Finite Element Modeling of the Transition Zone between Aggregat and Mortar in Concrete

Visual observations to the Interfacial Transition Zone (ITZ) between aggregate and mortar in concrete showed that this area differs significantly to the bulk mortar, further away from the ITZ. This ITZ has a higher porosity with a dissimilar crystal formation, therefore becoming the weak link in the material. In the past, concrete was seen as a two-phase material consisting of mortar and aggregates only. However, analyzing the material as a three-phase composite including the ITZ, will give a more realistic representation to its behavior. A Finite Element Model (FEM) was developed. The ITZ is modeled as a linkage element having a double spring, perpendicular and parallel to the ITZ surface. The individual load-deformation responses of these springs were obtained from laboratory tested specimens. Non-linearity is generated by evaluating the principal stresses at Gauss points, using the Kupfer-Hilsdorf-Rusch (1969) failure envelope and the CEB-FIB 2010 code. Iteration is conducted by the arc-length method developed by Riks-Wempners. The load-displacement curves resulted by the FEM were validated to laboratory tested specimens curves, to compare its effectiveness and asses the sensitivity of the model

Revitalization of Cracked Flexural Members using Retrofitting and Synthetic Wrapping

The modification of the Indonesia earthquake code SNI 2002 to SNI 2012 resulted in a significantly higher performance demand. The basics of these amendments lay in the re-zoning of earthquake maps, and the consideration of the earthquake influence to gravity loads. Members designed based on the SNI 2002 most likely will result in failure under future earthquakes. A reinforcement method based on the ACI 440 provision was conducted on cracked flexural members. The tensile reinforcement of these members has yielded and was neglected in the design. The tensile strains and stresses were further carried by the synthetic wraps applied to the tensile concrete fibers. The shear capacity of the member was enhanced by confinement of the member using the same synthetic wrap. Prior to wrap application, the members were straightened and retrofitted with an epoxy resin injection. The member was tested using a one-point-loading system to simulate a maximum bending moment in combination with maximum shear forces. The load-displacement responses and the ultimate load carrying capacity under monotonic incremental loading were recorded. It was found that this method will provide a solution for revitalization of cracked members in bending, and offer a solution to the design code alterations. © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the organizing committee of SCESCM 2016

Analysis of castellated steel beam with oval openings

A castellated steel beam is per definition a wide flange (WF) or I shaped steel profile with openings, to reduce self-weight and improve the effectiveness in terms of material use. Recently, extensive study on these castellated steel beams has been conducted, involving different shapes in web openings. The main goal of these research works was to evaluate and analyze its optimum opening sizes and shapes configuration. More in-depth research work to the behavior and the influence of holes to WF beams need to be conducted. In this paper, an oval shaped web opening is chosen as alternate. The study involves a modification in the variation of oval web openings both in the horizontally and vertically direction. An experimental and numerical study based on the finite element method conducted with the Abaqus/CAE 6.12 software is used to analyze the buckling behavior of the web. The obtained results from the experimental test specimens are in good agreement with the obtained results from the finite element analysis. Furthermore, the numerical model can be expanded to be used as analyzing tool in evaluating and studying the effect and influencing factors of a variation in opening’s parameters

MODELING THE INTERFACIAL TRANSITION ZONE BETWEEN STEEL AND CONCRETE MATERIALS IN COMPOSITE CONSTRUCTIONS

The interfacial Transition Zone (ITZ) has long been recognized as the “weak link” in a structure. While steel materials behave relatively linear up to high stress levels, nonlinearity is a prominent characteristic of most cementitious based material. To obtain a more realistic representation to the overall behavior of composite steel-to-concrete structures, the response of the interface should be incorporated into the analysis. A Finite Element Program written in the Visual Basic programming language is developed to take into account nonlinearity of the cementitious materials, while incorporating the Interfacial Transition Zone behavior. The Transition Zone is modeled as two springs, perpendicular to each other. The individual load-deformation responses of the springs were obtained from laboratory tested specimens. The Federal Institute of Technology, Europe Model Code 2011 was used to model the cementitious material behavior. Failure criteria are analyzed based on the principal stresses at Gauss points

MODELLING THE TENSILE BEHAVIOR OF PLAIN CONCRETE UNDER FLEXURAL LOADING

The tensile behavior of plain concrete is customary assumed to be linear, and the stiffness modulus is approached by the value of the initial tangent stiffness modulus in compression. However, even two decades ago the contrary was proven by the experimental results on plain concrete in direct tension. The stress-strain behavior of concrete in tension was demonstrated to be highly non-linear, even at very low stress levels. One of the major difficulties in obtaining an accurate tensile stiffness response is to achieve a uniform tensile stress in the section, without creating stress concentrations at any point along the section. These stress disparities will lead to micro crack initiation and falsely recorded responses. A non-linear Finite Element Model (FEM) based on the anisotropic material approach, was developed to produce the load-displacement response of a concrete beam loaded with a two point loading system. The load-displacement curves and stress-strain curves were validated to laboratory tested specimens having identical material properties. It was shown that the stiffness behavior of plain concrete in flexure is non-linear, and follows a quadratic function. The research work also covered the evaluation of two failure criteria

An Experimental Study to the Influence of Fiber Reinforced Polymer (FRP) Confinement on Beams Subjected to Bending and Shear

AbstractThe changing of the Indonesia National Code provision for accommodating the earthquake responses which previously was the SNI 03-1726-2002 to the new SNI 03-1726-2012 had a significant influence to the design criteria of concrete structures. One of the most underlining necessities of this revision was the tsunami and earthquake disasters affecting Indonesia, leading to the differentiation in the earthquake zones used to designing the 2002 SNI code. The newly introduced code has a predominant influence on the amplification of the designed earthquake load. As a consequence, building designed based on the 2002 SNI code requires re-evaluation and strengthening. One method for strengthening concrete structural elements is by using Fiber Reinforced Polymer (FRP) components. Previous research work on short beams loaded in flexure and reinforced with FRP u-shaped shear strengthening around the perimeter of the beam, beneath the slab demonstrated that this reinforcement provided additional strengthening as mandated in the ACI 440 standard. In this study, the combination of FRP flexural and u-shaped shear strengthening in accordance to this ACI 440 is studied to evaluated the enhancement in the capacity of the beam

The Analysis of Concrete Fracture by the Numerical Method

Concrete is a heterogeneous material consisting of aggregates embedded in a cement-sand matrix (mortar). The compression behavior of the aggregate is linear up till failure and the mortar is a brittle-linear material, with a reversible deformation up to its limit, followed by a sudden failure. The resulting concrete demonstrates a quasi-ductile behavior with a progressive decrease in load bearing capacity under incremental monotonic loading. The fracture mechanism of plain concrete on the other hand, is highly influenced by the bond strength in the interface and the tensile strength of the mortar. A Finite Element Model (FEM) was developed for analyzing the fracture characteristic of concrete in flexure. Two failure criteria were evaluated, the Mӧhr-Coulomb envelope and the Kupfer-HilsdorfRusch criteria. The program was validated by experimentally tested specimens,and proven to be accurate. Further,this program served as tool to analyze the fracture response of a range of concrete strengths. This research work was conducted at the Structural and Material Laboratory, Diponegoro University in Semarang, Indonesia

Bond-shear Behavior of FRP Rods as a Function of Attachment Configuration

The use of external reinforcement to improve or enhances the flexural capacity of a member depends on the transfer capacity, and the failure behavior of the composite between the reinforcement, the epoxy resin and the concrete. The most influencing factor is the bond-shear capacity between the rod and the epoxy, and the epoxy to the concrete. Fiber Reinforced Polymer (FRP) rods are the latest alternate for fulfilling the external reinforcement scheme. In the field, the mandated embedment depth as outlined by the ACI 440 code, could customary not be achieved since factors such as the depth of the concrete cover, and presence of stirrups limits the space. This study is aimed to evaluate the effect of FRP rod configurations with respect to the concrete surface, to the effectiveness of external reinforcement. The study looked into the bond-shear capacity as well as the mode of failure, influence by the rod attachment depth. It was shown that the embedment depth significantly influenced the failure mode, and therefore the strain transfer capacity from the concrete to the rods

The Effect of Plane - Stress and Plane - Strain Model to the Tensile Splitting Strength of the Concrete Cylinder and Paving Block

Numerous experimental investigations have been conducted to analyze the tensile behavior of plain concrete. One of the most well-known methods, favored due to its ease in test set-up, is the cylindrical splitting test or the Brazilian test. Recently, attempts have been made to numerically simulate the concrete tensile behavior based on this splitting test method. Meanwhile, the question as to whether this case should be modeled as a plane-stress or plane-strain condition was looked into. The experimental testing was conducted in accordance to the ASTM C496. Additionally, paving blocks tested in accordance to the BS EN 1338:2003 standard based on the same principals as the Brazilian test, were performed. The specimens were simulated by a finite element program constructed in Visual Basic language. The load-displacement responses of the laboratory tested specimens, namely cylinders and paving blocks, functioned as a validation tool to the finite element program. Beside proving that the developed program was correct, it was also concluded that the plain-strain approach represented a better outcome to the cylinder splitting test, while the plain-stress mode provided a better characterization for the paving blocks

Experimental Study on the Concrete Surface Preparation Influence to the Tensile and Shear Bond Strength of Synthetic Wraps

Synthetic sheets are increasing in popularity due to its ease in application, and very high tensile strength characteristics. Previous studies on the utilization of wraps for concrete flexural members resulted in a shear-bond loss in the sheets-to-concrete interface. Although the preparation of concrete surface prior to wrap attachment was in accordance with the product manual, the result was not optimal. Improving the bond could result in an increase of the member’s load carrying capacity, so that the capacity of the FRP warp could be optimized. To obtain the most effective surface preparation method, two sets of tests were conducted; firstly to study the tensile-bond behavior, and secondly to investigate the shear-bond response. Four concrete surface preparation methods were explored, consisting of grove configurations with respect to the line of loading. In this research, an independent tensile and shear behavior was assumed. It was found that the commonly used surface preparation was sufficient in tensile, but could lead to de-bonding in shear. The research also concluded that all four proposed methods enhanced the shear-bond; the choice of method is thus influenced by economic aspects, time and application ease. The shear-bond testing method as proposed by the fib code needs to be perfected, since a variation in errors was detected. © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the organizing committee of SCESCM 2016