[001] Experimental and Analytical Model of Ferro Cement Slabs

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RESEARCH PAPER International Journal of Recent Trends in Engineering, Vol. 1, No. 6, May 2009

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Experimental and Analytical Model of

Ferrocement SlabsBoshra Aboul-Anen

1, Ahmed El-Shafey

2, and Mostafa El-Shami

3

1Assistant Lecturer, Civil Engineering Department, Faculty of Engineering, Menoufia University, Egypt

2 Assistant Professor, Civil Engineering Department, Faculty of Engineering, Menoufia University, Egypt3 Visiting Associate Professor, Civil and Environmental Engineering Department, Texas Tech University, USA

[email protected]

Abstract-This paper addresses the composite action between

the ferrocement slabs and steel sheeting. This is an

important issue that could impact the performance and

strength of space trusses. The current paper presents the

experimental models of ferrocement slabs with and without

steel sheeting and their numerical models using the finite

element method. Finite element models were developed to

simulate the behavior of the slab through nonlinear response

and up to failure, using the ANSYS Package. Additionally,

the comparison between the theoretical and experimental

models is presented and discussed.

Index Terms- space trusses, ferrocement, finite element

I. INTRODUCTIONSpace structures are a leaf taken from Nature. Natural

forms possess exceptional rigidity and use minimum

materials to a maximum structural advantage. HistoricallyRef. [1], the earliest space structures built were thedomes pioneered by the German Engineers Schwedlerand Zimmermann in the nineteenth century. Zimmermannachieved a span of 118.44 m for an exhibition structurebuilt at Lyons as early as 1894. In 1937, Mengeringhause

realized that the promotion of space structures on a largescale would only be possible if the system lent itself to

factory production and field assembly. To achieve thesetwo objectives, it was necessary to reduce variety anddevelop a means of easy assembly. In 1942,Mengeringhause successfully commercialized space

structures. His universal MERO node connector canaccepts as many as 18 members at different angles in

tapped holes over its surface.Two major approaches have been adopted foranalyzing the collapse of the space structures; one dealswith chord members in tension and the other deals with a

brittle type of failure caused by buckling of cord membersin compression. The buckling of cord members is the

main problem facing space structures and has been aresult, the subject of numerous experiments ([2], [3], [4]and [5]). It has been found that the compressive failure ofa space structure is principally governed by the post-

buckling load deflection characteristics of the struts.Several researchers ([6], [7], [3], [1] and [9]) have

studied the over-strengthening of the compression

members that can be adapted to prevent the brittlecollapse of a space structure. One of the majorsuggestions is to use the composite action of concrete

slabs at the top. This reduces the buckling problems ofthe compression cord members and increases their loadcap-cities. In general, the composite action has beenfound to improve joint stability and truss reliability; thus

leading to significant enhancements to truss stiffness,

strength and ductility. This approach also leads toimprovements in truss response to member loss anduneven support settlements. The only disadvantage ofusing concrete slabs is the weight, which controls chordmembers span. In order to come over this problem, the

authors suggest using light concrete slabs (ferrocement).This technique has been used since 1884 in the

construction of row boats, plant pots, seats, housing, andother items. This material is commonly constructed ofhydraulic cement mortar reinforced with closely spacedlayers of continuous and relatively small size wire mesh

Ref. [10]. The mesh may be made of metallic or othersuitable materials. steel wire mesh may be wire mesh

with closely spaced wires which is the most commonlyused in the ferrocement, expanded metal, woven orwelded wire fabric according to Ref. [11]. Thismaterial also used in repairing the reinforcementelement; beams or slabs or walls Ref. [12]. Severalrecent studies ([13], [14], [15] and [16]) have indicated

that ferrocement (with wiring meshes) is lightweightcomparing to the reinforcement concrete.

The main purpose of this research, then, was toinvestigate the possibility of using a top ferrocement slabto improve the behavior of space trusses. To constructspace trusses with top ferrocement slab, decking plates

(normally made of steel) should be used to support the

wet concrete. The sheets will act with the ferrocementslabs as composite sections. This action will affect thetotal nonlinear behavior of space trusses.

In this research, the authors focused on the compositeaction of the ferrocement slabs and steel sheets. In the

following pages, experimental models of ferrocementslab with and without steel sheeting and their numericalmodels using the finite element method will be presented. Finite element models are developed tosimulate the behavior of the slab through nonlinearresponse and up to failure, using the ANSYS package[17].

II. MODELS AND METHODSA.Experimental ModelFerrocement slabs both without steel sheeting (FS1) and

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with (FS2) were studied. The slabs dimensions were 0.8 x0.8 m and 0.025 m thickness. The two slabs contain

two wire meshes as shown in Figure 1. From theferrocement definition, Ref. [13], mortar matrix andsteel wire mesh are the main constituent materials of

ferrocement. Mortar matrix is a homogeneous mixcomposed primarily of ordinary Portland cement, fineaggregate (sand) and water Ref. [13]. The sieve

analysis was done on the sand used for the mortar mixand satisfied the Egyptian Standard Specifications(E.S.S.) requirements Ref. [18]. The chemical and physical properties of the cement were analyzedaccording to E.S.S. Ref. [18] for concrete works Freshdrinking water, free from impurities, was used for mixing

and curing of the test specimens.

a. Longitudinal section in the first ferrocement Slab(FS1)

b. Longitudinal section in the second ferrocementslab (FS2)

Figure 1. Specimens Details

According to Ref. [13], the sand/cement ratio and

water/cement ratio should be token 2 and 0.4;

respectively to achieve the maximum compressivestrength of the mortar mix. The woven wire mesh typewith 1.42 mm diameter and 15x15 mm grid size wasused. The used steel sheeting with thickness of 1 mm wascut into the required dimensions (0.8 X 0.8 m). Thensmall pieces (0.02 x 0.02 m) were cut, deformed andwelded in the sheet as shown in Figure 2. These pieces

were used as shear connector studs to assure thecomposite action between the ferocement slabs and thesteel sheets.

B. Properties of Used MaterialsCompression and tensile tests were carried out for the

hardened mortar according to E.S.S. Ref. [18]. Fromthe test results, the authors figured out that thecompressive stress was equal to 19700 kN/m

2and 33300

kN/m2 at 7 and 28 days; respectively. For tensilestrength, it was 2000 kN/m2. In order to determine thestress-strain curve and the modulus of elasticity of the

mortar, four cylinders specimens were tested undercompression. The strain was measured by means of anextensometer and demec points. The slope of the initialstage of the stress-strain is the modulus of elasticitywhich was calculated to be 3.0 E+7 kN/m2.The modulus of elasticity of the used steel meshes and

yield strength were 13.0 E+8 kN /m2

and 4.0 E+5 kN/m2;

respectively. For the steel sheets, the modulus ofelasticity and yield strength were 2.1 E+8 kN /m

2and 2.4

E+5 kN/m2;respectively.

Figure 2. Shear Connectors

C. Testing of Ferrocement SlabsTwo wooden forms with dimensions of 0.8 x 0.8 m

and thicknesses of 0.025 and 0.026 m were used for slabcasting. These forms were constructed with specific precautions to facilitate the removal of the slabs after

hardening. In both slabs FS1 and FS2 the following stepsfor casting and curing were followed:1- Put a layer of hardening mortar with thickness of 4.0

mm in the wooden form,2- Install the 1st wire mesh,3- Cast a small pieces of the hardening mortar to

support the 2nd

layer of wire mesh,4- Install the 2nd wire mesh,5- Apply the hardening mortar intermittently as seen in

Figure 3.6- Remove the specimens from the wooden forms

within 24 hours after casting.7- Store the specimens in the laboratory atmosphereand covering it with wet cloth using water sprinkled

twice a day for curing.8- Test the specimens after 28 days.It should be noted that in FS2, the steel sheet wasinstalled first before step # 1.

The faces of each specimen were painted in white tofacilitate crack detection before the testing. The specimen

was placed in the testing position on frame as shown inFigure 5. The load is applied from a celebrated hydraulicJake at the center line of the tested slab. The load wasapplied using the steel frame shown in Figure 4.

III.FINITE ELEMENT MODELA finite element package Ref. [17] was used to

simulate the behavior of ferrocement slabs. Mainly twotypes of elements were used; solid 65, and solid 45. The

properties of each element are as follows:-

A. Solid 65This element is considered as one of the solid

isoparametric elements which are formulated by directextension of procedure used for plane elements Ref.

[19]. It is defined by eight nodes as shown in Figure 5.Each node has three degrees of freedom, translations in x,

y, and z; respectively. This element has one solid materialand up to t hree rebar materials in the three directions



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Figure 3. Slab casting

Figure 4. Slab testing and loading system

This element is perfect to simulate reinforcement

concrete slabs where the solid material is used to modelthe concrete or mortar (as in this study) and the rebarmaterial to mode the reinforcement behavior.

Reinforcement is specified by its material, volume ratioand orientation angles. The volume ratio is defined as therebar volume divided by the total element volume. Theorientation is defined by two angles in degrees ( and )from the element coordinate system (see Figure 5).

This element has cracking and crushing capabilities.The most important aspect of this element is thetreatment of nonlinear material properties. The concreteor mortar is capable of cracking (in the three orthogonaldirections), crushing, plastic deformation, and creep. The

rebar (reinforcement) is capable of tension andcompression, but not shear. The rebar is also capable ofplastic deformation and creep Ref. [17]. In this study,

this element was used to simulate the ferrocement slabsas in FS1, and FS2.

Figure 5. Eight-node solid isoparametric element (solid65)

B. Solid 45The element is similar to the solid 65 in its

isoparametric properties. This element has a capability tohandle plasticity, creep, swelling, stress stiffening, largedeflection and large strain capabilities. In this study thiselement was used to simulate the steel sheeting in FS2.

C.ModelingTo model FS1, a block with dimensions of 0.8 x 0.8 x

0.025 m was built using solid 65 element type. The properties of its materials (mortar and wires) weredefined using the experimental results mentioned before.Longitudinal and transverse reinforcement of used wires

were applied using rebar in x-y plan. The steel wires in xand y directions are defined as two materials with same

properties as mentioned before. The reinforcement in ydirection is represented by rebar (1) with angles and equal to 90 and in x direction by rebar (2) with and

equal to Zero (see Figure 5).For FS2, the model was the same as FS1 with

exception of one addition. In FS1 one more block with

dimensions of 0.8 x 0.8 x 0.001 m was built under thatone used in FS1. This block was simulated the steelsheeting with properties mentioned above using solid 45element type. It should be noted that the elements of each

are oriented in the same way that they shear the samenode at the interface between the two blocks.

IV. RESULTS

Both slabs FS1 and FS2 were tested utill failure. The

failure load was measured for both slabs as 7.18 kN, and31.42 kN; respectively. The crack pattern in FS1 isshown in Figure 6. In FS2, as load was applied a crackoccurred between the steel sheet and the slab. This iscontact failure happened around load of 10 kN (seeFigure 7).

The comparison between the two slabs for applied

load and center deflection is given in Figure 8. Figure 9compares the theoretical and experimental load-centraldeflection relationships for FS1. This figure illustratesthat an excellent matching between both theoretical andexperimental models occurred. The ultimate load predicted by the theoretical model was higher than the

experimental one with only 7.89%.his might due to the



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assumption of perfect contact between mortar andreinforcements in the theoretical model.

Figure 6. Crack pattern of FS1

Figure 7. Contact failure in FS2

The comparison between theoretical and experimentalload-central deflection relationship curves of FS2 isshown in Figure 10. This curve indicates a greatmatching between the two solutions up to 10.0 kN at

which failure of bond between slab and steel sheetingoccurred (see Figure 7). After 10.0 kN, the experimentaland theoretical results continue to mismatch until failureload (Figure 10).

Figure.8.Theoretical load-deflection curve

Figure 9. Load verses deflection for FS1 (experimentaland theoretical)

Figure 10. Load verses deflection for FS2 (experimental

and theoretical)

V. CONCLUSIONS

The results of both experimental and analytical

investigations to examine the composite action betweenthe ferrocement slabs and steel sheeting are reported anddiscussed. This was done as an initial step towards usingthe ferrocement slabs to improve the behavior of

compression member in spaced trusses. Manly two typesof ferrocements slabs with and without steel sheeting

were tested. The finite element technique was used tomodel the behavior of these slabs. ANSYS [17] was usedto model all test specimens. The ANSYS modelaccommodates material non-linearities, cracking and

crushing of concrete (or mortar) and yielding of the steelsheeting and wiring meshes. The analytical results

compared well with the experimental for the ferrocementslabs without steel sheeting. For those specimens withsteel sheeting, the comparison was good until the failureof the bond between the slabs and the steel sheeting.Further experimentation is required to better understandthe role ferrocement slabs might play. It is believed that

the future experiments will need to include addition stepsand precautions to ensure better, even total, contactbetween ferrocement slabs and the steel sheeting.

0

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TotalLoad(KN)

Deflection (mm)

FS1

FS2

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Experimental

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REFERENCES

[1] A. I. El-Sheikh, Sensitivity of space trusses to member

geometric imperfections, International Journal of SpaceStructures, vol. 2, pp. 89-98, 1995.

[2] L.C. Schmidt, Load transfer for shear and torsion in plate-

like space trusses, Civil Engineering Transaction of the

Institution ofEngineers,pp. 1-7, Australia, 1981.

[3] A.I. El-Sheikh, and R.E. McConnel, Experimental study

of composite space trusses, Journal of Structural

Engineering, ASCE, vol. 3, pp. 747-766, 1993.

[4] R. Lecy, S. A. Hanaor, and N. Rizzuto, Experimental

investigation of prestressing in doubly-layer grids,

International Journal of SpaceStructures, vol. 1, pp. 21-26, 1994.

[5] A. I. El-Sheikh, and H. El-Bakry Experimental study of

behavior of new space truss system,Journal of Structural

Engineering, ASCE, vol. 8, pp. 845-853, 1996.[6] T. Bungey, Analysis of Space Truss Sensitivity to Member

Loss and the Effects of Composite Action, M.S. Thesis,

University of Dundee, UK, 1992.

[7] M. Ashraf, M. A. Javied, and Z. Ali, Composite double-

layer bridge grids, Fourth International Conference on

Space Structures, University of Surrey, Guildford, UK, pp.1518-1525, 1993.

[8] W. M. Sebastian, The Performance of A Composite Space

Truss Bridge with Glass Reinforced Plastic Panels, Ph.D.

Thesis, University of Cambridge, England, 1996.

[9] A. I. El-Sheikh, Design of web members in space

trusses,International Journal of Space Structures, vol. 1,

pp. 25-34, 1999.

[10] ACI, State-of-the-art report on ferrocement, 1980.[11] M. N. Soliman, Fleasibility of Using Fibrous Ferrocement

Concrete in Strengthening and Repairing of Structural

Elements, Ph.D. Thesis, Minufiya University, Egypt, 2006.[12] E. H. Fahmy, Y. B. Shaheen, and Y. S. Korany, "Use of

ferrocement laminates for repairing reinforced concrete

clabs,"Journal of Ferrocement, vol. 3, pp. 219-232, 1997.[13] L. S. Blake, Civil Engineer's Reference Book, Butterworth-

Heinemann, Reed Educational and Professional PublishingLtd, Oxford, 2001.

[14] M. M. Hoque, 3D Nonlinear Mixed Finite-Element

Analysis of RC Beams and Plates with and without FRP

Reinforcement, M.S. Thesis, University of Manitoba,

Canada, 2006.

[15] D. Kachlakev, Finite Element Modeling of ReinforcedConcrete Structures Strengthened with FRP Laminates,Ph.D. thesis, California Polytechnic State University,USA, 2001.

[16] A. A. Nasser, Behavior and Strength of FerrocementComposite Elements under Different Cases of Loading,

Ph.D. Thesis, Minufiya University, Egypt, 2004.[17] ANSYS, Program Help and Manual, 1999.

[18] Egyptian Standard Specifications, 2007.[19] R. Cook, D. S. Malkus, M. E. Plesha, Concepts and

Applications of Finite Elements Analysis, 4th ed., JohnWiley & Sons, Inc., 2001.


[001] Experimental and Analytical Model of Ferro Cement Slabs

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