ORIGINAL RESEARCH

Pull-out behavior of galva

g sgeericade. Tathth

cr

sorption, and fire behavior. The structural strength ofthese products is determined by the grade and thickness

steel strips, local deformations, and finally cracking. De-structive measurements of shear strength through pull-

Ramezani et al. International Journal of Advanced Structural Engineering 2013, 5:24http://www.advancedstructeng.com/content/5/1/24Al-mahmoud et al. 2007). Ben Romdhane and UlmEngineering, Auckland University of Technology, Auckland 1010New Zealandof the steel, the configuration of internal panel compo-nents, and by the features of infill material (Balendranet al. 2002).

out and push-in tests are commonly used methods toassess the quality of a connection between steel elementsand fillers, e.g., concrete.There are only few studies available in the literature

about the structural bond properties between lightweightconcrete and steel bars with pull-out test (see e.g., Caoand Chung 2001; De Lorenzis et al. 2002; Chang 2003;

* Correspondence: maziar.ramezani@aut.ac.nzCentre for Advanced Manufacturing Technology (CAMTEC), School ofIntroductionIn the industrialized world, new and modern techniquesand materials, such as composites, have become commonin today's construction industry. These new materials arelightweight, energy efficient, aesthetically attractive, andefficiently handled and erected. Composite structural as-semblies (CSAs) are products with performance superiorto existing building elements, based on combinations ofmaterials such as embedded light gauge steel components,settable fillers, and coatings of sheet materials to provide avariety of finishes (Akin et al. 2005). The materials arecombined or assembled in various ways to provide im-proved performance in strength and stiffness and associ-ated properties of acoustic filtering, thermal energyconservation, vibration resistance, moisture barriers or ab-

The current paper focuses on novel materials for ap-plication in CSAs and the bonding performance betweensteel and infill materials. The bond between concreteand steel elements is one of the most important proper-ties contributing to the successful functioning of a com-posite panel (Kayali 2004). The main contribution tobond strength comes from the chemical adhesion andthe friction resistance occurring between the steel andthe concrete as a result of the surface effects. Compositestructures made of various materials can fail in severalways depending on material properties of components,design methods, and loading cases, but the most import-ant is the cooperation of all elements (Alterman et al.2011). The lack of compatibility between elements leadsto bond failure, sliding of reinforcement bars and/orconcreteMaziar Ramezani*, Juan Vilches and Thomas Neitzert

Abstract

The interface and bond between concrete and reinforcinconcrete structures. In this paper, the pull-out strength ofpatterns in foam concrete blocks are investigated experimkg/m3 density were obtained by mixing cement and watfoaming agent and Quick-Gel as the viscosifier. A theoretrelationship between the strip and the concrete. This moof the pull-out tests through the ABAQUS user subroutineexperimental, theoretical, and finite element simulation anmaximum pull-out force is also studied, and it was foundand circumference areas have higher pull-out forces and

Keywords: Bond stress-versus-slip relationship; Foam con Ramezani et al.; licensee Springer. ThisAttribution License (http://creativecommons.orin any medium, provided the original work is p

2013Open Access

nized steel strip in foam

teel are the most fundamental problems of reinforcedalvanized steel strips with different geometries and holentally and numerically. Foam concrete mixtures of 1,200-in a mortar mixer together with ultrafoam as thel model is developed to predict the bond-slipl is further implemented in a finite element simulationhe results show good correlation betweenlyses. The influence of the steel strip geometries on theat the strips with the greatest hole area, hole diameter,e increase is nearly linear.

ete; Pull-out test; Steel stripis an Open Access article distributed under the terms of the Creative Commonsg/licenses/by/2.0), which permits unrestricted use, distribution, and reproductionroperly cited.

crete, respectively. Using Hooke's law leads to

dsdx

F sEsAs

Fc

EcAc4

where Es, As, Ec, and Ac are the modulus of elasticity ofthe strip in tension, the cross-sectional area of the strip,modulus of elasticity of the concrete in compression,and the load-carrying area of the concrete, respectively.As illustrated in Figure 1, the load application is idealizedas a single pull-out load P at the top of the strip (x = L)with a corresponding displacement d applied in x direc-tion. The global equilibrium of forces in an arbitrarychosen cross section yields

F s Fc 0: 5

For demonstration purposes (see Figure 2), the rela-tionship between and s is given as = s, where is

Ramezani et al. International Journal of Advanced Structural Engineering Page 2 of 122013, 5:24http://www.advancedstructeng.com/content/5/1/24(2002) investigated the steel-concrete interface withcomputational mechanics. They modelled micro-to-macro mechanisms of the interface and studied thenumerical implementation of this model in combinationwith a discrete crack model for concrete. Few finiteelement (FE) simulations of pull-out tests are also avail-able in the literature (e.g., Wu et al. 2009; Wei et al.2012), yet without accurate modelling of the interfaceand bond behavior. Casanova et al. (2012) presented anew finite element approach to model the steel-concretebond effects. Their model proposed to relate steel, repre-sented by truss elements, with the surrounding concretein the case where the two meshes are not necessarily co-incident. Most of the previous investigations aboutbonding behavior focused mainly on experimental andtheoretical studies of shear stress between reinforcingbars and concrete specimens (e.g., Bouazaoui and Li,2008; Fang et al. 2006; Khandaker and Hossain 2008),and plastic bars and concrete samples (e.g. Won et al.2008), but not directly on steel strips, which are applic-able to this project. This study investigates bonding per-formance and analyzes it through pull-out tests toprovide data for the theoretical and FE analysis of CSAs.Because bonding is a general problem for wall panel de-sign and other uses of concrete that employ steel to con-crete contact zone, this research undertakes an analysisof the influence of various steel strip designs to under-stand bonding behavior. With the obtained results, theresearch enables understanding on the main features ofmetal face materials commonly used in wall panels.

MethodsTheoretical modelTo have a better understanding of the pull-out test, atheoretical model is developed in this section which issuitable for pull-out test of a steel strip in concrete. Theshear bond properties between the two materials can bedetermined by this model in the form of the bondstress-versus-slip relation. The model is based on theprevious work of Banholzer et al. (2005), where themodel is modified to fit the steel strip as the reinforcingelement. Considering Figure 1, if an axial load P is ap-plied at the end of the steel strip (x = L), the change inload dFs over a distance dx along the strip is a functionof the shear stress in terms of x and the circumferenceof the strip in contact with the concrete:

dF sdx

2 a b 1

where Fs is the force in the strip, a and b are the lengthand width of the steel strip cross section, and is the

shear stress in the strip. By assuming that the interfaceis sheared due to an applied pull-out force andconsidering the absolute displacement of the concrete ata point x in relation to its origin as uc and that of thestrip as us, the slip s can be defined as the difference ofuc and us, as follows:

s us uc: 2

Differentiating Equation 2 with respect to x yields

dsdx

sc 3

where s and c are the strain of the strip and the con-

Figure 1 Pull-out test configuration and equilibrium of forces.constant. It should be pointed out that a linear depend-ence between the shear stress and the slip is not

Ramezani et al. International Journal of Advanced Structural Engineering Page 3 of 122013, 5:24http://www.advancedstructeng.com/content/5/1/24assumed throughout the contact zone. The theoreticalmodel uses a piecewise method where the nonlinear be-havior of the contact interface is simplified by several linearpieces as illustrated in Figure 2. Combining these linearpieces gives a good approximation of the general nonlinearbehavior. The pull-out problem can then be represented

Figure 2 N piecewise linear relationship of bond stress versus slip.by a second-order differential equation, as follows:

Fs2 F s 0; F s L P; F s 0 02 2 a b 1

EsAs 1EcAc

:

6

where is a material parameter which includes the bondstress-versus-slip relation. Another possible approach is tomodel the experimental situation in respect to the localslip s. After substituting Hooke's law for the strip and the

Figure 3 Patterns of holes in the steel strips (all sizes in mm).concrete respectively into Equation 3, differentiating theresults with respect to x and using Equations 1 and 5, thefollowing second-order differential equation in terms of scan be obtained:

1 1 s 2 a b EsAs

EcAc

s T s T s 2 a b s 1

EsAs 1EcAc

s F s

7

Equation 7 represents the basic relationships betweenthe second-order derivative of the local slip s and thelocal bond stress (s). Knowing that at x = 0 the force inthe strip is zero (s(0) = 0), assuming the slip s at theloaded strip end is d (s(L) = d), and denoting the

coordinate of the strip by 0 x L, the mathematical rep-resentation of the pull-out test can be expressed either as aboundary value problem

s T s ; s 0 0; s L d 8or as a corresponding initial value problem for a stripend slip at x = 0

s T s ; s 0 0; s 0 : 9Banholzer et al. (2005) assumed an N piecewise linear

bond law with no limitation of N (Figure 2) to achieve ageneral mathematical description of the bond law. The

analyzed for density and compressive strength based onthe standard testing methods for physical and mechanicalproperties (ASTM C495 and ASTM C39). Experimentsshowed that by using the theoretical design method ofKearsley and Mostert (2005), it is possible to predict thecompressive strength and density for the concrete mix-tures. Ordinary Portland Cement was used for the foamconcrete mixtures. To prepare the foam, ultrafoam wasused as the foaming agent and Quick-Gel (Baroid,Houston, TX, USA) as the viscosifier. These were mixedwith water in the foam generator until the foam bubblesize was uniform and stable (usually 2 min). Then, thefoam was added to the cement matrix while stirring, withcontinual mixing for 1 to 2 min. When the mixture offoam and cement matrix was uniform, the prepared foamconcrete was poured into the test mold with slight vibra-tions to fill up the mold completely. Specimens weredemolded after 24 h and then moist cured in a standardcuring room for a further 28 days in order to test the sam-ples with a standard testing machine.Standard cylinders of 100-mm diameter were used for

the compressive strength tests, which were carried out ina testing machine of 100-kN capacity at a loading displace-ment rate of 0.1 mm/s. Three cylinders were tested forcompressive strength after 28 days according to the

Ramezani et al. International Journal of Advanced Structural Engineering Page 4 of 122013, 5:24http://www.advancedstructeng.com/content/5/1/24function T(s) = 2 (a + b) (s) can be expressed for aninterval i (si 1 s si) as

T s mi ssi1 Ti1;

mi TiTi1sisi1 ; T 0 s0 0:

10

Consequently, the force Fs in the strip is normalized aswell:

q x F s x s x : 11The force in the strip at x = L corresponds to the pull-

out load P, and therefore, we have s(L) = q(L) = P.Now, the initial value problem (Equation 9) can be easilysolved in an iterative process for any given T(s) and ,with Runge-Kutta numerical integration procedure, and thenormalized pull-out force can be determined for a givendisplacement d, such that the boundary condition at thebottom of the strip s(0) = 0 is satisfied.

Experimental analysisFoam concrete mixtures were prepared at 1,200-kg/m3

density by using stable foam concrete compositions, whichwere designed based on the investigation of Kearsley andMostert (2005). Properties of the foam concrete were

Table 1 Relationships of hole patterns

Holepattern

Numberof holes

Radius of holes(mm)

Area of holes(mm2)

S0 0 0 0

S1-6 1 5.66 100.6

S4-3 4 2.83 100.6

S9-2 9 2 113.1

S1-8 1 8 201.1

S2-8 2 8 402.1

S14-3 14 3.46 526.5

S1-14 1 13.86 603.5S4-7 4 6.93 603.5

S9-5 9 4.9 678.9Figure 4 Testing mechanism with a freely adjustable ball jointand a plate with embedded bolts within foamconcrete samples.ASTM C39 standard test method for compressive strengthof cylindrical concrete specimens, and the mean value was

calculated. The average compressive strength of the foamconcrete was 8.8 MPa.The pull-out test method was used to evaluate the

shear bonding strength between the steel and the foamconcrete. All the pull-out tests followed the ASTM C900standard. The ram velocity for all the tests was set at 0.2mm/s to allow slow deformation of the concrete and thesteel strips. The pull-out test samples include a foamconcrete cube (100 mm 100 mm 100 mm) with gal-vanized steel sheet (50 mm 150 mm) standing in themiddle of the concrete cube. A hot-dip galvanized steelsheet, 0.75-mm thick, grade G250 from New ZealandSteel (Private Bag, New Zealand) was used. Steel sheetswere pre-cleaned and degreased by using soapy waterwithout damaging the coating before getting it in con-tact with the fresh concrete.The influence of the steel strip geometries was studied

as well. The major purpose of the pull-out test experi-ments was to investigate the effect of ten different holepatterns (Figure 3) in the steel strips on the bonding be-havior. Ten different hole patterns were prepared includ-ing different numbers of holes (0, 1, 2, 4, 9, and 14),radius, and distribution (Table 1). The reason for usingdifferent sizes and numbers of holes was to investigate

the influence of contact cross section and hole patternsof the strip on the pull-out strength. These holes werefilled with the concrete, and the effect of mechanicalinterlock produced by the concrete inside the holes willbe studied. In codifying the hole pattern produced, steelplates were denominated as S0, S1-6, S4-3, S9-2, S1-8,S2-8, S14-3, S1-14, S4-7, and S9-5, for each number andapproximate radius of holes.Three specimens for each single set of strips were pre-

pared and tested to determine the load-versus-displace-ment curves. Therefore, 30 tests had been carried out intotal for all hole patterns. The primary pull-out testsshowed that the results do not have significant varia-tions, and therefore, it was decided to use three repeti-tions for each set of strip geometries. The pull-out testswere carried out using a universal testing machineequipped with a frame, which holds cubic samples andwith a freely adjustable ball joint for pull-out tests asshown in Figure 4. Four M10 bolts were embeddedthrough the cubic foam concrete samples and fixed to aplate at the bottom of the foam concrete cube to hold thesample in place. The adjustable ball joint for pull-out testsassures that the pull-out forces were centric to the stripsduring loading. The load was applied to the metal strip

Ramezani et al. International Journal of Advanced Structural Engineering Page 5 of 122013, 5:24http://www.advancedstructeng.com/content/5/1/24Figure 5 Load and boundary conditions for the FE model.

Figure 6 Distribution of von Mises stress in pull-out test of the

Ramezani et al. International Journal of Advanced Structural Engineering Page 6 of 122013, 5:24http://www.advancedstructeng.com/content/5/1/24through a mechanical joint and evenly increased whilecontrolling the displacement at a rate of 0.05 mm/s. Boththe load applied and the displacement of the steel stripwere measured and recorded on a computer until the stripwas extracted from the cubic sample. Thus, a load-deformation curve was obtained from each experiment. Itis worth pointing out that the slippage is not equal to thegrip displacement throughout the contact zone. In the de-velopment of the theoretical model, it is only assumed thatthe slip s at the loaded strip end is equal to the grip dis-placement d (s(L) = d). The measured displacement isthen related to the slip of the contact zone using the equa-tions developed in the Theoretical model section (seeEquation 8).

Finite element simulationsThe pull-out test was further studied by finite elementsimulations. A three-dimensional finite element modelwas developed using ABAQUS release 6.12 (Simulia,Providence, RI, USA) for this purpose. This is an implicitanalysis code suitable for modelling both material andgeometric nonlinearities and has good contact model-ling. The FE analysis comprised an elastic-plastic simula-tion of the pull-out process and the determination of theload-displacement curve in the steel strip. The FE simu-lations were conducted for all the hole patterns depictedin Figure 3, and the FE results were compared with ex-perimental and theoretical results. The material data forFE simulations were obtained from compression test offoam concrete and tensile test of steel strip. The galvanizedsteel sheet had the elastic modulus of 200 GPa andPoisson's ratio of 0.3 with the ultimate yield stress of 357GPa. The foam concrete had a density of 1,200 kg/m3,Poisson's ratio of 0.2, and compressive strength of 8.8 MPa.The elastic modulus of the foam concrete was 5,535 MPa.In the FE simulations, the bond stress-slip ( s) rela-

tions obtained from experiments and theoretical model-ling were used as the input data for the FE model. Bondstress-slip relations are considered as the constitutive re-lations for the behavior of the contact interface. Thepull-out tests were then simulated by applying the shearconstitutive behavior to the FE model by a user-definedsubroutine. UINTER user-defined subroutine was usedto define the interfacial constitutive behavior which pro-poses a new numerical model for simulating the bond-slip behavior of the composite structure. User subroutineUINTER is called at points on the slave surface of a con-tact pair with a user-defined constitutive model definingthe interaction between the surfaces. The subroutine canbe used to define the mechanical (normal and shear) in-teractions between surfaces. In this way, any special orproprietary interfacial constitutive behavior could be de-

fined through the user subroutine UINTER written inFORTRAN in ABAQUS/Standard, which may include

steel strip S0 and foam concrete at d = 6 mm. (a) Wholestructure, (b) concrete block, and (c) steel strip.

Ramezani et al. International Journal of Advanced Structural Engineering Page 7 of 122013, 5:24http://www.advancedstructeng.com/content/5/1/24both the normal and tangential behaviors. This featureprovides a strong tool for simulating the bond-slip be-havior. User subroutine UINTER was called for eachcontact constraint location of affected contact pairs inevery increment of the ABAQUS/Standard analysis. Theinput to this user subroutine includes the current rela-tive position of a particular constraint point on the slavesurface with respect to the corresponding closest pointon the master surface, as well as the incremental relativemotion between these two points. The normal directionconstitutive behavior was modelled by using the penaltyapproach once the interaction surfaces are in contact;otherwise the normal strength is zero.To minimize computation time, a quarter of the model

was simulated due to symmetry and appropriate con-straints were imposed on the symmetry plan. The loadand boundary conditions are illustrated in Figure 5. Thebase of the concrete was fixed and the symmetry planeswere constrained to model the actual behavior of thewhole model. The pull-out load was applied to the topof the steel strip. The FE mesh was uniform and gener-ated using C3D8R element which is an eight-node linearbrick with reduced integration and hourglass control.Hourglass control formulation was used to control thedistortion of solid elements during the final stages of thepull-out tests. The FE simulations were repeated withouthourglass control, and the results clearly showed thatthe hourglass control formulation increases the accuracyof the model. In order to gauge how reasonable and ac-curate the results are on a given mesh, FE mesh conver-gence study was carried out. The results showed that themesh size presented in Figure 6 produces a satisfactorybalance of accuracy and computation time. The resultsshowed that the finer mesh produced typically the sameresult; however, as the mesh was made finer, the compu-tation time increased significantly.The concrete damaged plasticity model was assumed

for the concrete. The concrete damaged plasticity modelprovides a general capability for modelling concrete andother quasi-brittle materials in all types of structures.This model uses concepts of isotropic damaged elasti-city in combination with isotropic tensile and compres-

Figure 7 Distribution of von Mises stress in pull-out test of thesteel strip S9-5 and foam concrete at d = 6 mm. (a) Wholestructure, (b) concrete block, and (c) steel strip.sive plasticity to represent the inelastic behavior ofconcrete. The concrete damaged plasticity model isbased on the assumption of scalar (isotropic) damageand is designed for applications in which the concrete issubjected to arbitrary loading conditions. The modeltakes into consideration the degradation of elastic stiff-ness induced by plastic straining both in tension and

Figure 8 Load-displacement curves for the pull-out test of the steel strip S0.

Figure 9 Load-displacement curves for the pull-out tests of the steel strips. (a) S1-6, (b) S2-8, (c) S4-3, and (d) S9-5.

Ramezani et al. International Journal of Advanced Structural Engineering Page 8 of 122013, 5:24http://www.advancedstructeng.com/content/5/1/24

for

Ramezani et al. International Journal of Advanced Structural Engineering Page 9 of 122013, 5:24http://www.advancedstructeng.com/content/5/1/24compression. It also accounts for stiffness recovery ef-fects under cyclic loading.The node-to-surface contact between the strip and the

concrete was modelled through the master-slave algo-rithm. General contact automatically assigns master andslave roles for contact interactions, and ABAQUS calcu-lates an overclosure tolerance based on the size of theunderlying element facets on a slave surface. Slave sur-faces (or nodes) in a particular interaction are repositionedonto the associated master surface (or nodes) if the two

Figure 10 Comparison of experimental and FE simulation pull-outsurfaces are initially overclosed by a distance smaller thanthe calculated tolerance. Initial gaps between surfaces

Figure 11 The effect of hole area on the pull-out force.remain unchanged by default adjustments. If a portion ofa slave surface is initially overclosed by a distance greaterthan the calculated tolerance, ABAQUS automaticallygenerates a contact exclusion for this surface portion andits associated master surface. Therefore, general contactdoes not create interactions between surfaces (or portionsof surfaces) that are severely overclosed in the initial con-figuration of the model, and these surfaces can freelypenetrate each other throughout the analysis.A cohesive behavior was introduced between the con-

ces for different strip geometries.tact surfaces. Cohesive behavior was defined as part ofthe surface interaction properties that are assigned to a

The results of the pull-out tests between the steel stripsand the aerated concrete, and theoretical and FE analyses

Ramezani et al. International Journal of Advanced Structural Engineering Page 10 of 122013, 5:24http://www.advancedstructeng.com/content/5/1/24contact pair. Surface-based cohesive behavior was de-fined as a surface interaction property and was used tomodel the surface interaction between the foam concreteand the strip. The cohesive behavior assumes that failureof the cohesive bond is characterized by progressive deg-radation of the cohesive stiffness, which is driven by adamage process. It also allows the failed nodes to re-enter contact with post-failure cohesive behavior. Thenonlinear geometry NLGEOM option in ABAQUS was

Figure 12 The effect of hole total diameter on the pull-out force.used throughout the analysis. Figures 6 and 7 show thedistributions of the von Mises stress in the strips and

Figure 13 The effect of hole circumference area on the pull-out forceare presented and discussed here. The main purpose ofthe pull-out experiments was to find relationships be-the concrete blocks in the pull-out tests of the steelstrips S0 and S9-5, respectively.

Results and discussionstween ten-hole patterns and mechanical properties of aer-ated concrete in order to evaluate and predict the bonding

.

Ramezani et al. International Journal of Advanced Structural Engineering Page 11 of 122013, 5:24http://www.advancedstructeng.com/content/5/1/24between steel and lightweight concrete through a numer-ical simulation.Three specimens for each single set (three identical

samples) of strip design were prepared and tested to de-termine the bonding strength during pull-out tests. Thereference hole area was 100.6 mm2 with a 11.32-mmdiameter. The reference area was increased gradually inorder to verify the effect of the anchorage of the con-crete embedded into holes in various designs.The load-displacement curves for the original pull-out

test of the steel strip without hole is depicted in Figure 8for the experimental, theoretical, and FE simulation ana-lyses. It can be seen from the figure that the results showvery good correlation, with the FE model predictingslightly higher pull-out force. It is worth pointing outthat the theoretical model developed in the section The-oretical model is only valid for the pull-out test of thesteel strip without any hole in terms of predicting theload-displacement curve. However, the bond-slip relation-ship obtained from this model can be further used in FEsimulations of all other strip geometries through theuser-defined subroutine UINTER. The load-displacementcurves obtained from the experiments and FE simulationsfor all other strip geometries were also compared andshow very good agreement. For brevity, only the resultsfor four cases, S1-6, S2-8, S4-3, and S9-5, are presented inFigure 9; however, all other cases show the same trend. Itcan be seen from the figure that the pull-out load dropssuddenly after the maximum value is achieved and thenstarts to decrease slowly, which indicates that the loadingcapacity still exists even after debonding. It is found frompull-out experiments that a long softening stage (>20 d1)exists after the maximum load, where d1 is the displace-ment corresponding to the maximum pull-out load. Theexperimentally and FE simulation predicted maximumpull-out forces were measured and depicted in Figure 10for all the hole patterns. In general, the FE simulationstend to predict slightly higher pull-out force as shown inFigure 10 with the differences less than 10%.Figures 11, 12 and 13 illustrate the maximum pull-out

force for all pull-out results of the ten series of sampleswith respect to the total hole area, the total diameter ofthe holes, and the total circumference area of the holes,respectively. According to Figure 11, a correlation coeffi-cient of R2 = 0.5623 was achieved, which shows a weakrelationship of data for different hole patterns. However,it can be seen that by discarding the S1-14 sample, thecorrelation improves greatly. Figures 12 and 13 showstrong correlations of R2 = 0.9044 and R2 = 0.9043, re-spectively. In general, the figures reveal that there is anearly linear increase of the pull-out forces on steelstrips with holes with respect to specimens without

holes if the hole sizes are similar. In general terms, pull-out force increases when all the three parameters (totalhole area, diameter, and circumference area) increase.The main reason for the different behavior of S1-14 isthat the area of chemical adhesion was reduced due tothe holes cut into the steel strips, and the mechanicalinterlock introduced by the concrete inside the holes isnot enough to compensate for the loss of adhesion inweaker matrix.

ConclusionsThe goal of this paper was to describe bonding processesbetween steel and concrete specimens experimentallyand by applying analytical and FE methods. The resultsof investigations on the bonding behavior between light-weight concrete and steel strips enable a better under-standing on the use of lightweight concrete in wallpanels. The results show that the experimental, theoret-ical, and FE simulation results match very well. Threegeometrical parameters affecting the pull-out force werealso investigated in this paper, namely the total area ofthe holes, the diameter of the holes, and the circumfer-ence area of the holes. The diameter of the holes or cir-cumference area of the holes was found to give strongercorrelation with the pull-out forces; however, weakercorrelations exist between the pull-out forces and thetotal area of the holes. The strips with the greatest holearea, hole diameter, and circumference areas had higherpull-out forces, and the increase is nearly linear.

Competing interestsThe authors declare that they have no competing interests.

Authors contributionsMR carried out the theoretical and finite element simulation analyses. JVconducted the experimental tests and assisted the simulations. TNparticipated in the study design and team supervision. All authorscontributed to and approved the final manuscript.

AcknowledgementsThe authors like to thank the Foundation of Research, Science andTechnology (FRST) of New Zealand for the generous financial supportreceived during the investigation.

Received: 23 June 2013 Accepted: 30 August 2013Published:

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Cite this article as: Ramezani et al.: Pull-out behavior of galvanized steelstrip in foam concrete. International Journal of Advanced StructuralEngineering

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AbstractIntroductionMethodsTheoretical modelExperimental analysisFinite element simulations

Results and discussionsConclusionsCompeting interestsAuthors contributionsAcknowledgementsReferences

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