of flexural wall deformation. When a

comparison is made between HW2, HW4 and HW5, which have

the same axial-load ratio but a different amount of horizontal

reinforcement, it was noticed that all specimens had similar

stiffness degradation, although HW2 and HW4 had a higher

horizontal reinforcement ratio. Fig. 10(b) shows the decay in

the stiffness and plots the ratio ki=k y against displacement

ductility. The secant stiffness values in each half-cycle are ki.

The energy dissipation of the specimens under cyclic loading

was defined as the area enclosed by the base shear force–top

displacement hysteresis loops shown in Fig. 8. Graphs of

cumulative dissipated energy Et versus displacement ductility

are plotted in Fig 11(a), which shows that the amount of

energy dissipated prior to first significant cracking of the wall

is relatively small, but increases greatly once this level is

exceeded. It is obvious that the energy dissipation capacity

rises with the increase of axial-load ratio in boundary

elements. Fig.11(b) illustrates the relationship between

normalised energy dissipated and displacement ductility. The

200

300

400

500

100

�100

�200

�300

�400

�500

She

ar fo

rce:

kN

200

300

400

500

100

�100

�200

�300

�400

�500

She

ar fo

rce:

kN

200

300

400

500

100

�100

�200

�300

�400

�500

She

ar fo

rce:

kN

200

300

400

500

100

�100

�200

�300

�400

�500

She

ar fo

rce:

kN

200

300

400

500

100

�100

�200

�300

�400

�500

She

ar fo

rce:

kN

(a) (b)

(c) (d)

(e)

�80�70�60�50�40�30�20�10 10 20 30 40 50 60 70 80Displacement: mm

�80�70�60�50�40�30�20�10 10 20 30 40 50 60 70 80Displacement: mm

�80�70�60�50�40�30�20�10 10 20 30 40 50 60 70 80Displacement: mm

�80�70�60�50�40�30�20�10 10 20 30 40 50 60 70 80Displacement: mm

�80�70�60�50�40�30�20�10 10 20 30 40 50 60 70 80Displacement: mm

Fig. 8. Horizontal load plotted against top horizontal displacement: (a) HW1; (b) HW2; (c) HW3; (d) HW4; and (e) HW5


normalised energy dissipated is defined as the energy

dissipated in a half hysteresis loop corresponding to positive

load direction divided by 0:5V y� y, where V y and �y are the

yielding load and yielding displacement, respectively.

Comparing the curves for HW1 and HW3 found that the high

axial load had a detrimental effect on the energy dissipation

behaviour of the walls.

Total energy imparted to the wall during virgin loading can be

separated into three components: the recoverable energy, the

damping energy, and the damage energy. The energy dissipated

by the wall is the sum of the damage energy and the damping

energy. Another way of presenting the energy dissipated per

cycle during a cyclic loading test is by using the concept of an

equivalent viscous damping. This term has been used by

investigators to correlate hysteretic energy dissipation to the

standard concept of structural damping used for linear systems.

Generally, measurements of the dynamic response of actual

structures in the elastic range close to yield strength indicate

that equivalent viscous damping levels of 5–7% for reinforced

Specimen ACI 318-9913

AIJ Guideline14

Experimentalresults

Flexural strength Shear strength Flexural strengthShear

strength

Vy Vu Vs Vc þ Vs Vn Upperlimit

Vy Vu Vq

HW1 332·7 387·0 256·0 537·5 449·6 677·2 316·1 383·7 546·7 442·0HW2 272·4 331·5 256·0 475·9 449·6 677·2 355·7 293·5 513·3 375·0HW3 173·3 241·2 256·0 395·4 449·6 677·2 103·7 161·5 469·6 234·1HW4 272·4 331·5 512·0 774·7 763·9 677·2 235·7 293·5 595·0 362·6HW5 272·4 331·5 133·3 319·5 449·6 677·2 235·7 293·5 469·9 371·6

Table 4. Correlation of test and predicted strengths (unit: kN)

100

150

200

250

300

350

400

450

500

She

ar fo

rce:

kN

0 2 4 6 8 10 12 14Displacement ductility

(a)

HW1

HW2

HW3

HW4

HW5

HW4

HW3

HW2

HW1

HW5


(b)

0.4

0.5

0.6

0.7

0.8

0.9

1.0

1.1

Vi/V

u

Fig. 9. Strength characteristics: (a) strength; and (b)degradation of strength (Vi=Vu)

HW4

HW3

HW2

HW1

HW5

0

10

20

30

40

50

60

70

Sec

ant s

tiffn

ess:

kN

/mm


(a)

HW4

HW3

HW2

HW1

HW5


(b)

0.0

0.2

0.4

0.6

0.8

1.0

1.2

Ki/K

y

Fig. 10. Stiffness characteristics: (a) secant stiffness; and (b)degradation of stiffness (ki=k y)


concrete is appropriate.15

In the elastic range close to yield

strength, the equivalent viscous damping level of high-strength

concrete flexural walls tested was approximately 5%.

4. CONCLUSIONS

The following conclusions are drawn based on the results of

tests conducted on reduced scaled models of high-strength

concrete flexural walls.

• Testing of high-strength concrete structural walls subjected

to high axial stresses, up to 0:24 f 9c, shows that it is possible

to ensure a predominantly ductile performance by

promoting flexural yielding of the vertical reinforcement.

Thus, in this respect, the behaviour of high-strength

concrete is not significantly different from that of normal-

strength concrete.

• The axial-load ratio had an important effect on the failure

mode, hysteresis loop, stiffness and ductility of the high-

strength concrete flexural walls. High-strength concrete

flexural walls initially subjected to a high level of axial

stress, 0:24 f 9c, load showed an 89% enhancement in

horizontal load capacity compared with the capacity of

wall not subjected to axial load.

• Strengths and deformational characteristics of wall

specimens HW4 and HW5 incorporating twice and half the

amount of the horizontal reinforcement included in

specimen HW2, were similar to the corresponding

characteristics of specimen HW2.

• Greater depths of neutral axis were observed with

increasing levels of axial compressive load applied to the

wall specimen. HW1 and HW2 specimens, subjected to

axial load, failed in a predominantly flexural mode,

characterised by the concrete crushing and reinforcement

buckling at the lower compressive zone of the boundary

elements. The failure region — plastic hinge zone — was

more extensive with increasing axial load. Web concrete

crushing (HW3 and HW5 specimens) and sliding at the

fixed base (specimen HW4) were also observed.

• The predicted strengths from ACI 318-99 Building Code

and AIJ Guideline underestimated the measured load-

carrying capacities of the high-strength concrete flexural

walls tested. ACI and AIJ formulas seem slightly

conservative based on the experiment results.

5. ACKNOWLEDGEMENTS

The authors gratefully acknowledge the financial support from

STRESS (advanced STructure RESearch Station), Hanyang

University, Seoul, South Korea.

REFERENCES

1. FIORATO A. E., OESTERLE R. G. and CORLEY W. G. Behavior of

earthquake resistant structural walls before and after

repair. ACI Journal, 1983, 80, No. 5, Sept.–Oct., 403–413.

2. PAULAY T. A. Design of ductile reinforced concrete

structural walls for earthquake resistance. Earthquake

Spectra, 1986, 2, No. 4, 783–823.

3. LOPE M. S. and ELNASHAI A. S. Behavior of reinforced

concrete walls subjected to high cyclic shear. Proceedings

of the 9th European Conference on Earthquake Engineering,

Moscow, 1990, 6, 80–86.

4. TAYLOR C. P., COTE P. A. and WALLACE J. W. Design of

slender reinforced concrete walls with openings. ACI

Structural Journal, 1998, 95, No. 4, July–Aug., 420–433.

5. SALONIKIOS T. N., KAPPOS A. J., TEGOS I. A. and PENELIS G. G.

Cyclic load behavior of low-slenderness reinforced

concrete walls: design basis and test results. ACI Structural

Journal, 1999, 96, No. 4, July–Aug., 649–660.

6. LEFAS I. D. and KOTSOVOS M. D. Strength and deformation

characteristics of reinforced concrete walls under load

reversals. ACI Structural Journal, 1990, 87, No. 6, Nov.–

Dec., 716–726.

7. ZHANG Y. F. and WANG Z. H. Seismic behavior of reinforced

concrete shear walls subjected to high axial loading. ACI

Structural Journal, 2000, 97, No. 5, Sept.–Oct., 739–750.

8. MINISTRY OF CONSTRUCTION AND TRANSPORTATION. Standard of

Design Loads for Buildings. Seoul, South Korea, 2000.

9. INTERNATIONAL CONFERENCE OF BUILDING OFFICIALS. Uniform

Building Code. Whittier, USA, 1997.

10. NEVILLE A. M. A general relation for strengths of concrete

specimens of different shapes and sizes. ACI Material

Journal, 1996, 63, No. 10, 1095–1109.

11. CARPINTERI A., FERRO G. and MONETTO I. Scale effects in

uniaxially compressed concrete specimens. Magazine of

Concrete Research, 1999, 51, No. 3, 217–225.

12. PILAKOUTAS K. Earthquake Resistant Design of Reinforced

Concrete Walls. PhD thesis, University of London, 1990.

13. ACI COMMITTEE 318. Building Code Requirements for

Reinforced Concrete (ACI 318–99) and Commentary.

American Concrete Institute, Detroit, 1999.

14. ARCHITECTURAL INSTITUTE OF JAPAN. Ultimate Strength and

Deformation Capacity of Buildings in Seismic Design.

Tokyo, Japan, 1990.

HW4

HW3

HW2

HW1

HW5

0

50

150

200

250

300

350

400

100

450

Cum

ulat

ive

diss

ipat

ed e

nerg

y: k

J


(a)

HW4

HW3

HW2

HW1

HW5

0

50

150

200

250

300

350

400

100

450

Nor

mal

ised

ene

rgy

diss

ipat

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(b)

Fig. 11. Energy characteristics: (a) cumulative dissipatedenergy; and (b) normalised energy dissipated


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15. PAULAY T. A. and PRIESTLEY M. J. N. Seismic Design of

Reinforced Concrete and Masonry Buildings. Wiley, 1992.

16. YUN H. D. Seismic Performance of High Strength Reinforced

Concrete Structural Walls. PhD thesis, Hanyang University,

1995.

17. YUN H. D., CHOI C. S. and LEE L. H. Flexural and shear

response of high strength R/C structural walls under high

axial stress. Proceedings of the 3rd International

Symposium on Architectural Interchanges in Asia, Cheyn

Island, Korea 2000.

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Behaviour of high-strength concrete flexural walls