Amir Fateh

Effects of coordinated crowd motion on dynamic responses of composite floors in buildings

This paper explores the vibration behaviour of composite floors in an existing building using a comprehensive study of the modal dynamic responses. Different panels are subjected to loads induced by human motion. The computed fundamental natural frequency and vibration modes are first verified against experimental and numerical results from previous studies. Departing from close correlation established by comparisons, this study investigates the effects of coordinated passive live loads as additional stationary mass due to crowds jumping. In another case, the effects of different intensities and the loads created by different jumping crowd sizes are investigated. Thirty modes of vibrations are selected to obtain all the possible excitations and to make a third harmonic load frequency available to excite the critical modes. In addition, the presence of different coordinated passive live loads on the composite floor results in different behaviours for each particular panel that is associated with location of load and passive live load intensities. This study shows that an increase in crowd size and the intensity of the active load are not directly proportional to the dynamic responses especially for displacement. It is also found that the synchronisation of active load plays a part in reducing structural dynamic responses, an observation that has not been highlighted before in previous studies.

Dynamic Analysis of Variable Stiffness Bracing System in Structure

In this paper, the application of a variable stiffness bracing (VSB) system in structures subjected to earthquake excitation is presented. The considered variable stiffness system is includes of four curve leaf springs. The nonlinear geometry of leaf springs which are acting as bending component lead to nonlinear stiffness performance. The variable stiffness bracing system does not act much for small to intermediate vibration amplitudes but it’s operated to control unpredictably large story displacement. It means this retrofit’s technique avoid an increase force in structural component due to ordinary brace action. The single degree of freedom system (SDOF) is considered and dynamic analysis of aforementioned system, with Bare and normal braced frames are conducted and the results are compared. The efficiency of the proposed system is discussed and proved in light of numerical analysis.

Seismic Performance Evaluation of Steel Shear Wall by Equivalent Truss Approach Modeling

Steel plate shear wall is one of the efficient and economical lateral resistance systems which has been implemented in various structures, located in highly seismic prone. Infill steel panel is surrounded by beams and columns as boundary elements, to provide sufficient lateral stiffness of structure. This study presents verification between prior studies and computer modeling of various structures equipped by steel shear walls based on equivalent truss element method. Furthermore the efficiency of aforementioned system is compared with special brace frame in terms of maximum displacement, base shear, axial force, rotation of critical columns and material usage by aid of time history analysis. The results shows that existence of shear wall as lateral resistance system decrease maximum displacement, base shear, axial force, torsion of critical columns about 25 %, 60%, 50% and 80% respectively, compared with structure equipped by special steel concentrically braced frame.Both systems passed the code requirements for maximum displacement, but application of steel plate shear wall reduced total weight of structural steel elements around 21%. Furthermore results reveal that equivalent truss element is reliable method for modeling shear wall element in computer modeling since results are verified by previous studies as well.

Structural behavior in top-down excavation method

The top-down excavation technique is one of the alternative methods to effectively reduce the completion time of construction projects. In this study, the structural behavior of three casting stages of strut ring slab is assessed using finite element simulation. The stages are introduced to analyze various excavation steps before the completion of slab construction. Hence, the probability of excavation initiation can be investigated. The results indicate that whenever the slab is casted for one strip and excavation is subsequently commenced underneath, the moment value, steel requirement, slab stress, and support reaction are generally lower than the case when digging operation is started after the casting of the full ring. By contrast, if two thirds of the slab is constructed and excavation begins underneath, the moment value, deflection, stress, and support reactions are quite higher than those of a fully casted slab.

Comparison of Classical Tsunami Resistance Systems in RC Structure

The seismic performance response of reinforced concrete (RC) structures subjected to simultaneous Tsunami force and earthquake excitation is evaluated. Several classical resistance systems, such as bare frame, shear wall, steel brace, and dual systems, are employed in an eight-story RC building to resist these forces. The economic design of the systems is also considered. To satisfy the economic aspects, RC structures should utilize the minimum columns and beam size. Results show that the shear wall and bare frame systems failed because of their uneconomic properties compared with other resistance systems. On the basis of engineering and economical views, the dual system is accepted and commended among classical lateral resistance systems.