Applied Mechanics and Materials Vols. 284-287

Abstract: A recently new construction and reconstruction of the bridge have been required to minimize traffic congestion, environmental disadvantage, to reduce the period of construction, and to improve the quality and workability during the construction. For this reason, the application of modular bridge system, which is assembly of the structural members, is necessary to prepare for near future. Fall of girders can occur at the moment to connect between precast girders during the construction, so appropriate cross beams should be installed to solve the mentioned problem. In this study, understanding the structural characteristics and status of cross beam, alternative cross beam system for modular bridge was developed. To inspect the structural characteristics of the alternative system, specimens were built and static loading test was performed. Afterward, the behavior of cross beam in terms of joints and load distribution was observed. Experimental results were analyzed and compared with each data. Therefore, the appropriate cross beam system for modular bridge will be chosen and proposed in this paper.

Abstract: Rectangular concrete-filled tubes (RCFTs) have been widely used as columns of building and bridge piers due to several advantages such as their strength-to-size efficiency and facilitation of rapid construction. Recently, some researchers have tried to use RCFT as a wall system in a building. RCFT wall have a high aspect ratio while the aspect ratio of the RCFT column is usually one. Thus, the behavior of the RCFT wall is clearly different from that of RCFT column and it needs to be investigated. In this study, the axial behavior of the RCFT wall was investigated through analytical simulation, and the effects of the aspect ratio, internal stud, and through rebar on axial behavior of the RCFT wall were examined. From the results, it was found that axial load capacity is decreased with increasing aspect ratio due to local buckling of the steel tube, and this local buckling can be efficiently prevented by using internal through rebar.

Abstract: Various desired performances of concrete, i.e. strength, slump, durability, etc., cannot be always obtained by current conventional mix proportion design methods for recycled aggregate concrete (RAC), because recycled aggregate (RA) generally has lower quality than natural aggregate due to the residual cement paste attached on RA and various impurities. On the other hand, design of concrete mix proportion using RA can be solved as the multi-criteria problem to meet the various required performances. This paper suggests a new method for the mix proportion of RAC to reduce the number of trial mixes using genetic algorithm (GA) which has been an optimization technique to solve the multi-object problem throughout the simulated biological evolutionary process. In mix design method by GA, several fitness functions for the required properties of concrete, i.e., slump, strength, carbonation speed coefficient, price, and emission of CO2 were considered based on conventional data or adapted from various early studies. As a result, various optimum mix proportions for RAC that meet required performances were obtained according to assumed case studies.

Abstract: The behavior of concrete is highly nonlinear, even at very low loading levels. Steel, on the other hand, exhibits a relatively linear behavior up till yielding. The synergy between the two materials and their compatibility has long been the subject of research. While the failure criterion for steel is straight forward, concrete can be approached by various theories. The most prominent are the Kupfer-Hilsdorf-Rusch and the Möhr failure envelope. The behavior of material under bi-axial stresses subsequent to cracking can be assumed isotropic or orthotropic, resulting in a differentiation in the material constitutive matrix formulation. This work covers the finite element modeling of reinforced concrete elements, based on the two failure envelopes, while assessing the isotropic and orthotropic methodology. The Finite Element smeared crack approach is used to analyze stresses and the propagation of cracking pattern for the element. The resulting load – displacement curves are validated with identical laboratory tested specimens.

Abstract: The study evaluates the properties of concrete mixed with inorganic silicate admixture. The admixture was used in proportions of 3%, 5%, and 7% of the weight of the cement. We performed tests on compressive strength and elastic modulus to evaluate the mechanical properties of concrete. Results show that the addition of the inorganic silicate admixture has a positive influence on the mechanical properties of concrete, with the best results obtained with 3% admixture. MIP porosity measurements determined that the addition of inorganic silicate admixture increased the density of the porous structure. SEM microscopic analysis revealed many needle-like protrusions into the porous structure of concrete. XRF chemical composition analysis indicated that these structures comprised mainly Na2O and SiO2. Can with cement hydration products Ca(OH)2 bring in Chemical reaction. Inferred pore structure Within be C-S-H gel of needle-like protruding structure. it can improve the main cause of mechanical properties of concrete.

Abstract: Regarding the internal structure of cement-based materials, some major concerns the mode of distribution of pores, pore size, and the type in which they are connected. A thorough understanding of the distributive rules of pores and the approaches to break their links will be a considerable contribution to enhancing the durability of cement-based materials. There are several methods to discover the pores of cement-based materials, but cannot show the exact location of pores and the structural links. Magnetic resonance imaging (MRI) has been widely applied to physical examinations. This technique has matured and is now able to obtain information and 3-D images about the organs of recipients without causing damage. The signals from MRI indicate where the hydrogen nucleus is located. However, MRI is seldom used for cement-based materials. In this study, we use H2O as the source of MR image signals in the mortar. Through this experiment, we verify that MRI can be used to analyze the distribution of internal cracks in cement-based material.

Abstract: The paper deals with the seismic analysis of safety related structures of an operating nuclear power plant. At present time the nuclear power plants of VVER-400/213 type operate for over thirty years and there are arising requirements to verify the actual state of structures in order to assess their residual life in general. A sophisticated computation model has been developed for the seismic structural analysis using the ANSYS program package. The model involves the complex of all constrained structures of two main production blocks with equipment. In order to get a general view at the seismic load effects, seismic response analysis has been performed using direct integration of equations of motion in 25 sec interval at 0.01 sec step with excitation described by accelerograms. Combinations of dead loads and seismic loads have been considered in the stress assessment of the structures. The results of the performed analyses form a base for residual life prediction of selected structures

Abstract: Present control system of lateral displacement for super tall building has problems as follows, stress concentrate on some floor, shear lag, restriction on architectural design, etc. Thus in spite of superior structural ability the efficiency of system is so lessened. This study is about the system that using X type Floor brace and Partial 3D brace, for the purpose of lateral displacement control. This system is a method that distribute lateral loads equally inner wall. According to analysis result, Floor brace and Partial 3D brace system have equal or superior lateral displacement control ability of Outrigger system, by control of brace shape, arrangement, stiffness. When reducing core ratio, Floor brace system shows similar displacement control as outrigger system. If core shape becomes rectangular, Partial 3D brace system does not show difference in maximum displacement in X and Y directions as large as in Outrigger system. Also in case of Outrigger system, abrupt lateral displacement occurs by wind load nearby the outrigger floor. On the contrary, Partial 3D brace system is a structural system advantageous for habitability near specific floor since smaller lateral displacement is shown to reduce the effects of wind vibration and wind acceleration.

Abstract: The Shin Kong Tower located in Taipei City has a height of 244.15 m. It was the tallest building in northern Taiwan when it was built in 1993. This super tall building is susceptible to severe vibrations induced by strong winds or earthquakes. Safety of the building structures and its contents as well as the comfort of its occupants under such strong forces remains a significant engineering concern. Records by a structural array in the 51-story SK Building of the 1999 M7.6 Chi-Chi earthquake and 2004 Typhoon Aere are analyzed in this study. As a result, the structural dynamic characteristics of the high-rise building, including the transfer functions and natural frequencies, excited by the Chi-Chi earthquake, Typhoon Aere, and ambient vibrations are also determined and compared.

Abstract: Wind loads like typhoon and hurricane inflict numerous personal damages and tremendous property damages each year, and such wind loads are recognized as critical element for development of construction methods for the counteraction against them in consideration of climatic environments of buildings. While 2×4 construction system which burgeoned from North American and has been supplied throughout the world is recognized for its effectiveness, there has been no clear identification on how this system has adapted itself for wind loads in local conditions. This study has the purpose to clarify the local performance of 2×4 construction system through comparison of 6 countries on how this system has changed and is taking counteractions for wind loads the major climatic element. In this study, comparative analysis was conducted on the foundation, bottom, wall and joints of 2×4 construction system of each region to take counteractions against wind loads, and finally through summary of them, 2×4 construction system for counteraction against wind load was proposed.