سال:1384 | دوره: | شماره: |تعداد مقالات:8

Seismic evaluation standard for existing reinforced concrete buildings is outlined which has been in practical use from 1970' in Japan. An effective, efficient and economical method is introduced using polyester sheet for strengthening old and non-ductile buildings. The remarkable effectiveness on the improvement of deformability has been verified through a various seismic tests such as number of static column tests and a shaking table test of frames, and already in practical use for columns. The verification test on walls strengthened with the polyester sheet was conducted recently. Since the conventional detail for strengthening walls with fabric sheets is generally complicated, a new detail for strengthening walls was developed. The bare reinforced concrete wall failed in a brittle shear failure mode, while much higher shear strength and deformability after flexural yielding were observed generally for the walls strengthened with the sheet. The new detail improved the deformability much more than the conventional detail.    

Deep Creek Bridge was built in 1981 and is in the coastal area of the Northern NSW and subject to tidal salt water. The bridge has shown signs of premature deterioration, less than 20 years after construction, in the form of vertical cracking in the pier columns. Based on visual observations, it was suspected that alkali-aggregate reaction (AAR) and corrosion of reinforcement could be the two major probable causes of the cracking. Eight concrete cores were examined from the cracked pier columns of the bridge, and AAR has been confirmed in the concrete, caused by reactive quartz gravel of a gneissic origin. AAR is considered to be the major cause of the observed cracking, and reduction in the strength properties of the concrete. The large in-situ cast pier columns (950 mm diameter) may have been subjected to temperature rises to or beyond 80 °C, as a result of cement hydration, causing delayed ettringite formation. However, this would probably have had a minor contribution to the observed cracking. Temperature-induced cracking did not appear to have played a significant role in the cracking. Chloride-induced corrosion has also been identified, and may have been exacerbated by the AAR microcracking. The pier columns may require cathodic protection (CP) to arrest the progress of steel corrosion and damage to the structure. The adverse interaction of CP currents and AAR would need careful assessment as part of the rehabilitation of the structure, for which jacketing of columns with reinforced concrete is being considered.      

In this paper, previously developed matrices with canonical forms are generalized. These matrices arise in problems of structural mechanics such as stability and dynamics of structures. Application of these matrices to graphs leads to efficient methods for the eigensolution of Laplacian matrices. The use of the present method is especially beneficial for large-scale models with repeated submodels.      

An in-depth study into behaviour of high voltage transmission poles has been made covering their loading, analysis and design aspects. Due to large displacements produced, the secondary effects have to be accounted for in the solution of pole structure. Therefore, it becomes necessary to consider the geometric non-linearity while analysing a pole. The development of a new and efficient technique was considered necessary due to limitations of available methods of analysis for pole structures. For this purpose, "tapered modeling technique" has been introduced by the authors. The finite element method, considered to be providing exact solution, is based on use of thin shell elements, requires a considerably large computer time and memory. Other available modeling techniques are based on frame elements, solutions of which are not found in good agreement with the exact solution unless nodes selected are appreciably high in number. In this work, the analysis of poles is carried out by tapered model along with one of the standard packages based on finite element method. It is gratifying to note that the results obtained from developed tapered model are observed to be having close agreement with those of exact method.      

Results of an experimental investigation carried out to assess the effect of various concrete strength levels on behavior of steel fiber reinforced lightweight concrete (SFRLWC) under pure torsion are reported. The variables of the testing program were: compressive strength of concrete, volume of steel fibers, and the aspect ratio of steel fibers. The concrete strengths investigated are 9, 12, 30 and 61 MPa. Fiber content ranges from zero to 3.0 percent by volume of matrix. Addition of approximately two percent of fibers led to maximum torsional strength and toughness enhancement of SFRLWC; however, the improvement in higher strength concrete was more pronounced than that in lower strength concrete. In general, the torsion strength gained was higher for high strength level specimens with higher percentages of fiber volume and larger fiber aspect ratio. A proposed torsional strength formulation provided good agreement with the test results.      

Probabilistic Risk Analysis (PRA) of harp type cable stayed bridges is presented to determine their probabilities of failure under random ground motion. Seismic input to the bridge support is considered to be a risk consistent response spectrum. The bridge deck is modeled as a beam supported on springs at different points. The coupled stiffness matrix of the springs is determined by a separate 2D static analysis of cable-tower-deck system in which flexibility of the tower base due to soil-structure interaction is included. Damping due to soil is incorporated by the equivalent modal energy method. The response of the bridge deck is obtained by the response spectrum method of analysis for multi-degree of freedom system. The PRA includes uncertainties of responses due to the variation in ground motion, material property, modeling and method of analysis, and uncertainties of the capacity due to the variation of ductility factor and damage concentration effect. Failure mode of the bridge is assumed to be bending failure of the bridge deck at the point of maximum bending moment. Probability of failure of the bridge deck is determined by First Order Second Moment theory of reliability analysis. A three span double plane symmetrical harp type cable stayed bridge is used as an illustrative example. The fragility curves for the bridge deck failure are obtained under a number of parametric variations. The parameters include, base flexibility, degree of correlation of ground motion, angle of incidence of earthquake, ratio of the components of ground motion, seismic input. Study shows that flexible base condition provides significantly less value of probability of failure as compared to the fixed base. Further, angles of incidence, degree of correlation, ratio of components of ground motion and input response spectrums have considerable effects on the probability of failure.      

A 5m × 9m size interior panel of a framed structure has been designed as beam-slab construction, flat slab construction and using ferrocement box sections for 5 kN/m2 live load. The self-weight, floor/ roof height and cost of these options have been compared. It is found that the flat slab option is comparable in weight to the beam-slab option, about 58.2% less in floor height and 17.7% costlier than the conventional beam and slab construction. The ferrocement box section alternative is found to be 56.2% less in weight, comparable in floor height and 15.6% cheaper than the beam - slab construction. The ferrocement box sections being light in weight need less strong supporting structures. Being a precast product, they also increase speed of construction and can be used in bad weather conditions.      

The present paper investigates the impact of tall buildings on urban environment considering function, aesthetic, confinement and other aspects. The impacts of tall buildings considering aspects such as height, form, privacy and scale is also studied. This paper provides some criteria and proposals regarding proper site selection for tall building, and some regulations on construction of such buildings in Iran.