• Structural Engineering and Mechanics
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• v.67 no.6
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• pp.579-585
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• 2018

Masonry walls are of a complex (anisotropic) structure in terms of their mechanical properties. The mechanical properties of the walls are affected by the properties of the materials used in wall construction, joint thickness and the type of masonry bond. The carried-out studies, particularly in the seismic zones, have revealed that the most of the conventional masonry walls were constructed without considering any engineering approach. Along with that, large-scale damages were detected on such structural elements after major earthquake(s), and such damages were commonly occurred at the brick-joint interfaces. The aim of this study was to investigate the effect of joint thickness and also type of mortar on the mechanical behavior of the masonry walls. For this aim, the brick masonry walls were constructed through examination of both the literature and the conventional masonry walls. In the construction process, a single-type of brick was combined with two different types of mortar: cement mortar and hydraulic lime mortar. Three different joint thicknesses were used for each mortar type; thus, a total of six masonry walls were constructed in the laboratory. The mechanical properties of brick and mortars, and also of the constructed walls were determined. As a conclusion, it can be stated that the failure mechanism of the brick masonry walls differed due to the mechanical properties of the mortars. The use of bed joint thickness not less than 20 mm is recommended in construction of conventional masonry walls in order to maintain the act of brick in conjunction with mortar under load.

• Structural Engineering and Mechanics
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• v.18 no.5
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• pp.645-669
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• 2004

In seismic analysis of moment-resisting frames, beam-column connections are often modeled with rigid joint zones. However, it has been demonstrated that, in ductile reinforced concrete (RC) moment-resisting frames designed based on current codes (to say nothing of older non-ductile frames), the joint zones are in fact not rigid, but rather undergo significant shear deformations that contribute greatly to global drift. Therefore, the "rigid joint" assumption may result in misinterpretation of the global performance characteristics of frames and could consequently lead to miscalculation of strength and ductility demands on constituent frame members. The primary objective of this paper is to propose a rational method for estimating the hysteretic joint shear behavior of RC connections and for incorporating this behavior into frame analysis. The authors tested four RC edge beam-column-slab connection subassemblies subjected to earthquake-type lateral loading; hysteretic joint shear behavior is investigated based on these tests and other laboratory tests reported in the literature. An analytical scheme employing the modified compression field theory (MCFT) is developed to approximate joint shear stress vs. joint shear strain response. A connection model capable of explicitly considering hysteretic joint shear behavior is then formulated for nonlinear structural analysis. In the model, a joint is represented by rigid elements located along the joint edges and nonlinear rotational springs embedded in one of the four hinges linking adjacent rigid elements. The connection model is able to well represent the experimental hysteretic joint shear behavior and overall load-displacement response of connection subassemblies.

• BMB Reports
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• v.31 no.5
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• pp.459-467
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• 1998

A new set of functional group interaction energy descriptors relevant to the ACE (Angiotensin-Converting Enzyme) inhibitory peptide, QSAR (Quantitative Structure Activity Relationships), is presented. The functional group interaction energies approximate the charged interactions and distances between functional groups in molecules. The effective energies of the computationally derived geometries are useful parameters for deriving 3D-QSAR models, especially in the absence of experimentally known active site conformation. ACE is a regulatory zinc protease in the renin-angiotensin system. Therapeutic inhibition of this enzyme has proven to be a very effective treatment for the management of hypertension. The non bond interaction energy values among functional groups of six-feature of ACE inhibitory peptides were used as descriptor terms and analyzed for multivariate correlation with ACE inhibition activity. The functional group interaction energy descriptors used in the regression analysis were obtained by a series of inhibitor structures derived from molecular mechanics and semi-empirical calculations. The descriptors calculated using electrostatic and steric fields from the precisely defined functional group were sufficient to explain the biological activity of inhibitor. Application of the descriptors to the inhibition of ACE indicates that the derived QSAR has good predicting ability and provides insight into the mechanism of enzyme inhibition. The method, functional group interaction energy analysis, is expected to be applicable to predict enzyme inhibitory activity of the rationally designed inhibitors.

• Bulletin of the Korean Chemical Society
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• v.35 no.8
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• pp.2494-2504
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• 2014

P38 mitogen activated protein (MAP) kinase is an important anti-inflammatory drug target, which can be activated by responding to various stimuli such as stress and immune response. Based on the conformation of the conserved DFG loop (in or out), binding inhibitors are termed as type-I and II. Type-I inhibitors are ATP competitive, whereas type-II inhibitors bind in DFG-out conformation of allosteric pocket. It remains unclear that how these allosteric inhibitors stabilize the DFG-out conformation and interact. Organosilicon compounds provide unusual opportunity to enhance potency and diversity of drug molecules due to their low toxicity. However, very few examples have been reported to utilize this property. In this regard, we performed docking of an inhibitor (BIRB) and its silicon analog (Si-BIRB) in an allosteric binding pocket of p38. Further, molecular dynamics (MD) simulations were performed to study the dynamic behavior of the simulated complexes. The difference in the biological activity and mechanism of action of the simulated inhibitors could be explained based on the molecular mechanics/generalized Born surface area (MM/GBSA) binding free energy per residue decomposition. MM/GBSA showed that biological activities were related with calculated binding free energy of inhibitors. Analyses of the per-residue decomposed energy indicated that van der Waals and non-polar interactions were predominant in the ligand-protein interactions. Further, crucial residues identified for hydrogen bond, salt bridge and hydrophobic interactions were Tyr35, Lys53, Glu71, Leu74, Leu75, Ile84, Met109, Leu167, Asp168 and Phe169. Our results indicate that stronger hydrophobic interaction of Si-BIRB with the binding site residues could be responsible for its greater binding affinity compared with BIRB.

• Tunnel and Underground Space
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• v.25 no.3
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• pp.293-302
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• 2015

Thin Spray-on Liner (TSL) has been considered as a new rock support to replace shotcrete as well as wire mesh. However, the development of its original production technology is highly in demand since it is not open to the public. Therefore, two kinds of powder-type TSL prototypes were developed as the first development stage. Then, their mechanical properties were experimentally compared with those of a two-component foreign TSL material including both of liquid and powder components. From a series of experiments, the first TSL prototype mixing condition satisfied every TSL performance requirements specified by EFNRAC (2008), and showed much higher tensile and bond strengths than those of the two-component foreign TSL, even though the other TSL prototype cannot be used as a support member since its elongation at break is much lower than its corresponding EFNARC (2008) performance criterion. In addition, a further study to increase the ductility of the first TSL prototype might be necessary to guarantee its higher applicability to field conditions.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.27 no.2
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• pp.87-94
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• 2014

In solid mechanics, the peridynamics theory has provided a suitable framework for material failure and damage propagation simulation. Peridynamics is computationally expensive since it is required to solve enormous nonlocal interactions based upon integro-differential equations. Thus, multiscale coupling methods with other local models are of interest for efficient and accurate implementations of peridynamics. In this study, peridynamic models are restricted to regions where discontinuities or stress concentrations are present. In the domains characterized by smooth displacements, classical local models can be employed. We introduce a recently developed blending scheme to concurrently couple bond-based peridynamic models and the Navier equation of classical elasticity. We demonstrate numerically that the proposed blended model is suitable for point loads and static fracture, suggesting an alternative framework for cases where peridynamic models are too expensive, while classical local models are not accurate enough.

• Structural Engineering and Mechanics
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• v.75 no.6
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• pp.643-657
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• 2020

This study presents experimental and numerical investigations on circular steel tube confined ultra high performance concrete (UHPC) columns under axial compression. The plain UHPC without fibers was designed to achieve a compressive strength ranged between 150 MPa and 200 MPa. Test results revealed that loading on only the UHPC core can generate a significant confinement effect for the UHPC core, thus leading to an increase in both strength and ductility of columns, and restricting the inherent brittleness of unconfined UHPC. All tested columns failed by shear plane failure of the UHPC core, this causes a softening stage in the axial load versus axial strain curves. In addition, an increase in the steel tube thickness or the confinement index was found to increase the strength and ductility enhancement and to reduce the magnitude of the loss of load capacity. Besides, steel tube with higher yield strength can improve the post-peak behavior. Based on the test results, the load contribution of the steel tube and the concrete core to the total load was examined. It was found that no significant confinement effect can be developed before the peak load, while the ductility of post-peak stage is mainly affected by the degree of the confinement effect. A finite element model (FEM) was also constructed in ABAQUS software to validate the test results. The effect of bond strength between the steel tube and the UHPC core was also investigated through the change of friction coefficient in FEM. Furthermore, the mechanism of circular steel tube confined UHPC columns was examined using the established FEM. Based on the results of FEM, the confining pressures along the height of each modeled column were shown. Furthermore, the interaction between the steel tube and the UHPC core was displayed through the slip length and shear stresses between two surfaces of two materials.

• Structural Engineering and Mechanics
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• v.78 no.3
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• pp.231-253
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• 2021

Pure bending loading conditions are not frequently occurred in practical engineering, but the flexural researches are important since it's the basis of mechanical property researches under complex loading. Hence, the objective of this paper is to investigate the flexural behavior of concrete-filled rectangular steel tube (CFRT) through combined experimental and numerical studies. Flexural tests were conducted to investigate the mechanical performance of CFRT under bending. The load vs. deflection curves during the loading process was analyzed in detail. All the specimens behaved in a very ductile manner. Besides, based on the experimental result, the composite action between the steel tube and core concrete was studies and examined. Furthermore, the feasibility and accuracy of the numerical method was verified by comparing the computed results with experimental observations. The full curves analysis on the moment vs. curvature curves was further conducted, where the development of the stress and strain redistribution in the steel tube and core concrete was clarified comprehensively. It should be noted that there existed bond slip between the core concrete and steel tube during the loading process. And then, an extensive parametric study, including the steel strength, concrete strength, steel ratio and aspect ratio, was performed. Finally, design formula to calculate the ultimate moment and flexural stiffness of CFRTs were presented. The predicted results showed satisfactory agreement with the experimental and FE results. Additionally, the difference between the experimental/FE and predicted results using the related design codes were illustrated.

• Advances in nano research
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• v.7 no.1
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• pp.39-49
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• 2019

This paper focuses on two main objectives. The first one is to exploit an energy equivalent model and finite element method to evaluate the equivalent Young's modulus of single walled carbon nanotubes (SWCNTs) at any orientation angle by using tensile test. The calculated Young's modulus is validated with published experimental results. The second target is to exploit the finite element simulation to investigate mechanical buckling and natural frequencies of SWCNTs. Energy equivalent model is presented to describe the atomic bonding interactions and their chemical energy with mechanical structural energies. A Program of Nanotube modeler is used to generate a geometry of SWCNTs structure by defining its chirality angle, overall length of nanotube and bond length between two adjacent nodes. SWCNTs are simulated as a frame like structure; the bonds between each two neighboring atoms are treated as isotropic beam members with a uniform circular cross section. Carbon bonds is simulated as a beam and the atoms as nodes. A finite element model using 3D beam elements is built under the environment of ANSYS MAPDL environment to simulate a tensile test and characterize equivalent Young's modulus of whole CNT structure. Numerical results are presented to show critical buckling loads, axial and transverse natural frequencies of SWCNTs with different orientation angles and lengths. The understanding of mechanical behaviors of CNTs are essential in developing such structures due to their great potential in wide range of engineering applications.

• Structural Engineering and Mechanics
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• v.78 no.2
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• pp.163-174
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• 2021

Track-bridge interaction has become an essential part in the design of bridges and rails in terms of modern railways. As a unique ballastless slab track, the longitudinal continuous slab track (LCST) or referred to as the China railway track system Type-II (CRTS II) slab track, demonstrates a complex force mechanism. Therefore, a comprehensive track-bridge interaction study between multi-span simply supported beam bridges and the LCST is presented in this work. In specific, we have developed an integrated finite element model to investigate the overall interaction effects of the LCST-bridge system subjected to the actions of temperature changes, traffic loads, and braking forces. In that place, the deformation patterns of the track and bridge, and the distributions of longitudinal forces and the interfacial shear stress are studied. Our results show that the additional rail stress has been reduced under various loads and the rail's deformation has become much smoother after the transition of the two continuous structural layers of the LCST. However, the influence of the temperature difference of bridges is significant and cannot be ignored as this action can bend the bridge like the traffic load. The uniform temperature change causes the tensile stress of the concrete track structure and further induce cracks in them. Additionally, the influences of the friction coefficient of the sliding layer and the interfacial bond characteristics on the LCST's performance are discussed. The systematic study presented in this work may have some potential impacts on the understanding of the overall mechanical behavior of the LCST-bridge system.