• Earthquakes and Structures
• /
• 제7권5호
• /
• pp.627-645
• /
• 2014

Using OpenSees as a framework, constitutive models of reinforced, prestressed and prestressed steel fiber concrete found by the panel tests have been implemented into a finite element program called Simulation of Concrete Structures (SCS) to predict the seismic behavior of shear-critical reinforced and prestressed concrete structures. The developed finite element program was validated by tests on prestressed steel fiber concrete beams under monotonic loading, post tensioned precast concrete column under reversed cyclic loading, framed shear walls under reversed cyclic loading or shaking table excitations, and a seven-story wall building under shake table excitations. The comparison of analytical results with test outcomes indicates good agreement.

• Structural Engineering and Mechanics
• /
• 제45권6호
• /
• pp.723-740
• /
• 2013

This paper presents a parametric study of reinforced concrete bridge tall piers with hollow, rectangular sections. Such piers are typically used in railway construction of prestressed concrete viaducts. Twenty one different piers have been studied with seven column heights of 40, 50, 60, 70, 80, 90 and 100 m and three types of 10-span continuous viaducts, whose main span lengths are 40, 50 and 60 m. The piers studied are intermediate columns placed in the middle of the viaducts. The total number of optimization design variables varies from 139 for piers with column height of 40 m to 307 for piers with column height of 100 m. Further, the results presented are of much value for the preliminary design of the piers of prestressed concrete viaducts of high speed railway lines.

• Computers and Concrete
• /
• 제22권2호
• /
• pp.221-225
• /
• 2018

In this paper, vibration analysis of concrete foundations resting on soil medium is studied. The soil medium is simulated by Winkler model considering spring element. The concrete foundation is modeled by thick plate elements based on classical plate theory (CPT). Utilizing energy method consists of potential energy, kinetic energy and external works in conjunction with Hamilton's principle, the motion equations are derived. Assuming the simply supported boundary condition for the concrete foundation, the Navier method is used for calculating the frequency of the structure. The effect of different parameters such as soil medium, mode numbers, length to width ratio and length to thickness ratio of the concrete foundation are shown on the frequency of the structure. At the first, the results are validated with other published works in order to show the accuracy of the obtained results. The results show that considering the soil medium, the frequency of the structure increases significantly.

• Steel and Composite Structures
• /
• 제3권3호
• /
• pp.199-212
• /
• 2003

An experimental investigation of lightweight aggregate and foamed concrete contribution to the ultimate strength capacity of square and rectangular steel tube sections is presented in this study. Thirty-four simply supported beam specimens, 1000-mm long, filled with lightweight aggregate and foamed concretes were tested in pure flexural bending to calculate the ultimate moment capacity. Normal concrete-filled steel tubular and bare steel sections of identical dimensions were also tested and compared to the filled steel sections. Theoretical values of ultimate moment capacity of the beam specimens were also calculated in this study for comparison purposes. The test results showed that lightweight aggregate and foamed concrete significantly enhance the load carrying capacity of steel tubular sections. Furthermore, it can be concluded from this study that lightweight aggregate and foamed concretes can be used in composite construction to increase the flexural capacity of the steel tubular sections.

• Structural Engineering and Mechanics
• /
• 제54권6호
• /
• pp.1111-1133
• /
• 2015

Rebar corrosion in concrete is one of the main causes of reduction of service life of reinforced concrete buildings. This paper presents the influence of rebar corrosion on the structural behavior of reinforced concrete (RC) buildings subjected to strong earthquake ground motion. Different levels of rebar corrosion scenarios were applied on a typical four story RC frame. The deteriorated conditions as a result of these scenarios include loss in cross-sectional area and loss of mechanical properties of the reinforcement bars, loss in bond strength, and loss in concrete strength and its modulus of elasticity. Dynamic analyses of the frame with different corrosion scenarios are performed with selected strong earthquake ground motion records. The influences of degradation in both concrete and reinforcement on structural behavior are investigated by comparing the various parameters of the frame under different corrosion scenarios with respect to each other. The results show that the progressive deterioration of the frame due to rebar corrosion causes serious structural behavior changes such as change in failure mode. The intensity, propagation time, and extensity of rebar corrosion have very important effects on the level of degradation of steel and concrete, as well as on the earthquake behavior of the structure.

• Smart Structures and Systems
• /
• 제10권6호
• /
• pp.547-555
• /
• 2012

Measuring crack length in concrete fracture test is not a trivial problem due to high speed crack propagation. In this study, mechanoluminascent (ML) material, which emits visible light under stress condition, was employed to visualize crack propagation during concrete fracture test. Three-point bending test was conducted with a notched concrete beam specimen. The cracking images due to ML phenomenon were recorded by using a high speed camera as a function of time and external loadings. The experimental results successfully demonstrated the capability of ML material as a promising visualization tool for concrete crack propagation. In addition, an interesting cracking behavior of concrete bending fracture was observed in which the crack propagated fast while the load decreased slowly at early fracture stage.

• Structural Engineering and Mechanics
• /
• 제35권5호
• /
• pp.631-643
• /
• 2010

A numerical procedure for the geometrical and material nonlinear analysis of concrete beams prestressed with external tendons is described, where the effects of external prestressing are treated as the equivalent loads applied on the concrete beams. The geometrical nonlinearity is considered not only the eccentricity variations of external tendons (second-order effects) but also the large displacement effects of the structure. The numerical method can predict the nonlinear response of externally prestressed concrete beams throughout the entire loading history with considerable accuracy. An evaluation of second-order effects of externally prestressed concrete beams is carried out using the proposed analysis. The analysis shows that the second-order effects have significant influence on the response characteristics of externally prestressed concrete beams. They lead to inferior ultimate load and strength capacities and a lower ultimate stress increase in tendons. Based on the current analysis, it is recommended that, for simply-supported externally prestressed beams with straight horizontal tendons, one deviator at midspan instead of two deviators at one-third span be furnished to minimize these effects.

• Computers and Concrete
• /
• 제13권4호
• /
• pp.437-456
• /
• 2014

This work incorporates newly introduced Lattice Discrete Particle Model (LDPM) to assess the failure mechanism and strength of hollow concrete blocks. Alongside, a method for the graphical representation of cracked surfaces in the LDPM is outlined. A slightly modified calibration procedure is also suggested and used to estimate required model parameters for a tested concrete sample. Next, the model is verified for a compressively loaded hollow block made of the very same concrete. Finally, four geometries commonly used in the production of hollow concrete blocks are selected, numerically simulated, and their failure properties are explored under concentric and eccentric compressions.

• Computers and Concrete
• /
• 제13권2호
• /
• pp.235-253
• /
• 2014

The theoretical basis and the main results of a design procedure, which attempts to provide the optimal layout of ordinary reinforcement in prestressed concrete beams, subjected to bending moment and shear force are presented. The difficulties encountered in simulating the actual behaviour of prestressed concrete beam in presence of coupled forces bending moment - shear force are discussed; particular emphasis is put on plastic models and stress fields approaches. A unified model for reinforced and prestressed concrete beams under axial force - bending moment - shear force interaction is provided. This analytical model is validated against both experimental results collected in literature and nonlinear numerical analyses. Finally, for illustrating the applicability of the proposed procedure, an example of design for a full-scale prestressed concrete beam is shown.

• Computers and Concrete
• /
• 제11권4호
• /
• pp.291-304
• /
• 2013

By considering the creep characteristics of concrete core under eccentric compression, a creep model of concrete filled steel tubes (CFT) columns under eccentric compressive loads is proposed based on the concrete creep model B3. In this proposed model, a discrete element method is introduced to transform the eccentric loading into axial loading. The validity of the model is verified by comparing the predicting results with the published creep experiments results on CFT specimens under compressive loading, together with the predicting values based on other concrete creep models, such as ACI209, CEB90, GL2000 and elastic continuation and plastic flow theory. By using the proposed model, a parameters study is carried out to analysis the effects of practical design parameters, such as concrete mix (e.g. water to cement ratio, aggregate to cement ratio), steel ratio and eccentricity ratio, on the creep of CFT columns under eccentric compressive loading.