That is why steel bars are embedded in the concrete for the structures to carry tensile loads. The steel reinforced bars take the tensile load when the concrete cracks in tension. On another hand, the concrete protects the steel reinforced bars from the environment and prevents corrosion. However, the cracks in the concrete form a major problem which affects the durability
CHAPTER-1 INTRODUCTION 1.1 PREAMBLE Earthquake is a manifestation of rapid release of stress waves during a brittle rupture of rock. The complexity of earthquake ground motion is primarily due to factors such as source effect, path effect and local site effect. Earthquake causes ground to vibrate and structures supported on ground in turn are subjected to this motion. Thus the dynamic loading on the structure during an earthquake is not external loading, but due to motion of support. The various factors contributing to the structural damage during earthquake are vertical irregularities, irregularity in strength and stiffness, mass irregularity, torsional irregularity etc.
When the large numbers of dislocations get accumulated near the grain boundary, dislocation 'pile up' occurs. These pile up causes dislocation diffusion across the grain boundary, allowing further deformation in the material. Now the larger grain brakes into two or more parts to reduce the additional pile up across the grain boundary. More grains in the structure means more number of grain boundaries, therefore, these additional grain boundaries itself act as a barrier for the movement of dislocations and ultimately the yield strength of material increases. Thus, there is then an inverse relationship between grain size and yield strength, as demonstrated by the Hall–Petch equation.
The MR of center-point loading is greater than MR of third-point loading. (ASTM C 78 and ESS 203) Figure (2.23): Test set-up for flexure strength. (ASTM C 293 and ASTM C 78) The concept of modulus of rupture is based on the elastic beam theory. The modulus of rupture is defined as the maximum normal stress in the beam calculated from the maximum (ultimate) bending moment Mu under the assumption that the beam behaves elastically. Like compressive strength, MR is influenced by mix design parameters including: • w/c ratio; • Cement type; • Cement content; • Aggregate properties (type, maximum size, gradation, and surface texture).
The spindle speed is chosen on the basis of the material is being cut. More increment in the spindle speed will result in wearing of tool, breakages and various defects such as chattering of the tool which results in dangerous condition. It means that tool life is increased with the help of correct selection of spindle speed for the particular material. As spindle speed increases so the temperature of the heat affected zone is also increased. That means there is a basic need to identify the optimal range of spindle speed.
The tensile strength of the material increases because the subsequent application of tensile stress must nullify the compressive prestress. • This can result in improved structural capacity and serviceability compared to conventionally reinforced concrete. • High-strength tendons are used to produce compression. They are made of high- tensile steels, carbon fibers etc. and consist of threaded bars, single or multiple
A structural engineer needs to develop an effective lateral load resisting system, which would prevent collapse and damage to life and property. In the event of an earthquake, the structure is subjected to lateral forces which are generated by the structure’s inertia resisting motion. These forces can be very high in magnitude. To design a structure to remain elastic during earthquake would be impractical and uneconomical. A number of techniques and devices have been proposed, tested and successfully installed in structures for
Both sides of the bridge are on reclaimed land and foundations are large diameter bored piles to bedrock. Components in the Stonecutters Bridge: The corrosion resistance of these steels is provided by the alloying element chromium; improved resistance is provided by the addition of 2 to 3% of molybdenum. Deck Steel was used on the deck of the main span. It is a twin-box girder arrangement. The box section deck provides convenient anchorages and has significant torsional properties.
Brittle and expensive, low conductivity. Polymer Concrete- Low Young’s Modulus, low thermal conductivity, high damping properties. Tensile and impact strengths lower, creep more under sustained load Polymer-Impregnated Concrete (PIC)- Bond strength is low and mechanical properties are only slightly better than those of conventional concrete. The advantages of Polymer concrete available from literature are- • The extremely low thermal diffusivity of polymer castings makes them stable and robust from thermal point of view. • Its structural damping is comparable to that of cast iron, • Mineral-cast elements are resistant against oils, coolants and other aggressive liquids.
From a strength perspective (ultimate tensile strength of 880 MPa or 90 kg/mm2), the C– Mn rail is popularly known as90 UTS rail or Grade 880 rail. The pre-reinforced concrete sleeper is the second component of the rail track. The entire track structure is more stable due to the heavier weight of concrete sleepers5. A grooved rubber pad (made of styrene butadiene, poly butadiene rubber or natural rubber) is placed between the rail and the sleeper. This absorbs vibrations and impact, provides insulation and also increases the coefficient of friction between the sleeper and the rail6.