Umesh Kumar Sharma

Strengthening of Heat Damaged Reinforced Concrete Short Columns

The purpose of this study was to investigate the effectiveness of different strengthening schemes in strengthening heat damaged reinforced concrete short columns. A series of 63 heat damaged specimens were tested under concentric compression after jacketing externally with High Strength Fiber Reinforced Concrete (HSFRC), Ferrocement (FC) and Glass Fiber Reinforced Polymer (GFRP) jackets. The specimens were subjected to various heating and cooling regimes. The overall response of strengthened specimens was investigated with reference to un-strengthened specimens in terms of axial compressive strength, ductility, lateral stress-strain, and axial stress-strain behaviour. It was observed that while the GFRP jacketing is quite effective in improving compressive strength and energy dissipation, it is not capable of improving stiffness. On the contrary FC and HSFRC jacketing were mainly effective in improving stiffness property. Overall GFRP jacketing was found to be the most effective method of strengthening fire or heat damaged concrete columns.

Optimization of Post-Fire Residual Compressive Strenghth of Concrete by Taguchi Method

This paper presents results of an experimental study undertaken to optimize the residual compressive strength of heated concrete with respect to various mix design parameters using the Taguchi method. The design of experiments (DoE) was carried out by standard L9 (34) orthogonal array (OA) of four factors with three material parameter levels. The factors considered were water-cement ratio, cement content, super-plasticizer dosage and fine aggregate content. The specimens were heated up to 200°C, 400°C, 600°C and 800°C target temperatures and were subsequently tested under axial compressive loads in cooled condition. Based on the results, the material parameter responses of optimum performance characteristics were analyzed by statistical analysis of signal to noise ratio (S/N) and analysis of variance (ANOVA) techniques to maximize the post-fire residual compressive strength of concrete. The results indicate that the best level of control factors paid their own contribution of compressive strength at vario...

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...

A Full Scale Fire Test on a Pre Damaged RC Framed Structure

A full scale Reinforced concrete (RC) frame assemblage was constructed and induced a predefined level of damage by subjecting the frame to simulated seismic loads and then was tested against a designed 1 h compartment fire. The RC frame was instrumented with a number of sensors which recorded strains, displacements and temperatures during the test. This paper provides a report on a full scale RC frame subjected to post earthquake fire. The frame could withstand the fire without collapse however the residual capacity of the frame was reduced to 65 % of the original. Important observations have been made about the development of the temperatures and displacements in various elements during the test.

Residual Compressive Stress-Strain Relationship for Concrete Subjected to Elevated Temperatures

This study attempts to investigate the post-fire residual stress-strain behaviour of unconfined plain and fibrous concretes under axial compression. The experimental variables of the study were concrete strength levels, volume fractions of flat crimped steel fibres and polypropylene fibres, inclusion of hybrid fibres and temperature of exposure. A total of 147 cylindrical specimens (150 x 450 mm) were cast and tested under this study. The specimens were first exposed to temperatures ranging from room temperature to 800°C and then tested under uni-axial compression after cooling to obtain complete residual stress-strain response. Based on the test data obtained, a simple empirical model is proposed to describe the complete residual stress-strain relationships of plain and fibre reinforced concrete after exposure at elevated temperatures. Important observations have been made in the paper about the influence of temperature on various mechanical properties namely strength, stress-strain curves, compressive t...

Postheated Model of Confined High Strength Fibrous Concrete

HSC normally suffers from low stiffness and poor strain capacity after exposure to high temperature. High strength confined fibrous concrete (HSCFC) is being used in industrial structures and other high rise buildings that may be subjected to high temperature during operation or in case of an accidental fire. The proper understanding of the effect of elevated temperature on the stress-strain relationship of HSCFC is necessary for the assessment of structural safety. Further stress-strain model of HSCFC after exposure to high temperature is scarce in literature. Experimental results are used to generate the complete stress-strain curves of HSCFC after exposure to high temperature in compression. The variation in concrete mixes was achieved by varying the types of fibre, volume fraction of fibres, and temperature of exposure from ambient to 800°C. The degree of confinement was kept constant in all the specimens. A comparative assessment of different models on the high strength confined concrete was also conducted at different temperature for the accuracy of proposed model. The proposed empirical stress-strain equations are suitable for both high strength confined concrete and HSCFC after exposure to high temperature in compression. The predictions were found to be in good agreement and well fit with experimental results.

Three-Dimensional Finite Element Modeling of Confined High-Strength Concrete Columns

The use of high-strength concrete (HSC) tied columns is becoming increasingly popular in engineering practice. Researchers are working to obtain the proper post-peak behavior of tied columns with concrete strength greater than 60 MPa. Many empirical confinement models have been reported in the literature for the prediction of stress-strain behavior under concentric loading. However, nothing significant has been said about the numerical modeling of the problems wherein the nonlinear response of HSC tied columns may be reasonably predicted. In the present study, the nonlinear behavior of concrete material has been idealized by William-Warnke five-parameter model, which, to date, is the most widely accepted and sophisticated criterion. Within the framework of rate independent associative elasto-plasticity, a full backward Euler integration algorithm for stress updating has been implemented in the present work. A fixed crack smeared approach based upon fracture energy concept and non-local material softening law has been employed for the tensile modeling of concrete material. The computational model also involves the provision for cover spalling. A couple of examples have also been presented for validation of the numerical methodology proposed in this work.

A ureteral mass presenting as deep vein thrombosis: a very rare presentation

A 45 year old post-menopausal female presented to her primary physician with complaints of left foot swelling which gradually progressed to involve the entire left lower limb. She did not give any antecedent history of trauma, ulceration on lower limb, haematuria, lower urinary tract symptoms, bowel complaints, vaginal bleeding, loss of weight, loss of appetite, previous history of DVT. There was no history of previous surgeries and co-existing morbidities. Her left lower limb was reddish in color, tense and tender to touch. Pervaginal examination revealed induration with in the left fornix. Rest of the general and systemic examination, were within normal limits. A venous Doppler revealed a partial thrombus of the Left Proximal external iliac vein and Left Common Iliac vein. Thrombophillic screen (PT-INR, aPTT, Protein C, Protein S, D, and Factor V Leiden Mutation) was within normal limits. Patient was started on Warfarin and put on total bed rest. Due to absence of any predisposing factors, further evaluation was considered and an ultrasound of the abdomen was done. It revealed a grossly dilated left renal pelvis with thinned out parenchyma & a 1.3*1.1cm lesion near the left vesicoureteric junction. Contrast-Enhanced CT of Abdomen & Pelvis Figure 1 was done which shows poorly functioning left kidney with gross hydronephrosis & thinned out parenchyma, large 6.6*4.5cm heterogeneously enhancing solid cystic mass in the left ureter at the level of the iliac vessel crossing and 3.5*2.1cm heterogeneously enhancing solid cystic lesion in left distal ureter extending up to VUJ. Her hemoglobin, serum creatinine, liver function tests, urinalysis were within normal limits. Urine for malignant cytology was negative. Cystoscopy showed a bulge just lateral to the left ureteric orifice and no other visible mass. The left ureteric orifice could not be cannulated. Considering the diagnosis of a ureteric mass, a Left Nephrouretectomy with bladder cuff excision was planned. Warfarin was stopped 5 days before surgery and patient was put on bridging therapy with low molecular weight heparin. A cardiology consult was taken and it was decided to insert an IVC filter 24 hours before surgery as prophylaxis to decrease risk of intra-operative and postoperative pulmonary embolism. Intra-operatively DVT pump was not applied. A Radical Nephroureterectomy along with Hysterectomy and Left Salpingo-oophorectomy (Figure 2) (Figure 3) was done with gynecological assistance in view of local invasion of cervix. Mid ureteric mass was dissected off the iliac vessels with CTVS assistance and final specimen consisted of the Left kidney, ureter, Uterus, Left Ovary along with Lymph Node dissection. Total intra-operative blood loss was 600ml. Post-operatively patient was kept in the ICU before shifting to the ward. Warfarin was re-started on day 3. Patient had a relatively uneventful post-operative period.

Study on bond behaviour exposed to fire using beam specimen

The composite action of concrete and steel in a reinforced concrete structure depends upon the bond between them. Bond behaviour is studied in terms of bond-slip relationship. The bond between them depends upon mechanical properties of concrete and steel. In an event of fire these mechanical properties degrades and hence the bond behaviour changes. Some researches were performed to study the effect of temperature on the bond-slip relationship which are based on pull out specimens. Generally these relationships are obtained using pull out specimen which over estimates the bond properties. In this study beam specimens were used which is recommended by Rilem. These specimens were exposed to elevated temperatures up to 650 °C and there bond-slip behaviour were studied. The study shows that bond strength decreases while peak slip increases with increases in temperature. Also an equation proposed was proposed which can predict the bond strength between concrete and steel exposed up to the temperature of 650 °C.