Vibration of Ultrasonic has used for scaling
and periodontal curettage, it is also has used for metal crown and
metal-ceramic crown removal, subsequently, using the tips whether for
scaling or removing crown, they will be in direct contact with th
is crown,
This research aimed to evaluate the surface of metal-ceramic crown
after exposure to Vibration of Ultrasonic tips.
This research addresses analytica of the faults suffered by high reservoirs with concrete products field study of a number of reservoirs in the central area in Syria, and identifying its defects occurring therein, and proposing solutions to address them.
A computational model of the fatigue crack initiation period on the helical gears
,with consideration of the heat treatment by carburization and friction effects, is presented.
In order to calculate the number of stress cycles required for the appe
arance of the initial
cracks, and study the influence of dynamic behavior. For this end, a dynamic model of gear
with two freedom degrees in torsion developed in Matlab and fatigue criteria are used. The
computational results are compared with those obtained using strain- life method. The
obtained results show that appearance of initial fatigue crack depends strongly on the
friction coefficient between the surfaces, heat treatment, and on the dynamic load.
This paper makes an experimental and analytical investigation of cracks characteristics in Fiber Reinforced Polymer strengthened RC beams under different levels of sustained load and Reinforced ratio.
As the equations available for conventional RC b
eams are inappropriate for the calculation of the short-term crack width in FRP-strengthened RC beams[8], a statistical analysis is carried out on available test data from international sources [6-9-10] and from the test results obtained in the current study (Concrete Labor- Civil engineering Department- Damascus University-2014) to establish a new equation that considers the effect of the FRP laminates. This equation is a correlation of stress in steel bars, concrete surface tension , and effective side cover.
The long-term crack width is then related to the instantaneous crack width by empirical equations which are derived from the test results obtained in the current study.
Cracks are considered important defects in concrete elements, it was noticed after constructing the reinforced concrete walls related to the Foundation, that after a short time after the hardening of concrete and without any overloading on the wall,
there have been vertical cracks of regular distances along each wall we noticed this phenomenon it had happened in many construction projects. We have described the situation, we have also explained, analyzed it by examining its reasons. By a thorough study of three projects carried out in lattakia including scale decanter, building of a tourist hotel and a trade centre, which crack width ranging from 1.25 mm to 3 mm, the height differed in each case studied. Ultimately we have found the practical solutions to avoid this phenomenon including adoption of longitudinal joints for reinforced concrete walls, spacing is about thirty times the wall thickness in order to avoid cracks caused by shrinkage and thermal stress where the depth of joint about 20 mm and the width ranging between 15 mm to 20 mm implemented on both sides of the wall internal and external. After hardening of concrete and lifting the wooden template fill the joints with filler flexible materials.
The extended crack resistance of concrete is necessary in the desisn of nonlinear behavior of structural It can be described through the intensity stress factor and the critical crack opening under maximum
force. The length of the crack is necessary
for calculating intensity stress factor and the critical crack opening under maximum force.
The aim of this work is to conehede the relations between intensity stress factor and the critical crack opening under maximum force with the material properties of concrete such as paste volume, compressive strength and maximum aggregate diameter. The length of crack is calculated using the analytical model of Olesen that depends on bilinear softening, and the parameters of the softening curve were found using inverse analysis. The experimental results of three point bending test for beams with different sizes which are made from concretes with different compressive strengths are used in the inverse analysis.
It is found that intensity stress factor and the critical crack opening under maximum force depend on paste volume and they increase when F'c increases, while they are independent from maximum
aggregate size.
Tunnels are usually considered as important and costly constructions and
therefore it is very necessary to estimate their performance and analyze
their structural behavior to maintain their safety in order to ensure their
reliability and performan
ce during their hypothetical life.
In this issue we reviewed the situation of Syrian railway tunnels on Aleppo –
Lattakia axis from the field observations which show that these tunnel
linings are cracked.
The numerical method, which is known as Distinct Element Method, was
used in the analysis of cracked lining. This method performs modeling of
discontinuous systems. We focused in this study on the concrete type
through elasticity modulus and lining thickness. The result analysis shows
that the effects of cracks modify the distribution of stresses and
displacements in the lining. This modification is related to concrete elasticity
modulus and mechanical crack characteristics.
