static and dynamic loading tests on the haro armour unit

8/10/2019 STATIC AND DYNAMIC LOADING TESTS ON THE HARO ARMOUR UNIT

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CHAPTER 3 1

STATIC AND DYNAMIC LOADING TESTS ON THE HARO ARMOUR UNIT

L. Van Damme1 J. De Rouck2

L. Taerwe3

R. Dedeyne4

J. Degrieck5

1. ABSTRACT

During he harbour xtension works t Zeebrugge new rmour unit has been developed he ARO. ests n av e lume nd ave ank howed ery ood hydraulic tability, omparable o hat of th e dolos. Static nd dynamic oading ests n th e aboratory nd endulum ests n ite onfirm he ARO s xcellent tructural performance, omparable o hat f he ube. ased n he esults f xhaustive investigations one an tate hat he HARO s afe nd conomical olution or he protection of maritime structures.

2. INTRODUCTION

The HARO s plain oncrete block or he protection of maritime tructures (breakwaters, ea walls, groynes ..) gainst wave attack. t found n extensive application n he harbour xtension works t Zeebrugge. t s lso urrently being used or th e Gwadar Port in Pakistan. The name HARO is registered by HAECON N.V.

The HARO s ompact oncrete block with arge entral opening fig. ). Both hort sides re made wider t th e base. The orners re symmetrically apered n plan. Thanks to the large central opening, the protuberances at th e short sides and

Ministry of Public Works, Coastal Department, Ostend, Belgium 2HAECON N.V. nd Ghent State University, Ghent, Belgium 3Magnel Laboratory fo r Reinforced Concrete, Ghent State University, Ghent, Belgium

4Bureau SECO, Brussels, Belgium department fo r Mechanics of Materials and Structures, Ghent State University, Ghent, Belgium.

1755


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1756 COASTAL ENGINEERING-1990

a-1.10

CROSS ECTION

PLAN IEW

CROSS - SECTION -

Figure

.

Geometry of the HARO

armour unit

conform n ppropriate lacement attern, orosity s igh s 1-53 % can e achieved.

An xhaustive aboratory nvestigation onducted t he ydraulic esearch Laboratory n Borgerhout Antwerp) howed very good hydraulic tability which s comparable o hat of th e dolos De Rouck t al 987; Wens t al., 990). However, the reliability of th e armour layer and thus the whole rubble mound breakwater, not only depends on the hydraulic stability of th e armour units but also o large xtent on their structural trength. Unfortunately, ailures n the late seventies nd n he arly ighties showed this point al l too clearly. n order to verify the structural strength of the HARO, static nd ynamic oading ests were arried out n he Magnel Laboratory of Ghent State University an d on the site.

3. STATIC LOADING TEST

The test set-up or th e static loading test on a 50 kN HARO s shown in fig. . The block was urned on ts ide nd placed n wo upporting oncrete beams ith variable depth. n he upper urface, ircular teel disc 3 00 mm 0) , n which he load P was applied, was placed. This load application point is located on the axis passing through he entroid of cross-section BB fig. ). During he est, he otal oad P was


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ARMOUR UNIT LOADING TESTS 1757

LV LA.SV BM.BA LOAD P 0A.0M.OV.RV.RA STRAIN AUOE3 0A.0M.OV.I

Figure 2. Test set-up fo r the static loading test


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increased by ncrements of 200 kN . At ach oa d evel he deformation of th e oncrete surface was easured t 0 different points by means f train gauges ith gauge length of 6 0 mm. he train gauges were positioned parallel o he original upper nd lower aces f he block. he hortening of he minor xis f he entral ole as measured along three verticals.

Rupture of the block occured at a load level of 2400 kN which corresponds to 6 times the weight of the block itself. Fig. shows the HARO after failure.

Figure 3 . Block after th e static loading test

The shortening of the short central axis BM-OM in relation to th e applied load P is shown in fig. . From this figure it appears that the elastic state extends to bout 1600 kN. eyond his value he hortening of the xis BM-OM ncreases t higher rate. his on-linear behaviour s onfirmed y he train gauge eadings. easured strains nd trains ound n upporting -dimensional inear lastic inite lement analysis orrespond reasonably well or loads up o P = 6 00 kN, s s hown in fig. fo r train gauge LA. From his oad evel on , he ourse of th e measured train signals varies ather widely depending on he ocation of th e train gauges. his s du e o he fact that during th e loading process th e internal tress distribution gradually changes nd that only local trains re measured. The maximum measured tensile) train quals 90 1 0 6 (strain gauge BV).

As he tatic oading est oncerns, he otal nput nergy s btained s he surface under th e load-displacement curve. Associating th e decrease Ad of th e xis BM- OM with th e displacement at th e point load, on e can obtain from fig. th e energy values mentioned in table .


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Figure 4 . Shortening of the axis BM-OM as function of th e load P

2400

2000

1600

1200

a o o

400

kN

MEA 3URED

i

/ CALCULATED 3D. Ei

STRA N o 6 20 40 60 80 100

Figure 5. Comparison of measured an d calculated strain at LA


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1760 COASTAL ENGINEERING- 1990

TABLE - Static loading test

P k N A d m m E i k J )

1 6 0 0 0 . 2 1 0 . 2 5 2

2 4 0 0 0 . 5 0 . 8 0 0

2 4 0 0 0 . 7 1 . 2 8 0

After th e est, ores were drilled t he upper nd ower ace of the block. n the ores 1 13 mm n diameter nd 00 mm n height) ompression nd plitting ests were performed. ompressive trengths qual o 3 .4 M Pa nd 8.7 M Pa were ound respectively or he upper nd ower urface. Values of 3.08 M Pa upper urface) nd 3.67 Pa lower urface) ere obtained or he plitting ensile trength. ac h value represents the mean of three test results.

4. DYNAMIC LOADING TEST IN THE LABORATORY

The est et-up or he dynamic oading es t s ssentially he am e s or he static one. The impact is performed by means of a falling steel block, having a mass of 51 6 kg. The vertical movement of the block is guided by tw o steel laths which fit, with some

margin,

n

vertical

notches

at

tw o

opposite

side

faces

of the

steel

block.

The

lifting

hook is designed in such a way that delocking takes place almost instantaneously.

Figure 6 . Block after th e dynamic loading test


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ARMOUR UNIT LOADING TESTS 1 7 6 1

The height of fall, being equal o 0 mm he first time, was uccessively increased by 50 mm ncrements until omplete failure of th e HARO took place. The following cracking sequence could be observed by the naked eye - drop height of 6 50 mm ertical rack t he upper nner ace, xtending o he ront

an d back face. - drop height of 700 mm ertical crack at th e lower inner face. - drop height of 750 mm orizontal crack at the left inner face. - drop height of 800 mm xtension of th e vertical racks nd upture of the block nto

tw o parts (fig. ).

In fig. , he maximum tensile strain, ecorded during the impact at the locations RA, BM, LA nd OM s plotted. t ollows that fter he mpact rom 50 mm height, cracking lready ccured t he ower nner ace OM). he aximum train t he upper nner ace ppears o emain lmost onstant t value of 80 microstrain ro m th e

mpact

ro m

50

mm height

on. oteworthy s hat

he

maximum

oncrete

train,

again orresponds o he sual ange .e . 50-200 0 6, s ncountered n he tatic loading test.

200 strain 10~6

200 400

drop height m m )

600 800

Figure 7. Measured peak strains during impact

The nergy nput orresponding o he otential nergy f he mpactor s obtained from

E; = m;g Ah (1 )


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where mj mass of the impactor (516 kg) g gravitational acceleration

Ah drop height.

For Ah qual o 50 mm onset of damage) nd 00 mm complete upture) he values Ej, mentioned in table 2, are obtained. As it was observed that rebound of the impactor

TABLE 2 - Dynamic test in th e laboratory

Ah Ei(kJ)

550 mm 2.784

800 mm 4.050

remained very limited, hese values an reasonably be considered as th e energy bsorbed by the HARO block. The values mentioned in table re considerably smaller than those given in table 2.

From the dynamic measurements, he impact time was calculated as 0.7 ms.

5. PENDULUM TESTS ON THE SITE

5.1. General description

Armour units hould be ble o ithstand mpacts rom djacent units. hese impacts an occur while placing the units on th e slope or under wave attack. n order to simulate these impacts, pendulum tests were carried out on site.

A 50 kN HARO suspended by a cable at th e top of a crane jib was first given a horizontal deviation d rom ts quilibrium position an d then swung gainst other blocks at rest on a rock be d fig. ). Two different impact situations were envisaged fig. ). n th e first test, he impact block hits tw o blocks of an adjacent row. n the second test, n edge of the impact block hits another block on its weakest side. The first situation results from he design placement pattern (a block of an upper row ests gainst tw o blocks of the lower row). The second is deemed to correspond to an exceptional event.

5.2. First test series

The irst series of tests s performed ccording o he irst mpact ituation. The horizontal deviation d before elease was progressively ncreased by 0.50 m. he inal deviation mounted o .00 . o urther ncrement as ossible ue o echnical limitations imposed by the crane. None of the blocks was broken. Only the three directly involved blocks were locally damaged at the protuberances.

In

able

,

alues

of the

maximum

ccelerations

measured

t different

ocations

on he back ide of he mpact block re mentioned. o eliable train measurements were obtained during the test series.


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OASTAL ENGINEERING 1990

TABLE 3 - First test series accelerations an d potential energies Ej

Horizontal deviation d

(m)

Ah (m)

Accelerations (m/s2) Ei(kJ) 0.5 Ej (kJ)

Al A2 A3 Mean

3.0 0.174 51 0 220 180 3 00 25.6 12.8

4.0 0.310 53 0 3 4 0 4 00 4 00 45.6 22.8

4.5 0.392 110 3 0 20 50 57.7 28.8

5.0 0.485 6 20 270 3 6 0 4 20 71.4 35.7

5.5 0.588 4 20 3 70 3 00 3 6 0 86.5 43 .3

6.0 0.702 280 200 3 1 0 26 0 103.2 51.6 6.5 0.826 83 0 1010 750 86 0 121.5 60.8

7.0 0.960 1000 1020 780 93 0 141.2 70.6

The deviation was rogressively ncreased by teps of . he arget block showed evere transverse cracks fter the mpact ou t from the 4 m deviation. n table 4 , peak values of accelerations nd trains re mentioned. The locations of th e ccelerome- ters A and th e strain gauges R are as follows

- Al nd A2 back side of target block (opposite to the impact face) - A3 ront side of impact block (opposite to th e impact face) - Rl nner back face of target block - R2 nner side face of target block - R3 nner front face of target block - R5 nner back face of impact block - R6 nner side face of impact block.

TABLE 4 - Second est series

Deviation d (m) Peak accelerations (m/s2)

Peak strains (1 0

) / indi tes str in g uge failure

Al A2 A3 Rl R2 R3 R5 R6

200 190 21 0 9 2 3 - -

2 3 6 0 220 140 140 6 14 50 -

3 4 50 880 3 3 0 160 10 25 12 2

4 73 0 1590 850 41 8 16


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The maximum peak strain, before rupture of strain gauge Rl, s equal to 60 0 ~6 which indicates that fo r th e three tests onsidered so far, he maximum concrete strain could be considered s useful ailure riterion. n ig. 9, he ecorded train ignal ro m train gauge R3 is shown fo r th e impact from d = m. t follows that the impact time is about 12

s.

ig .

0

hows

he

cceleration

ignal

3

or

he

am e

mpact

ituation.

he

second mpact at bout 295 msec s aused by th e rotation of the mpact block fter th e first contact at one of th e edges. t has to be noted that th e time scales of figs. nd 0 are different.

Only n very imited zone of th e front face of th e arget block, ocal rushing of he oncrete occured uring he irst ew mpacts. his ndicates hat he nergy release n th e contact zone remained mall. This locally damaged zone had diameter of about 0.25 m an d was located at a height of about 0.50 m.

5.4. Third test series

The third test series was lso performed ccording to the second impact situation. The target block was replaced by new on e bu t the impact block was th e same as n the second est eries. nly eviations qual o nd ere ealized. t he atter impact, evere transverse cracks occcured his time n th e impact block. Measured peak accelerations of th e impact block are given in table 5.

TABLE 5 - Third test series accelerations m/s2

Deviation d (m) Al A2 A3

90 20 6 0

4 720 1350 4 1 0

5.5. General emarks

- he esults f he ests ccording o he irst mpact ituation, hich ould occur during egular lacing f he locks, ndicate hat nder hese ircumstances o rupture of th e blocks seems possible in practice.

- he econd, ccidental mpact ituation, ppears o be more ritical. omparison of th e econd nd hird est eries ndicates hat he tress ields generated both n he impact nd he arget block, ause amage f omparable agnitude. ence he mention of 0.5 Ej in table 3 .

- he input energy t Ah = 00 mm n the laboratory test equals 4.05 kJ whereas t d = m, value of 22.8 J s obtained or he pendulum est. omparison nly based

on

energy

values,

ppears

not to

be appropriate.

- Interpretation of th e dynamic behaviour on the basis of th e acceleration measurements


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Strain 3 do

Figure 9. Strain signal R3 during impact from d = m (second test series)

Acceleration 3 m/sa

time ms

4C

Figure 0. Acceleration signal A3 during impact from d = m (second test series)


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ARMOUR UNIT LOADING TESTS

76 7

is ot traightforward. egarding he irst mpact ituation, ontact ith he wo adjacent blocks t rest never occurs imultaneously nd hence th e nergy distribution between he ifferent blocks urns ut o e uite omplex. n he econd mpact situation onsidered, he mpact block tarts o otate during he dge ontact. This results n ontribution of rotations o he measured otal cceleration ignal which cannot be separated from th e acceleration due to the main pendulum movement.

6. FURTHER CONSIDERATIONS WITH REGARD TO STRENGTH

For plain concrete armour units, tructural ntegrity depends o large xtent on th e bscence of significant racks, nd hus on th e oncrete ensile trength. major problem n his espect s racking ue o hermal tresses aused y he ydration process. Temperature measurements n both grooved cubes nd HAROs were carried out during th e first days fter casting (Van Damme t al., 988). Due to the central opening in he HARO he emperature ncrease emained mall nd esulted n onsiderable reduction of he hermal tresses t arly ge. o hermal racks re observed n he approximately 1000 HARO units manufactured in Zeebrugge. 7. CONCLUSIONS

- uring tatic oading est n he aboratory, he HARO block ailed t oad f 2400 kN, which represents 6 times its own weight.

- uring dynamic oading est n he aboratory, upture of a block took place fter the impact of a steel block with a mass of 51 6 kg from a drop height of 800 mm.

- endulum ests on he ite were performed ccording o wo different onfigurations (lower part of igure ). hen he mpact block was wung n between wo other blocks, p ro m orizontal eviation of , nly ocal amage f he blocks occured. When he mpact block hit n djacent block t ts weakest ide, ailure of the blocks occured for a horizontal deviation of 4 m.

- lthough he general tructural hape of he HARO s ess obust han assive cube, he esults of static nd dynamic oading ests on 50 kN block onfirm he adequate structural performance. ndeed, he tests prove that during regular placing of

th e individual

armour

elements

no

rupture of the

blocks seems

possible

in

practice.

Even n ase of an ccident, .g. ropping of a block during placement, he hance fo r damage of th e blocks remains negligible.

- ro m tructural point of view he maximum oncrete train an be onsidered s useful failure criterion both in static an d dynamic loading conditions. Further research on concrete to oncrete impact with large-scale tests would provide a better understan- ding of th e failure mechanism.

- t an be stated that all nvestigations hydraulic stability, un up, tructural trength, durability), he xperience on ite fabrication nd placement on he lope) nd he favourable ost price how hat he HARO perfectly ulfils ll performance riteria required for armour units.


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OASTAL ENGINEERING- 1990

8. ACKNOWLEDGMENT

The uthors gratefully cknowledge he ssistance of J. yncke formerly with he Magnel aboratory, ow ith he cientific nd echnical entre or he uilding

Industry at Brussels) during th e dynamic test in the laboratory. 9. REFERENCES

1. De Rouck J., Wens F., Van Damme L., Lemmers J. nvestigations nto he merits of the HARO-breakwater armour unit, Proc. nd COPEDEC, Bejing 987, Vol. II. pp. 054-1068.

2. Van Damme L., aerwe L., edeyne R., e Rouck . uality nd durability of conrete armour units, Proc. XXIst I.C.C.E., Torremolinos - Malaga, Spain 1988. Vol. . Ch. 56 , p. 102-2115.

3 . Wens F., e Rouck J., an Damme L. omparative aboratory nvestigations on HARO, grooved cubes, dolos an d tetrapods, (to be published in Coastal Engineering , Delft).

static and dynamic loading tests on the haro armour unit

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