Composite Structures 28 (1994) 441-448 © 1994 Elsevier Science Limited

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ELSEVIER

Long-term static testing of an FRP prototype highway structure

J. Lee, L. Hollaway, A. Thorne Composite Research Unit, University of Surrey, Guildford, Surrey, UK

&

P. Head Maunsell Structural Plastics, Beckenham, Kent, UK

In recent years it has become apparent that the labour and maintenance costs of highway structures fabricated from conventional constructional materials (i.e. steel and concrete) are rising, and therefore the whole life cost of these struc- tures is being significantly affected. Highway structures manufactured from advanced composite materials provide a viable solution to reduce substantially both the labour and the maintenance costs, whilst providing structures that behave in accordance with the present British code of practice for highway structures.

The principle objectives of the investigations were to undertake experi- mentally and to verify, where applicable, numerically the suitability of advanced fibre-reinforced polymer (FRP) composite materials manufactured in the form of box beams for use as highway structures. It was also important to research into any unique behaviour exhibited by the FRP structures while under test and to develop relevant theoretical models and formulae to characterize completely this behaviour.

The composite box beam showed no signs of global deterioration and generally behaved as predicted; the short term stiffness of the beam measured at specific times during the test did not decrease to any extent. There was some local flexural cracking in the connectors at the position of the applied loads, but this can be eliminated by design. The creep and deflections of the beam at the end of the test were well within acceptable limits.

1 INTRODUCTION completed by connecting the ten planks through longitudinal under cut grooves, bonding and 'dog-

The objective of this research was to investigate bone' connectors. The outside overall dimensions the long-tem performance of fibre-reinforced of the box beam are 0-76 m deep by 18 m long polymer (FRP) composites for use in highway and 2.13 m wide. The panel dimensions are 80 structures. Of particular interest were the effects mm deep by 18 m long and 0"6 m wide. The of prolonged environmental exposure on engi- composite was made from polyester resin manu- neering characteristics, such as material integrity factured by DSM Resins UK, Ltd, Lancashire, and structural strength and stiffness. UK and essentially unidirectional aligned E-glass

This paper discusses the full-scale experimental fibre manufactured by Vetrotex (U.K.) Ltd, and numerical tests undertaken on two box beams Oxfordshire, UK. The reinforcement also con- fabricated from the Maunsell Structural Plastics sisted of randomly oriented fibre on the two exter- ACCS (advanced composite construction system) nal faces of the laminates and a surface veil on the Plank. The main components of the beams con- exposed surface ofthe pultruded panels. The total sisted ot ten such planks which were manufac- fibre/matrix volume by weight was 68%; in the tured by the pultrusion technique by GEC subsequent analyses the material is considered to Reinforced Plastics Ltd, Lancashire, UK; the be orthotropic. The epoxy resin used to bond the cross-section is shown in Fig. 1. The beam is panels to the connector pieces along the longitudi-

441

442 J. Lee, L. Hollaway, T. Thorne, P. Head

I "" Elevation "-I

N 8 [] [] [] [] 7 o n [] o [] gl

~nont.Laul:l~ r~l;~Olglt.~Jl2 ,..'..' !glOlgll~Iglt.Ll f.:.:

L. 2310 d i - .~ w-!

Cross section

Key Notes

[ ] 80 x 80 voided eolmeetor (i) All dimensions are in millimetres 11~l~ll3rnl3r'll 603 x 80 voided plank (ii) All voids are 80 x 76 mm

Fig. 1. Prototype general arrangement drawings (not to scale).

nal length of the panel was from CIBA, Duxford, on both edges of each beam by precise levelling at Cambridge, UK. the extremities (the jack positions), at the sup-

ports, at the quarter joints of the central span and at the centre of the beams. Figure 3 shows these

2 EXPERIMENTAL TECHNIQUE various positions. A lap-top computer was used to ensure that the precise level measurements were

The loaded environmental test beams were within the required accuracy. Vibrating wire reacted against each other under a four-point (VW) gauges were used to monitor the strain loading system; this gave approximately the same distribution through the depth of the beam at its numerical values for the bending moment at mid- centre line on both outer webs of one box beam; span as would be experienced for a footbridge demec studs were bonded on to both of the outer structure loaded in accordance with the present webs of the two beams near to their centrelines; bridge loading. 1 Figure 2 shows the experimental the readings from the demec gauges verified those set-up. The beams were supported at quarter- of the VW gauges. Continuous monitoring of the point positions on brick piers through a series of temperature and humidity of the environment was arrangement consisting of soft timber planks and undertaken using a 'Psion' data logger. At specific a universal I-section distribution beam; this location points thermocouple readings were taken system simulated a line load reaction. The load during particularly hot days for 25 h (see Figs 4 was applied to the system through four hydraulic and 5; these readings were obtained using a Grant jacks, two at each end of the beam. Each jack was Squirrel data logger). A frequency distribution of in series with a load cell and rocker and two of temperature and humidity obtained from the these systems were reacted through a universal Psion is shown in Figs 6 and 7, respectively. In I-section distribution steel beam and soft timber addition to these environmental readings, meteor- planks all manufactured specifically for these ological data from the meteorological office at tests; the rockers were manufactured to allow Bracknell was obtained; these contained daily rotation and horizontal translation to enable the rainfall, sunshine and maximum and minimum creep and the expansion and contraction of the temperature readings for the period January to beam to take place freely. September 1992. Physical and in-service proper-

The deflections of the beams were measured ties of the beam are given in Table 1.

Long-term static testing of an FRP prototype highway structure 443

Centre fine , High tensile Mac Alloy bars ; Steel channel sections

Steel box section * (channels are jointed to the box i ;i beams, for clarity full channe l#4 . ~ Rockersteel bearingarrangementl beam ; length is not shown) [ . . . ~ ; Softwood bearing

; _ ~,......---~ Steel fixing channel i ~ Soft wood bearing

"~ l " [ 4 " " Upper prototype FRP box beam

~ Note___.~s Steel beating I beam i (i) Dimensions in 10 no. disc springs in series i millimetres Di 80 kN capacity jack i (ii) Bracing for wind jack Hydraulic load cell i loads is not shown Rocker arrangement !

, Steel bearing I beam / ; l+-i+ I -4~ - Soft wood bearing

; Lower prototype FRP box beam

i Details same as above. !" Steel fixin,, channel i but inverted Existing ground i level

Mortar base Brick pier Mac Alloy lock nut Reinforced concrete pad foundation

v I " "" I

Fig. 2. Prototype set-up for testing in the natural environment.

I ++ i + + l + + l + + l + + l ++ N

D i m e n s i o n s in m m

• P L r e f e r e n c e point n u m b e r

Plan view of box beam showing PL point

Top of web

- - 2 . .

- - 3 - ~ - - 4 • - ~ - - 5 - • S South side of beam - - 6 . N North side of beam - - 7 • • L ~ e r b e a m

Bottom of web U Upper beam V VW guage

-- VW guage DM '~Demec pipe • . DM pipe PL Precise level

Typical web elevation showing VW & DM locations

Fig. 3. Precise levelling (PL) and Demec (DM) locations points on both box beams.

4 4 4 J. Lee, L. Hollaway, T. Thorne, P. Head

40 100 rCMO1

3s ...-. ........................................ ~ ........ i ............. i ............ \ : /', 8 0 i . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . , . . . . . . . . . . . . . . . . . . . . . .

"" 30 ........ , .............. r ! ............ • . A ~ ~ 6o i~ ~ i ~ . .

O 25 " " i', • TCIvI04i ' 'i (~ ! " :

4o io'. st,,, ,,! i

, ,I', ,,# : 20 ~ .......... ;---~!~ ,. .............. ~i .............. ~i"i//",' ~ ................... .. ,.'~-':,';-.'" ~.

[~ I0 15 ........... i ~ ~ ~ il ............. ~ ......... ix i ............ i~"' .......... !i ............ ~ ~ 200 ......... ......................... _.~:.:_ ;-7.. k.~.; " :: "~" " .." %. ~.-L !"::" ......... .,-il ]i.~,..:.r. r .............. .:~ . . ..:::i ................... ....... ,'....':i:: ............

5 -20 I

0 5 I0 15 20 25 30 -I0 0 I0 20 30 40 50

H o u r s A m b i e n t t e m p e r a t u r e ( ° C )

- - Ambient . . . . . TCM03 Fig. 6. Ambien t tempera ture during the test period.

- TCM06 . . . . . TCM01

- - - - - TCM04 600 I I

Meastxement s t a r t t i m e 12.00 hrs 6 ~ J u l y 992 ,. ~

Measurements refer to the lower b o x ~ m Records were

Fig. 4. T h e r m o c o u p l e readings. ~ 500 ............ i .............. i .............. ~ ............ taken htmrly~ - :: i i ." Tolerenee 2%

4 0 0 ............ i .............. i .............. i ; ........ i .............. i ............

3 5 ~ I 4CM21 rCM2~ I ~ 300 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . , . . . . . . . . . . . . . . . . . . . . . . . . . . . . : . . . . . . . . . . . .

. . . . . . . . . . . . . . . . ! , . , . . . .~ 2 0 0 .......................................... : ' : ...................... i . . . . . . . . . .

I.L~ r ~"" : L) 25 .......... .\.'-.~ ......... i [ ................................... i ............ ~" ~ RH meter . , : - - - . - , ~ . - , , ./ ""

- i - 'x ~ 'CMl l l O /~/-:-'-,,'x~/'~'~ x>,, : : , ,: 1 0 0 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . i . . . . . . . . . . . . . i ..... wet ' " " " . . . . . . . . . . . . . . . " " " i i 20 ~ N ...... ......

i ~,, i i / i f ' " , i i , ' .............. i 0 . . . . . . . L , , ~ - ~ . - . _ ~ . . . . 15 ...................... ----i-~-'k,w.--'-----.--------~'/-:------ 0 2 0 4 0 6 0 8 0 100 120

# R e l a t i v e h u m i d i t y ( % )

10 ~ ............. i ............ Fig. 7. Relative humidity during the test period.

5 I I 0 5 10 15 20 25 30 Table 1. Proper t ies of the box beam

H o u r s Property Uni ts Value used

- - Ambient . . . . . TCM12 I~, plank mm 4 i f9 X 106 - T C M l l . . . . . TCM22 Ac/s plank mm 2 5550

I box beam m 4 0.0056 - - - - - TCM21 Ac/s box beam m 2 0.056

Density kg /m 3 1850 M e a s u r e m e n t start l i m e 12.00 hrs 6 th Ju ly 1992 Diffusivity (long) mm2/s 18 X 10 -7

Measmcments refer to the lower box b e a m Diffusivity (trans) mm2/s 30.0 x 1 0 - 7

Fig. 5. T h e r m o c o u p l e readings. Vf (by mass) - - 0"68

C/S = cross section, Vf = volume fraction, I = second moment of area, A = area.

3 NUMERICAL TECHNIQUE programme by Hibbit, Karlsson and Sorenson

The numerical analyses of the loaded beams were Inc., Providence Rhode Island, USA; the section undertaken by the finite element procedure. The of the program used was based on material non- analyses were carried out using the ABAQUS linearity. The finite element analyses were under-

Long-term static testing of an FRP prototype highway structure 445

taken to provide a numerical comparison with the Abaqus using the Ramberg-Osgood model 2) for experimental solution and to validate material this material, five integration points per e l e m e n t models and parameters. In the analyses two ele- were the minimum required to determine the ment types were considered for the modelling of response of the plank; 3 reduced integration was the plank and thence for the modelling of the box used to provide the solution. beams. The first was a shell element of 80 In order to model the plank, three layers of mm x 86 mmx 3 mm thick and was modelled as a element type 2 were considered; the outer layer single laminate (this element will hereafter be (the face material) modelled the flanges of the referred to as element type 1). The upper and panel using laminate theory, whilst the interme- lower flanges of the panel consist of seven rows diate layer (the core material) modelled the webs each containing 225 of these elements and like- of the panel; the face and core materials had wise the eight webs associated with the plank each orthotropic material properties. The panel con- had one row of 225 elements. The second ele- sisted of four elements across the width and 120 ment type from the ABAQUS element library elements along its length. It is clear than the shell utilised in the analyses was a laminated shell ele- element type 1 models the box beam with a high ment coded $8R5 and shown in Fig. 8. This ele- degree of accuracy. It has the disadvantage, ment will be referred to as element type 2; it can however, that it requires a very long computa- be described as a bi-quadratic, quadrilateral, iso- tional time and large computer storage for this parametric doubly curved and multi-layered shell problem compared with element type 2. This element. From a mathematical viewpoint, the latter element is a sophisticated one and suits the cross-section was formed by numerical integra- plank idealisation well. However, under static tion, thus allowing complete generality in material loading it was necessary to undertake a com- modelling. This was advantageous since the parison of the panel and the box beam, as experimentally obtained mechanical properties modelled, using the two different elements. could be incorporated into the element to calculate During this examination, the models were loaded the stiffness matrix of the pseudo-plank. To opti- in five increments up to 90% of the yield value for mise the calculation rate of the element, three this material and at each increment displacements displacements and only two in-plane rotational and strains were normalised with respect to the components at each node of the element were relevant maximum response obtained; a graph of considered; the out-of-plane rotation at each node normalised deflection and strain for both ele- was constrained. Due to the non-linear nature of ments was plotted and is shown in Fig. 9. It was the stress/strain curves (which were modelled in shown that the finite shell element type 2 models

0.7 I

- i # o Vertical displacement i /

0.6 ........ [] Longitudinal strain ....... i ................. Y ...................

:80 ~ o Transverse stnu ::i /

0.5 ............................................................................ 7 r

0.4 ................... .- ..................... , ................... ~ ............................................................. 180 /

_ /~

i 0.3 ..................................... ~ ..................................................................................... 177.5 (flange) / i

190 (web) 0.2 ................... ~ ..................... ~ ..................................................................................... a /

Dimensions shown are in mm /

Upper and lower layers of the shell element o.I I O. 1 0.2 0.3 0.4 0.5 0.6 0.7

Intermediate layer of the shell element • Node Nonnalised reslxmses from element 1

Fig. 9. Comparison of type 1 and type 2 elements. Fig. 8. The laminated shell element used in the numerical Mechanical properties are normaliscd to 90% of the

analysis, material's theoretical yield point.

446 Z Lee, L. Hollaway, T. Thorne, P. Head

the box beam to within 1% of the deflection and beam at the specified times; therefore creep defor- bending stress, but the difference between the two marion was included during decrements. elements with respect to shear strains was 6%. The stiffness remains relatively constant over

the period; the slight variations may be due to temperature differences at the time of loading and

4 EXPERIMENTAL STATIC LOAD TEST to the different loadings procedures. At 0 and 10 PROCEDURE weeks the load was incremented to its working

values in four stages, whereas at 19 weeks the load The beams were loaded in increments of 20 kN was incremented in only two stages. up to a maximum value of 200 kN and for each The strain values obtained from the VW and loading increment, strain values and deflections the demec gauges at the centre span of the envi- were obtained; one day was allowed for each ronmental box beams are shown in Fig. 10. loading increment. At full load the structure was Referring to the bottom environmental beam, allowed to creep; strain and displacement read- these values and their distributions obtained from ings were taken at preset times. After 56, 116 and the two methods compare well; the maximum 178 days exposure, the structures were unloaded, strain reached in the plank was 650 micro-strain allowed to recover for 24 h and then reloaded, at ten days from the start of the test. with the exception of the last load cycle when the At the end of the nine months test, the experi- structure was unloaded only. This operation was mental deflections of the central part of the beam to enable a value of the stiffness of the beams to relative to the supports was 17.4 mm (average), be computed at specific times during the test without temperature compensation but including program to ascertain whether the system was the effects of the two loading cycles in April and degrading under natural weathering and continu- June and the creep of the material; the cantilever ous loading. The mechanical test results of the deflection relative to the support was 73-25 mm unloading and reloading cycles over the period of (average). The equivalent numerical values using nine months are given in two forms; these are the ABAQUS equations were 15.3 mm and 59.2 mm, actual deflections at the centre and ends of the respectively. These displacements correspond to a beams and the stiffness of the beams at the pre- 1/200 deflection span ratio; visually the deflec- scribed times (see Table 2). tions appeared larger in the prototype due to the

back-to-back arrangement. It should be remem- bered that a total of 200 kN over a period of 9

5 RESULTS AND OBSERVATIONS ON months is a considerable load for this beam to ENVIRONMENTAL TESTS FOR THE TWO BOX BEAMS

0.4

Stiffness has been calculated during an incre- ~ , / o mental load by measuring the central deflection / relative to the internal supports when a pure ~" moment is applied at these supports, the value of E 0.2

"O

which was the product of the cantilever span and "~ o the applied load at the cantilever end. The deflec- ~ o / / / [ tion values are those which were recorded imme- E 0

®

diately before the load was removed from the ~ ® oE e-

Table 2. The stiffness and deflection values of the beam at ~- (0.2) specific time intervals during the environmental test rn /

Time Flexural Central o / rigidity deflection

(weeks) (N/m 2 per metre (ram) (0.4_~000 i , , , t -500 0 500 1000 micro Strain

width) Vibrating Demec Numerical wire studs analysis

0 95"3 x 106 16"25 o o 10 9"20 × 106 18"93 19 93"8 x 106 20" 10 Fig. I fl. Compar i son of vibrating wire, demec and numeri -

cal results.

Long-term static testing of an FRP prototype highway structure 447

20 - e t

0 "/" A

(20) t ~

0 . ,~_

C~ (40)

160) I I I

0 5 10 15 Distance along lower beam (m)

Finite element Experimental readings Experimental readings analysis south side north side

/k o

Fig. 11. Experimental and numerical longitudinal beam profile.

maintain. Figure 11 shows the actual longitudinal extra vibrating wire gauges on to the vertical profile of the box beam over the nine-month test surfaces of the box beam. period. During the test, at the extreme end of the During the latter part of the exposure of the beam, some slippage was observed at the corner two beams, yellowing of the surface was observed connectors and the vertical planks in the tensile particularly on the top surface of the top beam and compressive zones; this occurred towards the and the south-facing sides of the two beams. The end of the nine-month test period and may have early months of the summer period were very been caused by bond failure in the adhesive, sunny and warm and it must be assumed that this although the evidence is not conclusive; it could discolourafion was due to UV effects from the have been a function of the test set-up. The maxi- sun. At the end of the test a small area of the mum slippage at the end of the test occurred at the affected surface was lightly scraped and the south-west corner of the beam. original colour of the beam was restored. This

The temperature inside the box beam during demonstrated that the depth of penetration of the hot periods is not significantly greater than that of UV was minimal. Generally, unpigrnented lami- the ambient air and is similar to that on the face of nares discolour. Discolourafion does not signifi- the beam away from the direct rays of the sun (i .e. cantly affect the mechanical properties of the on the north-facing surfaces of the beam). Figures laminates. 4 and 5 indicate the magnitude of the tempera- ture, at the positions shown, for a period of 25 h.

Moisture ingress to the inside of the box beams 6 CONCLUSIONS and inside the planks did occur, but it is uncertain exactly where the point of entry occurred. It is The objective of the sixteen-month test pro- unlikely that water gained access through the gramme was to gain a better understanding of the bonded joints as these appeared to be water-tight, long-term behaviour, under various load condi- It is believed that rain water entered through the fions, of E-glass fibre/polyester matrix pultruded junction of the end cover plates to the planks; composite units manufactured to a particular these plates were positioned for the purpose of specificatioin. Twenty 'Maunsell Planks' were this test only and were not a permanent feature of fabricated into two 18 m span box beams and the beam. During the test these end cover plates these were reacted against each other under a 200 became debonded at the top of the beams. Conse- kN load in the natural environment. Simultane- quently, moisture became trapped in the plank ously, coupon specimens were tested to charac- section, as was discovered during the test when terise the properties of the material (the results of holes were drilled through these units to place these tests will be given in Ref. 4). At the end of

448 J. Lee, L. Hollaway, T. Thorne, P. Head

the environmental test one of the large box beams Some UV attack on large exposed surfaces of was loaded to failure (the results of these tests will FRP was observed, but the discolouration did not be given in Ref. 5). affect the strength of the beam; indeed, it was only

The loaded environmental box beams showed a surface problem which was removed at the end no signs of global deterioration and generally of the test by scraping. For reasons of schedule, no behaved as predicted. However, there was some UV pigments or stablisers were incorporated into local flexural cracking in the connectors at the the pultrusions at the time of manufacture. Dis- position of the applied line load; this area of colouration tests on coupon specimens showed potential failure did not occur in the planks, that much better UV resistance can be attained by where diaphragms were positioned parallel to the using stabilisers. line load.

The short-term stiffness of the beam during the test did not decrease to any appreciable extent; at ACKNOWLEDGEMENTS the end of the test the value was 97% of its initial

value. Over the test period, the deflection at the The authors acknowledge the financial support of centre of the beam, which was under a pure the SERC, Department of Transport and the moment of 430 kN m increased by 13% of the LINK partners who have made this programme of static value at time zero. At the end of the nine- work possible. The LINK Partners are: Maunsell month test period, the rate of creep was practi- Structural Plastics (who were also the designers of cally zero; 60% of the creep took place over the the beam and mangers of the LINK-project), CU first forty days of the loaded period. Bridges, CIBA-Geigy, Duxford, Vetrotex (UK)

The deflection at the free end of the beam, and DSM resins (UK). which was under a maximum moment and a shear load of 430 kN m and 100 kN, respectively, increased by 40% of the static value at time zero. The rate of creep deformation at the free end of REFERENCES the beams appeared to remain constant through- out the test. At the end of the test, it appeared that 1. Department of Transport, London BD 37/88, Loads for

Highway Bridges. © Crown Copyright 1989. from a visual point of view the bonding/fixing of 2. Hibbit, Karlsson and Sorensen, Abaqus Theory Manual. the planks to the connectors over the pure bend- © 1987, Hibbitt, Karlsson and Sorensen Inc, pp. 5.12.1-1 ing region had performed well. In the cantilever to 6. region there was some slippage between the plank 3. Dawe, D. J., Matrix and Finite Element Displacement and connectors and it is still unclear where the Analysis of Structure. Oxford Science Publications,

Oxford, UK, 1984. debonding occurred. However, in regions of bond 4. Lee, J., Hollaway, L. & Cadei, J., The structural charac- line edges, a series of composite dowl pins could terization of an orthotropic composite material (in pre- be incorporated through the connector and face paration). 5. Lee, J., Hollaway, L. & Thorne, T., Dynamic and static material of the plank to resist movement between tests to failure on a 12 meter prototype composite box- the two component parts, beam (in preparation).