MODIFIED FIXED-ANGLE STRUT-AND-TIE MODEL FOR HIGH STRENGTH REINFORCED CONCRETE BEAMS

Nonlinear finite element analysis was applied to various reinforced concrete beams using a set of constitutive models established in the modified fixed-angle softened-truss model (MFA-STM). The model was implemented by modifying the general-purpose program FEAPpv. The model can take account of the six important characteristics of cracked reinforced concrete: (1) the softening effect of concrete in tension-compression; (2) the tension-stiffening effect of concrete in tension; (3) the average stress-strain curve of steel bars embedded in concrete; (4) the shear modulus of concrete; (5) the aggregate interlock; and (6) dowel action. The comparison shows the aggregate interlock and dowel action can reduce the overestimation of the shear capacity of high strength reinforced beam, especially the high strength reinforced deep beam without web reinforcement. Moreover, the model is suitable for being implemented numerical procedures due its simplicity

Element Size Effects in Nonlinear Analysis of Reinforced Concrete Beams without Web Reinforcement

A new approach is developed to the nonlinear analysis of reinforced concrete beams without stirrups subjected to a monotonically increasing loading from zero up to the ultimate load. The softening effect of concrete in tensioncompression, the tension-stiffening and tension-softening of concrete in tension are all taken into account in the proposed model. The effect of finite element mesh size is investigated by applying the crack band theory (Bazant and Oh, 1983) and taking into account the plastic strain of concrete under tension. A simple procedure for calculating the stressstrain curve of plain concrete under tension was developed and implemented into the nonlinear finite element formulation. The proposed model gives relatively good agreement with the experimental results

A Constitutive Model for Plain Concrete Subjected to Static Loading

A numerical model based on the new theoretical micromechanical and lattice models has been proposed to simulate the fracture behavior of concrete specimens. The numerical model has been developed to implement the proposed theoretical micromechanical model using finite element method which employing the lattice model. Using the program developed, the numerical model has been used to simulate concrete specimens under direct tension and bending load conditions. Close agreement between the numerical results and the experimental data in literature indicated that the model is reasonably good, even in predicting the crack development. The numerical lattice model can, therefore, be an effective and useful tool for the analysis of the micro-structural behavior of concrete and for the design of concrete structures

Strut and tie model optimization for reinforced concrete bridge pier head structure using a genetic algorithm

Strut and tie model (STM) is more suitable to design the pierhead structures which resist high shear forces transferred from the girders. These pierhead structures behave like the disturbed regions as in reinforced concrete deep beam. The design of the struts and ties elements requires the initial geometry configuration of the truss model where its boundaries are limited by the shape of the pier head structures. To find the optimum topological shape of the truss model, the genetic algorithm (GA) optimization technique is used in this paper. The objective functions in the GA optimization consisted of minimizing the usage of concrete and steel reinforcement material and ensuring all the stress ratio of the strut and tie elements are less than equal to unity. Both prestressed and non-prestressed pierheads are investigated in this paper. The use of prestressing in the pierhead structures reduces the stresses in the main tension tie significantly and allowing some members of the shear tie and compression struts to have almost zero stresses. For these elements with zero stresses, the elements can be removed and reduces the concrete and rebar materials usage. Furthermore, the genetic algorithm optimization is found to be successful to ensure all the stress ratio in the members to be less than equal to unity

Strut and tie model optimization for reinforced concrete deep beam using genetic algorithm

This paper presents strut and tie model structural optimization of reinforced concrete deep beam using genetic algorithm. Genetic algorithm is used as the optimization platform as it does not require differentiation of the exact mathematical formulation to get the optimum solution. The force analysis is carried out using two-dimensional linear finite element method with truss element. The struts and ties design are based on ACI 318. One RC deep beam example is presented as an example. During optimization, there are two constraints which consisted of strength of the member alone and combination with deformation limit of the nodes. The stress ratio for both struts and ties are set to not exceed unity while the deformation was limited to 2.0 mm. From the optimization analysis, it can be concluded that genetic algorithm can be used to get the most optimum structural configuration which yield the most economical solution for design purposes. On the other hand, it is found out that optimizing only the strength alone can yield a more economical solution compared to the design references. However, if deformation constraint is added in the optimization parameters, larger deep beam depth is required to satisfy the deformation limits

Performance of square reinforced concrete columns externally confined by steel angle collars under combined axial and lateral load

Providing good ductility has become research interest in the area of seismic resistant structures. Particularly in Reinforced Concrete (RC) structure, such ductility is commonly achieved by providing good confinement. Confinement can be conventionally provided by internal stirrups, and also additional external elements which are commonly used as strengthening or retrofit works. Attaching external steel collars on concrete columns is one of many techniques in enhancing the ductility. In this study, performance of such retrofitting method is investigated through laboratory experiment. Totally five specimens are built for this investigation. The first two specimens (CS1-1, and CS1-2) are control specimens, which are conventionally confined by stirrups. The other three specimens (S1-3, S1-4, and S1-5) are only confined externally with the steel angle collars. All five specimens are tested under combined axial and lateral load. The axial load is kept constant at 30% of plain concrete axial capacity to model the gravity load. The lateral load given is according to ACI 374.1-05 quasi-static cyclic loading protocol. Lateral load resistance is recorded throughout the cyclic loading, and plotted against the corresponding lateral displacement. Results show that specimens with smaller volumetric ratio of confining element suffered brittle failure (poor ductility). Specimens with adequate confinement show good deformability and ductile failure. In conclusion, the retrofitting method by providing external steel angle collars is very promising

FE Model of Low Grade Rubber for Modeling Housing’s Low-Cost Rubber Base Isolators

An accurate selection of strain energy function (SEF) plays a very important role for predicting the actual behavior of rubber material in the finite element analysis (FEA). The common method for selecting the SEF is by using the curve fitting procedure. However, the behavior of some typical rubbers, such as low grade rubbers (average hardness value of 47.2), cannot be predicted well by only using the curve fitting procedure. To accurately predict the actual behavior of such specifically nearly incompressible material, a series of FEA were carried out to simulate the actual behavior of four physical testing materials, namely the uniaxial, the planar shear, the equibiaxial, and the volumetric tests. This FEA is intended to examine the most suitable constitutive model in representing the rubber characteristics and behavior. From the comparisons, it can be concluded that the Ogden model provides a reasonably accurate prediction compared to the remaining investigated constitutive material models. Finally, the appropriate SEF, i.e. the Ogden model, was adopted for modeling a low-cost rubber base isolator (LCRBI) in the finite element analysis (FEA). The simple uniaxial compression test of the LCRBI is required for validating that the selected SEF works for predicting the actual behavior of LCRBI

Shear Behavior of Joint The Partial Prestressed Concrete Beam-Column Reinforced Concrete of Ductile Frame Structure Building In a Scure Residents and for Settlement Environment

   Concentration of this study is to create a Specimens model of Joint Interior Beam - Column using Partial Prestressed Concrete Beams elements connected with Reinforced Concrete Column. Design capacity of Beam- Column Joint Shear is the horizontal shear reinforcement in the form of stirrups Æ 10-50 mm to fill the empty space bj = 288 mm . The capacity Shear that can be deployed by the cross bar = 103.62 kN. Total shear force that is capable of detained by the beam-column joint structures are Vjh = 409 kN. This study is a continuation of research SRPMK models shaped beam - column joint with beam section 250/400 mm , and the column section 400/400 mm , the source of funds from Research Ditlitabmas Decentralization Program of Higher Education , through ITS Featured Research Grant in 2013 .  Experimental studies have been conducted with Cyclic loading ( pseudo dynamic ) lateral , static axial load on the column as a stabilizer . Specimens ability to withstand Ultimate Lateral Cyclic Load : conditions Load push (press) = 470.90 kN and Load Pull = 465.80 kN. Everything is > 409 kN.Ductility structure also qualified in 3.50% Drift Ratio: Conditions Press m = 1.27 > 1.20, Pull Conditions m = 1.29 > 1.20. In general, behavioral modeling structure has qualified as a reliable protection occupancy when the building was hit by an earthquake

Optimasi Desain Balok dan Kolom Gedung Twin Tower Makassar dengan Menggunakan Microsoft Excel VBA terhadap Sisi Kekuatan Lentur, Geser, dan Biaya

Makassar merupakan kota terbesar keempat di Indonesia dan juga merupakan Ibu kota Sulawesi Selatan sehingga mendorong pemerintah untuk menghadirkan fasilitas untuk menunjang kegiatan masyarakat, salah satunya adalah pembangunan infrastruktur. Karena lahan yang semakin sempit, dipilihlah bangunan secara vertikal yang dinilai lebih efektif dan efisien dengan kondisi eksisting yang ada. Twin Tower Makassar merupakan salah satu gedung tinggi dengan 36 lantai dan tinggi 170,95 m yang terletak di Makassar. Gedung ini dibangun di kawasan Center Point of Indonesia dan akan menjadi gedung pemerintahan Sulawesi Selatan. Menara ini akan menyatukan kantor-kantor pemerintahan Sulawesi Selatan dan juga menjadi bentuk sinergitas, solidaritas serta kolaborasi antara perangkat pemerintah sehingga diharapkan dapat membangun Sulawesi Selatan dengan efisien. Twin Tower juga akan dilengkapi dengan pusat bisnis dan jasa, serta fasilitas publik seperti mall, hotel, dan restoran. Pentingnya optimasi elemen struktur utama yaitu balok dan kolom adalah untuk mengurangi biaya pembangunan dan mengoptimalkan penggunaan bahan bangunan. Optimasi dilakukan dengan bantuan program sederhana dari Microsoft Excel yaitu Visual Basic Analysis (VBA). Pelaksanaan proses optimasi dilakukan dengan VBA karena proses optimasi dapat dilakukan secara otomatis hanya dengan memasukan syarat serta rumus-rumus sesuai peraturan saja sehingga dapat memudahkan proses penentuan dimensi sampai ke kebutuhan tulangan dari elemen struktur gedung. Pada tugas akhir ini dilakukan optimasi untuk elemen struktur balok dan kolom gedung Twin Tower Makassar menggunakan Microsoft Excel Visual Basic Analysis (VBA). Dari hasil analisa yang telah dilakukan didapatkan bahwa balok dapat menjadi lebih efisien dari sisi lentur dan gesernya dengan pengurangan harga hingga 31% dan kolom dapat menjadi lebih efisien dari sisi lentur dan gesernya dengan pengurangan harga hingga 57%