The transient behaviour of plain concrete at elevated temperatures

This thesis describes an investigation of the effect of elevated temperatures upon the properties of plain concrete containing a siliceous aggregate. A complete stress-strain relationship and creep behaviour are studied. Transient effects (non-steady state) are also examined in order to simulate more realistic conditions. A temperature range of 20-700ºC is used. corresponding to the temperatures generally attained during an actual fire. In order to carry out the requisite tests, a stiff compression testing machine has been designed and built. The overall control of the test rig is provided by a logger/computer system by developing appropriate software, thus enabling the load to be held constant for any period of tlme. Before outlining any details of the development of the testing apparatus which includes an electric furnace and the.associated instrumentation, previous work on properties of both concrete and. steel at elevated temperatures is reviewed. The test programme comprises four series of tests:stress-strain tests (with and without pre-load), transient tests (heating to failure under constant stress) and creep tests (constant stress and constant temperature). Where 3 stress levels are examined: 0.2, 0.4 & 0.6 fc. The experimental results show that the properties of concrete are significantly affected by temperature and the magnitude of the load. The slope of the descending portion branch of the stress-strain curves (strain softening) is found to be temperature dependent. After normalizing the data, the stress-strain curves for different temperatures are represented by a single curve. The creep results are analysed using an approach involving the activation energy which is found to be constant. The analysis shows that the time-dependent deformation is sensibly linear with the applied stress. The total strain concept is shown to hold for the test data within limits

Numerical Study on Shear Stress Variation of RC Wall with L Shaped Section

In recent years, and after the 2003 Boumerdes earthquake, a new type of building is being constructed in Algeria. The new concept is based on the concentration of reinforced concrete shear walls with L shape at the building corners. The seismic behavior of such configuration is not well known nowadays. Numerical investigation was carried out on reinforced concrete structure to evaluate the stress distribution at the base of the corner L shaped walls. Influence of number of stories, length of the shear wall as well as the thickness of the wall was considered in our investigation. In total, more than 200 numerical models were crated and analyzed. The analyses showed that, reinforced concrete wall with 15 cm, or less, in thickness should have a minimum length of 10 times the thickness; however, for RC walls with a thickness of more than 20 cm, the length of the wall should be greater than 7  times the thickness. In this paper the main results of this investigation are presented

Local Ductility and Global Behavior Factor of Steel Frame Structures Braced by Centered Bars System

When an earthquake occurs, civil engineering structures are subjected to forces that lead to a non linear behavior. This is often the case for designed steel structures. So, they absorb a larger part of the seismic energy transmitted to its resistant elements (columns and diagonals). This ability to dissipate energy through plastic deformation is expressed by the q behavior factor, used in the seismic design codes. In this paper a distribution of the local required ductility as a function of the behavior factor is given for steel structures braced by the stability bents of X shape

Study and modeling of the compressive and splitting tensile strengths of polypropylene fiber reinforced concrete containing recycled asphalt pavement

In a context of sustainable development and material recycling, the present study aims to study mechanical properties of a recycled asphalt pavement (RAP) concrete, reinforced with polypropylene fibers (PF). First, five formulations were designed with different RAP content with a maximum of 50% at a water cement ratio (W/C) of 0,50. Experimental results showed that the more RAP content increases in mix, the more mechanical strengths decrease, mainly due to the weak interfacial transition zone (ITZ) between the mortar and the recycled material. Reinforcement of PF at 0.1% and 1% volume fraction was realized on all mixes and the experimental results showed that the compressive strength is increased while the splitting strength is decreased. Then, an experimental linear relationship between the splitting tensile strength and the compressive strength is proposed. In the second part of the study, the mechanical strengths were modeled using a factorial plan 22, giving a quantification of the individual effect of both introduction of the RAP and the reinforcement and the combined effect, on response in terms of compressive strength and splitting tensile strength. Established model predicted the mechanical strength of a hardened concrete, whatever the RAP content and whatever the PF reinforcement content

Transverse Vibration Analysis of Uniform Beams under Various Ends Restraints

AbstractThe beam analysis, based on the assumptions of the Bernoulli-Euler theory, in free vibration has been largely investigated. Many researches focused on the transverse vibrations study, under the application of different boundary constraints where different theories were applied. The considered stiffness and mass matrices are those obtained by assembling the elementary ones resulting from the FEM use The Jacobi method allowed the solution of the eigenvalue problem. These well known concepts were applied to the study of beams with constant geometrical and mechanical characteristics having one to two overhangs with variable lengths. Murphy studied, by an algebraic solving approach, a simply supported beam with two overhangs of arbitrary length, which allows an experimental determination of the E elastic modulus.The advantage of our paper offers a possibility of extending this approach to many interesting problems formed by beams vibrating transversally with various ends restraints

STUDENT ENGAGEMENT IN NURSING SCHOOL: A SECONDARY ANALYSIS OF THE NATIONAL SURVEY OF STUDENT ENGAGEMENT DATA

Student engagement has received considerable attention in higher education research because of the link between increased student knowledge, greater student satisfaction with educational experience, and increased student retention and persistence. The National Survey of Student Engagement (NSSE) has been used since 2000 to assess engagement in undergraduate college students. NSSE results have been used to gain an understanding about levels of academic engagement for freshman and senior college students. Institutions use NSSE results to make changes in policies and practices to improve undergraduate education. This comparative descriptive study examined levels of undergraduate nursing students’ engagement during college by conducting a secondary analysis of NSSE data. The overall aim of this study was to gain a better understanding of nursing students’ levels of engagement at two points in time and comparing two geographic regions, and how they spent their time while in college. In a 2007 report, the National Leadership Council for Liberal Education and America’s Promise (LEAP) identified ten innovative high-impact practices in higher education. Since then, these practices have been implemented across the nation and have been associated with gains in student learning and personal development (Kuh, 2008). This study compared senior nursing students’ levels of engagement before and after these high-impact practices were recommended to see if engagement levels in senior nursing students differed between 2003 and 2010. Astin’s student involvement theory was used as a guiding framework for this study to examine how nursing students engage in the learning process and what educational resources nursing students use to become involved in the learning process. Astin’s theory focuses on what the college student does to be an active participant in the learning process and describes the environmental influences on college student development. Although statistically significant, the differences between the 2003 and 2010 nationwide cohorts of nursing students for the Level of Academic Challenge and Student-Faculty Interaction benchmarks were trivial. Senior nursing students were equally as engaged in 2010 as they were in 2003. This finding suggests consistency and stability in nursing education with regard to the Level of Academic Challenge and Student-Faculty Interaction benchmarks. Senior nursing students from Kansas and Missouri were compared to senior nursing students from all other states. Senior nursing students from KS/MO were similar to students from all other states in relation to Level of Academic Challenge and Active and Collaborative Learning benchmarks and how they spent their time in a typical 7-day week. Although statistically significant, the difference between the KS/MO cohort of nursing students and cohort of nursing students from other states for the Student-Faculty Interaction benchmark was trivial. In general, senior nursing students in 2010 were as engaged in their education as they were in 2003, reflecting stability in nursing education during this same time period. Senior nursing students from KS/MO were as engaged and spent their time in a similar manner as senior nursing students from all other states. This indicates that nursing students from these Midwest states have similar educational engagement as nursing students from other states and nursing education in the Midwest is consistent with the rest of the country. These findings of stability and consistency over time and across regions of the US are encouraging for nursing education. Nurse educators and higher-education administrators can build upon this strong foundation and make concerted efforts to further increase engagement in nursing students

Effect of glass powder on the behaviour of high performance concrete at elevated temperatures

International audienceIn recent years, many studies have been done on the performance of concrete containing glass powder (GP). For the purpose of widespread use of GP in concrete mixes, a knowledge of the performance of such a mixture after a fire is essential for the perspective of structural use. This research work was carried out to evaluate the performance of High Performance Concrete (HPC) made with GP after being exposed to elevated temperature. The studied mixtures include partial replacement of cement by GP with up to 30%. The mechanical performance and structural alterations were assessed after high temperature treatment from 200 degrees C to 800 degrees C. The mechanical performance was evaluated by testing the specimens to the compressive and tensile strength. In addition, the mass loss and the porosity were measured to notice the structural alterations. Changes in microstructure due to temperature was also investigated by the X-ray diffraction (XRD) and thermal gravimetric analyses (TGA) as well as porosity adsorption tests. The results of the concrete strength tests showed a slight difference in compressive strength and the same tensile strength performance when replacing a part of the cement by GP. However, after high temperature exposition, concrete with GP showed better performance than the reference concrete for temperature below 600 degrees C. But, after heating at 800 degrees C, the strength of the concrete with GP drop slightly more than reference concrete. This is accompanied by an important increase in mass loss and water porosity. After the microstructure analysis, no important changes happened differently for concrete with GP at high temperature except a new calcium silica form appears after the 800 degrees C heating