سال:1380 | دوره: | شماره: |تعداد مقالات:7

Results from experimental studies of time-harmonic excited structures with installed Tuned Liquid Column Dampers (TLCDs) are presented. The experimental model consists of a smalls-scale plane one-story shear frame, made of aluminum, with a TLCD mounted to its rigid beam. A TLCD is a U-shaped tube of constant cross-section, and it is filled with liquid (pure water). The natural frequencies of the shear frame and the TLCD are tuned by modifying the length of the liquid. The effectiveness of TLCDs in the reduction of the dynamic response of structures is demonstrated by means of frequency sweep response functions. The optimal tuning ratio and the optimal geometry of the TLCD container are determined. TLCDs of different shape are studied and subsequently evaluated.

Finite element models are suggested for the analysis of a special type of semi-rigid connections of frame structures, generally known as saddle-like connections. The performance of these models is verified through the available experimental results. Non-linear finite element analysis is performed for a total number of 138 connections, and M-fdiagrams are obtained. Each diagram is represented by a multi-linear relationship through seven points. A neural network is trained for the prediction of M-f diagrams for saddle-like connections. The results obtained by the trained back propagation neural network are found to be quite satisfactory compared to those of the finite element analysis. The computational time for such a prediction is of the order of one second compared to approximately 12 hours for a complete non-linear finite element analysis.

Corrosion of steel reinforcement in bridge structures is of concern to the State Road Authorities (RAS) who control in excess of 8,000 concrete bridges and 16,000 culverts. This paper deals with investigations on two Victorian bridges, located in an aggressive marine environment, to estimate their service life and determine their management needs. The bridges are multi-span structures carrying major traffic over tidal rivers and are 9 and 30 years old. The work relates to the identification of potential corrosion problems at an early stage, before damage becomes visible, so that early intervention can be adopted to protect the integrity of the structure and extend their service life. Both field and laboratory investigations have been carried out on the bridges, including electrochemical measurements (half-cell potential, receptivity, corrosion rate), strength testing, determination of carbonation depth and chloride penetration profile, and petrography examination of concrete. The results have shown that the concrete quality is good and there is currently no visible corrosion. However, considerable cr has penetrated the concrete at the base of columns and pile cap, but it has not reached the level of the reinforcement. Electrochemical data also indicate that these areas are at risk. Based on the results of the investigations the paper discusses the remaining service life of the structure and its management needs in order to extend its service life.

The theory of plate bending contains contradictions such as those introduced with the Kirchhoff hypothesis. These contradictions affect the convergence of the finite element analysis of plates with decreasing mesh size. For square plates, the bending moment under a point load does not converge, whereas the corner forces do converge. A new triangular finite element with C1-continuity is developed in this paper. It is used to study the influence of the contradictions in plate theory on the finite element analysis of skewed plates. The new element reduces the storage space for finite element analysis, as compared to an analysis of equal accuracy with the standard element, by a factor 8 and the run time by a factor 16. In addition it assures convergence with decreasing mesh size within the limitations of plate theory. It is shown that the finite element analysis of the corner force and the bending moments at obtuse corners of skewed plates does not converge. The overall behavior of the plate is not affected by this divergence.

This paper presents a method of analysis for evaluating the softening behavior of RC members. In order to obtain mesh objective results, a non-local fiber element model is introduced. The resisting force of each section, in the .non-local fiber element model, is calculated using a proposed differential hysteretic model, which is especially developed for modeling softening behavior under cyclic loading. The section hysteretic response is determine using microphone constitutive model for concrete and bi-linear elasto-plastic model for reinforcements. The calculated hysteretic behavior of sections is employed to scale the parameters of the differential hysteretic model. The proposed method is verified by the available experimental results. Close agreements between the numerical and experimental results are obtained. The method provides insight to the procedure of flexural localization. Also, due to computational efficiency of the method, it is possible to extend its use for analyzing RC frames with softening members.

This paper briefly reviews the development of earthquake resistant design of buildings. The state-of-the-art of seismic design is discussed from the viewpoint of the performance criteria of buildings. These are (a), serviceability from frequent minor-intensity earthquake motions, (b) reparability from an infrequent but major-intensity earthquake motion, and (c) life safety from the maximum possible earthquake motion. The relation between the strength and ductility is discussed in length. With the introduction of performance-based engineering, the importance of reparability and serviceability criteria is emphasized. The concept of capacity design is outlined. A weak-beam strong-column mechanism is selected as an example of the target yielding mechanism for design.

This paper presents a method for failure analysis and studying post failure behavior of masonry shear wall. Masonry structures are blocky systems that have great importance in civil engineering. Masonry structures such as stone and brick walls, arches and vaults in tunnel supports and bridges, constitute a great percent of existing structures especially some with historical value all over the world. It is very important that a method can analytically model masonry structures and their behavior under vertical and horizontal loads in order to determine their short and long-term stability. Masonry structures generally consist of intact units (masonry blocks, stone, brick, clay units) separated by discontinuities (mortar joints). Laboratory and field observations have showed that these discontinuities have a strong and non-linear effect and dominate the deformation and strength behavior of masonry structures. The occurrence and propagation of the brittle cracking and sliding also have a great effect in behavior of masonry structures. This modified DDA method can capture the behavior and can handle the problem adequately. For considering the effect of cracking and fracturing in blocks some modifications to the original method have been developed and implemented in the original DDA code. Finally with some simple examples capability of this new method has been demonstrated.