Investigation of dynamic response of masonry minaret structures

Almost all historical minarets in Turkey were constructed using cut stone, masonry blocks or combination of these two materials. The structural and geometrical properties of each masonry minaret, or slender tower structure, depend on many factors including the structural knowledge and applications at the time of construction, experience of the architect or engineer, seismicity of the region, and availability of construction materials in that area. Recent earthquakes in Turkey have shown that most masonry minarets in high seismic regions are vulnerable to structural damage and collapse. In this study, in order to investigate the dynamic behavior of historical unreinforced masonry minarets, three representative minarets with 20, 25, and 30 m height were modeled and analyzed using two ground motions recorded during the 1999 Kocaeli and Duzce, Turkey earthquakes. The modal analyses of the models have shown that the structural periods and the overall structural response are influenced by the minaret height and spectral characteristics of the input motion. The dynamic displacement and axial stress time histories are computed at the critical points on the minarets. During recent earthquakes, most minaret failures occurred above the base of the structure. Consistent with the observed response, the largest stresses were calculated at the same location.     

A new model for analyzing nonlinear torsion behavior of concrete filled steel tube columns with rectangular section

An experimental study on concrete filled steel tube columns with rectangular section subjected to compressionflexure-torsion combined action has been carried out. The failure modes and load-deformation hysteretic relations were obtained. Based on the principles of classical material mechanics, the relations between the torsion curvature of the section and the shear strain of the fiber on the section were established. Then the strain distribution on the rectangular section of concrete filled steel tube columns subjected to torsion was analyzed. The three-dimensional refined finite element model was also built, in order to make the precision verification. The matrix forms of the relation between the torsion curvature of the section and the shear strain of the fiber on the section were derived, and introduced into the fiber beam model considering nonlinear torsion effect on the section. The comparison between test results and calculation results showed that the fiber beam model considering nonlinear torsion effect had high modeling efficiency and solution precision for predicting the torsion behavior of concrete filled steel tube columns with rectangular sections, and was suitable for analyzing the dynamic response of various structures subjected to the combined cyclic load caused by the earthquake load.     

PML solution of longitudinal wave propagation in heterogeneous media

This paper describes the development of a model for unbounded heterogeneous domains with radiation damping produced by an unphysical wave absorbing layer. The Perfectly Matched Layer (PML) approach is used along with a displacement-based finite element. The heterogeneous model is validated using the closed-form solution of a benchmark problem: a free rod with two-part modulus subjected to a specified time history. Both elastically supported and unsupported semi-infinite rods with different degrees of inhomogeneity and loading are considered. Numerical results illustrate the effects of inhomogeneity on the response and are compared with those for equivalent homogeneous domains. The effects of characteristic features of the inhomogeneous problem, presence of local maxima and cut-off frequency are determined. A degenerate case of a homogeneous semi-infinite rod on elastic foundations is produced by tending the magnitude of the foundation stiffness to zero. The response of the latter is compared with that of a free rod. The importance of proper selection of the PML parameters to highly accurate and efficient results is demonstrated by example problems.     

Cryogenic Core Collection (C3) from Unconsolidated Subsurface Media

We evaluated tools and methods for in situ freezing of cores in unconsolidated subsurface media. Our approach, referred to as cryogenic core collection (C₃), has key aspects that include downhole circulation of liquid nitrogen (LN) via a cooling system, strategic use of thermal insulation to focus cooling into the core, and controlling LN back pressure to optimize cooling. Two cooling systems (copper coil and dual‐wall cylinder) are described. For both systems, the time to freeze a single 2.5‐foot (76‐cm) long by 2.5‐inch (63‐mm) diameter core is 5 to 7 min. Frozen core collection rates of about 30 feet/day (10 m/day) were achieved at two field sites, one impacted by petroleum‐based light nonaqueous phase liquids (LNAPLs) and the other by chlorinated solvents. Merits of C₃ include (1) improved core recovery, (2) potential control of flowing sand, and (3) improved preservation of critical sediment attributes. Development of the C₃ method creates novel opportunities to characterize sediment with respect to physical, chemical, and biological properties. For example, we were able to resolve water, LNAPL, and gas saturations above and below the water table. By eliminating drainage of water, gas and LNAPL saturations in the range of 6 to 23% and 1 to 3% of pore space, respectively, were measured in LNAPL‐impacted intervals below the water table.     

Delineation of Rajmahal basaltic flows,inter-trappeans and associated coal layers using Audio-magneto-telluric method

The extensive volcanic activity of Rajmahal occurred during early Cretaceous (~117 Ma). Potentially perspective Gondawana sediments containing coal seam is partially covered by these basalts. Basalts as well as coal are already known to be of immense economic importance over Rajmahal traps. The present study mainly deals with delineation of basaltic lava flows and associated coal layers using the Audio-magneto-telluric (AMT) study in the south central region of Rajmahal traps near Suri, West Bengal, India. Initially, the field situations have been simulated using forward model with top alluvium cover followed by basaltic lava flows, a wedge shaped inter-trappean sedimentary formation with second basaltic lava flows and basement at the bottom. The model was constrained using available litholog. The model study reveals the presence of moderately resistive basalts, relatively conductive inter-trappeans and the basement, except the top alluvium layer and thin inter-trappeans. Subsequently, threeAMT sounding have been carried out over Cholaguria, Hatgacha and Pachami, Suri, West Bengal. The field AMT study reveals three basaltic lava flows with varying thickness from ~40m to ~350m and composite thickness of ~620m to ~640m, which match well with the published borehole litholog. The inter-trappeans have been identified at 500m to 620m, 310m to 400m and 500m to 640m depths over Cholaguria, Hatgacha and Pachami, respectively. It is interesting to mention that the identified inter-trappeans are inferred to be coal/shaly-coal which are matching very well with the published borehole lithologs.     

On Data Interpolation at Three Croatian Repeat Stations by Using the Spherical Elementary Currents Systems Method

A general mathematical tool for expanding vector systems on a sphere into basis functions, spherical elementary current system (SECS) method, was applied for separation of the geomagnetic field variations into external and internal parts, over a limited region of central and southeastern Europe. The registered variations at three Croatian repeat stations were compared to the variations estimated by the SECS method using the variations from the different sets of observatories. The results of the SECS method were also compared to a simple assumption that the variations at repeat station are equal to those at particular observatory. The relevance of this comparison was to get an insight about the possibility of using the SECS method for estimating the geomagnetic field variations over Croatia. The guidelines for the application of the SECS method for the purpose of reducing repeat station data were also given.