Cone-Beam Computed Tomographic Evaluation of Artifact Effects of Three Different Sealers

Introduction: Cone-beam computed tomography (CBCT) is one of the most important diagnostic tools in maxillofacial imaging. Nowadays different sealers are used in root canal therapy and some of them can create artifact in CBCT images. The aim of this study was to evaluate the effect of different sealers including AH-26, Diadent, and Anyseal in creation of artifact bands in the CBCT images based on voxel size. Methods and Materials: A total of 44 single rooted extracted teeth were selected. The canals were prepared by crown-down technique. All teeth were manually filed up to master apical file (MAF) size 45 and 1 mm shorter than the apical foramen. The teeth were divided into 4 equal groups. The canals were filled with gutta-percha and either of sealers AH-26, Diadent or Anyseal by lateral condensation technique. The control group were filled just with gutta-percha without any sealer. The CBCT images were taken in voxel sizes of 0.3 and 0.15. The Fisher exact and McNemar tests were used for statistical analysis. Results: Although, the control group had the lowest ratio of presence to absence of artifact, the ratio of presence to absence of artifact in voxel size of 0.3 and 0.15 mm were significantly lower in Anyseal than AH-26 (P=0.031, P=0.020) and Diadent (P=0.001, P=0.002). No significant difference was detected between two voxel sizes (P>0.05). Conclusion: In this in vitro study, all evaluated sealers induced artifacts in the CBCT images. Anyseal sealer had the lowest artifact in both evaluated voxel sizes.Keywords: Artifacts; Canal Sealer; Cone-Beam Computed Tomography; Root Canal Filling Material; Root Fractur

Assessment of axial force effect on improved damage index of confined RC beam-column members

In recent years, different damage indexes have been introduced in engineering literature. The most prominent one among other counterparts is the 1985 Park and Ang's damage index (DIPA), which demonstrates well calibration against experimental results. Hence, it has traditionally had broad application in the field of structural engineering. Commonly, in DIPA relevant parameters are assessed based on plastic-hinge approach, which is not well suited to consider the coupled response between stress resultants (axial force and flexural moment) especially in grossly nonlinear domain. The reason is that named approach is utilized constant shape plastic moment-curvature curve, which is not capable of varying the shape throughout loading history. Another drawback of plastic-hinge method is the difficulty of representing precisely partial yielding of the cross-section. To remedy the situation, the fiber discretization technique is used in this paper. Based on the fiber discretization strategy, not only have the stiffness and strength degradation been characterized more accurately, but also the distribution of plasticity along the plastic zone has been considered. Besides, the multi-directional effect of axial force and flexural moment is considered to assess DI parameters. Additionally, this strategy directly incorporates the effect of transverse confinement into cross sectional constitutive behaviour

Seismic fragility analysis of liquid storage steel tanks considering shell buckling and anchor failure by added-mass method

Liquid storage tanks are vulnerable to a wide variety of failures under severe seismic excitation. Among all failure modes shell buckling and anchor bolt failures are the most critical forms of damage. Sometimes combination of different modes intensifies or accelerates liquid storage tank’s damage. Although the effect of each different failure modes has been studied separately by a number of researchers, few studies may have considered combination of main failure modes concurrently. Hence, in this paper, a cylindrical steel tank has been selected in order to study multiple damages due to dynamic loadings on the tank. All anchor bolts and steel thin wall and reinforced concrete pedestal have been modeled counting material and geometric non-linearity. The methodology for finite element modeling of fluid-structure interaction has included applying the added-mass strategy, followed by performing the numerical analyses. A suite of ground motions has been selected and matched to the target spectrum. Afterwards, incremental dynamic analyses have been conducted to obtain fragility curve according to simultaneous modes of failure. The results have indicated that anchor bolt failures along with shell buckling significantly have contributed to more flexible behavior of the thin-walled steel tank and distribution of buckling to uppermiddle part of tank which might increase seismic effects on the tank. Also, the design of steel tanks needs more considerations beyond current codes in major earthquake prone zones

Assessment of different failure modes in liquid storage tanks under horizontal ground motion

Steel storage tanks are generally vulnerable to dynamic failure under strong ground motion. The reason for that is partly because of small thickness of tank walls which contribute to either elastic buckling or inelastic post-buckling mechanisms. The tank aspect ratio plays a pivotal role in developing different failure modes. In order to investigate different failure mechanisms, case study tanks considering different aspect ratios that are fully anchored at the base are introduced. Dynamic fluid-structure interaction is utilised based on so-called added-mass method and tank walls are modelled using general purpose finite element platform to detect potential failure modes. Seven strong ground motions are selected from NGA database and spectrally matched with target spectrum. Incremental dynamic analyses are conducted to identify critical failure modes and construct fragility curves. The results demonstrate that changing tank aspect ratio contributes to different modes of failure ranging from elephant foot and diamond shape to secondary buckling modes