Current Issue : January - March Volume : 2014 Issue Number : 1 Articles : 5 Articles
A research project on the deformation capacity of unreinforced masonry structures is underway at the\r\nInstitute of Structural Engineering of ETH Zurich. The development of the basic building blocks for the\r\ndisplacement-based design of unreinforced masonry structures is the objective of the present research project,\r\nwhich should be seen as a first step in an initiative to investigate the limits of the deformation capacity of\r\nunreinforced masonry walls. This paper presents a summary review of previous experimental and analytical\r\nstudies on the deformation capacity of unreinforced masonry walls subjected to in-plane loading. This review\r\nis the first phase of the aforementioned research program. A summary of 71 shear tests on unreinforced\r\nmasonry walls is presented in the form of a database, along with the statistical analysis and discussion of the\r\ntests results. Furthermore, three different computational approaches for structural masonry, i.e. micromodelling,\r\nmacro-modelling and macro-element discretization, are discussed, and a review of macro-elements\r\nfor the in-plane response of unreinforced masonry walls is presented. The reviewed models are discussed and\r\na set of conclusions is given. Special attention is devoted to the deformation capacity parameter throughout\r\nthe paper. Finally, the paper shows the limitations of our current state of knowledge of the deformation\r\ncapacity of structural masonry....
Prestress losses assumed for bridge girder design and deflection analyses are dependent on the concrete modulus of\r\nelasticity (MOE). Most design specifications, such as the American Association of State Highways and Transportation Officials\r\n(AASHTO) bridge specifications, contain a constant value for the MOE based on the unit weight of concrete and the concrete\r\ncompressive strength at 28 days. It has been shown in the past that that the concrete MOE varies with the age of concrete. The\r\npurpose of this study was to evaluate the effect of a time-dependent and variable MOE on the prestress losses assumed for bridge\r\ngirder design. For this purpose, three different variable MOE models from the literature were investigated: Dischinger (Der\r\nBauingenieur 47/48(20):563ââ?¬â??572, 1939a; Der Bauingenieur 5/6(20):53ââ?¬â??63, 1939b; Der Bauingenieur, 21/22(20):286ââ?¬â??437,\r\n1939c), American Concrete Institute (ACI) 209 (Tech. Rep. ACI 209R-92, 1992) and CEB-FIP (CEB-FIP Model Code, 2010). A\r\ntypical bridge layout for the Dallas, Texas, USA, area was assumed herein. A prestressed concrete beam design and analysis\r\nprogram from the Texas Department of Transportation (TxDOT) was utilized to determine the prestress losses. The values of the\r\ntime dependent MOE and also specific prestress losses from each model were compared. The MOE predictions based on the ACI\r\nand the CEB-FIP models were close to each other; in long-term, they approach the constant AASHTO value. Dischingerââ?¬â?¢s model\r\nprovides for higher MOE values. The elastic shortening and the long term losses from the variable MOE models are lower than that\r\nusing a constant MOE up to deck casting time. In long term, the variable MOE-based losses approach that from the constant MOE\r\npredictions. The Dischinger model would result in more conservative girder design while the ACI and the CEB-FIP models would\r\nresult in designs more consistent with the AASHTO approach...
In this paper, the seismic vulnerability of Mashhad city, as the second largest city in Iran, has been investigated\r\nusing analytical fragility curves. Disaggregation analysis is first performed in order to identify the target epsilon at\r\ndifferent hazard levels. The disaggregation results revealed different epsilon values at the first mode period of two\r\nrepresentative structures, in the case of 72-, 475-, and 2,475-year return periods. Nonlinear incremental dynamic\r\nanalyses are then performed for two representative models of a typical steel frame with a concrete shear wall,\r\nusing independent suites of acceleration time histories that are selected based on the target epsilons. Structural\r\nlimit states are defined on each incremental dynamic analysis curve, and the corresponding damage measures are\r\nestimated. The results show that if e is neglected in the considered simulations, then the predicted median structural\r\ncapacities is decreased by around 10%, 15%, and 18%, respectively, for the three abovementioned hazard levels....
Since the occurrence of the Cairo earthquake on October 1992, the design of structures for earthquakes became a\r\nmajor demand enforced in the Egyptian design codes. The seismic response of building structures can be\r\nestimated through utilization of a variety of analysis methods that range from simple equivalent static analysis to\r\ncomplex nonlinear dynamic analysis. The traditional approach is to employ equivalent static analysis methods, while\r\ncurrent design practice is moving toward an increased emphasis on the nonlinear analysis method. The Egyptian\r\ncode provisions for building seismic design adopt the traditional approach of equivalent static load method as the\r\nmain method for evaluating seismic actions and recommend the response spectrum method for nonsymmetrical\r\nbuildings. This study aims to evaluate the Egyptian code provisions for the seismic design of moment-resistant\r\nframe multi-story building through using nonlinear time history analysis. The analysis procedures are evaluated for\r\ntheir ability to predict deformation demands in terms of inter-story drifts, potential failure mechanisms and story\r\nshear force demands. The results of the analysis of the different approaches are used to evaluate the advantages,\r\nlimitations, and ease of application of each approach for seismic analysis....
The interface and bond between concrete and reinforcing steel are the most fundamental problems of reinforced\r\nconcrete structures. In this paper, the pull-out strength of galvanized steel strips with different geometries and hole\r\npatterns in foam concrete blocks are investigated experimentally and numerically. Foam concrete mixtures of 1,200-\r\nkg/m3 density were obtained by mixing cement and water in a mortar mixer together with ultrafoam as the\r\nfoaming agent and Quick-Gel as the viscosifier. A theoretical model is developed to predict the bond-slip\r\nrelationship between the strip and the concrete. This model is further implemented in a finite element simulation\r\nof the pull-out tests through the ABAQUS user subroutine. The results show good correlation between\r\nexperimental, theoretical, and finite element simulation analyses. The influence of the steel strip geometries on the\r\nmaximum pull-out force is also studied, and it was found that the strips with the greatest hole area, hole diameter,\r\nand circumference areas have higher pull-out forces and the increase is nearly linear....
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