G.R. Reddy

Studies on Normal Strength Concrete Cubes Subjected to Elevated Temperatures

Concrete in structures is likely to be exposed to high temperatures during fire. The probability of its exposure to elevated temperatures is high due to natural hazards, accidents and sabotages. Therefore, the performance of concrete during and after exposure to elevated temperature is a subject of great importance and interest to the designer. Popular normal strength grades of concrete produced by Ready Mix Concrete (RMC) India, Mangalore have been used in production of test specimens (150 mm cubes), cured and tested by destructive method for gathering data on strength characteristics. Later, these test samples were subjected to elevated temperatures ranging from 100°C to 800°C, in steps of 100°C with a retention period of 2 hours. After exposure, weight losses and the residual compressive strength retention characteristics are studied. Test results indicated that weight and strength significantly reduces with an increase in temperature. Residual compressive strength prediction equations are proposed for...

Shake table tests and analytical simulations of a steel structure with shape memory alloy dampers

This study uses the pseudoelastic properties of Ni–Ti shape memory alloy wires for attenuation of the seismic response of a steel structure and evaluates its effectiveness and applicability in seismic response control. In this paper, shake table tests, carried out on a model of a steel structure with and without wire-based shape memory alloy dampers, are discussed in detail. Shake table tests, comprised of free vibration tests and spectrum compatible time history tests, were carried out. The former were used for the evaluation of the frequency and damping, and the later were used to prove the efficacy of the shape memory alloy dampers. Further analytical simulations are carried out using detailed time history analysis utilizing a thermomechanical model of an SMA and taking into account the residual martensite accumulation, which is irreversibly due to cyclic forward/reverse martensitic transformation. Moreover, a simple iterative response spectrum (IRS) method with equivalent damping and stiffness is also used to evaluate the response of the structure with SMA dampers, and it is proved that the method can be conservatively used by designers.

Pivot hysteresis model parameters for reinforced concrete columns, joints, and structures

Inelasticity in reinforced concrete (RC) frame structures due to seismic loads is generally considered to be concentrated in the form of hinges in beams, columns, and joints. In this paper, the parameters for rectangular RC beams, columns, and nonseismically detailed beam-column joints are suggested, keeping the simplicity of the original pivot hysteresis model. With the proposed parameters, the existing model can be effectively used to perform nonlinear dynamic analysis of nonseismically detailed RC structures. Two major improvements in the parameters for columns as compared to the original model are: 1) new parameters cover the complete range of axial load on the column; and 2) it gives due consideration to the transverse reinforcement on pinching behavior of the members. Additionally, several parameters are proposed for poorly detailed exterior joints. It is shown that the model with the proposed parameters nicely captures the hysteretic behavior of RC members, joints, and structures.

Thermal Analysis of Reinforced Concrete Structural Elements

The paper presents a comparative study of thermal properties of reinforced concrete structural elements. A total of 2 beams and 2 columns were selected from literature [1-3]. Thermal profiles of these elements were predicted using different thermal properties and were compared with the experimental results. The thermal analysis is carried out numerically using finite element analysis package, ABAQUS [4]. Comparisons of different analyses results have been made with the main focus laid on the effect of the boundary conditions i.e. prescribed temperature boundary condition, convection and radiation. During the heating phase, there was slight difference in the temperatures predicted using the two boundary conditions, whereas during cooling phase, there was a significant difference: the convective and radiation boundary condition yielded better results. A reduction in discrepancy between the simulated and experimental result was observed on using thermal properties as per the formulation in Eurocode2 which took into account the moisture content.

Effect of Ductile Detailing on the Performance of a Reinforced Concrete Building Frame Subjected to Earthquake and Fire

AbstractA nonductile reinforced concrete (RC) frame was constructed and was subjected to a predefined level of damage by subjecting the frame to simulated earthquake loading. The damaged RC frame was then subjected to 1-h designed compartment fire. The RC frame was instrumented with a number of sensors that recorded strains, displacements, and temperatures during the test. The resulting data provided a distinctive record of earthquake-damaged RC structures in fire through a complete heating–cooling cycle. The experimental results were compared with the results from an earlier test done on the RC frame having ductile detailing. The results show a marked influence of reinforcement detailing on the postearthquake fire performance of the concrete structures. The simulated earthquake loading caused wider cracks and more severe concrete spalling in the frame without ductile detailing compared to the frame with ductile detailing. The fire damage was also more pronounced with extensive spalling due to the attainm...

Seismic stability of two interconnected steel structures freely standing on the floor

Nuclear fuel fabrication and reprocessing facilities have glove boxes that are extensively used as a primary containment for radiological material. These equipment are maintained under negative pressure using ventilation system and possess high degree of leak tightness. Sometimes, they are used as a standalone structure and many a times, interconnected to each other. Normally, they are not anchored to the floor, which raises serious concerns about their seismic performance. To check seismic stability of the glove boxes and evaluate safety margins in design, tri directional fullscale shake table experiments of two interconnected glove boxes had been carried out. Two configurations were compared; in first, both the boxes were connected through flexible linkage (material transfer tunnel) and in second both were rigidly connected via structural members. Objective of experiments was to observe effects of seismic excitation on leak tightness, structural integrity and overall stability of two interconnected glove boxes. Subsequently, nonlinear finite element analysis was carried out to establish and develop analysis methodology. Experimental results were utilized for model benchmarking. Furthermore, a numerical method was developed to determine safe upper bounds on sliding displacements. This paper highlighted critical findings emanated from experimental results and examined their effect on seismic stability. Enhanced seismic stability in case of rigidly connected boxes was observed. Rigid body motions (mainly sliding and low magnitude rocking) dominated the response with very limited effect of elastic motions. Methodology used for modelling and analyzing glove boxes under seismic loading using finite element methods was also presented.